5 files changed, 624 insertions, 0 deletions
diff --git a/src/go/format/benchmark_test.go b/src/go/format/benchmark_test.go
new file mode 100644
index 0000000..ac19aa3
--- /dev/null
+++ b/src/go/format/benchmark_test.go
@@ -0,0 +1,91 @@
+// 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.
+
+// This file provides a simple framework to add benchmarks
+// based on generated input (source) files.
+
+package format_test
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"os"
+	"testing"
+)
+
+var debug = flag.Bool("debug", false, "write .src files containing formatting input; for debugging")
+
+// array1 generates an array literal with n elements of the form:
+//
+// var _ = [...]byte{
+// 	// 0
+// 	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+// 	0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+// 	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+// 	0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+// 	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
+// 	// 40
+// 	0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+// 	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+// 	...
+//
+func array1(buf *bytes.Buffer, n int) {
+	buf.WriteString("var _ = [...]byte{\n")
+	for i := 0; i < n; {
+		if i%10 == 0 {
+			fmt.Fprintf(buf, "\t// %d\n", i)
+		}
+		buf.WriteByte('\t')
+		for j := 0; j < 8; j++ {
+			fmt.Fprintf(buf, "0x%02x, ", byte(i))
+			i++
+		}
+		buf.WriteString("\n")
+	}
+	buf.WriteString("}\n")
+}
+
+var tests = []struct {
+	name string
+	gen  func(*bytes.Buffer, int)
+	n    int
+}{
+	{"array1", array1, 10000},
+	// add new test cases here as needed
+}
+
+func BenchmarkFormat(b *testing.B) {
+	var src bytes.Buffer
+	for _, t := range tests {
+		src.Reset()
+		src.WriteString("package p\n")
+		t.gen(&src, t.n)
+		data := src.Bytes()
+
+		if *debug {
+			filename := t.name + ".src"
+			err := os.WriteFile(filename, data, 0660)
+			if err != nil {
+				b.Fatalf("couldn't write %s: %v", filename, err)
+			}
+		}
+
+		b.Run(fmt.Sprintf("%s-%d", t.name, t.n), func(b *testing.B) {
+			b.SetBytes(int64(len(data)))
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				var err error
+				sink, err = format.Source(data)
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}
+
+var sink []byte
diff --git a/src/go/format/example_test.go b/src/go/format/example_test.go
new file mode 100644
index 0000000..5b6789a
--- /dev/null
+++ b/src/go/format/example_test.go
@@ -0,0 +1,39 @@
+// 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 format_test
+
+import (
+	"bytes"
+	"fmt"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"log"
+)
+
+func ExampleNode() {
+	const expr = "(6+2*3)/4"
+
+	// parser.ParseExpr parses the argument and returns the
+	// corresponding ast.Node.
+	node, err := parser.ParseExpr(expr)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Create a FileSet for node. Since the node does not come
+	// from a real source file, fset will be empty.
+	fset := token.NewFileSet()
+
+	var buf bytes.Buffer
+	err = format.Node(&buf, fset, node)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(buf.String())
+
+	// Output: (6 + 2*3) / 4
+}
diff --git a/src/go/format/format.go b/src/go/format/format.go
new file mode 100644
index 0000000..a603d96
--- /dev/null
+++ b/src/go/format/format.go
@@ -0,0 +1,135 @@
+// 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 format implements standard formatting of Go source.
+//
+// Note that formatting of Go source code changes over time, so tools relying on
+// consistent formatting should execute a specific version of the gofmt binary
+// instead of using this package. That way, the formatting will be stable, and
+// the tools won't need to be recompiled each time gofmt changes.
+//
+// For example, pre-submit checks that use this package directly would behave
+// differently depending on what Go version each developer uses, causing the
+// check to be inherently fragile.
+package format
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"io"
+)
+
+// Keep these in sync with cmd/gofmt/gofmt.go.
+const (
+	tabWidth    = 8
+	printerMode = printer.UseSpaces | printer.TabIndent | printerNormalizeNumbers
+
+	// printerNormalizeNumbers means to canonicalize number literal prefixes
+	// and exponents while printing. See https://golang.org/doc/go1.13#gofmt.
+	//
+	// This value is defined in go/printer specifically for go/format and cmd/gofmt.
+	printerNormalizeNumbers = 1 << 30
+)
+
+var config = printer.Config{Mode: printerMode, Tabwidth: tabWidth}
+
+const parserMode = parser.ParseComments
+
+// Node formats node in canonical gofmt style and writes the result to dst.
+//
+// The node type must be *ast.File, *printer.CommentedNode, []ast.Decl,
+// []ast.Stmt, or assignment-compatible to ast.Expr, ast.Decl, ast.Spec,
+// or ast.Stmt. Node does not modify node. Imports are not sorted for
+// nodes representing partial source files (for instance, if the node is
+// not an *ast.File or a *printer.CommentedNode not wrapping an *ast.File).
