Adding upstream version 1.21.8.upstream/1.21.8

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

40 files changed, 6235 insertions, 0 deletions

diff --git a/src/go/parser/error_test.go b/src/go/parser/error_test.go
new file mode 100644
index 0000000..a4e17dd
--- /dev/null
+++ b/src/go/parser/error_test.go
@@ -0,0 +1,202 @@
+// 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 file implements a parser test harness. The files in the testdata
+// directory are parsed and the errors reported are compared against the
+// error messages expected in the test files. The test files must end in
+// .src rather than .go so that they are not disturbed by gofmt runs.
+//
+// Expected errors are indicated in the test files by putting a comment
+// of the form /* ERROR "rx" */ immediately following an offending token.
+// The harness will verify that an error matching the regular expression
+// rx is reported at that source position.
+//
+// For instance, the following test file indicates that a "not declared"
+// error should be reported for the undeclared variable x:
+//
+//	package p
+//	func f() {
+//		_ = x /* ERROR "not declared" */ + 1
+//	}
+
+package parser
+
+import (
+	"flag"
+	"go/scanner"
+	"go/token"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+var traceErrs = flag.Bool("trace_errs", false, "whether to enable tracing for error tests")
+
+const testdata = "testdata"
+
+// getFile assumes that each filename occurs at most once
+func getFile(fset *token.FileSet, filename string) (file *token.File) {
+	fset.Iterate(func(f *token.File) bool {
+		if f.Name() == filename {
+			if file != nil {
+				panic(filename + " used multiple times")
+			}
+			file = f
+		}
+		return true
+	})
+	return file
+}
+
+func getPos(fset *token.FileSet, filename string, offset int) token.Pos {
+	if f := getFile(fset, filename); f != nil {
+		return f.Pos(offset)
+	}
+	return token.NoPos
+}
+
+// ERROR comments must be of the form /* ERROR "rx" */ and rx is
+// a regular expression that matches the expected error message.
+// The special form /* ERROR HERE "rx" */ must be used for error
+// messages that appear immediately after a token, rather than at
+// a token's position, and ERROR AFTER means after the comment
+// (e.g. at end of line).
+var errRx = regexp.MustCompile(`^/\* *ERROR *(HERE|AFTER)? *"([^"]*)" *\*/$`)
+
+// expectedErrors collects the regular expressions of ERROR comments found
+// in files and returns them as a map of error positions to error messages.
+func expectedErrors(fset *token.FileSet, filename string, src []byte) map[token.Pos]string {
+	errors := make(map[token.Pos]string)
+
+	var s scanner.Scanner
+	// file was parsed already - do not add it again to the file
+	// set otherwise the position information returned here will
+	// not match the position information collected by the parser
+	s.Init(getFile(fset, filename), src, nil, scanner.ScanComments)
+	var prev token.Pos // position of last non-comment, non-semicolon token
+	var here token.Pos // position immediately after the token at position prev
+
+	for {
+		pos, tok, lit := s.Scan()
+		switch tok {
+		case token.EOF:
+			return errors
+		case token.COMMENT:
+			s := errRx.FindStringSubmatch(lit)
+			if len(s) == 3 {
+				if s[1] == "HERE" {
+					pos = here // start of comment
+				} else if s[1] == "AFTER" {
+					pos += token.Pos(len(lit)) // end of comment
+				} else {
+					pos = prev // token prior to comment
+				}
+				errors[pos] = s[2]
+			}
+		case token.SEMICOLON:
+			// don't use the position of auto-inserted (invisible) semicolons
+			if lit != ";" {
+				break
+			}
+			fallthrough
+		default:
+			prev = pos
+			var l int // token length
+			if tok.IsLiteral() {
+				l = len(lit)
+			} else {
+				l = len(tok.String())
+			}
+			here = prev + token.Pos(l)
+		}
+	}
+}
+
+// compareErrors compares the map of expected error messages with the list
+// of found errors and reports discrepancies.
+func compareErrors(t *testing.T, fset *token.FileSet, expected map[token.Pos]string, found scanner.ErrorList) {
+	t.Helper()
+	for _, error := range found {
+		// error.Pos is a token.Position, but we want
+		// a token.Pos so we can do a map lookup
+		pos := getPos(fset, error.Pos.Filename, error.Pos.Offset)
+		if msg, found := expected[pos]; found {
+			// we expect a message at pos; check if it matches
+			rx, err := regexp.Compile(msg)
+			if err != nil {
+				t.Errorf("%s: %v", error.Pos, err)
+				continue
+			}
+			if match := rx.MatchString(error.Msg); !match {
+				t.Errorf("%s: %q does not match %q", error.Pos, error.Msg, msg)
+				continue
+			}
+			// we have a match - eliminate this error
+			delete(expected, pos)
+		} else {
+			// To keep in mind when analyzing failed test output:
+			// If the same error position occurs multiple times in errors,
+			// this message will be triggered (because the first error at
+			// the position removes this position from the expected errors).
+			t.Errorf("%s: unexpected error: %s", error.Pos, error.Msg)
+		}
+	}
+
+	// there should be no expected errors left
+	if len(expected) > 0 {
+		t.Errorf("%d errors not reported:", len(expected))
+		for pos, msg := range expected {
+			t.Errorf("%s: %s\n", fset.Position(pos), msg)
+		}
+	}
+}
+
+func checkErrors(t *testing.T, filename string, input any, mode Mode, expectErrors bool) {
+	t.Helper()
+	src, err := readSource(filename, input)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	fset := token.NewFileSet()
+	_, err = ParseFile(fset, filename, src, mode)
+	found, ok := err.(scanner.ErrorList)
+	if err != nil && !ok {
+		t.Error(err)
+		return
+	}
+	found.RemoveMultiples()
+
+	expected := map[token.Pos]string{}
+	if expectErrors {
+		// we are expecting the following errors
+		// (collect these after parsing a file so that it is found in the file set)
+		expected = expectedErrors(fset, filename, src)
+	}
+
+	// verify errors returned by the parser
+	compareErrors(t, fset, expected, found)
+}
+
+func TestErrors(t *testing.T) {
+	list, err := os.ReadDir(testdata)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, d := range list {
+		name := d.Name()
+		t.Run(name, func(t *testing.T) {
+			if !d.IsDir() && !strings.HasPrefix(name, ".") && (strings.HasSuffix(name, ".src") || strings.HasSuffix(name, ".go2")) {
+				mode := DeclarationErrors | AllErrors
+				if *traceErrs {
+					mode |= Trace
+				}
+				checkErrors(t, filepath.Join(testdata, name), nil, mode, true)
+			}
+		})
+	}
+}
diff --git a/src/go/parser/example_test.go b/src/go/parser/example_test.go
new file mode 100644
index 0000000..c2f7f29
--- /dev/null
+++ b/src/go/parser/example_test.go
@@ -0,0 +1,43 @@
+// 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 parser_test
+
+import (
+	"fmt"
+	"go/parser"
+	"go/token"
+)
+
+func ExampleParseFile() {
+	fset := token.NewFileSet() // positions are relative to fset
+
+	src := `package foo
+
+import (
+	"fmt"
+	"time"
+)
+
+func bar() {
+	fmt.Println(time.Now())
+}`
+
+	// Parse src but stop after processing the imports.
+	f, err := parser.ParseFile(fset, "", src, parser.ImportsOnly)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	// Print the imports from the file's AST.
+	for _, s := range f.Imports {
+		fmt.Println(s.Path.Value)
+	}
+
+	// output:
+	//
+	// "fmt"
+	// "time"
+}
diff --git a/src/go/parser/interface.go b/src/go/parser/interface.go
new file mode 100644
index 0000000..73cb162
--- /dev/null
+++ b/src/go/parser/interface.go
@@ -0,0 +1,238 @@
+// 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 contains the exported entry points for invoking the parser.
+
+package parser
+
+import (
+	"bytes"
+	"errors"
+	"go/ast"
+	"go/token"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// If src != nil, readSource converts src to a []byte if possible;
+// otherwise it returns an error. If src == nil, readSource returns
+// the result of reading the file specified by filename.
+func readSource(filename string, src any) ([]byte, error) {
+	if src != nil {
+		switch s := src.(type) {
+		case string:
+			return []byte(s), nil
+		case []byte:
+			return s, nil
+		case *bytes.Buffer:
+			// is io.Reader, but src is already available in []byte form
+			if s != nil {
+				return s.Bytes(), nil
+			}
+		case io.Reader:
+			return io.ReadAll(s)
+		}
+		return nil, errors.New("invalid source")
+	}
+	return os.ReadFile(filename)
+}
+
+// A Mode value is a set of flags (or 0).
+// They control the amount of source code parsed and other optional
+// parser functionality.
+type Mode uint
+
+const (
+	PackageClauseOnly    Mode             = 1 << iota // stop parsing after package clause
+	ImportsOnly                                       // stop parsing after import declarations
+	ParseComments                                     // parse comments and add them to AST
+	Trace                                             // print a trace of parsed productions
+	DeclarationErrors                                 // report declaration errors
+	SpuriousErrors                                    // same as AllErrors, for backward-compatibility
+	SkipObjectResolution                              // don't resolve identifiers to objects - see ParseFile
+	AllErrors            = SpuriousErrors             // report all errors (not just the first 10 on different lines)
+)
+
+// ParseFile parses the source code of a single Go source file and returns
+// the corresponding ast.File node. The source code may be provided via
+// the filename of the source file, or via the src parameter.
+//
+// If src != nil, ParseFile parses the source from src and the filename is
+// only used when recording position information. The type of the argument
+// for the src parameter must be string, []byte, or io.Reader.
+// If src == nil, ParseFile parses the file specified by filename.
+//
+// The mode parameter controls the amount of source text parsed and other
+// optional parser functionality. If the SkipObjectResolution mode bit is set,
+// the object resolution phase of parsing will be skipped, causing File.Scope,
+// File.Unresolved, and all Ident.Obj fields to be nil.
+//
+// Position information is recorded in the file set fset, which must not be
+// nil.
+//
+// If the source couldn't be read, the returned AST is nil and the error
+// indicates the specific failure. If the source was read but syntax
+// errors were found, the result is a partial AST (with ast.Bad* nodes
+// representing the fragments of erroneous source code). Multiple errors
+// are returned via a scanner.ErrorList which is sorted by source position.
+func ParseFile(fset *token.FileSet, filename string, src any, mode Mode) (f *ast.File, err error) {
+	if fset == nil {
+		panic("parser.ParseFile: no token.FileSet provided (fset == nil)")
+	}
+
+	// get source
+	text, err := readSource(filename, src)
+	if err != nil {
+		return nil, err
+	}
+
+	var p parser
+	defer func() {
+		if e := recover(); e != nil {
+			// resume same panic if it's not a bailout
+			bail, ok := e.(bailout)
+			if !ok {
+				panic(e)
+			} else if bail.msg != "" {
+				p.errors.Add(p.file.Position(bail.pos), bail.msg)
+			}
+		}
+
+		// set result values
+		if f == nil {
+			// source is not a valid Go source file - satisfy
+			// ParseFile API and return a valid (but) empty
+			// *ast.File
+			f = &ast.File{
+				Name:  new(ast.Ident),
+				Scope: ast.NewScope(nil),
+			}
+		}
+
+		p.errors.Sort()
+		err = p.errors.Err()
+	}()
+
+	// parse source
+	p.init(fset, filename, text, mode)
+	f = p.parseFile()
+
+	return
+}
+
+// ParseDir calls ParseFile for all files with names ending in ".go" in the
+// directory specified by path and returns a map of package name -> package
+// AST with all the packages found.
+//
+// If filter != nil, only the files with fs.FileInfo entries passing through
+// the filter (and ending in ".go") are considered. The mode bits are passed
+// to ParseFile unchanged. Position information is recorded in fset, which
+// must not be nil.
+//
+// If the directory couldn't be read, a nil map and the respective error are
+// returned. If a parse error occurred, a non-nil but incomplete map and the
+// first error encountered are returned.
+func ParseDir(fset *token.FileSet, path string, filter func(fs.FileInfo) bool, mode Mode) (pkgs map[string]*ast.Package, first error) {
+	list, err := os.ReadDir(path)
+	if err != nil {
+		return nil, err
+	}
+
+	pkgs = make(map[string]*ast.Package)
+	for _, d := range list {
+		if d.IsDir() || !strings.HasSuffix(d.Name(), ".go") {
+			continue
+		}
+		if filter != nil {
+			info, err := d.Info()
+			if err != nil {
+				return nil, err
+			}
+			if !filter(info) {
+				continue
+			}
+		}
+		filename := filepath.Join(path, d.Name())
+		if src, err := ParseFile(fset, filename, nil, mode); err == nil {
+			name := src.Name.Name
+			pkg, found := pkgs[name]
+			if !found {
+				pkg = &ast.Package{
+					Name:  name,
+					Files: make(map[string]*ast.File),
+				}
+				pkgs[name] = pkg
+			}
+			pkg.Files[filename] = src
+		} else if first == nil {
+			first = err
+		}
+	}
+
+	return
+}
+
+// ParseExprFrom is a convenience function for parsing an expression.
+// The arguments have the same meaning as for ParseFile, but the source must
+// be a valid Go (type or value) expression. Specifically, fset must not
+// be nil.
+//
+// If the source couldn't be read, the returned AST is nil and the error
+// indicates the specific failure. If the source was read but syntax
+// errors were found, the result is a partial AST (with ast.Bad* nodes
+// representing the fragments of erroneous source code). Multiple errors
+// are returned via a scanner.ErrorList which is sorted by source position.
+func ParseExprFrom(fset *token.FileSet, filename string, src any, mode Mode) (expr ast.Expr, err error) {
+	if fset == nil {
+		panic("parser.ParseExprFrom: no token.FileSet provided (fset == nil)")
+	}
+
+	// get source
+	text, err := readSource(filename, src)
+	if err != nil {
+		return nil, err
+	}
+
+	var p parser
+	defer func() {
+		if e := recover(); e != nil {
+			// resume same panic if it's not a bailout
+			bail, ok := e.(bailout)
+			if !ok {
+				panic(e)
+			} else if bail.msg != "" {
+				p.errors.Add(p.file.Position(bail.pos), bail.msg)
+			}
+		}
+		p.errors.Sort()
+		err = p.errors.Err()
+	}()
+
+	// parse expr
+	p.init(fset, filename, text, mode)
+	expr = p.parseRhs()
+
+	// If a semicolon was inserted, consume it;
+	// report an error if there's more tokens.
+	if p.tok == token.SEMICOLON && p.lit == "\n" {
+		p.next()
+	}
+	p.expect(token.EOF)
+
+	return
+}
+
+// ParseExpr is a convenience function for obtaining the AST of an expression x.
+// The position information recorded in the AST is undefined. The filename used
+// in error messages is the empty string.
+//
+// If syntax errors were found, the result is a partial AST (with ast.Bad* nodes
+// representing the fragments of erroneous source code). Multiple errors are
+// returned via a scanner.ErrorList which is sorted by source position.
+func ParseExpr(x string) (ast.Expr, error) {
+	return ParseExprFrom(token.NewFileSet(), "", []byte(x), 0)
+}
diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go
new file mode 100644
index 0000000..e1d941e
--- /dev/null
+++ b/src/go/parser/parser.go
@@ -0,0 +1,2882 @@
+// 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.
+//
+// The parser accepts a larger language than is syntactically permitted by
+// the Go spec, for simplicity, and for improved robustness in the presence
+// of syntax errors. For instance, in method declarations, the receiver is
+// treated like an ordinary parameter list and thus may contain multiple
+// entries where the spec permits exactly one. Consequently, the corresponding
+// field in the AST (ast.FuncDecl.Recv) field is not restricted to one entry.
+package parser
+
+import (
+	"fmt"
+	"go/ast"
+	"go/build/constraint"
+	"go/internal/typeparams"
+	"go/scanner"
+	"go/token"
+	"strings"
+)
+
+// The parser structure holds the parser's internal state.
+type parser struct {
+	file    *token.File
+	errors  scanner.ErrorList
+	scanner scanner.Scanner
+
+	// Tracing/debugging
+	mode   Mode // parsing mode
+	trace  bool // == (mode&Trace != 0)
+	indent int  // indentation used for tracing output
+
+	// Comments
+	comments    []*ast.CommentGroup
+	leadComment *ast.CommentGroup // last lead comment
+	lineComment *ast.CommentGroup // last line comment
+	top         bool              // in top of file (before package clause)
+	goVersion   string            // minimum Go version found in //go:build comment
+
+	// Next token
+	pos token.Pos   // token position
+	tok token.Token // one token look-ahead
+	lit string      // token literal
+
+	// Error recovery
+	// (used to limit the number of calls to parser.advance
+	// w/o making scanning progress - avoids potential endless
+	// loops across multiple parser functions during error recovery)
+	syncPos token.Pos // last synchronization position
+	syncCnt int       // number of parser.advance calls without progress
+
+	// Non-syntactic parser control
+	exprLev int  // < 0: in control clause, >= 0: in expression
+	inRhs   bool // if set, the parser is parsing a rhs expression
+
+	imports []*ast.ImportSpec // list of imports
+
+	// nestLev is used to track and limit the recursion depth
+	// during parsing.
+	nestLev int
+}
+
+func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode Mode) {
+	p.file = fset.AddFile(filename, -1, len(src))
+	eh := func(pos token.Position, msg string) { p.errors.Add(pos, msg) }
+	p.scanner.Init(p.file, src, eh, scanner.ScanComments)
+
+	p.top = true
+	p.mode = mode
+	p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
+	p.next()
+}
+
+// ----------------------------------------------------------------------------
+// Parsing support
+
+func (p *parser) printTrace(a ...any) {
+	const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
+	const n = len(dots)
+	pos := p.file.Position(p.pos)
+	fmt.Printf("%5d:%3d: ", pos.Line, pos.Column)
+	i := 2 * p.indent
+	for i > n {
+		fmt.Print(dots)
+		i -= n
+	}
+	// i <= n
+	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(")")
+}
+
+// maxNestLev is the deepest we're willing to recurse during parsing
+const maxNestLev int = 1e5
+
+func incNestLev(p *parser) *parser {
+	p.nestLev++
+	if p.nestLev > maxNestLev {
+		p.error(p.pos, "exceeded max nesting depth")
+		panic(bailout{})
+	}
+	return p
+}
+
+// decNestLev is used to track nesting depth during parsing to prevent stack exhaustion.
+// It is used along with incNestLev in a similar fashion to how un and trace are used.
+func decNestLev(p *parser) {
+	p.nestLev--
+}
+
+// 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)
+		}
+	}
+
+	for {
+		p.pos, p.tok, p.lit = p.scanner.Scan()
+		if p.tok == token.COMMENT {
+			if p.top && strings.HasPrefix(p.lit, "//go:build") {
+				if x, err := constraint.Parse(p.lit); err == nil {
+					p.goVersion = constraint.GoVersion(x)
+				}
+			}
+			if p.mode&ParseComments == 0 {
+				continue
+			}
+		} else {
+			// Found a non-comment; top of file is over.
+			p.top = false
+		}
+		break
+	}
+}
+
+// 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{Slash: p.pos, Text: 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. A non-comment token or n
+// empty lines terminate a comment group.
+func (p *parser) consumeCommentGroup(n int) (comments *ast.CommentGroup, endline int) {
+	var list []*ast.Comment
+	endline = p.file.Line(p.pos)
+	for p.tok == token.COMMENT && p.file.Line(p.pos) <= endline+n {
+		var comment *ast.Comment
+		comment, endline = p.consumeComment()
+		list = append(list, comment)
+	}
+
+	// add comment group to the comments list
+	comments = &ast.CommentGroup{List: 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
+	prev := p.pos
+	p.next0()
+
+	if p.tok == token.COMMENT {
+		var comment *ast.CommentGroup
+		var endline int
+
+		if p.file.Line(p.pos) == p.file.Line(prev) {
+			// 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(0)
+			if p.file.Line(p.pos) != endline || p.tok == token.SEMICOLON || p.tok == token.EOF {
+				// 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(1)
+		}
+
+		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
+		}
+	}
+}
+
+// A bailout panic is raised to indicate early termination. pos and msg are
+// only populated when bailing out of object resolution.
+type bailout struct {
+	pos token.Pos
+	msg string
+}
+
+func (p *parser) error(pos token.Pos, msg string) {
+	if p.trace {
+		defer un(trace(p, "error: "+msg))
+	}
+
+	epos := p.file.Position(pos)
+
+	// If AllErrors is not set, discard errors reported on the same line
+	// as the last recorded error and stop parsing if there are more than
+	// 10 errors.
+	if p.mode&AllErrors == 0 {
+		n := len(p.errors)
+		if n > 0 && p.errors[n-1].Pos.Line == epos.Line {
+			return // discard - likely a spurious error
+		}
+		if n > 10 {
+			panic(bailout{})
+		}
+	}
+
+	p.errors.Add(epos, 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
+		switch {
+		case p.tok == token.SEMICOLON && p.lit == "\n":
+			msg += ", found newline"
+		case p.tok.IsLiteral():
+			// print 123 rather than 'INT', etc.
+			msg += ", found " + p.lit
+		default:
+			msg += ", found '" + p.tok.String() + "'"
+		}
+	}
+	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
+}
+
+// expect2 is like expect, but it returns an invalid position
+// if the expected token is not found.
+func (p *parser) expect2(tok token.Token) (pos token.Pos) {
+	if p.tok == tok {
+		pos = p.pos
+	} else {
+		p.errorExpected(p.pos, "'"+tok.String()+"'")
+	}
+	p.next() // make progress
+	return
+}
+
+// expectClosing is like expect but provides a better error message
+// for the common case of a missing comma before a newline.
+func (p *parser) expectClosing(tok token.Token, context string) token.Pos {
+	if p.tok != tok && p.tok == token.SEMICOLON && p.lit == "\n" {
+		p.error(p.pos, "missing ',' before newline in "+context)
+		p.next()
+	}
+	return p.expect(tok)
+}
+
+// expectSemi consumes a semicolon and returns the applicable line comment.
+func (p *parser) expectSemi() (comment *ast.CommentGroup) {
+	// semicolon is optional before a closing ')' or '}'
+	if p.tok != token.RPAREN && p.tok != token.RBRACE {
+		switch p.tok {
+		case token.COMMA:
+			// permit a ',' instead of a ';' but complain
+			p.errorExpected(p.pos, "';'")
+			fallthrough
+		case token.SEMICOLON:
+			if p.lit == ";" {
+				// explicit semicolon
+				p.next()
+				comment = p.lineComment // use following comments
+			} else {
+				// artificial semicolon
+				comment = p.lineComment // use preceding comments
+				p.next()
+			}
+			return comment
+		default:
+			p.errorExpected(p.pos, "';'")
+			p.advance(stmtStart)
+		}
+	}
+	return nil
+}
+
+func (p *parser) atComma(context string, follow token.Token) bool {
+	if p.tok == token.COMMA {
+		return true
+	}
+	if p.tok != follow {
+		msg := "missing ','"
+		if p.tok == token.SEMICOLON && p.lit == "\n" {
+			msg += " before newline"
+		}
+		p.error(p.pos, msg+" in "+context)
+		return true // "insert" comma and continue
+	}
+	return false
+}
+
+func assert(cond bool, msg string) {
+	if !cond {
+		panic("go/parser internal error: " + msg)
+	}
+}
+
+// advance consumes tokens until the current token p.tok
+// is in the 'to' set, or token.EOF. For error recovery.
+func (p *parser) advance(to map[token.Token]bool) {
+	for ; p.tok != token.EOF; p.next() {
+		if to[p.tok] {
+			// Return only if parser made some progress since last
+			// sync or if it has not reached 10 advance calls without
+			// progress. Otherwise consume at least one token to
+			// avoid an endless parser loop (it is possible that
+			// both parseOperand and parseStmt call advance and
+			// correctly do not advance, thus the need for the
+			// invocation limit p.syncCnt).
