Adding upstream version 1.20.14.upstream/1.20.14upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

51 files changed, 16471 insertions, 0 deletions

diff --git a/src/go/printer/comment.go b/src/go/printer/comment.go
new file mode 100644
index 0000000..9012714
--- /dev/null
+++ b/src/go/printer/comment.go
@@ -0,0 +1,155 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package printer
+
+import (
+	"go/ast"
+	"go/doc/comment"
+	"strings"
+)
+
+// formatDocComment reformats the doc comment list,
+// returning the canonical formatting.
+func formatDocComment(list []*ast.Comment) []*ast.Comment {
+	// Extract comment text (removing comment markers).
+	var kind, text string
+	var directives []*ast.Comment
+	if len(list) == 1 && strings.HasPrefix(list[0].Text, "/*") {
+		kind = "/*"
+		text = list[0].Text
+		if !strings.Contains(text, "\n") || allStars(text) {
+			// Single-line /* .. */ comment in doc comment position,
+			// or multiline old-style comment like
+			//	/*
+			//	 * Comment
+			//	 * text here.
+			//	 */
+			// Should not happen, since it will not work well as a
+			// doc comment, but if it does, just ignore:
+			// reformatting it will only make the situation worse.
+			return list
+		}
+		text = text[2 : len(text)-2] // cut /* and */
+	} else if strings.HasPrefix(list[0].Text, "//") {
+		kind = "//"
+		var b strings.Builder
+		for _, c := range list {
+			after, found := strings.CutPrefix(c.Text, "//")
+			if !found {
+				return list
+			}
+			// Accumulate //go:build etc lines separately.
+			if isDirective(after) {
+				directives = append(directives, c)
+				continue
+			}
+			b.WriteString(strings.TrimPrefix(after, " "))
+			b.WriteString("\n")
+		}
+		text = b.String()
+	} else {
+		// Not sure what this is, so leave alone.
+		return list
+	}
+
+	if text == "" {
+		return list
+	}
+
+	// Parse comment and reformat as text.
+	var p comment.Parser
+	d := p.Parse(text)
+
+	var pr comment.Printer
+	text = string(pr.Comment(d))
+
+	// For /* */ comment, return one big comment with text inside.
+	slash := list[0].Slash
+	if kind == "/*" {
+		c := &ast.Comment{
+			Slash: slash,
+			Text:  "/*\n" + text + "*/",
+		}
+		return []*ast.Comment{c}
+	}
+
+	// For // comment, return sequence of // lines.
+	var out []*ast.Comment
+	for text != "" {
+		var line string
+		line, text, _ = strings.Cut(text, "\n")
+		if line == "" {
+			line = "//"
+		} else if strings.HasPrefix(line, "\t") {
+			line = "//" + line
+		} else {
+			line = "// " + line
+		}
+		out = append(out, &ast.Comment{
+			Slash: slash,
+			Text:  line,
+		})
+	}
+	if len(directives) > 0 {
+		out = append(out, &ast.Comment{
+			Slash: slash,
+			Text:  "//",
+		})
+		for _, c := range directives {
+			out = append(out, &ast.Comment{
+				Slash: slash,
+				Text:  c.Text,
+			})
+		}
+	}
+	return out
+}
+
+// isDirective reports whether c is a comment directive.
+// See go.dev/issue/37974.
+// This code is also in go/ast.
+func isDirective(c string) bool {
+	// "//line " is a line directive.
+	// "//extern " is for gccgo.
+	// "//export " is for cgo.
+	// (The // has been removed.)
+	if strings.HasPrefix(c, "line ") || strings.HasPrefix(c, "extern ") || strings.HasPrefix(c, "export ") {
+		return true
+	}
+
+	// "//[a-z0-9]+:[a-z0-9]"
+	// (The // has been removed.)
+	colon := strings.Index(c, ":")
+	if colon <= 0 || colon+1 >= len(c) {
+		return false
+	}
+	for i := 0; i <= colon+1; i++ {
+		if i == colon {
+			continue
+		}
+		b := c[i]
+		if !('a' <= b && b <= 'z' || '0' <= b && b <= '9') {
+			return false
+		}
+	}
+	return true
+}
+
+// allStars reports whether text is the interior of an
+// old-style /* */ comment with a star at the start of each line.
+func allStars(text string) bool {
+	for i := 0; i < len(text); i++ {
+		if text[i] == '\n' {
+			j := i + 1
+			for j < len(text) && (text[j] == ' ' || text[j] == '\t') {
+				j++
+			}
+			if j < len(text) && text[j] != '*' {
+				return false
+			}
+		}
+	}
+	return true
+}
diff --git a/src/go/printer/example_test.go b/src/go/printer/example_test.go
new file mode 100644
index 0000000..f7d72d1
--- /dev/null
+++ b/src/go/printer/example_test.go
@@ -0,0 +1,67 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package printer_test
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"strings"
+)
+
+func parseFunc(filename, functionname string) (fun *ast.FuncDecl, fset *token.FileSet) {
+	fset = token.NewFileSet()
+	if file, err := parser.ParseFile(fset, filename, nil, 0); err == nil {
+		for _, d := range file.Decls {
+			if f, ok := d.(*ast.FuncDecl); ok && f.Name.Name == functionname {
+				fun = f
+				return
+			}
+		}
+	}
+	panic("function not found")
+}
+
+func printSelf() {
+	// Parse source file and extract the AST without comments for
+	// this function, with position information referring to the
+	// file set fset.
+	funcAST, fset := parseFunc("example_test.go", "printSelf")
+
+	// Print the function body into buffer buf.
+	// The file set is provided to the printer so that it knows
+	// about the original source formatting and can add additional
+	// line breaks where they were present in the source.
+	var buf bytes.Buffer
+	printer.Fprint(&buf, fset, funcAST.Body)
+
+	// Remove braces {} enclosing the function body, unindent,
+	// and trim leading and trailing white space.
+	s := buf.String()
+	s = s[1 : len(s)-1]
+	s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
+
+	// Print the cleaned-up body text to stdout.
+	fmt.Println(s)
+}
+
+func ExampleFprint() {
+	printSelf()
+
+	// Output:
+	// funcAST, fset := parseFunc("example_test.go", "printSelf")
+	//
+	// var buf bytes.Buffer
+	// printer.Fprint(&buf, fset, funcAST.Body)
+	//
+	// s := buf.String()
+	// s = s[1 : len(s)-1]
+	// s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
+	//
+	// fmt.Println(s)
+}
diff --git a/src/go/printer/gobuild.go b/src/go/printer/gobuild.go
new file mode 100644
index 0000000..f00492d
--- /dev/null
+++ b/src/go/printer/gobuild.go
@@ -0,0 +1,170 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package printer
+
+import (
+	"go/build/constraint"
+	"sort"
+	"text/tabwriter"
+)
+
+func (p *printer) fixGoBuildLines() {
+	if len(p.goBuild)+len(p.plusBuild) == 0 {
+		return
+	}
+
+	// Find latest possible placement of //go:build and // +build comments.
+	// That's just after the last blank line before we find a non-comment.
+	// (We'll add another blank line after our comment block.)
+	// When we start dropping // +build comments, we can skip over /* */ comments too.
+	// Note that we are processing tabwriter input, so every comment
+	// begins and ends with a tabwriter.Escape byte.
+	// And some newlines have turned into \f bytes.
+	insert := 0
+	for pos := 0; ; {
+		// Skip leading space at beginning of line.
+		blank := true
+		for pos < len(p.output) && (p.output[pos] == ' ' || p.output[pos] == '\t') {
+			pos++
+		}
+		// Skip over // comment if any.
+		if pos+3 < len(p.output) && p.output[pos] == tabwriter.Escape && p.output[pos+1] == '/' && p.output[pos+2] == '/' {
+			blank = false
+			for pos < len(p.output) && !isNL(p.output[pos]) {
+				pos++
+			}
+		}
+		// Skip over \n at end of line.
+		if pos >= len(p.output) || !isNL(p.output[pos]) {
+			break
+		}
+		pos++
+
+		if blank {
+			insert = pos
+		}
+	}
+
+	// If there is a //go:build comment before the place we identified,
+	// use that point instead. (Earlier in the file is always fine.)
+	if len(p.goBuild) > 0 && p.goBuild[0] < insert {
+		insert = p.goBuild[0]
+	} else if len(p.plusBuild) > 0 && p.plusBuild[0] < insert {
+		insert = p.plusBuild[0]
+	}
+
+	var x constraint.Expr
+	switch len(p.goBuild) {
+	case 0:
+		// Synthesize //go:build expression from // +build lines.
+		for _, pos := range p.plusBuild {
+			y, err := constraint.Parse(p.commentTextAt(pos))
+			if err != nil {
+				x = nil
+				break
+			}
+			if x == nil {
+				x = y
+			} else {
+				x = &constraint.AndExpr{X: x, Y: y}
+			}
+		}
+	case 1:
+		// Parse //go:build expression.
+		x, _ = constraint.Parse(p.commentTextAt(p.goBuild[0]))
+	}
+
+	var block []byte
+	if x == nil {
+		// Don't have a valid //go:build expression to treat as truth.
+		// Bring all the lines together but leave them alone.
+		// Note that these are already tabwriter-escaped.
+		for _, pos := range p.goBuild {
+			block = append(block, p.lineAt(pos)...)
+		}
+		for _, pos := range p.plusBuild {
+			block = append(block, p.lineAt(pos)...)
+		}
+	} else {
+		block = append(block, tabwriter.Escape)
+		block = append(block, "//go:build "...)
+		block = append(block, x.String()...)
+		block = append(block, tabwriter.Escape, '\n')
+		if len(p.plusBuild) > 0 {
+			lines, err := constraint.PlusBuildLines(x)
+			if err != nil {
+				lines = []string{"// +build error: " + err.Error()}
+			}
+			for _, line := range lines {
+				block = append(block, tabwriter.Escape)
+				block = append(block, line...)
+				block = append(block, tabwriter.Escape, '\n')
+			}
+		}
+	}
+	block = append(block, '\n')
+
+	// Build sorted list of lines to delete from remainder of output.
+	toDelete := append(p.goBuild, p.plusBuild...)
+	sort.Ints(toDelete)
+
+	// Collect output after insertion point, with lines deleted, into after.
+	var after []byte
+	start := insert
+	for _, end := range toDelete {
+		if end < start {
+			continue
+		}
+		after = appendLines(after, p.output[start:end])
+		start = end + len(p.lineAt(end))
+	}
+	after = appendLines(after, p.output[start:])
+	if n := len(after); n >= 2 && isNL(after[n-1]) && isNL(after[n-2]) {
+		after = after[:n-1]
+	}
+
+	p.output = p.output[:insert]
+	p.output = append(p.output, block...)
+	p.output = append(p.output, after...)
+}
+
+// appendLines is like append(x, y...)
+// but it avoids creating doubled blank lines,
+// which would not be gofmt-standard output.
+// It assumes that only whole blocks of lines are being appended,
+// not line fragments.
+func appendLines(x, y []byte) []byte {
+	if len(y) > 0 && isNL(y[0]) && // y starts in blank line
+		(len(x) == 0 || len(x) >= 2 && isNL(x[len(x)-1]) && isNL(x[len(x)-2])) { // x is empty or ends in blank line
+		y = y[1:] // delete y's leading blank line
+	}
+	return append(x, y...)
+}
+
+func (p *printer) lineAt(start int) []byte {
+	pos := start
+	for pos < len(p.output) && !isNL(p.output[pos]) {
+		pos++
+	}
+	if pos < len(p.output) {
+		pos++
+	}
+	return p.output[start:pos]
+}
+
+func (p *printer) commentTextAt(start int) string {
+	if start < len(p.output) && p.output[start] == tabwriter.Escape {
+		start++
+	}
+	pos := start
+	for pos < len(p.output) && p.output[pos] != tabwriter.Escape && !isNL(p.output[pos]) {
+		pos++
+	}
+	return string(p.output[start:pos])
+}
+
+func isNL(b byte) bool {
+	return b == '\n' || b == '\f'
+}
diff --git a/src/go/printer/nodes.go b/src/go/printer/nodes.go
new file mode 100644
index 0000000..e41ffc1
--- /dev/null
+++ b/src/go/printer/nodes.go
@@ -0,0 +1,2001 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements printing of AST nodes; specifically
+// expressions, statements, declarations, and files. It uses
+// the print functionality implemented in printer.go.
+
+package printer
+
+import (
+	"go/ast"
+	"go/token"
+	"math"
+	"strconv"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// Formatting issues:
+// - better comment formatting for /*-style comments at the end of a line (e.g. a declaration)
+//   when the comment spans multiple lines; if such a comment is just two lines, formatting is
+//   not idempotent
+// - formatting of expression lists
+// - should use blank instead of tab to separate one-line function bodies from
+//   the function header unless there is a group of consecutive one-liners
+
+// ----------------------------------------------------------------------------
+// Common AST nodes.
+
+// Print as many newlines as necessary (but at least min newlines) to get to
+// the current line. ws is printed before the first line break. If newSection
+// is set, the first line break is printed as formfeed. Returns 0 if no line
+// breaks were printed, returns 1 if there was exactly one newline printed,
+// and returns a value > 1 if there was a formfeed or more than one newline
+// printed.
+//
+// TODO(gri): linebreak may add too many lines if the next statement at "line"
+// is preceded by comments because the computation of n assumes
+// the current position before the comment and the target position
+// after the comment. Thus, after interspersing such comments, the
+// space taken up by them is not considered to reduce the number of
+// linebreaks. At the moment there is no easy way to know about
+// future (not yet interspersed) comments in this function.
+func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (nbreaks int) {
+	n := nlimit(line - p.pos.Line)
+	if n < min {
+		n = min
+	}
+	if n > 0 {
+		p.print(ws)
+		if newSection {
+			p.print(formfeed)
+			n--
+			nbreaks = 2
+		}
+		nbreaks += n
+		for ; n > 0; n-- {
+			p.print(newline)
+		}
+	}
+	return
+}
+
+// setComment sets g as the next comment if g != nil and if node comments
+// are enabled - this mode is used when printing source code fragments such
+// as exports only. It assumes that there is no pending comment in p.comments
+// and at most one pending comment in the p.comment cache.
+func (p *printer) setComment(g *ast.CommentGroup) {
+	if g == nil || !p.useNodeComments {
+		return
+	}
+	if p.comments == nil {
+		// initialize p.comments lazily
+		p.comments = make([]*ast.CommentGroup, 1)
+	} else if p.cindex < len(p.comments) {
+		// for some reason there are pending comments; this
+		// should never happen - handle gracefully and flush
+		// all comments up to g, ignore anything after that
+		p.flush(p.posFor(g.List[0].Pos()), token.ILLEGAL)
+		p.comments = p.comments[0:1]
+		// in debug mode, report error
+		p.internalError("setComment found pending comments")
+	}
+	p.comments[0] = g
+	p.cindex = 0
+	// don't overwrite any pending comment in the p.comment cache
+	// (there may be a pending comment when a line comment is
+	// immediately followed by a lead comment with no other
+	// tokens between)
+	if p.commentOffset == infinity {
+		p.nextComment() // get comment ready for use
+	}
+}
+
+type exprListMode uint
+
+const (
+	commaTerm exprListMode = 1 << iota // list is optionally terminated by a comma
+	noIndent                           // no extra indentation in multi-line lists
+)
+
+// If indent is set, a multi-line identifier list is indented after the
+// first linebreak encountered.
+func (p *printer) identList(list []*ast.Ident, indent bool) {
+	// convert into an expression list so we can re-use exprList formatting
+	xlist := make([]ast.Expr, len(list))
+	for i, x := range list {
+		xlist[i] = x
+	}
+	var mode exprListMode
+	if !indent {
+		mode = noIndent
+	}
+	p.exprList(token.NoPos, xlist, 1, mode, token.NoPos, false)
+}
+
+const filteredMsg = "contains filtered or unexported fields"
+
+// Print a list of expressions. If the list spans multiple
+// source lines, the original line breaks are respected between
+// expressions.
+//
+// TODO(gri) Consider rewriting this to be independent of []ast.Expr
+// so that we can use the algorithm for any kind of list
+//
+//	(e.g., pass list via a channel over which to range).
+func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exprListMode, next0 token.Pos, isIncomplete bool) {
+	if len(list) == 0 {
+		if isIncomplete {
+			prev := p.posFor(prev0)
+			next := p.posFor(next0)
+			if prev.IsValid() && prev.Line == next.Line {
+				p.print("/* " + filteredMsg + " */")
+			} else {
+				p.print(newline)
+				p.print(indent, "// "+filteredMsg, unindent, newline)
+			}
+		}
+		return
+	}
+
+	prev := p.posFor(prev0)
+	next := p.posFor(next0)
+	line := p.lineFor(list[0].Pos())
+	endLine := p.lineFor(list[len(list)-1].End())
+
+	if prev.IsValid() && prev.Line == line && line == endLine {
+		// all list entries on a single line
+		for i, x := range list {
+			if i > 0 {
+				// use position of expression following the comma as
+				// comma position for correct comment placement
+				p.setPos(x.Pos())
+				p.print(token.COMMA, blank)
+			}
+			p.expr0(x, depth)
+		}
+		if isIncomplete {
+			p.print(token.COMMA, blank, "/* "+filteredMsg+" */")
+		}
+		return
+	}
+
+	// list entries span multiple lines;
+	// use source code positions to guide line breaks
+
+	// Don't add extra indentation if noIndent is set;
+	// i.e., pretend that the first line is already indented.
+	ws := ignore
+	if mode&noIndent == 0 {
+		ws = indent
+	}
+
+	// The first linebreak is always a formfeed since this section must not
+	// depend on any previous formatting.
+	prevBreak := -1 // index of last expression that was followed by a linebreak
+	if prev.IsValid() && prev.Line < line && p.linebreak(line, 0, ws, true) > 0 {
+		ws = ignore
+		prevBreak = 0
+	}
+
+	// initialize expression/key size: a zero value indicates expr/key doesn't fit on a single line
+	size := 0
+
+	// We use the ratio between the geometric mean of the previous key sizes and
+	// the current size to determine if there should be a break in the alignment.
+	// To compute the geometric mean we accumulate the ln(size) values (lnsum)
+	// and the number of sizes included (count).
+	lnsum := 0.0
+	count := 0
+
+	// print all list elements
+	prevLine := prev.Line
+	for i, x := range list {
+		line = p.lineFor(x.Pos())
+
+		// Determine if the next linebreak, if any, needs to use formfeed:
+		// in general, use the entire node size to make the decision; for
+		// key:value expressions, use the key size.
+		// TODO(gri) for a better result, should probably incorporate both
+		//           the key and the node size into the decision process
+		useFF := true
+
+		// Determine element size: All bets are off if we don't have
+		// position information for the previous and next token (likely
+		// generated code - simply ignore the size in this case by setting
+		// it to 0).
+		prevSize := size
+		const infinity = 1e6 // larger than any source line
+		size = p.nodeSize(x, infinity)
+		pair, isPair := x.(*ast.KeyValueExpr)
+		if size <= infinity && prev.IsValid() && next.IsValid() {
+			// x fits on a single line
+			if isPair {
+				size = p.nodeSize(pair.Key, infinity) // size <= infinity
+			}
+		} else {
+			// size too large or we don't have good layout information
+			size = 0
+		}
+
+		// If the previous line and the current line had single-
+		// line-expressions and the key sizes are small or the
+		// ratio between the current key and the geometric mean
+		// if the previous key sizes does not exceed a threshold,
+		// align columns and do not use formfeed.
+		if prevSize > 0 && size > 0 {
+			const smallSize = 40
+			if count == 0 || prevSize <= smallSize && size <= smallSize {
+				useFF = false
+			} else {
+				const r = 2.5                               // threshold
+				geomean := math.Exp(lnsum / float64(count)) // count > 0
+				ratio := float64(size) / geomean
+				useFF = r*ratio <= 1 || r <= ratio
+			}
+		}
+
+		needsLinebreak := 0 < prevLine && prevLine < line
+		if i > 0 {
+			// Use position of expression following the comma as
+			// comma position for correct comment placement, but
+			// only if the expression is on the same line.
+			if !needsLinebreak {
+				p.setPos(x.Pos())
+			}
+			p.print(token.COMMA)
+			needsBlank := true
+			if needsLinebreak {
+				// Lines are broken using newlines so comments remain aligned
+				// unless useFF is set or there are multiple expressions on
+				// the same line in which case formfeed is used.
+				nbreaks := p.linebreak(line, 0, ws, useFF || prevBreak+1 < i)
+				if nbreaks > 0 {
+					ws = ignore
+					prevBreak = i
+					needsBlank = false // we got a line break instead
+				}
+				// If there was a new section or more than one new line
+				// (which means that the tabwriter will implicitly break
+				// the section), reset the geomean variables since we are
+				// starting a new group of elements with the next element.
+				if nbreaks > 1 {
+					lnsum = 0
+					count = 0
+				}
+			}
+			if needsBlank {
+				p.print(blank)
+			}
+		}
+
+		if len(list) > 1 && isPair && size > 0 && needsLinebreak {
+			// We have a key:value expression that fits onto one line
+			// and it's not on the same line as the prior expression:
+			// Use a column for the key such that consecutive entries
+			// can align if possible.
+			// (needsLinebreak is set if we started a new line before)
+			p.expr(pair.Key)
+			p.setPos(pair.Colon)
+			p.print(token.COLON, vtab)
+			p.expr(pair.Value)
+		} else {
+			p.expr0(x, depth)
+		}
+
+		if size > 0 {
+			lnsum += math.Log(float64(size))
+			count++
+		}
+
+		prevLine = line
+	}
+
+	if mode&commaTerm != 0 && next.IsValid() && p.pos.Line < next.Line {
+		// Print a terminating comma if the next token is on a new line.
+		p.print(token.COMMA)
+		if isIncomplete {
+			p.print(newline)
+			p.print("// " + filteredMsg)
+		}
+		if ws == ignore && mode&noIndent == 0 {
+			// unindent if we indented
+			p.print(unindent)
+		}
+		p.print(formfeed) // terminating comma needs a line break to look good
+		return
+	}
+
+	if isIncomplete {
+		p.print(token.COMMA, newline)
+		p.print("// "+filteredMsg, newline)
+	}
+
+	if ws == ignore && mode&noIndent == 0 {
+		// unindent if we indented
+		p.print(unindent)
+	}
+}
+
+type paramMode int
+
+const (
+	funcParam paramMode = iota
+	funcTParam
+	typeTParam
+)
+
+func (p *printer) parameters(fields *ast.FieldList, mode paramMode) {
+	openTok, closeTok := token.LPAREN, token.RPAREN
+	if mode != funcParam {
+		openTok, closeTok = token.LBRACK, token.RBRACK
+	}
+	p.setPos(fields.Opening)
+	p.print(openTok)
+	if len(fields.List) > 0 {
+		prevLine := p.lineFor(fields.Opening)
+		ws := indent
+		for i, par := range fields.List {
+			// determine par begin and end line (may be different
+			// if there are multiple parameter names for this par
+			// or the type is on a separate line)
+			parLineBeg := p.lineFor(par.Pos())
+			parLineEnd := p.lineFor(par.End())
+			// separating "," if needed
+			needsLinebreak := 0 < prevLine && prevLine < parLineBeg
+			if i > 0 {
+				// use position of parameter following the comma as
+				// comma position for correct comma placement, but
+				// only if the next parameter is on the same line
+				if !needsLinebreak {
+					p.setPos(par.Pos())
+				}
+				p.print(token.COMMA)
+			}
+			// separator if needed (linebreak or blank)
+			if needsLinebreak && p.linebreak(parLineBeg, 0, ws, true) > 0 {
+				// break line if the opening "(" or previous parameter ended on a different line
+				ws = ignore
+			} else if i > 0 {
+				p.print(blank)
+			}
+			// parameter names
+			if len(par.Names) > 0 {
+				// Very subtle: If we indented before (ws == ignore), identList
+				// won't indent again. If we didn't (ws == indent), identList will
+				// indent if the identList spans multiple lines, and it will outdent
+				// again at the end (and still ws == indent). Thus, a subsequent indent
+				// by a linebreak call after a type, or in the next multi-line identList
+				// will do the right thing.
+				p.identList(par.Names, ws == indent)
+				p.print(blank)
+			}
+			// parameter type
+			p.expr(stripParensAlways(par.Type))
+			prevLine = parLineEnd
+		}
+
+		// if the closing ")" is on a separate line from the last parameter,
+		// print an additional "," and line break
+		if closing := p.lineFor(fields.Closing); 0 < prevLine && prevLine < closing {
+			p.print(token.COMMA)
+			p.linebreak(closing, 0, ignore, true)
+		} else if mode == typeTParam && fields.NumFields() == 1 && combinesWithName(fields.List[0].Type) {
+			// A type parameter list [P T] where the name P and the type expression T syntactically
+			// combine to another valid (value) expression requires a trailing comma, as in [P *T,]
+			// (or an enclosing interface as in [P interface(*T)]), so that the type parameter list
+			// is not parsed as an array length [P*T].
+			p.print(token.COMMA)
+		}
+
+		// unindent if we indented
+		if ws == ignore {
+			p.print(unindent)
+		}
+	}
+
+	p.setPos(fields.Closing)
+	p.print(closeTok)
+}
+
+// combinesWithName reports whether a name followed by the expression x
+// syntactically combines to another valid (value) expression. For instance
+// using *T for x, "name *T" syntactically appears as the expression x*T.
+// On the other hand, using  P|Q or *P|~Q for x, "name P|Q" or name *P|~Q"
+// cannot be combined into a valid (value) expression.
+func combinesWithName(x ast.Expr) bool {
+	switch x := x.(type) {
+	case *ast.StarExpr:
+		// name *x.X combines to name*x.X if x.X is not a type element
+		return !isTypeElem(x.X)
+	case *ast.BinaryExpr:
+		return combinesWithName(x.X) && !isTypeElem(x.Y)
+	case *ast.ParenExpr:
+		// name(x) combines but we are making sure at
+		// the call site that x is never parenthesized.
+		panic("unexpected parenthesized expression")
+	}
+	return false
+}
+
+// isTypeElem reports whether x is a (possibly parenthesized) type element expression.
+// The result is false if x could be a type element OR an ordinary (value) expression.
+func isTypeElem(x ast.Expr) bool {
+	switch x := x.(type) {
+	case *ast.ArrayType, *ast.StructType, *ast.FuncType, *ast.InterfaceType, *ast.MapType, *ast.ChanType:
+		return true
+	case *ast.UnaryExpr:
+		return x.Op == token.TILDE
+	case *ast.BinaryExpr:
+		return isTypeElem(x.X) || isTypeElem(x.Y)
+	case *ast.ParenExpr:
+		return isTypeElem(x.X)
+	}
+	return false
+}
+
+func (p *printer) signature(sig *ast.FuncType) {
+	if sig.TypeParams != nil {
+		p.parameters(sig.TypeParams, funcTParam)
+	}
+	if sig.Params != nil {
+		p.parameters(sig.Params, funcParam)
+	} else {
+		p.print(token.LPAREN, token.RPAREN)
+	}
+	res := sig.Results
+	n := res.NumFields()
+	if n > 0 {
+		// res != nil
+		p.print(blank)
+		if n == 1 && res.List[0].Names == nil {
+			// single anonymous res; no ()'s
+			p.expr(stripParensAlways(res.List[0].Type))
+			return
+		}
+		p.parameters(res, funcParam)
+	}
+}
+
+func identListSize(list []*ast.Ident, maxSize int) (size int) {
+	for i, x := range list {
+		if i > 0 {
+			size += len(", ")
+		}
+		size += utf8.RuneCountInString(x.Name)
+		if size >= maxSize {
+			break
+		}
+	}
+	return
+}
+
+func (p *printer) isOneLineFieldList(list []*ast.Field) bool {
+	if len(list) != 1 {
+		return false // allow only one field
+	}
+	f := list[0]
+	if f.Tag != nil || f.Comment != nil {
+		return false // don't allow tags or comments
+	}
+	// only name(s) and type
+	const maxSize = 30 // adjust as appropriate, this is an approximate value
+	namesSize := identListSize(f.Names, maxSize)
+	if namesSize > 0 {
+		namesSize = 1 // blank between names and types
+	}
+	typeSize := p.nodeSize(f.Type, maxSize)
+	return namesSize+typeSize <= maxSize
+}
+
+func (p *printer) setLineComment(text string) {
+	p.setComment(&ast.CommentGroup{List: []*ast.Comment{{Slash: token.NoPos, Text: text}}})
+}
+
+func (p *printer) fieldList(fields *ast.FieldList, isStruct, isIncomplete bool) {
+	lbrace := fields.Opening
+	list := fields.List
+	rbrace := fields.Closing
+	hasComments := isIncomplete || p.commentBefore(p.posFor(rbrace))
+	srcIsOneLine := lbrace.IsValid() && rbrace.IsValid() && p.lineFor(lbrace) == p.lineFor(rbrace)
+
+	if !hasComments && srcIsOneLine {
+		// possibly a one-line struct/interface
+		if len(list) == 0 {
+			// no blank between keyword and {} in this case
+			p.setPos(lbrace)
+			p.print(token.LBRACE)
+			p.setPos(rbrace)
+			p.print(token.RBRACE)
+			return
+		} else if p.isOneLineFieldList(list) {
+			// small enough - print on one line
+			// (don't use identList and ignore source line breaks)
+			p.setPos(lbrace)
+			p.print(token.LBRACE, blank)
+			f := list[0]
+			if isStruct {
+				for i, x := range f.Names {
+					if i > 0 {
+						// no comments so no need for comma position
+						p.print(token.COMMA, blank)
+					}
+					p.expr(x)
+				}
+				if len(f.Names) > 0 {
+					p.print(blank)
+				}
+				p.expr(f.Type)
+			} else { // interface
+				if len(f.Names) > 0 {
+					name := f.Names[0] // method name
+					p.expr(name)
+					p.signature(f.Type.(*ast.FuncType)) // don't print "func"
+				} else {
+					// embedded interface
+					p.expr(f.Type)
+				}
+			}
+			p.print(blank)
+			p.setPos(rbrace)
+			p.print(token.RBRACE)
+			return
+		}
+	}
+	// hasComments || !srcIsOneLine
+
+	p.print(blank)
+	p.setPos(lbrace)
+	p.print(token.LBRACE, indent)
+	if hasComments || len(list) > 0 {
+		p.print(formfeed)
+	}
+
+	if isStruct {
+
+		sep := vtab
+		if len(list) == 1 {
+			sep = blank
+		}
+		var line int
+		for i, f := range list {
+			if i > 0 {
+				p.linebreak(p.lineFor(f.Pos()), 1, ignore, p.linesFrom(line) > 0)
+			}
+			extraTabs := 0
+			p.setComment(f.Doc)
+			p.recordLine(&line)
+			if len(f.Names) > 0 {
+				// named fields
+				p.identList(f.Names, false)
+				p.print(sep)
+				p.expr(f.Type)
+				extraTabs = 1
+			} else {
+				// anonymous field
+				p.expr(f.Type)
+				extraTabs = 2
+			}
+			if f.Tag != nil {
+				if len(f.Names) > 0 && sep == vtab {
+					p.print(sep)
+				}
+				p.print(sep)
+				p.expr(f.Tag)
+				extraTabs = 0
+			}
+			if f.Comment != nil {
+				for ; extraTabs > 0; extraTabs-- {
+					p.print(sep)
+				}
+				p.setComment(f.Comment)
+			}
+		}
+		if isIncomplete {
+			if len(list) > 0 {
+				p.print(formfeed)
+			}
+			p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
+			p.setLineComment("// " + filteredMsg)
+		}
+
+	} else { // interface
+
+		var line int
+		var prev *ast.Ident // previous "type" identifier
+		for i, f := range list {
+			var name *ast.Ident // first name, or nil
+			if len(f.Names) > 0 {
+				name = f.Names[0]
+			}
+			if i > 0 {
+				// don't do a line break (min == 0) if we are printing a list of types
+				// TODO(gri) this doesn't work quite right if the list of types is
+				//           spread across multiple lines
+				min := 1
+				if prev != nil && name == prev {
+					min = 0
+				}
+				p.linebreak(p.lineFor(f.Pos()), min, ignore, p.linesFrom(line) > 0)
+			}
+			p.setComment(f.Doc)
+			p.recordLine(&line)
+			if name != nil {
+				// method
+				p.expr(name)
+				p.signature(f.Type.(*ast.FuncType)) // don't print "func"
+				prev = nil
+			} else {
+				// embedded interface
+				p.expr(f.Type)
+				prev = nil
+			}
+			p.setComment(f.Comment)
+		}
+		if isIncomplete {
+			if len(list) > 0 {
+				p.print(formfeed)
+			}
+			p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
+			p.setLineComment("// contains filtered or unexported methods")
+		}
+
+	}
+	p.print(unindent, formfeed)
+	p.setPos(rbrace)
+	p.print(token.RBRACE)
+}
+
+// ----------------------------------------------------------------------------
+// Expressions
+
+func walkBinary(e *ast.BinaryExpr) (has4, has5 bool, maxProblem int) {
+	switch e.Op.Precedence() {
+	case 4:
+		has4 = true
+	case 5:
+		has5 = true
+	}
+
+	switch l := e.X.(type) {
+	case *ast.BinaryExpr:
+		if l.Op.Precedence() < e.Op.Precedence() {
+			// parens will be inserted.
+			// pretend this is an *ast.ParenExpr and do nothing.
+			break
+		}
+		h4, h5, mp := walkBinary(l)
+		has4 = has4 || h4
+		has5 = has5 || h5
+		if maxProblem < mp {
+			maxProblem = mp
+		}
+	}
+
+	switch r := e.Y.(type) {
+	case *ast.BinaryExpr:
+		if r.Op.Precedence() <= e.Op.Precedence() {
+			// parens will be inserted.
+			// pretend this is an *ast.ParenExpr and do nothing.
+			break
+		}
+		h4, h5, mp := walkBinary(r)
+		has4 = has4 || h4
+		has5 = has5 || h5
+		if maxProblem < mp {
+			maxProblem = mp
+		}
+
+	case *ast.StarExpr:
+		if e.Op == token.QUO { // `*/`
+			maxProblem = 5
+		}
+
+	case *ast.UnaryExpr:
+		switch e.Op.String() + r.Op.String() {
+		case "/*", "&&", "&^":
+			maxProblem = 5
+		case "++", "--":
+			if maxProblem < 4 {
+				maxProblem = 4
+			}
+		}
+	}
+	return
+}
+
+func cutoff(e *ast.BinaryExpr, depth int) int {
+	has4, has5, maxProblem := walkBinary(e)
+	if maxProblem > 0 {
+		return maxProblem + 1
+	}
+	if has4 && has5 {
+		if depth == 1 {
+			return 5
+		}
+		return 4
+	}
+	if depth == 1 {
+		return 6
+	}
+	return 4
+}
+
+func diffPrec(expr ast.Expr, prec int) int {
+	x, ok := expr.(*ast.BinaryExpr)
+	if !ok || prec != x.Op.Precedence() {
+		return 1
+	}
+	return 0
+}
+
+func reduceDepth(depth int) int {
+	depth--
+	if depth < 1 {
+		depth = 1
+	}
+	return depth
+}
+
+// Format the binary expression: decide the cutoff and then format.
+// Let's call depth == 1 Normal mode, and depth > 1 Compact mode.
+// (Algorithm suggestion by Russ Cox.)
+//
+// The precedences are:
+//
+//	5             *  /  %  <<  >>  &  &^
+//	4             +  -  |  ^
+//	3             ==  !=  <  <=  >  >=
+//	2             &&
+//	1             ||
+//
+// The only decision is whether there will be spaces around levels 4 and 5.
+// There are never spaces at level 6 (unary), and always spaces at levels 3 and below.
+//
+// To choose the cutoff, look at the whole expression but excluding primary
+// expressions (function calls, parenthesized exprs), and apply these rules:
+//
+//  1. If there is a binary operator with a right side unary operand
+//     that would clash without a space, the cutoff must be (in order):
+//
+//     /*	6
+//     &&	6
+//     &^	6
+//     ++	5
+//     --	5
+//
+//     (Comparison operators always have spaces around them.)
+//
+//  2. If there is a mix of level 5 and level 4 operators, then the cutoff
+//     is 5 (use spaces to distinguish precedence) in Normal mode
+//     and 4 (never use spaces) in Compact mode.
+//
+//  3. If there are no level 4 operators or no level 5 operators, then the
+//     cutoff is 6 (always use spaces) in Normal mode
+//     and 4 (never use spaces) in Compact mode.
+func (p *printer) binaryExpr(x *ast.BinaryExpr, prec1, cutoff, depth int) {
+	prec := x.Op.Precedence()
+	if prec < prec1 {
+		// parenthesis needed
+		// Note: The parser inserts an ast.ParenExpr node; thus this case
+		//       can only occur if the AST is created in a different way.
+		p.print(token.LPAREN)
+		p.expr0(x, reduceDepth(depth)) // parentheses undo one level of depth
+		p.print(token.RPAREN)
+		return
+	}
+
+	printBlank := prec < cutoff
+
+	ws := indent
+	p.expr1(x.X, prec, depth+diffPrec(x.X, prec))
+	if printBlank {
+		p.print(blank)
+	}
+	xline := p.pos.Line // before the operator (it may be on the next line!)
+	yline := p.lineFor(x.Y.Pos())
+	p.setPos(x.OpPos)
+	p.print(x.Op)
+	if xline != yline && xline > 0 && yline > 0 {
+		// at least one line break, but respect an extra empty line
+		// in the source
+		if p.linebreak(yline, 1, ws, true) > 0 {
+			ws = ignore
+			printBlank = false // no blank after line break
+		}
+	}
+	if printBlank {
+		p.print(blank)
+	}
+	p.expr1(x.Y, prec+1, depth+1)
+	if ws == ignore {
+		p.print(unindent)
+	}
+}
+
+func isBinary(expr ast.Expr) bool {
+	_, ok := expr.(*ast.BinaryExpr)
+	return ok
+}
+
+func (p *printer) expr1(expr ast.Expr, prec1, depth int) {
+	p.setPos(expr.Pos())
+
+	switch x := expr.(type) {
+	case *ast.BadExpr:
+		p.print("BadExpr")
+
+	case *ast.Ident:
+		p.print(x)
+
+	case *ast.BinaryExpr:
+		if depth < 1 {
+			p.internalError("depth < 1:", depth)
+			depth = 1
+		}
+		p.binaryExpr(x, prec1, cutoff(x, depth), depth)
+
+	case *ast.KeyValueExpr:
+		p.expr(x.Key)
+		p.setPos(x.Colon)
+		p.print(token.COLON, blank)
+		p.expr(x.Value)
+
+	case *ast.StarExpr:
+		const prec = token.UnaryPrec
+		if prec < prec1 {
+			// parenthesis needed
+			p.print(token.LPAREN)
+			p.print(token.MUL)
+			p.expr(x.X)
+			p.print(token.RPAREN)
+		} else {
+			// no parenthesis needed
+			p.print(token.MUL)
+			p.expr(x.X)
+		}
+
+	case *ast.UnaryExpr:
+		const prec = token.UnaryPrec
+		if prec < prec1 {
+			// parenthesis needed
+			p.print(token.LPAREN)
+			p.expr(x)
+			p.print(token.RPAREN)
+		} else {
+			// no parenthesis needed
+			p.print(x.Op)
+			if x.Op == token.RANGE {
+				// TODO(gri) Remove this code if it cannot be reached.
+				p.print(blank)
+			}
+			p.expr1(x.X, prec, depth)
+		}
+
+	case *ast.BasicLit:
+		if p.Config.Mode&normalizeNumbers != 0 {
+			x = normalizedNumber(x)
+		}
+		p.print(x)
+
+	case *ast.FuncLit:
+		p.setPos(x.Type.Pos())
+		p.print(token.FUNC)
+		// See the comment in funcDecl about how the header size is computed.
+		startCol := p.out.Column - len("func")
+		p.signature(x.Type)
+		p.funcBody(p.distanceFrom(x.Type.Pos(), startCol), blank, x.Body)
+
+	case *ast.ParenExpr:
+		if _, hasParens := x.X.(*ast.ParenExpr); hasParens {
+			// don't print parentheses around an already parenthesized expression
+			// TODO(gri) consider making this more general and incorporate precedence levels
+			p.expr0(x.X, depth)
+		} else {
+			p.print(token.LPAREN)
+			p.expr0(x.X, reduceDepth(depth)) // parentheses undo one level of depth
+			p.setPos(x.Rparen)
+			p.print(token.RPAREN)
+		}
+
+	case *ast.SelectorExpr:
+		p.selectorExpr(x, depth, false)
+
+	case *ast.TypeAssertExpr:
+		p.expr1(x.X, token.HighestPrec, depth)
+		p.print(token.PERIOD)
+		p.setPos(x.Lparen)
+		p.print(token.LPAREN)
+		if x.Type != nil {
+			p.expr(x.Type)
+		} else {
+			p.print(token.TYPE)
+		}
+		p.setPos(x.Rparen)
+		p.print(token.RPAREN)
+
+	case *ast.IndexExpr:
+		// TODO(gri): should treat[] like parentheses and undo one level of depth
+		p.expr1(x.X, token.HighestPrec, 1)
+		p.setPos(x.Lbrack)
+		p.print(token.LBRACK)
+		p.expr0(x.Index, depth+1)
+		p.setPos(x.Rbrack)
+		p.print(token.RBRACK)
+
+	case *ast.IndexListExpr:
+		// TODO(gri): as for IndexExpr, should treat [] like parentheses and undo
+		// one level of depth
+		p.expr1(x.X, token.HighestPrec, 1)
+		p.setPos(x.Lbrack)
+		p.print(token.LBRACK)
+		p.exprList(x.Lbrack, x.Indices, depth+1, commaTerm, x.Rbrack, false)
+		p.setPos(x.Rbrack)
+		p.print(token.RBRACK)
+
+	case *ast.SliceExpr:
+		// TODO(gri): should treat[] like parentheses and undo one level of depth
+		p.expr1(x.X, token.HighestPrec, 1)
+		p.setPos(x.Lbrack)
+		p.print(token.LBRACK)
+		indices := []ast.Expr{x.Low, x.High}
+		if x.Max != nil {
+			indices = append(indices, x.Max)
+		}
+		// determine if we need extra blanks around ':'
+		var needsBlanks bool
+		if depth <= 1 {
+			var indexCount int
+			var hasBinaries bool
+			for _, x := range indices {
+				if x != nil {
+					indexCount++
+					if isBinary(x) {
+						hasBinaries = true
+					}
+				}
+			}
+			if indexCount > 1 && hasBinaries {
+				needsBlanks = true
+			}
+		}
+		for i, x := range indices {
+			if i > 0 {
+				if indices[i-1] != nil && needsBlanks {
+					p.print(blank)
+				}
+				p.print(token.COLON)
+				if x != nil && needsBlanks {
+					p.print(blank)
+				}
+			}
+			if x != nil {
+				p.expr0(x, depth+1)
+			}
+		}
+		p.setPos(x.Rbrack)
+		p.print(token.RBRACK)
+
+	case *ast.CallExpr:
+		if len(x.Args) > 1 {
+			depth++
+		}
+		var wasIndented bool
+		if _, ok := x.Fun.(*ast.FuncType); ok {
+			// conversions to literal function types require parentheses around the type
+			p.print(token.LPAREN)
+			wasIndented = p.possibleSelectorExpr(x.Fun, token.HighestPrec, depth)
+			p.print(token.RPAREN)
+		} else {
+			wasIndented = p.possibleSelectorExpr(x.Fun, token.HighestPrec, depth)
+		}
+		p.setPos(x.Lparen)
+		p.print(token.LPAREN)
+		if x.Ellipsis.IsValid() {
+			p.exprList(x.Lparen, x.Args, depth, 0, x.Ellipsis, false)
+			p.setPos(x.Ellipsis)
+			p.print(token.ELLIPSIS)
+			if x.Rparen.IsValid() && p.lineFor(x.Ellipsis) < p.lineFor(x.Rparen) {
+				p.print(token.COMMA, formfeed)
+			}
+		} else {
+			p.exprList(x.Lparen, x.Args, depth, commaTerm, x.Rparen, false)
+		}
+		p.setPos(x.Rparen)
+		p.print(token.RPAREN)
+		if wasIndented {
+			p.print(unindent)
+		}
+
+	case *ast.CompositeLit:
+		// composite literal elements that are composite literals themselves may have the type omitted
+		if x.Type != nil {
+			p.expr1(x.Type, token.HighestPrec, depth)
+		}
+		p.level++
+		p.setPos(x.Lbrace)
+		p.print(token.LBRACE)
+		p.exprList(x.Lbrace, x.Elts, 1, commaTerm, x.Rbrace, x.Incomplete)
+		// do not insert extra line break following a /*-style comment
+		// before the closing '}' as it might break the code if there
+		// is no trailing ','
+		mode := noExtraLinebreak
+		// do not insert extra blank following a /*-style comment
+		// before the closing '}' unless the literal is empty
+		if len(x.Elts) > 0 {
+			mode |= noExtraBlank
+		}
+		// need the initial indent to print lone comments with
+		// the proper level of indentation
+		p.print(indent, unindent, mode)
+		p.setPos(x.Rbrace)
+		p.print(token.RBRACE, mode)
+		p.level--
+
+	case *ast.Ellipsis:
+		p.print(token.ELLIPSIS)
+		if x.Elt != nil {
+			p.expr(x.Elt)
+		}
+
+	case *ast.ArrayType:
+		p.print(token.LBRACK)
+		if x.Len != nil {
+			p.expr(x.Len)
+		}
+		p.print(token.RBRACK)
+		p.expr(x.Elt)
+
+	case *ast.StructType:
+		p.print(token.STRUCT)
+		p.fieldList(x.Fields, true, x.Incomplete)
+
+	case *ast.FuncType:
+		p.print(token.FUNC)
+		p.signature(x)
+
+	case *ast.InterfaceType:
+		p.print(token.INTERFACE)
+		p.fieldList(x.Methods, false, x.Incomplete)
+
+	case *ast.MapType:
+		p.print(token.MAP, token.LBRACK)
+		p.expr(x.Key)
+		p.print(token.RBRACK)
+		p.expr(x.Value)
+
+	case *ast.ChanType:
+		switch x.Dir {
+		case ast.SEND | ast.RECV:
+			p.print(token.CHAN)
+		case ast.RECV:
+			p.print(token.ARROW, token.CHAN) // x.Arrow and x.Pos() are the same
+		case ast.SEND:
+			p.print(token.CHAN)
+			p.setPos(x.Arrow)
+			p.print(token.ARROW)
+		}
+		p.print(blank)
+		p.expr(x.Value)
+
+	default:
+		panic("unreachable")
+	}
+}
+
+// normalizedNumber rewrites base prefixes and exponents
+// of numbers to use lower-case letters (0X123 to 0x123 and 1.2E3 to 1.2e3),
+// and removes leading 0's from integer imaginary literals (0765i to 765i).
+// It leaves hexadecimal digits alone.
+//
+// normalizedNumber doesn't modify the ast.BasicLit value lit points to.
+// If lit is not a number or a number in canonical format already,
+// lit is returned as is. Otherwise a new ast.BasicLit is created.
+func normalizedNumber(lit *ast.BasicLit) *ast.BasicLit {
+	if lit.Kind != token.INT && lit.Kind != token.FLOAT && lit.Kind != token.IMAG {
+		return lit // not a number - nothing to do
+	}
+	if len(lit.Value) < 2 {
+		return lit // only one digit (common case) - nothing to do
+	}
+	// len(lit.Value) >= 2
+
+	// We ignore lit.Kind because for lit.Kind == token.IMAG the literal may be an integer
+	// or floating-point value, decimal or not. Instead, just consider the literal pattern.
+	x := lit.Value
+	switch x[:2] {
+	default:
+		// 0-prefix octal, decimal int, or float (possibly with 'i' suffix)
+		if i := strings.LastIndexByte(x, 'E'); i >= 0 {
+			x = x[:i] + "e" + x[i+1:]
+			break
+		}
+		// remove leading 0's from integer (but not floating-point) imaginary literals
+		if x[len(x)-1] == 'i' && !strings.ContainsAny(x, ".e") {
+			x = strings.TrimLeft(x, "0_")
+			if x == "i" {
+				x = "0i"
+			}
+		}
+	case "0X":
+		x = "0x" + x[2:]
+		// possibly a hexadecimal float
+		if i := strings.LastIndexByte(x, 'P'); i >= 0 {
+			x = x[:i] + "p" + x[i+1:]
+		}
+	case "0x":
+		// possibly a hexadecimal float
+		i := strings.LastIndexByte(x, 'P')
+		if i == -1 {
+			return lit // nothing to do
+		}
+		x = x[:i] + "p" + x[i+1:]
+	case "0O":
+		x = "0o" + x[2:]
+	case "0o":
+		return lit // nothing to do
+	case "0B":
+		x = "0b" + x[2:]
+	case "0b":
+		return lit // nothing to do
+	}
+
+	return &ast.BasicLit{ValuePos: lit.ValuePos, Kind: lit.Kind, Value: x}
+}
+
+func (p *printer) possibleSelectorExpr(expr ast.Expr, prec1, depth int) bool {
+	if x, ok := expr.(*ast.SelectorExpr); ok {
+		return p.selectorExpr(x, depth, true)
+	}
+	p.expr1(expr, prec1, depth)
+	return false
+}
+
+// selectorExpr handles an *ast.SelectorExpr node and reports whether x spans
+// multiple lines.
+func (p *printer) selectorExpr(x *ast.SelectorExpr, depth int, isMethod bool) bool {
+	p.expr1(x.X, token.HighestPrec, depth)
+	p.print(token.PERIOD)
+	if line := p.lineFor(x.Sel.Pos()); p.pos.IsValid() && p.pos.Line < line {
+		p.print(indent, newline)
+		p.setPos(x.Sel.Pos())
+		p.print(x.Sel)
+		if !isMethod {
+			p.print(unindent)
+		}
+		return true
+	}
+	p.setPos(x.Sel.Pos())
+	p.print(x.Sel)
+	return false
+}
+
+func (p *printer) expr0(x ast.Expr, depth int) {
+	p.expr1(x, token.LowestPrec, depth)
+}
+
+func (p *printer) expr(x ast.Expr) {
+	const depth = 1
+	p.expr1(x, token.LowestPrec, depth)
+}
+
+// ----------------------------------------------------------------------------
+// Statements
+
+// Print the statement list indented, but without a newline after the last statement.
+// Extra line breaks between statements in the source are respected but at most one
+// empty line is printed between statements.
+func (p *printer) stmtList(list []ast.Stmt, nindent int, nextIsRBrace bool) {
+	if nindent > 0 {
+		p.print(indent)
+	}
+	var line int
+	i := 0
+	for _, s := range list {
+		// ignore empty statements (was issue 3466)
+		if _, isEmpty := s.(*ast.EmptyStmt); !isEmpty {
+			// nindent == 0 only for lists of switch/select case clauses;
+			// in those cases each clause is a new section
+			if len(p.output) > 0 {
+				// only print line break if we are not at the beginning of the output
+				// (i.e., we are not printing only a partial program)
+				p.linebreak(p.lineFor(s.Pos()), 1, ignore, i == 0 || nindent == 0 || p.linesFrom(line) > 0)
+			}
+			p.recordLine(&line)
+			p.stmt(s, nextIsRBrace && i == len(list)-1)
+			// labeled statements put labels on a separate line, but here
+			// we only care about the start line of the actual statement
+			// without label - correct line for each label
+			for t := s; ; {
+				lt, _ := t.(*ast.LabeledStmt)
+				if lt == nil {
+					break
+				}
+				line++
+				t = lt.Stmt
+			}
+			i++
+		}
+	}
+	if nindent > 0 {
+		p.print(unindent)
+	}
+}
+
+// block prints an *ast.BlockStmt; it always spans at least two lines.