+//
+// The function may return early (before the entire result is written)
+// and return a formatting error, for instance due to an incorrect AST.
+//
+func Node(dst io.Writer, fset *token.FileSet, node interface{}) error {
+	// Determine if we have a complete source file (file != nil).
+	var file *ast.File
+	var cnode *printer.CommentedNode
+	switch n := node.(type) {
+	case *ast.File:
+		file = n
+	case *printer.CommentedNode:
+		if f, ok := n.Node.(*ast.File); ok {
+			file = f
+			cnode = n
+		}
+	}
+
+	// Sort imports if necessary.
+	if file != nil && hasUnsortedImports(file) {
+		// Make a copy of the AST because ast.SortImports is destructive.
+		// TODO(gri) Do this more efficiently.
+		var buf bytes.Buffer
+		err := config.Fprint(&buf, fset, file)
+		if err != nil {
+			return err
+		}
+		file, err = parser.ParseFile(fset, "", buf.Bytes(), parserMode)
+		if err != nil {
+			// We should never get here. If we do, provide good diagnostic.
+			return fmt.Errorf("format.Node internal error (%s)", err)
+		}
+		ast.SortImports(fset, file)
+
+		// Use new file with sorted imports.
+		node = file
+		if cnode != nil {
+			node = &printer.CommentedNode{Node: file, Comments: cnode.Comments}
+		}
+	}
+
+	return config.Fprint(dst, fset, node)
+}
+
+// Source formats src in canonical gofmt style and returns the result
+// or an (I/O or syntax) error. src is expected to be a syntactically
+// correct Go source file, or a list of Go declarations or statements.
+//
+// If src is a partial source file, the leading and trailing space of src
+// is applied to the result (such that it has the same leading and trailing
+// space as src), and the result is indented by the same amount as the first
+// line of src containing code. Imports are not sorted for partial source files.
+//
+func Source(src []byte) ([]byte, error) {
+	fset := token.NewFileSet()
+	file, sourceAdj, indentAdj, err := parse(fset, "", src, true)
+	if err != nil {
+		return nil, err
+	}
+
+	if sourceAdj == nil {
+		// Complete source file.
+		// TODO(gri) consider doing this always.
+		ast.SortImports(fset, file)
+	}
+
+	return format(fset, file, sourceAdj, indentAdj, src, config)
+}
+
+func hasUnsortedImports(file *ast.File) bool {
+	for _, d := range file.Decls {
+		d, ok := d.(*ast.GenDecl)
+		if !ok || d.Tok != token.IMPORT {
+			// Not an import declaration, so we're done.
+			// Imports are always first.
+			return false
+		}
+		if d.Lparen.IsValid() {
+			// For now assume all grouped imports are unsorted.
+			// TODO(gri) Should check if they are sorted already.
+			return true
+		}
+		// Ungrouped imports are sorted by default.
+	}
+	return false
+}
diff --git a/src/go/format/format_test.go b/src/go/format/format_test.go
new file mode 100644
index 0000000..27f4c74
--- /dev/null
+++ b/src/go/format/format_test.go
@@ -0,0 +1,183 @@
+// 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 format
+
+import (
+	"bytes"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"os"
+	"strings"
+	"testing"
+)
+
+const testfile = "format_test.go"
+
+func diff(t *testing.T, dst, src []byte) {
+	line := 1
+	offs := 0 // line offset
+	for i := 0; i < len(dst) && i < len(src); i++ {
+		d := dst[i]
+		s := src[i]
+		if d != s {
+			t.Errorf("dst:%d: %s\n", line, dst[offs:i+1])
+			t.Errorf("src:%d: %s\n", line, src[offs:i+1])
+			return
+		}
+		if s == '\n' {
+			line++
+			offs = i + 1
+		}
+	}
+	if len(dst) != len(src) {
+		t.Errorf("len(dst) = %d, len(src) = %d\nsrc = %q", len(dst), len(src), src)
+	}
+}
+
+func TestNode(t *testing.T) {
+	src, err := os.ReadFile(testfile)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, testfile, src, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf bytes.Buffer
+
+	if err = Node(&buf, fset, file); err != nil {
+		t.Fatal("Node failed:", err)
+	}
+
+	diff(t, buf.Bytes(), src)
+}
+
+// Node is documented to not modify the AST.
+// Test that it is so even when numbers are normalized.
+func TestNodeNoModify(t *testing.T) {
+	const (
+		src    = "package p\n\nconst _ = 0000000123i\n"
+		golden = "package p\n\nconst _ = 123i\n"
+	)
+
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Capture original address and value of a BasicLit node
+	// which will undergo formatting changes during printing.