+			if p.pos == p.syncPos && p.syncCnt < 10 {
+				p.syncCnt++
+				return
+			}
+			if p.pos > p.syncPos {
+				p.syncPos = p.pos
+				p.syncCnt = 0
+				return
+			}
+			// Reaching here indicates a parser bug, likely an
+			// incorrect token list in this function, but it only
+			// leads to skipping of possibly correct code if a
+			// previous error is present, and thus is preferred
+			// over a non-terminating parse.
+		}
+	}
+}
+
+var stmtStart = map[token.Token]bool{
+	token.BREAK:       true,
+	token.CONST:       true,
+	token.CONTINUE:    true,
+	token.DEFER:       true,
+	token.FALLTHROUGH: true,
+	token.FOR:         true,
+	token.GO:          true,
+	token.GOTO:        true,
+	token.IF:          true,
+	token.RETURN:      true,
+	token.SELECT:      true,
+	token.SWITCH:      true,
+	token.TYPE:        true,
+	token.VAR:         true,
+}
+
+var declStart = map[token.Token]bool{
+	token.IMPORT: true,
+	token.CONST:  true,
+	token.TYPE:   true,
+	token.VAR:    true,
+}
+
+var exprEnd = map[token.Token]bool{
+	token.COMMA:     true,
+	token.COLON:     true,
+	token.SEMICOLON: true,
+	token.RPAREN:    true,
+	token.RBRACK:    true,
+	token.RBRACE:    true,
+}
+
+// safePos returns a valid file position for a given position: If pos
+// is valid to begin with, safePos returns pos. If pos is out-of-range,
+// safePos returns the EOF position.
+//
+// This is hack to work around "artificial" end positions in the AST which
+// are computed by adding 1 to (presumably valid) token positions. If the
+// token positions are invalid due to parse errors, the resulting end position
+// may be past the file's EOF position, which would lead to panics if used
+// later on.
+func (p *parser) safePos(pos token.Pos) (res token.Pos) {
+	defer func() {
+		if recover() != nil {
+			res = token.Pos(p.file.Base() + p.file.Size()) // EOF position
+		}
+	}()
+	_ = p.file.Offset(pos) // trigger a panic if position is out-of-range
+	return pos
+}
+
+// ----------------------------------------------------------------------------
+// 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{NamePos: pos, Name: name}
+}
+
+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() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ExpressionList"))
+	}
+
+	list = append(list, p.parseExpr())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseExpr())
+	}
+
+	return
+}
+
+func (p *parser) parseList(inRhs bool) []ast.Expr {
+	old := p.inRhs
+	p.inRhs = inRhs
+	list := p.parseExprList()
+	p.inRhs = old
+	return list
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+func (p *parser) parseType() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Type"))
+	}
+
+	typ := p.tryIdentOrType()
+
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.advance(exprEnd)
+		return &ast.BadExpr{From: pos, To: p.pos}
+	}
+
+	return typ
+}
+
+func (p *parser) parseQualifiedIdent(ident *ast.Ident) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "QualifiedIdent"))
+	}
+
+	typ := p.parseTypeName(ident)
+	if p.tok == token.LBRACK {
+		typ = p.parseTypeInstance(typ)
+	}
+
+	return typ
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) parseTypeName(ident *ast.Ident) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeName"))
+	}
+
+	if ident == nil {
+		ident = p.parseIdent()
+	}
+
+	if p.tok == token.PERIOD {
+		// ident is a package name
+		p.next()
+		sel := p.parseIdent()
+		return &ast.SelectorExpr{X: ident, Sel: sel}
+	}
+
+	return ident
+}
+
+// "[" has already been consumed, and lbrack is its position.
+// If len != nil it is the already consumed array length.
+func (p *parser) parseArrayType(lbrack token.Pos, len ast.Expr) *ast.ArrayType {
+	if p.trace {
+		defer un(trace(p, "ArrayType"))
+	}
+
+	if len == nil {
+		p.exprLev++
+		// always permit ellipsis for more fault-tolerant parsing
+		if p.tok == token.ELLIPSIS {
+			len = &ast.Ellipsis{Ellipsis: p.pos}
+			p.next()
+		} else if p.tok != token.RBRACK {
+			len = p.parseRhs()
+		}
+		p.exprLev--
+	}
+	if p.tok == token.COMMA {
+		// Trailing commas are accepted in type parameter
+		// lists but not in array type declarations.
+		// Accept for better error handling but complain.
+		p.error(p.pos, "unexpected comma; expecting ]")
+		p.next()
+	}
+	p.expect(token.RBRACK)
+	elt := p.parseType()
+	return &ast.ArrayType{Lbrack: lbrack, Len: len, Elt: elt}
+}
+
+func (p *parser) parseArrayFieldOrTypeInstance(x *ast.Ident) (*ast.Ident, ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ArrayFieldOrTypeInstance"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	trailingComma := token.NoPos // if valid, the position of a trailing comma preceding the ']'
+	var args []ast.Expr
+	if p.tok != token.RBRACK {
+		p.exprLev++
+		args = append(args, p.parseRhs())
+		for p.tok == token.COMMA {
+			comma := p.pos
+			p.next()
+			if p.tok == token.RBRACK {
+				trailingComma = comma
+				break
+			}
+			args = append(args, p.parseRhs())
+		}
+		p.exprLev--
+	}
+	rbrack := p.expect(token.RBRACK)
+
+	if len(args) == 0 {
+		// x []E
+		elt := p.parseType()
+		return x, &ast.ArrayType{Lbrack: lbrack, Elt: elt}
+	}
+
+	// x [P]E or x[P]
+	if len(args) == 1 {
+		elt := p.tryIdentOrType()
+		if elt != nil {
+			// x [P]E
+			if trailingComma.IsValid() {
+				// Trailing commas are invalid in array type fields.
+				p.error(trailingComma, "unexpected comma; expecting ]")
+			}
+			return x, &ast.ArrayType{Lbrack: lbrack, Len: args[0], Elt: elt}
+		}
+	}
+
+	// x[P], x[P1, P2], ...
+	return nil, typeparams.PackIndexExpr(x, lbrack, args, rbrack)
+}
+
+func (p *parser) parseFieldDecl() *ast.Field {
+	if p.trace {
+		defer un(trace(p, "FieldDecl"))
+	}
+
+	doc := p.leadComment
+
+	var names []*ast.Ident
+	var typ ast.Expr
+	switch p.tok {
+	case token.IDENT:
+		name := p.parseIdent()
+		if p.tok == token.PERIOD || p.tok == token.STRING || p.tok == token.SEMICOLON || p.tok == token.RBRACE {
+			// embedded type
+			typ = name
+			if p.tok == token.PERIOD {
+				typ = p.parseQualifiedIdent(name)
+			}
+		} else {
+			// name1, name2, ... T
+			names = []*ast.Ident{name}
+			for p.tok == token.COMMA {
+				p.next()
+				names = append(names, p.parseIdent())
+			}
+			// Careful dance: We don't know if we have an embedded instantiated
+			// type T[P1, P2, ...] or a field T of array type []E or [P]E.
+			if len(names) == 1 && p.tok == token.LBRACK {
+				name, typ = p.parseArrayFieldOrTypeInstance(name)
+				if name == nil {
+					names = nil
+				}
+			} else {
+				// T P
+				typ = p.parseType()
+			}
+		}
+	case token.MUL:
+		star := p.pos
+		p.next()
+		if p.tok == token.LPAREN {
+			// *(T)
+			p.error(p.pos, "cannot parenthesize embedded type")
+			p.next()
+			typ = p.parseQualifiedIdent(nil)
+			// expect closing ')' but no need to complain if missing
+			if p.tok == token.RPAREN {
+				p.next()
+			}
+		} else {
+			// *T
+			typ = p.parseQualifiedIdent(nil)
+		}
+		typ = &ast.StarExpr{Star: star, X: typ}
+
+	case token.LPAREN:
+		p.error(p.pos, "cannot parenthesize embedded type")
+		p.next()
+		if p.tok == token.MUL {
+			// (*T)
+			star := p.pos
+			p.next()
+			typ = &ast.StarExpr{Star: star, X: p.parseQualifiedIdent(nil)}
+		} else {
+			// (T)
+			typ = p.parseQualifiedIdent(nil)
+		}
+		// expect closing ')' but no need to complain if missing
+		if p.tok == token.RPAREN {
+			p.next()
+		}
+
+	default:
+		pos := p.pos
+		p.errorExpected(pos, "field name or embedded type")
+		p.advance(exprEnd)
+		typ = &ast.BadExpr{From: pos, To: p.pos}
+	}
+
+	var tag *ast.BasicLit
+	if p.tok == token.STRING {
+		tag = &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
+		p.next()
+	}
+
+	comment := p.expectSemi()
+
+	field := &ast.Field{Doc: doc, Names: names, Type: typ, Tag: tag, Comment: comment}
+	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)
+	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())
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.StructType{
+		Struct: pos,
+		Fields: &ast.FieldList{
+			Opening: lbrace,
+			List:    list,
+			Closing: rbrace,
+		},
+	}
+}
+
+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: star, X: base}
+}
+
+func (p *parser) parseDotsType() *ast.Ellipsis {
+	if p.trace {
+		defer un(trace(p, "DotsType"))
+	}
+
+	pos := p.expect(token.ELLIPSIS)
+	elt := p.parseType()
+
+	return &ast.Ellipsis{Ellipsis: pos, Elt: elt}
+}
+
+type field struct {
+	name *ast.Ident
+	typ  ast.Expr
+}
+
+func (p *parser) parseParamDecl(name *ast.Ident, typeSetsOK bool) (f field) {
+	// TODO(rFindley) refactor to be more similar to paramDeclOrNil in the syntax
+	// package
+	if p.trace {
+		defer un(trace(p, "ParamDeclOrNil"))
+	}
+
+	ptok := p.tok
+	if name != nil {
+		p.tok = token.IDENT // force token.IDENT case in switch below
+	} else if typeSetsOK && p.tok == token.TILDE {
+		// "~" ...
+		return field{nil, p.embeddedElem(nil)}
+	}
+
+	switch p.tok {
+	case token.IDENT:
+		// name
+		if name != nil {
+			f.name = name
+			p.tok = ptok
+		} else {
+			f.name = p.parseIdent()
+		}
+		switch p.tok {
+		case token.IDENT, token.MUL, token.ARROW, token.FUNC, token.CHAN, token.MAP, token.STRUCT, token.INTERFACE, token.LPAREN:
+			// name type
+			f.typ = p.parseType()
+
+		case token.LBRACK:
+			// name "[" type1, ..., typeN "]" or name "[" n "]" type
+			f.name, f.typ = p.parseArrayFieldOrTypeInstance(f.name)
+
+		case token.ELLIPSIS:
+			// name "..." type
+			f.typ = p.parseDotsType()
+			return // don't allow ...type "|" ...
+
+		case token.PERIOD:
+			// name "." ...
+			f.typ = p.parseQualifiedIdent(f.name)
+			f.name = nil
+
+		case token.TILDE:
+			if typeSetsOK {
+				f.typ = p.embeddedElem(nil)
+				return
+			}
+
+		case token.OR:
+			if typeSetsOK {
+				// name "|" typeset
+				f.typ = p.embeddedElem(f.name)
+				f.name = nil
+				return
+			}
+		}
+
+	case token.MUL, token.ARROW, token.FUNC, token.LBRACK, token.CHAN, token.MAP, token.STRUCT, token.INTERFACE, token.LPAREN:
+		// type
+		f.typ = p.parseType()
+
+	case token.ELLIPSIS:
+		// "..." type
+		// (always accepted)
+		f.typ = p.parseDotsType()
+		return // don't allow ...type "|" ...
+
+	default:
+		// TODO(rfindley): this is incorrect in the case of type parameter lists
+		//                 (should be "']'" in that case)
+		p.errorExpected(p.pos, "')'")
+		p.advance(exprEnd)
+	}
+
+	// [name] type "|"
+	if typeSetsOK && p.tok == token.OR && f.typ != nil {
+		f.typ = p.embeddedElem(f.typ)
+	}
+
+	return
+}
+
+func (p *parser) parseParameterList(name0 *ast.Ident, typ0 ast.Expr, closing token.Token) (params []*ast.Field) {
+	if p.trace {
+		defer un(trace(p, "ParameterList"))
+	}
+
+	// Type parameters are the only parameter list closed by ']'.
+	tparams := closing == token.RBRACK
+	// Type set notation is ok in type parameter lists.
+	typeSetsOK := tparams
+
+	pos := p.pos
+	if name0 != nil {
+		pos = name0.Pos()
+	}
+
+	var list []field
+	var named int // number of parameters that have an explicit name and type
+
+	for name0 != nil || p.tok != closing && p.tok != token.EOF {
+		var par field
+		if typ0 != nil {
+			if typeSetsOK {
+				typ0 = p.embeddedElem(typ0)
+			}
+			par = field{name0, typ0}
+		} else {
+			par = p.parseParamDecl(name0, typeSetsOK)
+		}
+		name0 = nil // 1st name was consumed if present
+		typ0 = nil  // 1st typ was consumed if present
+		if par.name != nil || par.typ != nil {
+			list = append(list, par)
+			if par.name != nil && par.typ != nil {
+				named++
+			}
+		}
+		if !p.atComma("parameter list", closing) {
+			break
+		}
+		p.next()
+	}
+
+	if len(list) == 0 {
+		return // not uncommon
+	}
+
+	// TODO(gri) parameter distribution and conversion to []*ast.Field
+	//           can be combined and made more efficient
+
+	// distribute parameter types
+	if named == 0 {
+		// all unnamed => found names are type names
+		for i := 0; i < len(list); i++ {
+			par := &list[i]
+			if typ := par.name; typ != nil {
+				par.typ = typ
+				par.name = nil
+			}
+		}
+		if tparams {
+			p.error(pos, "type parameters must be named")
+		}
+	} else if named != len(list) {
+		// some named => all must be named
+		ok := true
+		var typ ast.Expr
+		missingName := pos
+		for i := len(list) - 1; i >= 0; i-- {
+			if par := &list[i]; par.typ != nil {
+				typ = par.typ
+				if par.name == nil {
+					ok = false
+					missingName = par.typ.Pos()
+					n := ast.NewIdent("_")
+					n.NamePos = typ.Pos() // correct position
+					par.name = n
+				}
+			} else if typ != nil {
+				par.typ = typ
+			} else {
+				// par.typ == nil && typ == nil => we only have a par.name
+				ok = false
+				missingName = par.name.Pos()
+				par.typ = &ast.BadExpr{From: par.name.Pos(), To: p.pos}
+			}
+		}
+		if !ok {
+			if tparams {
+				p.error(missingName, "type parameters must be named")
+			} else {
+				p.error(pos, "mixed named and unnamed parameters")
+			}
+		}
+	}
+
+	// convert list []*ast.Field
+	if named == 0 {
+		// parameter list consists of types only
+		for _, par := range list {
+			assert(par.typ != nil, "nil type in unnamed parameter list")
+			params = append(params, &ast.Field{Type: par.typ})
+		}
+		return
+	}
+
+	// parameter list consists of named parameters with types
+	var names []*ast.Ident
+	var typ ast.Expr
+	addParams := func() {
+		assert(typ != nil, "nil type in named parameter list")
+		field := &ast.Field{Names: names, Type: typ}
+		params = append(params, field)
+		names = nil
+	}
+	for _, par := range list {
+		if par.typ != typ {
+			if len(names) > 0 {
+				addParams()
+			}
+			typ = par.typ
+		}
+		names = append(names, par.name)
+	}
+	if len(names) > 0 {
+		addParams()
+	}
+	return
+}
+
+func (p *parser) parseParameters(acceptTParams bool) (tparams, params *ast.FieldList) {
+	if p.trace {
+		defer un(trace(p, "Parameters"))
+	}
+
+	if acceptTParams && p.tok == token.LBRACK {
+		opening := p.pos
+		p.next()
+		// [T any](params) syntax
+		list := p.parseParameterList(nil, nil, token.RBRACK)
+		rbrack := p.expect(token.RBRACK)
+		tparams = &ast.FieldList{Opening: opening, List: list, Closing: rbrack}
+		// Type parameter lists must not be empty.
+		if tparams.NumFields() == 0 {
+			p.error(tparams.Closing, "empty type parameter list")
+			tparams = nil // avoid follow-on errors
+		}
+	}
+
+	opening := p.expect(token.LPAREN)
+
+	var fields []*ast.Field
+	if p.tok != token.RPAREN {
+		fields = p.parseParameterList(nil, nil, token.RPAREN)
+	}
+
+	rparen := p.expect(token.RPAREN)
+	params = &ast.FieldList{Opening: opening, List: fields, Closing: rparen}
+
+	return
+}
+
+func (p *parser) parseResult() *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Result"))
+	}
+
+	if p.tok == token.LPAREN {
+		_, results := p.parseParameters(false)
+		return results
+	}
+
+	typ := p.tryIdentOrType()
+	if typ != nil {
+		list := make([]*ast.Field, 1)
+		list[0] = &ast.Field{Type: typ}
+		return &ast.FieldList{List: list}
+	}
+
+	return nil
+}
+
+func (p *parser) parseFuncType() *ast.FuncType {
+	if p.trace {
+		defer un(trace(p, "FuncType"))
+	}
+
+	pos := p.expect(token.FUNC)
+	tparams, params := p.parseParameters(true)
+	if tparams != nil {
+		p.error(tparams.Pos(), "function type must have no type parameters")
+	}
+	results := p.parseResult()
+
+	return &ast.FuncType{Func: pos, Params: params, Results: results}
+}
+
+func (p *parser) parseMethodSpec() *ast.Field {
+	if p.trace {
+		defer un(trace(p, "MethodSpec"))
+	}
+
+	doc := p.leadComment
+	var idents []*ast.Ident
+	var typ ast.Expr
+	x := p.parseTypeName(nil)
+	if ident, _ := x.(*ast.Ident); ident != nil {
+		switch {
+		case p.tok == token.LBRACK:
+			// generic method or embedded instantiated type
+			lbrack := p.pos
+			p.next()
+			p.exprLev++
+			x := p.parseExpr()
+			p.exprLev--
+			if name0, _ := x.(*ast.Ident); name0 != nil && p.tok != token.COMMA && p.tok != token.RBRACK {
+				// generic method m[T any]
+				//
+				// Interface methods do not have type parameters. We parse them for a
+				// better error message and improved error recovery.
+				_ = p.parseParameterList(name0, nil, token.RBRACK)
+				_ = p.expect(token.RBRACK)
+				p.error(lbrack, "interface method must have no type parameters")
+
+				// TODO(rfindley) refactor to share code with parseFuncType.
+				_, params := p.parseParameters(false)
+				results := p.parseResult()
+				idents = []*ast.Ident{ident}
+				typ = &ast.FuncType{
+					Func:    token.NoPos,
+					Params:  params,
+					Results: results,
+				}
+			} else {
+				// embedded instantiated type
+				// TODO(rfindley) should resolve all identifiers in x.
+				list := []ast.Expr{x}
+				if p.atComma("type argument list", token.RBRACK) {
+					p.exprLev++
+					p.next()
+					for p.tok != token.RBRACK && p.tok != token.EOF {
+						list = append(list, p.parseType())
+						if !p.atComma("type argument list", token.RBRACK) {
+							break
+						}
+						p.next()
+					}
+					p.exprLev--
+				}
+				rbrack := p.expectClosing(token.RBRACK, "type argument list")
+				typ = typeparams.PackIndexExpr(ident, lbrack, list, rbrack)
+			}
+		case p.tok == token.LPAREN:
+			// ordinary method
+			// TODO(rfindley) refactor to share code with parseFuncType.
+			_, params := p.parseParameters(false)
+			results := p.parseResult()
+			idents = []*ast.Ident{ident}
+			typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
+		default:
+			// embedded type
+			typ = x
+		}
+	} else {
+		// embedded, possibly instantiated type
+		typ = x
+		if p.tok == token.LBRACK {
+			// embedded instantiated interface
+			typ = p.parseTypeInstance(typ)
+		}
+	}
+
+	// Comment is added at the callsite: the field below may joined with
+	// additional type specs using '|'.
+	// TODO(rfindley) this should be refactored.
+	// TODO(rfindley) add more tests for comment handling.
+	return &ast.Field{Doc: doc, Names: idents, Type: typ}
+}
+
+func (p *parser) embeddedElem(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "EmbeddedElem"))
+	}
+	if x == nil {
+		x = p.embeddedTerm()
+	}
+	for p.tok == token.OR {
+		t := new(ast.BinaryExpr)
+		t.OpPos = p.pos
+		t.Op = token.OR
+		p.next()
+		t.X = x
+		t.Y = p.embeddedTerm()
+		x = t
+	}
+	return x
+}
+
+func (p *parser) embeddedTerm() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "EmbeddedTerm"))
+	}
+	if p.tok == token.TILDE {
+		t := new(ast.UnaryExpr)
+		t.OpPos = p.pos
+		t.Op = token.TILDE
+		p.next()
+		t.X = p.parseType()
+		return t
+	}
+
+	t := p.tryIdentOrType()
+	if t == nil {
+		pos := p.pos
+		p.errorExpected(pos, "~ term or type")
+		p.advance(exprEnd)
+		return &ast.BadExpr{From: pos, To: p.pos}
+	}
+
+	return t
+}
+
+func (p *parser) parseInterfaceType() *ast.InterfaceType {
+	if p.trace {
+		defer un(trace(p, "InterfaceType"))
+	}
+
+	pos := p.expect(token.INTERFACE)
+	lbrace := p.expect(token.LBRACE)
+
+	var list []*ast.Field
+
+parseElements:
+	for {
+		switch {
+		case p.tok == token.IDENT:
+			f := p.parseMethodSpec()
+			if f.Names == nil {
+				f.Type = p.embeddedElem(f.Type)
+			}
+			f.Comment = p.expectSemi()
+			list = append(list, f)
+		case p.tok == token.TILDE:
+			typ := p.embeddedElem(nil)
+			comment := p.expectSemi()
+			list = append(list, &ast.Field{Type: typ, Comment: comment})
+		default:
+			if t := p.tryIdentOrType(); t != nil {
+				typ := p.embeddedElem(t)
+				comment := p.expectSemi()
+				list = append(list, &ast.Field{Type: typ, Comment: comment})
+			} else {
+				break parseElements
+			}
+		}
+	}
+
+	// TODO(rfindley): the error produced here could be improved, since we could
+	// accept an identifier, 'type', or a '}' at this point.