+func (p *printer) block(b *ast.BlockStmt, nindent int) {
+	p.setPos(b.Lbrace)
+	p.print(token.LBRACE)
+	p.stmtList(b.List, nindent, true)
+	p.linebreak(p.lineFor(b.Rbrace), 1, ignore, true)
+	p.setPos(b.Rbrace)
+	p.print(token.RBRACE)
+}
+
+func isTypeName(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.Ident:
+		return true
+	case *ast.SelectorExpr:
+		return isTypeName(t.X)
+	}
+	return false
+}
+
+func stripParens(x ast.Expr) ast.Expr {
+	if px, strip := x.(*ast.ParenExpr); strip {
+		// parentheses must not be stripped if there are any
+		// unparenthesized composite literals starting with
+		// a type name
+		ast.Inspect(px.X, func(node ast.Node) bool {
+			switch x := node.(type) {
+			case *ast.ParenExpr:
+				// parentheses protect enclosed composite literals
+				return false
+			case *ast.CompositeLit:
+				if isTypeName(x.Type) {
+					strip = false // do not strip parentheses
+				}
+				return false
+			}
+			// in all other cases, keep inspecting
+			return true
+		})
+		if strip {
+			return stripParens(px.X)
+		}
+	}
+	return x
+}
+
+func stripParensAlways(x ast.Expr) ast.Expr {
+	if x, ok := x.(*ast.ParenExpr); ok {
+		return stripParensAlways(x.X)
+	}
+	return x
+}
+
+func (p *printer) controlClause(isForStmt bool, init ast.Stmt, expr ast.Expr, post ast.Stmt) {
+	p.print(blank)
+	needsBlank := false
+	if init == nil && post == nil {
+		// no semicolons required
+		if expr != nil {
+			p.expr(stripParens(expr))
+			needsBlank = true
+		}
+	} else {
+		// all semicolons required
+		// (they are not separators, print them explicitly)
+		if init != nil {
+			p.stmt(init, false)
+		}
+		p.print(token.SEMICOLON, blank)
+		if expr != nil {
+			p.expr(stripParens(expr))
+			needsBlank = true
+		}
+		if isForStmt {
+			p.print(token.SEMICOLON, blank)
+			needsBlank = false
+			if post != nil {
+				p.stmt(post, false)
+				needsBlank = true
+			}
+		}
+	}
+	if needsBlank {
+		p.print(blank)
+	}
+}
+
+// indentList reports whether an expression list would look better if it
+// were indented wholesale (starting with the very first element, rather
+// than starting at the first line break).
+func (p *printer) indentList(list []ast.Expr) bool {
+	// Heuristic: indentList reports whether there are more than one multi-
+	// line element in the list, or if there is any element that is not
+	// starting on the same line as the previous one ends.
+	if len(list) >= 2 {
+		var b = p.lineFor(list[0].Pos())
+		var e = p.lineFor(list[len(list)-1].End())
+		if 0 < b && b < e {
+			// list spans multiple lines
+			n := 0 // multi-line element count
+			line := b
+			for _, x := range list {
+				xb := p.lineFor(x.Pos())
+				xe := p.lineFor(x.End())
+				if line < xb {
+					// x is not starting on the same
+					// line as the previous one ended
+					return true
+				}
+				if xb < xe {
+					// x is a multi-line element
+					n++
+				}
+				line = xe
+			}
+			return n > 1
+		}
+	}
+	return false
+}
+
+func (p *printer) stmt(stmt ast.Stmt, nextIsRBrace bool) {
+	p.setPos(stmt.Pos())
+
+	switch s := stmt.(type) {
+	case *ast.BadStmt:
+		p.print("BadStmt")
+
+	case *ast.DeclStmt:
+		p.decl(s.Decl)
+
+	case *ast.EmptyStmt:
+		// nothing to do
+
+	case *ast.LabeledStmt:
+		// a "correcting" unindent immediately following a line break
+		// is applied before the line break if there is no comment
+		// between (see writeWhitespace)
+		p.print(unindent)
+		p.expr(s.Label)
+		p.setPos(s.Colon)
+		p.print(token.COLON, indent)
+		if e, isEmpty := s.Stmt.(*ast.EmptyStmt); isEmpty {
+			if !nextIsRBrace {
+				p.print(newline)
+				p.setPos(e.Pos())
+				p.print(token.SEMICOLON)
+				break
+			}
+		} else {
+			p.linebreak(p.lineFor(s.Stmt.Pos()), 1, ignore, true)
+		}
+		p.stmt(s.Stmt, nextIsRBrace)
+
+	case *ast.ExprStmt:
+		const depth = 1
+		p.expr0(s.X, depth)
+
+	case *ast.SendStmt:
+		const depth = 1
+		p.expr0(s.Chan, depth)
+		p.print(blank)
+		p.setPos(s.Arrow)
+		p.print(token.ARROW, blank)
+		p.expr0(s.Value, depth)
+
+	case *ast.IncDecStmt:
+		const depth = 1
+		p.expr0(s.X, depth+1)
+		p.setPos(s.TokPos)
+		p.print(s.Tok)
+
+	case *ast.AssignStmt:
+		var depth = 1
+		if len(s.Lhs) > 1 && len(s.Rhs) > 1 {
+			depth++
+		}
+		p.exprList(s.Pos(), s.Lhs, depth, 0, s.TokPos, false)
+		p.print(blank)
+		p.setPos(s.TokPos)
+		p.print(s.Tok, blank)
+		p.exprList(s.TokPos, s.Rhs, depth, 0, token.NoPos, false)
+
+	case *ast.GoStmt:
+		p.print(token.GO, blank)
+		p.expr(s.Call)
+
+	case *ast.DeferStmt:
+		p.print(token.DEFER, blank)
+		p.expr(s.Call)
+
+	case *ast.ReturnStmt:
+		p.print(token.RETURN)
+		if s.Results != nil {
+			p.print(blank)
+			// Use indentList heuristic to make corner cases look
+			// better (issue 1207). A more systematic approach would
+			// always indent, but this would cause significant
+			// reformatting of the code base and not necessarily
+			// lead to more nicely formatted code in general.
+			if p.indentList(s.Results) {
+				p.print(indent)
+				// Use NoPos so that a newline never goes before
+				// the results (see issue #32854).
+				p.exprList(token.NoPos, s.Results, 1, noIndent, token.NoPos, false)
+				p.print(unindent)
+			} else {
+				p.exprList(token.NoPos, s.Results, 1, 0, token.NoPos, false)
+			}
+		}
+
+	case *ast.BranchStmt:
+		p.print(s.Tok)
+		if s.Label != nil {
+			p.print(blank)
+			p.expr(s.Label)
+		}
+
+	case *ast.BlockStmt:
+		p.block(s, 1)
+
+	case *ast.IfStmt:
+		p.print(token.IF)
+		p.controlClause(false, s.Init, s.Cond, nil)
+		p.block(s.Body, 1)
+		if s.Else != nil {
+			p.print(blank, token.ELSE, blank)
+			switch s.Else.(type) {
+			case *ast.BlockStmt, *ast.IfStmt:
+				p.stmt(s.Else, nextIsRBrace)
+			default:
+				// This can only happen with an incorrectly
+				// constructed AST. Permit it but print so
+				// that it can be parsed without errors.
+				p.print(token.LBRACE, indent, formfeed)
+				p.stmt(s.Else, true)
+				p.print(unindent, formfeed, token.RBRACE)
+			}
+		}
+
+	case *ast.CaseClause:
+		if s.List != nil {
+			p.print(token.CASE, blank)
+			p.exprList(s.Pos(), s.List, 1, 0, s.Colon, false)
+		} else {
+			p.print(token.DEFAULT)
+		}
+		p.setPos(s.Colon)
+		p.print(token.COLON)
+		p.stmtList(s.Body, 1, nextIsRBrace)
+
+	case *ast.SwitchStmt:
+		p.print(token.SWITCH)
+		p.controlClause(false, s.Init, s.Tag, nil)
+		p.block(s.Body, 0)
+
+	case *ast.TypeSwitchStmt:
+		p.print(token.SWITCH)
+		if s.Init != nil {
+			p.print(blank)
+			p.stmt(s.Init, false)
+			p.print(token.SEMICOLON)
+		}
+		p.print(blank)
+		p.stmt(s.Assign, false)
+		p.print(blank)
+		p.block(s.Body, 0)
+
+	case *ast.CommClause:
+		if s.Comm != nil {
+			p.print(token.CASE, blank)
+			p.stmt(s.Comm, false)
+		} else {
+			p.print(token.DEFAULT)
+		}
+		p.setPos(s.Colon)
+		p.print(token.COLON)
+		p.stmtList(s.Body, 1, nextIsRBrace)
+
+	case *ast.SelectStmt:
+		p.print(token.SELECT, blank)
+		body := s.Body
+		if len(body.List) == 0 && !p.commentBefore(p.posFor(body.Rbrace)) {
+			// print empty select statement w/o comments on one line
+			p.setPos(body.Lbrace)
+			p.print(token.LBRACE)
+			p.setPos(body.Rbrace)
+			p.print(token.RBRACE)
+		} else {
+			p.block(body, 0)
+		}
+
+	case *ast.ForStmt:
+		p.print(token.FOR)
+		p.controlClause(true, s.Init, s.Cond, s.Post)
+		p.block(s.Body, 1)
+
+	case *ast.RangeStmt:
+		p.print(token.FOR, blank)
+		if s.Key != nil {
+			p.expr(s.Key)
+			if s.Value != nil {
+				// use position of value following the comma as
+				// comma position for correct comment placement
+				p.setPos(s.Value.Pos())
+				p.print(token.COMMA, blank)
+				p.expr(s.Value)
+			}
+			p.print(blank)
+			p.setPos(s.TokPos)
+			p.print(s.Tok, blank)
+		}
+		p.print(token.RANGE, blank)
+		p.expr(stripParens(s.X))
+		p.print(blank)
+		p.block(s.Body, 1)
+
+	default:
+		panic("unreachable")
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+// The keepTypeColumn function determines if the type column of a series of
+// consecutive const or var declarations must be kept, or if initialization
+// values (V) can be placed in the type column (T) instead. The i'th entry
+// in the result slice is true if the type column in spec[i] must be kept.
+//
+// For example, the declaration:
+//
+//		const (
+//			foobar int = 42 // comment
+//			x          = 7  // comment
+//			foo
+//	             bar = 991
+//		)
+//
+// leads to the type/values matrix below. A run of value columns (V) can
+// be moved into the type column if there is no type for any of the values
+// in that column (we only move entire columns so that they align properly).
+//
+//		matrix        formatted     result
+//	                   matrix
+//		T  V    ->    T  V     ->   true      there is a T and so the type
+//		-  V          -  V          true      column must be kept
+//		-  -          -  -          false
+//		-  V          V  -          false     V is moved into T column
+func keepTypeColumn(specs []ast.Spec) []bool {
+	m := make([]bool, len(specs))
+
+	populate := func(i, j int, keepType bool) {
+		if keepType {
+			for ; i < j; i++ {
+				m[i] = true
+			}
+		}
+	}
+
+	i0 := -1 // if i0 >= 0 we are in a run and i0 is the start of the run
+	var keepType bool
+	for i, s := range specs {
+		t := s.(*ast.ValueSpec)
+		if t.Values != nil {
+			if i0 < 0 {
+				// start of a run of ValueSpecs with non-nil Values
+				i0 = i
+				keepType = false
+			}
+		} else {
+			if i0 >= 0 {
+				// end of a run
+				populate(i0, i, keepType)
+				i0 = -1
+			}
+		}
+		if t.Type != nil {
+			keepType = true
+		}
+	}
+	if i0 >= 0 {
+		// end of a run
+		populate(i0, len(specs), keepType)
+	}
+
+	return m
+}
+
+func (p *printer) valueSpec(s *ast.ValueSpec, keepType bool) {
+	p.setComment(s.Doc)
+	p.identList(s.Names, false) // always present
+	extraTabs := 3
+	if s.Type != nil || keepType {
+		p.print(vtab)
+		extraTabs--
+	}
+	if s.Type != nil {
+		p.expr(s.Type)
+	}
+	if s.Values != nil {
+		p.print(vtab, token.ASSIGN, blank)
+		p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
+		extraTabs--
+	}
+	if s.Comment != nil {
+		for ; extraTabs > 0; extraTabs-- {
+			p.print(vtab)
+		}
+		p.setComment(s.Comment)
+	}
+}
+
+func sanitizeImportPath(lit *ast.BasicLit) *ast.BasicLit {
+	// Note: An unmodified AST generated by go/parser will already
+	// contain a backward- or double-quoted path string that does
+	// not contain any invalid characters, and most of the work
+	// here is not needed. However, a modified or generated AST
+	// may possibly contain non-canonical paths. Do the work in
+	// all cases since it's not too hard and not speed-critical.
+
+	// if we don't have a proper string, be conservative and return whatever we have
+	if lit.Kind != token.STRING {
+		return lit
+	}
+	s, err := strconv.Unquote(lit.Value)
+	if err != nil {
+		return lit
+	}
+
+	// if the string is an invalid path, return whatever we have
+	//
+	// spec: "Implementation restriction: A compiler may restrict
+	// ImportPaths to non-empty strings using only characters belonging
+	// to Unicode's L, M, N, P, and S general categories (the Graphic
+	// characters without spaces) and may also exclude the characters
+	// !"#$%&'()*,:;<=>?[\]^`{|} and the Unicode replacement character
+	// U+FFFD."
+	if s == "" {
+		return lit
+	}
+	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
+	for _, r := range s {
+		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
+			return lit
+		}
+	}
+
+	// otherwise, return the double-quoted path
+	s = strconv.Quote(s)
+	if s == lit.Value {
+		return lit // nothing wrong with lit
+	}
+	return &ast.BasicLit{ValuePos: lit.ValuePos, Kind: token.STRING, Value: s}
+}
+
+// The parameter n is the number of specs in the group. If doIndent is set,
+// multi-line identifier lists in the spec are indented when the first
+// linebreak is encountered.
+func (p *printer) spec(spec ast.Spec, n int, doIndent bool) {
+	switch s := spec.(type) {
+	case *ast.ImportSpec:
+		p.setComment(s.Doc)
+		if s.Name != nil {
+			p.expr(s.Name)
+			p.print(blank)
+		}
+		p.expr(sanitizeImportPath(s.Path))
+		p.setComment(s.Comment)
+		p.setPos(s.EndPos)
+
+	case *ast.ValueSpec:
+		if n != 1 {
+			p.internalError("expected n = 1; got", n)
+		}
+		p.setComment(s.Doc)
+		p.identList(s.Names, doIndent) // always present
+		if s.Type != nil {
+			p.print(blank)
+			p.expr(s.Type)
+		}
+		if s.Values != nil {
+			p.print(blank, token.ASSIGN, blank)
+			p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
+		}
+		p.setComment(s.Comment)
+
+	case *ast.TypeSpec:
+		p.setComment(s.Doc)
+		p.expr(s.Name)
+		if s.TypeParams != nil {
+			p.parameters(s.TypeParams, typeTParam)
+		}
+		if n == 1 {
+			p.print(blank)
+		} else {
+			p.print(vtab)
+		}
+		if s.Assign.IsValid() {
+			p.print(token.ASSIGN, blank)
+		}
+		p.expr(s.Type)
+		p.setComment(s.Comment)
+
+	default:
+		panic("unreachable")
+	}
+}
+
+func (p *printer) genDecl(d *ast.GenDecl) {
+	p.setComment(d.Doc)
+	p.setPos(d.Pos())
+	p.print(d.Tok, blank)
+
+	if d.Lparen.IsValid() || len(d.Specs) > 1 {
+		// group of parenthesized declarations
+		p.setPos(d.Lparen)
+		p.print(token.LPAREN)
+		if n := len(d.Specs); n > 0 {
+			p.print(indent, formfeed)
+			if n > 1 && (d.Tok == token.CONST || d.Tok == token.VAR) {
+				// two or more grouped const/var declarations:
+				// determine if the type column must be kept
+				keepType := keepTypeColumn(d.Specs)
+				var line int
+				for i, s := range d.Specs {
+					if i > 0 {
+						p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
+					}
+					p.recordLine(&line)
+					p.valueSpec(s.(*ast.ValueSpec), keepType[i])
+				}
+			} else {
+				var line int
+				for i, s := range d.Specs {
+					if i > 0 {
+						p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
+					}
+					p.recordLine(&line)
+					p.spec(s, n, false)
+				}
+			}
+			p.print(unindent, formfeed)
+		}
+		p.setPos(d.Rparen)
+		p.print(token.RPAREN)
+
+	} else if len(d.Specs) > 0 {
+		// single declaration
+		p.spec(d.Specs[0], 1, true)
+	}
+}
+
+// sizeCounter is an io.Writer which counts the number of bytes written,
+// as well as whether a newline character was seen.
+type sizeCounter struct {
+	hasNewline bool
+	size       int
+}
+
+func (c *sizeCounter) Write(p []byte) (int, error) {
+	if !c.hasNewline {
+		for _, b := range p {
+			if b == '\n' || b == '\f' {
+				c.hasNewline = true
+				break
+			}
+		}
+	}
+	c.size += len(p)
+	return len(p), nil
+}
+
+// nodeSize determines the size of n in chars after formatting.
+// The result is <= maxSize if the node fits on one line with at
+// most maxSize chars and the formatted output doesn't contain
+// any control chars. Otherwise, the result is > maxSize.
+func (p *printer) nodeSize(n ast.Node, maxSize int) (size int) {
+	// nodeSize invokes the printer, which may invoke nodeSize
+	// recursively. For deep composite literal nests, this can
+	// lead to an exponential algorithm. Remember previous
+	// results to prune the recursion (was issue 1628).
+	if size, found := p.nodeSizes[n]; found {
+		return size
+	}
+
+	size = maxSize + 1 // assume n doesn't fit
+	p.nodeSizes[n] = size
+
+	// nodeSize computation must be independent of particular
+	// style so that we always get the same decision; print
+	// in RawFormat
+	cfg := Config{Mode: RawFormat}
+	var counter sizeCounter
+	if err := cfg.fprint(&counter, p.fset, n, p.nodeSizes); err != nil {
+		return
+	}
+	if counter.size <= maxSize && !counter.hasNewline {
+		// n fits in a single line
+		size = counter.size
+		p.nodeSizes[n] = size
+	}
+	return
+}
+
+// numLines returns the number of lines spanned by node n in the original source.
+func (p *printer) numLines(n ast.Node) int {
+	if from := n.Pos(); from.IsValid() {
+		if to := n.End(); to.IsValid() {
+			return p.lineFor(to) - p.lineFor(from) + 1
+		}
+	}
+	return infinity
+}
+
+// bodySize is like nodeSize but it is specialized for *ast.BlockStmt's.
+func (p *printer) bodySize(b *ast.BlockStmt, maxSize int) int {
+	pos1 := b.Pos()
+	pos2 := b.Rbrace
+	if pos1.IsValid() && pos2.IsValid() && p.lineFor(pos1) != p.lineFor(pos2) {
+		// opening and closing brace are on different lines - don't make it a one-liner
+		return maxSize + 1
+	}
+	if len(b.List) > 5 {
+		// too many statements - don't make it a one-liner
+		return maxSize + 1
+	}
+	// otherwise, estimate body size
+	bodySize := p.commentSizeBefore(p.posFor(pos2))
+	for i, s := range b.List {
+		if bodySize > maxSize {
+			break // no need to continue
+		}
+		if i > 0 {
+			bodySize += 2 // space for a semicolon and blank
+		}
+		bodySize += p.nodeSize(s, maxSize)
+	}
+	return bodySize
+}
+
+// funcBody prints a function body following a function header of given headerSize.
+// If the header's and block's size are "small enough" and the block is "simple enough",
+// the block is printed on the current line, without line breaks, spaced from the header
+// by sep. Otherwise the block's opening "{" is printed on the current line, followed by
+// lines for the block's statements and its closing "}".
+func (p *printer) funcBody(headerSize int, sep whiteSpace, b *ast.BlockStmt) {
+	if b == nil {
+		return
+	}
+
+	// save/restore composite literal nesting level
+	defer func(level int) {
+		p.level = level
+	}(p.level)
+	p.level = 0
+
+	const maxSize = 100
+	if headerSize+p.bodySize(b, maxSize) <= maxSize {
+		p.print(sep)
+		p.setPos(b.Lbrace)
+		p.print(token.LBRACE)
+		if len(b.List) > 0 {
+			p.print(blank)
+			for i, s := range b.List {
+				if i > 0 {
+					p.print(token.SEMICOLON, blank)
+				}
+				p.stmt(s, i == len(b.List)-1)
+			}
+			p.print(blank)
+		}
+		p.print(noExtraLinebreak)
+		p.setPos(b.Rbrace)
+		p.print(token.RBRACE, noExtraLinebreak)
+		return
+	}
+
+	if sep != ignore {
+		p.print(blank) // always use blank
+	}
+	p.block(b, 1)
+}
+
+// distanceFrom returns the column difference between p.out (the current output
+// position) and startOutCol. If the start position is on a different line from
+// the current position (or either is unknown), the result is infinity.
+func (p *printer) distanceFrom(startPos token.Pos, startOutCol int) int {
+	if startPos.IsValid() && p.pos.IsValid() && p.posFor(startPos).Line == p.pos.Line {
+		return p.out.Column - startOutCol
+	}
+	return infinity
+}
+
+func (p *printer) funcDecl(d *ast.FuncDecl) {
+	p.setComment(d.Doc)
+	p.setPos(d.Pos())
+	p.print(token.FUNC, blank)
+	// We have to save startCol only after emitting FUNC; otherwise it can be on a
+	// different line (all whitespace preceding the FUNC is emitted only when the
+	// FUNC is emitted).
+	startCol := p.out.Column - len("func ")
+	if d.Recv != nil {
+		p.parameters(d.Recv, funcParam) // method: print receiver
+		p.print(blank)
+	}
+	p.expr(d.Name)
+	p.signature(d.Type)
+	p.funcBody(p.distanceFrom(d.Pos(), startCol), vtab, d.Body)
+}
+
+func (p *printer) decl(decl ast.Decl) {
+	switch d := decl.(type) {
+	case *ast.BadDecl:
+		p.setPos(d.Pos())
+		p.print("BadDecl")
+	case *ast.GenDecl:
+		p.genDecl(d)
+	case *ast.FuncDecl:
+		p.funcDecl(d)
+	default:
+		panic("unreachable")
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Files
+
+func declToken(decl ast.Decl) (tok token.Token) {
+	tok = token.ILLEGAL
+	switch d := decl.(type) {
+	case *ast.GenDecl:
+		tok = d.Tok
+	case *ast.FuncDecl:
+		tok = token.FUNC
+	}
+	return
+}
+
+func (p *printer) declList(list []ast.Decl) {
+	tok := token.ILLEGAL
+	for _, d := range list {
+		prev := tok
+		tok = declToken(d)
+		// If the declaration token changed (e.g., from CONST to TYPE)
+		// or the next declaration has documentation associated with it,
+		// print an empty line between top-level declarations.
+		// (because p.linebreak is called with the position of d, which
+		// is past any documentation, the minimum requirement is satisfied
+		// even w/o the extra getDoc(d) nil-check - leave it in case the
+		// linebreak logic improves - there's already a TODO).
+		if len(p.output) > 0 {
+			// only print line break if we are not at the beginning of the output
+			// (i.e., we are not printing only a partial program)
+			min := 1
+			if prev != tok || getDoc(d) != nil {
+				min = 2
+			}
+			// start a new section if the next declaration is a function
+			// that spans multiple lines (see also issue #19544)
+			p.linebreak(p.lineFor(d.Pos()), min, ignore, tok == token.FUNC && p.numLines(d) > 1)
+		}
+		p.decl(d)
+	}
+}
+
+func (p *printer) file(src *ast.File) {
+	p.setComment(src.Doc)
+	p.setPos(src.Pos())
+	p.print(token.PACKAGE, blank)
+	p.expr(src.Name)
+	p.declList(src.Decls)
+	p.print(newline)
+}
diff --git a/src/go/printer/performance_test.go b/src/go/printer/performance_test.go
new file mode 100644
index 0000000..c58f6d4
--- /dev/null
+++ b/src/go/printer/performance_test.go
@@ -0,0 +1,91 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements a simple printer performance benchmark:
+// go test -bench=BenchmarkPrint
+
+package printer
+
+import (
+	"bytes"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"io"
+	"log"
+	"os"
+	"testing"
+)
+
+var (
+	fileNode *ast.File
+	fileSize int64
+
+	declNode ast.Decl
+	declSize int64
+)
+
+func testprint(out io.Writer, node ast.Node) {
+	if err := (&Config{TabIndent | UseSpaces | normalizeNumbers, 8, 0}).Fprint(out, fset, node); err != nil {
+		log.Fatalf("print error: %s", err)
+	}
+}
+
+// cannot initialize in init because (printer) Fprint launches goroutines.
+func initialize() {
+	const filename = "testdata/parser.go"
+
+	src, err := os.ReadFile(filename)
+	if err != nil {
+		log.Fatalf("%s", err)
+	}
+
+	file, err := parser.ParseFile(fset, filename, src, parser.ParseComments)
+	if err != nil {
+		log.Fatalf("%s", err)
+	}
+
+	var buf bytes.Buffer
+	testprint(&buf, file)
+	if !bytes.Equal(buf.Bytes(), src) {
+		log.Fatalf("print error: %s not idempotent", filename)
+	}
+
+	fileNode = file
+	fileSize = int64(len(src))
+
+	for _, decl := range file.Decls {
+		// The first global variable, which is pretty short:
+		//
+		//	var unresolved = new(ast.Object)
+		if decl, ok := decl.(*ast.GenDecl); ok && decl.Tok == token.VAR {
+			declNode = decl
+			declSize = int64(fset.Position(decl.End()).Offset - fset.Position(decl.Pos()).Offset)
+			break
+		}
+
+	}
+}
+
+func BenchmarkPrintFile(b *testing.B) {
+	if fileNode == nil {
+		initialize()
+	}
+	b.ReportAllocs()
+	b.SetBytes(fileSize)
+	for i := 0; i < b.N; i++ {
+		testprint(io.Discard, fileNode)
+	}
+}
+
+func BenchmarkPrintDecl(b *testing.B) {
+	if declNode == nil {
+		initialize()
+	}
+	b.ReportAllocs()
+	b.SetBytes(declSize)
+	for i := 0; i < b.N; i++ {
+		testprint(io.Discard, declNode)
+	}
+}
diff --git a/src/go/printer/printer.go b/src/go/printer/printer.go
new file mode 100644
index 0000000..46131c6
--- /dev/null
+++ b/src/go/printer/printer.go
@@ -0,0 +1,1436 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package printer implements printing of AST nodes.
+package printer
+
+import (
+	"fmt"
+	"go/ast"
+	"go/build/constraint"
+	"go/token"
+	"io"
+	"os"
+	"strings"
+	"sync"
+	"text/tabwriter"
+	"unicode"
+)
+
+const (
+	maxNewlines = 2     // max. number of newlines between source text
+	debug       = false // enable for debugging
+	infinity    = 1 << 30
+)
+
+type whiteSpace byte
+
+const (
+	ignore   = whiteSpace(0)
+	blank    = whiteSpace(' ')
+	vtab     = whiteSpace('\v')
+	newline  = whiteSpace('\n')
+	formfeed = whiteSpace('\f')
+	indent   = whiteSpace('>')
+	unindent = whiteSpace('<')
+)
+
+// A pmode value represents the current printer mode.
+type pmode int
+
+const (
+	noExtraBlank     pmode = 1 << iota // disables extra blank after /*-style comment
+	noExtraLinebreak                   // disables extra line break after /*-style comment
+)
+
+type commentInfo struct {
+	cindex         int               // current comment index
+	comment        *ast.CommentGroup // = printer.comments[cindex]; or nil
+	commentOffset  int               // = printer.posFor(printer.comments[cindex].List[0].Pos()).Offset; or infinity
+	commentNewline bool              // true if the comment group contains newlines
+}
+
+type printer struct {
+	// Configuration (does not change after initialization)
+	Config
+	fset *token.FileSet
+
+	// Current state
+	output       []byte       // raw printer result
+	indent       int          // current indentation
+	level        int          // level == 0: outside composite literal; level > 0: inside composite literal
+	mode         pmode        // current printer mode
+	endAlignment bool         // if set, terminate alignment immediately
+	impliedSemi  bool         // if set, a linebreak implies a semicolon
+	lastTok      token.Token  // last token printed (token.ILLEGAL if it's whitespace)
+	prevOpen     token.Token  // previous non-brace "open" token (, [, or token.ILLEGAL
+	wsbuf        []whiteSpace // delayed white space
+	goBuild      []int        // start index of all //go:build comments in output
+	plusBuild    []int        // start index of all // +build comments in output
+
+	// Positions
+	// The out position differs from the pos position when the result
+	// formatting differs from the source formatting (in the amount of
+	// white space). If there's a difference and SourcePos is set in
+	// ConfigMode, //line directives are used in the output to restore
+	// original source positions for a reader.
+	pos          token.Position // current position in AST (source) space
+	out          token.Position // current position in output space
+	last         token.Position // value of pos after calling writeString
+	linePtr      *int           // if set, record out.Line for the next token in *linePtr
+	sourcePosErr error          // if non-nil, the first error emitting a //line directive
+
+	// The list of all source comments, in order of appearance.
+	comments        []*ast.CommentGroup // may be nil
+	useNodeComments bool                // if not set, ignore lead and line comments of nodes
+
+	// Information about p.comments[p.cindex]; set up by nextComment.
+	commentInfo
+
+	// Cache of already computed node sizes.
+	nodeSizes map[ast.Node]int
+
+	// Cache of most recently computed line position.
+	cachedPos  token.Pos
+	cachedLine int // line corresponding to cachedPos
+}
+
+func (p *printer) internalError(msg ...any) {
+	if debug {
+		fmt.Print(p.pos.String() + ": ")
+		fmt.Println(msg...)
+		panic("go/printer")
+	}
+}
+
+// commentsHaveNewline reports whether a list of comments belonging to
+// an *ast.CommentGroup contains newlines. Because the position information
+// may only be partially correct, we also have to read the comment text.
+func (p *printer) commentsHaveNewline(list []*ast.Comment) bool {
+	// len(list) > 0
+	line := p.lineFor(list[0].Pos())
+	for i, c := range list {
+		if i > 0 && p.lineFor(list[i].Pos()) != line {
+			// not all comments on the same line
+			return true
+		}
+		if t := c.Text; len(t) >= 2 && (t[1] == '/' || strings.Contains(t, "\n")) {
+			return true
+		}
+	}
+	_ = line
+	return false
+}
+
+func (p *printer) nextComment() {
+	for p.cindex < len(p.comments) {
+		c := p.comments[p.cindex]
+		p.cindex++
+		if list := c.List; len(list) > 0 {
+			p.comment = c
+			p.commentOffset = p.posFor(list[0].Pos()).Offset
+			p.commentNewline = p.commentsHaveNewline(list)
+			return
+		}
+		// we should not reach here (correct ASTs don't have empty
+		// ast.CommentGroup nodes), but be conservative and try again
+	}
+	// no more comments
+	p.commentOffset = infinity
+}
+
+// commentBefore reports whether the current comment group occurs
+// before the next position in the source code and printing it does
+// not introduce implicit semicolons.
+func (p *printer) commentBefore(next token.Position) bool {
+	return p.commentOffset < next.Offset && (!p.impliedSemi || !p.commentNewline)
+}
+
+// commentSizeBefore returns the estimated size of the
+// comments on the same line before the next position.
+func (p *printer) commentSizeBefore(next token.Position) int {
+	// save/restore current p.commentInfo (p.nextComment() modifies it)
+	defer func(info commentInfo) {
+		p.commentInfo = info
+	}(p.commentInfo)
+
+	size := 0
+	for p.commentBefore(next) {
+		for _, c := range p.comment.List {
+			size += len(c.Text)
+		}
+		p.nextComment()
+	}
+	return size
+}
+
+// recordLine records the output line number for the next non-whitespace
+// token in *linePtr. It is used to compute an accurate line number for a
+// formatted construct, independent of pending (not yet emitted) whitespace
+// or comments.
+func (p *printer) recordLine(linePtr *int) {
+	p.linePtr = linePtr
+}
+
+// linesFrom returns the number of output lines between the current
+// output line and the line argument, ignoring any pending (not yet
+// emitted) whitespace or comments. It is used to compute an accurate
+// size (in number of lines) for a formatted construct.
+func (p *printer) linesFrom(line int) int {
+	return p.out.Line - line
+}
+
+func (p *printer) posFor(pos token.Pos) token.Position {
+	// not used frequently enough to cache entire token.Position
+	return p.fset.PositionFor(pos, false /* absolute position */)
+}
+
+func (p *printer) lineFor(pos token.Pos) int {
+	if pos != p.cachedPos {
+		p.cachedPos = pos
+		p.cachedLine = p.fset.PositionFor(pos, false /* absolute position */).Line
+	}
+	return p.cachedLine
+}
+
+// writeLineDirective writes a //line directive if necessary.
+func (p *printer) writeLineDirective(pos token.Position) {
+	if pos.IsValid() && (p.out.Line != pos.Line || p.out.Filename != pos.Filename) {
+		if strings.ContainsAny(pos.Filename, "\r\n") {
+			if p.sourcePosErr == nil {
+				p.sourcePosErr = fmt.Errorf("go/printer: source filename contains unexpected newline character: %q", pos.Filename)
+			}
+			return
+		}
+
+		p.output = append(p.output, tabwriter.Escape) // protect '\n' in //line from tabwriter interpretation
+		p.output = append(p.output, fmt.Sprintf("//line %s:%d\n", pos.Filename, pos.Line)...)
+		p.output = append(p.output, tabwriter.Escape)
+		// p.out must match the //line directive
+		p.out.Filename = pos.Filename
+		p.out.Line = pos.Line
+	}
+}
+
+// writeIndent writes indentation.
+func (p *printer) writeIndent() {
+	// use "hard" htabs - indentation columns
+	// must not be discarded by the tabwriter
+	n := p.Config.Indent + p.indent // include base indentation
+	for i := 0; i < n; i++ {
+		p.output = append(p.output, '\t')
+	}
+
+	// update positions
+	p.pos.Offset += n
+	p.pos.Column += n
+	p.out.Column += n
+}
+
+// writeByte writes ch n times to p.output and updates p.pos.
+// Only used to write formatting (white space) characters.
+func (p *printer) writeByte(ch byte, n int) {
+	if p.endAlignment {
+		// Ignore any alignment control character;
+		// and at the end of the line, break with
+		// a formfeed to indicate termination of
+		// existing columns.
+		switch ch {
+		case '\t', '\v':
+			ch = ' '
+		case '\n', '\f':
+			ch = '\f'
+			p.endAlignment = false
+		}
+	}
+
+	if p.out.Column == 1 {
+		// no need to write line directives before white space
+		p.writeIndent()
+	}
+
+	for i := 0; i < n; i++ {
+		p.output = append(p.output, ch)
+	}
+
+	// update positions
+	p.pos.Offset += n
+	if ch == '\n' || ch == '\f' {
+		p.pos.Line += n
+		p.out.Line += n
+		p.pos.Column = 1
+		p.out.Column = 1
+		return
+	}
+	p.pos.Column += n
+	p.out.Column += n
+}
+
+// writeString writes the string s to p.output and updates p.pos, p.out,
+// and p.last. If isLit is set, s is escaped w/ tabwriter.Escape characters
+// to protect s from being interpreted by the tabwriter.
+//
+// Note: writeString is only used to write Go tokens, literals, and
+// comments, all of which must be written literally. Thus, it is correct
+// to always set isLit = true. However, setting it explicitly only when
+// needed (i.e., when we don't know that s contains no tabs or line breaks)
+// avoids processing extra escape characters and reduces run time of the
+// printer benchmark by up to 10%.
+func (p *printer) writeString(pos token.Position, s string, isLit bool) {
+	if p.out.Column == 1 {
+		if p.Config.Mode&SourcePos != 0 {
+			p.writeLineDirective(pos)
+		}
+		p.writeIndent()
+	}
+
+	if pos.IsValid() {
+		// update p.pos (if pos is invalid, continue with existing p.pos)
+		// Note: Must do this after handling line beginnings because
+		// writeIndent updates p.pos if there's indentation, but p.pos
+		// is the position of s.
+		p.pos = pos
+	}
+
+	if isLit {
+		// Protect s such that is passes through the tabwriter
+		// unchanged. Note that valid Go programs cannot contain
+		// tabwriter.Escape bytes since they do not appear in legal
+		// UTF-8 sequences.
+		p.output = append(p.output, tabwriter.Escape)
+	}
+
+	if debug {
+		p.output = append(p.output, fmt.Sprintf("/*%s*/", pos)...) // do not update p.pos!
+	}
+	p.output = append(p.output, s...)
+
+	// update positions
+	nlines := 0
+	var li int // index of last newline; valid if nlines > 0
+	for i := 0; i < len(s); i++ {
+		// Raw string literals may contain any character except back quote (`).
+		if ch := s[i]; ch == '\n' || ch == '\f' {
+			// account for line break
+			nlines++
+			li = i
+			// A line break inside a literal will break whatever column
+			// formatting is in place; ignore any further alignment through
+			// the end of the line.
+			p.endAlignment = true
+		}
+	}
+	p.pos.Offset += len(s)
+	if nlines > 0 {
+		p.pos.Line += nlines
+		p.out.Line += nlines
+		c := len(s) - li
+		p.pos.Column = c
+		p.out.Column = c
+	} else {
+		p.pos.Column += len(s)
+		p.out.Column += len(s)
+	}
+
+	if isLit {
+		p.output = append(p.output, tabwriter.Escape)
+	}
+
+	p.last = p.pos
+}
+
+// writeCommentPrefix writes the whitespace before a comment.
+// If there is any pending whitespace, it consumes as much of
+// it as is likely to help position the comment nicely.
+// pos is the comment position, next the position of the item
+// after all pending comments, prev is the previous comment in
+// a group of comments (or nil), and tok is the next token.
+func (p *printer) writeCommentPrefix(pos, next token.Position, prev *ast.Comment, tok token.Token) {
+	if len(p.output) == 0 {
+		// the comment is the first item to be printed - don't write any whitespace
+		return
+	}
+
+	if pos.IsValid() && pos.Filename != p.last.Filename {
+		// comment in a different file - separate with newlines
+		p.writeByte('\f', maxNewlines)
+		return
+	}
+
+	if pos.Line == p.last.Line && (prev == nil || prev.Text[1] != '/') {
+		// comment on the same line as last item:
+		// separate with at least one separator
+		hasSep := false
+		if prev == nil {
+			// first comment of a comment group
+			j := 0
+			for i, ch := range p.wsbuf {
+				switch ch {
+				case blank:
+					// ignore any blanks before a comment
+					p.wsbuf[i] = ignore
+					continue
+				case vtab:
+					// respect existing tabs - important
+					// for proper formatting of commented structs
+					hasSep = true
+					continue
+				case indent:
+					// apply pending indentation
+					continue
+				}
+				j = i
+				break
+			}
+			p.writeWhitespace(j)
+		}
+		// make sure there is at least one separator
+		if !hasSep {
+			sep := byte('\t')
+			if pos.Line == next.Line {
+				// next item is on the same line as the comment
+				// (which must be a /*-style comment): separate
+				// with a blank instead of a tab
+				sep = ' '
+			}
+			p.writeByte(sep, 1)
+		}
+
+	} else {
+		// comment on a different line:
+		// separate with at least one line break
+		droppedLinebreak := false
+		j := 0
+		for i, ch := range p.wsbuf {
+			switch ch {
+			case blank, vtab:
+				// ignore any horizontal whitespace before line breaks
+				p.wsbuf[i] = ignore
+				continue
+			case indent:
+				// apply pending indentation
+				continue
+			case unindent:
+				// if this is not the last unindent, apply it
+				// as it is (likely) belonging to the last
+				// construct (e.g., a multi-line expression list)
+				// and is not part of closing a block
+				if i+1 < len(p.wsbuf) && p.wsbuf[i+1] == unindent {
+					continue
+				}
+				// if the next token is not a closing }, apply the unindent
+				// if it appears that the comment is aligned with the
+				// token; otherwise assume the unindent is part of a
+				// closing block and stop (this scenario appears with
+				// comments before a case label where the comments
+				// apply to the next case instead of the current one)
+				if tok != token.RBRACE && pos.Column == next.Column {
+					continue
+				}
+			case newline, formfeed:
+				p.wsbuf[i] = ignore
+				droppedLinebreak = prev == nil // record only if first comment of a group
+			}
+			j = i
+			break
+		}
+		p.writeWhitespace(j)
+
+		// determine number of linebreaks before the comment
+		n := 0
+		if pos.IsValid() && p.last.IsValid() {
+			n = pos.Line - p.last.Line
+			if n < 0 { // should never happen
+				n = 0
+			}
+		}
+
+		// at the package scope level only (p.indent == 0),
+		// add an extra newline if we dropped one before:
+		// this preserves a blank line before documentation
+		// comments at the package scope level (issue 2570)
+		if p.indent == 0 && droppedLinebreak {
+			n++
+		}
+
+		// make sure there is at least one line break
+		// if the previous comment was a line comment
+		if n == 0 && prev != nil && prev.Text[1] == '/' {
+			n = 1
+		}
+
+		if n > 0 {
+			// use formfeeds to break columns before a comment;
+			// this is analogous to using formfeeds to separate
+			// individual lines of /*-style comments
+			p.writeByte('\f', nlimit(n))
+		}
+	}
+}
+
+// Returns true if s contains only white space
+// (only tabs and blanks can appear in the printer's context).
+func isBlank(s string) bool {
+	for i := 0; i < len(s); i++ {
+		if s[i] > ' ' {
+			return false
+		}
+	}
+	return true
+}
+
+// commonPrefix returns the common prefix of a and b.
+func commonPrefix(a, b string) string {
+	i := 0
+	for i < len(a) && i < len(b) && a[i] == b[i] && (a[i] <= ' ' || a[i] == '*') {
+		i++
+	}
+	return a[0:i]
+}
+
+// trimRight returns s with trailing whitespace removed.
+func trimRight(s string) string {
+	return strings.TrimRightFunc(s, unicode.IsSpace)
+}
+
+// stripCommonPrefix removes a common prefix from /*-style comment lines (unless no
+// comment line is indented, all but the first line have some form of space prefix).
+// The prefix is computed using heuristics such that is likely that the comment
+// contents are nicely laid out after re-printing each line using the printer's
+// current indentation.
+func stripCommonPrefix(lines []string) {
+	if len(lines) <= 1 {
+		return // at most one line - nothing to do
+	}
+	// len(lines) > 1
+
+	// The heuristic in this function tries to handle a few
+	// common patterns of /*-style comments: Comments where
+	// the opening /* and closing */ are aligned and the
+	// rest of the comment text is aligned and indented with
+	// blanks or tabs, cases with a vertical "line of stars"
+	// on the left, and cases where the closing */ is on the
+	// same line as the last comment text.
+
+	// Compute maximum common white prefix of all but the first,
+	// last, and blank lines, and replace blank lines with empty
+	// lines (the first line starts with /* and has no prefix).
+	// In cases where only the first and last lines are not blank,
+	// such as two-line comments, or comments where all inner lines
+	// are blank, consider the last line for the prefix computation
+	// since otherwise the prefix would be empty.
+	//
+	// Note that the first and last line are never empty (they
+	// contain the opening /* and closing */ respectively) and
+	// thus they can be ignored by the blank line check.
+	prefix := ""
+	prefixSet := false
+	if len(lines) > 2 {
+		for i, line := range lines[1 : len(lines)-1] {
+			if isBlank(line) {
+				lines[1+i] = "" // range starts with lines[1]
+			} else {
+				if !prefixSet {
+					prefix = line
+					prefixSet = true
+				}
+				prefix = commonPrefix(prefix, line)
+			}
+
+		}
+	}
+	// If we don't have a prefix yet, consider the last line.
+	if !prefixSet {
+		line := lines[len(lines)-1]
+		prefix = commonPrefix(line, line)
+	}
+
+	/*
+	 * Check for vertical "line of stars" and correct prefix accordingly.
+	 */
+	lineOfStars := false
+	if p, _, ok := strings.Cut(prefix, "*"); ok {
+		// remove trailing blank from prefix so stars remain aligned
+		prefix = strings.TrimSuffix(p, " ")
+		lineOfStars = true
+	} else {
+		// No line of stars present.
+		// Determine the white space on the first line after the /*
+		// and before the beginning of the comment text, assume two
+		// blanks instead of the /* unless the first character after
+		// the /* is a tab. If the first comment line is empty but
+		// for the opening /*, assume up to 3 blanks or a tab. This
+		// whitespace may be found as suffix in the common prefix.
+		first := lines[0]
+		if isBlank(first[2:]) {
+			// no comment text on the first line:
+			// reduce prefix by up to 3 blanks or a tab
+			// if present - this keeps comment text indented
+			// relative to the /* and */'s if it was indented
+			// in the first place
+			i := len(prefix)
+			for n := 0; n < 3 && i > 0 && prefix[i-1] == ' '; n++ {
+				i--
+			}
+			if i == len(prefix) && i > 0 && prefix[i-1] == '\t' {
+				i--
+			}
+			prefix = prefix[0:i]
+		} else {
+			// comment text on the first line
+			suffix := make([]byte, len(first))
+			n := 2 // start after opening /*
+			for n < len(first) && first[n] <= ' ' {
+				suffix[n] = first[n]
+				n++
+			}
+			if n > 2 && suffix[2] == '\t' {
+				// assume the '\t' compensates for the /*
+				suffix = suffix[2:n]
+			} else {
+				// otherwise assume two blanks
+				suffix[0], suffix[1] = ' ', ' '
+				suffix = suffix[0:n]
+			}
+			// Shorten the computed common prefix by the length of
+			// suffix, if it is found as suffix of the prefix.
+			prefix = strings.TrimSuffix(prefix, string(suffix))
+		}
+	}
+
+	// Handle last line: If it only contains a closing */, align it
+	// with the opening /*, otherwise align the text with the other
+	// lines.
+	last := lines[len(lines)-1]
+	closing := "*/"
+	before, _, _ := strings.Cut(last, closing) // closing always present
+	if isBlank(before) {
+		// last line only contains closing */
+		if lineOfStars {
+			closing = " */" // add blank to align final star
+		}
+		lines[len(lines)-1] = prefix + closing
+	} else {
+		// last line contains more comment text - assume
+		// it is aligned like the other lines and include
+		// in prefix computation
+		prefix = commonPrefix(prefix, last)
+	}
+
+	// Remove the common prefix from all but the first and empty lines.
+	for i, line := range lines {
+		if i > 0 && line != "" {
+			lines[i] = line[len(prefix):]
+		}
+	}
+}
+
+func (p *printer) writeComment(comment *ast.Comment) {
+	text := comment.Text
+	pos := p.posFor(comment.Pos())
+
+	const linePrefix = "//line "
+	if strings.HasPrefix(text, linePrefix) && (!pos.IsValid() || pos.Column == 1) {
+		// Possibly a //-style line directive.
+		// Suspend indentation temporarily to keep line directive valid.
+		defer func(indent int) { p.indent = indent }(p.indent)
+		p.indent = 0
+	}
+
+	// shortcut common case of //-style comments
+	if text[1] == '/' {
+		if constraint.IsGoBuild(text) {
+			p.goBuild = append(p.goBuild, len(p.output))
+		} else if constraint.IsPlusBuild(text) {
+			p.plusBuild = append(p.plusBuild, len(p.output))
+		}
+		p.writeString(pos, trimRight(text), true)
+		return
+	}
+
+	// for /*-style comments, print line by line and let the
+	// write function take care of the proper indentation
+	lines := strings.Split(text, "\n")
+
+	// The comment started in the first column but is going
+	// to be indented. For an idempotent result, add indentation
+	// to all lines such that they look like they were indented
+	// before - this will make sure the common prefix computation
+	// is the same independent of how many times formatting is
+	// applied (was issue 1835).
+	if pos.IsValid() && pos.Column == 1 && p.indent > 0 {
+		for i, line := range lines[1:] {
+			lines[1+i] = "   " + line
+		}
+	}
+
+	stripCommonPrefix(lines)
+
+	// write comment lines, separated by formfeed,
+	// without a line break after the last line
+	for i, line := range lines {
+		if i > 0 {
+			p.writeByte('\f', 1)
+			pos = p.pos
+		}
+		if len(line) > 0 {
+			p.writeString(pos, trimRight(line), true)
+		}
+	}
+}
+
+// writeCommentSuffix writes a line break after a comment if indicated
+// and processes any leftover indentation information. If a line break
+// is needed, the kind of break (newline vs formfeed) depends on the
+// pending whitespace. The writeCommentSuffix result indicates if a
+// newline was written or if a formfeed was dropped from the whitespace
+// buffer.
+func (p *printer) writeCommentSuffix(needsLinebreak bool) (wroteNewline, droppedFF bool) {
+	for i, ch := range p.wsbuf {
+		switch ch {
+		case blank, vtab:
+			// ignore trailing whitespace
+			p.wsbuf[i] = ignore
+		case indent, unindent:
+			// don't lose indentation information
+		case newline, formfeed:
+			// if we need a line break, keep exactly one
+			// but remember if we dropped any formfeeds
+			if needsLinebreak {
+				needsLinebreak = false
+				wroteNewline = true
+			} else {
+				if ch == formfeed {
+					droppedFF = true
+				}
+				p.wsbuf[i] = ignore
+			}
+		}
+	}
+	p.writeWhitespace(len(p.wsbuf))
+
+	// make sure we have a line break
+	if needsLinebreak {
+		p.writeByte('\n', 1)
+		wroteNewline = true
+	}
+
+	return
+}
+
+// containsLinebreak reports whether the whitespace buffer contains any line breaks.
+func (p *printer) containsLinebreak() bool {
+	for _, ch := range p.wsbuf {
+		if ch == newline || ch == formfeed {
+			return true
+		}
+	}
+	return false
+}
+
+// intersperseComments consumes all comments that appear before the next token
+// tok and prints it together with the buffered whitespace (i.e., the whitespace
+// that needs to be written before the next token). A heuristic is used to mix
+// the comments and whitespace. The intersperseComments result indicates if a
+// newline was written or if a formfeed was dropped from the whitespace buffer.
+func (p *printer) intersperseComments(next token.Position, tok token.Token) (wroteNewline, droppedFF bool) {
+	var last *ast.Comment
+	for p.commentBefore(next) {
+		list := p.comment.List
+		changed := false
+		if p.lastTok != token.IMPORT && // do not rewrite cgo's import "C" comments
+			p.posFor(p.comment.Pos()).Column == 1 &&
+			p.posFor(p.comment.End()+1) == next {
+			// Unindented comment abutting next token position:
+			// a top-level doc comment.
+			list = formatDocComment(list)
+			changed = true
+
+			if len(p.comment.List) > 0 && len(list) == 0 {
+				// The doc comment was removed entirely.
+				// Keep preceding whitespace.
+				p.writeCommentPrefix(p.posFor(p.comment.Pos()), next, last, tok)
+				// Change print state to continue at next.
+				p.pos = next
+				p.last = next
+				// There can't be any more comments.
+				p.nextComment()
+				return p.writeCommentSuffix(false)
+			}
+		}
+		for _, c := range list {
+			p.writeCommentPrefix(p.posFor(c.Pos()), next, last, tok)
+			p.writeComment(c)
+			last = c
+		}
+		// In case list was rewritten, change print state to where
+		// the original list would have ended.
+		if len(p.comment.List) > 0 && changed {
+			last = p.comment.List[len(p.comment.List)-1]
+			p.pos = p.posFor(last.End())
+			p.last = p.pos
+		}
+		p.nextComment()
+	}
+
+	if last != nil {
+		// If the last comment is a /*-style comment and the next item
+		// follows on the same line but is not a comma, and not a "closing"
+		// token immediately following its corresponding "opening" token,
+		// add an extra separator unless explicitly disabled. Use a blank
+		// as separator unless we have pending linebreaks, they are not
+		// disabled, and we are outside a composite literal, in which case
+		// we want a linebreak (issue 15137).