+	wantLit := file.Decls[0].(*ast.GenDecl).Specs[0].(*ast.ValueSpec).Values[0].(*ast.BasicLit)
+	wantVal := wantLit.Value
+
+	var buf bytes.Buffer
+	if err = Node(&buf, fset, file); err != nil {
+		t.Fatal("Node failed:", err)
+	}
+	diff(t, buf.Bytes(), []byte(golden))
+
+	// Check if anything changed after Node returned.
+	gotLit := file.Decls[0].(*ast.GenDecl).Specs[0].(*ast.ValueSpec).Values[0].(*ast.BasicLit)
+	gotVal := gotLit.Value
+
+	if gotLit != wantLit {
+		t.Errorf("got *ast.BasicLit address %p, want %p", gotLit, wantLit)
+	}
+	if gotVal != wantVal {
+		t.Errorf("got *ast.BasicLit value %q, want %q", gotVal, wantVal)
+	}
+}
+
+func TestSource(t *testing.T) {
+	src, err := os.ReadFile(testfile)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	res, err := Source(src)
+	if err != nil {
+		t.Fatal("Source failed:", err)
+	}
+
+	diff(t, res, src)
+}
+
+// Test cases that are expected to fail are marked by the prefix "ERROR".
+// The formatted result must look the same as the input for successful tests.
+var tests = []string{
+	// declaration lists
+	`import "go/format"`,
+	"var x int",
+	"var x int\n\ntype T struct{}",
+
+	// statement lists
+	"x := 0",
+	"f(a, b, c)\nvar x int = f(1, 2, 3)",
+
+	// indentation, leading and trailing space
+	"\tx := 0\n\tgo f()",
+	"\tx := 0\n\tgo f()\n\n\n",
+	"\n\t\t\n\n\tx := 0\n\tgo f()\n\n\n",
+	"\n\t\t\n\n\t\t\tx := 0\n\t\t\tgo f()\n\n\n",
+	"\n\t\t\n\n\t\t\tx := 0\n\t\t\tconst s = `\nfoo\n`\n\n\n",     // no indentation added inside raw strings
+	"\n\t\t\n\n\t\t\tx := 0\n\t\t\tconst s = `\n\t\tfoo\n`\n\n\n", // no indentation removed inside raw strings
+
+	// comments
+	"/* Comment */",
+	"\t/* Comment */ ",
+	"\n/* Comment */ ",
+	"i := 5 /* Comment */",         // issue #5551
+	"\ta()\n//line :1",             // issue #11276
+	"\t//xxx\n\ta()\n//line :2",    // issue #11276
+	"\ta() //line :1\n\tb()\n",     // issue #11276
+	"x := 0\n//line :1\n//line :2", // issue #11276
+
+	// whitespace
+	"",     // issue #11275
+	" ",    // issue #11275
+	"\t",   // issue #11275
+	"\t\t", // issue #11275
+	"\n",   // issue #11275
+	"\n\n", // issue #11275
+	"\t\n", // issue #11275
+
+	// erroneous programs
+	"ERROR1 + 2 +",
+	"ERRORx :=  0",
+}
+
+func String(s string) (string, error) {
+	res, err := Source([]byte(s))
+	if err != nil {
+		return "", err
+	}
+	return string(res), nil
+}
+
+func TestPartial(t *testing.T) {
+	for _, src := range tests {
+		if strings.HasPrefix(src, "ERROR") {
+			// test expected to fail
+			src = src[5:] // remove ERROR prefix
+			res, err := String(src)
+			if err == nil && res == src {
+				t.Errorf("formatting succeeded but was expected to fail:\n%q", src)
+			}
+		} else {
+			// test expected to succeed
+			res, err := String(src)
+			if err != nil {
+				t.Errorf("formatting failed (%s):\n%q", err, src)
+			} else if res != src {
+				t.Errorf("formatting incorrect:\nsource: %q\nresult: %q", src, res)
+			}
+		}
+	}
+}
diff --git a/src/go/format/internal.go b/src/go/format/internal.go
new file mode 100644
index 0000000..2f3b0e4
--- /dev/null
+++ b/src/go/format/internal.go
@@ -0,0 +1,176 @@
+// Copyright 2015 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(gri): This file and the file src/cmd/gofmt/internal.go are
+// the same (but for this comment and the package name). Do not modify
+// one without the other. Determine if we can factor out functionality
+// in a public API. See also #11844 for context.
+
+package format
+
+import (
+	"bytes"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"strings"
+)
+
+// parse parses src, which was read from the named file,
+// as a Go source file, declaration, or statement list.
+func parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
+	file *ast.File,
+	sourceAdj func(src []byte, indent int) []byte,
+	indentAdj int,
+	err error,
+) {
+	// Try as whole source file.
+	file, err = parser.ParseFile(fset, filename, src, parserMode)
+	// If there's no error, return. If the error is that the source file didn't begin with a
+	// package line and source fragments are ok, fall through to
+	// try as a source fragment. Stop and return on any other error.