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.InterfaceType{
+		Interface: pos,
+		Methods: &ast.FieldList{
+			Opening: lbrace,
+			List:    list,
+			Closing: rbrace,
+		},
+	}
+}
+
+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{Map: pos, Key: key, Value: value}
+}
+
+func (p *parser) parseChanType() *ast.ChanType {
+	if p.trace {
+		defer un(trace(p, "ChanType"))
+	}
+
+	pos := p.pos
+	dir := ast.SEND | ast.RECV
+	var arrow token.Pos
+	if p.tok == token.CHAN {
+		p.next()
+		if p.tok == token.ARROW {
+			arrow = p.pos
+			p.next()
+			dir = ast.SEND
+		}
+	} else {
+		arrow = p.expect(token.ARROW)
+		p.expect(token.CHAN)
+		dir = ast.RECV
+	}
+	value := p.parseType()
+
+	return &ast.ChanType{Begin: pos, Arrow: arrow, Dir: dir, Value: value}
+}
+
+func (p *parser) parseTypeInstance(typ ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeInstance"))
+	}
+
+	opening := p.expect(token.LBRACK)
+	p.exprLev++
+	var list []ast.Expr
+	for p.tok != token.RBRACK && p.tok != token.EOF {
+		list = append(list, p.parseType())
+		if !p.atComma("type argument list", token.RBRACK) {
+			break
+		}
+		p.next()
+	}
+	p.exprLev--
+
+	closing := p.expectClosing(token.RBRACK, "type argument list")
+
+	if len(list) == 0 {
+		p.errorExpected(closing, "type argument list")
+		return &ast.IndexExpr{
+			X:      typ,
+			Lbrack: opening,
+			Index:  &ast.BadExpr{From: opening + 1, To: closing},
+			Rbrack: closing,
+		}
+	}
+
+	return typeparams.PackIndexExpr(typ, opening, list, closing)
+}
+
+func (p *parser) tryIdentOrType() ast.Expr {
+	defer decNestLev(incNestLev(p))
+
+	switch p.tok {
+	case token.IDENT:
+		typ := p.parseTypeName(nil)
+		if p.tok == token.LBRACK {
+			typ = p.parseTypeInstance(typ)
+		}
+		return typ
+	case token.LBRACK:
+		lbrack := p.expect(token.LBRACK)
+		return p.parseArrayType(lbrack, nil)
+	case token.STRUCT:
+		return p.parseStructType()
+	case token.MUL:
+		return p.parsePointerType()
+	case token.FUNC:
+		return p.parseFuncType()
+	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: lparen, X: typ, Rparen: rparen}
+	}
+
+	// no type found
+	return nil
+}
+
+// ----------------------------------------------------------------------------
+// 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() *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "Body"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	list := p.parseStmtList()
+	rbrace := p.expect2(token.RBRACE)
+
+	return &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
+}
+
+func (p *parser) parseBlockStmt() *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "BlockStmt"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	list := p.parseStmtList()
+	rbrace := p.expect2(token.RBRACE)
+
+	return &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
+}
+
+// ----------------------------------------------------------------------------
+// Expressions
+
+func (p *parser) parseFuncTypeOrLit() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "FuncTypeOrLit"))
+	}
+
+	typ := p.parseFuncType()
+	if p.tok != token.LBRACE {
+		// function type only
+		return typ
+	}
+
+	p.exprLev++
+	body := p.parseBody()
+	p.exprLev--
+
+	return &ast.FuncLit{Type: typ, Body: body}
+}
+
+// parseOperand may return an expression or a raw type (incl. array
+// types of the form [...]T). Callers must verify the result.
+func (p *parser) parseOperand() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Operand"))
+	}
+
+	switch p.tok {
+	case token.IDENT:
+		x := p.parseIdent()
+		return x
+
+	case token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING:
+		x := &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
+		p.next()
+		return x
+
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		p.exprLev++
+		x := p.parseRhs() // types may be parenthesized: (some type)
+		p.exprLev--
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{Lparen: lparen, X: x, Rparen: rparen}
+
+	case token.FUNC:
+		return p.parseFuncTypeOrLit()
+	}
+
+	if typ := p.tryIdentOrType(); typ != nil { // do not consume trailing type parameters
+		// could be type for composite literal or conversion
+		_, isIdent := typ.(*ast.Ident)
+		assert(!isIdent, "type cannot be identifier")
+		return typ
+	}
+
+	// we have an error
+	pos := p.pos
+	p.errorExpected(pos, "operand")
+	p.advance(stmtStart)
+	return &ast.BadExpr{From: pos, To: 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: x, Sel: sel}
+}
+
+func (p *parser) parseTypeAssertion(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeAssertion"))
+	}
+
+	lparen := p.expect(token.LPAREN)
+	var typ ast.Expr
+	if p.tok == token.TYPE {
+		// type switch: typ == nil
+		p.next()
+	} else {
+		typ = p.parseType()
+	}
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.TypeAssertExpr{X: x, Type: typ, Lparen: lparen, Rparen: rparen}
+}
+
+func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "parseIndexOrSliceOrInstance"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	if p.tok == token.RBRACK {
+		// empty index, slice or index expressions are not permitted;
+		// accept them for parsing tolerance, but complain
+		p.errorExpected(p.pos, "operand")
+		rbrack := p.pos
+		p.next()
+		return &ast.IndexExpr{
+			X:      x,
+			Lbrack: lbrack,
+			Index:  &ast.BadExpr{From: rbrack, To: rbrack},
+			Rbrack: rbrack,
+		}
+	}
+	p.exprLev++
+
+	const N = 3 // change the 3 to 2 to disable 3-index slices
+	var args []ast.Expr
+	var index [N]ast.Expr
+	var colons [N - 1]token.Pos
+	if p.tok != token.COLON {
+		// We can't know if we have an index expression or a type instantiation;
+		// so even if we see a (named) type we are not going to be in type context.
+		index[0] = p.parseRhs()
+	}
+	ncolons := 0
+	switch p.tok {
+	case token.COLON:
+		// slice expression
+		for p.tok == token.COLON && ncolons < len(colons) {
+			colons[ncolons] = p.pos
+			ncolons++
+			p.next()
+			if p.tok != token.COLON && p.tok != token.RBRACK && p.tok != token.EOF {
+				index[ncolons] = p.parseRhs()
+			}
+		}
+	case token.COMMA:
+		// instance expression
+		args = append(args, index[0])
+		for p.tok == token.COMMA {
+			p.next()
+			if p.tok != token.RBRACK && p.tok != token.EOF {
+				args = append(args, p.parseType())
+			}
+		}
+	}
+
+	p.exprLev--
+	rbrack := p.expect(token.RBRACK)
+
+	if ncolons > 0 {
+		// slice expression
+		slice3 := false
+		if ncolons == 2 {
+			slice3 = true
+			// Check presence of middle and final index here rather than during type-checking
+			// to prevent erroneous programs from passing through gofmt (was issue 7305).
+			if index[1] == nil {
+				p.error(colons[0], "middle index required in 3-index slice")
+				index[1] = &ast.BadExpr{From: colons[0] + 1, To: colons[1]}
+			}
+			if index[2] == nil {
+				p.error(colons[1], "final index required in 3-index slice")
+				index[2] = &ast.BadExpr{From: colons[1] + 1, To: rbrack}
+			}
+		}
+		return &ast.SliceExpr{X: x, Lbrack: lbrack, Low: index[0], High: index[1], Max: index[2], Slice3: slice3, Rbrack: rbrack}
+	}
+
+	if len(args) == 0 {
+		// index expression
+		return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: rbrack}
+	}
+
+	// instance expression
+	return typeparams.PackIndexExpr(x, lbrack, args, 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()) // builtins may expect a type: make(some type, ...)
+		if p.tok == token.ELLIPSIS {
+			ellipsis = p.pos
+			p.next()
+		}
+		if !p.atComma("argument list", token.RPAREN) {
+			break
+		}
+		p.next()
+	}
+	p.exprLev--
+	rparen := p.expectClosing(token.RPAREN, "argument list")
+
+	return &ast.CallExpr{Fun: fun, Lparen: lparen, Args: list, Ellipsis: ellipsis, Rparen: rparen}
+}
+
+func (p *parser) parseValue() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Element"))
+	}
+
+	if p.tok == token.LBRACE {
+		return p.parseLiteralValue(nil)
+	}
+
+	x := p.parseExpr()
+
+	return x
+}
+
+func (p *parser) parseElement() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Element"))
+	}
+
+	x := p.parseValue()
+	if p.tok == token.COLON {
+		colon := p.pos
+		p.next()
+		x = &ast.KeyValueExpr{Key: x, Colon: colon, Value: p.parseValue()}
+	}
+
+	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())
+		if !p.atComma("composite literal", token.RBRACE) {
+			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.expectClosing(token.RBRACE, "composite literal")
+	return &ast.CompositeLit{Type: typ, Lbrace: lbrace, Elts: elts, Rbrace: rbrace}
+}
+
+// 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
+}
+
+func (p *parser) parsePrimaryExpr(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "PrimaryExpr"))
+	}
+
+	if x == nil {
+		x = p.parseOperand()
+	}
+	// We track the nesting here rather than at the entry for the function,
+	// since it can iteratively produce a nested output, and we want to
+	// limit how deep a structure we generate.
+	var n int
+	defer func() { p.nestLev -= n }()
+	for n = 1; ; n++ {
+		incNestLev(p)
+		switch p.tok {
+		case token.PERIOD:
+			p.next()
+			switch p.tok {
+			case token.IDENT:
+				x = p.parseSelector(x)
+			case token.LPAREN:
+				x = p.parseTypeAssertion(x)
+			default:
+				pos := p.pos
+				p.errorExpected(pos, "selector or type assertion")
+				// TODO(rFindley) The check for token.RBRACE below is a targeted fix
+				//                to error recovery sufficient to make the x/tools tests to
+				//                pass with the new parsing logic introduced for type
+				//                parameters. Remove this once error recovery has been
+				//                more generally reconsidered.
+				if p.tok != token.RBRACE {
+					p.next() // make progress
+				}
+				sel := &ast.Ident{NamePos: pos, Name: "_"}
+				x = &ast.SelectorExpr{X: x, Sel: sel}
+			}
+		case token.LBRACK:
+			x = p.parseIndexOrSliceOrInstance(x)
+		case token.LPAREN:
+			x = p.parseCallOrConversion(x)
+		case token.LBRACE:
+			// operand may have returned a parenthesized complit
+			// type; accept it but complain if we have a complit
+			t := unparen(x)
+			// determine if '{' belongs to a composite literal or a block statement
+			switch t.(type) {
+			case *ast.BadExpr, *ast.Ident, *ast.SelectorExpr:
+				if p.exprLev < 0 {
+					return x
+				}
+				// x is possibly a composite literal type
+			case *ast.IndexExpr, *ast.IndexListExpr:
+				if p.exprLev < 0 {
+					return x
+				}
+				// x is possibly a composite literal type
+			case *ast.ArrayType, *ast.StructType, *ast.MapType:
+				// x is a composite literal type
+			default:
+				return x
+			}
+			if t != x {
+				p.error(t.Pos(), "cannot parenthesize type in composite literal")
+				// already progressed, no need to advance
+			}
+			x = p.parseLiteralValue(x)
+		default:
+			return x
+		}
+	}
+}
+
+func (p *parser) parseUnaryExpr() ast.Expr {
+	defer decNestLev(incNestLev(p))
+
+	if p.trace {
+		defer un(trace(p, "UnaryExpr"))
+	}
+
+	switch p.tok {
+	case token.ADD, token.SUB, token.NOT, token.XOR, token.AND, token.TILDE:
+		pos, op := p.pos, p.tok
+		p.next()
+		x := p.parseUnaryExpr()
+		return &ast.UnaryExpr{OpPos: pos, Op: op, X: x}
+
+	case token.ARROW:
+		// channel type or receive expression
+		arrow := p.pos
+		p.next()
+
+		// If the next token is token.CHAN we still don't know if it
+		// is a channel type or a receive operation - we only know
+		// once we have found the end of the unary expression. There
+		// are two cases:
+		//
+		//   <- type  => (<-type) must be channel type
+		//   <- expr  => <-(expr) is a receive from an expression
+		//
+		// In the first case, the arrow must be re-associated with
+		// the channel type parsed already:
+		//
+		//   <- (chan type)    =>  (<-chan type)
+		//   <- (chan<- type)  =>  (<-chan (<-type))
+
+		x := p.parseUnaryExpr()
+
+		// determine which case we have
+		if typ, ok := x.(*ast.ChanType); ok {
+			// (<-type)
+
+			// re-associate position info and <-
+			dir := ast.SEND
+			for ok && dir == ast.SEND {
+				if typ.Dir == ast.RECV {
+					// error: (<-type) is (<-(<-chan T))
+					p.errorExpected(typ.Arrow, "'chan'")
+				}
+				arrow, typ.Begin, typ.Arrow = typ.Arrow, arrow, arrow
+				dir, typ.Dir = typ.Dir, ast.RECV
+				typ, ok = typ.Value.(*ast.ChanType)
+			}
+			if dir == ast.SEND {
+				p.errorExpected(arrow, "channel type")
+			}
+
+			return x
+		}
+
+		// <-(expr)
+		return &ast.UnaryExpr{OpPos: arrow, Op: token.ARROW, X: x}
+
+	case token.MUL:
+		// pointer type or unary "*" expression
+		pos := p.pos
+		p.next()
+		x := p.parseUnaryExpr()
+		return &ast.StarExpr{Star: pos, X: x}
+	}
+
+	return p.parsePrimaryExpr(nil)
+}
+
+func (p *parser) tokPrec() (token.Token, int) {
+	tok := p.tok
+	if p.inRhs && tok == token.ASSIGN {
+		tok = token.EQL
+	}
+	return tok, tok.Precedence()
+}
+
+// parseBinaryExpr parses a (possibly) binary expression.
+// If x is non-nil, it is used as the left operand.
+//
+// TODO(rfindley): parseBinaryExpr has become overloaded. Consider refactoring.
+func (p *parser) parseBinaryExpr(x ast.Expr, prec1 int) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "BinaryExpr"))
+	}
+
+	if x == nil {
+		x = p.parseUnaryExpr()
+	}
+	// We track the nesting here rather than at the entry for the function,
+	// since it can iteratively produce a nested output, and we want to
+	// limit how deep a structure we generate.
+	var n int
+	defer func() { p.nestLev -= n }()
+	for n = 1; ; n++ {
+		incNestLev(p)
+		op, oprec := p.tokPrec()
+		if oprec < prec1 {
+			return x
+		}
+		pos := p.expect(op)
+		y := p.parseBinaryExpr(nil, oprec+1)
+		x = &ast.BinaryExpr{X: x, OpPos: pos, Op: op, Y: y}
+	}
+}
+
+// The result may be a type or even a raw type ([...]int).
+func (p *parser) parseExpr() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Expression"))
+	}
+
+	return p.parseBinaryExpr(nil, token.LowestPrec+1)
+}
+
+func (p *parser) parseRhs() ast.Expr {
+	old := p.inRhs
+	p.inRhs = true
+	x := p.parseExpr()
+	p.inRhs = old
+	return x
+}
+
+// ----------------------------------------------------------------------------
+// Statements
+
+// Parsing modes for parseSimpleStmt.
+const (
+	basic = iota
+	labelOk
+	rangeOk
+)
+
+// parseSimpleStmt returns true as 2nd result if it parsed the assignment
+// of a range clause (with mode == rangeOk). The returned statement is an
+// assignment with a right-hand side that is a single unary expression of
+// the form "range x". No guarantees are given for the left-hand side.
+func (p *parser) parseSimpleStmt(mode int) (ast.Stmt, bool) {
+	if p.trace {
+		defer un(trace(p, "SimpleStmt"))
+	}
+
+	x := p.parseList(false)
+
+	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, possibly part of a range clause
+		pos, tok := p.pos, p.tok
+		p.next()
+		var y []ast.Expr
+		isRange := false
+		if mode == rangeOk && p.tok == token.RANGE && (tok == token.DEFINE || tok == token.ASSIGN) {
+			pos := p.pos
+			p.next()
+			y = []ast.Expr{&ast.UnaryExpr{OpPos: pos, Op: token.RANGE, X: p.parseRhs()}}
+			isRange = true
+		} else {
+			y = p.parseList(true)
+		}
+		return &ast.AssignStmt{Lhs: x, TokPos: pos, Tok: tok, Rhs: y}, isRange
+	}
+
+	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); mode == 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: label, Colon: colon, Stmt: p.parseStmt()}
+			return stmt, false
+		}
+		// The label declaration typically starts at x[0].Pos(), but the label
+		// declaration may be erroneous due to a token after that position (and
+		// before the ':'). If SpuriousErrors is not set, the (only) error
+		// reported for the line is the illegal label error instead of the token
+		// before the ':' that caused the problem. Thus, use the (latest) colon
+		// position for error reporting.
+		p.error(colon, "illegal label declaration")
+		return &ast.BadStmt{From: x[0].Pos(), To: colon + 1}, false
+
+	case token.ARROW:
+		// send statement
+		arrow := p.pos
+		p.next()
+		y := p.parseRhs()
+		return &ast.SendStmt{Chan: x[0], Arrow: arrow, Value: y}, false
+
+	case token.INC, token.DEC:
+		// increment or decrement
+		s := &ast.IncDecStmt{X: x[0], TokPos: p.pos, Tok: p.tok}
+		p.next()
+		return s, false
+	}
+
+	// expression
+	return &ast.ExprStmt{X: x[0]}, false
+}
+
+func (p *parser) parseCallExpr(callType string) *ast.CallExpr {
+	x := p.parseRhs() // could be a conversion: (some type)(x)
+	if t := unparen(x); t != x {
+		p.error(x.Pos(), fmt.Sprintf("expression in %s must not be parenthesized", callType))
+		x = t
+	}
+	if call, isCall := x.(*ast.CallExpr); isCall {
+		return call
+	}
+	if _, isBad := x.(*ast.BadExpr); !isBad {
+		// only report error if it's a new one
+		p.error(p.safePos(x.End()), fmt.Sprintf("expression in %s must be function call", callType))
+	}
+	return nil
+}
+
+func (p *parser) parseGoStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "GoStmt"))
+	}
+
+	pos := p.expect(token.GO)
+	call := p.parseCallExpr("go")
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{From: pos, To: pos + 2} // len("go")
+	}
+
+	return &ast.GoStmt{Go: pos, Call: call}
+}
+
+func (p *parser) parseDeferStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "DeferStmt"))
+	}
+
+	pos := p.expect(token.DEFER)
+	call := p.parseCallExpr("defer")
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{From: pos, To: pos + 5} // len("defer")
+	}
+
+	return &ast.DeferStmt{Defer: pos, Call: 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.parseList(true)
+	}
+	p.expectSemi()
+
+	return &ast.ReturnStmt{Return: pos, Results: 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()
+	}
+	p.expectSemi()
+
+	return &ast.BranchStmt{TokPos: pos, Tok: tok, Label: label}
+}
+
+func (p *parser) makeExpr(s ast.Stmt, want string) ast.Expr {
+	if s == nil {
+		return nil
+	}
+	if es, isExpr := s.(*ast.ExprStmt); isExpr {
+		return es.X
+	}
+	found := "simple statement"
+	if _, isAss := s.(*ast.AssignStmt); isAss {
+		found = "assignment"
+	}
+	p.error(s.Pos(), fmt.Sprintf("expected %s, found %s (missing parentheses around composite literal?)", want, found))
+	return &ast.BadExpr{From: s.Pos(), To: p.safePos(s.End())}
+}
+
+// parseIfHeader is an adjusted version of parser.header
+// in cmd/compile/internal/syntax/parser.go, which has
+// been tuned for better error handling.
+func (p *parser) parseIfHeader() (init ast.Stmt, cond ast.Expr) {
+	if p.tok == token.LBRACE {
+		p.error(p.pos, "missing condition in if statement")
+		cond = &ast.BadExpr{From: p.pos, To: p.pos}
+		return
+	}
+	// p.tok != token.LBRACE
+
+	prevLev := p.exprLev
+	p.exprLev = -1
+
+	if p.tok != token.SEMICOLON {
+		// accept potential variable declaration but complain
+		if p.tok == token.VAR {
+			p.next()
+			p.error(p.pos, "var declaration not allowed in if initializer")
+		}
+		init, _ = p.parseSimpleStmt(basic)
+	}
+
+	var condStmt ast.Stmt
+	var semi struct {
+		pos token.Pos
+		lit string // ";" or "\n"; valid if pos.IsValid()
+	}
+	if p.tok != token.LBRACE {
+		if p.tok == token.SEMICOLON {
+			semi.pos = p.pos
+			semi.lit = p.lit
+			p.next()
+		} else {
+			p.expect(token.SEMICOLON)
+		}
+		if p.tok != token.LBRACE {
+			condStmt, _ = p.parseSimpleStmt(basic)
+		}
+	} else {
+		condStmt = init
+		init = nil
+	}
+
+	if condStmt != nil {
+		cond = p.makeExpr(condStmt, "boolean expression")
+	} else if semi.pos.IsValid() {
+		if semi.lit == "\n" {
+			p.error(semi.pos, "unexpected newline, expecting { after if clause")
+		} else {
+			p.error(semi.pos, "missing condition in if statement")
+		}
+	}
+
+	// make sure we have a valid AST
+	if cond == nil {
+		cond = &ast.BadExpr{From: p.pos, To: p.pos}
+	}
+
+	p.exprLev = prevLev
+	return
+}
+
+func (p *parser) parseIfStmt() *ast.IfStmt {
+	defer decNestLev(incNestLev(p))
+
+	if p.trace {
+		defer un(trace(p, "IfStmt"))
+	}
+
+	pos := p.expect(token.IF)
+
+	init, cond := p.parseIfHeader()
+	body := p.parseBlockStmt()
+
+	var else_ ast.Stmt
+	if p.tok == token.ELSE {
+		p.next()
+		switch p.tok {
+		case token.IF:
+			else_ = p.parseIfStmt()
+		case token.LBRACE:
+			else_ = p.parseBlockStmt()
+			p.expectSemi()
+		default:
+			p.errorExpected(p.pos, "if statement or block")
+			else_ = &ast.BadStmt{From: p.pos, To: p.pos}
+		}
+	} else {
+		p.expectSemi()
+	}
+
+	return &ast.IfStmt{If: pos, Init: init, Cond: cond, Body: body, Else: else_}
+}
+
+func (p *parser) parseCaseClause() *ast.CaseClause {
+	if p.trace {
+		defer un(trace(p, "CaseClause"))
+	}
+
+	pos := p.pos
+	var list []ast.Expr
+	if p.tok == token.CASE {
+		p.next()
+		list = p.parseList(true)
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	body := p.parseStmtList()
+
+	return &ast.CaseClause{Case: pos, List: list, Colon: colon, Body: body}
+}
+
+func isTypeSwitchAssert(x ast.Expr) bool {
+	a, ok := x.(*ast.TypeAssertExpr)
+	return ok && a.Type == nil
+}
+
+func (p *parser) isTypeSwitchGuard(s ast.Stmt) bool {
+	switch t := s.(type) {
+	case *ast.ExprStmt:
+		// x.(type)
+		return isTypeSwitchAssert(t.X)
+	case *ast.AssignStmt:
+		// v := x.(type)
+		if len(t.Lhs) == 1 && len(t.Rhs) == 1 && isTypeSwitchAssert(t.Rhs[0]) {
+			switch t.Tok {
+			case token.ASSIGN:
+				// permit v = x.(type) but complain
+				p.error(t.TokPos, "expected ':=', found '='")
+				fallthrough
+			case token.DEFINE:
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (p *parser) parseSwitchStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "SwitchStmt"))
+	}
+
+	pos := p.expect(token.SWITCH)
+
+	var s1, s2 ast.Stmt
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2, _ = p.parseSimpleStmt(basic)
+		}
+		if p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.LBRACE {
+				// A TypeSwitchGuard may declare a variable in addition
+				// to the variable declared in the initial SimpleStmt.
+				// Introduce extra scope to avoid redeclaration errors:
+				//
+				//	switch t := 0; t := x.(T) { ... }
+				//
+				// (this code is not valid Go because the first t
+				// cannot be accessed and thus is never used, the extra
+				// scope is needed for the correct error message).
+				//
+				// If we don't have a type switch, s2 must be an expression.
+				// Having the extra nested but empty scope won't affect it.