+		// TODO(gri) This has become overly complicated. We should be able
+		// to track whether we're inside an expression or statement and
+		// use that information to decide more directly.
+		needsLinebreak := false
+		if p.mode&noExtraBlank == 0 &&
+			last.Text[1] == '*' && p.lineFor(last.Pos()) == next.Line &&
+			tok != token.COMMA &&
+			(tok != token.RPAREN || p.prevOpen == token.LPAREN) &&
+			(tok != token.RBRACK || p.prevOpen == token.LBRACK) {
+			if p.containsLinebreak() && p.mode&noExtraLinebreak == 0 && p.level == 0 {
+				needsLinebreak = true
+			} else {
+				p.writeByte(' ', 1)
+			}
+		}
+		// Ensure that there is a line break after a //-style comment,
+		// before EOF, and before a closing '}' unless explicitly disabled.
+		if last.Text[1] == '/' ||
+			tok == token.EOF ||
+			tok == token.RBRACE && p.mode&noExtraLinebreak == 0 {
+			needsLinebreak = true
+		}
+		return p.writeCommentSuffix(needsLinebreak)
+	}
+
+	// no comment was written - we should never reach here since
+	// intersperseComments should not be called in that case
+	p.internalError("intersperseComments called without pending comments")
+	return
+}
+
+// whiteWhitespace writes the first n whitespace entries.
+func (p *printer) writeWhitespace(n int) {
+	// write entries
+	for i := 0; i < n; i++ {
+		switch ch := p.wsbuf[i]; ch {
+		case ignore:
+			// ignore!
+		case indent:
+			p.indent++
+		case unindent:
+			p.indent--
+			if p.indent < 0 {
+				p.internalError("negative indentation:", p.indent)
+				p.indent = 0
+			}
+		case newline, formfeed:
+			// A line break immediately followed by a "correcting"
+			// unindent is swapped with the unindent - this permits
+			// proper label positioning. If a comment is between
+			// the line break and the label, the unindent is not
+			// part of the comment whitespace prefix and the comment
+			// will be positioned correctly indented.
+			if i+1 < n && p.wsbuf[i+1] == unindent {
+				// Use a formfeed to terminate the current section.
+				// Otherwise, a long label name on the next line leading
+				// to a wide column may increase the indentation column
+				// of lines before the label; effectively leading to wrong
+				// indentation.
+				p.wsbuf[i], p.wsbuf[i+1] = unindent, formfeed
+				i-- // do it again
+				continue
+			}
+			fallthrough
+		default:
+			p.writeByte(byte(ch), 1)
+		}
+	}
+
+	// shift remaining entries down
+	l := copy(p.wsbuf, p.wsbuf[n:])
+	p.wsbuf = p.wsbuf[:l]
+}
+
+// ----------------------------------------------------------------------------
+// Printing interface
+
+// nlimit limits n to maxNewlines.
+func nlimit(n int) int {
+	if n > maxNewlines {
+		n = maxNewlines
+	}
+	return n
+}
+
+func mayCombine(prev token.Token, next byte) (b bool) {
+	switch prev {
+	case token.INT:
+		b = next == '.' // 1.
+	case token.ADD:
+		b = next == '+' // ++
+	case token.SUB:
+		b = next == '-' // --
+	case token.QUO:
+		b = next == '*' // /*
+	case token.LSS:
+		b = next == '-' || next == '<' // <- or <<
+	case token.AND:
+		b = next == '&' || next == '^' // && or &^
+	}
+	return
+}
+
+func (p *printer) setPos(pos token.Pos) {
+	if pos.IsValid() {
+		p.pos = p.posFor(pos) // accurate position of next item
+	}
+}
+
+// print prints a list of "items" (roughly corresponding to syntactic
+// tokens, but also including whitespace and formatting information).
+// It is the only print function that should be called directly from
+// any of the AST printing functions in nodes.go.
+//
+// Whitespace is accumulated until a non-whitespace token appears. Any
+// comments that need to appear before that token are printed first,
+// taking into account the amount and structure of any pending white-
+// space for best comment placement. Then, any leftover whitespace is
+// printed, followed by the actual token.
+func (p *printer) print(args ...any) {
+	for _, arg := range args {
+		// information about the current arg
+		var data string
+		var isLit bool
+		var impliedSemi bool // value for p.impliedSemi after this arg
+
+		// record previous opening token, if any
+		switch p.lastTok {
+		case token.ILLEGAL:
+			// ignore (white space)
+		case token.LPAREN, token.LBRACK:
+			p.prevOpen = p.lastTok
+		default:
+			// other tokens followed any opening token
+			p.prevOpen = token.ILLEGAL
+		}
+
+		switch x := arg.(type) {
+		case pmode:
+			// toggle printer mode
+			p.mode ^= x
+			continue
+
+		case whiteSpace:
+			if x == ignore {
+				// don't add ignore's to the buffer; they
+				// may screw up "correcting" unindents (see
+				// LabeledStmt)
+				continue
+			}
+			i := len(p.wsbuf)
+			if i == cap(p.wsbuf) {
+				// Whitespace sequences are very short so this should
+				// never happen. Handle gracefully (but possibly with
+				// bad comment placement) if it does happen.
+				p.writeWhitespace(i)
+				i = 0
+			}
+			p.wsbuf = p.wsbuf[0 : i+1]
+			p.wsbuf[i] = x
+			if x == newline || x == formfeed {
+				// newlines affect the current state (p.impliedSemi)
+				// and not the state after printing arg (impliedSemi)
+				// because comments can be interspersed before the arg
+				// in this case
+				p.impliedSemi = false
+			}
+			p.lastTok = token.ILLEGAL
+			continue
+
+		case *ast.Ident:
+			data = x.Name
+			impliedSemi = true
+			p.lastTok = token.IDENT
+
+		case *ast.BasicLit:
+			data = x.Value
+			isLit = true
+			impliedSemi = true
+			p.lastTok = x.Kind
+
+		case token.Token:
+			s := x.String()
+			if mayCombine(p.lastTok, s[0]) {
+				// the previous and the current token must be
+				// separated by a blank otherwise they combine
+				// into a different incorrect token sequence
+				// (except for token.INT followed by a '.' this
+				// should never happen because it is taken care
+				// of via binary expression formatting)
+				if len(p.wsbuf) != 0 {
+					p.internalError("whitespace buffer not empty")
+				}
+				p.wsbuf = p.wsbuf[0:1]
+				p.wsbuf[0] = ' '
+			}
+			data = s
+			// some keywords followed by a newline imply a semicolon
+			switch x {
+			case token.BREAK, token.CONTINUE, token.FALLTHROUGH, token.RETURN,
+				token.INC, token.DEC, token.RPAREN, token.RBRACK, token.RBRACE:
+				impliedSemi = true
+			}
+			p.lastTok = x
+
+		case string:
+			// incorrect AST - print error message
+			data = x
+			isLit = true
+			impliedSemi = true
+			p.lastTok = token.STRING
+
+		default:
+			fmt.Fprintf(os.Stderr, "print: unsupported argument %v (%T)\n", arg, arg)
+			panic("go/printer type")
+		}
+		// data != ""
+
+		next := p.pos // estimated/accurate position of next item
+		wroteNewline, droppedFF := p.flush(next, p.lastTok)
+
+		// intersperse extra newlines if present in the source and
+		// if they don't cause extra semicolons (don't do this in
+		// flush as it will cause extra newlines at the end of a file)
+		if !p.impliedSemi {
+			n := nlimit(next.Line - p.pos.Line)
+			// don't exceed maxNewlines if we already wrote one
+			if wroteNewline && n == maxNewlines {
+				n = maxNewlines - 1
+			}
+			if n > 0 {
+				ch := byte('\n')
+				if droppedFF {
+					ch = '\f' // use formfeed since we dropped one before
+				}
+				p.writeByte(ch, n)
+				impliedSemi = false
+			}
+		}
+
+		// the next token starts now - record its line number if requested
+		if p.linePtr != nil {
+			*p.linePtr = p.out.Line
+			p.linePtr = nil
+		}
+
+		p.writeString(next, data, isLit)
+		p.impliedSemi = impliedSemi
+	}
+}
+
+// flush prints any pending comments and whitespace occurring textually
+// before the position of the next token tok. The flush result indicates
+// if a newline was written or if a formfeed was dropped from the whitespace
+// buffer.
+func (p *printer) flush(next token.Position, tok token.Token) (wroteNewline, droppedFF bool) {
+	if p.commentBefore(next) {
+		// if there are comments before the next item, intersperse them
+		wroteNewline, droppedFF = p.intersperseComments(next, tok)
+	} else {
+		// otherwise, write any leftover whitespace
+		p.writeWhitespace(len(p.wsbuf))
+	}
+	return
+}
+
+// getDoc returns the ast.CommentGroup associated with n, if any.
+func getDoc(n ast.Node) *ast.CommentGroup {
+	switch n := n.(type) {
+	case *ast.Field:
+		return n.Doc
+	case *ast.ImportSpec:
+		return n.Doc
+	case *ast.ValueSpec:
+		return n.Doc
+	case *ast.TypeSpec:
+		return n.Doc
+	case *ast.GenDecl:
+		return n.Doc
+	case *ast.FuncDecl:
+		return n.Doc
+	case *ast.File:
+		return n.Doc
+	}
+	return nil
+}
+
+func getLastComment(n ast.Node) *ast.CommentGroup {
+	switch n := n.(type) {
+	case *ast.Field:
+		return n.Comment
+	case *ast.ImportSpec:
+		return n.Comment
+	case *ast.ValueSpec:
+		return n.Comment
+	case *ast.TypeSpec:
+		return n.Comment
+	case *ast.GenDecl:
+		if len(n.Specs) > 0 {
+			return getLastComment(n.Specs[len(n.Specs)-1])
+		}
+	case *ast.File:
+		if len(n.Comments) > 0 {
+			return n.Comments[len(n.Comments)-1]
+		}
+	}
+	return nil
+}
+
+func (p *printer) printNode(node any) error {
+	// unpack *CommentedNode, if any
+	var comments []*ast.CommentGroup
+	if cnode, ok := node.(*CommentedNode); ok {
+		node = cnode.Node
+		comments = cnode.Comments
+	}
+
+	if comments != nil {
+		// commented node - restrict comment list to relevant range
+		n, ok := node.(ast.Node)
+		if !ok {
+			goto unsupported
+		}
+		beg := n.Pos()
+		end := n.End()
+		// if the node has associated documentation,
+		// include that commentgroup in the range
+		// (the comment list is sorted in the order
+		// of the comment appearance in the source code)
+		if doc := getDoc(n); doc != nil {
+			beg = doc.Pos()
+		}
+		if com := getLastComment(n); com != nil {
+			if e := com.End(); e > end {
+				end = e
+			}
+		}
+		// token.Pos values are global offsets, we can
+		// compare them directly
+		i := 0
+		for i < len(comments) && comments[i].End() < beg {
+			i++
+		}
+		j := i
+		for j < len(comments) && comments[j].Pos() < end {
+			j++
+		}
+		if i < j {
+			p.comments = comments[i:j]
+		}
+	} else if n, ok := node.(*ast.File); ok {
+		// use ast.File comments, if any
+		p.comments = n.Comments
+	}
+
+	// if there are no comments, use node comments
+	p.useNodeComments = p.comments == nil
+
+	// get comments ready for use
+	p.nextComment()
+
+	p.print(pmode(0))
+
+	// format node
+	switch n := node.(type) {
+	case ast.Expr:
+		p.expr(n)
+	case ast.Stmt:
+		// A labeled statement will un-indent to position the label.
+		// Set p.indent to 1 so we don't get indent "underflow".
+		if _, ok := n.(*ast.LabeledStmt); ok {
+			p.indent = 1
+		}
+		p.stmt(n, false)
+	case ast.Decl:
+		p.decl(n)
+	case ast.Spec:
+		p.spec(n, 1, false)
+	case []ast.Stmt:
+		// A labeled statement will un-indent to position the label.
+		// Set p.indent to 1 so we don't get indent "underflow".
+		for _, s := range n {
+			if _, ok := s.(*ast.LabeledStmt); ok {
+				p.indent = 1
+			}
+		}
+		p.stmtList(n, 0, false)
+	case []ast.Decl:
+		p.declList(n)
+	case *ast.File:
+		p.file(n)
+	default:
+		goto unsupported
+	}
+
+	return p.sourcePosErr
+
+unsupported:
+	return fmt.Errorf("go/printer: unsupported node type %T", node)
+}
+
+// ----------------------------------------------------------------------------
+// Trimmer
+
+// A trimmer is an io.Writer filter for stripping tabwriter.Escape
+// characters, trailing blanks and tabs, and for converting formfeed
+// and vtab characters into newlines and htabs (in case no tabwriter
+// is used). Text bracketed by tabwriter.Escape characters is passed
+// through unchanged.
+type trimmer struct {
+	output io.Writer
+	state  int
+	space  []byte
+}
+
+// trimmer is implemented as a state machine.
+// It can be in one of the following states:
+const (
+	inSpace  = iota // inside space
+	inEscape        // inside text bracketed by tabwriter.Escapes
+	inText          // inside text
+)
+
+func (p *trimmer) resetSpace() {
+	p.state = inSpace
+	p.space = p.space[0:0]
+}
+
+// Design note: It is tempting to eliminate extra blanks occurring in
+//              whitespace in this function as it could simplify some
+//              of the blanks logic in the node printing functions.
+//              However, this would mess up any formatting done by
+//              the tabwriter.
+
+var aNewline = []byte("\n")
+
+func (p *trimmer) Write(data []byte) (n int, err error) {
+	// invariants:
+	// p.state == inSpace:
+	//	p.space is unwritten
+	// p.state == inEscape, inText:
+	//	data[m:n] is unwritten
+	m := 0
+	var b byte
+	for n, b = range data {
+		if b == '\v' {
+			b = '\t' // convert to htab
+		}
+		switch p.state {
+		case inSpace:
+			switch b {
+			case '\t', ' ':
+				p.space = append(p.space, b)
+			case '\n', '\f':
+				p.resetSpace() // discard trailing space
+				_, err = p.output.Write(aNewline)
+			case tabwriter.Escape:
+				_, err = p.output.Write(p.space)
+				p.state = inEscape
+				m = n + 1 // +1: skip tabwriter.Escape
+			default:
+				_, err = p.output.Write(p.space)
+				p.state = inText
+				m = n
+			}
+		case inEscape:
+			if b == tabwriter.Escape {
+				_, err = p.output.Write(data[m:n])
+				p.resetSpace()
+			}
+		case inText:
+			switch b {
+			case '\t', ' ':
+				_, err = p.output.Write(data[m:n])
+				p.resetSpace()
+				p.space = append(p.space, b)
+			case '\n', '\f':
+				_, err = p.output.Write(data[m:n])
+				p.resetSpace()
+				if err == nil {
+					_, err = p.output.Write(aNewline)
+				}
+			case tabwriter.Escape:
+				_, err = p.output.Write(data[m:n])
+				p.state = inEscape
+				m = n + 1 // +1: skip tabwriter.Escape
+			}
+		default:
+			panic("unreachable")
+		}
+		if err != nil {
+			return
+		}
+	}
+	n = len(data)
+
+	switch p.state {
+	case inEscape, inText:
+		_, err = p.output.Write(data[m:n])
+		p.resetSpace()
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Public interface
+
+// A Mode value is a set of flags (or 0). They control printing.
+type Mode uint
+
+const (
+	RawFormat Mode = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
+	TabIndent                  // use tabs for indentation independent of UseSpaces
+	UseSpaces                  // use spaces instead of tabs for alignment
+	SourcePos                  // emit //line directives to preserve original source positions
+)
+
+// The mode below is not included in printer's public API because
+// editing code text is deemed out of scope. Because this mode is
+// unexported, it's also possible to modify or remove it based on
+// the evolving needs of go/format and cmd/gofmt without breaking
+// users. See discussion in CL 240683.
+const (
+	// normalizeNumbers means to canonicalize number
+	// literal prefixes and exponents while printing.
+	//
+	// This value is known in and used by go/format and cmd/gofmt.
+	// It is currently more convenient and performant for those
+	// packages to apply number normalization during printing,
+	// rather than by modifying the AST in advance.
+	normalizeNumbers Mode = 1 << 30
+)
+
+// A Config node controls the output of Fprint.
+type Config struct {
+	Mode     Mode // default: 0
+	Tabwidth int  // default: 8
+	Indent   int  // default: 0 (all code is indented at least by this much)
+}
+
+var printerPool = sync.Pool{
+	New: func() any {
+		return &printer{
+			// Whitespace sequences are short.
+			wsbuf: make([]whiteSpace, 0, 16),
+			// We start the printer with a 16K output buffer, which is currently
+			// larger than about 80% of Go files in the standard library.
+			output: make([]byte, 0, 16<<10),
+		}
+	},
+}
+
+func newPrinter(cfg *Config, fset *token.FileSet, nodeSizes map[ast.Node]int) *printer {
+	p := printerPool.Get().(*printer)
+	*p = printer{
+		Config:    *cfg,
+		fset:      fset,
+		pos:       token.Position{Line: 1, Column: 1},
+		out:       token.Position{Line: 1, Column: 1},
+		wsbuf:     p.wsbuf[:0],
+		nodeSizes: nodeSizes,
+		cachedPos: -1,
+		output:    p.output[:0],
+	}
+	return p
+}
+
+func (p *printer) free() {
+	// Hard limit on buffer size; see https://golang.org/issue/23199.
+	if cap(p.output) > 64<<10 {
+		return
+	}
+
+	printerPool.Put(p)
+}
+
+// fprint implements Fprint and takes a nodesSizes map for setting up the printer state.
+func (cfg *Config) fprint(output io.Writer, fset *token.FileSet, node any, nodeSizes map[ast.Node]int) (err error) {
+	// print node
+	p := newPrinter(cfg, fset, nodeSizes)
+	defer p.free()
+	if err = p.printNode(node); err != nil {
+		return
+	}
+	// print outstanding comments
+	p.impliedSemi = false // EOF acts like a newline
+	p.flush(token.Position{Offset: infinity, Line: infinity}, token.EOF)
+
+	// output is buffered in p.output now.
+	// fix //go:build and // +build comments if needed.
+	p.fixGoBuildLines()
+
+	// redirect output through a trimmer to eliminate trailing whitespace
+	// (Input to a tabwriter must be untrimmed since trailing tabs provide
+	// formatting information. The tabwriter could provide trimming
+	// functionality but no tabwriter is used when RawFormat is set.)
+	output = &trimmer{output: output}
+
+	// redirect output through a tabwriter if necessary
+	if cfg.Mode&RawFormat == 0 {
+		minwidth := cfg.Tabwidth
+
+		padchar := byte('\t')
+		if cfg.Mode&UseSpaces != 0 {
+			padchar = ' '
+		}
+
+		twmode := tabwriter.DiscardEmptyColumns
+		if cfg.Mode&TabIndent != 0 {
+			minwidth = 0
+			twmode |= tabwriter.TabIndent
+		}
+
+		output = tabwriter.NewWriter(output, minwidth, cfg.Tabwidth, 1, padchar, twmode)
+	}
+
+	// write printer result via tabwriter/trimmer to output
+	if _, err = output.Write(p.output); err != nil {
+		return
+	}
+
+	// flush tabwriter, if any
+	if tw, _ := output.(*tabwriter.Writer); tw != nil {
+		err = tw.Flush()
+	}
+
+	return
+}
+
+// A CommentedNode bundles an AST node and corresponding comments.
+// It may be provided as argument to any of the Fprint functions.
+type CommentedNode struct {
+	Node     any // *ast.File, or ast.Expr, ast.Decl, ast.Spec, or ast.Stmt
+	Comments []*ast.CommentGroup
+}
+
+// Fprint "pretty-prints" an AST node to output for a given configuration cfg.
+// Position information is interpreted relative to the file set fset.
+// The node type must be *ast.File, *CommentedNode, []ast.Decl, []ast.Stmt,
+// or assignment-compatible to ast.Expr, ast.Decl, ast.Spec, or ast.Stmt.
+func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node any) error {
+	return cfg.fprint(output, fset, node, make(map[ast.Node]int))
+}
+
+// Fprint "pretty-prints" an AST node to output.
+// It calls Config.Fprint with default settings.
+// Note that gofmt uses tabs for indentation but spaces for alignment;
+// use format.Node (package go/format) for output that matches gofmt.
+func Fprint(output io.Writer, fset *token.FileSet, node any) error {
+	return (&Config{Tabwidth: 8}).Fprint(output, fset, node)
+}
diff --git a/src/go/printer/printer_test.go b/src/go/printer/printer_test.go
new file mode 100644
index 0000000..3a8ce60
--- /dev/null
+++ b/src/go/printer/printer_test.go
@@ -0,0 +1,827 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package printer
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"internal/diff"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+const (
+	dataDir  = "testdata"
+	tabwidth = 8
+)
+
+var update = flag.Bool("update", false, "update golden files")
+
+var fset = token.NewFileSet()
+
+type checkMode uint
+
+const (
+	export checkMode = 1 << iota
+	rawFormat
+	normNumber
+	idempotent
+	allowTypeParams
+)
+
+// format parses src, prints the corresponding AST, verifies the resulting
+// src is syntactically correct, and returns the resulting src or an error
+// if any.
+func format(src []byte, mode checkMode) ([]byte, error) {
+	// parse src
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err != nil {
+		return nil, fmt.Errorf("parse: %s\n%s", err, src)
+	}
+
+	// filter exports if necessary
+	if mode&export != 0 {
+		ast.FileExports(f) // ignore result
+		f.Comments = nil   // don't print comments that are not in AST
+	}
+
+	// determine printer configuration
+	cfg := Config{Tabwidth: tabwidth}
+	if mode&rawFormat != 0 {
+		cfg.Mode |= RawFormat
+	}
+	if mode&normNumber != 0 {
+		cfg.Mode |= normalizeNumbers
+	}
+
+	// print AST
+	var buf bytes.Buffer
+	if err := cfg.Fprint(&buf, fset, f); err != nil {
+		return nil, fmt.Errorf("print: %s", err)
+	}
+
+	// make sure formatted output is syntactically correct
+	res := buf.Bytes()
+	if _, err := parser.ParseFile(fset, "", res, parser.ParseComments); err != nil {
+		return nil, fmt.Errorf("re-parse: %s\n%s", err, buf.Bytes())
+	}
+
+	return res, nil
+}
+
+// lineAt returns the line in text starting at offset offs.
+func lineAt(text []byte, offs int) []byte {
+	i := offs
+	for i < len(text) && text[i] != '\n' {
+		i++
+	}
+	return text[offs:i]
+}
+
+// checkEqual compares a and b.
+func checkEqual(aname, bname string, a, b []byte) error {
+	if bytes.Equal(a, b) {
+		return nil
+	}
+	return errors.New(string(diff.Diff(aname, a, bname, b)))
+}
+
+func runcheck(t *testing.T, source, golden string, mode checkMode) {
+	src, err := os.ReadFile(source)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	res, err := format(src, mode)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	// update golden files if necessary
+	if *update {
+		if err := os.WriteFile(golden, res, 0644); err != nil {
+			t.Error(err)
+		}
+		return
+	}
+
+	// get golden
+	gld, err := os.ReadFile(golden)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	// formatted source and golden must be the same
+	if err := checkEqual(source, golden, res, gld); err != nil {
+		t.Error(err)
+		return
+	}
+
+	if mode&idempotent != 0 {
+		// formatting golden must be idempotent
+		// (This is very difficult to achieve in general and for now
+		// it is only checked for files explicitly marked as such.)
+		res, err = format(gld, mode)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		if err := checkEqual(golden, fmt.Sprintf("format(%s)", golden), gld, res); err != nil {
+			t.Errorf("golden is not idempotent: %s", err)
+		}
+	}
+}
+
+func check(t *testing.T, source, golden string, mode checkMode) {
+	// run the test
+	cc := make(chan int, 1)
+	go func() {
+		runcheck(t, source, golden, mode)
+		cc <- 0
+	}()
+
+	// wait with timeout
+	select {
+	case <-time.After(10 * time.Second): // plenty of a safety margin, even for very slow machines
+		// test running past time out
+		t.Errorf("%s: running too slowly", source)
+	case <-cc:
+		// test finished within allotted time margin
+	}
+}
+
+type entry struct {
+	source, golden string
+	mode           checkMode
+}
+
+// Use go test -update to create/update the respective golden files.
+var data = []entry{
+	{"empty.input", "empty.golden", idempotent},
+	{"comments.input", "comments.golden", 0},
+	{"comments.input", "comments.x", export},
+	{"comments2.input", "comments2.golden", idempotent},
+	{"alignment.input", "alignment.golden", idempotent},
+	{"linebreaks.input", "linebreaks.golden", idempotent},
+	{"expressions.input", "expressions.golden", idempotent},
+	{"expressions.input", "expressions.raw", rawFormat | idempotent},
+	{"declarations.input", "declarations.golden", 0},
+	{"statements.input", "statements.golden", 0},
+	{"slow.input", "slow.golden", idempotent},
+	{"complit.input", "complit.x", export},
+	{"go2numbers.input", "go2numbers.golden", idempotent},
+	{"go2numbers.input", "go2numbers.norm", normNumber | idempotent},
+	{"generics.input", "generics.golden", idempotent | allowTypeParams},
+	{"gobuild1.input", "gobuild1.golden", idempotent},
+	{"gobuild2.input", "gobuild2.golden", idempotent},
+	{"gobuild3.input", "gobuild3.golden", idempotent},
+	{"gobuild4.input", "gobuild4.golden", idempotent},
+	{"gobuild5.input", "gobuild5.golden", idempotent},
+	{"gobuild6.input", "gobuild6.golden", idempotent},
+	{"gobuild7.input", "gobuild7.golden", idempotent},
+}
+
+func TestFiles(t *testing.T) {
+	t.Parallel()
+	for _, e := range data {
+		source := filepath.Join(dataDir, e.source)
+		golden := filepath.Join(dataDir, e.golden)
+		mode := e.mode
+		t.Run(e.source, func(t *testing.T) {
+			t.Parallel()
+			check(t, source, golden, mode)
+			// TODO(gri) check that golden is idempotent
+			//check(t, golden, golden, e.mode)
+		})
+	}
+}
+
+// TestLineComments, using a simple test case, checks that consecutive line
+// comments are properly terminated with a newline even if the AST position
+// information is incorrect.
+func TestLineComments(t *testing.T) {
+	const src = `// comment 1
+	// comment 2
+	// comment 3
+	package main
+	`
+
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err != nil {
+		panic(err) // error in test
+	}
+
+	var buf bytes.Buffer
+	fset = token.NewFileSet() // use the wrong file set
+	Fprint(&buf, fset, f)
+
+	nlines := 0
+	for _, ch := range buf.Bytes() {
+		if ch == '\n' {
+			nlines++
+		}
+	}
+
+	const expected = 3
+	if nlines < expected {
+		t.Errorf("got %d, expected %d\n", nlines, expected)
+		t.Errorf("result:\n%s", buf.Bytes())
+	}
+}
+
+// Verify that the printer can be invoked during initialization.
+func init() {
+	const name = "foobar"
+	var buf bytes.Buffer
+	if err := Fprint(&buf, fset, &ast.Ident{Name: name}); err != nil {
+		panic(err) // error in test
+	}
+	// in debug mode, the result contains additional information;
+	// ignore it
+	if s := buf.String(); !debug && s != name {
+		panic("got " + s + ", want " + name)
+	}
+}
+
+// Verify that the printer doesn't crash if the AST contains BadXXX nodes.
+func TestBadNodes(t *testing.T) {
+	const src = "package p\n("
+	const res = "package p\nBadDecl\n"
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err == nil {
+		t.Error("expected illegal program") // error in test
+	}
+	var buf bytes.Buffer
+	Fprint(&buf, fset, f)
+	if buf.String() != res {
+		t.Errorf("got %q, expected %q", buf.String(), res)
+	}
+}
+
+// testComment verifies that f can be parsed again after printing it
+// with its first comment set to comment at any possible source offset.
+func testComment(t *testing.T, f *ast.File, srclen int, comment *ast.Comment) {
+	f.Comments[0].List[0] = comment
+	var buf bytes.Buffer
+	for offs := 0; offs <= srclen; offs++ {
+		buf.Reset()
+		// Printing f should result in a correct program no
+		// matter what the (incorrect) comment position is.
+		if err := Fprint(&buf, fset, f); err != nil {
+			t.Error(err)
+		}
+		if _, err := parser.ParseFile(fset, "", buf.Bytes(), 0); err != nil {
+			t.Fatalf("incorrect program for pos = %d:\n%s", comment.Slash, buf.String())
+		}
+		// Position information is just an offset.
+		// Move comment one byte down in the source.
+		comment.Slash++
+	}
+}
+
+// Verify that the printer produces a correct program
+// even if the position information of comments introducing newlines
+// is incorrect.
+func TestBadComments(t *testing.T) {
+	t.Parallel()
+	const src = `
+// first comment - text and position changed by test
+package p
+import "fmt"
+const pi = 3.14 // rough circle
+var (
+	x, y, z int = 1, 2, 3
+	u, v float64
+)
+func fibo(n int) {
+	if n < 2 {
+		return n /* seed values */
+	}
+	return fibo(n-1) + fibo(n-2)
+}
+`
+
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err != nil {
+		t.Error(err) // error in test
+	}
+
+	comment := f.Comments[0].List[0]
+	pos := comment.Pos()
+	if fset.PositionFor(pos, false /* absolute position */).Offset != 1 {
+		t.Error("expected offset 1") // error in test
+	}
+
+	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "//-style comment"})
+	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "/*-style comment */"})
+	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "/*-style \n comment */"})
+	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "/*-style comment \n\n\n */"})
+}
+
+type visitor chan *ast.Ident
+
+func (v visitor) Visit(n ast.Node) (w ast.Visitor) {
+	if ident, ok := n.(*ast.Ident); ok {
+		v <- ident
+	}
+	return v
+}
+
+// idents is an iterator that returns all idents in f via the result channel.
+func idents(f *ast.File) <-chan *ast.Ident {
+	v := make(visitor)
+	go func() {
+		ast.Walk(v, f)
+		close(v)
+	}()
+	return v
+}
+
+// identCount returns the number of identifiers found in f.
+func identCount(f *ast.File) int {
+	n := 0
+	for range idents(f) {
+		n++
+	}
+	return n
+}
+
+// Verify that the SourcePos mode emits correct //line directives
+// by testing that position information for matching identifiers
+// is maintained.
+func TestSourcePos(t *testing.T) {
+	const src = `
+package p
+import ( "go/printer"; "math" )
+const pi = 3.14; var x = 0
+type t struct{ x, y, z int; u, v, w float32 }
+func (t *t) foo(a, b, c int) int {
+	return a*t.x + b*t.y +
+		// two extra lines here
+		// ...
+		c*t.z
+}
+`
+
+	// parse original
+	f1, err := parser.ParseFile(fset, "src", src, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// pretty-print original
+	var buf bytes.Buffer
+	err = (&Config{Mode: UseSpaces | SourcePos, Tabwidth: 8}).Fprint(&buf, fset, f1)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// parse pretty printed original
+	// (//line directives must be interpreted even w/o parser.ParseComments set)
+	f2, err := parser.ParseFile(fset, "", buf.Bytes(), 0)
+	if err != nil {
+		t.Fatalf("%s\n%s", err, buf.Bytes())
+	}
+
+	// At this point the position information of identifiers in f2 should
+	// match the position information of corresponding identifiers in f1.
+
+	// number of identifiers must be > 0 (test should run) and must match
+	n1 := identCount(f1)
+	n2 := identCount(f2)
+	if n1 == 0 {
+		t.Fatal("got no idents")
+	}
+	if n2 != n1 {
+		t.Errorf("got %d idents; want %d", n2, n1)
+	}
+
+	// verify that all identifiers have correct line information
+	i2range := idents(f2)
+	for i1 := range idents(f1) {
+		i2 := <-i2range
+
+		if i2.Name != i1.Name {
+			t.Errorf("got ident %s; want %s", i2.Name, i1.Name)
+		}
+
+		// here we care about the relative (line-directive adjusted) positions
+		l1 := fset.Position(i1.Pos()).Line
+		l2 := fset.Position(i2.Pos()).Line
+		if l2 != l1 {
+			t.Errorf("got line %d; want %d for %s", l2, l1, i1.Name)
+		}
+	}
+
+	if t.Failed() {
+		t.Logf("\n%s", buf.Bytes())
+	}
+}
+
+// Verify that the SourcePos mode doesn't emit unnecessary //line directives
+// before empty lines.
+func TestIssue5945(t *testing.T) {
+	const orig = `
+package p   // line 2
+func f() {} // line 3
+
+var x, y, z int
+
+
+func g() { // line 8
+}
+`
+
+	const want = `//line src.go:2
+package p
+
+//line src.go:3
+func f() {}
+
+var x, y, z int
+
+//line src.go:8
+func g() {
+}
+`
+
+	// parse original
+	f1, err := parser.ParseFile(fset, "src.go", orig, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// pretty-print original
+	var buf bytes.Buffer
+	err = (&Config{Mode: UseSpaces | SourcePos, Tabwidth: 8}).Fprint(&buf, fset, f1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := buf.String()
+
+	// compare original with desired output
+	if got != want {
+		t.Errorf("got:\n%s\nwant:\n%s\n", got, want)
+	}
+}
+
+var decls = []string{
+	`import "fmt"`,
+	"const pi = 3.1415\nconst e = 2.71828\n\nvar x = pi",
+	"func sum(x, y int) int\t{ return x + y }",
+}
+
+func TestDeclLists(t *testing.T) {
+	for _, src := range decls {
+		file, err := parser.ParseFile(fset, "", "package p;"+src, parser.ParseComments)
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		var buf bytes.Buffer
+		err = Fprint(&buf, fset, file.Decls) // only print declarations
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		out := buf.String()
+		if out != src {
+			t.Errorf("\ngot : %q\nwant: %q\n", out, src)
+		}
+	}
+}
+
+var stmts = []string{
+	"i := 0",
+	"select {}\nvar a, b = 1, 2\nreturn a + b",
+	"go f()\ndefer func() {}()",
+}
+
+func TestStmtLists(t *testing.T) {
+	for _, src := range stmts {
+		file, err := parser.ParseFile(fset, "", "package p; func _() {"+src+"}", parser.ParseComments)
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		var buf bytes.Buffer
+		err = Fprint(&buf, fset, file.Decls[0].(*ast.FuncDecl).Body.List) // only print statements
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		out := buf.String()
+		if out != src {
+			t.Errorf("\ngot : %q\nwant: %q\n", out, src)
+		}
+	}
+}
+
+func TestBaseIndent(t *testing.T) {
+	t.Parallel()
+	// The testfile must not contain multi-line raw strings since those
+	// are not indented (because their values must not change) and make
+	// this test fail.
+	const filename = "printer.go"
+	src, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err) // error in test
+	}
+
+	file, err := parser.ParseFile(fset, filename, src, 0)
+	if err != nil {
+		panic(err) // error in test
+	}
+
+	for indent := 0; indent < 4; indent++ {
+		indent := indent
+		t.Run(fmt.Sprint(indent), func(t *testing.T) {
+			t.Parallel()
+			var buf bytes.Buffer
+			(&Config{Tabwidth: tabwidth, Indent: indent}).Fprint(&buf, fset, file)
+			// all code must be indented by at least 'indent' tabs
+			lines := bytes.Split(buf.Bytes(), []byte{'\n'})
+			for i, line := range lines {
+				if len(line) == 0 {
+					continue // empty lines don't have indentation
+				}
+				n := 0
+				for j, b := range line {
+					if b != '\t' {
+						// end of indentation
+						n = j
+						break
+					}
+				}
+				if n < indent {
+					t.Errorf("line %d: got only %d tabs; want at least %d: %q", i, n, indent, line)
+				}
+			}
+		})
+	}
+}
+
+// TestFuncType tests that an ast.FuncType with a nil Params field
+// can be printed (per go/ast specification). Test case for issue 3870.
+func TestFuncType(t *testing.T) {
+	src := &ast.File{
+		Name: &ast.Ident{Name: "p"},
+		Decls: []ast.Decl{
+			&ast.FuncDecl{
+				Name: &ast.Ident{Name: "f"},
+				Type: &ast.FuncType{},
+			},
+		},
+	}
+
+	var buf bytes.Buffer
+	if err := Fprint(&buf, fset, src); err != nil {
+		t.Fatal(err)
+	}
+	got := buf.String()
+
+	const want = `package p
+
+func f()
+`
+
+	if got != want {
+		t.Fatalf("got:\n%s\nwant:\n%s\n", got, want)
+	}
+}
+
+type limitWriter struct {
+	remaining int
+	errCount  int
+}
+
+func (l *limitWriter) Write(buf []byte) (n int, err error) {
+	n = len(buf)
+	if n >= l.remaining {
+		n = l.remaining
+		err = io.EOF
+		l.errCount++
+	}
+	l.remaining -= n
+	return n, err
+}
+
+// Test whether the printer stops writing after the first error
+func TestWriteErrors(t *testing.T) {
+	t.Parallel()
+	const filename = "printer.go"
+	src, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err) // error in test
+	}
+	file, err := parser.ParseFile(fset, filename, src, 0)
+	if err != nil {
+		panic(err) // error in test
+	}
+	for i := 0; i < 20; i++ {
+		lw := &limitWriter{remaining: i}
+		err := (&Config{Mode: RawFormat}).Fprint(lw, fset, file)
+		if lw.errCount > 1 {
+			t.Fatal("Writes continued after first error returned")
+		}
+		// We expect errCount be 1 iff err is set
+		if (lw.errCount != 0) != (err != nil) {
+			t.Fatal("Expected err when errCount != 0")
+		}
+	}
+}
+
+// TextX is a skeleton test that can be filled in for debugging one-off cases.
+// Do not remove.
+func TestX(t *testing.T) {
+	const src = `
+package p
+func _() {}
+`
+	_, err := format([]byte(src), 0)
+	if err != nil {
+		t.Error(err)
+	}
+}
+
+func TestCommentedNode(t *testing.T) {
+	const (
+		input = `package main
+
+func foo() {
+	// comment inside func
+}
+
+// leading comment
+type bar int // comment2
+
+`
+
+		foo = `func foo() {
+	// comment inside func
+}`
+
+		bar = `// leading comment
+type bar int	// comment2
+`
+	)
+
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "input.go", input, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf bytes.Buffer
+
+	err = Fprint(&buf, fset, &CommentedNode{Node: f.Decls[0], Comments: f.Comments})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if buf.String() != foo {
+		t.Errorf("got %q, want %q", buf.String(), foo)
+	}
+
+	buf.Reset()
+
+	err = Fprint(&buf, fset, &CommentedNode{Node: f.Decls[1], Comments: f.Comments})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if buf.String() != bar {
+		t.Errorf("got %q, want %q", buf.String(), bar)
+	}
+}
+
+func TestIssue11151(t *testing.T) {
+	const src = "package p\t/*\r/1\r*\r/2*\r\r\r\r/3*\r\r+\r\r/4*/\n"
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf bytes.Buffer
+	Fprint(&buf, fset, f)
+	got := buf.String()
+	const want = "package p\t/*/1*\r/2*\r/3*+/4*/\n" // \r following opening /* should be stripped
+	if got != want {
+		t.Errorf("\ngot : %q\nwant: %q", got, want)
+	}
+
+	// the resulting program must be valid
+	_, err = parser.ParseFile(fset, "", got, 0)
+	if err != nil {
+		t.Errorf("%v\norig: %q\ngot : %q", err, src, got)
+	}
+}
+
+// If a declaration has multiple specifications, a parenthesized
+// declaration must be printed even if Lparen is token.NoPos.
+func TestParenthesizedDecl(t *testing.T) {
+	// a package with multiple specs in a single declaration
+	const src = "package p; var ( a float64; b int )"
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "", src, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// print the original package
+	var buf bytes.Buffer
+	err = Fprint(&buf, fset, f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	original := buf.String()
+
+	// now remove parentheses from the declaration
+	for i := 0; i != len(f.Decls); i++ {
+		f.Decls[i].(*ast.GenDecl).Lparen = token.NoPos
+	}
+	buf.Reset()
+	err = Fprint(&buf, fset, f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	noparen := buf.String()
+
+	if noparen != original {
+		t.Errorf("got %q, want %q", noparen, original)
+	}
+}
+
+// Verify that we don't print a newline between "return" and its results, as
+// that would incorrectly cause a naked return.
+func TestIssue32854(t *testing.T) {
+	src := `package foo
+
+func f() {
+        return Composite{
+                call(),
+        }
+}`
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, "", src, 0)
+	if err != nil {
+		panic(err)
+	}
+
+	// Replace the result with call(), which is on the next line.
+	fd := file.Decls[0].(*ast.FuncDecl)
+	ret := fd.Body.List[0].(*ast.ReturnStmt)
+	ret.Results[0] = ret.Results[0].(*ast.CompositeLit).Elts[0]
+
+	var buf bytes.Buffer
+	if err := Fprint(&buf, fset, ret); err != nil {
+		t.Fatal(err)
+	}
+	want := "return call()"
+	if got := buf.String(); got != want {
+		t.Fatalf("got %q, want %q", got, want)
+	}
+}
+
+func TestSourcePosNewline(t *testing.T) {
+	// We don't provide a syntax for escaping or unescaping characters in line
+	// directives (see https://go.dev/issue/24183#issuecomment-372449628).
+	// As a result, we cannot write a line directive with the correct path for a
+	// filename containing newlines. We should return an error rather than
+	// silently dropping or mangling it.
+
+	fname := "foo\nbar/bar.go"
+	src := `package bar`
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, fname, src, parser.ParseComments|parser.AllErrors|parser.SkipObjectResolution)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cfg := &Config{
+		Mode:     SourcePos, // emit line comments
+		Tabwidth: 8,
+	}
+	var buf bytes.Buffer
+	if err := cfg.Fprint(&buf, fset, f); err == nil {
+		t.Errorf("Fprint did not error for source file path containing newline")
+	}
+	if buf.Len() != 0 {
+		t.Errorf("unexpected Fprint output:\n%s", buf.Bytes())
+	}
+}
diff --git a/src/go/printer/testdata/alignment.golden b/src/go/printer/testdata/alignment.golden
new file mode 100644
index 0000000..96086ed
--- /dev/null
+++ b/src/go/printer/testdata/alignment.golden
@@ -0,0 +1,172 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package alignment
+
+// ----------------------------------------------------------------------------
+// Examples from issue #7335.
+
+func main() {
+	z := MyStruct{
+		Foo:		"foo",
+		Bar:		"bar",
+		Name:		"name",
+		LongName:	"longname",
+		Baz:		"baz",
+	}
+	y := MyStruct{
+		Foo:			"foo",
+		Bar:			"bar",
+		NameXX:			"name",
+		LongNameXXXXXXXXXXXXX:	"longname",
+		Baz:			"baz",
+	}
+	z := MyStruct{
+		Foo:			"foo",
+		Bar:			"bar",
+		Name:			"name",
+		LongNameXXXXXXXXXXXXX:	"longname",
+		Baz:			"baz",
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #10392.
+
+var kcfg = KubeletConfig{
+	Address:			s.Address,
+	AllowPrivileged:		s.AllowPrivileged,
+	HostNetworkSources:		hostNetworkSources,
+	HostnameOverride:		s.HostnameOverride,
+	RootDirectory:			s.RootDirectory,
+	ConfigFile:			s.Config,
+	ManifestURL:			s.ManifestURL,
+	FileCheckFrequency:		s.FileCheckFrequency,
+	HTTPCheckFrequency:		s.HTTPCheckFrequency,
+	PodInfraContainerImage:		s.PodInfraContainerImage,
+	SyncFrequency:			s.SyncFrequency,
+	RegistryPullQPS:		s.RegistryPullQPS,
+	RegistryBurst:			s.RegistryBurst,
+	MinimumGCAge:			s.MinimumGCAge,
+	MaxPerPodContainerCount:	s.MaxPerPodContainerCount,
+	MaxContainerCount:		s.MaxContainerCount,
+	ClusterDomain:			s.ClusterDomain,
+	ClusterDNS:			s.ClusterDNS,
+	Runonce:			s.RunOnce,
+	Port:				s.Port,
+	ReadOnlyPort:			s.ReadOnlyPort,
+	CadvisorInterface:		cadvisorInterface,
+	EnableServer:			s.EnableServer,
+	EnableDebuggingHandlers:	s.EnableDebuggingHandlers,
+	DockerClient:			dockertools.ConnectToDockerOrDie(s.DockerEndpoint),
+	KubeClient:			client,
+	MasterServiceNamespace:		s.MasterServiceNamespace,
+	VolumePlugins:			ProbeVolumePlugins(),
+	NetworkPlugins:			ProbeNetworkPlugins(),
+	NetworkPluginName:		s.NetworkPluginName,
+	StreamingConnectionIdleTimeout:	s.StreamingConnectionIdleTimeout,
+	TLSOptions:			tlsOptions,
+	ImageGCPolicy:			imageGCPolicy, imageGCPolicy,
+	Cloud:				cloud,
+	NodeStatusUpdateFrequency:	s.NodeStatusUpdateFrequency,
+}
+
+var a = A{
+	Long:					1,
+	LongLong:				1,
+	LongLongLong:				1,
+	LongLongLongLong:			1,
+	LongLongLongLongLong:			1,
+	LongLongLongLongLongLong:		1,
+	LongLongLongLongLongLongLong:		1,
+	LongLongLongLongLongLongLongLong:	1,
+	Short:					1,
+	LongLongLongLongLongLongLongLongLong:	3,
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #22852.
+
+var fmtMap = map[string]string{
+	"1":					"123",
+	"12":					"123",
+	"123":					"123",
+	"1234":					"123",
+	"12345":				"123",
+	"123456":				"123",
+	"12345678901234567890123456789":	"123",
+	"abcde":				"123",
+	"123456789012345678901234567890":	"123",
+	"1234567":				"123",
+	"abcdefghijklmnopqrstuvwxyzabcd":	"123",
+	"abcd":					"123",
+}
+
+type Fmt struct {
+	abcdefghijklmnopqrstuvwx	string
+	abcdefghijklmnopqrstuvwxy	string
+	abcdefghijklmnopqrstuvwxyz	string
+	abcdefghijklmnopqrstuvwxyza	string
+	abcdefghijklmnopqrstuvwxyzab	string
+	abcdefghijklmnopqrstuvwxyzabc	string
+	abcde				string
+	abcdefghijklmnopqrstuvwxyzabcde	string
+	abcdefg				string
+}
+
+func main() {
+	_ := Fmt{
+		abcdefghijklmnopqrstuvwx:		"foo",
+		abcdefghijklmnopqrstuvwxyza:		"foo",
+		abcdefghijklmnopqrstuvwxyzab:		"foo",
+		abcdefghijklmnopqrstuvwxyzabc:		"foo",
+		abcde:					"foo",
+		abcdefghijklmnopqrstuvwxyzabcde:	"foo",
+		abcdefg:				"foo",
+		abcdefghijklmnopqrstuvwxy:		"foo",
+		abcdefghijklmnopqrstuvwxyz:		"foo",
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #26352.
+
+var _ = map[int]string{
+	1:	"",
+
+	12345678901234567890123456789:		"",
+	12345678901234567890123456789012345678:	"",
+}
+
+func f() {
+	_ = map[int]string{
+		1:	"",
+
+		12345678901234567:				"",
+		12345678901234567890123456789012345678901:	"",
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #26930.
+
+var _ = S{
+	F1:	[]string{},
+	F2____:	[]string{},
+}
+
+var _ = S{
+	F1:	[]string{},
+	F2____:	[]string{},
+}
+
+var _ = S{
+	F1____:	[]string{},
+	F2:	[]string{},
+}
+
+var _ = S{
+	F1____:	[]string{},
+	F2:	[]string{},
+}
diff --git a/src/go/printer/testdata/alignment.input b/src/go/printer/testdata/alignment.input
new file mode 100644
index 0000000..323d268
--- /dev/null
+++ b/src/go/printer/testdata/alignment.input
@@ -0,0 +1,179 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package alignment
+
+// ----------------------------------------------------------------------------
+// Examples from issue #7335.
+
+func main() {
+    z := MyStruct{
+        Foo:      "foo",
+        Bar:      "bar",
+        Name:     "name",
+        LongName: "longname",
+        Baz:      "baz",
+    }
+    y := MyStruct{
+        Foo:                   "foo",
+        Bar:                   "bar",
+        NameXX:                "name",
+        LongNameXXXXXXXXXXXXX: "longname",
+        Baz: "baz",
+    }
+    z := MyStruct{
+        Foo:  "foo",
+        Bar:  "bar",
+        Name: "name",
+        LongNameXXXXXXXXXXXXX: "longname",
+        Baz: "baz",
+    }
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #10392.
+
+var kcfg = KubeletConfig{
+    Address:                        s.Address,
+    AllowPrivileged:                s.AllowPrivileged,
+    HostNetworkSources:             hostNetworkSources,
+    HostnameOverride:               s.HostnameOverride,
+    RootDirectory:                  s.RootDirectory,
+    ConfigFile:                     s.Config,
+    ManifestURL:                    s.ManifestURL,
+    FileCheckFrequency:             s.FileCheckFrequency,
+    HTTPCheckFrequency:             s.HTTPCheckFrequency,
+    PodInfraContainerImage:         s.PodInfraContainerImage,
+    SyncFrequency:                  s.SyncFrequency,
+    RegistryPullQPS:                s.RegistryPullQPS,
+    RegistryBurst:                  s.RegistryBurst,
+    MinimumGCAge:                   s.MinimumGCAge,
+    MaxPerPodContainerCount:        s.MaxPerPodContainerCount,
+    MaxContainerCount:              s.MaxContainerCount,
+    ClusterDomain:                  s.ClusterDomain,
+    ClusterDNS:                     s.ClusterDNS,
+    Runonce:                        s.RunOnce,
+    Port:                           s.Port,
+    ReadOnlyPort:                   s.ReadOnlyPort,
+    CadvisorInterface:              cadvisorInterface,
+    EnableServer:                   s.EnableServer,
+    EnableDebuggingHandlers:        s.EnableDebuggingHandlers,
+    DockerClient:                   dockertools.ConnectToDockerOrDie(s.DockerEndpoint),
+    KubeClient:                     client,
+    MasterServiceNamespace:         s.MasterServiceNamespace,
+    VolumePlugins:                  ProbeVolumePlugins(),
+    NetworkPlugins:                 ProbeNetworkPlugins(),
+    NetworkPluginName:              s.NetworkPluginName,
+    StreamingConnectionIdleTimeout: s.StreamingConnectionIdleTimeout,
+    TLSOptions:                     tlsOptions,
+    ImageGCPolicy:                  imageGCPolicy,imageGCPolicy,
+    Cloud:                          cloud,
+    NodeStatusUpdateFrequency: s.NodeStatusUpdateFrequency,
+}
+
+var a = A{
+    Long:                             1,
+    LongLong:                         1,
+    LongLongLong:                     1,
+    LongLongLongLong:                 1,
+    LongLongLongLongLong:             1,
+    LongLongLongLongLongLong:         1,
+    LongLongLongLongLongLongLong:     1,
+    LongLongLongLongLongLongLongLong: 1,
+    Short: 1,
+    LongLongLongLongLongLongLongLongLong: 3,
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #22852.
