13 files changed, 3947 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..358a844
--- /dev/null
+++ b/src/go/parser/error_test.go
@@ -0,0 +1,187 @@
+// 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 (
+	"go/scanner"
+	"go/token"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+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.
+//
+var errRx = regexp.MustCompile(`^/\* *ERROR *(HERE)? *"([^"]*)" *\*/$`)
+
+// 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 {
+				pos := prev
+				if s[1] == "HERE" {
+					pos = here
+				}
+				errors[pos] = string(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) {
+	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 interface{}) {
+	src, err := readSource(filename, input)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	fset := token.NewFileSet()
+	_, err = ParseFile(fset, filename, src, DeclarationErrors|AllErrors)
+	found, ok := err.(scanner.ErrorList)
+	if err != nil && !ok {
+		t.Error(err)
+		return
+	}
+	found.RemoveMultiples()
+
+	// 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()
+		if !d.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".src") {
+			checkErrors(t, filepath.Join(testdata, name), nil)
+		}
+	}
+}
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..56ff5fe
--- /dev/null
+++ b/src/go/parser/interface.go
@@ -0,0 +1,241 @@
+// 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 interface{}) ([]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
+	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. 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 interface{}, 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
+			if _, ok := e.(bailout); !ok {
+				panic(e)
+			}
+		}
+
+		// 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 interface{}, 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
+			if _, ok := e.(bailout); !ok {
+				panic(e)
+			}
+		}
+		p.errors.Sort()
+		err = p.errors.Err()
+	}()
+
+	// parse expr
+	p.init(fset, filename, text, mode)
+	// Set up pkg-level scopes to avoid nil-pointer errors.
+	// This is not needed for a correct expression x as the
+	// parser will be ok with a nil topScope, but be cautious
+	// in case of an erroneous x.
+	p.openScope()
+	p.pkgScope = p.topScope
+	expr = p.parseRhsOrType()
+	p.closeScope()
+	assert(p.topScope == nil, "unbalanced scopes")
+
+	// 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..31a7398
--- /dev/null
+++ b/src/go/parser/parser.go
@@ -0,0 +1,2591 @@
+// 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/scanner"
+	"go/token"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// 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
+
+	// 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
+
+	// Ordinary identifier scopes
+	pkgScope   *ast.Scope        // pkgScope.Outer == nil
+	topScope   *ast.Scope        // top-most scope; may be pkgScope
+	unresolved []*ast.Ident      // unresolved identifiers
+	imports    []*ast.ImportSpec // list of imports
+
+	// Label scopes
+	// (maintained by open/close LabelScope)
+	labelScope  *ast.Scope     // label scope for current function
+	targetStack [][]*ast.Ident // stack of unresolved labels
+}
+
+func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode Mode) {
+	p.file = fset.AddFile(filename, -1, len(src))
+	var m scanner.Mode
+	if mode&ParseComments != 0 {
+		m = scanner.ScanComments
+	}
+	eh := func(pos token.Position, msg string) { p.errors.Add(pos, msg) }
+	p.scanner.Init(p.file, src, eh, m)
+
+	p.mode = mode
+	p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
+
+	p.next()
+}
+
+// ----------------------------------------------------------------------------
+// Scoping support
+
+func (p *parser) openScope() {
+	p.topScope = ast.NewScope(p.topScope)
+}
+
+func (p *parser) closeScope() {
+	p.topScope = p.topScope.Outer
+}
+
+func (p *parser) openLabelScope() {
+	p.labelScope = ast.NewScope(p.labelScope)
+	p.targetStack = append(p.targetStack, nil)
+}
+
+func (p *parser) closeLabelScope() {
+	// resolve labels
+	n := len(p.targetStack) - 1
+	scope := p.labelScope
+	for _, ident := range p.targetStack[n] {
+		ident.Obj = scope.Lookup(ident.Name)
+		if ident.Obj == nil && p.mode&DeclarationErrors != 0 {
+			p.error(ident.Pos(), fmt.Sprintf("label %s undefined", ident.Name))
+		}
+	}
+	// pop label scope
+	p.targetStack = p.targetStack[0:n]
+	p.labelScope = p.labelScope.Outer
+}
+
+func (p *parser) declare(decl, data interface{}, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