+				s2, _ = p.parseSimpleStmt(basic)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	typeSwitch := p.isTypeSwitchGuard(s2)
+	lbrace := p.expect(token.LBRACE)
+	var list []ast.Stmt
+	for p.tok == token.CASE || p.tok == token.DEFAULT {
+		list = append(list, p.parseCaseClause())
+	}
+	rbrace := p.expect(token.RBRACE)
+	p.expectSemi()
+	body := &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
+
+	if typeSwitch {
+		return &ast.TypeSwitchStmt{Switch: pos, Init: s1, Assign: s2, Body: body}
+	}
+
+	return &ast.SwitchStmt{Switch: pos, Init: s1, Tag: p.makeExpr(s2, "switch expression"), Body: body}
+}
+
+func (p *parser) parseCommClause() *ast.CommClause {
+	if p.trace {
+		defer un(trace(p, "CommClause"))
+	}
+
+	pos := p.pos
+	var comm ast.Stmt
+	if p.tok == token.CASE {
+		p.next()
+		lhs := p.parseList(false)
+		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{Chan: lhs[0], Arrow: arrow, Value: rhs}
+		} else {
+			// RecvStmt
+			if tok := p.tok; 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]
+				}
+				pos := p.pos
+				p.next()
+				rhs := p.parseRhs()
+				comm = &ast.AssignStmt{Lhs: lhs, TokPos: pos, Tok: tok, Rhs: []ast.Expr{rhs}}
+			} else {
+				// lhs must be single receive operation
+				if len(lhs) > 1 {
+					p.errorExpected(lhs[0].Pos(), "1 expression")
+					// continue with first expression
+				}
+				comm = &ast.ExprStmt{X: lhs[0]}
+			}
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	body := p.parseStmtList()
+
+	return &ast.CommClause{Case: pos, Comm: comm, Colon: colon, Body: 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: lbrace, List: list, Rbrace: rbrace}
+
+	return &ast.SelectStmt{Select: pos, Body: body}
+}
+
+func (p *parser) parseForStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "ForStmt"))
+	}
+
+	pos := p.expect(token.FOR)
+
+	var s1, s2, s3 ast.Stmt
+	var isRange bool
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			if p.tok == token.RANGE {
+				// "for range x" (nil lhs in assignment)
+				pos := p.pos
+				p.next()
+				y := []ast.Expr{&ast.UnaryExpr{OpPos: pos, Op: token.RANGE, X: p.parseRhs()}}
+				s2 = &ast.AssignStmt{Rhs: y}
+				isRange = true
+			} else {
+				s2, isRange = p.parseSimpleStmt(rangeOk)
+			}
+		}
+		if !isRange && p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.SEMICOLON {
+				s2, _ = p.parseSimpleStmt(basic)
+			}
+			p.expectSemi()
+			if p.tok != token.LBRACE {
+				s3, _ = p.parseSimpleStmt(basic)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	body := p.parseBlockStmt()
+	p.expectSemi()
+
+	if isRange {
+		as := s2.(*ast.AssignStmt)
+		// check lhs
+		var key, value ast.Expr
+		switch len(as.Lhs) {
+		case 0:
+			// nothing to do
+		case 1:
+			key = as.Lhs[0]
+		case 2:
+			key, value = as.Lhs[0], as.Lhs[1]
+		default:
+			p.errorExpected(as.Lhs[len(as.Lhs)-1].Pos(), "at most 2 expressions")
+			return &ast.BadStmt{From: pos, To: p.safePos(body.End())}
+		}
+		// parseSimpleStmt returned a right-hand side that
+		// is a single unary expression of the form "range x"
+		x := as.Rhs[0].(*ast.UnaryExpr).X
+		return &ast.RangeStmt{
+			For:    pos,
+			Key:    key,
+			Value:  value,
+			TokPos: as.TokPos,
+			Tok:    as.Tok,
+			Range:  as.Rhs[0].Pos(),
+			X:      x,
+			Body:   body,
+		}
+	}
+
+	// regular for statement
+	return &ast.ForStmt{
+		For:  pos,
+		Init: s1,
+		Cond: p.makeExpr(s2, "boolean or range expression"),
+		Post: s3,
+		Body: body,
+	}
+}
+
+func (p *parser) parseStmt() (s ast.Stmt) {
+	defer decNestLev(incNestLev(p))
+
+	if p.trace {
+		defer un(trace(p, "Statement"))
+	}
+
+	switch p.tok {
+	case token.CONST, token.TYPE, token.VAR:
+		s = &ast.DeclStmt{Decl: p.parseDecl(stmtStart)}
+	case
+		// tokens that may start an expression
+		token.IDENT, token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING, token.FUNC, token.LPAREN, // operands
+		token.LBRACK, token.STRUCT, token.MAP, token.CHAN, token.INTERFACE, // composite types
+		token.ADD, token.SUB, token.MUL, token.AND, token.XOR, token.ARROW, token.NOT: // unary operators
+		s, _ = p.parseSimpleStmt(labelOk)
+		// 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:
+		// Is it ever possible to have an implicit semicolon
+		// producing an empty statement in a valid program?
+		// (handle correctly anyway)
+		s = &ast.EmptyStmt{Semicolon: p.pos, Implicit: p.lit == "\n"}
+		p.next()
+	case token.RBRACE:
+		// a semicolon may be omitted before a closing "}"
+		s = &ast.EmptyStmt{Semicolon: p.pos, Implicit: true}
+	default:
+		// no statement found
+		pos := p.pos
+		p.errorExpected(pos, "statement")
+		p.advance(stmtStart)
+		s = &ast.BadStmt{From: pos, To: p.pos}
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+type parseSpecFunction func(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec
+
+func (p *parser) parseImportSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "ImportSpec"))
+	}
+
+	var ident *ast.Ident
+	switch p.tok {
+	case token.IDENT:
+		ident = p.parseIdent()
+	case token.PERIOD:
+		ident = &ast.Ident{NamePos: p.pos, Name: "."}
+		p.next()
+	}
+
+	pos := p.pos
+	var path string
+	if p.tok == token.STRING {
+		path = p.lit
+		p.next()
+	} else if p.tok.IsLiteral() {
+		p.error(pos, "import path must be a string")
+		p.next()
+	} else {
+		p.error(pos, "missing import path")
+		p.advance(exprEnd)
+	}
+	comment := p.expectSemi()
+
+	// collect imports
+	spec := &ast.ImportSpec{
+		Doc:     doc,
+		Name:    ident,
+		Path:    &ast.BasicLit{ValuePos: pos, Kind: token.STRING, Value: path},
+		Comment: comment,
+	}
+	p.imports = append(p.imports, spec)
+
+	return spec
+}
+
+func (p *parser) parseValueSpec(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, keyword.String()+"Spec"))
+	}
+
+	idents := p.parseIdentList()
+	var typ ast.Expr
+	var values []ast.Expr
+	switch keyword {
+	case token.CONST:
+		// always permit optional type and initialization for more tolerant parsing
+		if p.tok != token.EOF && p.tok != token.SEMICOLON && p.tok != token.RPAREN {
+			typ = p.tryIdentOrType()
+			if p.tok == token.ASSIGN {
+				p.next()
+				values = p.parseList(true)
+			}
+		}
+	case token.VAR:
+		if p.tok != token.ASSIGN {
+			typ = p.parseType()
+		}
+		if p.tok == token.ASSIGN {
+			p.next()
+			values = p.parseList(true)
+		}
+	default:
+		panic("unreachable")
+	}
+	comment := p.expectSemi()
+
+	spec := &ast.ValueSpec{
+		Doc:     doc,
+		Names:   idents,
+		Type:    typ,
+		Values:  values,
+		Comment: comment,
+	}
+	return spec
+}
+
+func (p *parser) parseGenericType(spec *ast.TypeSpec, openPos token.Pos, name0 *ast.Ident, typ0 ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "parseGenericType"))
+	}
+
+	list := p.parseParameterList(name0, typ0, token.RBRACK)
+	closePos := p.expect(token.RBRACK)
+	spec.TypeParams = &ast.FieldList{Opening: openPos, List: list, Closing: closePos}
+	// Let the type checker decide whether to accept type parameters on aliases:
+	// see issue #46477.
+	if p.tok == token.ASSIGN {
+		// type alias
+		spec.Assign = p.pos
+		p.next()
+	}
+	spec.Type = p.parseType()
+}
+
+func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "TypeSpec"))
+	}
+
+	name := p.parseIdent()
+	spec := &ast.TypeSpec{Doc: doc, Name: name}
+
+	if p.tok == token.LBRACK {
+		// spec.Name "[" ...
+		// array/slice type or type parameter list
+		lbrack := p.pos
+		p.next()
+		if p.tok == token.IDENT {
+			// We may have an array type or a type parameter list.
+			// In either case we expect an expression x (which may
+			// just be a name, or a more complex expression) which
+			// we can analyze further.
+			//
+			// A type parameter list may have a type bound starting
+			// with a "[" as in: P []E. In that case, simply parsing
+			// an expression would lead to an error: P[] is invalid.
+			// But since index or slice expressions are never constant
+			// and thus invalid array length expressions, if the name
+			// is followed by "[" it must be the start of an array or
+			// slice constraint. Only if we don't see a "[" do we
+			// need to parse a full expression. Notably, name <- x
+			// is not a concern because name <- x is a statement and
+			// not an expression.
+			var x ast.Expr = p.parseIdent()
+			if p.tok != token.LBRACK {
+				// To parse the expression starting with name, expand
+				// the call sequence we would get by passing in name
+				// to parser.expr, and pass in name to parsePrimaryExpr.
+				p.exprLev++
+				lhs := p.parsePrimaryExpr(x)
+				x = p.parseBinaryExpr(lhs, token.LowestPrec+1)
+				p.exprLev--
+			}
+			// Analyze expression x. If we can split x into a type parameter
+			// name, possibly followed by a type parameter type, we consider
+			// this the start of a type parameter list, with some caveats:
+			// a single name followed by "]" tilts the decision towards an
+			// array declaration; a type parameter type that could also be
+			// an ordinary expression but which is followed by a comma tilts
+			// the decision towards a type parameter list.
+			if pname, ptype := extractName(x, p.tok == token.COMMA); pname != nil && (ptype != nil || p.tok != token.RBRACK) {
+				// spec.Name "[" pname ...
+				// spec.Name "[" pname ptype ...
+				// spec.Name "[" pname ptype "," ...
+				p.parseGenericType(spec, lbrack, pname, ptype) // ptype may be nil
+			} else {
+				// spec.Name "[" pname "]" ...
+				// spec.Name "[" x ...
+				spec.Type = p.parseArrayType(lbrack, x)
+			}
+		} else {
+			// array type
+			spec.Type = p.parseArrayType(lbrack, nil)
+		}
+	} else {
+		// no type parameters
+		if p.tok == token.ASSIGN {
+			// type alias
+			spec.Assign = p.pos
+			p.next()
+		}
+		spec.Type = p.parseType()
+	}
+
+	spec.Comment = p.expectSemi()
+
+	return spec
+}
+
+// extractName splits the expression x into (name, expr) if syntactically
+// x can be written as name expr. The split only happens if expr is a type
+// element (per the isTypeElem predicate) or if force is set.
+// If x is just a name, the result is (name, nil). If the split succeeds,
+// the result is (name, expr). Otherwise the result is (nil, x).
+// Examples:
+//
+//	x           force    name    expr
+//	------------------------------------
+//	P*[]int     T/F      P       *[]int
+//	P*E         T        P       *E
+//	P*E         F        nil     P*E
+//	P([]int)    T/F      P       []int
+//	P(E)        T        P       E
+//	P(E)        F        nil     P(E)
+//	P*E|F|~G    T/F      P       *E|F|~G
+//	P*E|F|G     T        P       *E|F|G
+//	P*E|F|G     F        nil     P*E|F|G
+func extractName(x ast.Expr, force bool) (*ast.Ident, ast.Expr) {
+	switch x := x.(type) {
+	case *ast.Ident:
+		return x, nil
+	case *ast.BinaryExpr:
+		switch x.Op {
+		case token.MUL:
+			if name, _ := x.X.(*ast.Ident); name != nil && (force || isTypeElem(x.Y)) {
+				// x = name *x.Y
+				return name, &ast.StarExpr{Star: x.OpPos, X: x.Y}
+			}
+		case token.OR:
+			if name, lhs := extractName(x.X, force || isTypeElem(x.Y)); name != nil && lhs != nil {
+				// x = name lhs|x.Y
+				op := *x
+				op.X = lhs
+				return name, &op
+			}
+		}
+	case *ast.CallExpr:
+		if name, _ := x.Fun.(*ast.Ident); name != nil {
+			if len(x.Args) == 1 && x.Ellipsis == token.NoPos && (force || isTypeElem(x.Args[0])) {
+				// x = name "(" x.ArgList[0] ")"
+				return name, x.Args[0]
+			}
+		}
+	}
+	return nil, x
+}
+
+// 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.BinaryExpr:
+		return isTypeElem(x.X) || isTypeElem(x.Y)
+	case *ast.UnaryExpr:
+		return x.Op == token.TILDE
+	case *ast.ParenExpr:
+		return isTypeElem(x.X)
+	}
+	return false
+}
+
+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.leadComment, keyword, iota))
+		}
+		rparen = p.expect(token.RPAREN)
+		p.expectSemi()
+	} else {
+		list = append(list, f(nil, keyword, 0))
+	}
+
+	return &ast.GenDecl{
+		Doc:    doc,
+		TokPos: pos,
+		Tok:    keyword,
+		Lparen: lparen,
+		Specs:  list,
+		Rparen: rparen,
+	}
+}
+
+func (p *parser) parseFuncDecl() *ast.FuncDecl {
+	if p.trace {
+		defer un(trace(p, "FunctionDecl"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(token.FUNC)
+
+	var recv *ast.FieldList
+	if p.tok == token.LPAREN {
+		_, recv = p.parseParameters(false)
+	}
+
+	ident := p.parseIdent()
+
+	tparams, params := p.parseParameters(true)
+	if recv != nil && tparams != nil {
+		// Method declarations do not have type parameters. We parse them for a
+		// better error message and improved error recovery.
+		p.error(tparams.Opening, "method must have no type parameters")
+		tparams = nil
+	}
+	results := p.parseResult()
+
+	var body *ast.BlockStmt
+	switch p.tok {
+	case token.LBRACE:
+		body = p.parseBody()
+		p.expectSemi()
+	case token.SEMICOLON:
+		p.next()
+		if p.tok == token.LBRACE {
+			// opening { of function declaration on next line
+			p.error(p.pos, "unexpected semicolon or newline before {")
+			body = p.parseBody()
+			p.expectSemi()
+		}
+	default:
+		p.expectSemi()
+	}
+
+	decl := &ast.FuncDecl{
+		Doc:  doc,
+		Recv: recv,
+		Name: ident,
+		Type: &ast.FuncType{
+			Func:       pos,
+			TypeParams: tparams,
+			Params:     params,
+			Results:    results,
+		},
+		Body: body,
+	}
+	return decl
+}
+
+func (p *parser) parseDecl(sync map[token.Token]bool) ast.Decl {
+	if p.trace {
+		defer un(trace(p, "Declaration"))
+	}
+
+	var f parseSpecFunction
+	switch p.tok {
+	case token.IMPORT:
+		f = p.parseImportSpec
+
+	case token.CONST, token.VAR:
+		f = p.parseValueSpec
+
+	case token.TYPE:
+		f = p.parseTypeSpec
+
+	case token.FUNC:
+		return p.parseFuncDecl()
+
+	default:
+		pos := p.pos
+		p.errorExpected(pos, "declaration")
+		p.advance(sync)
+		return &ast.BadDecl{From: pos, To: p.pos}
+	}
+
+	return p.parseGenDecl(p.tok, f)
+}
+
+// ----------------------------------------------------------------------------
+// Source files
+
+func (p *parser) parseFile() *ast.File {
+	if p.trace {
+		defer un(trace(p, "File"))
+	}
+
+	// Don't bother parsing the rest if we had errors scanning the first token.
+	// Likely not a Go source file at all.
+	if p.errors.Len() != 0 {
+		return nil
+	}
+
+	// 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.mode&DeclarationErrors != 0 {
+		p.error(p.pos, "invalid package name _")
+	}
+	p.expectSemi()
+
+	// Don't bother parsing the rest if we had errors parsing the package clause.
+	// Likely not a Go source file at all.
+	if p.errors.Len() != 0 {
+		return nil
+	}
+
+	var decls []ast.Decl
+	if p.mode&PackageClauseOnly == 0 {
+		// import decls
+		for p.tok == token.IMPORT {
+			decls = append(decls, p.parseGenDecl(token.IMPORT, p.parseImportSpec))
+		}
+
+		if p.mode&ImportsOnly == 0 {
+			// rest of package body
+			prev := token.IMPORT
+			for p.tok != token.EOF {
+				// Continue to accept import declarations for error tolerance, but complain.
+				if p.tok == token.IMPORT && prev != token.IMPORT {
+					p.error(p.pos, "imports must appear before other declarations")
+				}
+				prev = p.tok
+
+				decls = append(decls, p.parseDecl(declStart))
+			}
+		}
+	}
+
+	f := &ast.File{
+		Doc:       doc,
+		Package:   pos,
+		Name:      ident,
+		Decls:     decls,
+		FileStart: token.Pos(p.file.Base()),
+		FileEnd:   token.Pos(p.file.Base() + p.file.Size()),
+		Imports:   p.imports,
+		Comments:  p.comments,
+		GoVersion: p.goVersion,
+	}
+	var declErr func(token.Pos, string)
+	if p.mode&DeclarationErrors != 0 {
+		declErr = p.error
+	}
+	if p.mode&SkipObjectResolution == 0 {
+		resolveFile(f, p.file, declErr)
+	}
+
+	return f
+}
diff --git a/src/go/parser/parser_test.go b/src/go/parser/parser_test.go
new file mode 100644
index 0000000..0848aca
--- /dev/null
+++ b/src/go/parser/parser_test.go
@@ -0,0 +1,802 @@
+// 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
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"io/fs"
+	"strings"
+	"testing"
+)
+
+var validFiles = []string{
+	"parser.go",
+	"parser_test.go",
+	"error_test.go",
+	"short_test.go",
+}
+
+func TestParse(t *testing.T) {
+	for _, filename := range validFiles {
+		_, err := ParseFile(token.NewFileSet(), filename, nil, DeclarationErrors)
+		if err != nil {
+			t.Fatalf("ParseFile(%s): %v", filename, err)
+		}
+	}
+}
+
+func nameFilter(filename string) bool {
+	switch filename {
+	case "parser.go", "interface.go", "parser_test.go":
+		return true
+	case "parser.go.orig":
+		return true // permit but should be ignored by ParseDir
+	}
+	return false
+}
+
+func dirFilter(f fs.FileInfo) bool { return nameFilter(f.Name()) }
+
+func TestParseFile(t *testing.T) {
+	src := "package p\nvar _=s[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]"
+	_, err := ParseFile(token.NewFileSet(), "", src, 0)
+	if err == nil {
+		t.Errorf("ParseFile(%s) succeeded unexpectedly", src)
+	}
+}
+
+func TestParseExprFrom(t *testing.T) {
+	src := "s[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]"
+	_, err := ParseExprFrom(token.NewFileSet(), "", src, 0)
+	if err == nil {
+		t.Errorf("ParseExprFrom(%s) succeeded unexpectedly", src)
+	}
+}
+
+func TestParseDir(t *testing.T) {
+	path := "."
+	pkgs, err := ParseDir(token.NewFileSet(), path, dirFilter, 0)
+	if err != nil {
+		t.Fatalf("ParseDir(%s): %v", path, err)
+	}
+	if n := len(pkgs); n != 1 {
+		t.Errorf("got %d packages; want 1", n)
+	}
+	pkg := pkgs["parser"]
+	if pkg == nil {
+		t.Errorf(`package "parser" not found`)
+		return
+	}
+	if n := len(pkg.Files); n != 3 {
+		t.Errorf("got %d package files; want 3", n)
+	}
+	for filename := range pkg.Files {
+		if !nameFilter(filename) {
+			t.Errorf("unexpected package file: %s", filename)
+		}
+	}
+}
+
+func TestIssue42951(t *testing.T) {
+	path := "./testdata/issue42951"
+	_, err := ParseDir(token.NewFileSet(), path, nil, 0)
+	if err != nil {
+		t.Errorf("ParseDir(%s): %v", path, err)
+	}
+}
+
+func TestParseExpr(t *testing.T) {
+	// just kicking the tires:
+	// a valid arithmetic expression
+	src := "a + b"
+	x, err := ParseExpr(src)
+	if err != nil {
+		t.Errorf("ParseExpr(%q): %v", src, err)
+	}
+	// sanity check
+	if _, ok := x.(*ast.BinaryExpr); !ok {
+		t.Errorf("ParseExpr(%q): got %T, want *ast.BinaryExpr", src, x)
+	}
+
+	// a valid type expression
+	src = "struct{x *int}"
+	x, err = ParseExpr(src)
+	if err != nil {
+		t.Errorf("ParseExpr(%q): %v", src, err)
+	}
+	// sanity check
+	if _, ok := x.(*ast.StructType); !ok {
+		t.Errorf("ParseExpr(%q): got %T, want *ast.StructType", src, x)
+	}
+
+	// an invalid expression
+	src = "a + *"
+	x, err = ParseExpr(src)
+	if err == nil {
+		t.Errorf("ParseExpr(%q): got no error", src)
+	}
+	if x == nil {
+		t.Errorf("ParseExpr(%q): got no (partial) result", src)
+	}
+	if _, ok := x.(*ast.BinaryExpr); !ok {
+		t.Errorf("ParseExpr(%q): got %T, want *ast.BinaryExpr", src, x)
+	}
+
+	// a valid expression followed by extra tokens is invalid
+	src = "a[i] := x"
+	if _, err := ParseExpr(src); err == nil {
+		t.Errorf("ParseExpr(%q): got no error", src)
+	}
+
+	// a semicolon is not permitted unless automatically inserted
+	src = "a + b\n"
+	if _, err := ParseExpr(src); err != nil {
+		t.Errorf("ParseExpr(%q): got error %s", src, err)
+	}
+	src = "a + b;"
+	if _, err := ParseExpr(src); err == nil {
+		t.Errorf("ParseExpr(%q): got no error", src)
+	}
+
+	// various other stuff following a valid expression
+	const validExpr = "a + b"
+	const anything = "dh3*#D)#_"
+	for _, c := range "!)]};," {
+		src := validExpr + string(c) + anything
+		if _, err := ParseExpr(src); err == nil {
+			t.Errorf("ParseExpr(%q): got no error", src)
+		}
+	}
+
+	// ParseExpr must not crash
+	for _, src := range valids {
+		ParseExpr(src)
+	}
+}
+
+func TestColonEqualsScope(t *testing.T) {
+	f, err := ParseFile(token.NewFileSet(), "", `package p; func f() { x, y, z := x, y, z }`, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// RHS refers to undefined globals; LHS does not.
+	as := f.Decls[0].(*ast.FuncDecl).Body.List[0].(*ast.AssignStmt)
+	for _, v := range as.Rhs {
+		id := v.(*ast.Ident)
+		if id.Obj != nil {
+			t.Errorf("rhs %s has Obj, should not", id.Name)
+		}
+	}
+	for _, v := range as.Lhs {
+		id := v.(*ast.Ident)
+		if id.Obj == nil {
+			t.Errorf("lhs %s does not have Obj, should", id.Name)
+		}
+	}
+}
+
+func TestVarScope(t *testing.T) {
+	f, err := ParseFile(token.NewFileSet(), "", `package p; func f() { var x, y, z = x, y, z }`, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// RHS refers to undefined globals; LHS does not.