+
+var fmtMap = map[string]string{
+	"1": "123",
+	"12": "123",
+	"123": "123",
+	"1234": "123",
+	"12345": "123",
+	"123456": "123",
+	"12345678901234567890123456789": "123",
+	"abcde": "123",
+	"123456789012345678901234567890": "123",
+	"1234567": "123",
+	"abcdefghijklmnopqrstuvwxyzabcd": "123",
+	"abcd": "123",
+}
+
+type Fmt struct {
+	abcdefghijklmnopqrstuvwx string
+	abcdefghijklmnopqrstuvwxy string
+	abcdefghijklmnopqrstuvwxyz string
+	abcdefghijklmnopqrstuvwxyza string
+	abcdefghijklmnopqrstuvwxyzab string
+	abcdefghijklmnopqrstuvwxyzabc string
+	abcde string
+	abcdefghijklmnopqrstuvwxyzabcde string
+	abcdefg string
+}
+
+func main() {
+	_ := Fmt{
+		abcdefghijklmnopqrstuvwx: "foo",
+		abcdefghijklmnopqrstuvwxyza: "foo",
+		abcdefghijklmnopqrstuvwxyzab: "foo",
+		abcdefghijklmnopqrstuvwxyzabc: "foo",
+		abcde: "foo",
+		abcdefghijklmnopqrstuvwxyzabcde: "foo",
+		abcdefg: "foo",
+		abcdefghijklmnopqrstuvwxy: "foo",
+		abcdefghijklmnopqrstuvwxyz: "foo",
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #26352.
+
+var _ = map[int]string{
+	1: "",
+
+	12345678901234567890123456789: "",
+	12345678901234567890123456789012345678: "",
+}
+
+func f() {
+	_ = map[int]string{
+		1: "",
+
+		12345678901234567: "",
+		12345678901234567890123456789012345678901: "",
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #26930.
+
+var _ = S{
+	F1: []string{
+	},
+	F2____: []string{},
+}
+
+var _ = S{
+	F1: []string{
+
+
+	},
+	F2____: []string{},
+}
+
+var _ = S{
+	F1____: []string{
+	},
+	F2: []string{},
+}
+
+var _ = S{
+	F1____: []string{
+
+	},
+	F2: []string{},
+}
diff --git a/src/go/printer/testdata/comments.golden b/src/go/printer/testdata/comments.golden
new file mode 100644
index 0000000..1e5d17b
--- /dev/null
+++ b/src/go/printer/testdata/comments.golden
@@ -0,0 +1,774 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This is a package for testing comment placement by go/printer.
+package main
+
+import "fmt"	// fmt
+
+const c0 = 0	// zero
+const (
+	c1	= iota	// c1
+	c2		// c2
+)
+
+// Alignment of comments in declarations>
+const (
+	_	T	= iota	// comment
+	_			// comment
+	_			// comment
+	_	= iota + 10
+	_	// comments
+
+	_		= 10	// comment
+	_	T	= 20	// comment
+)
+
+const (
+	_____	= iota	// foo
+	_		// bar
+	_	= 0	// bal
+	_		// bat
+)
+
+const (
+	_	T	= iota	// comment
+	_			// comment
+	_			// comment
+	_	= iota + 10
+	_		// comment
+	_		= 10
+	_		= 20	// comment
+	_	T	= 0	// comment
+)
+
+// The SZ struct; it is empty.
+type SZ struct{}
+
+// The S0 struct; no field is exported.
+type S0 struct {
+	int
+	x, y, z	int	// 3 unexported fields
+}
+
+// The S1 struct; some fields are not exported.
+type S1 struct {
+	S0
+	A, B, C	float	// 3 exported fields
+	D, b, c	int	// 2 unexported fields
+}
+
+// The S2 struct; all fields are exported.
+type S2 struct {
+	S1
+	A, B, C	float	// 3 exported fields
+}
+
+// The IZ interface; it is empty.
+type SZ interface{}
+
+// The I0 interface; no method is exported.
+type I0 interface {
+	f(x int) int	// unexported method
+}
+
+// The I1 interface; some methods are not exported.
+type I1 interface {
+	I0
+	F(x float) float	// exported methods
+	g(x int) int		// unexported method
+}
+
+// The I2 interface; all methods are exported.
+type I2 interface {
+	I0
+	F(x float) float	// exported method
+	G(x float) float	// exported method
+}
+
+// The S3 struct; all comments except for the last one must appear in the export.
+type S3 struct {
+	// lead comment for F1
+	F1	int	// line comment for F1
+	// lead comment for F2
+	F2	int	// line comment for F2
+	f3	int	// f3 is not exported
+}
+
+// Here is a comment.
+// Here is an accidentally unindented line.
+// More comment.
+//
+//dir:ect ive
+type directiveCheck struct{}
+
+// This comment group should be separated
+// with a newline from the next comment
+// group.
+
+// This comment should NOT be associated with the next declaration.
+
+var x int	// x
+var ()
+
+// This comment SHOULD be associated with f0.
+func f0() {
+	const pi = 3.14	// pi
+	var s1 struct{}	/* an empty struct */	/* foo */
+	// a struct constructor
+	// --------------------
+	var s2 struct{} = struct{}{}
+	x := pi
+}
+
+// This comment should be associated with f1, with one blank line before the comment.
+func f1() {
+	f0()
+	/* 1 */
+	// 2
+	/* 3 */
+	/* 4 */
+	f0()
+}
+
+func _() {
+	// this comment should be properly indented
+}
+
+func _(x int) int {
+	if x < 0 {	// the tab printed before this comment's // must not affect the remaining lines
+		return -x	// this statement should be properly indented
+	}
+	if x < 0 {	/* the tab printed before this comment's /* must not affect the remaining lines */
+		return -x	// this statement should be properly indented
+	}
+	return x
+}
+
+func typeswitch(x interface{}) {
+	switch v := x.(type) {
+	case bool, int, float:
+	case string:
+	default:
+	}
+
+	switch x.(type) {
+	}
+
+	switch v0, ok := x.(int); v := x.(type) {
+	}
+
+	switch v0, ok := x.(int); x.(type) {
+	case byte:	// this comment should be on the same line as the keyword
+		// this comment should be normally indented
+		_ = 0
+	case bool, int, float:
+		// this comment should be indented
+	case string:
+	default:
+		// this comment should be indented
+	}
+	// this comment should not be indented
+}
+
+//
+// Indentation of comments after possibly indented multi-line constructs
+// (test cases for issue 3147).
+//
+
+func _() {
+	s := 1 +
+		2
+	// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2	// comment
+	// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2	// comment
+	// should be indented like s
+	_ = 0
+}
+
+func _() {
+	s := 1 +
+		2
+	// should be indented like s
+	_ = 0
+}
+
+func _() {
+	s := 1 +
+		2
+
+	// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2	// comment
+
+	// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2	// comment
+
+	// should be indented like s
+	_ = 0
+}
+
+func _() {
+	s := 1 +
+		2
+
+	// should be indented like s
+	_ = 0
+}
+
+// Test case from issue 3147.
+func f() {
+	templateText := "a" +	// A
+		"b" +	// B
+		"c"	// C
+
+	// should be aligned with f()
+	f()
+}
+
+// Modified test case from issue 3147.
+func f() {
+	templateText := "a" +	// A
+		"b" +	// B
+		"c"	// C
+
+		// may not be aligned with f() (source is not aligned)
+	f()
+}
+
+//
+// Test cases for alignment of lines in general comments.
+//
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line */
+}
+
+// Issue 9751.
+func _() {
+	/*a string
+
+	b string*/
+
+	/*A string
+
+
+
+	Z string*/
+
+	/*a string
+
+	b string
+
+	c string*/
+
+	{
+		/*a string
+		b string*/
+
+		/*a string
+
+		b string*/
+
+		/*a string
+
+		b string
+
+		c string*/
+	}
+
+	{
+		/*a string
+		b string*/
+
+		/*a string
+
+		b string*/
+
+		/*a string
+
+		b string
+
+		c string*/
+	}
+
+	/*
+	 */
+
+	/*
+
+	 */
+
+	/*
+
+	 * line
+
+	 */
+}
+
+/*
+ * line
+ * of
+ * stars
+ */
+
+/* another line
+ * of
+ * stars */
+
+/*	and another line
+ *	of
+ *	stars */
+
+/* a line of
+ * stars */
+
+/*	and another line of
+ *	stars */
+
+/* a line of stars
+ */
+
+/*	and another line of
+ */
+
+/* a line of stars
+ */
+
+/*	and another line of
+ */
+
+/*
+aligned in middle
+here
+        not here
+*/
+
+/*
+blank line in middle:
+
+with no leading spaces on blank line.
+*/
+
+/*
+   aligned in middle
+   here
+           not here
+*/
+
+/*
+	blank line in middle:
+
+	with no leading spaces on blank line.
+*/
+
+func _() {
+	/*
+	 * line
+	 * of
+	 * stars
+	 */
+
+	/*
+		aligned in middle
+		here
+			not here
+	*/
+
+	/*
+		blank line in middle:
+
+		with no leading spaces on blank line.
+	*/
+}
+
+// Some interesting interspersed comments.
+// See below for more common cases.
+func _( /* this */ x /* is */ /* an */ int) {
+}
+
+func _( /* no params - extra blank before and after comment */ )	{}
+func _(a, b int /* params - no extra blank after comment */)		{}
+
+func _()	{ f( /* no args - extra blank before and after comment */ ) }
+func _()	{ f(a, b /* args - no extra blank after comment */) }
+
+func _() {
+	f( /* no args - extra blank before and after comment */ )
+	f(a, b /* args - no extra blank after comment */)
+}
+
+func ( /* comment1 */ T /* comment2 */) _()	{}
+
+func _()	{ /* "short-ish one-line functions with comments are formatted as multi-line functions */ }
+func _()	{ x := 0; /* comment */ y = x /* comment */ }
+
+func _() {
+	_ = 0
+	/* closing curly brace should be on new line */
+}
+
+func _() {
+	_ = []int{0, 1 /* don't introduce a newline after this comment - was issue 1365 */}
+}
+
+// Test cases from issue 1542:
+// Comments must not be placed before commas and cause invalid programs.
+func _() {
+	var a = []int{1, 2	/*jasldf*/}
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2}/*jasldf
+	 */
+
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2}// jasldf
+
+	_ = a
+}
+
+// Test cases from issues 11274, 15137:
+// Semicolon must not be lost when multiple statements are on the same line with a comment.
+func _() {
+	x := 0 /**/
+	y := 1
+}
+
+func _() {
+	f()
+	f()
+	f() /* comment */
+	f()
+	f() /* comment */
+	f()
+	f() /* a */ /* b */
+	f()
+	f() /* a */ /* b */
+	f()
+	f() /* a */ /* b */
+	f()
+}
+
+func _() {
+	f() /* a */ /* b */
+}
+
+// Comments immediately adjacent to punctuation followed by a newline
+// remain after the punctuation (looks better and permits alignment of
+// comments).
+func _() {
+	_ = T{
+		1,	// comment after comma
+		2,	/* comment after comma */
+		3,	// comment after comma
+	}
+	_ = T{
+		1,	// comment after comma
+		2,	/* comment after comma */
+		3,	// comment after comma
+	}
+	_ = T{
+		/* comment before literal */ 1,
+		2,	/* comment before comma - ok to move after comma */
+		3,	/* comment before comma - ok to move after comma */
+	}
+
+	for i = 0;	// comment after semicolon
+	i < 9;		/* comment after semicolon */
+	i++ {		// comment after opening curly brace
+	}
+
+	// TODO(gri) the last comment in this example should be aligned */
+	for i = 0;	// comment after semicolon
+	i < 9;		/* comment before semicolon - ok to move after semicolon */
+	i++ /* comment before opening curly brace */ {
+	}
+}
+
+// If there is no newline following punctuation, commas move before the punctuation.
+// This way, commas interspersed in lists stay with the respective expression.
+func f(x /* comment */, y int, z int /* comment */, u, v, w int /* comment */) {
+	f(x /* comment */, y)
+	f(x,	/* comment */
+		y)
+	f(
+		x,	/* comment */
+	)
+}
+
+func g(
+	x int,	/* comment */
+) {
+}
+
+type _ struct {
+	a, b /* comment */, c int
+}
+
+type _ struct {
+	a, b /* comment */, c int
+}
+
+func _() {
+	for a /* comment */, b := range x {
+	}
+}
+
+//extern foo
+func foo()	{}
+
+//export bar
+func bar()	{}
+
+// Print line directives correctly.
+
+// The following is a legal line directive.
+//
+//line foo:1
+func _() {
+	_ = 0
+	// The following is a legal line directive. It must not be indented:
+//line foo:2
+	_ = 1
+
+	// The following is not a legal line directive (it doesn't start in column 1):
+	//line foo:2
+	_ = 2
+
+	// The following is not a legal line directive (missing colon):
+//line foo -3
+	_ = 3
+}
+
+// Line comments with tabs
+func _() {
+	var finput *bufio.Reader	// input file
+	var stderr *bufio.Writer
+	var ftable *bufio.Writer	// y.go file
+	var foutput *bufio.Writer	// y.output file
+
+	var oflag string	// -o [y.go]		- y.go file
+	var vflag string	// -v [y.output]	- y.output file
+	var lflag bool		// -l			- disable line directives
+}
+
+// Trailing white space in comments should be trimmed
+func _() {
+	// This comment has 4 blanks following that should be trimmed:
+	/* Each line of this comment has blanks or tabs following that should be trimmed:
+	   line 2:
+	   line 3:
+	*/
+}
+
+var _ = []T{ /* lone comment */ }
+
+var _ = []T{
+	/* lone comment */
+}
+
+var _ = []T{
+	// lone comments
+	// in composite lit
+}
+
+var _ = [][]T{
+	{
+		// lone comments
+		// in composite lit
+	},
+}
+
+// TODO: gofmt doesn't add these tabs; make it so that these golden
+// tests run the printer in a way that it's exactly like gofmt.
+
+var _ = []T{	// lone comment
+}
+
+var _ = []T{	// lone comments
+	// in composite lit
+}
+
+func _()	{}
+
+func _()	{}
+
+/* This comment is the last entry in this file. It must be printed and should be followed by a newline */
diff --git a/src/go/printer/testdata/comments.input b/src/go/printer/testdata/comments.input
new file mode 100644
index 0000000..40aa55b
--- /dev/null
+++ b/src/go/printer/testdata/comments.input
@@ -0,0 +1,773 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This is a package for testing comment placement by go/printer.
+//
+package main
+
+import "fmt"  // fmt
+
+const c0 = 0  // zero
+const (
+	c1 = iota  // c1
+	c2  // c2
+)
+
+// Alignment of comments in declarations>
+const (
+	_ T = iota  // comment
+	_  // comment
+	_  // comment
+	_ = iota+10
+	_  // comments
+
+	_ = 10  // comment
+	_ T = 20  // comment
+)
+
+const (
+	_____ = iota // foo
+	_ // bar
+	_  = 0    // bal
+	_ // bat
+)
+
+const (
+	_ T = iota // comment
+	_ // comment
+	_ // comment
+	_ = iota + 10
+	_ // comment
+	_ = 10
+	_ = 20 // comment
+	_ T = 0 // comment
+)
+
+// The SZ struct; it is empty.
+type SZ struct {}
+
+// The S0 struct; no field is exported.
+type S0 struct {
+	int
+	x, y, z int  // 3 unexported fields
+}
+
+// The S1 struct; some fields are not exported.
+type S1 struct {
+	S0
+	A, B, C float  // 3 exported fields
+	D, b, c int  // 2 unexported fields
+}
+
+// The S2 struct; all fields are exported.
+type S2 struct {
+	S1
+	A, B, C float  // 3 exported fields
+}
+
+// The IZ interface; it is empty.
+type SZ interface {}
+
+// The I0 interface; no method is exported.
+type I0 interface {
+	f(x int) int  // unexported method
+}
+
+// The I1 interface; some methods are not exported.
+type I1 interface {
+	I0
+	F(x float) float  // exported methods
+	g(x int) int  // unexported method
+}
+
+// The I2 interface; all methods are exported.
+type I2 interface {
+	I0
+	F(x float) float  // exported method
+	G(x float) float  // exported method
+}
+
+// The S3 struct; all comments except for the last one must appear in the export.
+type S3 struct {
+	// lead comment for F1
+	F1 int // line comment for F1
+	// lead comment for F2
+	F2 int // line comment for F2
+	f3 int // f3 is not exported
+}
+
+// Here is a comment.
+//Here is an accidentally unindented line.
+//dir:ect ive
+// More comment.
+type directiveCheck struct{}
+
+// This comment group should be separated
+// with a newline from the next comment
+// group.
+
+// This comment should NOT be associated with the next declaration.
+
+var x int  // x
+var ()
+
+
+// This comment SHOULD be associated with f0.
+func f0() {
+	const pi = 3.14  // pi
+	var s1 struct {}  /* an empty struct */ /* foo */
+	// a struct constructor
+	// --------------------
+	var s2 struct {} = struct {}{}
+	x := pi
+}
+//
+// This comment should be associated with f1, with one blank line before the comment.
+//
+func f1() {
+	f0()
+	/* 1 */
+	// 2
+	/* 3 */
+	/* 4 */
+	f0()
+}
+
+
+func _() {
+// this comment should be properly indented
+}
+
+
+func _(x int) int {
+	if x < 0 {  // the tab printed before this comment's // must not affect the remaining lines
+		return -x  // this statement should be properly indented
+	}
+	if x < 0 {  /* the tab printed before this comment's /* must not affect the remaining lines */
+		return -x  // this statement should be properly indented
+	}
+	return x
+}
+
+
+func typeswitch(x interface{}) {
+	switch v := x.(type) {
+	case bool, int, float:
+	case string:
+	default:
+	}
+
+	switch x.(type) {
+	}
+
+	switch v0, ok := x.(int); v := x.(type) {
+	}
+
+	switch v0, ok := x.(int); x.(type) {
+	case byte:  // this comment should be on the same line as the keyword
+		// this comment should be normally indented
+		_ = 0
+	case bool, int, float:
+		// this comment should be indented
+	case string:
+	default:
+		// this comment should be indented
+	}
+	// this comment should not be indented
+}
+
+//
+// Indentation of comments after possibly indented multi-line constructs
+// (test cases for issue 3147).
+//
+
+func _() {
+	s := 1 +
+		2
+// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2 // comment
+		// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2 // comment
+	// should be indented like s
+	_ = 0
+}
+
+func _() {
+	s := 1 +
+		2
+	// should be indented like s
+	_ = 0
+}
+
+func _() {
+	s := 1 +
+		2
+
+// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2 // comment
+
+		// should be indented like s
+}
+
+func _() {
+	s := 1 +
+		2 // comment
+
+	// should be indented like s
+	_ = 0
+}
+
+func _() {
+	s := 1 +
+		2
+
+	// should be indented like s
+	_ = 0
+}
+
+// Test case from issue 3147.
+func f() {
+	templateText := "a" + // A
+		"b" + // B
+		"c" // C
+
+	// should be aligned with f()
+	f()
+}
+
+// Modified test case from issue 3147.
+func f() {
+	templateText := "a" + // A
+		"b" + // B
+		"c" // C
+
+		// may not be aligned with f() (source is not aligned)
+	f()
+}
+
+//
+// Test cases for alignment of lines in general comments.
+//
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	   */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+		*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line */
+}
+
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	   */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+		*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	   */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+		*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line */
+}
+
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	   */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+		*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line */
+}
+
+// Issue 9751.
+func _() {
+	/*a string
+
+	b string*/
+
+	/*A string
+
+
+
+	Z string*/
+
+	/*a string
+
+	b string
+
+	c string*/
+
+	{
+		/*a string
+b string*/
+
+		/*a string
+
+b string*/
+
+		/*a string
+
+b string
+
+c string*/
+	}
+
+	{
+		/*a string
+				b string*/
+
+		/*a string
+
+				b string*/
+
+		/*a string
+
+				b string
+
+				c string*/
+	}
+
+	/*
+	*/
+
+	/*
+
+	*/
+
+	/*
+
+	 * line
+
+	*/
+}
+
+/*
+ * line
+ * of
+ * stars
+ */
+
+/* another line
+ * of
+ * stars */
+
+/*	and another line
+ *	of
+ *	stars */
+
+/* a line of
+ * stars */
+
+/*	and another line of
+ *	stars */
+
+/* a line of stars
+*/
+
+/*	and another line of
+*/
+
+/* a line of stars
+ */
+
+/*	and another line of
+ */
+
+/*
+aligned in middle
+here
+        not here
+*/
+
+/*
+blank line in middle:
+
+with no leading spaces on blank line.
+*/
+
+/*
+   aligned in middle
+   here
+           not here
+*/
+
+/*
+	blank line in middle:
+
+	with no leading spaces on blank line.
+*/
+
+func _() {
+	/*
+	 * line
+	 * of
+	 * stars
+	 */
+
+	/*
+	aligned in middle
+	here
+		not here
+	*/
+
+	/*
+	blank line in middle:
+
+	with no leading spaces on blank line.
+*/
+}
+
+
+// Some interesting interspersed comments.
+// See below for more common cases.
+func _(/* this */x/* is *//* an */ int) {
+}
+
+func _(/* no params - extra blank before and after comment */) {}
+func _(a, b int /* params - no extra blank after comment */) {}
+
+func _() { f(/* no args - extra blank before and after comment */) }
+func _() { f(a, b /* args - no extra blank after comment */) }
+
+func _() {
+	f(/* no args - extra blank before and after comment */)
+	f(a, b /* args - no extra blank after comment */)
+}
+
+func (/* comment1 */ T /* comment2 */) _() {}
+
+func _() { /* "short-ish one-line functions with comments are formatted as multi-line functions */ }
+func _() { x := 0; /* comment */ y = x /* comment */ }
+
+func _() {
+	_ = 0
+	/* closing curly brace should be on new line */ }
+
+func _() {
+	_ = []int{0, 1 /* don't introduce a newline after this comment - was issue 1365 */}
+}
+
+// Test cases from issue 1542:
+// Comments must not be placed before commas and cause invalid programs.
+func _() {
+	var a = []int{1, 2, /*jasldf*/
+	}
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2, /*jasldf
+						*/
+	}
+	_ = a
+}
+
+func _() {
+	var a = []int{1, 2, // jasldf
+	}
+	_ = a
+}
+
+// Test cases from issues 11274, 15137:
+// Semicolon must not be lost when multiple statements are on the same line with a comment.
+func _() {
+    x := 0 /**/; y := 1
+}
+
+func _() {
+	f(); f()
+	f(); /* comment */ f()
+	f() /* comment */; f()
+	f(); /* a */ /* b */ f()
+	f() /* a */ /* b */; f()
+	f() /* a */; /* b */ f()
+}
+
+func _() {
+	f() /* a */ /* b */ }
+
+// Comments immediately adjacent to punctuation followed by a newline
+// remain after the punctuation (looks better and permits alignment of
+// comments).
+func _() {
+	_ = T{
+		1,    // comment after comma
+		2,    /* comment after comma */
+		3  ,  // comment after comma
+	}
+	_ = T{
+		1  ,// comment after comma
+		2  ,/* comment after comma */
+		3,// comment after comma
+	}
+	_ = T{
+		/* comment before literal */1,
+		2/* comment before comma - ok to move after comma */,
+		3  /* comment before comma - ok to move after comma */  ,
+	}
+
+	for
+		i=0;// comment after semicolon
+		i<9;/* comment after semicolon */
+		i++{// comment after opening curly brace
+	}
+
+	// TODO(gri) the last comment in this example should be aligned */
+	for
+		i=0;// comment after semicolon
+		i<9/* comment before semicolon - ok to move after semicolon */;
+		i++ /* comment before opening curly brace */ {
+	}
+}
+
+// If there is no newline following punctuation, commas move before the punctuation.
+// This way, commas interspersed in lists stay with the respective expression.
+func f(x/* comment */, y int, z int /* comment */, u, v, w int /* comment */) {
+	f(x /* comment */, y)
+	f(x /* comment */,
+	y)
+	f(
+		x /* comment */,
+	)
+}
+
+func g(
+	x int /* comment */,
+) {}
+
+type _ struct {
+	a, b /* comment */, c int
+}
+
+type _ struct { a, b /* comment */, c int }
+
+func _() {
+	for a /* comment */, b := range x {
+	}
+}
+
+//extern foo
+func foo() {}
+
+//export bar
+func bar() {}
+
+// Print line directives correctly.
+
+// The following is a legal line directive.
+//line foo:1
+func _() {
+	_ = 0
+// The following is a legal line directive. It must not be indented:
+//line foo:2
+	_ = 1
+
+// The following is not a legal line directive (it doesn't start in column 1):
+	//line foo:2
+	_ = 2
+
+// The following is not a legal line directive (missing colon):
+//line foo -3
+	_ = 3
+}
+
+// Line comments with tabs
+func _() {
+var	finput		*bufio.Reader			// input file
+var	stderr		*bufio.Writer
+var	ftable		*bufio.Writer			// y.go file
+var	foutput		*bufio.Writer			// y.output file
+
+var	oflag		string				// -o [y.go]		- y.go file
+var	vflag		string				// -v [y.output]	- y.output file
+var	lflag		bool				// -l			- disable line directives
+}
+
+// Trailing white space in comments should be trimmed
+func _() {
+// This comment has 4 blanks following that should be trimmed:
+/* Each line of this comment has blanks or tabs following that should be trimmed:
+   line 2:
+   line 3:
+*/
+}
+
+var _ = []T{/* lone comment */}
+
+var _ = []T{
+/* lone comment */
+}
+
+var _ = []T{
+// lone comments
+// in composite lit
+}
+
+var _ = [][]T{
+	{
+		// lone comments
+		// in composite lit
+	},
+}
+
+// TODO: gofmt doesn't add these tabs; make it so that these golden
+// tests run the printer in a way that it's exactly like gofmt.
+
+var _ = []T{// lone comment
+}
+
+var _ = []T{// lone comments
+// in composite lit
+}
+
+func _() {}
+
+//
+func _() {}
+
+/* This comment is the last entry in this file. It must be printed and should be followed by a newline */
diff --git a/src/go/printer/testdata/comments.x b/src/go/printer/testdata/comments.x
new file mode 100644
index 0000000..5d088ab
--- /dev/null
+++ b/src/go/printer/testdata/comments.x
@@ -0,0 +1,55 @@
+// This is a package for testing comment placement by go/printer.
+package main
+
+// The SZ struct; it is empty.
+type SZ struct{}
+
+// The S0 struct; no field is exported.
+type S0 struct {
+	// contains filtered or unexported fields
+}
+
+// The S1 struct; some fields are not exported.
+type S1 struct {
+	S0
+	A, B, C	float	// 3 exported fields
+	D	int	// 2 unexported fields
+	// contains filtered or unexported fields
+}
+
+// The S2 struct; all fields are exported.
+type S2 struct {
+	S1
+	A, B, C	float	// 3 exported fields
+}
+
+// The IZ interface; it is empty.
+type SZ interface{}
+
+// The I0 interface; no method is exported.
+type I0 interface {
+	// contains filtered or unexported methods
+}
+
+// The I1 interface; some methods are not exported.
+type I1 interface {
+	I0
+	F(x float) float	// exported methods
+	// contains filtered or unexported methods
+}
+
+// The I2 interface; all methods are exported.
+type I2 interface {
+	I0
+	F(x float) float	// exported method
+	G(x float) float	// exported method
+}
+
+// The S3 struct; all comments except for the last one must appear in the export.
+type S3 struct {
+	// lead comment for F1
+	F1	int	// line comment for F1
+	// lead comment for F2
+	F2	int	// line comment for F2
+	// contains filtered or unexported fields
+}
diff --git a/src/go/printer/testdata/comments2.golden b/src/go/printer/testdata/comments2.golden
new file mode 100644
index 0000000..83213d1
--- /dev/null
+++ b/src/go/printer/testdata/comments2.golden
@@ -0,0 +1,163 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This is a package for testing comment placement by go/printer.
+package main
+
+// Test cases for idempotent comment formatting (was issue 1835).
+/*
+c1a
+*/
+/*
+   c1b
+*/
+/* foo
+c1c
+*/
+/* foo
+   c1d
+*/
+/*
+c1e
+foo */
+/*
+   c1f
+   foo */
+
+func f() {
+	/*
+	   c2a
+	*/
+	/*
+	   c2b
+	*/
+	/* foo
+	   c2c
+	*/
+	/* foo
+	   c2d
+	*/
+	/*
+	   c2e
+	   foo */
+	/*
+	   c2f
+	   foo */
+}
+
+func g() {
+	/*
+	   c3a
+	*/
+	/*
+	   c3b
+	*/
+	/* foo
+	   c3c
+	*/
+	/* foo
+	   c3d
+	*/
+	/*
+	   c3e
+	   foo */
+	/*
+	   c3f
+	   foo */
+}
+
+// Test case taken literally from issue 1835.
+func main() {
+	/*
+	   prints test 5 times
+	*/
+	for i := 0; i < 5; i++ {
+		println("test")
+	}
+}
+
+func issue5623() {
+L:
+	_ = yyyyyyyyyyyyyyyy			// comment - should be aligned
+	_ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx	/* comment */
+
+	_ = yyyyyyyyyyyyyyyy			/* comment - should be aligned */
+	_ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx	// comment
+
+LLLLLLL:
+	_ = yyyyyyyyyyyyyyyy			// comment - should be aligned
+	_ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx	// comment
+
+LL:
+LLLLL:
+	_ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx	/* comment */
+	_ = yyyyyyyyyyyyyyyy			/* comment - should be aligned */
+
+	_ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx	// comment
+	_ = yyyyyyyyyyyyyyyy			// comment - should be aligned
+
+	// test case from issue
+label:
+	mask := uint64(1)<<c - 1		// Allocation mask
+	used := atomic.LoadUint64(&h.used)	// Current allocations
+}
+
+// Test cases for issue 18782
+var _ = [][]int{
+	/*       a, b, c, d, e */
+	/* a */ {0, 0, 0, 0, 0},
+	/* b */ {0, 5, 4, 4, 4},
+	/* c */ {0, 4, 5, 4, 4},
+	/* d */ {0, 4, 4, 5, 4},
+	/* e */ {0, 4, 4, 4, 5},
+}
+
+var _ = T{ /* a */ 0}
+
+var _ = T{ /* a */ /* b */ 0}
+
+var _ = T{	/* a */	/* b */
+	/* c */ 0,
+}
+
+var _ = T{	/* a */	/* b */
+	/* c */
+	/* d */ 0,
+}
+
+var _ = T{
+	/* a */
+	/* b */ 0,
+}
+
+var _ = T{ /* a */ {}}
+
+var _ = T{ /* a */ /* b */ {}}
+
+var _ = T{	/* a */	/* b */
+	/* c */ {},
+}
+
+var _ = T{	/* a */	/* b */
+	/* c */
+	/* d */ {},
+}
+
+var _ = T{
+	/* a */
+	/* b */ {},
+}
+
+var _ = []T{
+	func() {
+		var _ = [][]int{
+			/*       a, b, c, d, e */
+			/* a */ {0, 0, 0, 0, 0},
+			/* b */ {0, 5, 4, 4, 4},
+			/* c */ {0, 4, 5, 4, 4},
+			/* d */ {0, 4, 4, 5, 4},
+			/* e */ {0, 4, 4, 4, 5},
+		}
+	},
+}
diff --git a/src/go/printer/testdata/comments2.input b/src/go/printer/testdata/comments2.input
new file mode 100644
index 0000000..8d38c41
--- /dev/null
+++ b/src/go/printer/testdata/comments2.input
@@ -0,0 +1,168 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This is a package for testing comment placement by go/printer.
+//
+package main
+
+// Test cases for idempotent comment formatting (was issue 1835).
+/*
+c1a
+*/
+/*
+   c1b
+*/
+/* foo
+c1c
+*/
+/* foo
+   c1d
+*/
+/*
+c1e
+foo */
+/*
+   c1f
+   foo */
+
+func f() {
+/*
+c2a
+*/
+/*
+   c2b
+*/
+/* foo
+c2c
+*/
+/* foo
+   c2d
+*/
+/*
+c2e
+foo */
+/*
+   c2f
+   foo */
+}
+
+func g() {
+/*
+c3a
+*/
+/*
+   c3b
+*/
+/* foo
+c3c
+*/
+/* foo
+   c3d
+*/
+/*
+c3e
+foo */
+/*
+   c3f
+   foo */
+}
+
+// Test case taken literally from issue 1835.
+func main() {
+/*
+prints test 5 times
+*/
+   for i := 0; i < 5; i++ {
+      println("test")
+   }
+}
+
+func issue5623() {
+L:
+   _ = yyyyyyyyyyyyyyyy // comment - should be aligned
+   _ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx /* comment */
+
+   _ = yyyyyyyyyyyyyyyy /* comment - should be aligned */
+   _ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx // comment
+
+LLLLLLL:
+   _ = yyyyyyyyyyyyyyyy // comment - should be aligned
+   _ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx // comment
+
+LL:
+LLLLL:
+   _ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx /* comment */
+   _ = yyyyyyyyyyyyyyyy /* comment - should be aligned */
+
+   _ = xxxxxxxxxxxxxxxxxxxxxxxxxxxx // comment
+   _ = yyyyyyyyyyyyyyyy // comment - should be aligned
+
+// test case from issue
+label:
+   mask := uint64(1)<<c - 1 // Allocation mask
+   used := atomic.LoadUint64(&h.used) // Current allocations
+}
+
+// Test cases for issue 18782
+var _ = [][]int{
+   /*       a, b, c, d, e */
+   /* a */ {0, 0, 0, 0, 0},
+   /* b */ {0, 5, 4, 4, 4},
+   /* c */ {0, 4, 5, 4, 4},
+   /* d */ {0, 4, 4, 5, 4},
+   /* e */ {0, 4, 4, 4, 5},
+}
+
+var _ = T{ /* a */ 0,
+}
+
+var _ = T{ /* a */ /* b */ 0,
+}
+
+var _ = T{ /* a */ /* b */
+   /* c */ 0,
+}
+
+var _ = T{ /* a */ /* b */
+   /* c */
+   /* d */ 0,
+}
+
+var _ = T{
+   /* a */
+   /* b */ 0,
+}
+
+var _ = T{ /* a */ {},
+}
+
+var _ = T{ /* a */ /* b */ {},
+}
+
+var _ = T{ /* a */ /* b */
+   /* c */ {},
+}
+
+var _ = T{ /* a */ /* b */
+   /* c */
+   /* d */ {},
+}
+
+var _ = T{
+   /* a */
+   /* b */ {},
+}
+
+var _ = []T{
+   func() {
+      var _ = [][]int{
+         /*       a, b, c, d, e */
+         /* a */ {0, 0, 0, 0, 0},
+         /* b */ {0, 5, 4, 4, 4},
+         /* c */ {0, 4, 5, 4, 4},
+         /* d */ {0, 4, 4, 5, 4},
+         /* e */ {0, 4, 4, 4, 5},
+      }
+   },
+}
diff --git a/src/go/printer/testdata/complit.input b/src/go/printer/testdata/complit.input
new file mode 100644
index 0000000..82806a4
--- /dev/null
+++ b/src/go/printer/testdata/complit.input
@@ -0,0 +1,65 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package complit
+
+var (
+	// Multi-line declarations
+	V1 = T{
+		F1: "hello",
+		f2: 1,
+	}
+	V2 = T{
+		f2: 1,
+		F1: "hello",
+	}
+	V3 = T{
+		F1: "hello",
+		F2: T2{
+			A: "world",
+			b: "hidden",
+		},
+		f3: T2{
+			A: "world",
+		},
+	}
+	V4 = T{
+		f2: 1,
+	}
+
+	// Single-line declarations
+	V5 = T{F1: "hello", f2: 1}
+	V6 = T{f2: 1, F1: "hello"}
+	V7 = T{f2: 1}
+
+	// Mixed-mode declarations
+	V8 = T{
+		F1: "hello", f2: 1,
+		F3: "world",
+		f4: 2}
+	V9 = T{
+	f2: 1, F1: "hello",}
+	V10 = T{
+		F1: "hello", f2: 1,
+		f3: 2,
+		F4: "world", f5: 3,
+	}
+
+	// Other miscellaneous declarations
+	V11 = T{
+		t{
+			A: "world",
+			b: "hidden",
+		},
+		f2: t{
+			A: "world",
+			b: "hidden",
+		},
+	}
+	V12 = T{
+		F1: make(chan int),
+		f2: []int{},
+		F3: make(map[int]string), f4: 1,
+	}
+)
\ No newline at end of file
diff --git a/src/go/printer/testdata/complit.x b/src/go/printer/testdata/complit.x
new file mode 100644
index 0000000..458ac61
--- /dev/null
+++ b/src/go/printer/testdata/complit.x
@@ -0,0 +1,62 @@
+package complit
+
+var (
+	// Multi-line declarations
+	V1	= T{
+		F1: "hello",
+		// contains filtered or unexported fields
+	}
+	V2	= T{
+
+		F1: "hello",
+		// contains filtered or unexported fields
+	}
+	V3	= T{
+		F1:	"hello",
+		F2: T2{
+			A: "world",
+			// contains filtered or unexported fields
+		},
+		// contains filtered or unexported fields
+	}
+	V4	= T{
+		// contains filtered or unexported fields
+	}
+
+	// Single-line declarations
+	V5	= T{F1: "hello", /* contains filtered or unexported fields */}
+	V6	= T{F1: "hello", /* contains filtered or unexported fields */}
+	V7	= T{/* contains filtered or unexported fields */}
+
+	// Mixed-mode declarations
+	V8	= T{
+		F1:	"hello",
+		F3:	"world",
+		// contains filtered or unexported fields
+	}
+	V9	= T{
+		F1: "hello",
+		// contains filtered or unexported fields
+	}
+	V10	= T{
+		F1:	"hello",
+
+		F4:	"world",
+		// contains filtered or unexported fields
+	}
+
+	// Other miscellaneous declarations
+	V11	= T{
+		t{
+			A: "world",
+			// contains filtered or unexported fields
+		},
+		// contains filtered or unexported fields
+	}
+	V12	= T{
+		F1:	make(chan int),
+
+		F3:	make(map[int]string),
+		// contains filtered or unexported fields
+	}
+)
diff --git a/src/go/printer/testdata/declarations.golden b/src/go/printer/testdata/declarations.golden
new file mode 100644
index 0000000..fe0f783
--- /dev/null
+++ b/src/go/printer/testdata/declarations.golden
@@ -0,0 +1,1008 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package imports
+
+import "io"
+
+import (
+	_ "io"
+)
+
+import _ "io"
+
+import (
+	"io"
+	"io"
+	"io"
+)
+
+import (
+	"io"
+	aLongRename "io"
+
+	b "io"
+)
+
+import (
+	"unrenamed"
+	renamed "renameMe"
+	. "io"
+	_ "io"
+	"io"
+	. "os"
+)
+
+// no newlines between consecutive single imports, but
+// respect extra line breaks in the source (at most one empty line)
+import _ "io"
+import _ "io"
+import _ "io"
+
+import _ "os"
+import _ "os"
+import _ "os"
+
+import _ "fmt"
+import _ "fmt"
+import _ "fmt"
+
+import "foo"	// a comment
+import "bar"	// a comment
+
+import (
+	_ "foo"
+	// a comment
+	"bar"
+	"foo"	// a comment
+	"bar"	// a comment
+)
+
+// comments + renames
+import (
+	"unrenamed"	// a comment
+	renamed "renameMe"
+	. "io"		/* a comment */
+	_ "io/ioutil"	// a comment
+	"io"		// testing alignment
+	. "os"
+	// a comment
+)
+
+// a case that caused problems in the past (comment placement)
+import (
+	. "fmt"
+	"io"
+	"malloc"	// for the malloc count test only
+	"math"
+	"strings"
+	"testing"
+)
+
+// more import examples
+import (
+	"xxx"
+	"much_longer_name"	// comment
+	"short_name"		// comment
+)
+
+import (
+	_ "xxx"
+	"much_longer_name"	// comment
+)
+
+import (
+	mymath "math"
+	"/foo/bar/long_package_path"	// a comment
+)
+
+import (
+	"package_a"	// comment
+	"package_b"
+	my_better_c "package_c"	// comment
+	"package_d"		// comment
+	my_e "package_e"	// comment
+
+	"package_a"	// comment
+	"package_bb"
+	"package_ccc"	// comment
+	"package_dddd"	// comment
+)
+
+// print import paths as double-quoted strings
+// (we would like more test cases but the go/parser
+// already excludes most incorrect paths, and we don't
+// bother setting up test-ASTs manually)
+import (
+	"fmt"
+	"math"
+)
+
+// at least one empty line between declarations of different kind
+import _ "io"
+
+var _ int
+
+// at least one empty line between declarations of the same kind
+// if there is associated documentation (was issue 2570)
+type T1 struct{}
+
+// T2 comment
+type T2 struct {
+}	// should be a two-line struct
+
+// T3 comment
+type T2 struct {
+}	// should be a two-line struct
+
+// printing of constant literals
+const (
+	_	= "foobar"
+	_	= "a۰۱۸"
+	_	= "foo६४"
+	_	= "bar９８７６"
+	_	= 0
+	_	= 1
+	_	= 123456789012345678890
+	_	= 01234567
+	_	= 0xcafebabe
+	_	= 0.
+	_	= .0
+	_	= 3.14159265
+	_	= 1e0
+	_	= 1e+100
+	_	= 1e-100
+	_	= 2.71828e-1000
+	_	= 0i
+	_	= 1i
+	_	= 012345678901234567889i
+	_	= 123456789012345678890i
+	_	= 0.i
+	_	= .0i
+	_	= 3.14159265i
+	_	= 1e0i
+	_	= 1e+100i
+	_	= 1e-100i
+	_	= 2.71828e-1000i
+	_	= 'a'
+	_	= '\000'
+	_	= '\xFF'
+	_	= '\uff16'
+	_	= '\U0000ff16'
+	_	= `foobar`
+	_	= `foo
+---
+---
+bar`
+)
+
+func _() {
+	type _ int
+	type _ *int
+	type _ []int
+	type _ map[string]int
+	type _ chan int
+	type _ func() int
+
+	var _ int
+	var _ *int
+	var _ []int
+	var _ map[string]int
+	var _ chan int
+	var _ func() int
+
+	type _ struct{}
+	type _ *struct{}
+	type _ []struct{}
+	type _ map[string]struct{}
+	type _ chan struct{}
+	type _ func() struct{}
+
+	type _ interface{}
+	type _ *interface{}
+	type _ []interface{}
+	type _ map[string]interface{}
+	type _ chan interface{}
+	type _ func() interface{}
+
+	var _ struct{}
+	var _ *struct{}
+	var _ []struct{}
+	var _ map[string]struct{}
+	var _ chan struct{}
+	var _ func() struct{}
+
+	var _ interface{}
+	var _ *interface{}
+	var _ []interface{}
+	var _ map[string]interface{}
+	var _ chan interface{}
+	var _ func() interface{}
+}
+
+// don't lose blank lines in grouped declarations
+const (
+	_	int	= 0
+	_	float	= 1
+
+	_	string	= "foo"
+
+	_	= iota
+	_
+
+	// a comment
+	_
+
+	_
+)
+
+type (
+	_	int
+	_	struct{}
+
+	_	interface{}
+
+	// a comment
+	_	map[string]int
+)
+
+var (
+	_	int	= 0
+	_	float	= 1
+
+	_	string	= "foo"
+
+	_	bool
+
+	// a comment
+	_	bool
+)
+
+// don't lose blank lines in this struct
+type _ struct {
+	String	struct {
+		Str, Len int
+	}
+	Slice	struct {
+		Array, Len, Cap int
+	}
+	Eface	struct {
+		Typ, Ptr int
+	}
+
+	UncommonType	struct {
+		Name, PkgPath int
+	}
+	CommonType	struct {
+		Size, Hash, Alg, Align, FieldAlign, String, UncommonType int
+	}
+	Type	struct {
+		Typ, Ptr int
+	}
+	StructField	struct {
+		Name, PkgPath, Typ, Tag, Offset int
+	}
+	StructType	struct {
+		Fields int
+	}
+	PtrType	struct {
+		Elem int
+	}
+	SliceType	struct {
+		Elem int
+	}
+	ArrayType	struct {
+		Elem, Len int
+	}
+
+	Stktop	struct {
+		Stackguard, Stackbase, Gobuf int
+	}
+	Gobuf	struct {
+		Sp, Pc, G int
+	}
+	G	struct {
+		Stackbase, Sched, Status, Alllink int
+	}
+}
+
+// no blank lines in empty structs and interfaces, but leave 1- or 2-line layout alone
+type _ struct{}
+type _ struct {
+}
+
+type _ interface{}
+type _ interface {
+}
+
+// no tabs for single or ungrouped decls
+func _() {
+	const xxxxxx = 0
+	type x int
+	var xxx int
+	var yyyy float = 3.14
+	var zzzzz = "bar"
+
+	const (
+		xxxxxx = 0
+	)
+	type (
+		x int
+	)
+	var (
+		xxx int
+	)
+	var (
+		yyyy float = 3.14
+	)
+	var (
+		zzzzz = "bar"
+	)
+}
+
+// tabs for multiple or grouped decls
+func _() {
+	// no entry has a type
+	const (
+		zzzzzz	= 1
+		z	= 2
+		zzz	= 3
+	)
+	// some entries have a type
+	const (
+		xxxxxx			= 1
+		x			= 2
+		xxx			= 3
+		yyyyyyyy	float	= iota
+		yyyy			= "bar"
+		yyy
+		yy	= 2
+	)
+}
+
+func _() {
+	// no entry has a type
+	var (
+		zzzzzz	= 1
+		z	= 2
+		zzz	= 3
+	)
+	// no entry has a value
+	var (
+		_	int
+		_	float
+		_	string
+
+		_	int	// comment
+		_	float	// comment
+		_	string	// comment
+	)
+	// some entries have a type
+	var (
+		xxxxxx		int
+		x		float
+		xxx		string
+		yyyyyyyy	int	= 1234
+		y		float	= 3.14
+		yyyy			= "bar"
+		yyy		string	= "foo"
+	)
+	// mixed entries - all comments should be aligned
+	var (
+		a, b, c			int
+		x			= 10
+		d			int			// comment
+		y				= 20		// comment
+		f, ff, fff, ffff	int	= 0, 1, 2, 3	// comment
+	)
+	// respect original line breaks
+	var _ = []T{
+		T{0x20, "Telugu"},
+	}
+	var _ = []T{
+		// respect original line breaks
+		T{0x20, "Telugu"},
+	}
+}
+
+// use the formatted output rather than the input to decide when to align
+// (was issue 4505)
+const (
+	short		= 2 * (1 + 2)
+	aMuchLongerName	= 3
+)
+
+var (
+	short		= X{}
+	aMuchLongerName	= X{}
+
+	x1	= X{}	// foo
+	x2	= X{}	// foo
+)
+
+func _() {
+	type (
+		xxxxxx	int
+		x	float
+		xxx	string
+		xxxxx	[]x
+		xx	struct{}
+		xxxxxxx	struct {
+			_, _	int
+			_	float
+		}
+		xxxx	chan<- string
+	)
+}
+
+// alignment of "=" in consecutive lines (extended example from issue 1414)
+const (
+	umax	uint	= ^uint(0)		// maximum value for a uint
+	bpu		= 1 << (5 + umax>>63)	// bits per uint
+	foo
+	bar	= -1
+)
+
+// typical enum
+const (
+	a	MyType	= iota
+	abcd
+	b
+	c
+	def
+)
+
+// excerpt from godoc.go
+var (
+	goroot		= flag.String("goroot", runtime.GOROOT(), "Go root directory")
+	testDir		= flag.String("testdir", "", "Go root subdirectory - for testing only (faster startups)")
+	pkgPath		= flag.String("path", "", "additional package directories (colon-separated)")
+	filter		= flag.String("filter", "", "filter file containing permitted package directory paths")
+	filterMin	= flag.Int("filter_minutes", 0, "filter file update interval in minutes; disabled if <= 0")
+	filterDelay	delayTime	// actual filter update interval in minutes; usually filterDelay == filterMin, but filterDelay may back off exponentially
+)
+
+// formatting of structs
+type _ struct{}
+
+type _ struct { /* this comment should be visible */
+}
+
+type _ struct {
+	// this comment should be visible and properly indented
+}
+
+type _ struct {	// this comment must not change indentation
+	f			int
+	f, ff, fff, ffff	int
+}
+
+type _ struct {
+	string
+}
+
+type _ struct {
+	string	// comment
+}
+
+type _ struct {
+	string "tag"
+}
+
+type _ struct {
+	string "tag"	// comment
+}
+
+type _ struct {
+	f int
+}
+
+type _ struct {
+	f int	// comment
+}
+
+type _ struct {
+	f int "tag"
+}
+
+type _ struct {
+	f int "tag"	// comment
+}
+
+type _ struct {
+	bool
+	a, b, c			int
+	int			"tag"
+	ES				// comment
+	float			"tag"	// comment
+	f			int	// comment
+	f, ff, fff, ffff	int	// comment
+	g			float	"tag"
+	h			float	"tag"	// comment
+}
+
+type _ struct {
+	a, b,
+	c, d	int	// this line should be indented
+	u, v, w, x	float	// this line should be indented
+	p, q,
+	r, s	float	// this line should be indented
+}
+
+// difficult cases
+type _ struct {
+	bool		// comment
+	text	[]byte	// comment
+}
+
+// formatting of interfaces
+type EI interface{}
+
+type _ interface {
+	EI
+}
+
+type _ interface {
+	f()
+	fffff()
+}
+
+type _ interface {
+	EI
+	f()
+	fffffg()
+}
+
+type _ interface {	// this comment must not change indentation
+	EI				// here's a comment
+	f()				// no blank between identifier and ()
+	fffff()				// no blank between identifier and ()
+	gggggggggggg(x, y, z int)	// hurray
+}
+
+// formatting of variable declarations
+func _() {
+	type day struct {
+		n		int
+		short, long	string
+	}
+	var (
+		Sunday		= day{0, "SUN", "Sunday"}
+		Monday		= day{1, "MON", "Monday"}
+		Tuesday		= day{2, "TUE", "Tuesday"}
+		Wednesday	= day{3, "WED", "Wednesday"}
+		Thursday	= day{4, "THU", "Thursday"}
+		Friday		= day{5, "FRI", "Friday"}
+		Saturday	= day{6, "SAT", "Saturday"}
+	)
+}
+
+// formatting of multi-line variable declarations
+var a1, b1, c1 int	// all on one line
+
+var a2, b2,
+	c2 int	// this line should be indented
+
+var (
+	a3, b3,
+	c3, d3	int	// this line should be indented
+	a4, b4, c4	int	// this line should be indented
+)
+
+// Test case from issue 3304: multi-line declarations must end
+// a formatting section and not influence indentation of the
+// next line.
+var (
+	minRefreshTimeSec	= flag.Int64("min_refresh_time_sec", 604800,
+		"minimum time window between two refreshes for a given user.")