+	for _, ident := range idents {
+		assert(ident.Obj == nil, "identifier already declared or resolved")
+		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
+		ident.Obj = obj
+		if ident.Name != "_" {
+			if alt := scope.Insert(obj); alt != nil && p.mode&DeclarationErrors != 0 {
+				prevDecl := ""
+				if pos := alt.Pos(); pos.IsValid() {
+					prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.file.Position(pos))
+				}
+				p.error(ident.Pos(), fmt.Sprintf("%s redeclared in this block%s", ident.Name, prevDecl))
+			}
+		}
+	}
+}
+
+func (p *parser) shortVarDecl(decl *ast.AssignStmt, list []ast.Expr) {
+	// 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 list {
+		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 alt := p.topScope.Insert(obj); alt != nil {
+					ident.Obj = alt // redeclaration
+				} else {
+					n++ // new declaration
+				}
+			}
+		} else {
+			p.errorExpected(x.Pos(), "identifier on left side of :=")
+		}
+	}
+	if n == 0 && p.mode&DeclarationErrors != 0 {
+		p.error(list[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, tryResolve 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 (p *parser) tryResolve(x ast.Expr, collectUnresolved bool) {
+	// nothing to do if x is not an identifier or the blank identifier
+	ident, _ := x.(*ast.Ident)
+	if ident == nil {
+		return
+	}
+	assert(ident.Obj == nil, "identifier already declared or resolved")
+	if ident.Name == "_" {
+		return
+	}
+	// try to resolve the identifier
+	for s := p.topScope; s != nil; s = s.Outer {
+		if obj := s.Lookup(ident.Name); obj != nil {
+			ident.Obj = obj
+			return
+		}
+	}
+	// all local scopes are known, so any unresolved identifier
+	// must be found either in the file scope, package scope
+	// (perhaps in another file), or universe scope --- collect
+	// them so that they can be resolved later
+	if collectUnresolved {
+		ident.Obj = unresolved
+		p.unresolved = append(p.unresolved, ident)
+	}
+}
+
+func (p *parser) resolve(x ast.Expr) {
+	p.tryResolve(x, true)
+}
+
+// ----------------------------------------------------------------------------
+// Parsing support
+
+func (p *parser) printTrace(a ...interface{}) {
+	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(")")
+}
+
+// Advance to the next token.
+func (p *parser) next0() {
+	// Because of one-token look-ahead, print the previous token
+	// when tracing as it provides a more readable output. The
+	// very first token (!p.pos.IsValid()) is not initialized
+	// (it is token.ILLEGAL), so don't print it .
+	if p.trace && p.pos.IsValid() {
+		s := p.tok.String()
+		switch {
+		case p.tok.IsLiteral():
+			p.printTrace(s, p.lit)
+		case p.tok.IsOperator(), p.tok.IsKeyword():
+			p.printTrace("\"" + s + "\"")
+		default:
+			p.printTrace(s)
+		}
+	}
+
+	p.pos, p.tok, p.lit = p.scanner.Scan()
+}
+
+// Consume a comment and return it and the line on which it ends.
+func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
+	// /*-style comments may end on a different line than where they start.
+	// Scan the comment for '\n' chars and adjust endline accordingly.
+	endline = p.file.Line(p.pos)
+	if p.lit[1] == '*' {
+		// don't use range here - no need to decode Unicode code points
+		for i := 0; i < len(p.lit); i++ {
+			if p.lit[i] == '\n' {
+				endline++
+			}
+		}
+	}
+
+	comment = &ast.Comment{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.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.
+type bailout struct{}
+
+func (p *parser) error(pos token.Pos, msg string) {
+	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)
+}
+
+func (p *parser) expectSemi() {
+	// 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:
+			p.next()
+		default:
+			p.errorExpected(p.pos, "';'")
+			p.advance(stmtStart)
+		}
+	}
+}
+
+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.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(lhs bool) (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ExpressionList"))
+	}
+
+	list = append(list, p.checkExpr(p.parseExpr(lhs)))
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.checkExpr(p.parseExpr(lhs)))
+	}
+
+	return
+}
+
+func (p *parser) parseLhsList() []ast.Expr {
+	old := p.inRhs
+	p.inRhs = false
+	list := p.parseExprList(true)
+	switch p.tok {
+	case token.DEFINE:
+		// lhs of a short variable declaration
+		// but doesn't enter scope until later:
+		// caller must call p.shortVarDecl(p.makeIdentList(list))
+		// at appropriate time.