+	as := f.Decls[0].(*ast.FuncDecl).Body.List[0].(*ast.DeclStmt).Decl.(*ast.GenDecl).Specs[0].(*ast.ValueSpec)
+	for _, v := range as.Values {
+		id := v.(*ast.Ident)
+		if id.Obj != nil {
+			t.Errorf("rhs %s has Obj, should not", id.Name)
+		}
+	}
+	for _, id := range as.Names {
+		if id.Obj == nil {
+			t.Errorf("lhs %s does not have Obj, should", id.Name)
+		}
+	}
+}
+
+func TestObjects(t *testing.T) {
+	const src = `
+package p
+import fmt "fmt"
+const pi = 3.14
+type T struct{}
+var x int
+func f() { L: }
+`
+
+	f, err := ParseFile(token.NewFileSet(), "", src, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	objects := map[string]ast.ObjKind{
+		"p":   ast.Bad, // not in a scope
+		"fmt": ast.Bad, // not resolved yet
+		"pi":  ast.Con,
+		"T":   ast.Typ,
+		"x":   ast.Var,
+		"int": ast.Bad, // not resolved yet
+		"f":   ast.Fun,
+		"L":   ast.Lbl,
+	}
+
+	ast.Inspect(f, func(n ast.Node) bool {
+		if ident, ok := n.(*ast.Ident); ok {
+			obj := ident.Obj
+			if obj == nil {
+				if objects[ident.Name] != ast.Bad {
+					t.Errorf("no object for %s", ident.Name)
+				}
+				return true
+			}
+			if obj.Name != ident.Name {
+				t.Errorf("names don't match: obj.Name = %s, ident.Name = %s", obj.Name, ident.Name)
+			}
+			kind := objects[ident.Name]
+			if obj.Kind != kind {
+				t.Errorf("%s: obj.Kind = %s; want %s", ident.Name, obj.Kind, kind)
+			}
+		}
+		return true
+	})
+}
+
+func TestUnresolved(t *testing.T) {
+	f, err := ParseFile(token.NewFileSet(), "", `
+package p
+//
+func f1a(int)
+func f2a(byte, int, float)
+func f3a(a, b int, c float)
+func f4a(...complex)
+func f5a(a s1a, b ...complex)
+//
+func f1b(*int)
+func f2b([]byte, (int), *float)
+func f3b(a, b *int, c []float)
+func f4b(...*complex)
+func f5b(a s1a, b ...[]complex)
+//
+type s1a struct { int }
+type s2a struct { byte; int; s1a }
+type s3a struct { a, b int; c float }
+//
+type s1b struct { *int }
+type s2b struct { byte; int; *float }
+type s3b struct { a, b *s3b; c []float }
+`, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := "int " + // f1a
+		"byte int float " + // f2a
+		"int float " + // f3a
+		"complex " + // f4a
+		"complex " + // f5a
+		//
+		"int " + // f1b
+		"byte int float " + // f2b
+		"int float " + // f3b
+		"complex " + // f4b
+		"complex " + // f5b
+		//
+		"int " + // s1a
+		"byte int " + // s2a
+		"int float " + // s3a
+		//
+		"int " + // s1a
+		"byte int float " + // s2a
+		"float " // s3a
+
+	// collect unresolved identifiers
+	var buf strings.Builder
+	for _, u := range f.Unresolved {
+		buf.WriteString(u.Name)
+		buf.WriteByte(' ')
+	}
+	got := buf.String()
+
+	if got != want {
+		t.Errorf("\ngot:  %s\nwant: %s", got, want)
+	}
+}
+
+func TestCommentGroups(t *testing.T) {
+	f, err := ParseFile(token.NewFileSet(), "", `
+package p /* 1a */ /* 1b */      /* 1c */ // 1d
+/* 2a
+*/
+// 2b
+const pi = 3.1415
+/* 3a */ // 3b
+/* 3c */ const e = 2.7182
+
+// Example from issue 3139
+func ExampleCount() {
+	fmt.Println(strings.Count("cheese", "e"))
+	fmt.Println(strings.Count("five", "")) // before & after each rune
+	// Output:
+	// 3
+	// 5
+}
+`, ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected := [][]string{
+		{"/* 1a */", "/* 1b */", "/* 1c */", "// 1d"},
+		{"/* 2a\n*/", "// 2b"},
+		{"/* 3a */", "// 3b", "/* 3c */"},
+		{"// Example from issue 3139"},
+		{"// before & after each rune"},
+		{"// Output:", "// 3", "// 5"},
+	}
+	if len(f.Comments) != len(expected) {
+		t.Fatalf("got %d comment groups; expected %d", len(f.Comments), len(expected))
+	}
+	for i, exp := range expected {
+		got := f.Comments[i].List
+		if len(got) != len(exp) {
+			t.Errorf("got %d comments in group %d; expected %d", len(got), i, len(exp))
+			continue
+		}
+		for j, exp := range exp {
+			got := got[j].Text
+			if got != exp {
+				t.Errorf("got %q in group %d; expected %q", got, i, exp)
+			}
+		}
+	}
+}
+
+func getField(file *ast.File, fieldname string) *ast.Field {
+	parts := strings.Split(fieldname, ".")
+	for _, d := range file.Decls {
+		if d, ok := d.(*ast.GenDecl); ok && d.Tok == token.TYPE {
+			for _, s := range d.Specs {
+				if s, ok := s.(*ast.TypeSpec); ok && s.Name.Name == parts[0] {
+					if s, ok := s.Type.(*ast.StructType); ok {
+						for _, f := range s.Fields.List {
+							for _, name := range f.Names {
+								if name.Name == parts[1] {
+									return f
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// Don't use ast.CommentGroup.Text() - we want to see exact comment text.
+func commentText(c *ast.CommentGroup) string {
+	var buf strings.Builder
+	if c != nil {
+		for _, c := range c.List {
+			buf.WriteString(c.Text)
+		}
+	}
+	return buf.String()
+}
+
+func checkFieldComments(t *testing.T, file *ast.File, fieldname, lead, line string) {
+	f := getField(file, fieldname)
+	if f == nil {
+		t.Fatalf("field not found: %s", fieldname)
+	}
+	if got := commentText(f.Doc); got != lead {
+		t.Errorf("got lead comment %q; expected %q", got, lead)
+	}
+	if got := commentText(f.Comment); got != line {
+		t.Errorf("got line comment %q; expected %q", got, line)
+	}
+}
+
+func TestLeadAndLineComments(t *testing.T) {
+	f, err := ParseFile(token.NewFileSet(), "", `
+package p
+type T struct {
+	/* F1 lead comment */
+	//
+	F1 int  /* F1 */ // line comment
+	// F2 lead
+	// comment
+	F2 int  // F2 line comment
+	// f3 lead comment
+	f3 int  // f3 line comment
+
+	f4 int   /* not a line comment */ ;
+        f5 int ; // f5 line comment
+	f6 int ; /* f6 line comment */
+	f7 int ; /*f7a*/ /*f7b*/ //f7c
+}
+`, ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkFieldComments(t, f, "T.F1", "/* F1 lead comment *///", "/* F1 */// line comment")
+	checkFieldComments(t, f, "T.F2", "// F2 lead// comment", "// F2 line comment")
+	checkFieldComments(t, f, "T.f3", "// f3 lead comment", "// f3 line comment")
+	checkFieldComments(t, f, "T.f4", "", "")
+	checkFieldComments(t, f, "T.f5", "", "// f5 line comment")
+	checkFieldComments(t, f, "T.f6", "", "/* f6 line comment */")
+	checkFieldComments(t, f, "T.f7", "", "/*f7a*//*f7b*///f7c")
+
+	ast.FileExports(f)
+	checkFieldComments(t, f, "T.F1", "/* F1 lead comment *///", "/* F1 */// line comment")
+	checkFieldComments(t, f, "T.F2", "// F2 lead// comment", "// F2 line comment")
+	if getField(f, "T.f3") != nil {
+		t.Error("not expected to find T.f3")
+	}
+}
+
+// TestIssue9979 verifies that empty statements are contained within their enclosing blocks.
+func TestIssue9979(t *testing.T) {
+	for _, src := range []string{
+		"package p; func f() {;}",
+		"package p; func f() {L:}",
+		"package p; func f() {L:;}",
+		"package p; func f() {L:\n}",
+		"package p; func f() {L:\n;}",
+		"package p; func f() { ; }",
+		"package p; func f() { L: }",
+		"package p; func f() { L: ; }",
+		"package p; func f() { L: \n}",
+		"package p; func f() { L: \n; }",
+	} {
+		fset := token.NewFileSet()
+		f, err := ParseFile(fset, "", src, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		var pos, end token.Pos
+		ast.Inspect(f, func(x ast.Node) bool {
+			switch s := x.(type) {
+			case *ast.BlockStmt:
+				pos, end = s.Pos()+1, s.End()-1 // exclude "{", "}"
+			case *ast.LabeledStmt:
+				pos, end = s.Pos()+2, s.End() // exclude "L:"
+			case *ast.EmptyStmt:
+				// check containment
+				if s.Pos() < pos || s.End() > end {
+					t.Errorf("%s: %T[%d, %d] not inside [%d, %d]", src, s, s.Pos(), s.End(), pos, end)
+				}
+				// check semicolon
+				offs := fset.Position(s.Pos()).Offset
+				if ch := src[offs]; ch != ';' != s.Implicit {
+					want := "want ';'"
+					if s.Implicit {
+						want = "but ';' is implicit"
+					}
+					t.Errorf("%s: found %q at offset %d; %s", src, ch, offs, want)
+				}
+			}
+			return true
+		})
+	}
+}
+
+func TestFileStartEndPos(t *testing.T) {
+	const src = `// Copyright
+
+//+build tag
+
+// Package p doc comment.
+package p
+
+var lastDecl int
+
+/* end of file */
+`
+	fset := token.NewFileSet()
+	f, err := ParseFile(fset, "file.go", src, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// File{Start,End} spans the entire file, not just the declarations.
+	if got, want := fset.Position(f.FileStart).String(), "file.go:1:1"; got != want {
+		t.Errorf("for File.FileStart, got %s, want %s", got, want)
+	}
+	// The end position is the newline at the end of the /* end of file */ line.
+	if got, want := fset.Position(f.FileEnd).String(), "file.go:10:19"; got != want {
+		t.Errorf("for File.FileEnd, got %s, want %s", got, want)
+	}
+}
+
+// TestIncompleteSelection ensures that an incomplete selector
+// expression is parsed as a (blank) *ast.SelectorExpr, not a
+// *ast.BadExpr.
+func TestIncompleteSelection(t *testing.T) {
+	for _, src := range []string{
+		"package p; var _ = fmt.",             // at EOF
+		"package p; var _ = fmt.\ntype X int", // not at EOF
+	} {
+		fset := token.NewFileSet()
+		f, err := ParseFile(fset, "", src, 0)
+		if err == nil {
+			t.Errorf("ParseFile(%s) succeeded unexpectedly", src)
+			continue
+		}
+
+		const wantErr = "expected selector or type assertion"
+		if !strings.Contains(err.Error(), wantErr) {
+			t.Errorf("ParseFile returned wrong error %q, want %q", err, wantErr)
+		}
+
+		var sel *ast.SelectorExpr
+		ast.Inspect(f, func(n ast.Node) bool {
+			if n, ok := n.(*ast.SelectorExpr); ok {
+				sel = n
+			}
+			return true
+		})
+		if sel == nil {
+			t.Error("found no *ast.SelectorExpr")
+			continue
+		}
+		const wantSel = "&{fmt _}"
+		if fmt.Sprint(sel) != wantSel {
+			t.Errorf("found selector %s, want %s", sel, wantSel)
+			continue
+		}
+	}
+}
+
+func TestLastLineComment(t *testing.T) {
+	const src = `package main
+type x int // comment
+`
+	fset := token.NewFileSet()
+	f, err := ParseFile(fset, "", src, ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	comment := f.Decls[0].(*ast.GenDecl).Specs[0].(*ast.TypeSpec).Comment.List[0].Text
+	if comment != "// comment" {
+		t.Errorf("got %q, want %q", comment, "// comment")
+	}
+}
+
+var parseDepthTests = []struct {
+	name   string
+	format string
+	// multiplier is used when a single statement may result in more than one
+	// change in the depth level, for instance "1+(..." produces a BinaryExpr
+	// followed by a UnaryExpr, which increments the depth twice. The test
+	// case comment explains which nodes are triggering the multiple depth
+	// changes.
+	parseMultiplier int
+	// scope is true if we should also test the statement for the resolver scope
+	// depth limit.
+	scope bool
+	// scopeMultiplier does the same as parseMultiplier, but for the scope
+	// depths.
+	scopeMultiplier int
+}{
+	// The format expands the part inside « » many times.
+	// A second set of brackets nested inside the first stops the repetition,
+	// so that for example «(«1»)» expands to (((...((((1))))...))).
+	{name: "array", format: "package main; var x «[1]»int"},
+	{name: "slice", format: "package main; var x «[]»int"},
+	{name: "struct", format: "package main; var x «struct { X «int» }»", scope: true},
+	{name: "pointer", format: "package main; var x «*»int"},
+	{name: "func", format: "package main; var x «func()»int", scope: true},
+	{name: "chan", format: "package main; var x «chan »int"},
+	{name: "chan2", format: "package main; var x «<-chan »int"},
+	{name: "interface", format: "package main; var x «interface { M() «int» }»", scope: true, scopeMultiplier: 2}, // Scopes: InterfaceType, FuncType
+	{name: "map", format: "package main; var x «map[int]»int"},
+	{name: "slicelit", format: "package main; var x = «[]any{«»}»", parseMultiplier: 2},             // Parser nodes: UnaryExpr, CompositeLit
+	{name: "arraylit", format: "package main; var x = «[1]any{«nil»}»", parseMultiplier: 2},         // Parser nodes: UnaryExpr, CompositeLit
+	{name: "structlit", format: "package main; var x = «struct{x any}{«nil»}»", parseMultiplier: 2}, // Parser nodes: UnaryExpr, CompositeLit
+	{name: "maplit", format: "package main; var x = «map[int]any{1:«nil»}»", parseMultiplier: 2},    // Parser nodes: CompositeLit, KeyValueExpr
+	{name: "dot", format: "package main; var x = «x.»x"},
+	{name: "index", format: "package main; var x = x«[1]»"},
+	{name: "slice", format: "package main; var x = x«[1:2]»"},
+	{name: "slice3", format: "package main; var x = x«[1:2:3]»"},
+	{name: "dottype", format: "package main; var x = x«.(any)»"},
+	{name: "callseq", format: "package main; var x = x«()»"},
+	{name: "methseq", format: "package main; var x = x«.m()»", parseMultiplier: 2}, // Parser nodes: SelectorExpr, CallExpr
+	{name: "binary", format: "package main; var x = «1+»1"},
+	{name: "binaryparen", format: "package main; var x = «1+(«1»)»", parseMultiplier: 2}, // Parser nodes: BinaryExpr, ParenExpr
+	{name: "unary", format: "package main; var x = «^»1"},
+	{name: "addr", format: "package main; var x = «& »x"},
+	{name: "star", format: "package main; var x = «*»x"},
+	{name: "recv", format: "package main; var x = «<-»x"},
+	{name: "call", format: "package main; var x = «f(«1»)»", parseMultiplier: 2},    // Parser nodes: Ident, CallExpr
+	{name: "conv", format: "package main; var x = «(*T)(«1»)»", parseMultiplier: 2}, // Parser nodes: ParenExpr, CallExpr
+	{name: "label", format: "package main; func main() { «Label:» }"},
+	{name: "if", format: "package main; func main() { «if true { «» }»}", parseMultiplier: 2, scope: true, scopeMultiplier: 2}, // Parser nodes: IfStmt, BlockStmt. Scopes: IfStmt, BlockStmt
+	{name: "ifelse", format: "package main; func main() { «if true {} else » {} }", scope: true},
+	{name: "switch", format: "package main; func main() { «switch { default: «» }»}", scope: true, scopeMultiplier: 2},               // Scopes: TypeSwitchStmt, CaseClause
+	{name: "typeswitch", format: "package main; func main() { «switch x.(type) { default: «» }» }", scope: true, scopeMultiplier: 2}, // Scopes: TypeSwitchStmt, CaseClause
+	{name: "for0", format: "package main; func main() { «for { «» }» }", scope: true, scopeMultiplier: 2},                            // Scopes: ForStmt, BlockStmt
+	{name: "for1", format: "package main; func main() { «for x { «» }» }", scope: true, scopeMultiplier: 2},                          // Scopes: ForStmt, BlockStmt
+	{name: "for3", format: "package main; func main() { «for f(); g(); h() { «» }» }", scope: true, scopeMultiplier: 2},              // Scopes: ForStmt, BlockStmt
+	{name: "forrange0", format: "package main; func main() { «for range x { «» }» }", scope: true, scopeMultiplier: 2},               // Scopes: RangeStmt, BlockStmt
+	{name: "forrange1", format: "package main; func main() { «for x = range z { «» }» }", scope: true, scopeMultiplier: 2},           // Scopes: RangeStmt, BlockStmt
+	{name: "forrange2", format: "package main; func main() { «for x, y = range z { «» }» }", scope: true, scopeMultiplier: 2},        // Scopes: RangeStmt, BlockStmt
+	{name: "go", format: "package main; func main() { «go func() { «» }()» }", parseMultiplier: 2, scope: true},                      // Parser nodes: GoStmt, FuncLit
+	{name: "defer", format: "package main; func main() { «defer func() { «» }()» }", parseMultiplier: 2, scope: true},                // Parser nodes: DeferStmt, FuncLit
+	{name: "select", format: "package main; func main() { «select { default: «» }» }", scope: true},
+}
+
+// split splits pre«mid»post into pre, mid, post.
+// If the string does not have that form, split returns x, "", "".
+func split(x string) (pre, mid, post string) {
+	start, end := strings.Index(x, "«"), strings.LastIndex(x, "»")
+	if start < 0 || end < 0 {
+		return x, "", ""
+	}
+	return x[:start], x[start+len("«") : end], x[end+len("»"):]
+}
+
+func TestParseDepthLimit(t *testing.T) {
+	if testing.Short() {
+		t.Skip("test requires significant memory")
+	}
+	for _, tt := range parseDepthTests {
+		for _, size := range []string{"small", "big"} {
+			t.Run(tt.name+"/"+size, func(t *testing.T) {
+				n := maxNestLev + 1
+				if tt.parseMultiplier > 0 {
+					n /= tt.parseMultiplier
+				}
+				if size == "small" {
+					// Decrease the number of statements by 10, in order to check
+					// that we do not fail when under the limit. 10 is used to
+					// provide some wiggle room for cases where the surrounding
+					// scaffolding syntax adds some noise to the depth that changes
+					// on a per testcase basis.
+					n -= 10
+				}
+
+				pre, mid, post := split(tt.format)
+				if strings.Contains(mid, "«") {
+					left, base, right := split(mid)
+					mid = strings.Repeat(left, n) + base + strings.Repeat(right, n)
+				} else {
+					mid = strings.Repeat(mid, n)
+				}
+				input := pre + mid + post
+
+				fset := token.NewFileSet()
+				_, err := ParseFile(fset, "", input, ParseComments|SkipObjectResolution)
+				if size == "small" {
+					if err != nil {
+						t.Errorf("ParseFile(...): %v (want success)", err)
+					}
+				} else {
+					expected := "exceeded max nesting depth"
+					if err == nil || !strings.HasSuffix(err.Error(), expected) {
+						t.Errorf("ParseFile(...) = _, %v, want %q", err, expected)
+					}
+				}
+			})
+		}
+	}
+}
+
+func TestScopeDepthLimit(t *testing.T) {
+	for _, tt := range parseDepthTests {
+		if !tt.scope {
+			continue
+		}
+		for _, size := range []string{"small", "big"} {
+			t.Run(tt.name+"/"+size, func(t *testing.T) {
+				n := maxScopeDepth + 1
+				if tt.scopeMultiplier > 0 {
+					n /= tt.scopeMultiplier
+				}
+				if size == "small" {
+					// Decrease the number of statements by 10, in order to check
+					// that we do not fail when under the limit. 10 is used to
+					// provide some wiggle room for cases where the surrounding
+					// scaffolding syntax adds some noise to the depth that changes
+					// on a per testcase basis.
+					n -= 10
+				}
+
+				pre, mid, post := split(tt.format)
+				if strings.Contains(mid, "«") {
+					left, base, right := split(mid)
+					mid = strings.Repeat(left, n) + base + strings.Repeat(right, n)
+				} else {
+					mid = strings.Repeat(mid, n)
+				}
+				input := pre + mid + post
+
+				fset := token.NewFileSet()
+				_, err := ParseFile(fset, "", input, DeclarationErrors)
+				if size == "small" {
+					if err != nil {
+						t.Errorf("ParseFile(...): %v (want success)", err)
+					}
+				} else {
+					expected := "exceeded max scope depth during object resolution"
+					if err == nil || !strings.HasSuffix(err.Error(), expected) {
+						t.Errorf("ParseFile(...) = _, %v, want %q", err, expected)
+					}
+				}
+			})
+		}
+	}
+}
+
+// proposal #50429
+func TestRangePos(t *testing.T) {
+	testcases := []string{
+		"package p; func _() { for range x {} }",
+		"package p; func _() { for i = range x {} }",
+		"package p; func _() { for i := range x {} }",
+		"package p; func _() { for k, v = range x {} }",
+		"package p; func _() { for k, v := range x {} }",
+	}
+
+	for _, src := range testcases {
+		fset := token.NewFileSet()
+		f, err := ParseFile(fset, src, src, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		ast.Inspect(f, func(x ast.Node) bool {
+			switch s := x.(type) {
+			case *ast.RangeStmt:
+				pos := fset.Position(s.Range)
+				if pos.Offset != strings.Index(src, "range") {
+					t.Errorf("%s: got offset %v, want %v", src, pos.Offset, strings.Index(src, "range"))
+				}
+			}
+			return true
+		})
+	}
+}
+
+// TestIssue59180 tests that line number overflow doesn't cause an infinite loop.
+func TestIssue59180(t *testing.T) {
+	testcases := []string{
+		"package p\n//line :9223372036854775806\n\n//",
+		"package p\n//line :1:9223372036854775806\n\n//",
+		"package p\n//line file:9223372036854775806\n\n//",
+	}
+
+	for _, src := range testcases {
+		_, err := ParseFile(token.NewFileSet(), "", src, ParseComments)
+		if err == nil {
+			t.Errorf("ParseFile(%s) succeeded unexpectedly", src)
+		}
+	}
+}
+
+func TestGoVersion(t *testing.T) {
+	fset := token.NewFileSet()
+	pkgs, err := ParseDir(fset, "./testdata/goversion", nil, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, p := range pkgs {
+		want := strings.ReplaceAll(p.Name, "_", ".")
+		if want == "none" {
+			want = ""
+		}
+		for _, f := range p.Files {
+			if f.GoVersion != want {
+				t.Errorf("%s: GoVersion = %q, want %q", fset.Position(f.Pos()), f.GoVersion, want)
+			}
+		}
+	}
+}
diff --git a/src/go/parser/performance_test.go b/src/go/parser/performance_test.go
new file mode 100644
index 0000000..1308f21
--- /dev/null
+++ b/src/go/parser/performance_test.go
@@ -0,0 +1,54 @@
+// 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 parser
+
+import (
+	"go/token"
+	"os"
+	"testing"
+)
+
+var src = readFile("../printer/nodes.go")
+
+func readFile(filename string) []byte {
+	data, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err)
+	}
+	return data
+}
+
+func BenchmarkParse(b *testing.B) {
+	b.SetBytes(int64(len(src)))
+	for i := 0; i < b.N; i++ {
+		if _, err := ParseFile(token.NewFileSet(), "", src, ParseComments); err != nil {
+			b.Fatalf("benchmark failed due to parse error: %s", err)
+		}
+	}
+}
+
+func BenchmarkParseOnly(b *testing.B) {
+	b.SetBytes(int64(len(src)))
+	for i := 0; i < b.N; i++ {
+		if _, err := ParseFile(token.NewFileSet(), "", src, ParseComments|SkipObjectResolution); err != nil {
+			b.Fatalf("benchmark failed due to parse error: %s", err)
+		}
+	}
+}
+
+func BenchmarkResolve(b *testing.B) {
+	b.SetBytes(int64(len(src)))
+	for i := 0; i < b.N; i++ {
+		b.StopTimer()
+		fset := token.NewFileSet()
+		file, err := ParseFile(fset, "", src, SkipObjectResolution)
+		if err != nil {
+			b.Fatalf("benchmark failed due to parse error: %s", err)
+		}
+		b.StartTimer()
+		handle := fset.File(file.Package)
+		resolveFile(file, handle, nil)
+	}
+}
diff --git a/src/go/parser/resolver.go b/src/go/parser/resolver.go
new file mode 100644
index 0000000..f8ff618
--- /dev/null
+++ b/src/go/parser/resolver.go
@@ -0,0 +1,612 @@
+// Copyright 2021 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
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"strings"
+)
+
+const debugResolve = false
+
+// resolveFile walks the given file to resolve identifiers within the file
+// scope, updating ast.Ident.Obj fields with declaration information.
+//
+// If declErr is non-nil, it is used to report declaration errors during
+// resolution. tok is used to format position in error messages.