+	x	= flag.Int64("refresh_user_rollout_percent", 100,
+		"temporary flag to ramp up the refresh user rpc")
+	aVeryLongVariableName	= stats.GetVarInt("refresh-user-count")
+)
+
+func _() {
+	var privateKey2 = &Block{Type: "RSA PRIVATE KEY",
+		Headers:	map[string]string{},
+		Bytes: []uint8{0x30, 0x82, 0x1, 0x3a, 0x2, 0x1, 0x0, 0x2,
+			0x41, 0x0, 0xb2, 0x99, 0xf, 0x49, 0xc4, 0x7d, 0xfa, 0x8c,
+			0xd4, 0x0, 0xae, 0x6a, 0x4d, 0x1b, 0x8a, 0x3b, 0x6a, 0x13,
+			0x64, 0x2b, 0x23, 0xf2, 0x8b, 0x0, 0x3b, 0xfb, 0x97, 0x79,
+		},
+	}
+}
+
+func _() {
+	var Universe = Scope{
+		Names: map[string]*Ident{
+			// basic types
+			"bool":		nil,
+			"byte":		nil,
+			"int8":		nil,
+			"int16":	nil,
+			"int32":	nil,
+			"int64":	nil,
+			"uint8":	nil,
+			"uint16":	nil,
+			"uint32":	nil,
+			"uint64":	nil,
+			"float32":	nil,
+			"float64":	nil,
+			"string":	nil,
+
+			// convenience types
+			"int":		nil,
+			"uint":		nil,
+			"uintptr":	nil,
+			"float":	nil,
+
+			// constants
+			"false":	nil,
+			"true":		nil,
+			"iota":		nil,
+			"nil":		nil,
+
+			// functions
+			"cap":		nil,
+			"len":		nil,
+			"new":		nil,
+			"make":		nil,
+			"panic":	nil,
+			"panicln":	nil,
+			"print":	nil,
+			"println":	nil,
+		},
+	}
+}
+
+// alignment of map composite entries
+var _ = map[int]int{
+	// small key sizes: always align even if size ratios are large
+	a:			a,
+	abcdefghabcdefgh:	a,
+	ab:			a,
+	abc:			a,
+	abcdefgabcdefg:		a,
+	abcd:			a,
+	abcde:			a,
+	abcdef:			a,
+
+	// mixed key sizes: align when key sizes change within accepted ratio
+	abcdefgh:		a,
+	abcdefghabcdefg:	a,
+	abcdefghij:		a,
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij:	a,	// outlier - do not align with previous line
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij:		a,	// align with previous line
+
+	ab:	a,	// do not align with previous line
+	abcde:	a,	// align with previous line
+}
+
+// alignment of map composite entries: test cases from issue 3965
+// aligned
+var _ = T1{
+	a:			x,
+	b:			y,
+	cccccccccccccccccccc:	z,
+}
+
+// not aligned
+var _ = T2{
+	a:			x,
+	b:			y,
+	ccccccccccccccccccccc:	z,
+}
+
+// aligned
+var _ = T3{
+	aaaaaaaaaaaaaaaaaaaa:	x,
+	b:			y,
+	c:			z,
+}
+
+// not aligned
+var _ = T4{
+	aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:	x,
+	b:						y,
+	c:						z,
+}
+
+// no alignment of map composite entries if they are not the first entry on a line
+var _ = T{0: 0}	// not aligned
+var _ = T{0: 0,	// not aligned
+	1:	1,				// aligned
+	22:	22,				// aligned
+	333:	333, 1234: 12, 12345: 0,	// first on line aligned
+}
+
+// test cases form issue 8685
+// not aligned
+var _ = map[int]string{1: "spring", 2: "summer",
+	3:	"autumn", 4: "winter"}
+
+// not aligned
+var _ = map[string]string{"a": "spring", "b": "summer",
+	"c":	"autumn", "d": "winter"}
+
+// aligned
+var _ = map[string]string{"a": "spring",
+	"b":	"summer",
+	"c":	"autumn",
+	"d":	"winter"}
+
+func _() {
+	var _ = T{
+		a,	// must introduce trailing comma
+	}
+}
+
+// formatting of function results
+func _() func()				{}
+func _() func(int)			{ return nil }
+func _() func(int) int			{ return nil }
+func _() func(int) func(int) func()	{ return nil }
+
+// formatting of consecutive single-line functions
+func _()	{}
+func _()	{}
+func _()	{}
+
+func _()	{}	// an empty line before this function
+func _()	{}
+func _()	{}
+
+func _()		{ f(1, 2, 3) }
+func _(x int) int	{ y := x; return y + 1 }
+func _() int		{ type T struct{}; var x T; return x }
+
+// these must remain multi-line since they are multi-line in the source
+func _() {
+	f(1, 2, 3)
+}
+func _(x int) int {
+	y := x
+	return y + 1
+}
+func _() int {
+	type T struct{}
+	var x T
+	return x
+}
+
+// making function declarations safe for new semicolon rules
+func _()	{ /* single-line function because of "short-ish" comment */ }
+func _() { /* multi-line function because of "long-ish" comment - much more comment text is following here */ /* and more */
+}
+
+func _() {
+	/* multi-line func because block is on multiple lines */
+}
+
+// test case for issue #19544
+func _()	{}
+func _longer_name_() {	// this comment must not force the {} from above to alignment
+	// multiple lines
+}
+
+// ellipsis parameters
+func _(...int)
+func _(...*int)
+func _(...[]int)
+func _(...struct{})
+func _(bool, ...interface{})
+func _(bool, ...func())
+func _(bool, ...func(...int))
+func _(bool, ...map[string]int)
+func _(bool, ...chan int)
+
+func _(b bool, x ...int)
+func _(b bool, x ...*int)
+func _(b bool, x ...[]int)
+func _(b bool, x ...struct{})
+func _(x ...interface{})
+func _(x ...func())
+func _(x ...func(...int))
+func _(x ...map[string]int)
+func _(x ...chan int)
+
+// these parameter lists must remain multi-line since they are multi-line in the source
+func _(bool,
+	int) {
+}
+func _(x bool,
+	y int) {
+}
+func _(x,
+	y bool) {
+}
+func _(bool,	// comment
+	int) {
+}
+func _(x bool,	// comment
+	y int) {
+}
+func _(x,	// comment
+	y bool) {
+}
+func _(bool,	// comment
+	// comment
+	int) {
+}
+func _(x bool,	// comment
+	// comment
+	y int) {
+}
+func _(x,	// comment
+	// comment
+	y bool) {
+}
+func _(bool,
+	// comment
+	int) {
+}
+func _(x bool,
+	// comment
+	y int) {
+}
+func _(x,
+	// comment
+	y bool) {
+}
+func _(x,	// comment
+	y,	// comment
+	z bool) {
+}
+func _(x,	// comment
+	y,	// comment
+	z bool) {
+}
+func _(x int,	// comment
+	y float,	// comment
+	z bool) {
+}
+
+// properly indent multi-line signatures
+func ManageStatus(in <-chan *Status, req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int) {
+}
+
+func MultiLineSignature0(
+	a, b, c int,
+) {
+}
+
+func MultiLineSignature1(
+	a, b, c int,
+	u, v, w float,
+) {
+}
+
+func MultiLineSignature2(
+	a, b,
+	c int,
+) {
+}
+
+func MultiLineSignature3(
+	a, b,
+	c int, u, v,
+	w float,
+	x ...int) {
+}
+
+func MultiLineSignature4(
+	a, b, c int,
+	u, v,
+	w float,
+	x ...int) {
+}
+
+func MultiLineSignature5(
+	a, b, c int,
+	u, v, w float,
+	p, q,
+	r string,
+	x ...int) {
+}
+
+// make sure it also works for methods in interfaces
+type _ interface {
+	MultiLineSignature0(
+		a, b, c int,
+	)
+
+	MultiLineSignature1(
+		a, b, c int,
+		u, v, w float,
+	)
+
+	MultiLineSignature2(
+		a, b,
+		c int,
+	)
+
+	MultiLineSignature3(
+		a, b,
+		c int, u, v,
+		w float,
+		x ...int)
+
+	MultiLineSignature4(
+		a, b, c int,
+		u, v,
+		w float,
+		x ...int)
+
+	MultiLineSignature5(
+		a, b, c int,
+		u, v, w float,
+		p, q,
+		r string,
+		x ...int)
+}
+
+// omit superfluous parentheses in parameter lists
+func _(int)
+func _(int)
+func _(x int)
+func _(x int)
+func _(x, y int)
+func _(x, y int)
+
+func _() int
+func _() int
+func _() int
+
+func _() (x int)
+func _() (x int)
+func _() (x int)
+
+// special cases: some channel types require parentheses
+func _(x chan (<-chan int))
+func _(x chan (<-chan int))
+func _(x chan (<-chan int))
+
+func _(x chan<- (chan int))
+func _(x chan<- (chan int))
+func _(x chan<- (chan int))
+
+// don't introduce comma after last parameter if the closing ) is on the same line
+// even if the parameter type itself is multi-line (test cases from issue 4533)
+func _(...interface{})
+func _(...interface {
+	m()
+	n()
+})	// no extra comma between } and )
+
+func (t *T) _(...interface{})
+func (t *T) _(...interface {
+	m()
+	n()
+})	// no extra comma between } and )
+
+func _(interface{})
+func _(interface {
+	m()
+})	// no extra comma between } and )
+
+func _(struct{})
+func _(struct {
+	x	int
+	y	int
+})	// no extra comma between } and )
+
+// alias declarations
+
+type c0 struct{}
+type c1 = C
+type c2 = struct{ x int }
+type c3 = p.C
+type (
+	s	struct{}
+	a	= A
+	b	= A
+	c	= foo
+	d	= interface{}
+	ddd	= p.Foo
+)
diff --git a/src/go/printer/testdata/declarations.input b/src/go/printer/testdata/declarations.input
new file mode 100644
index 0000000..f34395b
--- /dev/null
+++ b/src/go/printer/testdata/declarations.input
@@ -0,0 +1,1021 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package imports
+
+import "io"
+
+import (
+	_ "io"
+)
+
+import _ "io"
+
+import (
+	"io"
+	"io"
+	"io"
+)
+
+import (
+	"io"
+	aLongRename "io"
+
+	b "io"
+)
+
+import (
+       "unrenamed"
+       renamed "renameMe"
+       . "io"
+       _ "io"
+       "io"
+       . "os"
+)
+
+// no newlines between consecutive single imports, but
+// respect extra line breaks in the source (at most one empty line)
+import _ "io"
+import _ "io"
+import _ "io"
+
+import _ "os"
+import _ "os"
+import _ "os"
+
+
+import _ "fmt"
+import _ "fmt"
+import _ "fmt"
+
+import "foo"  // a comment
+import "bar"  // a comment
+
+import (
+	_ "foo"
+	// a comment
+	"bar"
+	"foo"  // a comment
+	"bar"  // a comment
+)
+
+// comments + renames
+import (
+       "unrenamed" // a comment
+       renamed "renameMe"
+       . "io" /* a comment */
+       _ "io/ioutil" // a comment
+       "io" // testing alignment
+       . "os"
+       // a comment
+)
+
+// a case that caused problems in the past (comment placement)
+import (
+	. "fmt"
+	"io"
+	"malloc"	// for the malloc count test only
+	"math"
+	"strings"
+	"testing"
+)
+
+// more import examples
+import (
+	"xxx"
+	"much_longer_name" // comment
+	"short_name" // comment
+)
+
+import (
+	_ "xxx"
+	"much_longer_name" // comment
+)
+
+import (
+	mymath "math"
+	"/foo/bar/long_package_path" // a comment
+)
+
+import (
+	"package_a" // comment
+	"package_b"
+	my_better_c "package_c" // comment
+	"package_d" // comment
+	my_e "package_e" // comment
+
+	"package_a"    // comment
+	"package_bb"
+	"package_ccc"  // comment
+	"package_dddd" // comment
+)
+
+// print import paths as double-quoted strings
+// (we would like more test cases but the go/parser
+// already excludes most incorrect paths, and we don't
+// bother setting up test-ASTs manually)
+import (
+	`fmt`
+	"math"
+)
+
+// at least one empty line between declarations of different kind
+import _ "io"
+var _ int
+
+// at least one empty line between declarations of the same kind
+// if there is associated documentation (was issue 2570)
+type T1 struct{}
+// T2 comment
+type T2 struct {
+} // should be a two-line struct
+
+
+// T3 comment
+type T2 struct {
+
+
+} // should be a two-line struct
+
+
+// printing of constant literals
+const (
+	_ = "foobar"
+	_ = "a۰۱۸"
+	_ = "foo६४"
+	_ = "bar９８７６"
+	_ = 0
+	_ = 1
+	_ = 123456789012345678890
+	_ = 01234567
+	_ = 0xcafebabe
+	_ = 0.
+	_ = .0
+	_ = 3.14159265
+	_ = 1e0
+	_ = 1e+100
+	_ = 1e-100
+	_ = 2.71828e-1000
+	_ = 0i
+	_ = 1i
+	_ = 012345678901234567889i
+	_ = 123456789012345678890i
+	_ = 0.i
+	_ = .0i
+	_ = 3.14159265i
+	_ = 1e0i
+	_ = 1e+100i
+	_ = 1e-100i
+	_ = 2.71828e-1000i
+	_ = 'a'
+	_ = '\000'
+	_ = '\xFF'
+	_ = '\uff16'
+	_ = '\U0000ff16'
+	_ = `foobar`
+	_ = `foo
+---
+---
+bar`
+)
+
+
+func _() {
+	type _ int
+	type _ *int
+	type _ []int
+	type _ map[string]int
+	type _ chan int
+	type _ func() int
+
+	var _ int
+	var _ *int
+	var _ []int
+	var _ map[string]int
+	var _ chan int
+	var _ func() int
+
+	type _ struct{}
+	type _ *struct{}
+	type _ []struct{}
+	type _ map[string]struct{}
+	type _ chan struct{}
+	type _ func() struct{}
+
+	type _ interface{}
+	type _ *interface{}
+	type _ []interface{}
+	type _ map[string]interface{}
+	type _ chan interface{}
+	type _ func() interface{}
+
+	var _ struct{}
+	var _ *struct{}
+	var _ []struct{}
+	var _ map[string]struct{}
+	var _ chan struct{}
+	var _ func() struct{}
+
+	var _ interface{}
+	var _ *interface{}
+	var _ []interface{}
+	var _ map[string]interface{}
+	var _ chan interface{}
+	var _ func() interface{}
+}
+
+
+// don't lose blank lines in grouped declarations
+const (
+	_ int = 0
+	_ float = 1
+
+	_ string = "foo"
+
+	_ = iota
+	_
+	
+	// a comment
+	_
+
+	_
+)
+
+
+type (
+	_ int
+	_ struct {}
+	
+	_ interface{}
+	
+	// a comment
+	_ map[string]int
+)
+
+
+var (
+	_ int = 0
+	_ float = 1
+
+	_ string = "foo"
+
+	_ bool
+	
+	// a comment
+	_ bool
+)
+
+
+// don't lose blank lines in this struct
+type _ struct {
+	String struct {
+		Str, Len int
+	}
+	Slice struct {
+		Array, Len, Cap int
+	}
+	Eface struct {
+		Typ, Ptr int
+	}
+
+	UncommonType struct {
+		Name, PkgPath int
+	}
+	CommonType struct {
+		Size, Hash, Alg, Align, FieldAlign, String, UncommonType int
+	}
+	Type struct {
+		Typ, Ptr int
+	}
+	StructField struct {
+		Name, PkgPath, Typ, Tag, Offset int
+	}
+	StructType struct {
+		Fields int
+	}
+	PtrType struct {
+		Elem int
+	}
+	SliceType struct {
+		Elem int
+	}
+	ArrayType struct {
+		Elem, Len int
+	}
+
+	Stktop struct {
+		Stackguard, Stackbase, Gobuf int
+	}
+	Gobuf struct {
+		Sp, Pc, G int
+	}
+	G struct {
+		Stackbase, Sched, Status, Alllink int
+	}
+}
+
+
+// no blank lines in empty structs and interfaces, but leave 1- or 2-line layout alone
+type _ struct{            }
+type _ struct {
+
+}
+
+type _ interface{            }
+type _ interface {
+
+}
+
+
+// no tabs for single or ungrouped decls
+func _() {
+	const xxxxxx = 0
+	type x int
+	var xxx int
+	var yyyy float = 3.14
+	var zzzzz = "bar"
+
+	const (
+		xxxxxx = 0
+	)
+	type (
+		x int
+	)
+	var (
+		xxx int
+	)
+	var (
+		yyyy float = 3.14
+	)
+	var (
+		zzzzz = "bar"
+	)
+}
+
+// tabs for multiple or grouped decls
+func _() {
+	// no entry has a type
+	const (
+		zzzzzz = 1
+		z = 2
+		zzz = 3
+	)
+	// some entries have a type
+	const (
+		xxxxxx = 1
+		x = 2
+		xxx = 3
+		yyyyyyyy float = iota
+		yyyy = "bar"
+		yyy
+		yy = 2
+	)
+}
+
+func _() {
+	// no entry has a type
+	var (
+		zzzzzz = 1
+		z = 2
+		zzz = 3
+	)
+	// no entry has a value
+	var (
+		_ int
+		_ float
+		_ string
+
+		_ int  // comment
+		_ float  // comment
+		_ string  // comment
+	)
+	// some entries have a type
+	var (
+		xxxxxx int
+		x float
+		xxx string
+		yyyyyyyy int = 1234
+		y float = 3.14
+		yyyy = "bar"
+		yyy string = "foo"
+	)
+	// mixed entries - all comments should be aligned
+	var (
+		a, b, c int
+		x = 10
+		d int  // comment
+		y = 20  // comment
+		f, ff, fff, ffff int = 0, 1, 2, 3  // comment
+	)
+	// respect original line breaks
+	var _ = []T {
+		T{0x20,	"Telugu"},
+	}
+	var _ = []T {
+		// respect original line breaks
+		T{0x20,	"Telugu"},
+	}
+}
+
+// use the formatted output rather than the input to decide when to align
+// (was issue 4505)
+const (
+	short = 2 * (
+	1 + 2)
+	aMuchLongerName = 3
+)
+
+var (
+	short = X{
+	}
+	aMuchLongerName = X{}
+
+	x1 = X{} // foo
+	x2 = X{
+	} // foo
+)
+
+func _() {
+	type (
+		xxxxxx int
+		x float
+		xxx string
+		xxxxx []x
+		xx struct{}
+		xxxxxxx struct {
+			_, _ int
+			_ float
+		}
+		xxxx chan<- string
+	)
+}
+
+// alignment of "=" in consecutive lines (extended example from issue 1414)
+const (
+	umax uint                  = ^uint(0) // maximum value for a uint
+	bpu  = 1 << (5 + umax>>63)            // bits per uint
+	foo
+	bar  = -1
+)
+
+// typical enum
+const (
+	a MyType = iota
+	abcd
+	b
+	c
+	def
+)
+
+// excerpt from godoc.go
+var (
+	goroot = flag.String("goroot", runtime.GOROOT(), "Go root directory")
+	testDir = flag.String("testdir", "", "Go root subdirectory - for testing only (faster startups)")
+	pkgPath = flag.String("path", "", "additional package directories (colon-separated)")
+	filter = flag.String("filter", "", "filter file containing permitted package directory paths")
+	filterMin = flag.Int("filter_minutes", 0, "filter file update interval in minutes; disabled if <= 0")
+	filterDelay delayTime // actual filter update interval in minutes; usually filterDelay == filterMin, but filterDelay may back off exponentially
+)
+
+
+// formatting of structs
+type _ struct{}
+
+type _ struct{ /* this comment should be visible */ }
+
+type _ struct{
+	// this comment should be visible and properly indented
+}
+
+type _ struct {  // this comment must not change indentation
+	f int
+	f, ff, fff, ffff int
+}
+
+type _ struct {
+	string
+}
+
+type _ struct {
+	string  // comment
+}
+
+type _ struct {
+	string "tag"
+}
+
+type _ struct {
+	string "tag"  // comment
+}
+
+type _ struct {
+	f int
+}
+
+type _ struct {
+	f int  // comment
+}
+
+type _ struct {
+	f int "tag"
+}
+
+type _ struct {
+	f int "tag"  // comment
+}
+
+type _ struct {
+	bool
+	a, b, c int
+	int "tag"
+	ES // comment
+	float "tag"  // comment
+	f int  // comment
+	f, ff, fff, ffff int  // comment
+	g float "tag"
+	h float "tag"  // comment
+}
+
+type _ struct { a, b,
+c, d int  // this line should be indented
+u, v, w, x float // this line should be indented
+p, q,
+r, s float // this line should be indented
+}
+
+
+// difficult cases
+type _ struct {
+	bool  // comment
+	text []byte  // comment
+}
+
+
+// formatting of interfaces
+type EI interface{}
+
+type _ interface {
+	EI
+}
+
+type _ interface {
+	f()
+	fffff()
+}
+
+type _ interface {
+	EI
+	f()
+	fffffg()
+}
+
+type _ interface {  // this comment must not change indentation
+	EI  // here's a comment
+	f()  // no blank between identifier and ()
+	fffff()  // no blank between identifier and ()
+	gggggggggggg(x, y, z int) ()  // hurray
+}
+
+
+// formatting of variable declarations
+func _() {
+	type day struct { n int; short, long string }
+	var (
+		Sunday = day{ 0, "SUN", "Sunday" }
+		Monday = day{ 1, "MON", "Monday" }
+		Tuesday = day{ 2, "TUE", "Tuesday" }
+		Wednesday = day{ 3, "WED", "Wednesday" }
+		Thursday = day{ 4, "THU", "Thursday" }
+		Friday = day{ 5, "FRI", "Friday" }
+		Saturday = day{ 6, "SAT", "Saturday" }
+	)
+}
+
+
+// formatting of multi-line variable declarations
+var a1, b1, c1 int  // all on one line
+
+var a2, b2,
+c2 int  // this line should be indented
+
+var (a3, b3,
+c3, d3 int  // this line should be indented
+a4, b4, c4 int  // this line should be indented
+)
+
+// Test case from issue 3304: multi-line declarations must end
+// a formatting section and not influence indentation of the
+// next line.
+var (
+	minRefreshTimeSec = flag.Int64("min_refresh_time_sec", 604800,
+		"minimum time window between two refreshes for a given user.")
+	x = flag.Int64("refresh_user_rollout_percent", 100,
+		"temporary flag to ramp up the refresh user rpc")
+	aVeryLongVariableName = stats.GetVarInt("refresh-user-count")
+)
+
+func _() {
+	var privateKey2 = &Block{Type: "RSA PRIVATE KEY",
+					Headers: map[string]string{},
+					Bytes: []uint8{0x30, 0x82, 0x1, 0x3a, 0x2, 0x1, 0x0, 0x2,
+			0x41, 0x0, 0xb2, 0x99, 0xf, 0x49, 0xc4, 0x7d, 0xfa, 0x8c,
+			0xd4, 0x0, 0xae, 0x6a, 0x4d, 0x1b, 0x8a, 0x3b, 0x6a, 0x13,
+			0x64, 0x2b, 0x23, 0xf2, 0x8b, 0x0, 0x3b, 0xfb, 0x97, 0x79,
+		},
+	}
+}
+
+
+func _() {
+	var Universe = Scope {
+		Names: map[string]*Ident {
+			// basic types
+			"bool": nil,
+			"byte": nil,
+			"int8": nil,
+			"int16": nil,
+			"int32": nil,
+			"int64": nil,
+			"uint8": nil,
+			"uint16": nil,
+			"uint32": nil,
+			"uint64": nil,
+			"float32": nil,
+			"float64": nil,
+			"string": nil,
+
+			// convenience types
+			"int": nil,
+			"uint": nil,
+			"uintptr": nil,
+			"float": nil,
+
+			// constants
+			"false": nil,
+			"true": nil,
+			"iota": nil,
+			"nil": nil,
+
+			// functions
+			"cap": nil,
+			"len": nil,
+			"new": nil,
+			"make": nil,
+			"panic": nil,
+			"panicln": nil,
+			"print": nil,
+			"println": nil,
+		},
+	}
+}
+
+
+// alignment of map composite entries
+var _ = map[int]int{
+	// small key sizes: always align even if size ratios are large
+	a: a,
+	abcdefghabcdefgh: a,
+	ab: a,
+	abc: a,
+	abcdefgabcdefg: a,
+	abcd: a,
+	abcde: a,
+	abcdef: a,
+
+	// mixed key sizes: align when key sizes change within accepted ratio
+	abcdefgh: a,
+	abcdefghabcdefg: a,
+	abcdefghij: a,
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij: a, // outlier - do not align with previous line
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij: a, // align with previous line
+
+	ab: a, // do not align with previous line
+	abcde: a, // align with previous line
+}
+
+// alignment of map composite entries: test cases from issue 3965
+// aligned
+var _ = T1{
+	a:                    x,
+	b:                    y,
+	cccccccccccccccccccc: z,
+}
+
+// not aligned
+var _ = T2{
+	a: x,
+	b: y,
+	ccccccccccccccccccccc: z,
+}
+
+// aligned
+var _ = T3{
+	aaaaaaaaaaaaaaaaaaaa: x,
+	b:                    y,
+	c:                    z,
+}
+
+// not aligned
+var _ = T4{
+	aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa: x,
+	b:                                       y,
+	c:                                       z,
+}
+
+
+// no alignment of map composite entries if they are not the first entry on a line
+var _ = T{0: 0} // not aligned
+var _ = T{0: 0, // not aligned
+	1: 1, // aligned
+	22: 22, // aligned
+	333: 333, 1234: 12, 12345: 0, // first on line aligned
+}
+
+
+// test cases form issue 8685
+// not aligned
+var _ = map[int]string{1: "spring", 2: "summer",
+					3:             "autumn", 4: "winter"}
+
+// not aligned
+var _ = map[string]string{"a": "spring", "b": "summer",
+	"c": "autumn", "d": "winter"}
+
+// aligned
+var _ = map[string]string{"a": "spring",
+"b": "summer",
+	"c": "autumn",
+"d": "winter"}
+
+
+func _() {
+	var _ = T{
+		a,	// must introduce trailing comma
+	}
+}
+
+
+// formatting of function results
+func _() func() {}
+func _() func(int) { return nil }
+func _() func(int) int { return nil }
+func _() func(int) func(int) func() { return nil }
+
+
+// formatting of consecutive single-line functions
+func _() {}
+func _() {}
+func _() {}
+
+func _() {}  // an empty line before this function
+func _() {}
+func _() {}
+
+func _() { f(1, 2, 3) }
+func _(x int) int { y := x; return y+1 }
+func _() int { type T struct{}; var x T; return x }
+
+// these must remain multi-line since they are multi-line in the source
+func _() {
+	f(1, 2, 3)
+}
+func _(x int) int {
+	y := x; return y+1
+}
+func _() int {
+	type T struct{}; var x T; return x
+}
+
+
+// making function declarations safe for new semicolon rules
+func _() { /* single-line function because of "short-ish" comment */ }
+func _() { /* multi-line function because of "long-ish" comment - much more comment text is following here */ /* and more */ }
+
+func _() {
+/* multi-line func because block is on multiple lines */ }
+
+// test case for issue #19544
+func _() {}
+func _longer_name_() { // this comment must not force the {} from above to alignment
+	// multiple lines
+}
+
+// ellipsis parameters
+func _(...int)
+func _(...*int)
+func _(...[]int)
+func _(...struct{})
+func _(bool, ...interface{})
+func _(bool, ...func())
+func _(bool, ...func(...int))
+func _(bool, ...map[string]int)
+func _(bool, ...chan int)
+
+func _(b bool, x ...int)
+func _(b bool, x ...*int)
+func _(b bool, x ...[]int)
+func _(b bool, x ...struct{})
+func _(x ...interface{})
+func _(x ...func())
+func _(x ...func(...int))
+func _(x ...map[string]int)
+func _(x ...chan int)
+
+
+// these parameter lists must remain multi-line since they are multi-line in the source
+func _(bool,
+int) {
+}
+func _(x bool,
+y int) {
+}
+func _(x,
+y bool) {
+}
+func _(bool, // comment
+int) {
+}
+func _(x bool, // comment
+y int) {
+}
+func _(x, // comment
+y bool) {
+}
+func _(bool, // comment
+// comment
+int) {
+}
+func _(x bool, // comment
+// comment
+y int) {
+}
+func _(x, // comment
+// comment
+y bool) {
+}
+func _(bool,
+// comment
+int) {
+}
+func _(x bool,
+// comment
+y int) {
+}
+func _(x,
+// comment
+y bool) {
+}
+func _(x, // comment
+y,// comment
+z bool) {
+}
+func _(x, // comment
+	y,// comment
+	z bool) {
+}
+func _(x int,	// comment
+	y float,	// comment
+	z bool) {
+}
+
+
+// properly indent multi-line signatures
+func ManageStatus(in <-chan *Status, req <-chan Request,
+stat chan<- *TargetInfo,
+TargetHistorySize int) {
+}
+
+func MultiLineSignature0(
+a, b, c int,
+) {}
+
+func MultiLineSignature1(
+a, b, c int,
+u, v, w float,
+) {}
+
+func MultiLineSignature2(
+a, b,
+c int,
+) {}
+
+func MultiLineSignature3(
+a, b,
+c int, u, v,
+w float,
+		x ...int) {}
+
+func MultiLineSignature4(
+a, b, c int,
+u, v,
+w float,
+		x ...int) {}
+
+func MultiLineSignature5(
+a, b, c int,
+u, v, w float,
+p, q,
+r string,
+		x ...int) {}
+
+// make sure it also works for methods in interfaces
+type _ interface {
+MultiLineSignature0(
+a, b, c int,
+)
+
+MultiLineSignature1(
+a, b, c int,
+u, v, w float,
+)
+
+MultiLineSignature2(
+a, b,
+c int,
+)
+
+MultiLineSignature3(
+a, b,
+c int, u, v,
+w float,
+		x ...int)
+
+MultiLineSignature4(
+a, b, c int,
+u, v,
+w float,
+		x ...int)
+
+MultiLineSignature5(
+a, b, c int,
+u, v, w float,
+p, q,
+r string,
+		x ...int)
+}
+
+// omit superfluous parentheses in parameter lists
+func _((int))
+func _((((((int))))))
+func _(x (int))
+func _(x (((((int))))))
+func _(x, y (int))
+func _(x, y (((((int))))))
+
+func _() (int)
+func _() ((int))
+func _() ((((((int))))))
+
+func _() (x int)
+func _() (x (int))
+func _() (x (((((int))))))
+
+// special cases: some channel types require parentheses
+func _(x chan(<-chan int))
+func _(x (chan(<-chan int)))
+func _(x ((((chan(<-chan int))))))
+
+func _(x chan<-(chan int))
+func _(x (chan<-(chan int)))
+func _(x ((((chan<-(chan int))))))
+
+// don't introduce comma after last parameter if the closing ) is on the same line
+// even if the parameter type itself is multi-line (test cases from issue 4533)
+func _(...interface{})
+func _(...interface {
+	m()
+	n()
+}) // no extra comma between } and )
+
+func (t *T) _(...interface{})
+func (t *T) _(...interface {
+	m()
+	n()
+}) // no extra comma between } and )
+
+func _(interface{})
+func _(interface {
+	m()
+}) // no extra comma between } and )
+
+func _(struct{})
+func _(struct {
+	x int
+	y int
+}) // no extra comma between } and )
+
+// alias declarations
+
+type c0 struct{}
+type c1 = C
+type c2 = struct{ x int}
+type c3 = p.C
+type (
+	s struct{}
+	a = A
+	b = A
+	c = foo
+	d = interface{}
+	ddd = p.Foo
+)
diff --git a/src/go/printer/testdata/doc.golden b/src/go/printer/testdata/doc.golden
new file mode 100644
index 0000000..7ac241a
--- /dev/null
+++ b/src/go/printer/testdata/doc.golden
@@ -0,0 +1,21 @@
+package p
+
+/*
+Doc comment.
+
+  - List1.
+
+  - List2.
+*/
+var X int
+
+/* erroneous doc comment */
+var Y int
+
+/*
+ * Another erroneous
+ * doc comment.
+ */
+var Z int
+
+
diff --git a/src/go/printer/testdata/doc.input b/src/go/printer/testdata/doc.input
new file mode 100644
index 0000000..5c057ed
--- /dev/null
+++ b/src/go/printer/testdata/doc.input
@@ -0,0 +1,20 @@
+package p
+
+/*
+Doc comment.
+  - List1.
+
+  - List2.
+*/
+var X int
+
+/* erroneous doc comment */
+var Y int
+
+/*
+ * Another erroneous
+ * doc comment.
+ */
+var Z int
+
+
diff --git a/src/go/printer/testdata/empty.golden b/src/go/printer/testdata/empty.golden
new file mode 100644
index 0000000..a055f47
--- /dev/null
+++ b/src/go/printer/testdata/empty.golden
@@ -0,0 +1,5 @@
+// a comment at the beginning of the file
+
+package empty
+
+// a comment at the end of the file
diff --git a/src/go/printer/testdata/empty.input b/src/go/printer/testdata/empty.input
new file mode 100644
index 0000000..a055f47
--- /dev/null
+++ b/src/go/printer/testdata/empty.input
@@ -0,0 +1,5 @@
+// a comment at the beginning of the file
+
+package empty
+
+// a comment at the end of the file
diff --git a/src/go/printer/testdata/expressions.golden b/src/go/printer/testdata/expressions.golden
new file mode 100644
index 0000000..16a68c7
--- /dev/null
+++ b/src/go/printer/testdata/expressions.golden
@@ -0,0 +1,743 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package expressions
+
+type T struct {
+	x, y, z int
+}
+
+var (
+	a, b, c, d, e						int
+	under_bar						int
+	longIdentifier1, longIdentifier2, longIdentifier3	int
+	t0, t1, t2						T
+	s							string
+	p							*int
+)
+
+func _() {
+	// no spaces around simple or parenthesized expressions
+	_ = (a + 0)
+	_ = a + b
+	_ = a + b + c
+	_ = a + b - c
+	_ = a - b - c
+	_ = a + (b * c)
+	_ = a + (b / c)
+	_ = a - (b % c)
+	_ = 1 + a
+	_ = a + 1
+	_ = a + b + 1
+	_ = s[a]
+	_ = s[a:]
+	_ = s[:b]
+	_ = s[1:2]
+	_ = s[a:b]
+	_ = s[0:len(s)]
+	_ = s[0] << 1
+	_ = (s[0] << 1) & 0xf
+	_ = s[0]<<2 | s[1]>>4
+	_ = "foo" + s
+	_ = s + "foo"
+	_ = 'a' + 'b'
+	_ = len(s) / 2
+	_ = len(t0.x) / a
+
+	// spaces around expressions of different precedence or expressions containing spaces
+	_ = a + -b
+	_ = a - ^b
+	_ = a / *p
+	_ = a + b*c
+	_ = 1 + b*c
+	_ = a + 2*c
+	_ = a + c*2
+	_ = 1 + 2*3
+	_ = s[1 : 2*3]
+	_ = s[a : b-c]
+	_ = s[0:]
+	_ = s[a+b]
+	_ = s[:b-c]
+	_ = s[a+b:]
+	_ = a[a<<b+1]
+	_ = a[a<<b+1:]
+	_ = s[a+b : len(s)]
+	_ = s[len(s):-a]
+	_ = s[a : len(s)+1]
+	_ = s[a:len(s)+1] + s
+
+	// spaces around operators with equal or lower precedence than comparisons
+	_ = a == b
+	_ = a != b
+	_ = a > b
+	_ = a >= b
+	_ = a < b
+	_ = a <= b
+	_ = a < b && c > d
+	_ = a < b || c > d
+
+	// spaces around "long" operands
+	_ = a + longIdentifier1
+	_ = longIdentifier1 + a
+	_ = longIdentifier1 + longIdentifier2*longIdentifier3
+	_ = s + "a longer string"
+
+	// some selected cases
+	_ = a + t0.x
+	_ = a + t0.x + t1.x*t2.x
+	_ = a + b + c + d + e + 2*3
+	_ = a + b + c + 2*3 + d + e
+	_ = (a + b + c) * 2
+	_ = a - b + c - d + (a + b + c) + d&e
+	_ = under_bar - 1
+	_ = Open(dpath+"/file", O_WRONLY|O_CREAT, 0666)
+	_ = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
+
+	// test case for issue 8021
+	// want:
+	//  ([]bool{})[([]int{})[((1)+(((1)+((((1)*(((1)+(1))+(1)))+(1))*(1)))+(1)))]]
+	_ = ([]bool{})[([]int{})[((1)+(((1)+((((1)*(((1)+(1))+(1)))+(1))*(1)))+(1)))]]
+
+	// the parser does not restrict expressions that may appear as statements
+	true
+	42
+	"foo"
+	x
+	(x)
+	a + b
+	a + b + c
+	a + (b * c)
+	a + (b / c)
+	1 + a
+	a + 1
+	s[a]
+	x << 1
+	(s[0] << 1) & 0xf
+	"foo" + s
+	x == y
+	x < y || z > 42
+}
+
+// slice expressions with cap
+func _() {
+	_ = x[a:b:c]
+	_ = x[a : b : c+d]
+	_ = x[a : b+d : c]
+	_ = x[a : b+d : c+d]
+	_ = x[a+d : b : c]
+	_ = x[a+d : b : c+d]
+	_ = x[a+d : b+d : c]
+	_ = x[a+d : b+d : c+d]
+
+	_ = x[:b:c]
+	_ = x[: b : c+d]
+	_ = x[: b+d : c]
+	_ = x[: b+d : c+d]
+}
+
+func issue22111() {
+	_ = x[:]
+
+	_ = x[:b]
+	_ = x[:b+1]
+
+	_ = x[a:]
+	_ = x[a+1:]
+
+	_ = x[a:b]
+	_ = x[a+1 : b]
+	_ = x[a : b+1]
+	_ = x[a+1 : b+1]
+
+	_ = x[:b:c]
+	_ = x[: b+1 : c]
+	_ = x[: b : c+1]
+	_ = x[: b+1 : c+1]
+
+	_ = x[a:b:c]
+	_ = x[a+1 : b : c]
+	_ = x[a : b+1 : c]
+	_ = x[a+1 : b+1 : c]
+	_ = x[a : b : c+1]
+	_ = x[a+1 : b : c+1]
+	_ = x[a : b+1 : c+1]
+	_ = x[a+1 : b+1 : c+1]
+}
+
+func _() {
+	_ = a + b
+	_ = a + b + c
+	_ = a + b*c
+	_ = a + (b * c)
+	_ = (a + b) * c
+	_ = a + (b * c * d)
+	_ = a + (b*c + d)
+
+	_ = 1 << x
+	_ = -1 << x
+	_ = 1<<x - 1
+	_ = -1<<x - 1
+
+	_ = f(a + b)
+	_ = f(a + b + c)
+	_ = f(a + b*c)
+	_ = f(a + (b * c))
+	_ = f(1<<x-1, 1<<x-2)
+
+	_ = 1<<d.logWindowSize - 1
+
+	buf = make(x, 2*cap(b.buf)+n)
+
+	dst[i*3+2] = dbuf[0] << 2
+	dst[i*3+2] = dbuf[0]<<2 | dbuf[1]>>4
+
+	b.buf = b.buf[0 : b.off+m+n]
+	b.buf = b.buf[0 : b.off+m*n]
+	f(b.buf[0 : b.off+m+n])
+
+	signed += ' ' * 8
+	tw.octal(header[148:155], chksum)
+
+	_ = x > 0 && i >= 0
+
+	x1, x0 := x>>w2, x&m2
+	z0 = t1<<w2 + t0
+	z1 = (t1 + t0>>w2) >> w2
+	q1, r1 := x1/d1, x1%d1
+	r1 = r1*b2 | x0>>w2
+	x1 = (x1 << z) | (x0 >> (uint(w) - z))
+	x1 = x1<<z | x0>>(uint(w)-z)
+
+	_ = buf[0 : len(buf)+1]
+	_ = buf[0 : n+1]
+
+	a, b = b, a
+	a = b + c
+	a = b*c + d
+	_ = a*b + c
+	_ = a - b - c
+	_ = a - (b - c)
+	_ = a - b*c
+	_ = a - (b * c)
+	_ = a * b / c
+	_ = a / *b
+	_ = x[a|^b]
+	_ = x[a / *b]
+	_ = a & ^b
+	_ = a + +b
+	_ = a - -b
+	_ = x[a*-b]
+	_ = x[a + +b]
+	_ = x ^ y ^ z
+	_ = b[a>>24] ^ b[(a>>16)&0xFF] ^ b[(a>>8)&0xFF] ^ b[a&0xFF]
+	_ = len(longVariableName) * 2
+
+	_ = token(matchType + xlength<<lengthShift + xoffset)
+}
+
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+
+	// make sure syntactically legal code remains syntactically legal
+	f(3, 42 ...)	// a blank must remain between 42 and ...
+	f(4, 42....)
+	f(5, 42....)
+	f(6, 42.0...)
+	f(7, 42.0...)
+	f(8, .42...)
+	f(9, .42...)
+	f(10, 42e0...)
+	f(11, 42e0...)
+
+	_ = 42 .x	// a blank must remain between 42 and .x
+	_ = 42..x
+	_ = 42..x
+	_ = 42.0.x
+	_ = 42.0.x
+	_ = .42.x
+	_ = .42.x
+	_ = 42e0.x
+	_ = 42e0.x
+
+	// a blank must remain between the binary operator and the 2nd operand
+	_ = x / *y
+	_ = x < -1
+	_ = x < <-1
+	_ = x + +1
+	_ = x - -1
+	_ = x & &x
+	_ = x & ^x
+
+	_ = f(x / *y, x < -1, x < <-1, x + +1, x - -1, x & &x, x & ^x)
+}
+
+func _() {
+	_ = T{}
+	_ = struct{}{}
+	_ = [10]T{}
+	_ = [...]T{}
+	_ = []T{}
+	_ = map[int]T{}
+}
+
+// one-line structs/interfaces in composite literals (up to a threshold)
+func _() {
+	_ = struct{}{}
+	_ = struct{ x int }{0}
+	_ = struct{ x, y, z int }{0, 1, 2}
+	_ = struct{ int }{0}
+	_ = struct{ s struct{ int } }{struct{ int }{0}}
+
+	_ = (interface{})(nil)
+	_ = (interface{ String() string })(nil)
+	_ = (interface {
+		String() string
+	})(nil)
+	_ = (interface{ fmt.Stringer })(nil)
+	_ = (interface {
+		fmt.Stringer
+	})(nil)
+}
+
+func _() {
+	// do not modify literals
+	_ = "tab1	tab2	tab3	end"	// string contains 3 tabs
+	_ = "tab1 tab2 tab3 end"	// same string with 3 blanks - may be unaligned because editors see tabs in strings
+	_ = ""				// this comment should be aligned with the one on the previous line
+	_ = ``
+	_ = `
+`
+	_ = `foo
+		bar`
+	_ = `three spaces before the end of the line starting here:   
+they must not be removed`
+}
+
+func _() {
+	// smart handling of indentation for multi-line raw strings
+	var _ = ``
+	var _ = `foo`
+	var _ = `foo
+bar`
+
+	var _ = ``
+	var _ = `foo`
+	var _ =
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ =	// comment
+	``
+	var _ =	// comment
+	`foo`
+	var _ =	// comment
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ = /* comment */ ``
+	var _ = /* comment */ `foo`
+	var _ = /* comment */ `foo
+bar`
+
+	var _ =	/* comment */
+	``
+	var _ =	/* comment */
+	`foo`
+	var _ =	/* comment */
+	// the next line should remain indented
+	`foo
+bar`
+
+	var board = []int(
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+	var state = S{
+		"foo",
+		// the next line should remain indented
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`,
+		"bar",
+	}
+}
+
+func _() {
+	// one-line function literals (body is on a single line)
+	_ = func() {}
+	_ = func() int { return 0 }
+	_ = func(x, y int) bool { m := (x + y) / 2; return m < 0 }
+
+	// multi-line function literals (body is not on one line)
+	_ = func() {
+	}
+	_ = func() int {
+		return 0
+	}
+	_ = func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	}
+
+	f(func() {
+	})
+	f(func() int {
+		return 0
+	})
+	f(func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	})
+}
+
+func _() {
+	_ = [][]int{
+		[]int{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		{1, 2},
+		{1, 2, 3},
+	}
+	_ = [][]int{{1}, {1, 2}, {1, 2, 3}}
+}
+
+// various multi-line expressions
+func _() {
+	// do not add extra indentation to multi-line string lists
+	_ = "foo" + "bar"
+	_ = "foo" +
+		"bar" +
+		"bah"
+	_ = []string{
+		"abc" +
+			"def",
+		"foo" +
+			"bar",
+	}
+}
+
+const _ = F1 +
+	`string = "%s";` +
+	`ptr = *;` +
+	`datafmt.T2 = s ["-" p "-"];`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+func _() {
+	_ = F1 +
+		`string = "%s";` +
+		`ptr = *;` +
+		`datafmt.T2 = s ["-" p "-"];`
+
+	_ =
+		`datafmt "datafmt";` +
+			`default = "%v";` +
+			`array = *;` +
+			`datafmt.T3 = s  {" " a a / ","};`
+
+	_ = `datafmt "datafmt";` +
+		`default = "%v";` +
+		`array = *;` +
+		`datafmt.T3 = s  {" " a a / ","};`
+}
+
+func _() {
+	// respect source lines in multi-line expressions
+	_ = a +
+		b +
+		c
+	_ = a < b ||
+		b < a
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_ = "170141183460469231731687303715884105727"	// prime
+}
+
+// Alignment after overlong lines
+const (
+	_	= "991"
+	_	= "2432902008176640000"	// 20!
+	_	= "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_	= "170141183460469231731687303715884105727"	// prime
+)
+
+// Correct placement of operators and comments in multi-line expressions
+func _() {
+	_ = a +	// comment
+		b +	// comment
+		c
+	_ = "a" +
+		"b" +	// comment
+		"c"
+	_ = "ba0408" + "7265717569726564"	// field 71, encoding 2, string "required"
+}
+
+// Correct placement of terminating comma/closing parentheses in multi-line calls.
+func _() {
+	f(1,
+		2,
+		3)
+	f(1,
+		2,
+		3,
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+}
+
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow,		// yellow
+	draw.Cyan,		// cyan
+	draw.Green,		// lime green
+	draw.GreyBlue,		// slate
+	draw.Red,		/* red */
+	draw.GreyGreen,		/* olive green */
+	draw.Blue,		/* blue */
+	draw.Color(0xFF55AAFF),	/* pink */
+	draw.Color(0xFFAAFFFF),	/* lavender */
+	draw.Color(0xBB005DFF),	/* maroon */
+}
+
+func same(t, u *Time) bool {
+	// respect source lines in multi-line expressions
+	return t.Year == u.Year &&
+		t.Month == u.Month &&
+		t.Day == u.Day &&
+		t.Hour == u.Hour &&
+		t.Minute == u.Minute &&
+		t.Second == u.Second &&
+		t.Weekday == u.Weekday &&
+		t.ZoneOffset == u.ZoneOffset &&
+		t.Zone == u.Zone
+}
+
+func (p *parser) charClass() {
+	// respect source lines in multi-line expressions
+	if cc.negate && len(cc.ranges) == 2 &&
+		cc.ranges[0] == '\n' && cc.ranges[1] == '\n' {
+		nl := new(_NotNl)
+		p.re.add(nl)
+	}
+}
+
+func addState(s []state, inst instr, match []int) {
+	// handle comments correctly in multi-line expressions
+	for i := 0; i < l; i++ {
+		if s[i].inst.index() == index &&	// same instruction
+			s[i].match[0] < pos {	// earlier match already going; leftmost wins
+			return s
+		}
+	}
+}
+
+func (self *T) foo(x int) *T	{ return self }
+
+func _()	{ module.Func1().Func2() }
+
+func _() {
+	_ = new(T).
+		foo(1).
+		foo(2).
+		foo(3)
+
+	_ = new(T).
+		foo(1).
+		foo(2).	// inline comments
+		foo(3)
+
+	_ = new(T).foo(1).foo(2).foo(3)
+
+	// handle multiline argument list correctly
+	_ = new(T).
+		foo(
+			1).
+		foo(2)
+
+	_ = new(T).foo(
+		1).foo(2)
+
+	_ = Array[3+
+		4]
+
+	_ = Method(1, 2,
+		3)
+
+	_ = new(T).
+		foo().
+		bar().(*Type)
+
+	_ = new(T).
+		foo().
+		bar().(*Type).
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()["idx"]
+
+	_ = new(T).
+		foo().
+		bar()["idx"].
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()[1:2]
+
+	_ = new(T).
+		foo().
+		bar()[1:2].
+		baz()
+
+	_ = new(T).
+		Field.
+		Array[3+
+		4].
+		Table["foo"].
+		Blob.(*Type).
+		Slices[1:4].
+		Method(1, 2,
+			3).
+		Thingy
+
+	_ = a.b.c
+	_ = a.
+		b.
+		c
+	_ = a.b().c
+	_ = a.
+		b().
+		c
+	_ = a.b[0].c
+	_ = a.
+		b[0].
+		c
+	_ = a.b[0:].c
+	_ = a.
+		b[0:].
+		c
+	_ = a.b.(T).c
+	_ = a.
+		b.(T).
+		c
+}
+
+// Don't introduce extra newlines in strangely formatted expression lists.
+func f() {
+	// os.Open parameters should remain on two lines
+	if writer, err = os.Open(outfile, s.O_WRONLY|os.O_CREATE|
+		os.O_TRUNC, 0666); err != nil {
+		log.Fatal(err)
+	}
+}
+
+// Handle multi-line argument lists ending in ... correctly.
+// Was issue 3130.
+func _() {
+	_ = append(s, a...)
+	_ = append(
+		s, a...)
+	_ = append(s,
+		a...)
+	_ = append(
+		s,
+		a...)
+	_ = append(s, a...,
+	)
+	_ = append(s,
+		a...,
+	)
+	_ = append(
+		s,
+		a...,
+	)
+}
+
+// Literal function types in conversions must be parenthesized;
+// for now go/parser accepts the unparenthesized form where it
+// is non-ambiguous.
+func _() {
+	// these conversions should be rewritten to look
+	// the same as the parenthesized conversions below
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+}
+
+func _() {
+	_ = f().
+		f(func() {
+			f()
+		}).
+		f(map[int]int{
+			1:	2,
+			3:	4,
+		})
+
+	_ = f().