+	if err == nil || !fragmentOk || !strings.Contains(err.Error(), "expected 'package'") {
+		return
+	}
+
+	// If this is a declaration list, make it a source file
+	// by inserting a package clause.
+	// Insert using a ';', not a newline, so that the line numbers
+	// in psrc match the ones in src.
+	psrc := append([]byte("package p;"), src...)
+	file, err = parser.ParseFile(fset, filename, psrc, parserMode)
+	if err == nil {
+		sourceAdj = func(src []byte, indent int) []byte {
+			// Remove the package clause.
+			// Gofmt has turned the ';' into a '\n'.
+			src = src[indent+len("package p\n"):]
+			return bytes.TrimSpace(src)
+		}
+		return
+	}
+	// If the error is that the source file didn't begin with a
+	// declaration, fall through to try as a statement list.
+	// Stop and return on any other error.
+	if !strings.Contains(err.Error(), "expected declaration") {
+		return
+	}
+
+	// If this is a statement list, make it a source file
+	// by inserting a package clause and turning the list
+	// into a function body. This handles expressions too.
+	// Insert using a ';', not a newline, so that the line numbers
+	// in fsrc match the ones in src. Add an extra '\n' before the '}'
+	// to make sure comments are flushed before the '}'.
+	fsrc := append(append([]byte("package p; func _() {"), src...), '\n', '\n', '}')
+	file, err = parser.ParseFile(fset, filename, fsrc, parserMode)
+	if err == nil {
+		sourceAdj = func(src []byte, indent int) []byte {
+			// Cap adjusted indent to zero.
+			if indent < 0 {
+				indent = 0
+			}
+			// Remove the wrapping.
+			// Gofmt has turned the "; " into a "\n\n".
+			// There will be two non-blank lines with indent, hence 2*indent.
+			src = src[2*indent+len("package p\n\nfunc _() {"):]
+			// Remove only the "}\n" suffix: remaining whitespaces will be trimmed anyway
+			src = src[:len(src)-len("}\n")]
+			return bytes.TrimSpace(src)
+		}
+		// Gofmt has also indented the function body one level.
+		// Adjust that with indentAdj.
+		indentAdj = -1
+	}
+
+	// Succeeded, or out of options.
+	return
+}
+
+// format formats the given package file originally obtained from src
+// and adjusts the result based on the original source via sourceAdj
+// and indentAdj.
+func format(
+	fset *token.FileSet,
+	file *ast.File,
+	sourceAdj func(src []byte, indent int) []byte,
+	indentAdj int,
+	src []byte,
+	cfg printer.Config,
+) ([]byte, error) {
+	if sourceAdj == nil {
+		// Complete source file.
+		var buf bytes.Buffer
+		err := cfg.Fprint(&buf, fset, file)
+		if err != nil {
+			return nil, err
+		}
+		return buf.Bytes(), nil
+	}
+
+	// Partial source file.
+	// Determine and prepend leading space.
+	i, j := 0, 0
+	for j < len(src) && isSpace(src[j]) {
+		if src[j] == '\n' {
+			i = j + 1 // byte offset of last line in leading space
+		}
+		j++
+	}
+	var res []byte
+	res = append(res, src[:i]...)
+
+	// Determine and prepend indentation of first code line.
+	// Spaces are ignored unless there are no tabs,
+	// in which case spaces count as one tab.
+	indent := 0
+	hasSpace := false
+	for _, b := range src[i:j] {
+		switch b {
+		case ' ':
+			hasSpace = true
+		case '\t':
+			indent++
+		}
+	}
+	if indent == 0 && hasSpace {
+		indent = 1
+	}
+	for i := 0; i < indent; i++ {
+		res = append(res, '\t')
+	}
+
+	// Format the source.
+	// Write it without any leading and trailing space.
+	cfg.Indent = indent + indentAdj
+	var buf bytes.Buffer
+	err := cfg.Fprint(&buf, fset, file)
+	if err != nil {
+		return nil, err
+	}
+	out := sourceAdj(buf.Bytes(), cfg.Indent)
+
+	// If the adjusted output is empty, the source
+	// was empty but (possibly) for white space.
+	// The result is the incoming source.
+	if len(out) == 0 {
+		return src, nil
+	}
+
+	// Otherwise, append output to leading space.
+	res = append(res, out...)
+
+	// Determine and append trailing space.
+	i = len(src)
+	for i > 0 && isSpace(src[i-1]) {
+		i--
+	}
+	return append(res, src[i:]...), nil
+}
+
+// isSpace reports whether the byte is a space character.
+// isSpace defines a space as being among the following bytes: ' ', '\t', '\n' and '\r'.
+func isSpace(b byte) bool {
+	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
+}