+func resolveFile(file *ast.File, handle *token.File, declErr func(token.Pos, string)) {
+	pkgScope := ast.NewScope(nil)
+	r := &resolver{
+		handle:   handle,
+		declErr:  declErr,
+		topScope: pkgScope,
+		pkgScope: pkgScope,
+		depth:    1,
+	}
+
+	for _, decl := range file.Decls {
+		ast.Walk(r, decl)
+	}
+
+	r.closeScope()
+	assert(r.topScope == nil, "unbalanced scopes")
+	assert(r.labelScope == nil, "unbalanced label scopes")
+
+	// resolve global identifiers within the same file
+	i := 0
+	for _, ident := range r.unresolved {
+		// i <= index for current ident
+		assert(ident.Obj == unresolved, "object already resolved")
+		ident.Obj = r.pkgScope.Lookup(ident.Name) // also removes unresolved sentinel
+		if ident.Obj == nil {
+			r.unresolved[i] = ident
+			i++
+		} else if debugResolve {
+			pos := ident.Obj.Decl.(interface{ Pos() token.Pos }).Pos()
+			r.trace("resolved %s@%v to package object %v", ident.Name, ident.Pos(), pos)
+		}
+	}
+	file.Scope = r.pkgScope
+	file.Unresolved = r.unresolved[0:i]
+}
+
+const maxScopeDepth int = 1e3
+
+type resolver struct {
+	handle  *token.File
+	declErr func(token.Pos, string)
+
+	// Ordinary identifier scopes
+	pkgScope   *ast.Scope   // pkgScope.Outer == nil
+	topScope   *ast.Scope   // top-most scope; may be pkgScope
+	unresolved []*ast.Ident // unresolved identifiers
+	depth      int          // scope depth
+
+	// Label scopes
+	// (maintained by open/close LabelScope)
+	labelScope  *ast.Scope     // label scope for current function
+	targetStack [][]*ast.Ident // stack of unresolved labels
+}
+
+func (r *resolver) trace(format string, args ...any) {
+	fmt.Println(strings.Repeat(". ", r.depth) + r.sprintf(format, args...))
+}
+
+func (r *resolver) sprintf(format string, args ...any) string {
+	for i, arg := range args {
+		switch arg := arg.(type) {
+		case token.Pos:
+			args[i] = r.handle.Position(arg)
+		}
+	}
+	return fmt.Sprintf(format, args...)
+}
+
+func (r *resolver) openScope(pos token.Pos) {
+	r.depth++
+	if r.depth > maxScopeDepth {
+		panic(bailout{pos: pos, msg: "exceeded max scope depth during object resolution"})
+	}
+	if debugResolve {
+		r.trace("opening scope @%v", pos)
+	}
+	r.topScope = ast.NewScope(r.topScope)
+}
+
+func (r *resolver) closeScope() {
+	r.depth--
+	if debugResolve {
+		r.trace("closing scope")
+	}
+	r.topScope = r.topScope.Outer
+}
+
+func (r *resolver) openLabelScope() {
+	r.labelScope = ast.NewScope(r.labelScope)
+	r.targetStack = append(r.targetStack, nil)
+}
+
+func (r *resolver) closeLabelScope() {
+	// resolve labels
+	n := len(r.targetStack) - 1
+	scope := r.labelScope
+	for _, ident := range r.targetStack[n] {
+		ident.Obj = scope.Lookup(ident.Name)
+		if ident.Obj == nil && r.declErr != nil {
+			r.declErr(ident.Pos(), fmt.Sprintf("label %s undefined", ident.Name))
+		}
+	}
+	// pop label scope
+	r.targetStack = r.targetStack[0:n]
+	r.labelScope = r.labelScope.Outer
+}
+
+func (r *resolver) declare(decl, data any, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
+	for _, ident := range idents {
+		if ident.Obj != nil {
+			panic(fmt.Sprintf("%v: identifier %s already declared or resolved", ident.Pos(), ident.Name))
+		}
+		obj := ast.NewObj(kind, ident.Name)
+		// remember the corresponding declaration for redeclaration
+		// errors and global variable resolution/typechecking phase
+		obj.Decl = decl
+		obj.Data = data
+		// Identifiers (for receiver type parameters) are written to the scope, but
+		// never set as the resolved object. See issue #50956.
+		if _, ok := decl.(*ast.Ident); !ok {
+			ident.Obj = obj
+		}
+		if ident.Name != "_" {
+			if debugResolve {
+				r.trace("declaring %s@%v", ident.Name, ident.Pos())
+			}
+			if alt := scope.Insert(obj); alt != nil && r.declErr != nil {
+				prevDecl := ""
+				if pos := alt.Pos(); pos.IsValid() {
+					prevDecl = r.sprintf("\n\tprevious declaration at %v", pos)
+				}
+				r.declErr(ident.Pos(), fmt.Sprintf("%s redeclared in this block%s", ident.Name, prevDecl))
+			}
+		}
+	}
+}
+
+func (r *resolver) shortVarDecl(decl *ast.AssignStmt) {
+	// 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 _, x := range decl.Lhs {
+		if ident, isIdent := x.(*ast.Ident); isIdent {
+			assert(ident.Obj == nil, "identifier already declared or resolved")
+			obj := ast.NewObj(ast.Var, ident.Name)
+			// remember corresponding assignment for other tools
+			obj.Decl = decl
+			ident.Obj = obj
+			if ident.Name != "_" {
+				if debugResolve {
+					r.trace("declaring %s@%v", ident.Name, ident.Pos())
+				}
+				if alt := r.topScope.Insert(obj); alt != nil {
+					ident.Obj = alt // redeclaration
+				} else {
+					n++ // new declaration
+				}
+			}
+		}
+	}
+	if n == 0 && r.declErr != nil {
+		r.declErr(decl.Lhs[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)
+
+// If x is an identifier, resolve attempts to resolve x by looking up
+// the object it denotes. If no object is found and collectUnresolved is
+// set, x is marked as unresolved and collected in the list of unresolved
+// identifiers.
+func (r *resolver) resolve(ident *ast.Ident, collectUnresolved bool) {
+	if ident.Obj != nil {
+		panic(r.sprintf("%v: identifier %s already declared or resolved", ident.Pos(), ident.Name))
+	}
+	// '_' should never refer to existing declarations, because it has special
+	// handling in the spec.
+	if ident.Name == "_" {
+		return
+	}
+	for s := r.topScope; s != nil; s = s.Outer {
+		if obj := s.Lookup(ident.Name); obj != nil {
+			if debugResolve {
+				r.trace("resolved %v:%s to %v", ident.Pos(), ident.Name, obj)
+			}
+			assert(obj.Name != "", "obj with no name")
+			// Identifiers (for receiver type parameters) are written to the scope,
+			// but never set as the resolved object. See issue #50956.
+			if _, ok := obj.Decl.(*ast.Ident); !ok {
+				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
+	if collectUnresolved {
+		ident.Obj = unresolved
+		r.unresolved = append(r.unresolved, ident)
+	}
+}
+
+func (r *resolver) walkExprs(list []ast.Expr) {
+	for _, node := range list {
+		ast.Walk(r, node)
+	}
+}
+
+func (r *resolver) walkLHS(list []ast.Expr) {
+	for _, expr := range list {
+		expr := unparen(expr)
+		if _, ok := expr.(*ast.Ident); !ok && expr != nil {
+			ast.Walk(r, expr)
+		}
+	}
+}
+
+func (r *resolver) walkStmts(list []ast.Stmt) {
+	for _, stmt := range list {
+		ast.Walk(r, stmt)
+	}
+}
+
+func (r *resolver) Visit(node ast.Node) ast.Visitor {
+	if debugResolve && node != nil {
+		r.trace("node %T@%v", node, node.Pos())
+	}
+
+	switch n := node.(type) {
+
+	// Expressions.
+	case *ast.Ident:
+		r.resolve(n, true)
+
+	case *ast.FuncLit:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		r.walkFuncType(n.Type)
+		r.walkBody(n.Body)
+
+	case *ast.SelectorExpr:
+		ast.Walk(r, n.X)
+		// Note: don't try to resolve n.Sel, as we don't support qualified
+		// resolution.
+
+	case *ast.StructType:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		r.walkFieldList(n.Fields, ast.Var)
+
+	case *ast.FuncType:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		r.walkFuncType(n)
+
+	case *ast.CompositeLit:
+		if n.Type != nil {
+			ast.Walk(r, n.Type)
+		}
+		for _, e := range n.Elts {
+			if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
+				// See issue #45160: try to resolve composite lit keys, but don't
+				// collect them as unresolved if resolution failed. This replicates
+				// existing behavior when resolving during parsing.
+				if ident, _ := kv.Key.(*ast.Ident); ident != nil {
+					r.resolve(ident, false)
+				} else {
+					ast.Walk(r, kv.Key)
+				}
+				ast.Walk(r, kv.Value)
+			} else {
+				ast.Walk(r, e)
+			}
+		}
+
+	case *ast.InterfaceType:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		r.walkFieldList(n.Methods, ast.Fun)
+
+	// Statements
+	case *ast.LabeledStmt:
+		r.declare(n, nil, r.labelScope, ast.Lbl, n.Label)
+		ast.Walk(r, n.Stmt)
+
+	case *ast.AssignStmt:
+		r.walkExprs(n.Rhs)
+		if n.Tok == token.DEFINE {
+			r.shortVarDecl(n)
+		} else {
+			r.walkExprs(n.Lhs)
+		}
+
+	case *ast.BranchStmt:
+		// add to list of unresolved targets
+		if n.Tok != token.FALLTHROUGH && n.Label != nil {
+			depth := len(r.targetStack) - 1
+			r.targetStack[depth] = append(r.targetStack[depth], n.Label)
+		}
+
+	case *ast.BlockStmt:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		r.walkStmts(n.List)
+
+	case *ast.IfStmt:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		if n.Init != nil {
+			ast.Walk(r, n.Init)
+		}
+		ast.Walk(r, n.Cond)
+		ast.Walk(r, n.Body)
+		if n.Else != nil {
+			ast.Walk(r, n.Else)
+		}
+
+	case *ast.CaseClause:
+		r.walkExprs(n.List)
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		r.walkStmts(n.Body)
+
+	case *ast.SwitchStmt:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		if n.Init != nil {
+			ast.Walk(r, n.Init)
+		}
+		if n.Tag != nil {
+			// The scope below reproduces some unnecessary behavior of the parser,
+			// opening an extra scope in case this is a type switch. It's not needed
+			// for expression switches.
+			// TODO: remove this once we've matched the parser resolution exactly.
+			if n.Init != nil {
+				r.openScope(n.Tag.Pos())
+				defer r.closeScope()
+			}
+			ast.Walk(r, n.Tag)
+		}
+		if n.Body != nil {
+			r.walkStmts(n.Body.List)
+		}
+
+	case *ast.TypeSwitchStmt:
+		if n.Init != nil {
+			r.openScope(n.Pos())
+			defer r.closeScope()
+			ast.Walk(r, n.Init)
+		}
+		r.openScope(n.Assign.Pos())
+		defer r.closeScope()
+		ast.Walk(r, n.Assign)
+		// s.Body consists only of case clauses, so does not get its own
+		// scope.
+		if n.Body != nil {
+			r.walkStmts(n.Body.List)
+		}
+
+	case *ast.CommClause:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		if n.Comm != nil {
+			ast.Walk(r, n.Comm)
+		}
+		r.walkStmts(n.Body)
+
+	case *ast.SelectStmt:
+		// as for switch statements, select statement bodies don't get their own
+		// scope.
+		if n.Body != nil {
+			r.walkStmts(n.Body.List)
+		}
+
+	case *ast.ForStmt:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		if n.Init != nil {
+			ast.Walk(r, n.Init)
+		}
+		if n.Cond != nil {
+			ast.Walk(r, n.Cond)
+		}
+		if n.Post != nil {
+			ast.Walk(r, n.Post)
+		}
+		ast.Walk(r, n.Body)
+
+	case *ast.RangeStmt:
+		r.openScope(n.Pos())
+		defer r.closeScope()
+		ast.Walk(r, n.X)
+		var lhs []ast.Expr
+		if n.Key != nil {
+			lhs = append(lhs, n.Key)
+		}
+		if n.Value != nil {
+			lhs = append(lhs, n.Value)
+		}
+		if len(lhs) > 0 {
+			if n.Tok == token.DEFINE {
+				// Note: we can't exactly match the behavior of object resolution
+				// during the parsing pass here, as it uses the position of the RANGE
+				// token for the RHS OpPos. That information is not contained within
+				// the AST.
+				as := &ast.AssignStmt{
+					Lhs:    lhs,
+					Tok:    token.DEFINE,
+					TokPos: n.TokPos,
+					Rhs:    []ast.Expr{&ast.UnaryExpr{Op: token.RANGE, X: n.X}},
+				}
+				// TODO(rFindley): this walkLHS reproduced the parser resolution, but
+				// is it necessary? By comparison, for a normal AssignStmt we don't
+				// walk the LHS in case there is an invalid identifier list.
+				r.walkLHS(lhs)
+				r.shortVarDecl(as)
+			} else {
+				r.walkExprs(lhs)
+			}
+		}
+		ast.Walk(r, n.Body)
+
+	// Declarations
+	case *ast.GenDecl:
+		switch n.Tok {
+		case token.CONST, token.VAR:
+			for i, spec := range n.Specs {
+				spec := spec.(*ast.ValueSpec)
+				kind := ast.Con
+				if n.Tok == token.VAR {
+					kind = ast.Var
+				}
+				r.walkExprs(spec.Values)
+				if spec.Type != nil {
+					ast.Walk(r, spec.Type)
+				}
+				r.declare(spec, i, r.topScope, kind, spec.Names...)
+			}
+		case token.TYPE:
+			for _, spec := range n.Specs {
+				spec := spec.(*ast.TypeSpec)
+				// 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.
+				r.declare(spec, nil, r.topScope, ast.Typ, spec.Name)
+				if spec.TypeParams != nil {
+					r.openScope(spec.Pos())
+					defer r.closeScope()
+					r.walkTParams(spec.TypeParams)
+				}
+				ast.Walk(r, spec.Type)
+			}
+		}
+
+	case *ast.FuncDecl:
+		// Open the function scope.
+		r.openScope(n.Pos())
+		defer r.closeScope()
+
+		r.walkRecv(n.Recv)
+
+		// Type parameters are walked normally: they can reference each other, and
+		// can be referenced by normal parameters.
+		if n.Type.TypeParams != nil {
+			r.walkTParams(n.Type.TypeParams)
+			// TODO(rFindley): need to address receiver type parameters.
+		}
+
+		// Resolve and declare parameters in a specific order to get duplicate
+		// declaration errors in the correct location.
+		r.resolveList(n.Type.Params)
+		r.resolveList(n.Type.Results)
+		r.declareList(n.Recv, ast.Var)
+		r.declareList(n.Type.Params, ast.Var)
+		r.declareList(n.Type.Results, ast.Var)
+
+		r.walkBody(n.Body)
+		if n.Recv == nil && n.Name.Name != "init" {
+			r.declare(n, nil, r.pkgScope, ast.Fun, n.Name)
+		}
+
+	default:
+		return r
+	}
+
+	return nil
+}
+
+func (r *resolver) walkFuncType(typ *ast.FuncType) {
+	// typ.TypeParams must be walked separately for FuncDecls.
+	r.resolveList(typ.Params)
+	r.resolveList(typ.Results)
+	r.declareList(typ.Params, ast.Var)
+	r.declareList(typ.Results, ast.Var)
+}
+
+func (r *resolver) resolveList(list *ast.FieldList) {
+	if list == nil {
+		return
+	}
+	for _, f := range list.List {
+		if f.Type != nil {
+			ast.Walk(r, f.Type)
+		}
+	}
+}
+
+func (r *resolver) declareList(list *ast.FieldList, kind ast.ObjKind) {
+	if list == nil {
+		return
+	}
+	for _, f := range list.List {
+		r.declare(f, nil, r.topScope, kind, f.Names...)
+	}
+}
+
+func (r *resolver) walkRecv(recv *ast.FieldList) {
+	// If our receiver has receiver type parameters, we must declare them before
+	// trying to resolve the rest of the receiver, and avoid re-resolving the
+	// type parameter identifiers.
+	if recv == nil || len(recv.List) == 0 {
+		return // nothing to do
+	}
+	typ := recv.List[0].Type
+	if ptr, ok := typ.(*ast.StarExpr); ok {
+		typ = ptr.X
+	}
+
+	var declareExprs []ast.Expr // exprs to declare
+	var resolveExprs []ast.Expr // exprs to resolve
+	switch typ := typ.(type) {
+	case *ast.IndexExpr:
+		declareExprs = []ast.Expr{typ.Index}
+		resolveExprs = append(resolveExprs, typ.X)
+	case *ast.IndexListExpr:
+		declareExprs = typ.Indices
+		resolveExprs = append(resolveExprs, typ.X)
+	default:
+		resolveExprs = append(resolveExprs, typ)
+	}
+	for _, expr := range declareExprs {
+		if id, _ := expr.(*ast.Ident); id != nil {
+			r.declare(expr, nil, r.topScope, ast.Typ, id)
+		} else {
+			// The receiver type parameter expression is invalid, but try to resolve
+			// it anyway for consistency.
+			resolveExprs = append(resolveExprs, expr)
+		}
+	}
+	for _, expr := range resolveExprs {
+		if expr != nil {
+			ast.Walk(r, expr)
+		}
+	}
+	// The receiver is invalid, but try to resolve it anyway for consistency.
+	for _, f := range recv.List[1:] {
+		if f.Type != nil {
+			ast.Walk(r, f.Type)
+		}
+	}
+}
+
+func (r *resolver) walkFieldList(list *ast.FieldList, kind ast.ObjKind) {
+	if list == nil {
+		return
+	}
+	r.resolveList(list)
+	r.declareList(list, kind)
+}
+
+// walkTParams is like walkFieldList, but declares type parameters eagerly so
+// that they may be resolved in the constraint expressions held in the field
+// Type.
+func (r *resolver) walkTParams(list *ast.FieldList) {
+	r.declareList(list, ast.Typ)
+	r.resolveList(list)
+}
+
+func (r *resolver) walkBody(body *ast.BlockStmt) {
+	if body == nil {
+		return
+	}
+	r.openLabelScope()
+	defer r.closeLabelScope()
+	r.walkStmts(body.List)
+}
diff --git a/src/go/parser/resolver_test.go b/src/go/parser/resolver_test.go
new file mode 100644
index 0000000..38739a3
--- /dev/null
+++ b/src/go/parser/resolver_test.go
@@ -0,0 +1,172 @@
+// Copyright 2021 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
+
+import (
+	"fmt"
+	"go/ast"
+	"go/scanner"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// TestResolution checks that identifiers are resolved to the declarations
+// annotated in the source, by comparing the positions of the resulting
+// Ident.Obj.Decl to positions marked in the source via special comments.
+//
+// In the test source, any comment prefixed with '=' or '@' (or both) marks the
+// previous token position as the declaration ('=') or a use ('@') of an
+// identifier. The text following '=' and '@' in the comment string is the
+// label to use for the location.  Declaration labels must be unique within the
+// file, and use labels must refer to an existing declaration label. It's OK
+// for a comment to denote both the declaration and use of a label (e.g.
+// '=@foo'). Leading and trailing whitespace is ignored. Any comment not
+// beginning with '=' or '@' is ignored.
+func TestResolution(t *testing.T) {
+	dir := filepath.Join("testdata", "resolution")
+	fis, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, fi := range fis {
+		t.Run(fi.Name(), func(t *testing.T) {
+			fset := token.NewFileSet()
+			path := filepath.Join(dir, fi.Name())
+			src := readFile(path) // panics on failure
+			var mode Mode
+			file, err := ParseFile(fset, path, src, mode)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// Compare the positions of objects resolved during parsing (fromParser)
+			// to those annotated in source comments (fromComments).
+
+			handle := fset.File(file.Package)
+			fromParser := declsFromParser(file)
+			fromComments := declsFromComments(handle, src)
+
+			pos := func(pos token.Pos) token.Position {
+				p := handle.Position(pos)
+				// The file name is implied by the subtest, so remove it to avoid
+				// clutter in error messages.
+				p.Filename = ""
+				return p
+			}
+			for k, want := range fromComments {
+				if got := fromParser[k]; got != want {
+					t.Errorf("%s resolved to %s, want %s", pos(k), pos(got), pos(want))
+				}
+				delete(fromParser, k)
+			}
+			// What remains in fromParser are unexpected resolutions.
+			for k, got := range fromParser {
+				t.Errorf("%s resolved to %s, want no object", pos(k), pos(got))
+			}
+		})
+	}
+}
+
+// declsFromParser walks the file and collects the map associating an
+// identifier position with its declaration position.
+func declsFromParser(file *ast.File) map[token.Pos]token.Pos {
+	objmap := map[token.Pos]token.Pos{}
+	ast.Inspect(file, func(node ast.Node) bool {
+		// Ignore blank identifiers to reduce noise.
+		if ident, _ := node.(*ast.Ident); ident != nil && ident.Obj != nil && ident.Name != "_" {
+			objmap[ident.Pos()] = ident.Obj.Pos()
+		}
+		return true
+	})
+	return objmap
+}
+
+// declsFromComments looks at comments annotating uses and declarations, and
+// maps each identifier use to its corresponding declaration. See the
+// description of these annotations in the documentation for TestResolution.
+func declsFromComments(handle *token.File, src []byte) map[token.Pos]token.Pos {
+	decls, uses := positionMarkers(handle, src)
+
+	objmap := make(map[token.Pos]token.Pos)
+	// Join decls and uses on name, to build the map of use->decl.
+	for name, posns := range uses {
+		declpos, ok := decls[name]
+		if !ok {
+			panic(fmt.Sprintf("missing declaration for %s", name))
+		}
+		for _, pos := range posns {
+			objmap[pos] = declpos
+		}
+	}
+	return objmap
+}
+
+// positionMarkers extracts named positions from the source denoted by comments
+// prefixed with '=' (declarations) and '@' (uses): for example '@foo' or
+// '=@bar'. It returns a map of name->position for declarations, and
+// name->position(s) for uses.
+func positionMarkers(handle *token.File, src []byte) (decls map[string]token.Pos, uses map[string][]token.Pos) {
+	var s scanner.Scanner
+	s.Init(handle, src, nil, scanner.ScanComments)
+	decls = make(map[string]token.Pos)
+	uses = make(map[string][]token.Pos)
+	var prev token.Pos // position of last non-comment, non-semicolon token
+
+scanFile:
+	for {
+		pos, tok, lit := s.Scan()
+		switch tok {
+		case token.EOF:
+			break scanFile
+		case token.COMMENT:
+			name, decl, use := annotatedObj(lit)
+			if len(name) > 0 {
+				if decl {
+					if _, ok := decls[name]; ok {
+						panic(fmt.Sprintf("duplicate declaration markers for %s", name))
+					}
+					decls[name] = prev
+				}
+				if use {
+					uses[name] = append(uses[name], prev)
+				}
+			}
+		case token.SEMICOLON:
+			// ignore automatically inserted semicolon
+			if lit == "\n" {
+				continue scanFile
+			}
+			fallthrough
+		default:
+			prev = pos
+		}
+	}
+	return decls, uses
+}
+
+func annotatedObj(lit string) (name string, decl, use bool) {
+	if lit[1] == '*' {
+		lit = lit[:len(lit)-2] // strip trailing */
+	}
+	lit = strings.TrimSpace(lit[2:])
+
+scanLit:
+	for idx, r := range lit {
+		switch r {
+		case '=':
+			decl = true
+		case '@':
+			use = true
+		default:
+			name = lit[idx:]
+			break scanLit
+		}
+	}
+	return
+}
diff --git a/src/go/parser/short_test.go b/src/go/parser/short_test.go
new file mode 100644
index 0000000..f9575e1
--- /dev/null
+++ b/src/go/parser/short_test.go
@@ -0,0 +1,214 @@
+// 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 contains test cases for short valid and invalid programs.