+		f(
+			func() {
+				f()
+			},
+		)
+}
diff --git a/src/go/printer/testdata/expressions.input b/src/go/printer/testdata/expressions.input
new file mode 100644
index 0000000..8c523b6
--- /dev/null
+++ b/src/go/printer/testdata/expressions.input
@@ -0,0 +1,771 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package expressions
+
+type T struct {
+	x, y, z int
+}
+
+var (
+	a, b, c, d, e int
+	under_bar int
+	longIdentifier1, longIdentifier2, longIdentifier3 int
+	t0, t1, t2 T
+	s string
+	p *int
+)
+
+
+func _() {
+	// no spaces around simple or parenthesized expressions
+	_ = (a+0)
+	_ = a+b
+	_ = a+b+c
+	_ = a+b-c
+	_ = a-b-c
+	_ = a+(b*c)
+	_ = a+(b/c)
+	_ = a-(b%c)
+	_ = 1+a
+	_ = a+1
+	_ = a+b+1
+	_ = s[a]
+	_ = s[a:]
+	_ = s[:b]
+	_ = s[1:2]
+	_ = s[a:b]
+	_ = s[0:len(s)]
+	_ = s[0]<<1
+	_ = (s[0]<<1)&0xf
+	_ = s[0] << 2 | s[1] >> 4
+	_ = "foo"+s
+	_ = s+"foo"
+	_ = 'a'+'b'
+	_ = len(s)/2
+	_ = len(t0.x)/a
+
+	// spaces around expressions of different precedence or expressions containing spaces
+	_ = a + -b
+	_ = a - ^b
+	_ = a / *p
+	_ = a + b*c
+	_ = 1 + b*c
+	_ = a + 2*c
+	_ = a + c*2
+	_ = 1 + 2*3
+	_ = s[1 : 2*3]
+	_ = s[a : b-c]
+	_ = s[0:]
+	_ = s[a+b]
+	_ = s[: b-c]
+	_ = s[a+b :]
+	_ = a[a<<b+1]
+	_ = a[a<<b+1 :]
+	_ = s[a+b : len(s)]
+	_ = s[len(s) : -a]
+	_ = s[a : len(s)+1]
+	_ = s[a : len(s)+1]+s
+
+	// spaces around operators with equal or lower precedence than comparisons
+	_ = a == b
+	_ = a != b
+	_ = a > b
+	_ = a >= b
+	_ = a < b
+	_ = a <= b
+	_ = a < b && c > d
+	_ = a < b || c > d
+
+	// spaces around "long" operands
+	_ = a + longIdentifier1
+	_ = longIdentifier1 + a
+	_ = longIdentifier1 + longIdentifier2 * longIdentifier3
+	_ = s + "a longer string"
+
+	// some selected cases
+	_ = a + t0.x
+	_ = a + t0.x + t1.x * t2.x
+	_ = a + b + c + d + e + 2*3
+	_ = a + b + c + 2*3 + d + e
+	_ = (a+b+c)*2
+	_ = a - b + c - d + (a+b+c) + d&e
+	_ = under_bar-1
+	_ = Open(dpath + "/file", O_WRONLY | O_CREAT, 0666)
+	_ = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
+
+	// test case for issue 8021
+	// want:
+	//  ([]bool{})[([]int{})[((1)+(((1)+((((1)*(((1)+(1))+(1)))+(1))*(1)))+(1)))]]
+	_ = ([]bool{})[([]int{})[((1) + (((((1) + (((((((1) * (((((1) + (1))) + (1))))) + (1))) * (1))))) + (1))))]]
+
+	// the parser does not restrict expressions that may appear as statements
+	true
+	42
+	"foo"
+	x
+	(x)
+	a+b
+	a+b+c
+	a+(b*c)
+	a+(b/c)
+	1+a
+	a+1
+	s[a]
+	x<<1
+	(s[0]<<1)&0xf
+	"foo"+s
+	x == y
+	x < y || z > 42
+}
+
+
+// slice expressions with cap
+func _() {
+	_ = x[a:b:c]
+	_ = x[a:b:c+d]
+	_ = x[a:b+d:c]
+	_ = x[a:b+d:c+d]
+	_ = x[a+d:b:c]
+	_ = x[a+d:b:c+d]
+	_ = x[a+d:b+d:c]
+	_ = x[a+d:b+d:c+d]
+
+	_ = x[:b:c]
+	_ = x[:b:c+d]
+	_ = x[:b+d:c]
+	_ = x[:b+d:c+d]
+}
+
+func issue22111() {
+	_ = x[:]
+
+	_ = x[:b]
+	_ = x[:b+1]
+
+	_ = x[a:]
+	_ = x[a+1:]
+
+	_ = x[a:b]
+	_ = x[a+1:b]
+	_ = x[a:b+1]
+	_ = x[a+1:b+1]
+
+	_ = x[:b:c]
+	_ = x[:b+1:c]
+	_ = x[:b:c+1]
+	_ = x[:b+1:c+1]
+
+	_ = x[a:b:c]
+	_ = x[a+1:b:c]
+	_ = x[a:b+1:c]
+	_ = x[a+1:b+1:c]
+	_ = x[a:b:c+1]
+	_ = x[a+1:b:c+1]
+	_ = x[a:b+1:c+1]
+	_ = x[a+1:b+1:c+1]
+}
+
+func _() {
+	_ = a+b
+	_ = a+b+c
+	_ = a+b*c
+	_ = a+(b*c)
+	_ = (a+b)*c
+	_ = a+(b*c*d)
+	_ = a+(b*c+d)
+
+	_ = 1<<x
+	_ = -1<<x
+	_ = 1<<x-1
+	_ = -1<<x-1
+
+	_ = f(a+b)
+	_ = f(a+b+c)
+	_ = f(a+b*c)
+	_ = f(a+(b*c))
+	_ = f(1<<x-1, 1<<x-2)
+
+	_ = 1<<d.logWindowSize-1
+
+	buf = make(x, 2*cap(b.buf) + n)
+
+	dst[i*3+2] = dbuf[0]<<2
+	dst[i*3+2] = dbuf[0]<<2 | dbuf[1]>>4
+
+	b.buf = b.buf[0:b.off+m+n]
+	b.buf = b.buf[0:b.off+m*n]
+	f(b.buf[0:b.off+m+n])
+
+	signed += ' '*8
+	tw.octal(header[148:155], chksum)
+
+	_ = x > 0 && i >= 0
+
+	x1, x0 := x>>w2, x&m2
+	z0 = t1<<w2+t0
+	z1 = (t1+t0>>w2)>>w2
+	q1, r1 := x1/d1, x1%d1
+	r1 = r1*b2 | x0>>w2
+	x1 = (x1<<z)|(x0>>(uint(w)-z))
+	x1 = x1<<z | x0>>(uint(w)-z)
+
+	_ = buf[0:len(buf)+1]
+	_ = buf[0:n+1]
+
+	a,b = b,a
+	a = b+c
+	a = b*c+d
+	_ = a*b+c
+	_ = a-b-c
+	_ = a-(b-c)
+	_ = a-b*c
+	_ = a-(b*c)
+	_ = a*b/c
+	_ = a/ *b
+	_ = x[a|^b]
+	_ = x[a/ *b]
+	_ = a& ^b
+	_ = a+ +b
+	_ = a- -b
+	_ = x[a*-b]
+	_ = x[a+ +b]
+	_ = x^y^z
+	_ = b[a>>24] ^ b[(a>>16)&0xFF] ^ b[(a>>8)&0xFF] ^ b[a&0xFF]
+	_ = len(longVariableName)*2
+
+	_ = token(matchType + xlength<<lengthShift + xoffset)
+}
+
+
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+
+	// make sure syntactically legal code remains syntactically legal
+	f(3, 42 ...) // a blank must remain between 42 and ...
+	f(4, 42. ...)
+	f(5, 42....)
+	f(6, 42.0 ...)
+	f(7, 42.0...)
+	f(8, .42 ...)
+	f(9, .42...)
+	f(10, 42e0 ...)
+	f(11, 42e0...)
+
+	_ = 42 .x // a blank must remain between 42 and .x
+	_ = 42. .x
+	_ = 42..x
+	_ = 42.0 .x
+	_ = 42.0.x
+	_ = .42 .x
+	_ = .42.x
+	_ = 42e0 .x
+	_ = 42e0.x
+
+	// a blank must remain between the binary operator and the 2nd operand
+	_ = x/ *y
+	_ = x< -1
+	_ = x< <-1
+	_ = x+ +1
+	_ = x- -1
+	_ = x& &x
+	_ = x& ^x
+
+	_ = f(x/ *y, x< -1, x< <-1, x+ +1, x- -1, x& &x, x& ^x)
+}
+
+
+func _() {
+	_ = T{}
+	_ = struct{}{}
+	_ = [10]T{}
+	_ = [...]T{}
+	_ = []T{}
+	_ = map[int]T{}
+}
+
+
+// one-line structs/interfaces in composite literals (up to a threshold)
+func _() {
+	_ = struct{}{}
+	_ = struct{ x int }{0}
+	_ = struct{ x, y, z int }{0, 1, 2}
+	_ = struct{ int }{0}
+	_ = struct{ s struct { int } }{struct{ int}{0} }
+
+	_ = (interface{})(nil)
+	_ = (interface{String() string})(nil)
+	_ = (interface{
+		String()    string
+	})(nil)
+	_ = (interface{fmt.Stringer})(nil)
+	_ = (interface{
+		    fmt.Stringer
+	})(nil)
+}
+
+func _() {
+	// do not modify literals
+	_ = "tab1	tab2	tab3	end"  // string contains 3 tabs
+	_ = "tab1 tab2 tab3 end"  // same string with 3 blanks - may be unaligned because editors see tabs in strings
+	_ = ""  // this comment should be aligned with the one on the previous line
+	_ = ``
+	_ = `
+`
+_ = `foo
+		bar`
+	_ = `three spaces before the end of the line starting here:   
+they must not be removed`
+}
+
+
+func _() {
+	// smart handling of indentation for multi-line raw strings
+	var _ = ``
+	var _ = `foo`
+	var _ = `foo
+bar`
+
+
+var _ =
+	``
+var _ =
+	`foo`
+var _ =
+	// the next line should remain indented
+	`foo
+bar`
+
+
+	var _ = // comment
+		``
+	var _ = // comment
+		`foo`
+	var _ = // comment
+		// the next line should remain indented
+		`foo
+bar`
+
+
+var _ = /* comment */ ``
+var _ = /* comment */ `foo`
+var _ = /* comment */ `foo
+bar`
+
+
+	var _ = /* comment */
+		``
+	var _ = /* comment */
+		`foo`
+	var _ = /* comment */
+		// the next line should remain indented
+		`foo
+bar`
+
+
+var board = []int(
+	`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+
+	var state = S{
+		"foo",
+		// the next line should remain indented
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`,
+		"bar",
+	}
+}
+
+
+func _() {
+	// one-line function literals (body is on a single line)
+	_ = func() {}
+	_ = func() int { return 0 }
+	_ = func(x, y int) bool { m := (x+y)/2; return m < 0 }
+
+	// multi-line function literals (body is not on one line)
+	_ = func() {
+	}
+	_ = func() int {
+		return 0
+	}
+	_ = func(x, y int) bool {
+		m := (x+y)/2; return x < y }
+
+	f(func() {
+	})
+	f(func() int {
+		return 0
+	})
+	f(func(x, y int) bool {
+		m := (x+y)/2; return x < y })
+}
+
+
+func _() {
+	_ = [][]int {
+		[]int{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int {
+		{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int {
+		{1},
+		{1, 2},
+		{1, 2, 3},
+	}
+	_ = [][]int {{1}, {1, 2}, {1, 2, 3}}
+}
+
+
+// various multi-line expressions
+func _() {
+	// do not add extra indentation to multi-line string lists
+	_ = "foo" + "bar"
+	_ = "foo" +
+	"bar" +
+	"bah"
+	_ = []string {
+		"abc" +
+		"def",
+		"foo" +
+		"bar",
+	}
+}
+
+
+const _ = F1 +
+	`string = "%s";` +
+	`ptr = *;` +
+	`datafmt.T2 = s ["-" p "-"];`
+
+
+const _ =
+	`datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+
+const _ = `datafmt "datafmt";` +
+`default = "%v";` +
+`array = *;` +
+`datafmt.T3 = s  {" " a a / ","};`
+
+
+func _() {
+	_ = F1 +
+		`string = "%s";` +
+		`ptr = *;` +
+		`datafmt.T2 = s ["-" p "-"];`
+
+	_ =
+		`datafmt "datafmt";` +
+		`default = "%v";` +
+		`array = *;` +
+		`datafmt.T3 = s  {" " a a / ","};`
+
+	_ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+}
+
+
+func _() {
+	// respect source lines in multi-line expressions
+	_ = a+
+	b+
+	c
+	_ = a < b ||
+		b < a
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+	"638952175999932299156089414639761565182862536979208272237582" +
+	"51185210916864000000000000000000000000"  // 100!
+	_ = "170141183460469231731687303715884105727"  // prime
+}
+
+
+// Alignment after overlong lines
+const (
+	_ = "991"
+	_ = "2432902008176640000"  // 20!
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+	"638952175999932299156089414639761565182862536979208272237582" +
+	"51185210916864000000000000000000000000"  // 100!
+	_ = "170141183460469231731687303715884105727"  // prime
+)
+
+
+// Correct placement of operators and comments in multi-line expressions
+func _() {
+	_ = a +  // comment
+		b +  // comment
+		c
+	_ = "a"	+
+		"b" +	// comment
+		"c"
+	_ = "ba0408" + "7265717569726564"     // field 71, encoding 2, string "required"
+}
+
+
+// Correct placement of terminating comma/closing parentheses in multi-line calls.
+func _() {
+	f(1,
+		2,
+		3)
+	f(1,
+		2,
+		3,
+	)
+	f(1,
+		2,
+		3)  // comment
+	f(1,
+		2,
+		3,  // comment
+	)
+	f(1,
+		2,
+		3)// comment
+	f(1,
+		2,
+		3,// comment
+	)
+}
+
+
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow, // yellow
+	draw.Cyan, // cyan
+	draw.Green, // lime green
+	draw.GreyBlue, // slate
+	draw.Red, /* red */
+	draw.GreyGreen, /* olive green */
+	draw.Blue, /* blue */
+	draw.Color(0xFF55AAFF), /* pink */
+	draw.Color(0xFFAAFFFF), /* lavender */
+	draw.Color(0xBB005DFF), /* maroon */
+}
+
+
+func same(t, u *Time) bool {
+	// respect source lines in multi-line expressions
+	return t.Year == u.Year &&
+		t.Month == u.Month &&
+		t.Day == u.Day &&
+		t.Hour == u.Hour &&
+		t.Minute == u.Minute &&
+		t.Second == u.Second &&
+		t.Weekday == u.Weekday &&
+		t.ZoneOffset == u.ZoneOffset &&
+		t.Zone == u.Zone
+}
+
+
+func (p *parser) charClass() {
+	// respect source lines in multi-line expressions
+	if cc.negate && len(cc.ranges) == 2 &&
+		cc.ranges[0] == '\n' && cc.ranges[1] == '\n' {
+		nl := new(_NotNl)
+		p.re.add(nl)
+	}
+}
+
+
+func addState(s []state, inst instr, match []int) {
+	// handle comments correctly in multi-line expressions
+	for i := 0; i < l; i++ {
+		if s[i].inst.index() == index && // same instruction
+		   s[i].match[0] < pos {	// earlier match already going; leftmost wins
+		   	return s
+		 }
+	}
+}
+
+func (self *T) foo(x int) *T { return self }
+
+func _() { module.Func1().Func2() }
+
+func _() {
+	_ = new(T).
+		foo(1).
+			foo(2).
+		foo(3)
+
+	_ = new(T).
+	foo(1).
+	foo(2). // inline comments
+	foo(3)
+
+	_ = new(T).foo(1).foo(2).foo(3)
+
+	// handle multiline argument list correctly
+	_ = new(T).
+	foo(
+		1).
+		foo(2)
+
+	_ = new(T).foo(
+		1).foo(2)
+
+	_ = Array[3 +
+4]
+
+	_ = Method(1, 2,
+		3)
+
+	_ = new(T).
+   foo().
+   bar() . (*Type)
+
+	_ = new(T).
+foo().
+bar().(*Type).
+baz()
+
+	_ = new(T).
+	foo().
+	bar()["idx"]
+
+	_ = new(T).
+	foo().
+	bar()["idx"]	.
+	baz()
+
+	_ = new(T).
+	foo().
+	bar()[1:2]
+
+	_ = new(T).
+	foo().
+	bar()[1:2].
+	baz()
+
+	_ = new(T).
+		Field.
+		Array[3+
+       		4].
+		Table ["foo"].
+		Blob. (*Type).
+	Slices[1:4].
+	Method(1, 2,
+	3).
+		Thingy
+
+	_ = a.b.c
+	_ = a.
+	b.
+	c
+	_ = a.b().c
+	_ = a.
+	b().
+	c
+	_ = a.b[0].c
+	_ = a.
+	b[0].
+	c
+	_ = a.b[0:].c
+	_ = a.
+	b[0:].
+	c
+	_ = a.b.(T).c
+	_ = a.
+	b.
+	(T).
+	c
+}
+
+
+// Don't introduce extra newlines in strangely formatted expression lists.
+func f() {
+	// os.Open parameters should remain on two lines
+	if writer, err = os.Open(outfile, s.O_WRONLY|os.O_CREATE|
+		os.O_TRUNC, 0666); err != nil {
+	    log.Fatal(err)
+	}
+}
+
+// Handle multi-line argument lists ending in ... correctly.
+// Was issue 3130.
+func _() {
+	_ = append(s, a...)
+	_ = append(
+		s, a...)
+	_ = append(s,
+		a...)
+	_ = append(
+		s,
+		a...)
+	_ = append(s, a...,
+	)
+	_ = append(s,
+		a...,
+	)
+	_ = append(
+		s,
+		a...,
+	)
+}
+
+// Literal function types in conversions must be parenthesized;
+// for now go/parser accepts the unparenthesized form where it
+// is non-ambiguous.
+func _() {
+	// these conversions should be rewritten to look
+	// the same as the parenthesized conversions below
+	_ = func()()(nil)
+	_ = func(x int)(float)(nil)
+	_ = func() func() func()()(nil)
+
+	_ = (func()())(nil)
+	_ = (func(x int)(float))(nil)
+	_ = (func() func() func()())(nil)
+}
+
+func _() {
+	_ = f().
+	f(func() {
+		f()
+	}).
+	f(map[int]int{
+	1: 2,
+	3: 4,
+})
+
+	_ = f().
+	f(
+	func() {
+		f()
+	},
+	)
+}
diff --git a/src/go/printer/testdata/expressions.raw b/src/go/printer/testdata/expressions.raw
new file mode 100644
index 0000000..058fded
--- /dev/null
+++ b/src/go/printer/testdata/expressions.raw
@@ -0,0 +1,743 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package expressions
+
+type T struct {
+	x, y, z int
+}
+
+var (
+	a, b, c, d, e	int
+	under_bar	int
+	longIdentifier1, longIdentifier2, longIdentifier3	int
+	t0, t1, t2	T
+	s	string
+	p	*int
+)
+
+func _() {
+	// no spaces around simple or parenthesized expressions
+	_ = (a + 0)
+	_ = a + b
+	_ = a + b + c
+	_ = a + b - c
+	_ = a - b - c
+	_ = a + (b * c)
+	_ = a + (b / c)
+	_ = a - (b % c)
+	_ = 1 + a
+	_ = a + 1
+	_ = a + b + 1
+	_ = s[a]
+	_ = s[a:]
+	_ = s[:b]
+	_ = s[1:2]
+	_ = s[a:b]
+	_ = s[0:len(s)]
+	_ = s[0] << 1
+	_ = (s[0] << 1) & 0xf
+	_ = s[0]<<2 | s[1]>>4
+	_ = "foo" + s
+	_ = s + "foo"
+	_ = 'a' + 'b'
+	_ = len(s) / 2
+	_ = len(t0.x) / a
+
+	// spaces around expressions of different precedence or expressions containing spaces
+	_ = a + -b
+	_ = a - ^b
+	_ = a / *p
+	_ = a + b*c
+	_ = 1 + b*c
+	_ = a + 2*c
+	_ = a + c*2
+	_ = 1 + 2*3
+	_ = s[1 : 2*3]
+	_ = s[a : b-c]
+	_ = s[0:]
+	_ = s[a+b]
+	_ = s[:b-c]
+	_ = s[a+b:]
+	_ = a[a<<b+1]
+	_ = a[a<<b+1:]
+	_ = s[a+b : len(s)]
+	_ = s[len(s):-a]
+	_ = s[a : len(s)+1]
+	_ = s[a:len(s)+1] + s
+
+	// spaces around operators with equal or lower precedence than comparisons
+	_ = a == b
+	_ = a != b
+	_ = a > b
+	_ = a >= b
+	_ = a < b
+	_ = a <= b
+	_ = a < b && c > d
+	_ = a < b || c > d
+
+	// spaces around "long" operands
+	_ = a + longIdentifier1
+	_ = longIdentifier1 + a
+	_ = longIdentifier1 + longIdentifier2*longIdentifier3
+	_ = s + "a longer string"
+
+	// some selected cases
+	_ = a + t0.x
+	_ = a + t0.x + t1.x*t2.x
+	_ = a + b + c + d + e + 2*3
+	_ = a + b + c + 2*3 + d + e
+	_ = (a + b + c) * 2
+	_ = a - b + c - d + (a + b + c) + d&e
+	_ = under_bar - 1
+	_ = Open(dpath+"/file", O_WRONLY|O_CREAT, 0666)
+	_ = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
+
+	// test case for issue 8021
+	// want:
+	//  ([]bool{})[([]int{})[((1)+(((1)+((((1)*(((1)+(1))+(1)))+(1))*(1)))+(1)))]]
+	_ = ([]bool{})[([]int{})[((1)+(((1)+((((1)*(((1)+(1))+(1)))+(1))*(1)))+(1)))]]
+
+	// the parser does not restrict expressions that may appear as statements
+	true
+	42
+	"foo"
+	x
+	(x)
+	a + b
+	a + b + c
+	a + (b * c)
+	a + (b / c)
+	1 + a
+	a + 1
+	s[a]
+	x << 1
+	(s[0] << 1) & 0xf
+	"foo" + s
+	x == y
+	x < y || z > 42
+}
+
+// slice expressions with cap
+func _() {
+	_ = x[a:b:c]
+	_ = x[a : b : c+d]
+	_ = x[a : b+d : c]
+	_ = x[a : b+d : c+d]
+	_ = x[a+d : b : c]
+	_ = x[a+d : b : c+d]
+	_ = x[a+d : b+d : c]
+	_ = x[a+d : b+d : c+d]
+
+	_ = x[:b:c]
+	_ = x[: b : c+d]
+	_ = x[: b+d : c]
+	_ = x[: b+d : c+d]
+}
+
+func issue22111() {
+	_ = x[:]
+
+	_ = x[:b]
+	_ = x[:b+1]
+
+	_ = x[a:]
+	_ = x[a+1:]
+
+	_ = x[a:b]
+	_ = x[a+1 : b]
+	_ = x[a : b+1]
+	_ = x[a+1 : b+1]
+
+	_ = x[:b:c]
+	_ = x[: b+1 : c]
+	_ = x[: b : c+1]
+	_ = x[: b+1 : c+1]
+
+	_ = x[a:b:c]
+	_ = x[a+1 : b : c]
+	_ = x[a : b+1 : c]
+	_ = x[a+1 : b+1 : c]
+	_ = x[a : b : c+1]
+	_ = x[a+1 : b : c+1]
+	_ = x[a : b+1 : c+1]
+	_ = x[a+1 : b+1 : c+1]
+}
+
+func _() {
+	_ = a + b
+	_ = a + b + c
+	_ = a + b*c
+	_ = a + (b * c)
+	_ = (a + b) * c
+	_ = a + (b * c * d)
+	_ = a + (b*c + d)
+
+	_ = 1 << x
+	_ = -1 << x
+	_ = 1<<x - 1
+	_ = -1<<x - 1
+
+	_ = f(a + b)
+	_ = f(a + b + c)
+	_ = f(a + b*c)
+	_ = f(a + (b * c))
+	_ = f(1<<x-1, 1<<x-2)
+
+	_ = 1<<d.logWindowSize - 1
+
+	buf = make(x, 2*cap(b.buf)+n)
+
+	dst[i*3+2] = dbuf[0] << 2
+	dst[i*3+2] = dbuf[0]<<2 | dbuf[1]>>4
+
+	b.buf = b.buf[0 : b.off+m+n]
+	b.buf = b.buf[0 : b.off+m*n]
+	f(b.buf[0 : b.off+m+n])
+
+	signed += ' ' * 8
+	tw.octal(header[148:155], chksum)
+
+	_ = x > 0 && i >= 0
+
+	x1, x0 := x>>w2, x&m2
+	z0 = t1<<w2 + t0
+	z1 = (t1 + t0>>w2) >> w2
+	q1, r1 := x1/d1, x1%d1
+	r1 = r1*b2 | x0>>w2
+	x1 = (x1 << z) | (x0 >> (uint(w) - z))
+	x1 = x1<<z | x0>>(uint(w)-z)
+
+	_ = buf[0 : len(buf)+1]
+	_ = buf[0 : n+1]
+
+	a, b = b, a
+	a = b + c
+	a = b*c + d
+	_ = a*b + c
+	_ = a - b - c
+	_ = a - (b - c)
+	_ = a - b*c
+	_ = a - (b * c)
+	_ = a * b / c
+	_ = a / *b
+	_ = x[a|^b]
+	_ = x[a / *b]
+	_ = a & ^b
+	_ = a + +b
+	_ = a - -b
+	_ = x[a*-b]
+	_ = x[a + +b]
+	_ = x ^ y ^ z
+	_ = b[a>>24] ^ b[(a>>16)&0xFF] ^ b[(a>>8)&0xFF] ^ b[a&0xFF]
+	_ = len(longVariableName) * 2
+
+	_ = token(matchType + xlength<<lengthShift + xoffset)
+}
+
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+
+	// make sure syntactically legal code remains syntactically legal
+	f(3, 42 ...)	// a blank must remain between 42 and ...
+	f(4, 42....)
+	f(5, 42....)
+	f(6, 42.0...)
+	f(7, 42.0...)
+	f(8, .42...)
+	f(9, .42...)
+	f(10, 42e0...)
+	f(11, 42e0...)
+
+	_ = 42 .x	// a blank must remain between 42 and .x
+	_ = 42..x
+	_ = 42..x
+	_ = 42.0.x
+	_ = 42.0.x
+	_ = .42.x
+	_ = .42.x
+	_ = 42e0.x
+	_ = 42e0.x
+
+	// a blank must remain between the binary operator and the 2nd operand
+	_ = x / *y
+	_ = x < -1
+	_ = x < <-1
+	_ = x + +1
+	_ = x - -1
+	_ = x & &x
+	_ = x & ^x
+
+	_ = f(x / *y, x < -1, x < <-1, x + +1, x - -1, x & &x, x & ^x)
+}
+
+func _() {
+	_ = T{}
+	_ = struct{}{}
+	_ = [10]T{}
+	_ = [...]T{}
+	_ = []T{}
+	_ = map[int]T{}
+}
+
+// one-line structs/interfaces in composite literals (up to a threshold)
+func _() {
+	_ = struct{}{}
+	_ = struct{ x int }{0}
+	_ = struct{ x, y, z int }{0, 1, 2}
+	_ = struct{ int }{0}
+	_ = struct{ s struct{ int } }{struct{ int }{0}}
+
+	_ = (interface{})(nil)
+	_ = (interface{ String() string })(nil)
+	_ = (interface {
+		String() string
+	})(nil)
+	_ = (interface{ fmt.Stringer })(nil)
+	_ = (interface {
+		fmt.Stringer
+	})(nil)
+}
+
+func _() {
+	// do not modify literals
+	_ = "tab1	tab2	tab3	end"	// string contains 3 tabs
+	_ = "tab1 tab2 tab3 end"	// same string with 3 blanks - may be unaligned because editors see tabs in strings
+	_ = ""	// this comment should be aligned with the one on the previous line
+	_ = ``
+	_ = `
+`
+	_ = `foo
+		bar`
+	_ = `three spaces before the end of the line starting here:   
+they must not be removed`
+}
+
+func _() {
+	// smart handling of indentation for multi-line raw strings
+	var _ = ``
+	var _ = `foo`
+	var _ = `foo
+bar`
+
+	var _ = ``
+	var _ = `foo`
+	var _ =
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ =	// comment
+	``
+	var _ =	// comment
+	`foo`
+	var _ =	// comment
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ = /* comment */ ``
+	var _ = /* comment */ `foo`
+	var _ = /* comment */ `foo
+bar`
+
+	var _ =	/* comment */
+	``
+	var _ =	/* comment */
+	`foo`
+	var _ =	/* comment */
+	// the next line should remain indented
+	`foo
+bar`
+
+	var board = []int(
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+	var state = S{
+		"foo",
+		// the next line should remain indented
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`,
+		"bar",
+	}
+}
+
+func _() {
+	// one-line function literals (body is on a single line)
+	_ = func() {}
+	_ = func() int { return 0 }
+	_ = func(x, y int) bool { m := (x + y) / 2; return m < 0 }
+
+	// multi-line function literals (body is not on one line)
+	_ = func() {
+	}
+	_ = func() int {
+		return 0
+	}
+	_ = func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	}
+
+	f(func() {
+	})
+	f(func() int {
+		return 0
+	})
+	f(func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	})
+}
+
+func _() {
+	_ = [][]int{
+		[]int{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		{1, 2},
+		{1, 2, 3},
+	}
+	_ = [][]int{{1}, {1, 2}, {1, 2, 3}}
+}
+
+// various multi-line expressions
+func _() {
+	// do not add extra indentation to multi-line string lists
+	_ = "foo" + "bar"
+	_ = "foo" +
+		"bar" +
+		"bah"
+	_ = []string{
+		"abc" +
+			"def",
+		"foo" +
+			"bar",
+	}
+}
+
+const _ = F1 +
+	`string = "%s";` +
+	`ptr = *;` +
+	`datafmt.T2 = s ["-" p "-"];`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+func _() {
+	_ = F1 +
+		`string = "%s";` +
+		`ptr = *;` +
+		`datafmt.T2 = s ["-" p "-"];`
+
+	_ =
+		`datafmt "datafmt";` +
+			`default = "%v";` +
+			`array = *;` +
+			`datafmt.T3 = s  {" " a a / ","};`
+
+	_ = `datafmt "datafmt";` +
+		`default = "%v";` +
+		`array = *;` +
+		`datafmt.T3 = s  {" " a a / ","};`
+}
+
+func _() {
+	// respect source lines in multi-line expressions
+	_ = a +
+		b +
+		c
+	_ = a < b ||
+		b < a
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_ = "170141183460469231731687303715884105727"	// prime
+}
+
+// Alignment after overlong lines
+const (
+	_	= "991"
+	_	= "2432902008176640000"		// 20!
+	_	= "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_	= "170141183460469231731687303715884105727"		// prime
+)
+
+// Correct placement of operators and comments in multi-line expressions
+func _() {
+	_ = a +	// comment
+		b +	// comment
+		c
+	_ = "a" +
+		"b" +	// comment
+		"c"
+	_ = "ba0408" + "7265717569726564"	// field 71, encoding 2, string "required"
+}
+
+// Correct placement of terminating comma/closing parentheses in multi-line calls.
+func _() {
+	f(1,
+		2,
+		3)
+	f(1,
+		2,
+		3,
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+}
+
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow,	// yellow
+	draw.Cyan,	// cyan
+	draw.Green,	// lime green
+	draw.GreyBlue,	// slate
+	draw.Red,	/* red */
+	draw.GreyGreen,	/* olive green */
+	draw.Blue,	/* blue */
+	draw.Color(0xFF55AAFF),	/* pink */
+	draw.Color(0xFFAAFFFF),	/* lavender */
+	draw.Color(0xBB005DFF),	/* maroon */
+}
+
+func same(t, u *Time) bool {
+	// respect source lines in multi-line expressions
+	return t.Year == u.Year &&
+		t.Month == u.Month &&
+		t.Day == u.Day &&
+		t.Hour == u.Hour &&
+		t.Minute == u.Minute &&
+		t.Second == u.Second &&
+		t.Weekday == u.Weekday &&
+		t.ZoneOffset == u.ZoneOffset &&
+		t.Zone == u.Zone
+}
+
+func (p *parser) charClass() {
+	// respect source lines in multi-line expressions
+	if cc.negate && len(cc.ranges) == 2 &&
+		cc.ranges[0] == '\n' && cc.ranges[1] == '\n' {
+		nl := new(_NotNl)
+		p.re.add(nl)
+	}
+}
+
+func addState(s []state, inst instr, match []int) {
+	// handle comments correctly in multi-line expressions
+	for i := 0; i < l; i++ {
+		if s[i].inst.index() == index &&	// same instruction
+			s[i].match[0] < pos {	// earlier match already going; leftmost wins
+			return s
+		}
+	}
+}
+
+func (self *T) foo(x int) *T	{ return self }
+
+func _()	{ module.Func1().Func2() }
+
+func _() {
+	_ = new(T).
+		foo(1).
+		foo(2).
+		foo(3)
+
+	_ = new(T).
+		foo(1).
+		foo(2).	// inline comments
+		foo(3)
+
+	_ = new(T).foo(1).foo(2).foo(3)
+
+	// handle multiline argument list correctly
+	_ = new(T).
+		foo(
+			1).
+		foo(2)
+
+	_ = new(T).foo(
+		1).foo(2)
+
+	_ = Array[3+
+		4]
+
+	_ = Method(1, 2,
+		3)
+
+	_ = new(T).
+		foo().
+		bar().(*Type)
+
+	_ = new(T).
+		foo().
+		bar().(*Type).
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()["idx"]
+
+	_ = new(T).
+		foo().
+		bar()["idx"].
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()[1:2]
+
+	_ = new(T).
+		foo().
+		bar()[1:2].
+		baz()
+
+	_ = new(T).
+		Field.
+		Array[3+
+		4].
+		Table["foo"].
+		Blob.(*Type).
+		Slices[1:4].
+		Method(1, 2,
+			3).
+		Thingy
+
+	_ = a.b.c
+	_ = a.
+		b.
+		c
+	_ = a.b().c
+	_ = a.
+		b().
+		c
+	_ = a.b[0].c
+	_ = a.
+		b[0].
+		c
+	_ = a.b[0:].c
+	_ = a.
+		b[0:].
+		c
+	_ = a.b.(T).c
+	_ = a.
+		b.(T).
+		c
+}
+
+// Don't introduce extra newlines in strangely formatted expression lists.
+func f() {
+	// os.Open parameters should remain on two lines
+	if writer, err = os.Open(outfile, s.O_WRONLY|os.O_CREATE|
+		os.O_TRUNC, 0666); err != nil {
+		log.Fatal(err)
+	}
+}
+
+// Handle multi-line argument lists ending in ... correctly.
+// Was issue 3130.
+func _() {
+	_ = append(s, a...)
+	_ = append(
+		s, a...)
+	_ = append(s,
+		a...)
+	_ = append(
+		s,
+		a...)
+	_ = append(s, a...,
+	)
+	_ = append(s,
+		a...,
+	)
+	_ = append(
+		s,
+		a...,
+	)
+}
+
+// Literal function types in conversions must be parenthesized;
+// for now go/parser accepts the unparenthesized form where it
+// is non-ambiguous.
+func _() {
+	// these conversions should be rewritten to look
+	// the same as the parenthesized conversions below
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+
+	_ = (func())(nil)
+	_ = (func(x int) float)(nil)
+	_ = (func() func() func())(nil)
+}
+
+func _() {
+	_ = f().
+		f(func() {
+			f()
+		}).
+		f(map[int]int{
+			1:	2,
+			3:	4,
+		})
+
+	_ = f().
+		f(
+			func() {
+				f()
+			},
+		)
+}
diff --git a/src/go/printer/testdata/generics.golden b/src/go/printer/testdata/generics.golden
new file mode 100644
index 0000000..7ddf20b
--- /dev/null
+++ b/src/go/printer/testdata/generics.golden
@@ -0,0 +1,109 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package generics
+
+func _[A, B any](a A, b B) int	{}
+func _[T any](x, y T) T
+
+type T[P any] struct{}
+type T[P1, P2, P3 any] struct{}
+
+type T[P C] struct{}
+type T[P1, P2, P3 C] struct{}
+
+type T[P C[P]] struct{}
+type T[P1, P2, P3 C[P1, P2, P3]] struct{}
+
+func f[P any](x P)
+func f[P1, P2, P3 any](x1 P1, x2 P2, x3 P3) struct{}
+
+func f[P interface{}](x P)
+func f[P1, P2, P3 interface {
+	m1(P1)
+	~P2 | ~P3
+}](x1 P1, x2 P2, x3 P3) struct{}
+func f[P any](T1[P], T2[P]) T3[P]
+
+func (x T[P]) m()
+func (T[P]) m(x T[P]) P
+
+func _() {
+	type _ []T[P]
+	var _ []T[P]
+	_ = []T[P]{}
+}
+
+// type constraint literals with elided interfaces
+func _[P ~int, Q int | string]()	{}
+func _[P struct{ f int }, Q *P]()	{}
+
+// various potentially ambiguous type parameter lists (issue #49482)
+type _[P *T,] struct{}
+type _[P T | T] struct{}
+type _[P T | T | T | T] struct{}
+type _[P *T, _ any] struct{}
+type _[P *T,] struct{}
+type _[P *T, _ any] struct{}
+type _[P T] struct{}
+type _[P T, _ any] struct{}
+
+type _[P *struct{}] struct{}
+type _ [P(*struct{})]struct{}
+type _[P []int] struct{}
+
+// a type literal in an |-expression indicates a type parameter list (blank after type parameter list and type)
+type _[P *[]int] struct{}
+type _[P *T | T, Q T] struct{}
+type _[P *[]T | T] struct{}
+type _[P *T | T | T | T | ~T] struct{}
+type _[P *T | T | T | ~T | T] struct{}
+type _[P *T | T | struct{} | T] struct{}
+type _[P <-chan int] struct{}
+type _[P *T | struct{} | T] struct{}
+
+// a trailing comma always indicates a (possibly invalid) type parameter list (blank after type parameter list and type)
+type _[P *T,] struct{}
+type _[P *T | T,] struct{}
+type _[P *T | <-T | T,] struct{}
+
+// slice/array type declarations (no blank between array length and element type)
+type _ []byte
+type _ [n]byte
+type _ [P(T)]byte
+type _ [P((T))]byte
+type _ [P * *T]byte
+type _ [P * T]byte
+type _ [P(*T)]byte
+type _ [P(**T)]byte
+type _ [P*T - T]byte
+type _ [P*T - T]byte
+type _ [P*T | T]byte
+type _ [P*T | <-T | T]byte
+
+// equivalent test cases for potentially ambiguous type parameter lists, except
+// for function declarations there is no ambiguity (issue #51548)
+func _[P *T]()		{}
+func _[P *T, _ any]()	{}
+func _[P *T]()		{}
+func _[P *T, _ any]()	{}
+func _[P T]()		{}
+func _[P T, _ any]()	{}
+
+func _[P *struct{}]()	{}
+func _[P *struct{}]()	{}
+func _[P []int]()	{}
+
+func _[P T]()	{}
+func _[P T]()	{}
+func _[P **T]()	{}
+func _[P *T]()	{}
+func _[P *T]()	{}
+func _[P **T]()	{}
+func _[P *T]()	{}
+
+func _[
+	P *T,
+]() {
+}
diff --git a/src/go/printer/testdata/generics.input b/src/go/printer/testdata/generics.input
new file mode 100644
index 0000000..4940f93
--- /dev/null
+++ b/src/go/printer/testdata/generics.input
@@ -0,0 +1,105 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package generics
+
+func _[A, B any](a A, b B) int {}
+func _[T any](x, y T) T
+
+type T[P any] struct{}
+type T[P1, P2, P3 any] struct{}
+
+type T[P C] struct{}
+type T[P1, P2, P3 C] struct{}
+
+type T[P C[P]] struct{}
+type T[P1, P2, P3 C[P1, P2, P3]] struct{}
+
+func f[P any](x P)
+func f[P1, P2, P3 any](x1 P1, x2 P2, x3 P3) struct{}
+
+func f[P interface{}](x P)
+func f[P1, P2, P3 interface{ m1(P1); ~P2|~P3 }](x1 P1, x2 P2, x3 P3) struct{}
+func f[P any](T1[P], T2[P]) T3[P]
+
+func (x T[P]) m()
+func ((T[P])) m(x T[P]) P
+
+func _() {
+	type _ []T[P]
+	var _ []T[P]
+	_ = []T[P]{}
+}
+
+// type constraint literals with elided interfaces
+func _[P ~int, Q int | string]() {}
+func _[P struct{f int}, Q *P]() {}
+
+// various potentially ambiguous type parameter lists (issue #49482)
+type _[P *T,] struct{}
+type _[P T | T] struct{}
+type _[P T | T | T | T] struct{}
+type _[P *T, _ any] struct{}
+type _[P (*T),] struct{}
+type _[P (*T), _ any] struct{}
+type _[P (T),] struct{}
+type _[P (T), _ any] struct{}
+
+type _[P *struct{}] struct{}
+type _[P (*struct{})] struct{}
+type _[P ([]int)] struct{}
+
+// a type literal in an |-expression indicates a type parameter list (blank after type parameter list and type)
+type _[P *[]int] struct{}
+type _[P *T | T, Q T] struct{}
+type _[P *[]T | T] struct{}
+type _[P *T | T | T | T | ~T] struct{}
+type _[P *T | T | T | ~T | T] struct{}
+type _[P *T | T | struct{} | T] struct{}
+type _[P <-chan int] struct{}
+type _[P *T | struct{} | T] struct{}
+
+// a trailing comma always indicates a (possibly invalid) type parameter list (blank after type parameter list and type)
+type _[P *T,] struct{}
+type _[P *T | T,] struct{}
+type _[P *T | <-T | T,] struct{}
+
+// slice/array type declarations (no blank between array length and element type)
+type _ []byte
+type _ [n]byte
+type _ [P(T)]byte
+type _ [P((T))]byte
+type _ [P * *T]byte
+type _ [P * T]byte
+type _ [P(*T)]byte
+type _ [P(**T)]byte
+type _ [P * T - T]byte
+type _ [P * T - T]byte
+type _ [P * T | T]byte
+type _ [P * T | <-T | T]byte
+
+// equivalent test cases for potentially ambiguous type parameter lists, except
+// for function declarations there is no ambiguity (issue #51548)
+func _[P *T,]() {}
+func _[P *T, _ any]() {}
+func _[P (*T),]() {}
+func _[P (*T), _ any]() {}
+func _[P (T),]() {}
+func _[P (T), _ any]() {}
+
+func _[P *struct{}] () {}
+func _[P (*struct{})] () {}
+func _[P ([]int)] () {}
+
+func _ [P(T)]() {}
+func _ [P((T))]() {}
+func _ [P * *T]() {}
+func _ [P * T]() {}
+func _ [P(*T)]() {}
+func _ [P(**T)]() {}
+func _ [P * T]() {}
+
+func _[
+	P *T,
+]() {}
diff --git a/src/go/printer/testdata/go2numbers.golden b/src/go/printer/testdata/go2numbers.golden
new file mode 100644
index 0000000..3c12049
--- /dev/null
+++ b/src/go/printer/testdata/go2numbers.golden
@@ -0,0 +1,186 @@
+package p
+
+const (
+	// 0-octals
+	_	= 0
+	_	= 0123
+	_	= 0123456
+
+	_	= 0_123
+	_	= 0123_456
+
+	// decimals
+	_	= 1
+	_	= 1234
+	_	= 1234567
+
+	_	= 1_234
+	_	= 1_234_567
+
+	// hexadecimals
+	_	= 0x0
+	_	= 0x1234
+	_	= 0xcafef00d
+
+	_	= 0X0
+	_	= 0X1234
+	_	= 0XCAFEf00d
+
+	_	= 0X_0
+	_	= 0X_1234
+	_	= 0X_CAFE_f00d
+
+	// octals
+	_	= 0o0
+	_	= 0o1234
+	_	= 0o01234567
+
+	_	= 0O0
+	_	= 0O1234
+	_	= 0O01234567
+
+	_	= 0o_0
+	_	= 0o_1234
+	_	= 0o0123_4567
+
+	_	= 0O_0
+	_	= 0O_1234
+	_	= 0O0123_4567
+
+	// binaries
+	_	= 0b0
+	_	= 0b1011
+	_	= 0b00101101
+
+	_	= 0B0
+	_	= 0B1011
+	_	= 0B00101101
+
+	_	= 0b_0
+	_	= 0b10_11
+	_	= 0b_0010_1101
+
+	// decimal floats
+	_	= 0.
+	_	= 123.
+	_	= 0123.
+
+	_	= .0
+	_	= .123
+	_	= .0123
+
+	_	= 0e0
+	_	= 123e+0
+	_	= 0123E-1
+
+	_	= 0e-0
+	_	= 123E+0
+	_	= 0123E123
+
+	_	= 0.e+1
+	_	= 123.E-10
+	_	= 0123.e123
+
+	_	= .0e-1
+	_	= .123E+10
+	_	= .0123E123
+
+	_	= 0.0
+	_	= 123.123
+	_	= 0123.0123
+
+	_	= 0.0e1
+	_	= 123.123E-10
+	_	= 0123.0123e+456
+
+	_	= 1_2_3.
+	_	= 0_123.
+
+	_	= 0_0e0
+	_	= 1_2_3e0
+	_	= 0_123e0
+
+	_	= 0e-0_0
+	_	= 1_2_3E+0
+	_	= 0123E1_2_3
+
+	_	= 0.e+1
+	_	= 123.E-1_0
+	_	= 01_23.e123
+
+	_	= .0e-1
+	_	= .123E+10
+	_	= .0123E123
+
+	_	= 1_2_3.123
+	_	= 0123.01_23
+
+	// hexadecimal floats
+	_	= 0x0.p+0
+	_	= 0Xdeadcafe.p-10
+	_	= 0x1234.P123
+
+	_	= 0x.1p-0
+	_	= 0X.deadcafep2
+	_	= 0x.1234P+10
+
+	_	= 0x0p0
+	_	= 0Xdeadcafep+1
+	_	= 0x1234P-10
+
+	_	= 0x0.0p0
+	_	= 0Xdead.cafep+1
+	_	= 0x12.34P-10
+
+	_	= 0Xdead_cafep+1
+	_	= 0x_1234P-10
+
+	_	= 0X_dead_cafe.p-10
+	_	= 0x12_34.P1_2_3
+	_	= 0X1_2_3_4.P-1_2_3
+
+	// imaginaries
+	_	= 0i
+	_	= 00i
+	_	= 08i
+	_	= 0000000000i
+	_	= 0123i
+	_	= 0000000123i
+	_	= 0000056789i
+	_	= 1234i
+	_	= 1234567i
+
+	_	= 0i
+	_	= 0_0i
+	_	= 0_8i
+	_	= 0_000_000_000i
+	_	= 0_123i
+	_	= 0_000_000_123i
+	_	= 0_000_056_789i
+	_	= 1_234i
+	_	= 1_234_567i
+
+	_	= 0.i
+	_	= 123.i
+	_	= 0123.i
+	_	= 000123.i
+
+	_	= 0e0i
+	_	= 123e0i
+	_	= 0123E0i
+	_	= 000123E0i
+
+	_	= 0.e+1i
+	_	= 123.E-1_0i
+	_	= 01_23.e123i
+	_	= 00_01_23.e123i
+
+	_	= 0b1010i
+	_	= 0B1010i
+	_	= 0o660i
+	_	= 0O660i
+	_	= 0xabcDEFi
+	_	= 0XabcDEFi
+	_	= 0xabcDEFP0i
+	_	= 0XabcDEFp0i
+)
diff --git a/src/go/printer/testdata/go2numbers.input b/src/go/printer/testdata/go2numbers.input
new file mode 100644
index 0000000..f3e7828
--- /dev/null
+++ b/src/go/printer/testdata/go2numbers.input
@@ -0,0 +1,186 @@
+package p
+
+const (
+	// 0-octals
+	_ = 0
+	_ = 0123
+	_ = 0123456
+
+	_ = 0_123
+	_ = 0123_456
+
+	// decimals
+	_ = 1
+	_ = 1234
+	_ = 1234567
+
+	_ = 1_234
+	_ = 1_234_567
+
+	// hexadecimals
+	_ = 0x0
+	_ = 0x1234
+	_ = 0xcafef00d
+
+	_ = 0X0
+	_ = 0X1234
+	_ = 0XCAFEf00d
+
+	_ = 0X_0
+	_ = 0X_1234
+	_ = 0X_CAFE_f00d
+
+	// octals
+	_ = 0o0
+	_ = 0o1234
+	_ = 0o01234567
+
+	_ = 0O0
+	_ = 0O1234
+	_ = 0O01234567
+
+	_ = 0o_0
+	_ = 0o_1234
+	_ = 0o0123_4567
+
+	_ = 0O_0
+	_ = 0O_1234
+	_ = 0O0123_4567
+
+	// binaries
+	_ = 0b0
+	_ = 0b1011
+	_ = 0b00101101
+
+	_ = 0B0
+	_ = 0B1011
+	_ = 0B00101101
+
+	_ = 0b_0
+	_ = 0b10_11
+	_ = 0b_0010_1101
+
+	// decimal floats
+	_ = 0.
+	_ = 123.
+	_ = 0123.
+
+	_ = .0
+	_ = .123
+	_ = .0123
+
+	_ = 0e0
+	_ = 123e+0
+	_ = 0123E-1
+
+	_ = 0e-0
+	_ = 123E+0
+	_ = 0123E123
+
+	_ = 0.e+1
+	_ = 123.E-10
+	_ = 0123.e123
+
+	_ = .0e-1
+	_ = .123E+10
+	_ = .0123E123
+
+	_ = 0.0
+	_ = 123.123
+	_ = 0123.0123
+
+	_ = 0.0e1
+	_ = 123.123E-10
+	_ = 0123.0123e+456
+
+	_ = 1_2_3.
+	_ = 0_123.
+
+	_ = 0_0e0
+	_ = 1_2_3e0
+	_ = 0_123e0
+
+	_ = 0e-0_0
+	_ = 1_2_3E+0
+	_ = 0123E1_2_3
+
+	_ = 0.e+1
+	_ = 123.E-1_0
+	_ = 01_23.e123
+
+	_ = .0e-1
+	_ = .123E+10
+	_ = .0123E123
+
+	_ = 1_2_3.123
+	_ = 0123.01_23
+
+	// hexadecimal floats
+	_ = 0x0.p+0
+	_ = 0Xdeadcafe.p-10
+	_ = 0x1234.P123
+
+	_ = 0x.1p-0
+	_ = 0X.deadcafep2
+	_ = 0x.1234P+10
+
+	_ = 0x0p0
+	_ = 0Xdeadcafep+1
+	_ = 0x1234P-10
+
+	_ = 0x0.0p0
+	_ = 0Xdead.cafep+1
+	_ = 0x12.34P-10
+
+	_ = 0Xdead_cafep+1
+	_ = 0x_1234P-10
+
+	_ = 0X_dead_cafe.p-10
+	_ = 0x12_34.P1_2_3
+	_ = 0X1_2_3_4.P-1_2_3
+
+	// imaginaries
+	_ = 0i
+	_ = 00i
+	_ = 08i
+	_ = 0000000000i
+	_ = 0123i
+	_ = 0000000123i
+	_ = 0000056789i
+	_ = 1234i
+	_ = 1234567i
+
+	_ = 0i
+	_ = 0_0i
+	_ = 0_8i
+	_ = 0_000_000_000i
+	_ = 0_123i
+	_ = 0_000_000_123i
+	_ = 0_000_056_789i
+	_ = 1_234i
+	_ = 1_234_567i
+
+	_ = 0.i
+	_ = 123.i
+	_ = 0123.i
+	_ = 000123.i
+
+	_ = 0e0i
+	_ = 123e0i
+	_ = 0123E0i
+	_ = 000123E0i
+
+	_ = 0.e+1i
+	_ = 123.E-1_0i
+	_ = 01_23.e123i
+	_ = 00_01_23.e123i
+
+	_ = 0b1010i
+	_ = 0B1010i
+	_ = 0o660i
+	_ = 0O660i
+	_ = 0xabcDEFi
+	_ = 0XabcDEFi
+	_ = 0xabcDEFP0i
+	_ = 0XabcDEFp0i
+)
diff --git a/src/go/printer/testdata/go2numbers.norm b/src/go/printer/testdata/go2numbers.norm
new file mode 100644
index 0000000..855f0fc
--- /dev/null
+++ b/src/go/printer/testdata/go2numbers.norm
@@ -0,0 +1,186 @@
+package p
+
+const (
+	// 0-octals
+	_	= 0
+	_	= 0123
+	_	= 0123456
+
+	_	= 0_123
+	_	= 0123_456
+
+	// decimals
+	_	= 1
+	_	= 1234
+	_	= 1234567
+
+	_	= 1_234
+	_	= 1_234_567
+
+	// hexadecimals
+	_	= 0x0
+	_	= 0x1234
+	_	= 0xcafef00d
+
+	_	= 0x0
+	_	= 0x1234
+	_	= 0xCAFEf00d
+
+	_	= 0x_0
+	_	= 0x_1234
+	_	= 0x_CAFE_f00d
+
+	// octals
+	_	= 0o0
+	_	= 0o1234
+	_	= 0o01234567
+
+	_	= 0o0
+	_	= 0o1234
+	_	= 0o01234567
+
+	_	= 0o_0
+	_	= 0o_1234
+	_	= 0o0123_4567
+
+	_	= 0o_0
+	_	= 0o_1234
+	_	= 0o0123_4567
+
+	// binaries
+	_	= 0b0
+	_	= 0b1011
+	_	= 0b00101101
+
+	_	= 0b0
+	_	= 0b1011
+	_	= 0b00101101
+
+	_	= 0b_0
+	_	= 0b10_11
+	_	= 0b_0010_1101
+
+	// decimal floats
+	_	= 0.
+	_	= 123.
+	_	= 0123.