+
+package parser
+
+import "testing"
+
+var valids = []string{
+	"package p\n",
+	`package p;`,
+	`package p; import "fmt"; func f() { fmt.Println("Hello, World!") };`,
+	`package p; func f() { if f(T{}) {} };`,
+	`package p; func f() { _ = <-chan int(nil) };`,
+	`package p; func f() { _ = (<-chan int)(nil) };`,
+	`package p; func f() { _ = (<-chan <-chan int)(nil) };`,
+	`package p; func f() { _ = <-chan <-chan <-chan <-chan <-int(nil) };`,
+	`package p; func f(func() func() func());`,
+	`package p; func f(...T);`,
+	`package p; func f(float, ...int);`,
+	`package p; func f(x int, a ...int) { f(0, a...); f(1, a...,) };`,
+	`package p; func f(int,) {};`,
+	`package p; func f(...int,) {};`,
+	`package p; func f(x ...int,) {};`,
+	`package p; type T []int; var a []bool; func f() { if a[T{42}[0]] {} };`,
+	`package p; type T []int; func g(int) bool { return true }; func f() { if g(T{42}[0]) {} };`,
+	`package p; type T []int; func f() { for _ = range []int{T{42}[0]} {} };`,
+	`package p; var a = T{{1, 2}, {3, 4}}`,
+	`package p; func f() { select { case <- c: case c <- d: case c <- <- d: case <-c <- d: } };`,
+	`package p; func f() { select { case x := (<-c): } };`,
+	`package p; func f() { if ; true {} };`,
+	`package p; func f() { switch ; {} };`,
+	`package p; func f() { for _ = range "foo" + "bar" {} };`,
+	`package p; func f() { var s []int; g(s[:], s[i:], s[:j], s[i:j], s[i:j:k], s[:j:k]) };`,
+	`package p; var ( _ = (struct {*T}).m; _ = (interface {T}).m )`,
+	`package p; func ((T),) m() {}`,
+	`package p; func ((*T),) m() {}`,
+	`package p; func (*(T),) m() {}`,
+	`package p; func _(x []int) { for range x {} }`,
+	`package p; func _() { if [T{}.n]int{} {} }`,
+	`package p; func _() { map[int]int{}[0]++; map[int]int{}[0] += 1 }`,
+	`package p; func _(x interface{f()}) { interface{f()}(x).f() }`,
+	`package p; func _(x chan int) { chan int(x) <- 0 }`,
+	`package p; const (x = 0; y; z)`, // issue 9639
+	`package p; var _ = map[P]int{P{}:0, {}:1}`,
+	`package p; var _ = map[*P]int{&P{}:0, {}:1}`,
+	`package p; type T = int`,
+	`package p; type (T = p.T; _ = struct{}; x = *T)`,
+	`package p; type T (*int)`,
+	`package p; type _ struct{ int }`,
+	`package p; type _ struct{ pkg.T }`,
+	`package p; type _ struct{ *pkg.T }`,
+	`package p; var _ = func()T(nil)`,
+	`package p; func _(T (P))`,
+	`package p; func _(T []E)`,
+	`package p; func _(T [P]E)`,
+	`package p; type _ [A+B]struct{}`,
+	`package p; func (R) _()`,
+	`package p; type _ struct{ f [n]E }`,
+	`package p; type _ struct{ f [a+b+c+d]E }`,
+	`package p; type I1 interface{}; type I2 interface{ I1 }`,
+
+	// generic code
+	`package p; type _ []T[int]`,
+	`package p; type T[P any] struct { P }`,
+	`package p; type T[P comparable] struct { P }`,
+	`package p; type T[P comparable[P]] struct { P }`,
+	`package p; type T[P1, P2 any] struct { P1; f []P2 }`,
+	`package p; func _[T any]()()`,
+	`package p; func _(T (P))`,
+	`package p; func f[A, B any](); func _() { _ = f[int, int] }`,
+	`package p; func _(x T[P1, P2, P3])`,
+	`package p; func _(x p.T[Q])`,
+	`package p; func _(p.T[Q])`,
+	`package p; type _[A interface{},] struct{}`,
+	`package p; type _[A interface{}] struct{}`,
+	`package p; type _[A,  B any,] struct{}`,
+	`package p; type _[A, B any] struct{}`,
+	`package p; type _[A any,] struct{}`,
+	`package p; type _[A any]struct{}`,
+	`package p; type _[A any] struct{ A }`,
+	`package p; func _[T any]()`,
+	`package p; func _[T any](x T)`,
+	`package p; func _[T1, T2 any](x T)`,
+	`package p; func _[A, B any](a A) B`,
+	`package p; func _[A, B C](a A) B`,
+	`package p; func _[A, B C[A, B]](a A) B`,
+
+	`package p; type _[A, B any] interface { _(a A) B }`,
+	`package p; type _[A, B C[A, B]] interface { _(a A) B }`,
+	`package p; func _[T1, T2 interface{}](x T1) T2`,
+	`package p; func _[T1 interface{ m() }, T2, T3 interface{}](x T1, y T3) T2`,
+	`package p; var _ = []T[int]{}`,
+	`package p; var _ = [10]T[int]{}`,
+	`package p; var _ = func()T[int]{}`,
+	`package p; var _ = map[T[int]]T[int]{}`,
+	`package p; var _ = chan T[int](x)`,
+	`package p; func _(_ T[P], T P) T[P]`,
+	`package p; var _ T[chan int]`,
+
+	`package p; func (_ R[P]) _(x T)`,
+	`package p; func (_ R[ P, Q]) _(x T)`,
+
+	`package p; func (R[P]) _()`,
+	`package p; func _(T[P])`,
+	`package p; func _(T[P1, P2, P3 ])`,
+	`package p; func _(T[P]) T[P]`,
+	`package p; type _ struct{ T[P]}`,
+	`package p; type _ struct{ T[struct{a, b, c int}] }`,
+	`package p; type _ interface{int|float32; bool; m(); string;}`,
+	`package p; type I1[T any] interface{}; type I2 interface{ I1[int] }`,
+	`package p; type I1[T any] interface{}; type I2[T any] interface{ I1[T] }`,
+	`package p; type _ interface { N[T] }`,
+	`package p; type T[P any] = T0`,
+}
+
+func TestValid(t *testing.T) {
+	for _, src := range valids {
+		checkErrors(t, src, src, DeclarationErrors|AllErrors, false)
+	}
+}
+
+// TestSingle is useful to track down a problem with a single short test program.
+func TestSingle(t *testing.T) {
+	const src = `package p; var _ = T{}`
+	checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
+}
+
+var invalids = []string{
+	`foo /* ERROR "expected 'package'" */ !`,
+	`package p; func f() { if { /* ERROR "missing condition" */ } };`,
+	`package p; func f() { if ; /* ERROR "missing condition" */ {} };`,
+	`package p; func f() { if f(); /* ERROR "missing condition" */ {} };`,
+	`package p; func f() { if _ = range /* ERROR "expected operand" */ x; true {} };`,
+	`package p; func f() { switch _ /* ERROR "expected switch expression" */ = range x; true {} };`,
+	`package p; func f() { for _ = range x ; /* ERROR "expected '{'" */ ; {} };`,
+	`package p; func f() { for ; ; _ = range /* ERROR "expected operand" */ x {} };`,
+	`package p; func f() { for ; _ /* ERROR "expected boolean or range expression" */ = range x ; {} };`,
+	`package p; func f() { switch t = /* ERROR "expected ':=', found '='" */ t.(type) {} };`,
+	`package p; func f() { switch t /* ERROR "expected switch expression" */ , t = t.(type) {} };`,
+	`package p; func f() { switch t /* ERROR "expected switch expression" */ = t.(type), t {} };`,
+	`package p; func f() { _ = (<-<- /* ERROR "expected 'chan'" */ chan int)(nil) };`,
+	`package p; func f() { _ = (<-chan<-chan<-chan<-chan<-chan<- /* ERROR "expected channel type" */ int)(nil) };`,
+	`package p; func f() { if x := g(); x /* ERROR "expected boolean expression" */ = 0 {}};`,
+	`package p; func f() { _ = x = /* ERROR "expected '=='" */ 0 {}};`,
+	`package p; func f() { _ = 1 == func()int { var x bool; x = x = /* ERROR "expected '=='" */ true; return x }() };`,
+	`package p; func f() { var s []int; _ = s[] /* ERROR "expected operand" */ };`,
+	`package p; func f() { var s []int; _ = s[i:j: /* ERROR "final index required" */ ] };`,
+	`package p; func f() { var s []int; _ = s[i: /* ERROR "middle index required" */ :k] };`,
+	`package p; func f() { var s []int; _ = s[i: /* ERROR "middle index required" */ :] };`,
+	`package p; func f() { var s []int; _ = s[: /* ERROR "middle index required" */ :] };`,
+	`package p; func f() { var s []int; _ = s[: /* ERROR "middle index required" */ ::] };`,
+	`package p; func f() { var s []int; _ = s[i:j:k: /* ERROR "expected ']'" */ l] };`,
+	`package p; func f() { for x /* ERROR "boolean or range expression" */ = []string {} }`,
+	`package p; func f() { for x /* ERROR "boolean or range expression" */ := []string {} }`,
+	`package p; func f() { for i /* ERROR "boolean or range expression" */ , x = []string {} }`,
+	`package p; func f() { for i /* ERROR "boolean or range expression" */ , x := []string {} }`,
+	`package p; func f() { go f /* ERROR HERE "must be function call" */ }`,
+	`package p; func f() { go ( /* ERROR "must not be parenthesized" */ f()) }`,
+	`package p; func f() { defer func() {} /* ERROR HERE "must be function call" */ }`,
+	`package p; func f() { defer ( /* ERROR "must not be parenthesized" */ f()) }`,
+	`package p; func f() { go func() { func() { f(x func /* ERROR "missing ','" */ (){}) } } }`,
+	`package p; func _() (type /* ERROR "found 'type'" */ T)(T)`,
+	`package p; func (type /* ERROR "found 'type'" */ T)(T) _()`,
+	`package p; type _[A+B, /* ERROR "unexpected comma" */ ] int`,
+
+	`package p; type _ struct{ [ /* ERROR "expected '}', found '\['" */ ]byte }`,
+	`package p; type _ struct{ ( /* ERROR "cannot parenthesize embedded type" */ int) }`,
+	`package p; type _ struct{ ( /* ERROR "cannot parenthesize embedded type" */ []byte) }`,
+	`package p; type _ struct{ *( /* ERROR "cannot parenthesize embedded type" */ int) }`,
+	`package p; type _ struct{ *( /* ERROR "cannot parenthesize embedded type" */ []byte) }`,
+
+	// issue 8656
+	`package p; func f() (a b string /* ERROR "missing ','" */ , ok bool)`,
+
+	// issue 9639
+	`package p; var x, y, z; /* ERROR "expected type" */`,
+
+	// issue 12437
+	`package p; var _ = struct { x int, /* ERROR "expected ';', found ','" */ }{};`,
+	`package p; var _ = struct { x int, /* ERROR "expected ';', found ','" */ y float }{};`,
+
+	// issue 11611
+	`package p; type _ struct { int, } /* ERROR "expected 'IDENT', found '}'" */ ;`,
+	`package p; type _ struct { int, float } /* ERROR "expected type, found '}'" */ ;`,
+
+	// issue 13475
+	`package p; func f() { if true {} else ; /* ERROR "expected if statement or block" */ }`,
+	`package p; func f() { if true {} else defer /* ERROR "expected if statement or block" */ f() }`,
+
+	// generic code
+	`package p; type _[_ any] int; var _ = T[] /* ERROR "expected operand" */ {}`,
+	`package p; var _ func[ /* ERROR "must have no type parameters" */ T any](T)`,
+	`package p; func _[]/* ERROR "empty type parameter list" */()`,
+
+	// TODO(rfindley) a better location would be after the ']'
+	`package p; type _[A /* ERROR "type parameters must be named" */ ,] struct{ A }`,
+
+	`package p; func _[type /* ERROR "found 'type'" */ P, *Q interface{}]()`,
+
+	`package p; func (T) _[ /* ERROR "must have no type parameters" */ A, B any](a A) B`,
+	`package p; func (T) _[ /* ERROR "must have no type parameters" */ A, B C](a A) B`,
+	`package p; func (T) _[ /* ERROR "must have no type parameters" */ A, B C[A, B]](a A) B`,
+
+	`package p; func(*T[e, e /* ERROR "e redeclared" */ ]) _()`,
+}
+
+func TestInvalid(t *testing.T) {
+	for _, src := range invalids {
+		checkErrors(t, src, src, DeclarationErrors|AllErrors, true)
+	}
+}
diff --git a/src/go/parser/testdata/chans.go2 b/src/go/parser/testdata/chans.go2
new file mode 100644
index 0000000..fad2bce
--- /dev/null
+++ b/src/go/parser/testdata/chans.go2
@@ -0,0 +1,62 @@
+package chans
+
+import "runtime"
+
+// Ranger returns a Sender and a Receiver. The Receiver provides a
+// Next method to retrieve values. The Sender provides a Send method
+// to send values and a Close method to stop sending values. The Next
+// method indicates when the Sender has been closed, and the Send
+// method indicates when the Receiver has been freed.
+//
+// This is a convenient way to exit a goroutine sending values when
+// the receiver stops reading them.
+func Ranger[T any]() (*Sender[T], *Receiver[T]) {
+	c := make(chan T)
+	d := make(chan bool)
+	s := &Sender[T]{values: c, done: d}
+	r := &Receiver[T]{values: c, done: d}
+	runtime.SetFinalizer(r, r.finalize)
+	return s, r
+}
+
+// A sender is used to send values to a Receiver.
+type Sender[T any] struct {
+	values chan<- T
+	done <-chan bool
+}
+
+// Send sends a value to the receiver. It returns whether any more
+// values may be sent; if it returns false the value was not sent.
+func (s *Sender[T]) Send(v T) bool {
+	select {
+	case s.values <- v:
+		return true
+	case <-s.done:
+		return false
+	}
+}
+
+// Close tells the receiver that no more values will arrive.
+// After Close is called, the Sender may no longer be used.
+func (s *Sender[T]) Close() {
+	close(s.values)
+}
+
+// A Receiver receives values from a Sender.
+type Receiver[T any] struct {
+	values <-chan T
+	done chan<- bool
+}
+
+// Next returns the next value from the channel. The bool result
+// indicates whether the value is valid, or whether the Sender has
+// been closed and no more values will be received.
+func (r *Receiver[T]) Next() (T, bool) {
+	v, ok := <-r.values
+	return v, ok
+}
+
+// finalize is a finalizer for the receiver.
+func (r *Receiver[T]) finalize() {
+	close(r.done)
+}
diff --git a/src/go/parser/testdata/commas.src b/src/go/parser/testdata/commas.src
new file mode 100644
index 0000000..2c52ae5
--- /dev/null
+++ b/src/go/parser/testdata/commas.src
@@ -0,0 +1,19 @@
+// 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.
+
+// Test case for error messages/parser synchronization
+// after missing commas.
+
+package p
+
+var _ = []int{
+	0/* ERROR AFTER "missing ','" */
+}
+
+var _ = []int{
+	0,
+	1,
+	2,
+	3/* ERROR AFTER "missing ','" */
+}
diff --git a/src/go/parser/testdata/goversion/t01.go b/src/go/parser/testdata/goversion/t01.go
new file mode 100644
index 0000000..5cfa0cc
--- /dev/null
+++ b/src/go/parser/testdata/goversion/t01.go
@@ -0,0 +1,3 @@
+//go:build windows
+
+package none
diff --git a/src/go/parser/testdata/goversion/t02.go b/src/go/parser/testdata/goversion/t02.go
new file mode 100644
index 0000000..d91f995
--- /dev/null
+++ b/src/go/parser/testdata/goversion/t02.go
@@ -0,0 +1,3 @@
+//go:build linux && go1.2
+
+package go1_2
diff --git a/src/go/parser/testdata/goversion/t03.go b/src/go/parser/testdata/goversion/t03.go
new file mode 100644
index 0000000..97fc9ae
--- /dev/null
+++ b/src/go/parser/testdata/goversion/t03.go
@@ -0,0 +1,3 @@
+//go:build linux && go1.2 || windows
+
+package none
diff --git a/src/go/parser/testdata/goversion/t04.go b/src/go/parser/testdata/goversion/t04.go
new file mode 100644
index 0000000..e81f9c0
--- /dev/null
+++ b/src/go/parser/testdata/goversion/t04.go
@@ -0,0 +1,5 @@
+// copyright notice
+
+//go:build (linux && go1.2) || (windows && go1.1)
+
+package go1_1
diff --git a/src/go/parser/testdata/goversion/t05.go b/src/go/parser/testdata/goversion/t05.go
new file mode 100644
index 0000000..42c6b33
--- /dev/null
+++ b/src/go/parser/testdata/goversion/t05.go
@@ -0,0 +1,3 @@
+//go:build linux && go1.2 && go1.4
+
+package go1_4
diff --git a/src/go/parser/testdata/goversion/t06.go b/src/go/parser/testdata/goversion/t06.go
new file mode 100644
index 0000000..22944de
--- /dev/null
+++ b/src/go/parser/testdata/goversion/t06.go
@@ -0,0 +1,3 @@
+//go:build go1
+
+package go1
diff --git a/src/go/parser/testdata/interface.go2 b/src/go/parser/testdata/interface.go2
new file mode 100644
index 0000000..2ed9339
--- /dev/null
+++ b/src/go/parser/testdata/interface.go2
@@ -0,0 +1,76 @@
+// Copyright 2021 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 contains test cases for interfaces containing
+// constraint elements.
+
+package p
+
+type _ interface {
+	m()
+	~int
+	~int|string
+	E
+}
+
+type _ interface {
+	m()
+	~int
+	int | string
+	int | ~string
+	~int | ~string
+}
+
+type _ interface {
+	m()
+	~int
+	T[int, string] | string
+	int | ~T[string, struct{}]
+	~int | ~string
+}
+
+type _ interface {
+	int
+	[]byte
+	[10]int
+	struct{}
+	*int
+	func()
+	interface{}
+	map[string]int
+	chan T
+	chan<- T
+	<-chan T
+	T[int]
+}
+
+type _ interface {
+	int | string
+	[]byte | string
+	[10]int | string
+	struct{} | string
+	*int | string
+	func() | string
+	interface{} | string
+	map[string]int | string
+	chan T | string
+	chan<- T | string
+	<-chan T | string
+	T[int] | string
+}
+
+type _ interface {
+	~int | string
+	~[]byte | string
+	~[10]int | string
+	~struct{} | string
+	~*int | string
+	~func() | string
+	~interface{} | string
+	~map[string]int | string
+	~chan T | string
+	~chan<- T | string
+	~<-chan T | string
+	~T[int] | string
+}
diff --git a/src/go/parser/testdata/issue11377.src b/src/go/parser/testdata/issue11377.src
new file mode 100644
index 0000000..1c43800
--- /dev/null
+++ b/src/go/parser/testdata/issue11377.src
@@ -0,0 +1,27 @@
+// 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.
+
+// Test case for issue 11377: Better synchronization of
+// parser after certain syntax errors.
+
+package p
+
+func bad1() {
+    if f()) /* ERROR "expected ';', found '\)'" */ {
+        return
+    }
+}
+
+// There shouldn't be any errors down below.
+
+func F1() {}
+func F2() {}
+func F3() {}
+func F4() {}
+func F5() {}
+func F6() {}
+func F7() {}
+func F8() {}
+func F9() {}
+func F10() {}
diff --git a/src/go/parser/testdata/issue23434.src b/src/go/parser/testdata/issue23434.src
new file mode 100644
index 0000000..24a0832
--- /dev/null
+++ b/src/go/parser/testdata/issue23434.src
@@ -0,0 +1,25 @@
+// 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.
+
+// Test case for issue 23434: Better synchronization of
+// parser after missing type. There should be exactly
+// one error each time, with now follow errors.
+
+package p
+
+func g() {
+	m := make(map[string]! /* ERROR "expected type, found '!'" */ )
+	for {
+		x := 1
+		print(x)
+	}
+}
+
+func f() {
+	m := make(map[string]) /* ERROR "expected type, found '\)'" */
+	for {
+		x := 1
+		print(x)
+	}
+}
diff --git a/src/go/parser/testdata/issue3106.src b/src/go/parser/testdata/issue3106.src
new file mode 100644
index 0000000..2db10be
--- /dev/null
+++ b/src/go/parser/testdata/issue3106.src
@@ -0,0 +1,46 @@
+// 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.
+
+// Test case for issue 3106: Better synchronization of
+// parser after certain syntax errors.
+
+package main
+
+func f() {
+	var m Mutex
+	c := MakeCond(&m)
+	percent := 0
+	const step = 10
+	for i := 0; i < 5; i++ {
+		go func() {
+			for {
+				// Emulates some useful work.
+				time.Sleep(1e8)
+				m.Lock()
+				defer
+				if /* ERROR "expected ';', found 'if'" */ percent == 100 {
+					m.Unlock()
+					break
+				}
+				percent++
+				if percent % step == 0 {
+					//c.Signal()
+				}
+				m.Unlock()
+			}
+		}()
+	}
+	for {
+		m.Lock()
+		if percent == 0 || percent % step != 0 {
+			c.Wait()
+		}
+		fmt.Print(",")
+		if percent == 100 {
+			m.Unlock()
+			break
+		}
+		m.Unlock()
+	}
+}
diff --git a/src/go/parser/testdata/issue34946.src b/src/go/parser/testdata/issue34946.src
new file mode 100644
index 0000000..6bb15e1
--- /dev/null
+++ b/src/go/parser/testdata/issue34946.src
@@ -0,0 +1,22 @@
+// Copyright 2019 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.
+
+// Test case for issue 34946: Better synchronization of
+// parser for function declarations that start their
+// body's opening { on a new line.
+
+package p
+
+// accept Allman/BSD-style declaration but complain
+// (implicit semicolon between signature and body)
+func _() int
+{ /* ERROR "unexpected semicolon or newline before {" */
+	{ return 0 }
+}
+
+func _() {}
+
+func _(); { /* ERROR "unexpected semicolon or newline before {" */ }
+
+func _() {}
diff --git a/src/go/parser/testdata/issue42951/not_a_file.go/invalid.go b/src/go/parser/testdata/issue42951/not_a_file.go/invalid.go
new file mode 100644
index 0000000..bb698be
--- /dev/null
+++ b/src/go/parser/testdata/issue42951/not_a_file.go/invalid.go
@@ -0,0 +1 @@
+This file should not be parsed by ParseDir.
diff --git a/src/go/parser/testdata/issue44504.src b/src/go/parser/testdata/issue44504.src
new file mode 100644
index 0000000..7791f4a
--- /dev/null
+++ b/src/go/parser/testdata/issue44504.src
@@ -0,0 +1,13 @@
+// Copyright 2021 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.
+
+// Test case for issue 44504: panic due to duplicate resolution of slice/index
+// operands. We should not try to resolve a LHS expression with invalid syntax.