+
+	_	= .0
+	_	= .123
+	_	= .0123
+
+	_	= 0e0
+	_	= 123e+0
+	_	= 0123e-1
+
+	_	= 0e-0
+	_	= 123e+0
+	_	= 0123e123
+
+	_	= 0.e+1
+	_	= 123.e-10
+	_	= 0123.e123
+
+	_	= .0e-1
+	_	= .123e+10
+	_	= .0123e123
+
+	_	= 0.0
+	_	= 123.123
+	_	= 0123.0123
+
+	_	= 0.0e1
+	_	= 123.123e-10
+	_	= 0123.0123e+456
+
+	_	= 1_2_3.
+	_	= 0_123.
+
+	_	= 0_0e0
+	_	= 1_2_3e0
+	_	= 0_123e0
+
+	_	= 0e-0_0
+	_	= 1_2_3e+0
+	_	= 0123e1_2_3
+
+	_	= 0.e+1
+	_	= 123.e-1_0
+	_	= 01_23.e123
+
+	_	= .0e-1
+	_	= .123e+10
+	_	= .0123e123
+
+	_	= 1_2_3.123
+	_	= 0123.01_23
+
+	// hexadecimal floats
+	_	= 0x0.p+0
+	_	= 0xdeadcafe.p-10
+	_	= 0x1234.p123
+
+	_	= 0x.1p-0
+	_	= 0x.deadcafep2
+	_	= 0x.1234p+10
+
+	_	= 0x0p0
+	_	= 0xdeadcafep+1
+	_	= 0x1234p-10
+
+	_	= 0x0.0p0
+	_	= 0xdead.cafep+1
+	_	= 0x12.34p-10
+
+	_	= 0xdead_cafep+1
+	_	= 0x_1234p-10
+
+	_	= 0x_dead_cafe.p-10
+	_	= 0x12_34.p1_2_3
+	_	= 0x1_2_3_4.p-1_2_3
+
+	// imaginaries
+	_	= 0i
+	_	= 0i
+	_	= 8i
+	_	= 0i
+	_	= 123i
+	_	= 123i
+	_	= 56789i
+	_	= 1234i
+	_	= 1234567i
+
+	_	= 0i
+	_	= 0i
+	_	= 8i
+	_	= 0i
+	_	= 123i
+	_	= 123i
+	_	= 56_789i
+	_	= 1_234i
+	_	= 1_234_567i
+
+	_	= 0.i
+	_	= 123.i
+	_	= 0123.i
+	_	= 000123.i
+
+	_	= 0e0i
+	_	= 123e0i
+	_	= 0123e0i
+	_	= 000123e0i
+
+	_	= 0.e+1i
+	_	= 123.e-1_0i
+	_	= 01_23.e123i
+	_	= 00_01_23.e123i
+
+	_	= 0b1010i
+	_	= 0b1010i
+	_	= 0o660i
+	_	= 0o660i
+	_	= 0xabcDEFi
+	_	= 0xabcDEFi
+	_	= 0xabcDEFp0i
+	_	= 0xabcDEFp0i
+)
diff --git a/src/go/printer/testdata/gobuild1.golden b/src/go/printer/testdata/gobuild1.golden
new file mode 100644
index 0000000..649da40
--- /dev/null
+++ b/src/go/printer/testdata/gobuild1.golden
@@ -0,0 +1,6 @@
+//go:build x
+// +build x
+
+package p
+
+func f()
diff --git a/src/go/printer/testdata/gobuild1.input b/src/go/printer/testdata/gobuild1.input
new file mode 100644
index 0000000..6538ee6
--- /dev/null
+++ b/src/go/printer/testdata/gobuild1.input
@@ -0,0 +1,7 @@
+package p
+
+//go:build x
+
+func f()
+
+// +build y
diff --git a/src/go/printer/testdata/gobuild2.golden b/src/go/printer/testdata/gobuild2.golden
new file mode 100644
index 0000000..c46fd34
--- /dev/null
+++ b/src/go/printer/testdata/gobuild2.golden
@@ -0,0 +1,8 @@
+//go:build x
+// +build x
+
+// other comment
+
+package p
+
+func f()
diff --git a/src/go/printer/testdata/gobuild2.input b/src/go/printer/testdata/gobuild2.input
new file mode 100644
index 0000000..f0f772a
--- /dev/null
+++ b/src/go/printer/testdata/gobuild2.input
@@ -0,0 +1,9 @@
+// +build y
+
+// other comment
+
+package p
+
+func f()
+
+//go:build x
diff --git a/src/go/printer/testdata/gobuild3.golden b/src/go/printer/testdata/gobuild3.golden
new file mode 100644
index 0000000..db92c57
--- /dev/null
+++ b/src/go/printer/testdata/gobuild3.golden
@@ -0,0 +1,10 @@
+// other comment
+
+//go:build x
+// +build x
+
+// yet another comment
+
+package p
+
+func f()
diff --git a/src/go/printer/testdata/gobuild3.input b/src/go/printer/testdata/gobuild3.input
new file mode 100644
index 0000000..d0c97b2
--- /dev/null
+++ b/src/go/printer/testdata/gobuild3.input
@@ -0,0 +1,11 @@
+// other comment
+
+// +build y
+
+// yet another comment
+
+package p
+
+//go:build x
+
+func f()
diff --git a/src/go/printer/testdata/gobuild4.golden b/src/go/printer/testdata/gobuild4.golden
new file mode 100644
index 0000000..b16477f
--- /dev/null
+++ b/src/go/printer/testdata/gobuild4.golden
@@ -0,0 +1,6 @@
+//go:build (x || y) && z
+// +build x y
+// +build z
+
+// doc comment
+package p
diff --git a/src/go/printer/testdata/gobuild4.input b/src/go/printer/testdata/gobuild4.input
new file mode 100644
index 0000000..29d5a0a
--- /dev/null
+++ b/src/go/printer/testdata/gobuild4.input
@@ -0,0 +1,5 @@
+// doc comment
+package p
+
+// +build x y
+// +build z
diff --git a/src/go/printer/testdata/gobuild5.golden b/src/go/printer/testdata/gobuild5.golden
new file mode 100644
index 0000000..2808a53
--- /dev/null
+++ b/src/go/printer/testdata/gobuild5.golden
@@ -0,0 +1,4 @@
+//go:build !(x || y) && z
+// +build !x,!y,z
+
+package p
diff --git a/src/go/printer/testdata/gobuild5.input b/src/go/printer/testdata/gobuild5.input
new file mode 100644
index 0000000..ec5815c
--- /dev/null
+++ b/src/go/printer/testdata/gobuild5.input
@@ -0,0 +1,4 @@
+//go:build !(x || y) && z
+// +build something else
+
+package p
diff --git a/src/go/printer/testdata/gobuild6.golden b/src/go/printer/testdata/gobuild6.golden
new file mode 100644
index 0000000..abb1e2a
--- /dev/null
+++ b/src/go/printer/testdata/gobuild6.golden
@@ -0,0 +1,5 @@
+//go:build !(x || y) && z
+
+// no +build line
+
+package p
diff --git a/src/go/printer/testdata/gobuild6.input b/src/go/printer/testdata/gobuild6.input
new file mode 100644
index 0000000..1621897
--- /dev/null
+++ b/src/go/printer/testdata/gobuild6.input
@@ -0,0 +1,4 @@
+//go:build !(x || y) && z
+// no +build line
+
+package p
diff --git a/src/go/printer/testdata/gobuild7.golden b/src/go/printer/testdata/gobuild7.golden
new file mode 100644
index 0000000..bf41dd4
--- /dev/null
+++ b/src/go/printer/testdata/gobuild7.golden
@@ -0,0 +1,11 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TODO(rsc): Delete this file once Go 1.17 comes out and we can retire Go 1.15 support.
+
+//go:build !go1.16
+// +build !go1.16
+
+// Package buildtag defines an Analyzer that checks build tags.
+package buildtag
diff --git a/src/go/printer/testdata/gobuild7.input b/src/go/printer/testdata/gobuild7.input
new file mode 100644
index 0000000..bf41dd4
--- /dev/null
+++ b/src/go/printer/testdata/gobuild7.input
@@ -0,0 +1,11 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TODO(rsc): Delete this file once Go 1.17 comes out and we can retire Go 1.15 support.
+
+//go:build !go1.16
+// +build !go1.16
+
+// Package buildtag defines an Analyzer that checks build tags.
+package buildtag
diff --git a/src/go/printer/testdata/linebreaks.golden b/src/go/printer/testdata/linebreaks.golden
new file mode 100644
index 0000000..17d2b5c
--- /dev/null
+++ b/src/go/printer/testdata/linebreaks.golden
@@ -0,0 +1,295 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package linebreaks
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+type writerTestEntry struct {
+	header		*Header
+	contents	string
+}
+
+type writerTest struct {
+	file	string	// filename of expected output
+	entries	[]*writerTestEntry
+}
+
+var writerTests = []*writerTest{
+	&writerTest{
+		file:	"testdata/writer.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name:		"small.txt",
+					Mode:		0640,
+					Uid:		73025,
+					Gid:		5000,
+					Size:		5,
+					Mtime:		1246508266,
+					Typeflag:	'0',
+					Uname:		"dsymonds",
+					Gname:		"eng",
+				},
+				contents:	"Kilts",
+			},
+			&writerTestEntry{
+				header: &Header{
+					Name:		"small2.txt",
+					Mode:		0640,
+					Uid:		73025,
+					Gid:		5000,
+					Size:		11,
+					Mtime:		1245217492,
+					Typeflag:	'0',
+					Uname:		"dsymonds",
+					Gname:		"eng",
+				},
+				contents:	"Google.com\n",
+			},
+		},
+	},
+	// The truncated test file was produced using these commands:
+	//   dd if=/dev/zero bs=1048576 count=16384 > /tmp/16gig.txt
+	//   tar -b 1 -c -f- /tmp/16gig.txt | dd bs=512 count=8 > writer-big.tar
+	&writerTest{
+		file:	"testdata/writer-big.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name:		"tmp/16gig.txt",
+					Mode:		0640,
+					Uid:		73025,
+					Gid:		5000,
+					Size:		16 << 30,
+					Mtime:		1254699560,
+					Typeflag:	'0',
+					Uname:		"dsymonds",
+					Gname:		"eng",
+				},
+				// no contents
+			},
+		},
+	},
+}
+
+type untarTest struct {
+	file	string
+	headers	[]*Header
+}
+
+var untarTests = []*untarTest{
+	&untarTest{
+		file:	"testdata/gnu.tar",
+		headers: []*Header{
+			&Header{
+				Name:		"small.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		5,
+				Mtime:		1244428340,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+			},
+			&Header{
+				Name:		"small2.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		11,
+				Mtime:		1244436044,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+			},
+		},
+	},
+	&untarTest{
+		file:	"testdata/star.tar",
+		headers: []*Header{
+			&Header{
+				Name:		"small.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		5,
+				Mtime:		1244592783,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+				Atime:		1244592783,
+				Ctime:		1244592783,
+			},
+			&Header{
+				Name:		"small2.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		11,
+				Mtime:		1244592783,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+				Atime:		1244592783,
+				Ctime:		1244592783,
+			},
+		},
+	},
+	&untarTest{
+		file:	"testdata/v7.tar",
+		headers: []*Header{
+			&Header{
+				Name:		"small.txt",
+				Mode:		0444,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		5,
+				Mtime:		1244593104,
+				Typeflag:	'\x00',
+			},
+			&Header{
+				Name:		"small2.txt",
+				Mode:		0444,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		11,
+				Mtime:		1244593104,
+				Typeflag:	'\x00',
+			},
+		},
+	},
+}
+
+var facts = map[int]string{
+	0:	"1",
+	1:	"1",
+	2:	"2",
+	10:	"3628800",
+	20:	"2432902008176640000",
+	100: "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000",
+}
+
+func usage() {
+	fmt.Fprintf(os.Stderr,
+		// TODO(gri): the 2nd string of this string list should not be indented
+		"usage: godoc package [name ...]\n"+
+			"	godoc -http=:6060\n")
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+func TestReader(t *testing.T) {
+testLoop:
+	for i, test := range untarTests {
+		f, err := os.Open(test.file, os.O_RDONLY, 0444)
+		if err != nil {
+			t.Errorf("test %d: Unexpected error: %v", i, err)
+			continue
+		}
+		tr := NewReader(f)
+		for j, header := range test.headers {
+			hdr, err := tr.Next()
+			if err != nil || hdr == nil {
+				t.Errorf("test %d, entry %d: Didn't get entry: %v", i, j, err)
+				f.Close()
+				continue testLoop
+			}
+			if !reflect.DeepEqual(hdr, header) {
+				t.Errorf("test %d, entry %d: Incorrect header:\nhave %+v\nwant %+v",
+					i, j, *hdr, *header)
+			}
+		}
+		hdr, err := tr.Next()
+		if hdr != nil || err != nil {
+			t.Errorf("test %d: Unexpected entry or error: hdr=%v err=%v", i, err)
+		}
+		f.Close()
+	}
+}
+
+// Respect line breaks in function calls.
+func _() {
+	f(x)
+	f(x,
+		x)
+	f(x,
+		x,
+	)
+	f(
+		x,
+		x)
+	f(
+		x,
+		x,
+	)
+}
+
+// Respect line breaks in function declarations.
+func _(x T)	{}
+func _(x T,
+	y T) {
+}
+func _(x T,
+	y T,
+) {
+}
+func _(
+	x T,
+	y T) {
+}
+func _(
+	x T,
+	y T,
+) {
+}
+
+// Example from issue #2597.
+func ManageStatus0(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int) {
+}
+
+func ManageStatus1(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int,
+) {
+}
+
+// Example from issue #9064.
+func (y *y) xerrors() error {
+	_ = "xerror.test"	//TODO-
+	_ = []byte(`
+foo bar foo bar foo bar
+`) //TODO-
+}
+
+func _() {
+	_ = "abc"		// foo
+	_ = `abc_0123456789_`	// foo
+}
+
+func _() {
+	_ = "abc"	// foo
+	_ = `abc
+0123456789
+` // foo
+}
+
+// There should be exactly one linebreak after this comment.
diff --git a/src/go/printer/testdata/linebreaks.input b/src/go/printer/testdata/linebreaks.input
new file mode 100644
index 0000000..9e714f3
--- /dev/null
+++ b/src/go/printer/testdata/linebreaks.input
@@ -0,0 +1,291 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package linebreaks
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+type writerTestEntry struct {
+	header *Header
+	contents string
+}
+
+type writerTest struct {
+	file string  // filename of expected output
+	entries []*writerTestEntry
+}
+
+var writerTests = []*writerTest{
+	&writerTest{
+		file: "testdata/writer.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name: "small.txt",
+					Mode: 0640,
+					Uid: 73025,
+					Gid: 5000,
+					Size: 5,
+					Mtime: 1246508266,
+					Typeflag: '0',
+					Uname: "dsymonds",
+					Gname: "eng",
+				},
+				contents: "Kilts",
+			},
+			&writerTestEntry{
+				header: &Header{
+					Name: "small2.txt",
+					Mode: 0640,
+					Uid: 73025,
+					Gid: 5000,
+					Size: 11,
+					Mtime: 1245217492,
+					Typeflag: '0',
+					Uname: "dsymonds",
+					Gname: "eng",
+				},
+				contents: "Google.com\n",
+			},
+		},
+	},
+	// The truncated test file was produced using these commands:
+	//   dd if=/dev/zero bs=1048576 count=16384 > /tmp/16gig.txt
+	//   tar -b 1 -c -f- /tmp/16gig.txt | dd bs=512 count=8 > writer-big.tar
+	&writerTest{
+		file: "testdata/writer-big.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name: "tmp/16gig.txt",
+					Mode: 0640,
+					Uid: 73025,
+					Gid: 5000,
+					Size: 16 << 30,
+					Mtime: 1254699560,
+					Typeflag: '0',
+					Uname: "dsymonds",
+					Gname: "eng",
+				},
+				// no contents
+			},
+		},
+	},
+}
+
+type untarTest struct {
+	file string
+	headers []*Header
+}
+
+var untarTests = []*untarTest{
+	&untarTest{
+		file: "testdata/gnu.tar",
+		headers: []*Header{
+			&Header{
+				Name: "small.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 5,
+				Mtime: 1244428340,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+			},
+			&Header{
+				Name: "small2.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 11,
+				Mtime: 1244436044,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+			},
+		},
+	},
+	&untarTest{
+		file: "testdata/star.tar",
+		headers: []*Header{
+			&Header{
+				Name: "small.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 5,
+				Mtime: 1244592783,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+				Atime: 1244592783,
+				Ctime: 1244592783,
+			},
+			&Header{
+				Name: "small2.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 11,
+				Mtime: 1244592783,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+				Atime: 1244592783,
+				Ctime: 1244592783,
+			},
+		},
+	},
+	&untarTest{
+		file: "testdata/v7.tar",
+		headers: []*Header{
+			&Header{
+				Name: "small.txt",
+				Mode: 0444,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 5,
+				Mtime: 1244593104,
+				Typeflag: '\x00',
+			},
+			&Header{
+				Name: "small2.txt",
+				Mode: 0444,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 11,
+				Mtime: 1244593104,
+				Typeflag: '\x00',
+			},
+		},
+	},
+}
+
+var facts = map[int] string {
+	0: "1",
+	1: "1",
+	2: "2",
+	10: "3628800",
+	20: "2432902008176640000",
+	100: "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000",
+}
+
+func usage() {
+	fmt.Fprintf(os.Stderr,
+		// TODO(gri): the 2nd string of this string list should not be indented
+		"usage: godoc package [name ...]\n" +
+		"	godoc -http=:6060\n")
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+func TestReader(t *testing.T) {
+testLoop:
+	for i, test := range untarTests {
+		f, err := os.Open(test.file, os.O_RDONLY, 0444)
+		if err != nil {
+			t.Errorf("test %d: Unexpected error: %v", i, err)
+			continue
+		}
+		tr := NewReader(f)
+		for j, header := range test.headers {
+			hdr, err := tr.Next()
+			if err != nil || hdr == nil {
+				t.Errorf("test %d, entry %d: Didn't get entry: %v", i, j, err)
+				f.Close()
+				continue testLoop
+			}
+			if !reflect.DeepEqual(hdr, header) {
+				t.Errorf("test %d, entry %d: Incorrect header:\nhave %+v\nwant %+v",
+					 i, j, *hdr, *header)
+			}
+		}
+		hdr, err := tr.Next()
+		if hdr != nil || err != nil {
+			t.Errorf("test %d: Unexpected entry or error: hdr=%v err=%v", i, err)
+		}
+		f.Close()
+	}
+}
+
+// Respect line breaks in function calls.
+func _() {
+	f(x)
+	f(x,
+	  x)
+	f(x,
+	  x,
+	)
+	f(
+	  x,
+	  x)
+	f(
+	  x,
+	  x,
+	)
+}
+
+// Respect line breaks in function declarations.
+func _(x T) {}
+func _(x T,
+       y T) {}
+func _(x T,
+       y T,
+) {}
+func _(
+       x T,
+       y T) {}
+func _(
+       x T,
+       y T,
+) {}
+
+// Example from issue #2597.
+func ManageStatus0(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int) {
+}
+    
+func ManageStatus1(
+	in <-chan *Status,
+	req <-chan Request,
+	stat chan<- *TargetInfo,
+	TargetHistorySize int,
+) {
+}
+
+// Example from issue #9064.
+func (y *y) xerrors() error {
+	_ = "xerror.test" //TODO-
+	_ = []byte(`
+foo bar foo bar foo bar
+`) //TODO-
+}
+
+func _() {
+	_ = "abc" // foo
+	_ = `abc_0123456789_` // foo
+}
+
+func _() {
+	_ = "abc" // foo
+	_ = `abc
+0123456789
+` // foo
+}
+
+// There should be exactly one linebreak after this comment.
diff --git a/src/go/printer/testdata/parser.go b/src/go/printer/testdata/parser.go
new file mode 100644
index 0000000..bb06c8d
--- /dev/null
+++ b/src/go/printer/testdata/parser.go
@@ -0,0 +1,2148 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package parser implements a parser for Go source files. Input may be
+// provided in a variety of forms (see the various Parse* functions); the
+// output is an abstract syntax tree (AST) representing the Go source. The
+// parser is invoked through one of the Parse* functions.
+
+package parser
+
+import (
+	"fmt"
+	"go/ast"
+	"go/scanner"
+	"go/token"
+)
+
+// The mode parameter to the Parse* functions is a set of flags (or 0).
+// They control the amount of source code parsed and other optional
+// parser functionality.
+const (
+	PackageClauseOnly uint = 1 << iota // parsing stops after package clause
+	ImportsOnly                        // parsing stops after import declarations
+	ParseComments                      // parse comments and add them to AST
+	Trace                              // print a trace of parsed productions
+	DeclarationErrors                  // report declaration errors
+)
+
+// The parser structure holds the parser's internal state.
+type parser struct {
+	file *token.File
+	scanner.ErrorVector
+	scanner scanner.Scanner
+
+	// Tracing/debugging
+	mode   uint // parsing mode
+	trace  bool // == (mode & Trace != 0)
+	indent uint // indentation used for tracing output
+
+	// Comments
+	comments    []*ast.CommentGroup
+	leadComment *ast.CommentGroup // last lead comment
+	lineComment *ast.CommentGroup // last line comment
+
+	// Next token
+	pos token.Pos   // token position
+	tok token.Token // one token look-ahead
+	lit string      // token literal
+
+	// Non-syntactic parser control
+	exprLev int // < 0: in control clause, >= 0: in expression
+
+	// Ordinary identifier scopes
+	pkgScope   *ast.Scope        // pkgScope.Outer == nil
+	topScope   *ast.Scope        // top-most scope; may be pkgScope
+	unresolved []*ast.Ident      // unresolved identifiers
+	imports    []*ast.ImportSpec // list of imports
+
+	// Label scope
+	// (maintained by open/close LabelScope)
+	labelScope  *ast.Scope     // label scope for current function
+	targetStack [][]*ast.Ident // stack of unresolved labels
+}
+
+// scannerMode returns the scanner mode bits given the parser's mode bits.
+func scannerMode(mode uint) uint {
+	var m uint = scanner.InsertSemis
+	if mode&ParseComments != 0 {
+		m |= scanner.ScanComments
+	}
+	return m
+}
+
+func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode uint) {
+	p.file = fset.AddFile(filename, fset.Base(), len(src))
+	p.scanner.Init(p.file, src, p, scannerMode(mode))
+
+	p.mode = mode
+	p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
+
+	p.next()
+
+	// set up the pkgScope here (as opposed to in parseFile) because
+	// there are other parser entry points (ParseExpr, etc.)
+	p.openScope()
+	p.pkgScope = p.topScope
+
+	// for the same reason, set up a label scope
+	p.openLabelScope()
+}
+
+// ----------------------------------------------------------------------------
+// Scoping support
+
+func (p *parser) openScope() {
+	p.topScope = ast.NewScope(p.topScope)
+}
+
+func (p *parser) closeScope() {
+	p.topScope = p.topScope.Outer
+}
+
+func (p *parser) openLabelScope() {
+	p.labelScope = ast.NewScope(p.labelScope)
+	p.targetStack = append(p.targetStack, nil)
+}
+
+func (p *parser) closeLabelScope() {
+	// resolve labels
+	n := len(p.targetStack) - 1
+	scope := p.labelScope
+	for _, ident := range p.targetStack[n] {
+		ident.Obj = scope.Lookup(ident.Name)
+		if ident.Obj == nil && p.mode&DeclarationErrors != 0 {
+			p.error(ident.Pos(), fmt.Sprintf("label %s undefined", ident.Name))
+		}
+	}
+	// pop label scope
+	p.targetStack = p.targetStack[0:n]
+	p.labelScope = p.labelScope.Outer
+}
+
+func (p *parser) declare(decl any, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
+	for _, ident := range idents {
+		assert(ident.Obj == nil, "identifier already declared or resolved")
+		if ident.Name != "_" {
+			obj := ast.NewObj(kind, ident.Name)
+			// remember the corresponding declaration for redeclaration
+			// errors and global variable resolution/typechecking phase
+			obj.Decl = decl
+			if alt := scope.Insert(obj); alt != nil && p.mode&DeclarationErrors != 0 {
+				prevDecl := ""
+				if pos := alt.Pos(); pos.IsValid() {
+					prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.file.Position(pos))
+				}
+				p.error(ident.Pos(), fmt.Sprintf("%s redeclared in this block%s", ident.Name, prevDecl))
+			}
+			ident.Obj = obj
+		}
+	}
+}
+
+func (p *parser) shortVarDecl(idents []*ast.Ident) {
+	// Go spec: A short variable declaration may redeclare variables
+	// provided they were originally declared in the same block with
+	// the same type, and at least one of the non-blank variables is new.
+	n := 0 // number of new variables
+	for _, ident := range idents {
+		assert(ident.Obj == nil, "identifier already declared or resolved")
+		if ident.Name != "_" {
+			obj := ast.NewObj(ast.Var, ident.Name)
+			// short var declarations cannot have redeclaration errors
+			// and are not global => no need to remember the respective
+			// declaration
+			alt := p.topScope.Insert(obj)
+			if alt == nil {
+				n++ // new declaration
+				alt = obj
+			}
+			ident.Obj = alt
+		}
+	}
+	if n == 0 && p.mode&DeclarationErrors != 0 {
+		p.error(idents[0].Pos(), "no new variables on left side of :=")
+	}
+}
+
+// The unresolved object is a sentinel to mark identifiers that have been added
+// to the list of unresolved identifiers. The sentinel is only used for verifying
+// internal consistency.
+var unresolved = new(ast.Object)
+
+func (p *parser) resolve(x ast.Expr) {
+	// nothing to do if x is not an identifier or the blank identifier
+	ident, _ := x.(*ast.Ident)
+	if ident == nil {
+		return
+	}
+	assert(ident.Obj == nil, "identifier already declared or resolved")
+	if ident.Name == "_" {
+		return
+	}
+	// try to resolve the identifier
+	for s := p.topScope; s != nil; s = s.Outer {
+		if obj := s.Lookup(ident.Name); obj != nil {
+			ident.Obj = obj
+			return
+		}
+	}
+	// all local scopes are known, so any unresolved identifier
+	// must be found either in the file scope, package scope
+	// (perhaps in another file), or universe scope --- collect
+	// them so that they can be resolved later
+	ident.Obj = unresolved
+	p.unresolved = append(p.unresolved, ident)
+}
+
+// ----------------------------------------------------------------------------
+// Parsing support
+
+func (p *parser) printTrace(a ...any) {
+	const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " +
+		". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
+	const n = uint(len(dots))
+	pos := p.file.Position(p.pos)
+	fmt.Printf("%5d:%3d: ", pos.Line, pos.Column)
+	i := 2 * p.indent
+	for ; i > n; i -= n {
+		fmt.Print(dots)
+	}
+	fmt.Print(dots[0:i])
+	fmt.Println(a...)
+}
+
+func trace(p *parser, msg string) *parser {
+	p.printTrace(msg, "(")
+	p.indent++
+	return p
+}
+
+// Usage pattern: defer un(trace(p, "..."));
+func un(p *parser) {
+	p.indent--
+	p.printTrace(")")
+}
+
+// Advance to the next token.
+func (p *parser) next0() {
+	// Because of one-token look-ahead, print the previous token
+	// when tracing as it provides a more readable output. The
+	// very first token (!p.pos.IsValid()) is not initialized
+	// (it is token.ILLEGAL), so don't print it.
+	if p.trace && p.pos.IsValid() {
+		s := p.tok.String()
+		switch {
+		case p.tok.IsLiteral():
+			p.printTrace(s, p.lit)
+		case p.tok.IsOperator(), p.tok.IsKeyword():
+			p.printTrace("\"" + s + "\"")
+		default:
+			p.printTrace(s)
+		}
+	}
+
+	p.pos, p.tok, p.lit = p.scanner.Scan()
+}
+
+// Consume a comment and return it and the line on which it ends.
+func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
+	// /*-style comments may end on a different line than where they start.
+	// Scan the comment for '\n' chars and adjust endline accordingly.
+	endline = p.file.Line(p.pos)
+	if p.lit[1] == '*' {
+		// don't use range here - no need to decode Unicode code points
+		for i := 0; i < len(p.lit); i++ {
+			if p.lit[i] == '\n' {
+				endline++
+			}
+		}
+	}
+
+	comment = &ast.Comment{p.pos, p.lit}
+	p.next0()
+
+	return
+}
+
+// Consume a group of adjacent comments, add it to the parser's
+// comments list, and return it together with the line at which
+// the last comment in the group ends. An empty line or non-comment
+// token terminates a comment group.
+func (p *parser) consumeCommentGroup() (comments *ast.CommentGroup, endline int) {
+	var list []*ast.Comment
+	endline = p.file.Line(p.pos)
+	for p.tok == token.COMMENT && endline+1 >= p.file.Line(p.pos) {
+		var comment *ast.Comment
+		comment, endline = p.consumeComment()
+		list = append(list, comment)
+	}
+
+	// add comment group to the comments list
+	comments = &ast.CommentGroup{list}
+	p.comments = append(p.comments, comments)
+
+	return
+}
+
+// Advance to the next non-comment token. In the process, collect
+// any comment groups encountered, and remember the last lead and
+// line comments.
+//
+// A lead comment is a comment group that starts and ends in a
+// line without any other tokens and that is followed by a non-comment
+// token on the line immediately after the comment group.
+//
+// A line comment is a comment group that follows a non-comment
+// token on the same line, and that has no tokens after it on the line
+// where it ends.
+//
+// Lead and line comments may be considered documentation that is
+// stored in the AST.
+func (p *parser) next() {
+	p.leadComment = nil
+	p.lineComment = nil
+	line := p.file.Line(p.pos) // current line
+	p.next0()
+
+	if p.tok == token.COMMENT {
+		var comment *ast.CommentGroup
+		var endline int
+
+		if p.file.Line(p.pos) == line {
+			// The comment is on same line as the previous token; it
+			// cannot be a lead comment but may be a line comment.
+			comment, endline = p.consumeCommentGroup()
+			if p.file.Line(p.pos) != endline {
+				// The next token is on a different line, thus
+				// the last comment group is a line comment.
+				p.lineComment = comment
+			}
+		}
+
+		// consume successor comments, if any
+		endline = -1
+		for p.tok == token.COMMENT {
+			comment, endline = p.consumeCommentGroup()
+		}
+
+		if endline+1 == p.file.Line(p.pos) {
+			// The next token is following on the line immediately after the
+			// comment group, thus the last comment group is a lead comment.
+			p.leadComment = comment
+		}
+	}
+}
+
+func (p *parser) error(pos token.Pos, msg string) {
+	p.Error(p.file.Position(pos), msg)
+}
+
+func (p *parser) errorExpected(pos token.Pos, msg string) {
+	msg = "expected " + msg
+	if pos == p.pos {
+		// the error happened at the current position;
+		// make the error message more specific
+		if p.tok == token.SEMICOLON && p.lit[0] == '\n' {
+			msg += ", found newline"
+		} else {
+			msg += ", found '" + p.tok.String() + "'"
+			if p.tok.IsLiteral() {
+				msg += " " + p.lit
+			}
+		}
+	}
+	p.error(pos, msg)
+}
+
+func (p *parser) expect(tok token.Token) token.Pos {
+	pos := p.pos
+	if p.tok != tok {
+		p.errorExpected(pos, "'"+tok.String()+"'")
+	}
+	p.next() // make progress
+	return pos
+}
+
+func (p *parser) expectSemi() {
+	if p.tok != token.RPAREN && p.tok != token.RBRACE {
+		p.expect(token.SEMICOLON)
+	}
+}
+
+func assert(cond bool, msg string) {
+	if !cond {
+		panic("go/parser internal error: " + msg)
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Identifiers
+
+func (p *parser) parseIdent() *ast.Ident {
+	pos := p.pos
+	name := "_"
+	if p.tok == token.IDENT {
+		name = p.lit
+		p.next()
+	} else {
+		p.expect(token.IDENT) // use expect() error handling
+	}
+	return &ast.Ident{pos, name, nil}
+}
+
+func (p *parser) parseIdentList() (list []*ast.Ident) {
+	if p.trace {
+		defer un(trace(p, "IdentList"))
+	}
+
+	list = append(list, p.parseIdent())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseIdent())
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Common productions
+
+// If lhs is set, result list elements which are identifiers are not resolved.
+func (p *parser) parseExprList(lhs bool) (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ExpressionList"))
+	}
+
+	list = append(list, p.parseExpr(lhs))
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseExpr(lhs))
+	}
+
+	return
+}
+
+func (p *parser) parseLhsList() []ast.Expr {
+	list := p.parseExprList(true)
+	switch p.tok {
+	case token.DEFINE:
+		// lhs of a short variable declaration
+		p.shortVarDecl(p.makeIdentList(list))
+	case token.COLON:
+		// lhs of a label declaration or a communication clause of a select
+		// statement (parseLhsList is not called when parsing the case clause
+		// of a switch statement):
+		// - labels are declared by the caller of parseLhsList
+		// - for communication clauses, if there is a stand-alone identifier
+		//   followed by a colon, we have a syntax error; there is no need
+		//   to resolve the identifier in that case
+	default:
+		// identifiers must be declared elsewhere
+		for _, x := range list {
+			p.resolve(x)
+		}
+	}
+	return list
+}
+
+func (p *parser) parseRhsList() []ast.Expr {
+	return p.parseExprList(false)
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+func (p *parser) parseType() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Type"))
+	}
+
+	typ := p.tryType()
+
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.next() // make progress
+		return &ast.BadExpr{pos, p.pos}
+	}
+
+	return typ
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) parseTypeName() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeName"))
+	}
+
+	ident := p.parseIdent()
+	// don't resolve ident yet - it may be a parameter or field name
+
+	if p.tok == token.PERIOD {
+		// ident is a package name
+		p.next()
+		p.resolve(ident)
+		sel := p.parseIdent()
+		return &ast.SelectorExpr{ident, sel}
+	}
+
+	return ident
+}
+
+func (p *parser) parseArrayType(ellipsisOk bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "ArrayType"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	var len ast.Expr
+	if ellipsisOk && p.tok == token.ELLIPSIS {
+		len = &ast.Ellipsis{p.pos, nil}
+		p.next()
+	} else if p.tok != token.RBRACK {
+		len = p.parseRhs()
+	}
+	p.expect(token.RBRACK)
+	elt := p.parseType()
+
+	return &ast.ArrayType{lbrack, len, elt}
+}
+
+func (p *parser) makeIdentList(list []ast.Expr) []*ast.Ident {
+	idents := make([]*ast.Ident, len(list))
+	for i, x := range list {
+		ident, isIdent := x.(*ast.Ident)
+		if !isIdent {
+			pos := x.(ast.Expr).Pos()
+			p.errorExpected(pos, "identifier")
+			ident = &ast.Ident{pos, "_", nil}
+		}
+		idents[i] = ident
+	}
+	return idents
+}
+
+func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "FieldDecl"))
+	}
+
+	doc := p.leadComment
+
+	// fields
+	list, typ := p.parseVarList(false)
+
+	// optional tag
+	var tag *ast.BasicLit
+	if p.tok == token.STRING {
+		tag = &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+	}
+
+	// analyze case
+	var idents []*ast.Ident
+	if typ != nil {
+		// IdentifierList Type
+		idents = p.makeIdentList(list)
+	} else {
+		// ["*"] TypeName (AnonymousField)
+		typ = list[0] // we always have at least one element
+		p.resolve(typ)
+		if n := len(list); n > 1 || !isTypeName(deref(typ)) {
+			pos := typ.Pos()
+			p.errorExpected(pos, "anonymous field")
+			typ = &ast.BadExpr{pos, list[n-1].End()}
+		}
+	}
+
+	p.expectSemi() // call before accessing p.linecomment
+
+	field := &ast.Field{doc, idents, typ, tag, p.lineComment}
+	p.declare(field, scope, ast.Var, idents...)
+
+	return field
+}
+
+func (p *parser) parseStructType() *ast.StructType {
+	if p.trace {
+		defer un(trace(p, "StructType"))
+	}
+
+	pos := p.expect(token.STRUCT)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // struct scope
+	var list []*ast.Field
+	for p.tok == token.IDENT || p.tok == token.MUL || p.tok == token.LPAREN {
+		// a field declaration cannot start with a '(' but we accept
+		// it here for more robust parsing and better error messages
+		// (parseFieldDecl will check and complain if necessary)
+		list = append(list, p.parseFieldDecl(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	// TODO(gri): store struct scope in AST
+	return &ast.StructType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
+}
+
+func (p *parser) parsePointerType() *ast.StarExpr {
+	if p.trace {
+		defer un(trace(p, "PointerType"))
+	}
+
+	star := p.expect(token.MUL)
+	base := p.parseType()
+
+	return &ast.StarExpr{star, base}
+}
+
+func (p *parser) tryVarType(isParam bool) ast.Expr {
+	if isParam && p.tok == token.ELLIPSIS {
+		pos := p.pos
+		p.next()
+		typ := p.tryIdentOrType(isParam) // don't use parseType so we can provide better error message
+		if typ == nil {
+			p.error(pos, "'...' parameter is missing type")
+			typ = &ast.BadExpr{pos, p.pos}
+		}
+		if p.tok != token.RPAREN {
+			p.error(pos, "can use '...' with last parameter type only")
+		}
+		return &ast.Ellipsis{pos, typ}
+	}
+	return p.tryIdentOrType(false)
+}
+
+func (p *parser) parseVarType(isParam bool) ast.Expr {
+	typ := p.tryVarType(isParam)
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.next() // make progress
+		typ = &ast.BadExpr{pos, p.pos}
+	}
+	return typ
+}
+
+func (p *parser) parseVarList(isParam bool) (list []ast.Expr, typ ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "VarList"))
+	}
+
+	// a list of identifiers looks like a list of type names
+	for {
+		// parseVarType accepts any type (including parenthesized ones)
+		// even though the syntax does not permit them here: we
+		// accept them all for more robust parsing and complain
+		// afterwards
+		list = append(list, p.parseVarType(isParam))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+
+	// if we had a list of identifiers, it must be followed by a type
+	typ = p.tryVarType(isParam)
+	if typ != nil {
+		p.resolve(typ)
+	}
+
+	return
+}
+
+func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params []*ast.Field) {
+	if p.trace {
+		defer un(trace(p, "ParameterList"))
+	}
+
+	list, typ := p.parseVarList(ellipsisOk)
+	if typ != nil {
+		// IdentifierList Type
+		idents := p.makeIdentList(list)
+		field := &ast.Field{nil, idents, typ, nil, nil}
+		params = append(params, field)
+		// Go spec: The scope of an identifier denoting a function
+		// parameter or result variable is the function body.
+		p.declare(field, scope, ast.Var, idents...)
+		if p.tok == token.COMMA {
+			p.next()
+		}
+
+		for p.tok != token.RPAREN && p.tok != token.EOF {
+			idents := p.parseIdentList()
+			typ := p.parseVarType(ellipsisOk)
+			field := &ast.Field{nil, idents, typ, nil, nil}
+			params = append(params, field)
+			// Go spec: The scope of an identifier denoting a function
+			// parameter or result variable is the function body.
+			p.declare(field, scope, ast.Var, idents...)
+			if p.tok != token.COMMA {
+				break
+			}
+			p.next()
+		}
+
+	} else {
+		// Type { "," Type } (anonymous parameters)
+		params = make([]*ast.Field, len(list))
+		for i, x := range list {
+			p.resolve(x)
+			params[i] = &ast.Field{Type: x}
+		}
+	}
+
+	return
+}
+
+func (p *parser) parseParameters(scope *ast.Scope, ellipsisOk bool) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Parameters"))
+	}
+
+	var params []*ast.Field
+	lparen := p.expect(token.LPAREN)
+	if p.tok != token.RPAREN {
+		params = p.parseParameterList(scope, ellipsisOk)
+	}
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.FieldList{lparen, params, rparen}
+}
+
+func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Result"))
+	}
+
+	if p.tok == token.LPAREN {
+		return p.parseParameters(scope, false)
+	}
+
+	typ := p.tryType()
+	if typ != nil {
+		list := make([]*ast.Field, 1)
+		list[0] = &ast.Field{Type: typ}
+		return &ast.FieldList{List: list}
+	}
+
+	return nil
+}
+
+func (p *parser) parseSignature(scope *ast.Scope) (params, results *ast.FieldList) {
+	if p.trace {
+		defer un(trace(p, "Signature"))
+	}
+
+	params = p.parseParameters(scope, true)
+	results = p.parseResult(scope)
+
+	return
+}
+
+func (p *parser) parseFuncType() (*ast.FuncType, *ast.Scope) {
+	if p.trace {
+		defer un(trace(p, "FuncType"))
+	}
+
+	pos := p.expect(token.FUNC)
+	scope := ast.NewScope(p.topScope) // function scope
+	params, results := p.parseSignature(scope)
+
+	return &ast.FuncType{pos, params, results}, scope
+}
+
+func (p *parser) parseMethodSpec(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "MethodSpec"))
+	}
+
+	doc := p.leadComment
+	var idents []*ast.Ident
+	var typ ast.Expr
+	x := p.parseTypeName()
+	if ident, isIdent := x.(*ast.Ident); isIdent && p.tok == token.LPAREN {
+		// method
+		idents = []*ast.Ident{ident}
+		scope := ast.NewScope(nil) // method scope
+		params, results := p.parseSignature(scope)
+		typ = &ast.FuncType{token.NoPos, params, results}
+	} else {
+		// embedded interface
+		typ = x
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	spec := &ast.Field{doc, idents, typ, nil, p.lineComment}
+	p.declare(spec, scope, ast.Fun, idents...)
+
+	return spec
+}
+
+func (p *parser) parseInterfaceType() *ast.InterfaceType {
+	if p.trace {
+		defer un(trace(p, "InterfaceType"))
+	}
+
+	pos := p.expect(token.INTERFACE)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // interface scope
+	var list []*ast.Field
+	for p.tok == token.IDENT {
+		list = append(list, p.parseMethodSpec(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	// TODO(gri): store interface scope in AST
+	return &ast.InterfaceType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
+}
+
+func (p *parser) parseMapType() *ast.MapType {
+	if p.trace {
+		defer un(trace(p, "MapType"))
+	}
+
+	pos := p.expect(token.MAP)
+	p.expect(token.LBRACK)
+	key := p.parseType()
+	p.expect(token.RBRACK)
+	value := p.parseType()
+
+	return &ast.MapType{pos, key, value}
+}
+
+func (p *parser) parseChanType() *ast.ChanType {
+	if p.trace {
+		defer un(trace(p, "ChanType"))
+	}
+
+	pos := p.pos
+	dir := ast.SEND | ast.RECV
+	if p.tok == token.CHAN {
+		p.next()
+		if p.tok == token.ARROW {
+			p.next()
+			dir = ast.SEND
+		}
+	} else {
+		p.expect(token.ARROW)
+		p.expect(token.CHAN)
+		dir = ast.RECV
+	}
+	value := p.parseType()
+
+	return &ast.ChanType{pos, dir, value}
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) tryIdentOrType(ellipsisOk bool) ast.Expr {
+	switch p.tok {
+	case token.IDENT:
+		return p.parseTypeName()
+	case token.LBRACK:
+		return p.parseArrayType(ellipsisOk)
+	case token.STRUCT:
+		return p.parseStructType()
+	case token.MUL:
+		return p.parsePointerType()
+	case token.FUNC:
+		typ, _ := p.parseFuncType()
+		return typ
+	case token.INTERFACE:
+		return p.parseInterfaceType()
+	case token.MAP:
+		return p.parseMapType()
+	case token.CHAN, token.ARROW:
+		return p.parseChanType()
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		typ := p.parseType()
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{lparen, typ, rparen}
+	}
+
+	// no type found
+	return nil
+}
+
+func (p *parser) tryType() ast.Expr {
+	typ := p.tryIdentOrType(false)
+	if typ != nil {
+		p.resolve(typ)
+	}
+	return typ
+}
+
+// ----------------------------------------------------------------------------
+// Blocks
+
+func (p *parser) parseStmtList() (list []ast.Stmt) {
+	if p.trace {
+		defer un(trace(p, "StatementList"))
+	}
+
+	for p.tok != token.CASE && p.tok != token.DEFAULT && p.tok != token.RBRACE && p.tok != token.EOF {
+		list = append(list, p.parseStmt())
+	}
+
+	return
+}
+
+func (p *parser) parseBody(scope *ast.Scope) *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "Body"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	p.topScope = scope // open function scope
+	p.openLabelScope()
+	list := p.parseStmtList()
+	p.closeLabelScope()
+	p.closeScope()
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.BlockStmt{lbrace, list, rbrace}
+}
+
+func (p *parser) parseBlockStmt() *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "BlockStmt"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	p.openScope()
+	list := p.parseStmtList()
+	p.closeScope()
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.BlockStmt{lbrace, list, rbrace}
+}
+
+// ----------------------------------------------------------------------------
+// Expressions
+
+func (p *parser) parseFuncTypeOrLit() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "FuncTypeOrLit"))
+	}
+
+	typ, scope := p.parseFuncType()
+	if p.tok != token.LBRACE {
+		// function type only
+		return typ
+	}
+
+	p.exprLev++
+	body := p.parseBody(scope)
+	p.exprLev--
+
+	return &ast.FuncLit{typ, body}
+}
+
+// parseOperand may return an expression or a raw type (incl. array
+// types of the form [...]T. Callers must verify the result.
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseOperand(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Operand"))
+	}
+
+	switch p.tok {
+	case token.IDENT:
+		x := p.parseIdent()
+		if !lhs {
+			p.resolve(x)
+		}
+		return x
+
+	case token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING:
+		x := &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+		return x
+
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		p.exprLev++
+		x := p.parseRhs()
+		p.exprLev--
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{lparen, x, rparen}
+
+	case token.FUNC:
+		return p.parseFuncTypeOrLit()
+
+	default:
+		if typ := p.tryIdentOrType(true); typ != nil {
+			// could be type for composite literal or conversion
+			_, isIdent := typ.(*ast.Ident)
+			assert(!isIdent, "type cannot be identifier")
+			return typ
+		}
+	}
+
+	pos := p.pos
+	p.errorExpected(pos, "operand")
+	p.next() // make progress
+	return &ast.BadExpr{pos, p.pos}
+}
+
+func (p *parser) parseSelector(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Selector"))
+	}
+
+	sel := p.parseIdent()
+
+	return &ast.SelectorExpr{x, sel}
+}
+
+func (p *parser) parseTypeAssertion(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeAssertion"))
+	}
+
+	p.expect(token.LPAREN)
+	var typ ast.Expr
+	if p.tok == token.TYPE {
+		// type switch: typ == nil
+		p.next()
+	} else {
+		typ = p.parseType()
+	}
+	p.expect(token.RPAREN)
+
+	return &ast.TypeAssertExpr{x, typ}
+}
+
+func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "IndexOrSlice"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	p.exprLev++
+	var low, high ast.Expr
+	isSlice := false
+	if p.tok != token.COLON {
+		low = p.parseRhs()
+	}
+	if p.tok == token.COLON {
+		isSlice = true
+		p.next()
+		if p.tok != token.RBRACK {
+			high = p.parseRhs()
+		}
+	}
+	p.exprLev--
+	rbrack := p.expect(token.RBRACK)
+
+	if isSlice {
+		return &ast.SliceExpr{x, lbrack, low, high, rbrack}
+	}
+	return &ast.IndexExpr{x, lbrack, low, rbrack}
+}
+
+func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
+	if p.trace {
+		defer un(trace(p, "CallOrConversion"))
+	}
+
+	lparen := p.expect(token.LPAREN)
+	p.exprLev++
+	var list []ast.Expr
+	var ellipsis token.Pos
+	for p.tok != token.RPAREN && p.tok != token.EOF && !ellipsis.IsValid() {
+		list = append(list, p.parseRhs())
+		if p.tok == token.ELLIPSIS {
+			ellipsis = p.pos
+			p.next()
+		}
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+	p.exprLev--
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.CallExpr{fun, lparen, list, ellipsis, rparen}
+}
+
+func (p *parser) parseElement(keyOk bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Element"))
+	}
+
+	if p.tok == token.LBRACE {
+		return p.parseLiteralValue(nil)
+	}
+
+	x := p.parseExpr(keyOk) // don't resolve if map key
+	if keyOk {
+		if p.tok == token.COLON {
+			colon := p.pos
+			p.next()
+			return &ast.KeyValueExpr{x, colon, p.parseElement(false)}
+		}
+		p.resolve(x) // not a map key
+	}
+
+	return x
+}
+
+func (p *parser) parseElementList() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ElementList"))
+	}
+
+	for p.tok != token.RBRACE && p.tok != token.EOF {
+		list = append(list, p.parseElement(true))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+
+	return
+}
+
+func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "LiteralValue"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	var elts []ast.Expr
+	p.exprLev++
+	if p.tok != token.RBRACE {
+		elts = p.parseElementList()
+	}
+	p.exprLev--
+	rbrace := p.expect(token.RBRACE)
+	return &ast.CompositeLit{typ, lbrace, elts, rbrace}
+}
+
+// checkExpr checks that x is an expression (and not a type).
+func (p *parser) checkExpr(x ast.Expr) ast.Expr {
+	switch t := unparen(x).(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.BasicLit:
+	case *ast.FuncLit:
+	case *ast.CompositeLit:
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.SelectorExpr:
+	case *ast.IndexExpr:
+	case *ast.SliceExpr:
+	case *ast.TypeAssertExpr:
+		if t.Type == nil {
+			// the form X.(type) is only allowed in type switch expressions
+			p.errorExpected(x.Pos(), "expression")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	case *ast.CallExpr:
+	case *ast.StarExpr:
+	case *ast.UnaryExpr:
+		if t.Op == token.RANGE {
+			// the range operator is only allowed at the top of a for statement
+			p.errorExpected(x.Pos(), "expression")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	case *ast.BinaryExpr:
+	default:
+		// all other nodes are not proper expressions
+		p.errorExpected(x.Pos(), "expression")
+		x = &ast.BadExpr{x.Pos(), x.End()}
+	}
+	return x
+}
+
+// isTypeName reports whether x is a (qualified) TypeName.
+func isTypeName(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	default:
+		return false // all other nodes are not type names
+	}
+	return true
+}
+
+// isLiteralType reports whether x is a legal composite literal type.
+func isLiteralType(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	case *ast.ArrayType:
+	case *ast.StructType:
+	case *ast.MapType:
+	default:
+		return false // all other nodes are not legal composite literal types
+	}
+	return true
+}
+
+// If x is of the form *T, deref returns T, otherwise it returns x.
+func deref(x ast.Expr) ast.Expr {
+	if p, isPtr := x.(*ast.StarExpr); isPtr {
+		x = p.X
+	}
+	return x
+}
+
+// If x is of the form (T), unparen returns unparen(T), otherwise it returns x.
+func unparen(x ast.Expr) ast.Expr {
+	if p, isParen := x.(*ast.ParenExpr); isParen {
+		x = unparen(p.X)
+	}
+	return x
+}
+
+// checkExprOrType checks that x is an expression or a type
+// (and not a raw type such as [...]T).