+
+package p
+
+func _() {
+  var items []bool
+  items[] /* ERROR "operand" */ = false
+}
diff --git a/src/go/parser/testdata/issue49174.go2 b/src/go/parser/testdata/issue49174.go2
new file mode 100644
index 0000000..77c1950
--- /dev/null
+++ b/src/go/parser/testdata/issue49174.go2
@@ -0,0 +1,8 @@
+// Copyright 2021 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 p
+
+func _[_ []int | int]() {}
+func _[_ int | []int]() {}
diff --git a/src/go/parser/testdata/issue49175.go2 b/src/go/parser/testdata/issue49175.go2
new file mode 100644
index 0000000..cf1c83c
--- /dev/null
+++ b/src/go/parser/testdata/issue49175.go2
@@ -0,0 +1,13 @@
+// Copyright 2021 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 p
+
+type _[_ []t]t
+type _[_ [1]t]t
+
+func _[_ []t]() {}
+func _[_ [1]t]() {}
+
+type t [t /* ERROR "type parameters must be named" */ [0]]t
diff --git a/src/go/parser/testdata/issue49482.go2 b/src/go/parser/testdata/issue49482.go2
new file mode 100644
index 0000000..d8385be
--- /dev/null
+++ b/src/go/parser/testdata/issue49482.go2
@@ -0,0 +1,34 @@
+// Copyright 2021 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 p
+
+type (
+        // these need a comma to disambiguate
+        _[P *T,] struct{}
+        _[P *T, _ any] struct{}
+        _[P (*T),] struct{}
+        _[P (*T), _ any] struct{}
+        _[P (T),] struct{}
+        _[P (T), _ any] struct{}
+
+        // these parse as name followed by type
+        _[P *struct{}] struct{}
+        _[P (*struct{})] struct{}
+        _[P ([]int)] struct{}
+
+        // array declarations
+        _ [P(T)]struct{}
+        _ [P((T))]struct{}
+        _ [P * *T]struct{}
+        _ [P * T]struct{}
+        _ [P(*T)]struct{}
+        _ [P(**T)]struct{}
+        _ [P * T - T]struct{}
+        _ [P*T-T, /* ERROR "unexpected comma" */ ]struct{}
+        _ [10, /* ERROR "unexpected comma" */ ]struct{}
+
+        _[P *struct{}|int] struct{}
+        _[P *struct{}|int|string] struct{}
+)
diff --git a/src/go/parser/testdata/issue50427.go2 b/src/go/parser/testdata/issue50427.go2
new file mode 100644
index 0000000..1521459
--- /dev/null
+++ b/src/go/parser/testdata/issue50427.go2
@@ -0,0 +1,19 @@
+// 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 p
+
+type T interface{ m[ /* ERROR "must have no type parameters" */ P any]() }
+
+func _(t T) {
+	var _ interface{ m[ /* ERROR "must have no type parameters" */ P any](); n() } = t
+}
+
+type S struct{}
+
+func (S) m[ /* ERROR "must have no type parameters" */ P any]() {}
+
+func _(s S) {
+	var _ interface{ m[ /* ERROR "must have no type parameters" */ P any](); n() } = s
+}
diff --git a/src/go/parser/testdata/linalg.go2 b/src/go/parser/testdata/linalg.go2
new file mode 100644
index 0000000..7ccb19c
--- /dev/null
+++ b/src/go/parser/testdata/linalg.go2
@@ -0,0 +1,83 @@
+// Copyright 2019 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 linalg
+
+import "math"
+
+// Numeric is type bound that matches any numeric type.
+// It would likely be in a constraints package in the standard library.
+type Numeric interface {
+	~int|~int8|~int16|~int32|~int64|
+		~uint|~uint8|~uint16|~uint32|~uint64|~uintptr|
+		~float32|~float64|
+		~complex64|~complex128
+}
+
+func DotProduct[T Numeric](s1, s2 []T) T {
+	if len(s1) != len(s2) {
+		panic("DotProduct: slices of unequal length")
+	}
+	var r T
+	for i := range s1 {
+		r += s1[i] * s2[i]
+	}
+	return r
+}
+
+// NumericAbs matches numeric types with an Abs method.
+type NumericAbs[T any] interface {
+	Numeric
+
+	Abs() T
+}
+
+// AbsDifference computes the absolute value of the difference of
+// a and b, where the absolute value is determined by the Abs method.
+func AbsDifference[T NumericAbs](a, b T) T {
+	d := a - b
+	return d.Abs()
+}
+
+// OrderedNumeric is a type bound that matches numeric types that support the < operator.
+type OrderedNumeric interface {
+	~int|~int8|~int16|~int32|~int64|
+		~uint|~uint8|~uint16|~uint32|~uint64|~uintptr|
+		~float32|~float64
+}
+
+// Complex is a type bound that matches the two complex types, which do not have a < operator.
+type Complex interface {
+	~complex64|~complex128
+}
+
+// OrderedAbs is a helper type that defines an Abs method for
+// ordered numeric types.
+type OrderedAbs[T OrderedNumeric] T
+
+func (a OrderedAbs[T]) Abs() OrderedAbs[T] {
+	if a < 0 {
+		return -a
+	}
+	return a
+}
+
+// ComplexAbs is a helper type that defines an Abs method for
+// complex types.
+type ComplexAbs[T Complex] T
+
+func (a ComplexAbs[T]) Abs() ComplexAbs[T] {
+	r := float64(real(a))
+	i := float64(imag(a))
+	d := math.Sqrt(r * r + i * i)
+	return ComplexAbs[T](complex(d, 0))
+}
+
+func OrderedAbsDifference[T OrderedNumeric](a, b T) T {
+	return T(AbsDifference(OrderedAbs[T](a), OrderedAbs[T](b)))
+}
+
+func ComplexAbsDifference[T Complex](a, b T) T {
+	return T(AbsDifference(ComplexAbs[T](a), ComplexAbs[T](b)))
+}
diff --git a/src/go/parser/testdata/map.go2 b/src/go/parser/testdata/map.go2
new file mode 100644
index 0000000..74c79ae
--- /dev/null
+++ b/src/go/parser/testdata/map.go2
@@ -0,0 +1,109 @@
+// Package orderedmap provides an ordered map, implemented as a binary tree.
+package orderedmap
+
+import "chans"
+
+// Map is an ordered map.
+type Map[K, V any] struct {
+	root    *node[K, V]
+	compare func(K, K) int
+}
+
+// node is the type of a node in the binary tree.
+type node[K, V any] struct {
+	key         K
+	val         V
+	left, right *node[K, V]
+}
+
+// New returns a new map.
+func New[K, V any](compare func(K, K) int) *Map[K, V] {
+        return &Map[K, V]{compare: compare}
+}
+
+// find looks up key in the map, and returns either a pointer
+// to the node holding key, or a pointer to the location where
+// such a node would go.
+func (m *Map[K, V]) find(key K) **node[K, V] {
+	pn := &m.root
+	for *pn != nil {
+		switch cmp := m.compare(key, (*pn).key); {
+		case cmp < 0:
+			pn = &(*pn).left
+		case cmp > 0:
+			pn = &(*pn).right
+		default:
+			return pn
+		}
+	}
+	return pn
+}
+
+// Insert inserts a new key/value into the map.
+// If the key is already present, the value is replaced.
+// Returns true if this is a new key, false if already present.
+func (m *Map[K, V]) Insert(key K, val V) bool {
+	pn := m.find(key)
+	if *pn != nil {
+		(*pn).val = val
+		return false
+	}
+        *pn = &node[K, V]{key: key, val: val}
+	return true
+}
+
+// Find returns the value associated with a key, or zero if not present.
+// The found result reports whether the key was found.
+func (m *Map[K, V]) Find(key K) (V, bool) {
+	pn := m.find(key)
+	if *pn == nil {
+		var zero V // see the discussion of zero values, above
+		return zero, false
+	}
+	return (*pn).val, true
+}
+
+// keyValue is a pair of key and value used when iterating.
+type keyValue[K, V any] struct {
+	key K
+	val V
+}
+
+// InOrder returns an iterator that does an in-order traversal of the map.
+func (m *Map[K, V]) InOrder() *Iterator[K, V] {
+	sender, receiver := chans.Ranger[keyValue[K, V]]()
+	var f func(*node[K, V]) bool
+	f = func(n *node[K, V]) bool {
+		if n == nil {
+			return true
+		}
+		// Stop sending values if sender.Send returns false,
+		// meaning that nothing is listening at the receiver end.
+		return f(n.left) &&
+                        // TODO
+			// sender.Send(keyValue[K, V]{n.key, n.val}) &&
+			f(n.right)
+	}
+	go func() {
+		f(m.root)
+		sender.Close()
+	}()
+	return &Iterator{receiver}
+}
+
+// Iterator is used to iterate over the map.
+type Iterator[K, V any] struct {
+	r *chans.Receiver[keyValue[K, V]]
+}
+
+// Next returns the next key and value pair, and a boolean indicating
+// whether they are valid or whether we have reached the end.
+func (it *Iterator[K, V]) Next() (K, V, bool) {
+	keyval, ok := it.r.Next()
+	if !ok {
+		var zerok K
+		var zerov V
+		return zerok, zerov, false
+	}
+	return keyval.key, keyval.val, true
+}
diff --git a/src/go/parser/testdata/metrics.go2 b/src/go/parser/testdata/metrics.go2
new file mode 100644
index 0000000..ef1c66b
--- /dev/null
+++ b/src/go/parser/testdata/metrics.go2
@@ -0,0 +1,58 @@
+package metrics
+
+import "sync"
+
+type Metric1[T comparable] struct {
+	mu sync.Mutex
+	m  map[T]int
+}
+
+func (m *Metric1[T]) Add(v T) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.m == nil {
+		m.m = make(map[T]int)
+	}
+	m[v]++
+}
+
+type key2[T1, T2 comparable] struct {
+	f1 T1
+	f2 T2
+}
+
+type Metric2[T1, T2 cmp2] struct {
+	mu sync.Mutex
+	m  map[key2[T1, T2]]int
+}
+
+func (m *Metric2[T1, T2]) Add(v1 T1, v2 T2) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.m == nil {
+		m.m = make(map[key2[T1, T2]]int)
+	}
+	m[key[T1, T2]{v1, v2}]++
+}
+
+type key3[T1, T2, T3 comparable] struct {
+	f1 T1
+	f2 T2
+	f3 T3
+}
+
+type Metric3[T1, T2, T3 comparable] struct {
+	mu sync.Mutex
+	m  map[key3[T1, T2, T3]]int
+}
+
+func (m *Metric3[T1, T2, T3]) Add(v1 T1, v2 T2, v3 T3) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.m == nil {
+		m.m = make(map[key3]int)
+	}
+	m[key[T1, T2, T3]{v1, v2, v3}]++
+}
+
+// Repeat for the maximum number of permitted arguments.
diff --git a/src/go/parser/testdata/resolution/issue45136.src b/src/go/parser/testdata/resolution/issue45136.src
new file mode 100644
index 0000000..e1d63d8
--- /dev/null
+++ b/src/go/parser/testdata/resolution/issue45136.src
@@ -0,0 +1,27 @@
+// Copyright 2021 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 issue45136
+
+type obj /* =@obj */ struct {
+	name /*=@name */ string
+}
+
+func _() {
+	var foo /* =@foo */ = "foo"
+	obj /* @obj */ ["foo"]
+	obj /* @obj */ .run()
+	obj /* @obj */ {
+		name: foo /* @foo */,
+	}
+	obj /* @obj */ {
+		name: "bar",
+	}.run()
+
+	var _ = File{key: obj /* @obj */ {}}
+	var _ = File{obj /* @obj */ {}}
+
+	[]obj /* @obj */ {foo /* @foo */}
+	x /* =@x1 */ := obj /* @obj */{}
+}
diff --git a/src/go/parser/testdata/resolution/issue45160.src b/src/go/parser/testdata/resolution/issue45160.src
new file mode 100644
index 0000000..6be933b
--- /dev/null
+++ b/src/go/parser/testdata/resolution/issue45160.src
@@ -0,0 +1,25 @@
+// Copyright 2021 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 issue45160
+
+func mklink1 /* =@mklink1func */() {}
+
+func _() {
+	var tests /* =@tests */ = []dirLinkTest /* @dirLinkTest */ {
+		{
+			mklink1 /* @mklink1func */: func() {},
+			mklink2: func(link /* =@link */, target /* =@target */ string) error {
+				return nil
+			},
+		},
+	}
+}
+
+type dirLinkTest /* =@dirLinkTest */ struct {
+	mklink1 /* =@mklink1field */ func(string, string) error
+	mklink2 /* =@mklink2field */ func(string, string) error
+}
+
+func mklink2 /* =@mklink2func */() {}
diff --git a/src/go/parser/testdata/resolution/resolution.src b/src/go/parser/testdata/resolution/resolution.src
new file mode 100644
index 0000000..a880dd1
--- /dev/null
+++ b/src/go/parser/testdata/resolution/resolution.src
@@ -0,0 +1,63 @@
+// Copyright 2021 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 resolution
+
+func f /* =@fdecl */(n /* =@narg */ ast.Node) bool {
+		if n /* =@ninit */, ok /* =@ok */ := n /* @narg */ .(*ast.SelectorExpr); ok /* @ok */ {
+			sel = n /* @ninit */
+	}
+}
+
+type c /* =@cdecl */ map[token.Pos]resolvedObj
+
+func (v /* =@vdecl */ c /* @cdecl */) Visit(node /* =@nodearg */ ast.Node) (w /* =@w */ ast.Visitor) {}
+
+const (
+	basic /* =@basic */ = iota
+	labelOk // =@labelOk
+)
+
+type T /* =@T */ int
+
+func _(count /* =@count */ T /* @T */) {
+	x /* =@x1 */ := c /* @cdecl */{}
+	switch x /* =@x2 */ := x /* @x1 */; x /* =@x3 */ := x /* @x2 */.(type) {
+	case c /* @cdecl */:
+	default:
+	}
+loop /* =@loop */:
+	for {
+		if true {
+			break loop /* @loop */
+		}
+	}
+	select {
+	case err /* =@err1 */ := <-_:
+		return err /* @err1 */
+	case err /* =@err2 */ := <-_:
+		return err /* @err2 */
+	}
+
+	_ = func(p1 /* =@p1 */ int, p2 /* =@p2 */ p1) {
+		closed /* =@closed */ := p1 // @p1
+		shadowed /* =@shadowed1 */ := p2 // @p2
+		_ = func(shadowed /* =@shadowed2 */ p2 /* @p2 */) {
+			closed /* @closed */ = 1
+			shadowed /* @shadowed2 */ = 2
+		}
+	}
+}
+
+func (r /* =@r */ c /* @cdecl */) m(_ r) c /* @cdecl */ { return r /* @r */ }
+
+var cycle /* =@cycle */ = cycle /* @cycle */ + 1
+
+type chain /* =@chain */ struct {
+	next /* =@next */ *chain /* @chain */
+}
+
+func recursive /* =@recursive */() {
+	recursive /* @recursive */ ()
+}
diff --git a/src/go/parser/testdata/resolution/typeparams.go2 b/src/go/parser/testdata/resolution/typeparams.go2
new file mode 100644
index 0000000..7395ca2
--- /dev/null
+++ b/src/go/parser/testdata/resolution/typeparams.go2
@@ -0,0 +1,51 @@
+// Copyright 2021 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 resolution
+
+type List /* =@List */ [E /* =@E */ any] []E // @E
+
+type Pair /* =@Pair */ [L /* =@L */, R /* =@R */ any] struct {
+	Left /* =@Left */ L // @L
+	Right /* =@Right */ R // @R
+	L /* =@Lfield */ int
+}
+
+var _ = Pair /* @Pair */ [int, string]{}
+
+type Addable /* =@Addable */ interface {
+	~int64|~float64
+}
+
+func Add /* =@AddDecl */[T /* =@T */ Addable /* @Addable */](l /* =@l */, r /* =@r */ T /* @T */) T /* @T */ {
+	var t /* =@t */ T /* @T */
+	return l /* @l */ + r /* @r */ + t /* @t */
+}
+
+type Receiver /* =@Receiver */[P /* =@P */ any] struct {}
+
+type RP /* =@RP1 */ struct{}
+
+// TODO(rFindley): make a decision on how/whether to resolve identifiers that
+// refer to receiver type parameters, as is the case for the 'P' result
+// parameter below.
+//
+// For now, we ensure that types are not incorrectly resolved when receiver
+// type parameters are in scope.
+func (r /* =@recv */ Receiver /* @Receiver */ [RP]) m(RP) RP {}
+
+func f /* =@f */[T1 /* =@T1 */ interface{~[]T2 /* @T2 */}, T2 /* =@T2 */ any](
+  x /* =@x */ T1 /* @T1 */, T1 /* =@T1_duplicate */ y,  // Note that this is a bug:
+                                                        // the duplicate T1 should
+							// not be allowed.
+  ){
+  // Note that duplicate short var declarations resolve to their alt declaration.
+  x /* @x */ := 0
+  y /* =@y */ := 0
+  T1 /* @T1 */ := 0
+  var t1var /* =@t1var */ T1 /* @T1 */
+}
+
+// From issue #39634
+func(*ph1[e, e])h(d)
diff --git a/src/go/parser/testdata/set.go2 b/src/go/parser/testdata/set.go2
new file mode 100644
index 0000000..0da6377
--- /dev/null
+++ b/src/go/parser/testdata/set.go2
@@ -0,0 +1,31 @@
+// Package set implements sets of any type.
+package set
+
+type Set[Elem comparable] map[Elem]struct{}
+
+func Make[Elem comparable]() Set[Elem] {
+	return make(Set(Elem))
+}
+
+func (s Set[Elem]) Add(v Elem) {
+	s[v] = struct{}{}
+}
+
+func (s Set[Elem]) Delete(v Elem) {
+	delete(s, v)
+}
+
+func (s Set[Elem]) Contains(v Elem) bool {
+	_, ok := s[v]
+	return ok
+}
+
+func (s Set[Elem]) Len() int {
+	return len(s)
+}
+
+func (s Set[Elem]) Iterate(f func(Elem)) {
+	for v := range s {
+		f(v)
+	}
+}
diff --git a/src/go/parser/testdata/slices.go2 b/src/go/parser/testdata/slices.go2
new file mode 100644
index 0000000..e060212
--- /dev/null
+++ b/src/go/parser/testdata/slices.go2
@@ -0,0 +1,31 @@
+// Package slices implements various slice algorithms.
+package slices
+
+// Map turns a []T1 to a []T2 using a mapping function.
+func Map[T1, T2 any](s []T1, f func(T1) T2) []T2 {
+	r := make([]T2, len(s))
+	for i, v := range s {
+		r[i] = f(v)
+	}
+	return r
+}
+
+// Reduce reduces a []T1 to a single value using a reduction function.
+func Reduce[T1, T2 any](s []T1, initializer T2, f func(T2, T1) T2) T2 {
+	r := initializer
+	for _, v := range s {
+		r = f(r, v)
+	}
+	return r
+}
+
+// Filter filters values from a slice using a filter function.
+func Filter[T any](s []T, f func(T) bool) []T {
+	var r []T
+	for _, v := range s {
+		if f(v) {
+			r = append(r, v)
+		}
+	}
+	return r
+}
diff --git a/src/go/parser/testdata/sort.go2 b/src/go/parser/testdata/sort.go2
new file mode 100644
index 0000000..88be79f
--- /dev/null
+++ b/src/go/parser/testdata/sort.go2
@@ -0,0 +1,27 @@
+package sort
+
+type orderedSlice[Elem comparable] []Elem
+
+func (s orderedSlice[Elem]) Len() int           { return len(s) }
+func (s orderedSlice[Elem]) Less(i, j int) bool { return s[i] < s[j] }
+func (s orderedSlice[Elem]) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+
+// OrderedSlice sorts the slice s in ascending order.
+// The elements of s must be ordered using the < operator.
+func OrderedSlice[Elem comparable](s []Elem) {
+	sort.Sort(orderedSlice[Elem](s))
+}
+
+type sliceFn[Elem any] struct {
+	s []Elem
+	f func(Elem, Elem) bool
+}
+
+func (s sliceFn[Elem]) Len() int           { return len(s.s) }
+func (s sliceFn[Elem]) Less(i, j int) bool { return s.f(s.s[i], s.s[j]) }
+func (s sliceFn[Elem]) Swap(i, j int)      { s.s[i], s.s[j] = s.s[j], s.s[i] }
+
+// SliceFn sorts the slice s according to the function f.
+func SliceFn[Elem any](s []Elem, f func(Elem, Elem) bool) {
+	Sort(sliceFn[Elem]{s, f})
+}
diff --git a/src/go/parser/testdata/tparams.go2 b/src/go/parser/testdata/tparams.go2
new file mode 100644
index 0000000..1a9a6c6
--- /dev/null
+++ b/src/go/parser/testdata/tparams.go2
@@ -0,0 +1,54 @@
+// 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 p
+
+type _[a /* ERROR "type parameters must be named" */, b] struct{}
+type _[a t, b t, c /* ERROR "type parameters must be named" */ ] struct{}
+type _ struct {
+	t [n]byte
+	t[a]
+	t[a,]
+	t[a, b]
+	t[a, b,]
+}
+type _ struct {
+	t [n, /* ERROR "unexpected comma; expecting ]" */ ]byte
+}
+type _ interface {
+	t[a]
+	t[a,]
+	m[ /* ERROR "method must have no type parameters" */ _ _, /* ERROR mixed */ _]()
+	t[a, b]
+	t[a, b,]
+}
+
+func _[] /* ERROR "empty type parameter list" */ ()
+func _[a /* ERROR "type parameters must be named" */, b ]()
+func _[a t, b t, c /* ERROR "type parameters must be named" */ ]()
+
+// TODO(rfindley) incorrect error message (see existing TODO in parser)
+func f[a b, 0 /* ERROR "expected '\)', found 0" */ ] ()
+
+// issue #49482
+type (
+	_[a *[]int] struct{}
+	_[a *t,] struct{}
+	_[a *t|[]int] struct{}
+	_[a *t|t,] struct{}
+	_[a *t|~t,] struct{}
+	_[a *struct{}|t] struct{}
+	_[a *t|struct{}] struct{}
+	_[a *struct{}|~t] struct{}
+)
+
+// issue #51488
+type (
+	_[a *t|t,] struct{}
+	_[a *t|t, b t] struct{}
+	_[a *t|t] struct{}
+	_[a *[]t|t] struct{}
+	_[a ([]t)] struct{}
+	_[a ([]t)|t] struct{}
+)
diff --git a/src/go/parser/testdata/typeset.go2 b/src/go/parser/testdata/typeset.go2
new file mode 100644
index 0000000..7844c22
--- /dev/null
+++ b/src/go/parser/testdata/typeset.go2
@@ -0,0 +1,72 @@
+// Copyright 2021 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 contains test cases for typeset-only constraint elements.
+// TODO(gri) gofmt once/if gofmt supports this notation.
+
+package p
+
+type (
+        _[_ t] t
+        _[_ ~t] t
+        _[_ t|t] t
+        _[_ ~t|t] t
+        _[_ t|~t] t
+        _[_ ~t|~t] t
+
+        _[_ t, _, _ t|t] t
+        _[_ t, _, _ ~t|t] t
+        _[_ t, _, _ t|~t] t
+        _[_ t, _, _ ~t|~t] t
+
+        _[_ t.t] t
+        _[_ ~t.t] t
+        _[_ t.t|t.t] t
+        _[_ ~t.t|t.t] t
+        _[_ t.t|~t.t] t
+        _[_ ~t.t|~t.t] t
+
+        _[_ t, _, _ t.t|t.t] t
+        _[_ t, _, _ ~t.t|t.t] t
+        _[_ t, _, _ t.t|~t.t] t
+        _[_ t, _, _ ~t.t|~t.t] t
+
+        _[_ struct{}] t
+        _[_ ~struct{}] t
+
+        _[_ struct{}|t] t
+        _[_ ~struct{}|t] t
+        _[_ struct{}|~t] t
+        _[_ ~struct{}|~t] t
+
+        _[_ t|struct{}] t
+        _[_ ~t|struct{}] t
+        _[_ t|~struct{}] t
+        _[_ ~t|~struct{}] t
+)
+
+// Single-expression type parameter lists and those that don't start
+// with a (type parameter) name are considered array sizes.
+// The term must be a valid expression (it could be a type incl. a
+// tilde term) but the type-checker will complain.
+type (
+        _[t] t
+        _[t|t] t
+
+        // These are invalid and the type-checker will complain.
+        _[~t] t
+        _[~t|t] t
+        _[t|~t] t
+        _[~t|~t] t
+)
+
+type _[_ t, t /* ERROR "type parameters must be named" */ ] t
+type _[_ ~t, t /* ERROR "type parameters must be named" */ ] t
+type _[_ t, ~ /* ERROR "type parameters must be named" */ t] t
+type _[_ ~t, ~ /* ERROR "type parameters must be named" */ t] t
+
+type _[_ t|t, t /* ERROR "type parameters must be named" */ |t] t
+type _[_ ~t|t, t /* ERROR "type parameters must be named" */ |t] t
+type _[_ t|t, ~ /* ERROR "type parameters must be named" */ t|t] t
+type _[_ ~t|t, ~ /* ERROR "type parameters must be named" */ t|t] t