+func (p *parser) checkExprOrType(x ast.Expr) ast.Expr {
+	switch t := unparen(x).(type) {
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.UnaryExpr:
+		if t.Op == token.RANGE {
+			// the range operator is only allowed at the top of a for statement
+			p.errorExpected(x.Pos(), "expression")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	case *ast.ArrayType:
+		if len, isEllipsis := t.Len.(*ast.Ellipsis); isEllipsis {
+			p.error(len.Pos(), "expected array length, found '...'")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	}
+
+	// all other nodes are expressions or types
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parsePrimaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "PrimaryExpr"))
+	}
+
+	x := p.parseOperand(lhs)
+L:
+	for {
+		switch p.tok {
+		case token.PERIOD:
+			p.next()
+			if lhs {
+				p.resolve(x)
+			}
+			switch p.tok {
+			case token.IDENT:
+				x = p.parseSelector(p.checkExpr(x))
+			case token.LPAREN:
+				x = p.parseTypeAssertion(p.checkExpr(x))
+			default:
+				pos := p.pos
+				p.next() // make progress
+				p.errorExpected(pos, "selector or type assertion")
+				x = &ast.BadExpr{pos, p.pos}
+			}
+		case token.LBRACK:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseIndexOrSlice(p.checkExpr(x))
+		case token.LPAREN:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseCallOrConversion(p.checkExprOrType(x))
+		case token.LBRACE:
+			if isLiteralType(x) && (p.exprLev >= 0 || !isTypeName(x)) {
+				if lhs {
+					p.resolve(x)
+				}
+				x = p.parseLiteralValue(x)
+			} else {
+				break L
+			}
+		default:
+			break L
+		}
+		lhs = false // no need to try to resolve again
+	}
+
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseUnaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "UnaryExpr"))
+	}
+
+	switch p.tok {
+	case token.ADD, token.SUB, token.NOT, token.XOR, token.AND, token.RANGE:
+		pos, op := p.pos, p.tok
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.UnaryExpr{pos, op, p.checkExpr(x)}
+
+	case token.ARROW:
+		// channel type or receive expression
+		pos := p.pos
+		p.next()
+		if p.tok == token.CHAN {
+			p.next()
+			value := p.parseType()
+			return &ast.ChanType{pos, ast.RECV, value}
+		}
+
+		x := p.parseUnaryExpr(false)
+		return &ast.UnaryExpr{pos, token.ARROW, p.checkExpr(x)}
+
+	case token.MUL:
+		// pointer type or unary "*" expression
+		pos := p.pos
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.StarExpr{pos, p.checkExprOrType(x)}
+	}
+
+	return p.parsePrimaryExpr(lhs)
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseBinaryExpr(lhs bool, prec1 int) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "BinaryExpr"))
+	}
+
+	x := p.parseUnaryExpr(lhs)
+	for prec := p.tok.Precedence(); prec >= prec1; prec-- {
+		for p.tok.Precedence() == prec {
+			pos, op := p.pos, p.tok
+			p.next()
+			if lhs {
+				p.resolve(x)
+				lhs = false
+			}
+			y := p.parseBinaryExpr(false, prec+1)
+			x = &ast.BinaryExpr{p.checkExpr(x), pos, op, p.checkExpr(y)}
+		}
+	}
+
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+// TODO(gri): parseExpr may return a type or even a raw type ([..]int) -
+// should reject when a type/raw type is obviously not allowed
+func (p *parser) parseExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Expression"))
+	}
+
+	return p.parseBinaryExpr(lhs, token.LowestPrec+1)
+}
+
+func (p *parser) parseRhs() ast.Expr {
+	return p.parseExpr(false)
+}
+
+// ----------------------------------------------------------------------------
+// Statements
+
+func (p *parser) parseSimpleStmt(labelOk bool) ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "SimpleStmt"))
+	}
+
+	x := p.parseLhsList()
+
+	switch p.tok {
+	case
+		token.DEFINE, token.ASSIGN, token.ADD_ASSIGN,
+		token.SUB_ASSIGN, token.MUL_ASSIGN, token.QUO_ASSIGN,
+		token.REM_ASSIGN, token.AND_ASSIGN, token.OR_ASSIGN,
+		token.XOR_ASSIGN, token.SHL_ASSIGN, token.SHR_ASSIGN, token.AND_NOT_ASSIGN:
+		// assignment statement
+		pos, tok := p.pos, p.tok
+		p.next()
+		y := p.parseRhsList()
+		return &ast.AssignStmt{x, pos, tok, y}
+	}
+
+	if len(x) > 1 {
+		p.errorExpected(x[0].Pos(), "1 expression")
+		// continue with first expression
+	}
+
+	switch p.tok {
+	case token.COLON:
+		// labeled statement
+		colon := p.pos
+		p.next()
+		if label, isIdent := x[0].(*ast.Ident); labelOk && isIdent {
+			// Go spec: The scope of a label is the body of the function
+			// in which it is declared and excludes the body of any nested
+			// function.
+			stmt := &ast.LabeledStmt{label, colon, p.parseStmt()}
+			p.declare(stmt, p.labelScope, ast.Lbl, label)
+			return stmt
+		}
+		p.error(x[0].Pos(), "illegal label declaration")
+		return &ast.BadStmt{x[0].Pos(), colon + 1}
+
+	case token.ARROW:
+		// send statement
+		arrow := p.pos
+		p.next() // consume "<-"
+		y := p.parseRhs()
+		return &ast.SendStmt{x[0], arrow, y}
+
+	case token.INC, token.DEC:
+		// increment or decrement
+		s := &ast.IncDecStmt{x[0], p.pos, p.tok}
+		p.next() // consume "++" or "--"
+		return s
+	}
+
+	// expression
+	return &ast.ExprStmt{x[0]}
+}
+
+func (p *parser) parseCallExpr() *ast.CallExpr {
+	x := p.parseRhs()
+	if call, isCall := x.(*ast.CallExpr); isCall {
+		return call
+	}
+	p.errorExpected(x.Pos(), "function/method call")
+	return nil
+}
+
+func (p *parser) parseGoStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "GoStmt"))
+	}
+
+	pos := p.expect(token.GO)
+	call := p.parseCallExpr()
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{pos, pos + 2} // len("go")
+	}
+
+	return &ast.GoStmt{pos, call}
+}
+
+func (p *parser) parseDeferStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "DeferStmt"))
+	}
+
+	pos := p.expect(token.DEFER)
+	call := p.parseCallExpr()
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{pos, pos + 5} // len("defer")
+	}
+
+	return &ast.DeferStmt{pos, call}
+}
+
+func (p *parser) parseReturnStmt() *ast.ReturnStmt {
+	if p.trace {
+		defer un(trace(p, "ReturnStmt"))
+	}
+
+	pos := p.pos
+	p.expect(token.RETURN)
+	var x []ast.Expr
+	if p.tok != token.SEMICOLON && p.tok != token.RBRACE {
+		x = p.parseRhsList()
+	}
+	p.expectSemi()
+
+	return &ast.ReturnStmt{pos, x}
+}
+
+func (p *parser) parseBranchStmt(tok token.Token) *ast.BranchStmt {
+	if p.trace {
+		defer un(trace(p, "BranchStmt"))
+	}
+
+	pos := p.expect(tok)
+	var label *ast.Ident
+	if tok != token.FALLTHROUGH && p.tok == token.IDENT {
+		label = p.parseIdent()
+		// add to list of unresolved targets
+		n := len(p.targetStack) - 1
+		p.targetStack[n] = append(p.targetStack[n], label)
+	}
+	p.expectSemi()
+
+	return &ast.BranchStmt{pos, tok, label}
+}
+
+func (p *parser) makeExpr(s ast.Stmt) ast.Expr {
+	if s == nil {
+		return nil
+	}
+	if es, isExpr := s.(*ast.ExprStmt); isExpr {
+		return p.checkExpr(es.X)
+	}
+	p.error(s.Pos(), "expected condition, found simple statement")
+	return &ast.BadExpr{s.Pos(), s.End()}
+}
+
+func (p *parser) parseIfStmt() *ast.IfStmt {
+	if p.trace {
+		defer un(trace(p, "IfStmt"))
+	}
+
+	pos := p.expect(token.IF)
+	p.openScope()
+	defer p.closeScope()
+
+	var s ast.Stmt
+	var x ast.Expr
+	{
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok == token.SEMICOLON {
+			p.next()
+			x = p.parseRhs()
+		} else {
+			s = p.parseSimpleStmt(false)
+			if p.tok == token.SEMICOLON {
+				p.next()
+				x = p.parseRhs()
+			} else {
+				x = p.makeExpr(s)
+				s = nil
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	body := p.parseBlockStmt()
+	var else_ ast.Stmt
+	if p.tok == token.ELSE {
+		p.next()
+		else_ = p.parseStmt()
+	} else {
+		p.expectSemi()
+	}
+
+	return &ast.IfStmt{pos, s, x, body, else_}
+}
+
+func (p *parser) parseTypeList() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "TypeList"))
+	}
+
+	list = append(list, p.parseType())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseType())
+	}
+
+	return
+}
+
+func (p *parser) parseCaseClause(exprSwitch bool) *ast.CaseClause {
+	if p.trace {
+		defer un(trace(p, "CaseClause"))
+	}
+
+	pos := p.pos
+	var list []ast.Expr
+	if p.tok == token.CASE {
+		p.next()
+		if exprSwitch {
+			list = p.parseRhsList()
+		} else {
+			list = p.parseTypeList()
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	p.openScope()
+	body := p.parseStmtList()
+	p.closeScope()
+
+	return &ast.CaseClause{pos, list, colon, body}
+}
+
+func isExprSwitch(s ast.Stmt) bool {
+	if s == nil {
+		return true
+	}
+	if e, ok := s.(*ast.ExprStmt); ok {
+		if a, ok := e.X.(*ast.TypeAssertExpr); ok {
+			return a.Type != nil // regular type assertion
+		}
+		return true
+	}
+	return false
+}
+
+func (p *parser) parseSwitchStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "SwitchStmt"))
+	}
+
+	pos := p.expect(token.SWITCH)
+	p.openScope()
+	defer p.closeScope()
+
+	var s1, s2 ast.Stmt
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2 = p.parseSimpleStmt(false)
+		}
+		if p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.LBRACE {
+				s2 = p.parseSimpleStmt(false)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	exprSwitch := isExprSwitch(s2)
+	lbrace := p.expect(token.LBRACE)
+	var list []ast.Stmt
+	for p.tok == token.CASE || p.tok == token.DEFAULT {
+		list = append(list, p.parseCaseClause(exprSwitch))
+	}
+	rbrace := p.expect(token.RBRACE)
+	p.expectSemi()
+	body := &ast.BlockStmt{lbrace, list, rbrace}
+
+	if exprSwitch {
+		return &ast.SwitchStmt{pos, s1, p.makeExpr(s2), body}
+	}
+	// type switch
+	// TODO(gri): do all the checks!
+	return &ast.TypeSwitchStmt{pos, s1, s2, body}
+}
+
+func (p *parser) parseCommClause() *ast.CommClause {
+	if p.trace {
+		defer un(trace(p, "CommClause"))
+	}
+
+	p.openScope()
+	pos := p.pos
+	var comm ast.Stmt
+	if p.tok == token.CASE {
+		p.next()
+		lhs := p.parseLhsList()
+		if p.tok == token.ARROW {
+			// SendStmt
+			if len(lhs) > 1 {
+				p.errorExpected(lhs[0].Pos(), "1 expression")
+				// continue with first expression
+			}
+			arrow := p.pos
+			p.next()
+			rhs := p.parseRhs()
+			comm = &ast.SendStmt{lhs[0], arrow, rhs}
+		} else {
+			// RecvStmt
+			pos := p.pos
+			tok := p.tok
+			var rhs ast.Expr
+			if tok == token.ASSIGN || tok == token.DEFINE {
+				// RecvStmt with assignment
+				if len(lhs) > 2 {
+					p.errorExpected(lhs[0].Pos(), "1 or 2 expressions")
+					// continue with first two expressions
+					lhs = lhs[0:2]
+				}
+				p.next()
+				rhs = p.parseRhs()
+			} else {
+				// rhs must be single receive operation
+				if len(lhs) > 1 {
+					p.errorExpected(lhs[0].Pos(), "1 expression")
+					// continue with first expression
+				}
+				rhs = lhs[0]
+				lhs = nil // there is no lhs
+			}
+			if x, isUnary := rhs.(*ast.UnaryExpr); !isUnary || x.Op != token.ARROW {
+				p.errorExpected(rhs.Pos(), "send or receive operation")
+				rhs = &ast.BadExpr{rhs.Pos(), rhs.End()}
+			}
+			if lhs != nil {
+				comm = &ast.AssignStmt{lhs, pos, tok, []ast.Expr{rhs}}
+			} else {
+				comm = &ast.ExprStmt{rhs}
+			}
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	body := p.parseStmtList()
+	p.closeScope()
+
+	return &ast.CommClause{pos, comm, colon, body}
+}
+
+func (p *parser) parseSelectStmt() *ast.SelectStmt {
+	if p.trace {
+		defer un(trace(p, "SelectStmt"))
+	}
+
+	pos := p.expect(token.SELECT)
+	lbrace := p.expect(token.LBRACE)
+	var list []ast.Stmt
+	for p.tok == token.CASE || p.tok == token.DEFAULT {
+		list = append(list, p.parseCommClause())
+	}
+	rbrace := p.expect(token.RBRACE)
+	p.expectSemi()
+	body := &ast.BlockStmt{lbrace, list, rbrace}
+
+	return &ast.SelectStmt{pos, body}
+}
+
+func (p *parser) parseForStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "ForStmt"))
+	}
+
+	pos := p.expect(token.FOR)
+	p.openScope()
+	defer p.closeScope()
+
+	var s1, s2, s3 ast.Stmt
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2 = p.parseSimpleStmt(false)
+		}
+		if p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.SEMICOLON {
+				s2 = p.parseSimpleStmt(false)
+			}
+			p.expectSemi()
+			if p.tok != token.LBRACE {
+				s3 = p.parseSimpleStmt(false)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	body := p.parseBlockStmt()
+	p.expectSemi()
+
+	if as, isAssign := s2.(*ast.AssignStmt); isAssign {
+		// possibly a for statement with a range clause; check assignment operator
+		if as.Tok != token.ASSIGN && as.Tok != token.DEFINE {
+			p.errorExpected(as.TokPos, "'=' or ':='")
+			return &ast.BadStmt{pos, body.End()}
+		}
+		// check lhs
+		var key, value ast.Expr
+		switch len(as.Lhs) {
+		case 2:
+			key, value = as.Lhs[0], as.Lhs[1]
+		case 1:
+			key = as.Lhs[0]
+		default:
+			p.errorExpected(as.Lhs[0].Pos(), "1 or 2 expressions")
+			return &ast.BadStmt{pos, body.End()}
+		}
+		// check rhs
+		if len(as.Rhs) != 1 {
+			p.errorExpected(as.Rhs[0].Pos(), "1 expression")
+			return &ast.BadStmt{pos, body.End()}
+		}
+		if rhs, isUnary := as.Rhs[0].(*ast.UnaryExpr); isUnary && rhs.Op == token.RANGE {
+			// rhs is range expression
+			// (any short variable declaration was handled by parseSimpleStat above)
+			return &ast.RangeStmt{pos, key, value, as.TokPos, as.Tok, rhs.X, body}
+		}
+		p.errorExpected(s2.Pos(), "range clause")
+		return &ast.BadStmt{pos, body.End()}
+	}
+
+	// regular for statement
+	return &ast.ForStmt{pos, s1, p.makeExpr(s2), s3, body}
+}
+
+func (p *parser) parseStmt() (s ast.Stmt) {
+	if p.trace {
+		defer un(trace(p, "Statement"))
+	}
+
+	switch p.tok {
+	case token.CONST, token.TYPE, token.VAR:
+		s = &ast.DeclStmt{p.parseDecl()}
+	case
+		// tokens that may start a top-level expression
+		token.IDENT, token.INT, token.FLOAT, token.CHAR, token.STRING, token.FUNC, token.LPAREN, // operand
+		token.LBRACK, token.STRUCT, // composite type
+		token.MUL, token.AND, token.ARROW, token.ADD, token.SUB, token.XOR: // unary operators
+		s = p.parseSimpleStmt(true)
+		// because of the required look-ahead, labeled statements are
+		// parsed by parseSimpleStmt - don't expect a semicolon after
+		// them
+		if _, isLabeledStmt := s.(*ast.LabeledStmt); !isLabeledStmt {
+			p.expectSemi()
+		}
+	case token.GO:
+		s = p.parseGoStmt()
+	case token.DEFER:
+		s = p.parseDeferStmt()
+	case token.RETURN:
+		s = p.parseReturnStmt()
+	case token.BREAK, token.CONTINUE, token.GOTO, token.FALLTHROUGH:
+		s = p.parseBranchStmt(p.tok)
+	case token.LBRACE:
+		s = p.parseBlockStmt()
+		p.expectSemi()
+	case token.IF:
+		s = p.parseIfStmt()
+	case token.SWITCH:
+		s = p.parseSwitchStmt()
+	case token.SELECT:
+		s = p.parseSelectStmt()
+	case token.FOR:
+		s = p.parseForStmt()
+	case token.SEMICOLON:
+		s = &ast.EmptyStmt{p.pos}
+		p.next()
+	case token.RBRACE:
+		// a semicolon may be omitted before a closing "}"
+		s = &ast.EmptyStmt{p.pos}
+	default:
+		// no statement found
+		pos := p.pos
+		p.errorExpected(pos, "statement")
+		p.next() // make progress
+		s = &ast.BadStmt{pos, p.pos}
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+type parseSpecFunction func(p *parser, doc *ast.CommentGroup, iota int) ast.Spec
+
+func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "ImportSpec"))
+	}
+
+	var ident *ast.Ident
+	switch p.tok {
+	case token.PERIOD:
+		ident = &ast.Ident{p.pos, ".", nil}
+		p.next()
+	case token.IDENT:
+		ident = p.parseIdent()
+	}
+
+	var path *ast.BasicLit
+	if p.tok == token.STRING {
+		path = &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+	} else {
+		p.expect(token.STRING) // use expect() error handling
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// collect imports
+	spec := &ast.ImportSpec{doc, ident, path, p.lineComment}
+	p.imports = append(p.imports, spec)
+
+	return spec
+}
+
+func parseConstSpec(p *parser, doc *ast.CommentGroup, iota int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "ConstSpec"))
+	}
+
+	idents := p.parseIdentList()
+	typ := p.tryType()
+	var values []ast.Expr
+	if typ != nil || p.tok == token.ASSIGN || iota == 0 {
+		p.expect(token.ASSIGN)
+		values = p.parseRhsList()
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// Go spec: The scope of a constant or variable identifier declared inside
+	// a function begins at the end of the ConstSpec or VarSpec and ends at
+	// the end of the innermost containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
+	p.declare(spec, p.topScope, ast.Con, idents...)
+
+	return spec
+}
+
+func parseTypeSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "TypeSpec"))
+	}
+
+	ident := p.parseIdent()
+
+	// Go spec: The scope of a type identifier declared inside a function begins
+	// at the identifier in the TypeSpec and ends at the end of the innermost
+	// containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.TypeSpec{doc, ident, nil, nil}
+	p.declare(spec, p.topScope, ast.Typ, ident)
+
+	spec.Type = p.parseType()
+	p.expectSemi() // call before accessing p.linecomment
+	spec.Comment = p.lineComment
+
+	return spec
+}
+
+func parseVarSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "VarSpec"))
+	}
+
+	idents := p.parseIdentList()
+	typ := p.tryType()
+	var values []ast.Expr
+	if typ == nil || p.tok == token.ASSIGN {
+		p.expect(token.ASSIGN)
+		values = p.parseRhsList()
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// Go spec: The scope of a constant or variable identifier declared inside
+	// a function begins at the end of the ConstSpec or VarSpec and ends at
+	// the end of the innermost containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
+	p.declare(spec, p.topScope, ast.Var, idents...)
+
+	return spec
+}
+
+func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
+	if p.trace {
+		defer un(trace(p, "GenDecl("+keyword.String()+")"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(keyword)
+	var lparen, rparen token.Pos
+	var list []ast.Spec
+	if p.tok == token.LPAREN {
+		lparen = p.pos
+		p.next()
+		for iota := 0; p.tok != token.RPAREN && p.tok != token.EOF; iota++ {
+			list = append(list, f(p, p.leadComment, iota))
+		}
+		rparen = p.expect(token.RPAREN)
+		p.expectSemi()
+	} else {
+		list = append(list, f(p, nil, 0))
+	}
+
+	return &ast.GenDecl{doc, pos, keyword, lparen, list, rparen}
+}
+
+func (p *parser) parseReceiver(scope *ast.Scope) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Receiver"))
+	}
+
+	pos := p.pos
+	par := p.parseParameters(scope, false)
+
+	// must have exactly one receiver
+	if par.NumFields() != 1 {
+		p.errorExpected(pos, "exactly one receiver")
+		// TODO determine a better range for BadExpr below
+		par.List = []*ast.Field{{Type: &ast.BadExpr{pos, pos}}}
+		return par
+	}
+
+	// recv type must be of the form ["*"] identifier
+	recv := par.List[0]
+	base := deref(recv.Type)
+	if _, isIdent := base.(*ast.Ident); !isIdent {
+		p.errorExpected(base.Pos(), "(unqualified) identifier")
+		par.List = []*ast.Field{{Type: &ast.BadExpr{recv.Pos(), recv.End()}}}
+	}
+
+	return par
+}
+
+func (p *parser) parseFuncDecl() *ast.FuncDecl {
+	if p.trace {
+		defer un(trace(p, "FunctionDecl"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(token.FUNC)
+	scope := ast.NewScope(p.topScope) // function scope
+
+	var recv *ast.FieldList
+	if p.tok == token.LPAREN {
+		recv = p.parseReceiver(scope)
+	}
+
+	ident := p.parseIdent()
+
+	params, results := p.parseSignature(scope)
+
+	var body *ast.BlockStmt
+	if p.tok == token.LBRACE {
+		body = p.parseBody(scope)
+	}
+	p.expectSemi()
+
+	decl := &ast.FuncDecl{doc, recv, ident, &ast.FuncType{pos, params, results}, body}
+	if recv == nil {
+		// Go spec: The scope of an identifier denoting a constant, type,
+		// variable, or function (but not method) declared at top level
+		// (outside any function) is the package block.
+		//
+		// init() functions cannot be referred to and there may
+		// be more than one - don't put them in the pkgScope
+		if ident.Name != "init" {
+			p.declare(decl, p.pkgScope, ast.Fun, ident)
+		}
+	}
+
+	return decl
+}
+
+func (p *parser) parseDecl() ast.Decl {
+	if p.trace {
+		defer un(trace(p, "Declaration"))
+	}
+
+	var f parseSpecFunction
+	switch p.tok {
+	case token.CONST:
+		f = parseConstSpec
+
+	case token.TYPE:
+		f = parseTypeSpec
+
+	case token.VAR:
+		f = parseVarSpec
+
+	case token.FUNC:
+		return p.parseFuncDecl()
+
+	default:
+		pos := p.pos
+		p.errorExpected(pos, "declaration")
+		p.next() // make progress
+		decl := &ast.BadDecl{pos, p.pos}
+		return decl
+	}
+
+	return p.parseGenDecl(p.tok, f)
+}
+
+func (p *parser) parseDeclList() (list []ast.Decl) {
+	if p.trace {
+		defer un(trace(p, "DeclList"))
+	}
+
+	for p.tok != token.EOF {
+		list = append(list, p.parseDecl())
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Source files
+
+func (p *parser) parseFile() *ast.File {
+	if p.trace {
+		defer un(trace(p, "File"))
+	}
+
+	// package clause
+	doc := p.leadComment
+	pos := p.expect(token.PACKAGE)
+	// Go spec: The package clause is not a declaration;
+	// the package name does not appear in any scope.
+	ident := p.parseIdent()
+	if ident.Name == "_" {
+		p.error(p.pos, "invalid package name _")
+	}
+	p.expectSemi()
+
+	var decls []ast.Decl
+
+	// Don't bother parsing the rest if we had errors already.
+	// Likely not a Go source file at all.
+
+	if p.ErrorCount() == 0 && p.mode&PackageClauseOnly == 0 {
+		// import decls
+		for p.tok == token.IMPORT {
+			decls = append(decls, p.parseGenDecl(token.IMPORT, parseImportSpec))
+		}
+
+		if p.mode&ImportsOnly == 0 {
+			// rest of package body
+			for p.tok != token.EOF {
+				decls = append(decls, p.parseDecl())
+			}
+		}
+	}
+
+	assert(p.topScope == p.pkgScope, "imbalanced scopes")
+
+	// resolve global identifiers within the same file
+	i := 0
+	for _, ident := range p.unresolved {
+		// i <= index for current ident
+		assert(ident.Obj == unresolved, "object already resolved")
+		ident.Obj = p.pkgScope.Lookup(ident.Name) // also removes unresolved sentinel
+		if ident.Obj == nil {
+			p.unresolved[i] = ident
+			i++
+		}
+	}
+
+	// TODO(gri): store p.imports in AST
+	return &ast.File{doc, pos, ident, decls, p.pkgScope, p.imports, p.unresolved[0:i], p.comments}
+}
diff --git a/src/go/printer/testdata/slow.golden b/src/go/printer/testdata/slow.golden
new file mode 100644
index 0000000..43a15cb
--- /dev/null
+++ b/src/go/printer/testdata/slow.golden
@@ -0,0 +1,85 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package deepequal_test
+
+import (
+	"testing"
+	"google3/spam/archer/frontend/deepequal"
+)
+
+func TestTwoNilValues(t *testing.T) {
+	if err := deepequal.Check(nil, nil); err != nil {
+		t.Errorf("expected nil, saw %v", err)
+	}
+}
+
+type Foo struct {
+	bar	*Bar
+	bang	*Bar
+}
+
+type Bar struct {
+	baz	*Baz
+	foo	[]*Foo
+}
+
+type Baz struct {
+	entries		map[int]interface{}
+	whatever	string
+}
+
+func newFoo() *Foo {
+	return &Foo{bar: &Bar{baz: &Baz{
+		entries: map[int]interface{}{
+			42:	&Foo{},
+			21:	&Bar{},
+			11:	&Baz{whatever: "it's just a test"}}}},
+		bang: &Bar{foo: []*Foo{
+			&Foo{bar: &Bar{baz: &Baz{
+				entries: map[int]interface{}{
+					43:	&Foo{},
+					22:	&Bar{},
+					13:	&Baz{whatever: "this is nuts"}}}},
+				bang: &Bar{foo: []*Foo{
+					&Foo{bar: &Bar{baz: &Baz{
+						entries: map[int]interface{}{
+							61:	&Foo{},
+							71:	&Bar{},
+							11:	&Baz{whatever: "no, it's Go"}}}},
+						bang: &Bar{foo: []*Foo{
+							&Foo{bar: &Bar{baz: &Baz{
+								entries: map[int]interface{}{
+									0:	&Foo{},
+									-2:	&Bar{},
+									-11:	&Baz{whatever: "we need to go deeper"}}}},
+								bang: &Bar{foo: []*Foo{
+									&Foo{bar: &Bar{baz: &Baz{
+										entries: map[int]interface{}{
+											-2:	&Foo{},
+											-5:	&Bar{},
+											-7:	&Baz{whatever: "are you serious?"}}}},
+										bang:	&Bar{foo: []*Foo{}}},
+									&Foo{bar: &Bar{baz: &Baz{
+										entries: map[int]interface{}{
+											-100:	&Foo{},
+											50:	&Bar{},
+											20:	&Baz{whatever: "na, not really ..."}}}},
+										bang:	&Bar{foo: []*Foo{}}}}}}}}},
+					&Foo{bar: &Bar{baz: &Baz{
+						entries: map[int]interface{}{
+							2:	&Foo{},
+							1:	&Bar{},
+							-1:	&Baz{whatever: "... it's just a test."}}}},
+						bang:	&Bar{foo: []*Foo{}}}}}}}}}
+}
+
+func TestElaborate(t *testing.T) {
+	a := newFoo()
+	b := newFoo()
+
+	if err := deepequal.Check(a, b); err != nil {
+		t.Errorf("expected nil, saw %v", err)
+	}
+}
diff --git a/src/go/printer/testdata/slow.input b/src/go/printer/testdata/slow.input
new file mode 100644
index 0000000..0e5a23d
--- /dev/null
+++ b/src/go/printer/testdata/slow.input
@@ -0,0 +1,85 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package deepequal_test
+
+import (
+        "testing"
+        "google3/spam/archer/frontend/deepequal"
+)
+
+func TestTwoNilValues(t *testing.T) {
+        if err := deepequal.Check(nil, nil); err != nil {
+                t.Errorf("expected nil, saw %v", err)
+        }
+}
+
+type Foo struct {
+        bar *Bar
+        bang *Bar
+}
+
+type Bar struct {
+        baz *Baz
+        foo []*Foo
+}
+
+type Baz struct {
+        entries  map[int]interface{}
+        whatever string
+}
+
+func newFoo() (*Foo) {
+return &Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+42: &Foo{},
+21: &Bar{},
+11: &Baz{ whatever: "it's just a test" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+43: &Foo{},
+22: &Bar{},
+13: &Baz{ whatever: "this is nuts" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+61: &Foo{},
+71: &Bar{},
+11: &Baz{ whatever: "no, it's Go" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+0: &Foo{},
+-2: &Bar{},
+-11: &Baz{ whatever: "we need to go deeper" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+-2: &Foo{},
+-5: &Bar{},
+-7: &Baz{ whatever: "are you serious?" }}}},
+        bang: &Bar{foo: []*Foo{}}},
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+-100: &Foo{},
+50: &Bar{},
+20: &Baz{ whatever: "na, not really ..." }}}},
+        bang: &Bar{foo: []*Foo{}}}}}}}}},
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+2: &Foo{},
+1: &Bar{},
+-1: &Baz{ whatever: "... it's just a test." }}}},
+        bang: &Bar{foo: []*Foo{}}}}}}}}}
+}
+
+func TestElaborate(t *testing.T) {
+        a := newFoo()
+        b := newFoo()
+
+        if err := deepequal.Check(a, b); err != nil {
+                t.Errorf("expected nil, saw %v", err)
+        }
+}
diff --git a/src/go/printer/testdata/statements.golden b/src/go/printer/testdata/statements.golden
new file mode 100644
index 0000000..4b13460
--- /dev/null
+++ b/src/go/printer/testdata/statements.golden
@@ -0,0 +1,644 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package statements
+
+var expr bool
+
+func use(x interface{})	{}
+
+// Formatting of multi-line return statements.
+func _f() {
+	return
+	return x, y, z
+	return T{}
+	return T{1, 2, 3},
+		x, y, z
+	return T{1, 2, 3},
+		x, y,
+		z
+	return T{1,
+		2,
+		3}
+	return T{1,
+		2,
+		3,
+	}
+	return T{
+		1,
+		2,
+		3}
+	return T{
+		1,
+		2,
+		3,
+	}
+	return T{
+		1,
+		T{1, 2, 3},
+		3,
+	}
+	return T{
+		1,
+		T{1,
+			2, 3},
+		3,
+	}
+	return T{
+		1,
+		T{1,
+			2,
+			3},
+		3,
+	}
+	return T{
+		1,
+		2,
+	}, nil
+	return T{
+			1,
+			2,
+		},
+		T{
+			x:	3,
+			y:	4,
+		}, nil
+	return T{
+			1,
+			2,
+		},
+		nil
+	return T{
+			1,
+			2,
+		},
+		T{
+			x:	3,
+			y:	4,
+		},
+		nil
+	return x + y +
+		z
+	return func() {}
+	return func() {
+			_ = 0
+		}, T{
+			1, 2,
+		}
+	return func() {
+		_ = 0
+	}
+	return func() T {
+		return T{
+			1, 2,
+		}
+	}
+}
+
+// Formatting of multi-line returns: test cases from issue 1207.
+func F() (*T, os.Error) {
+	return &T{
+			X:	1,
+			Y:	2,
+		},
+		nil
+}
+
+func G() (*T, *T, os.Error) {
+	return &T{
+			X:	1,
+			Y:	2,
+		},
+		&T{
+			X:	3,
+			Y:	4,
+		},
+		nil
+}
+
+func _() interface{} {
+	return &fileStat{
+		name:		basename(file.name),
+		size:		mkSize(d.FileSizeHigh, d.FileSizeLow),
+		modTime:	mkModTime(d.LastWriteTime),
+		mode:		mkMode(d.FileAttributes),
+		sys:		mkSysFromFI(&d),
+	}, nil
+}
+
+// Formatting of if-statement headers.
+func _() {
+	if true {
+	}
+	if true {
+	}	// no semicolon printed
+	if expr {
+	}
+	if expr {
+	}	// no semicolon printed
+	if expr {
+	}	// no parens printed
+	if expr {
+	}	// no semicolon and parens printed
+	if x := expr; true {
+		use(x)
+	}
+	if x := expr; expr {
+		use(x)
+	}
+}
+
+// Formatting of switch-statement headers.
+func _() {
+	switch {
+	}
+	switch {
+	}	// no semicolon printed
+	switch expr {
+	}
+	switch expr {
+	}	// no semicolon printed
+	switch expr {
+	}	// no parens printed
+	switch expr {
+	}	// no semicolon and parens printed
+	switch x := expr; {
+	default:
+		use(
+			x)
+	}
+	switch x := expr; expr {
+	default:
+		use(x)
+	}
+}
+
+// Formatting of switch statement bodies.
+func _() {
+	switch {
+	}
+
+	switch x := 0; x {
+	case 1:
+		use(x)
+		use(x)	// followed by an empty line
+
+	case 2:	// followed by an empty line
+
+		use(x)	// followed by an empty line
+
+	case 3:	// no empty lines
+		use(x)
+		use(x)
+	}
+
+	switch x {
+	case 0:
+		use(x)
+	case 1:	// this comment should have no effect on the previous or next line
+		use(x)
+	}
+
+	switch x := 0; x {
+	case 1:
+		x = 0
+		// this comment should be indented
+	case 2:
+		x = 0
+	// this comment should not be indented, it is aligned with the next case
+	case 3:
+		x = 0
+		/* indented comment
+		   aligned
+		   aligned
+		*/
+		// bla
+		/* and more */
+	case 4:
+		x = 0
+	/* not indented comment
+	   aligned
+	   aligned
+	*/
+	// bla
+	/* and more */
+	case 5:
+	}
+}
+
+// Formatting of selected select statements.
+func _() {
+	select {}
+	select { /* this comment should not be tab-aligned because the closing } is on the same line */
+	}
+	select {	/* this comment should be tab-aligned */
+	}
+	select {	// this comment should be tab-aligned
+	}
+	select {
+	case <-c:
+	}
+}
+
+// Formatting of for-statement headers for single-line for-loops.
+func _() {
+	for {
+	}
+	for expr {
+	}
+	for expr {
+	}	// no parens printed
+	for {
+	}	// no semicolons printed
+	for x := expr; ; {
+		use(x)
+	}
+	for expr {
+	}	// no semicolons printed
+	for expr {
+	}	// no semicolons and parens printed
+	for ; ; expr = false {
+	}
+	for x := expr; expr; {
+		use(x)
+	}
+	for x := expr; ; expr = false {
+		use(x)
+	}
+	for ; expr; expr = false {
+	}
+	for x := expr; expr; expr = false {
+		use(x)
+	}
+	for x := range []int{} {
+		use(x)
+	}
+	for x := range []int{} {
+		use(x)
+	}	// no parens printed
+}
+
+// Formatting of for-statement headers for multi-line for-loops.
+func _() {
+	for {
+	}
+	for expr {
+	}
+	for expr {
+	}	// no parens printed
+	for {
+	}	// no semicolons printed
+	for x := expr; ; {
+		use(x)
+	}
+	for expr {
+	}	// no semicolons printed
+	for expr {
+	}	// no semicolons and parens printed
+	for ; ; expr = false {
+	}
+	for x := expr; expr; {
+		use(x)
+	}
+	for x := expr; ; expr = false {
+		use(x)
+	}
+	for ; expr; expr = false {
+	}
+	for x := expr; expr; expr = false {
+		use(x)
+	}
+	for range []int{} {
+		println("foo")
+	}
+	for x := range []int{} {
+		use(x)
+	}
+	for x := range []int{} {
+		use(x)
+	}	// no parens printed
+}
+
+// Formatting of selected short single- and multi-line statements.
+func _() {
+	if cond {
+	}
+	if cond {
+	}	// multiple lines
+	if cond {
+	} else {
+	}	// else clause always requires multiple lines
+
+	for {
+	}
+	for i := 0; i < len(a); 1++ {
+	}
+	for i := 0; i < len(a); 1++ {
+		a[i] = i
+	}
+	for i := 0; i < len(a); 1++ {
+		a[i] = i
+	}	// multiple lines
+
+	for range a {
+	}
+	for _ = range a {
+	}
+	for _, _ = range a {
+	}
+	for i := range a {
+	}
+	for i := range a {
+		a[i] = i
+	}
+	for i := range a {
+		a[i] = i
+	}	// multiple lines
+
+	go func() {
+		for {
+			a <- <-b
+		}
+	}()
+	defer func() {
+		if x := recover(); x != nil {
+			err = fmt.Sprintf("error: %s", x.msg)
+		}
+	}()
+}
+
+// Don't remove mandatory parentheses around composite literals in control clauses.
+func _() {
+	// strip parentheses - no composite literals or composite literals don't start with a type name
+	if x {
+	}
+	if x {
+	}
+	if []T{} {
+	}
+	if []T{} {
+	}
+	if []T{} {
+	}
+
+	for x {
+	}
+	for x {
+	}
+	for []T{} {
+	}
+	for []T{} {
+	}
+	for []T{} {
+	}
+
+	switch x {
+	}
+	switch x {
+	}
+	switch []T{} {
+	}
+	switch []T{} {
+	}
+
+	for _ = range []T{T{42}} {
+	}
+
+	// leave parentheses - composite literals start with a type name
+	if (T{}) {
+	}
+	if (T{}) {
+	}
+	if (T{}) {
+	}
+
+	for (T{}) {
+	}
+	for (T{}) {
+	}
+	for (T{}) {
+	}
+
+	switch (T{}) {
+	}
+	switch (T{}) {
+	}
+
+	for _ = range (T1{T{42}}) {
+	}
+
+	if x == (T{42}[0]) {
+	}
+	if (x == T{42}[0]) {
+	}
+	if x == (T{42}[0]) {
+	}
+	if x == (T{42}[0]) {
+	}
+	if x == (T{42}[0]) {
+	}
+	if x == a+b*(T{42}[0]) {
+	}
+	if (x == a+b*T{42}[0]) {
+	}
+	if x == a+b*(T{42}[0]) {
+	}
+	if x == a+(b*(T{42}[0])) {
+	}
+	if x == a+b*(T{42}[0]) {
+	}
+	if (a + b*(T{42}[0])) == x {
+	}
+	if (a + b*(T{42}[0])) == x {
+	}
+
+	if struct{ x bool }{false}.x {
+	}
+	if (struct{ x bool }{false}.x) == false {
+	}
+	if struct{ x bool }{false}.x == false {
+	}
+}
+
+// Extra empty lines inside functions. Do respect source code line
+// breaks between statement boundaries but print at most one empty
+// line at a time.
+func _() {
+
+	const _ = 0
+
+	const _ = 1
+	type _ int
+	type _ float
+
+	var _ = 0
+	var x = 1
+
+	// Each use(x) call below should have at most one empty line before and after.
+	// Known bug: The first use call may have more than one empty line before
+	//            (see go/printer/nodes.go, func linebreak).
+
+	use(x)
+
+	if x < x {
+
+		use(x)
+
+	} else {
+
+		use(x)
+
+	}
+}
+
+// Formatting around labels.
+func _() {
+L:
+}
+
+func _() {
+	// this comment should be indented
+L:	// no semicolon needed
+}
+
+func _() {
+	switch 0 {
+	case 0:
+	L0:
+		;	// semicolon required
+	case 1:
+	L1:
+		;	// semicolon required
+	default:
+	L2:	// no semicolon needed
+	}
+}
+
+func _() {
+	f()
+L1:
+	f()
+L2:
+	;
+L3:
+}
+
+func _() {
+	// this comment should be indented
+L:
+}
+
+func _() {
+L:
+	_ = 0
+}
+
+func _() {
+	// this comment should be indented
+L:
+	_ = 0
+}
+
+func _() {
+	for {
+	L1:
+		_ = 0
+	L2:
+		_ = 0
+	}
+}
+
+func _() {
+	// this comment should be indented
+	for {
+	L1:
+		_ = 0
+	L2:
+		_ = 0
+	}
+}
+
+func _() {
+	if true {
+		_ = 0
+	}
+	_ = 0	// the indentation here should not be affected by the long label name
+AnOverlongLabel:
+	_ = 0
+
+	if true {
+		_ = 0
+	}
+	_ = 0
+
+L:
+	_ = 0
+}
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	MoreCode()
+}
+
+func _() {
+	for {
+		goto L
+	}
+L:	// A comment on the same line as the label, followed by a single empty line.
+	// Known bug: There may be more than one empty line before MoreCode()
+	//            (see go/printer/nodes.go, func linebreak).
+
+	MoreCode()
+}
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+func _() {
+	for {
+		goto AVeryLongLabelThatShouldNotAffectFormatting
+	}
+AVeryLongLabelThatShouldNotAffectFormatting:
+	// There should be a single empty line after this comment.
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+// Formatting of empty statements.
+func _() {
+
+}
+
+func _() {
+}
+
+func _() {
+}
+
+func _() {
+	f()
+}
+
+func _() {
+L:
+	;
+}
+
+func _() {
+L:
+	;
+	f()
+}
diff --git a/src/go/printer/testdata/statements.input b/src/go/printer/testdata/statements.input
new file mode 100644
index 0000000..cade157
--- /dev/null
+++ b/src/go/printer/testdata/statements.input
@@ -0,0 +1,555 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package statements
+
+var expr bool
+
+func use(x interface{}) {}
+
+// Formatting of multi-line return statements.
+func _f() {
+	return
+	return x, y, z
+	return T{}
+	return T{1, 2, 3},
+		x, y, z
+	return T{1, 2, 3},
+		x, y,
+		z
+	return T{1,
+		2,
+		3}
+	return T{1,
+		2,
+		3,
+	}
+	return T{
+		1,
+		2,
+		3}
+	return T{
+		1,
+		2,
+		3,
+	}
+	return T{
+		1,
+		T{1, 2, 3},
+		3,
+	}
+	return T{
+		1,
+		T{1,
+			2, 3},
+		3,
+	}
+	return T{
+		1,
+		T{1,
+			2,
+			3},
+		3,
+	}
+	return T{
+			1,
+			2,
+		}, nil
+	return T{
+			1,
+			2,
+		},
+		T{
+			x: 3,
+			y: 4,
+		}, nil
+	return T{
+			1,
+			2,
+		},
+		nil
+	return T{
+			1,
+			2,
+		},
+		T{
+			x: 3,
+			y: 4,
+		},
+		nil
+	return x + y +
+		z
+	return func() {}
+	return func() {
+		_ = 0
+	}, T{
+		1, 2,
+	}
+	return func() {
+		_ = 0
+	}
+	return func() T {
+		return T {
+			1, 2,
+		}
+	}
+}
+
+// Formatting of multi-line returns: test cases from issue 1207.
+func F() (*T, os.Error) {
+       return &T{
+               X: 1,
+               Y: 2,
+       },
+               nil
+}
+
+func G() (*T, *T, os.Error) {
+       return &T{
+               X: 1,
+               Y: 2,
+       },
+               &T{
+                       X: 3,
+                       Y: 4,
+               },
+               nil
+}
+
+func _() interface{} {
+	return &fileStat{
+			name:    basename(file.name),
+			size:    mkSize(d.FileSizeHigh, d.FileSizeLow),
+			modTime: mkModTime(d.LastWriteTime),
+			mode:    mkMode(d.FileAttributes),
+			sys:     mkSysFromFI(&d),
+		}, nil
+}
+
+// Formatting of if-statement headers.
+func _() {
+	if true {}
+	if; true {}  // no semicolon printed
+	if expr{}
+	if;expr{}  // no semicolon printed
+	if (expr){}  // no parens printed
+	if;((expr)){}  // no semicolon and parens printed
+	if x:=expr;true{
+	use(x)}
+	if x:=expr; expr {use(x)}
+}
+
+
+// Formatting of switch-statement headers.
+func _() {
+	switch {}
+	switch;{}  // no semicolon printed
+	switch expr {}
+	switch;expr{}  // no semicolon printed
+	switch (expr) {}  // no parens printed
+	switch;((expr)){}  // no semicolon and parens printed
+	switch x := expr; { default:use(
+x)
+	}
+	switch x := expr; expr {default:use(x)}
+}
+
+
+// Formatting of switch statement bodies.
+func _() {
+	switch {
+	}
+
+	switch x := 0; x {
+	case 1:
+		use(x)
+		use(x)  // followed by an empty line
+
+	case 2:  // followed by an empty line
+
+		use(x)  // followed by an empty line
+
+	case 3:  // no empty lines
+		use(x)
+		use(x)
+	}
+
+	switch x {
+	case 0:
+		use(x)
+	case 1:  // this comment should have no effect on the previous or next line
+		use(x)
+	}
+
+	switch x := 0; x {
+	case 1:
+		x = 0
+		// this comment should be indented
+	case 2:
+		x = 0
+	// this comment should not be indented, it is aligned with the next case
+	case 3:
+		x = 0
+		/* indented comment
+		   aligned
+		   aligned
+		*/
+		// bla
+		/* and more */
+	case 4:
+		x = 0
+	/* not indented comment
+	   aligned
+	   aligned
+	*/
+	// bla
+	/* and more */
+	case 5:
+	}
+}
+
+
+// Formatting of selected select statements.
+func _() {
+	select {
+	}
+	select { /* this comment should not be tab-aligned because the closing } is on the same line */ }
+	select { /* this comment should be tab-aligned */
+	}
+	select { // this comment should be tab-aligned
+	}
+	select { case <-c: }
+}
+
+
+// Formatting of for-statement headers for single-line for-loops.
+func _() {
+	for{}
+	for expr {}
+	for (expr) {}  // no parens printed
+	for;;{}  // no semicolons printed
+	for x :=expr;; {use( x)}
+	for; expr;{}  // no semicolons printed
+	for; ((expr));{}  // no semicolons and parens printed
+	for; ; expr = false {}
+	for x :=expr; expr; {use(x)}
+	for x := expr;; expr=false {use(x)}
+	for;expr;expr =false {}
+	for x := expr;expr;expr = false { use(x) }
+	for x := range []int{} { use(x) }
+	for x := range (([]int{})) { use(x) }  // no parens printed
+}
+
+
+// Formatting of for-statement headers for multi-line for-loops.
+func _() {
+	for{
+	}
+	for expr {
+	}
+	for (expr) {
+	}  // no parens printed
+	for;;{
+	}  // no semicolons printed
+	for x :=expr;; {use( x)
+	}
+	for; expr;{
+	}  // no semicolons printed
+	for; ((expr));{
+	}  // no semicolons and parens printed
+	for; ; expr = false {
+	}
+	for x :=expr; expr; {use(x)
+	}
+	for x := expr;; expr=false {use(x)
+	}
+	for;expr;expr =false {
+	}
+	for x := expr;expr;expr = false {
+	use(x)
+	}
+	for range []int{} {
+	println("foo")}
+	for x := range []int{} {
+	use(x) }
+	for x := range (([]int{})) {
+	use(x) }  // no parens printed
+}
+
+
+// Formatting of selected short single- and multi-line statements.
+func _() {
+	if cond {}
+	if cond {
+	} // multiple lines
+	if cond {} else {} // else clause always requires multiple lines
+
+	for {}
+	for i := 0; i < len(a); 1++ {}
+	for i := 0; i < len(a); 1++ { a[i] = i }
+	for i := 0; i < len(a); 1++ { a[i] = i
+	} // multiple lines
+
+	for range a{}
+	for _ = range a{}
+	for _, _ = range a{}
+	for i := range a {}
+	for i := range a { a[i] = i }
+	for i := range a { a[i] = i
+	} // multiple lines
+
+	go func() { for { a <- <-b } }()
+	defer func() { if x := recover(); x != nil { err = fmt.Sprintf("error: %s", x.msg) } }()
+}
+
+
+// Don't remove mandatory parentheses around composite literals in control clauses.
+func _() {
+	// strip parentheses - no composite literals or composite literals don't start with a type name
+	if (x) {}
+	if (((x))) {}
+	if ([]T{}) {}
+	if (([]T{})) {}
+	if ; (((([]T{})))) {}
+
+	for (x) {}
+	for (((x))) {}
+	for ([]T{}) {}
+	for (([]T{})) {}
+	for ; (((([]T{})))) ; {}
+
+	switch (x) {}
+	switch (((x))) {}
+	switch ([]T{}) {}
+	switch ; (((([]T{})))) {}
+
+	for _ = range ((([]T{T{42}}))) {}
+
+	// leave parentheses - composite literals start with a type name
+	if (T{}) {}
+	if ((T{})) {}
+	if ; ((((T{})))) {}
+
+	for (T{}) {}
+	for ((T{})) {}
+	for ; ((((T{})))) ; {}
+
+	switch (T{}) {}
+	switch ; ((((T{})))) {}
+
+	for _ = range (((T1{T{42}}))) {}
+
+	if x == (T{42}[0]) {}
+	if (x == T{42}[0]) {}
+	if (x == (T{42}[0])) {}
+	if (x == (((T{42}[0])))) {}
+	if (((x == (T{42}[0])))) {}
+	if x == a + b*(T{42}[0]) {}
+	if (x == a + b*T{42}[0]) {}
+	if (x == a + b*(T{42}[0])) {}
+	if (x == a + ((b * (T{42}[0])))) {}
+	if (((x == a + b * (T{42}[0])))) {}
+	if (((a + b * (T{42}[0])) == x)) {}
+	if (((a + b * (T{42}[0])))) == x {}
+
+	if (struct{x bool}{false}.x) {}
+	if (struct{x bool}{false}.x) == false {}
+	if (struct{x bool}{false}.x == false) {}
+}
+
+
+// Extra empty lines inside functions. Do respect source code line
+// breaks between statement boundaries but print at most one empty
+// line at a time.
+func _() {
+
+	const _ = 0
+
+	const _ = 1
+	type _ int
+	type _ float
+
+	var _ = 0
+	var x = 1
+
+	// Each use(x) call below should have at most one empty line before and after.
+	// Known bug: The first use call may have more than one empty line before
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+
+	use(x)
+
+	if x < x {
+
+		use(x)
+
+	} else {
+
+		use(x)
+
+	}
+}
+
+
+// Formatting around labels.
+func _() {
+	L:
+}
+
+
+func _() {
+	// this comment should be indented
+	L: ;  // no semicolon needed
+}
+
+
+func _() {
+	switch 0 {
+	case 0:
+		L0: ;  // semicolon required
+	case 1:
+		L1: ;  // semicolon required
+	default:
+		L2: ;  // no semicolon needed
+	}
+}
+
+
+func _() {
+	f()
+L1:
+	f()
+L2:
+	;
+L3:
+}
+
+
+func _() {
+	// this comment should be indented
+	L:
+}
+
+
+func _() {
+	L: _ = 0
+}
+
+
+func _() {
+	// this comment should be indented
+	L: _ = 0
+}
+
+
+func _() {
+	for {
+	L1: _ = 0
+	L2:
+		_ = 0
+	}
+}
+
+
+func _() {
+		// this comment should be indented
+	for {
+	L1: _ = 0
+	L2:
+		_ = 0
+	}
+}
+
+
+func _() {
+	if true {
+		_ = 0
+	}
+	_ = 0  // the indentation here should not be affected by the long label name
+AnOverlongLabel:
+	_ = 0
+	
+	if true {
+		_ = 0
+	}
+	_ = 0
+
+L:	_ = 0
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:	// A comment on the same line as the label, followed by a single empty line.
+	// Known bug: There may be more than one empty line before MoreCode()
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+
+
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto AVeryLongLabelThatShouldNotAffectFormatting
+	}
+AVeryLongLabelThatShouldNotAffectFormatting:
+	// There should be a single empty line after this comment.
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+
+// Formatting of empty statements.
+func _() {
+	;;;;;;;;;;;;;;;;;;;;;;;;;
+}
+
+func _() {;;;;;;;;;;;;;;;;;;;;;;;;;
+}
+
+func _() {;;;;;;;;;;;;;;;;;;;;;;;;;}
+
+func _() {
+f();;;;;;;;;;;;;;;;;;;;;;;;;
+}
+
+func _() {
+L:;;;;;;;;;;;;
+}
+
+func _() {
+L:;;;;;;;;;;;;
+	f()
+}