+	case token.COLON:
+		// lhs of a label declaration or a communication clause of a select
+		// statement (parseLhsList is not called when parsing the case clause
+		// of a switch statement):
+		// - labels are declared by the caller of parseLhsList
+		// - for communication clauses, if there is a stand-alone identifier
+		//   followed by a colon, we have a syntax error; there is no need
+		//   to resolve the identifier in that case
+	default:
+		// identifiers must be declared elsewhere
+		for _, x := range list {
+			p.resolve(x)
+		}
+	}
+	p.inRhs = old
+	return list
+}
+
+func (p *parser) parseRhsList() []ast.Expr {
+	old := p.inRhs
+	p.inRhs = true
+	list := p.parseExprList(false)
+	p.inRhs = old
+	return list
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+func (p *parser) parseType() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Type"))
+	}
+
+	typ := p.tryType()
+
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.advance(exprEnd)
+		return &ast.BadExpr{From: pos, To: p.pos}
+	}
+
+	return typ
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) parseTypeName() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeName"))
+	}
+
+	ident := p.parseIdent()
+	// don't resolve ident yet - it may be a parameter or field name
+
+	if p.tok == token.PERIOD {
+		// ident is a package name
+		p.next()
+		p.resolve(ident)
+		sel := p.parseIdent()
+		return &ast.SelectorExpr{X: ident, Sel: sel}
+	}
+
+	return ident
+}
+
+func (p *parser) parseArrayType() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "ArrayType"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	p.exprLev++
+	var len ast.Expr
+	// 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--
+	p.expect(token.RBRACK)
+	elt := p.parseType()
+
+	return &ast.ArrayType{Lbrack: lbrack, Len: len, Elt: elt}
+}
+
+func (p *parser) makeIdentList(list []ast.Expr) []*ast.Ident {
+	idents := make([]*ast.Ident, len(list))
+	for i, x := range list {
+		ident, isIdent := x.(*ast.Ident)
+		if !isIdent {
+			if _, isBad := x.(*ast.BadExpr); !isBad {
+				// only report error if it's a new one
+				p.errorExpected(x.Pos(), "identifier")
+			}
+			ident = &ast.Ident{NamePos: x.Pos(), Name: "_"}
+		}
+		idents[i] = ident
+	}
+	return idents
+}
+
+func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "FieldDecl"))
+	}
+
+	doc := p.leadComment
+
+	// 1st FieldDecl
+	// A type name used as an anonymous field looks like a field identifier.
+	var list []ast.Expr
+	for {
+		list = append(list, p.parseVarType(false))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+
+	typ := p.tryVarType(false)
+
+	// analyze case
+	var idents []*ast.Ident
+	if typ != nil {
+		// IdentifierList Type
+		idents = p.makeIdentList(list)
+	} else {
+		// ["*"] TypeName (AnonymousField)
+		typ = list[0] // we always have at least one element
+		if n := len(list); n > 1 {
+			p.errorExpected(p.pos, "type")
+			typ = &ast.BadExpr{From: p.pos, To: p.pos}
+		} else if !isTypeName(deref(typ)) {
+			p.errorExpected(typ.Pos(), "anonymous field")
+			typ = &ast.BadExpr{From: typ.Pos(), To: p.safePos(typ.End())}
+		}
+	}
+
+	// Tag
+	var tag *ast.BasicLit
+	if p.tok == token.STRING {
+		tag = &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
+		p.next()
+	}
+
+	p.expectSemi() // call before accessing p.linecomment
+
+	field := &ast.Field{Doc: doc, Names: idents, Type: typ, Tag: tag, Comment: p.lineComment}
+	p.declare(field, nil, scope, ast.Var, idents...)
+	p.resolve(typ)
+
+	return field
+}
+
+func (p *parser) parseStructType() *ast.StructType {
+	if p.trace {
+		defer un(trace(p, "StructType"))
+	}
+
+	pos := p.expect(token.STRUCT)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // struct scope
+	var list []*ast.Field
+	for p.tok == token.IDENT || p.tok == token.MUL || p.tok == token.LPAREN {
+		// a field declaration cannot start with a '(' but we accept
+		// it here for more robust parsing and better error messages
+		// (parseFieldDecl will check and complain if necessary)
+		list = append(list, p.parseFieldDecl(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	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}
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) tryVarType(isParam bool) ast.Expr {
+	if isParam && p.tok == token.ELLIPSIS {
+		pos := p.pos
+		p.next()
+		typ := p.tryIdentOrType() // don't use parseType so we can provide better error message
+		if typ != nil {
+			p.resolve(typ)
+		} else {
+			p.error(pos, "'...' parameter is missing type")
+			typ = &ast.BadExpr{From: pos, To: p.pos}
+		}
+		return &ast.Ellipsis{Ellipsis: pos, Elt: typ}
+	}
+	return p.tryIdentOrType()
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) parseVarType(isParam bool) ast.Expr {
+	typ := p.tryVarType(isParam)
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.next() // make progress
+		typ = &ast.BadExpr{From: pos, To: p.pos}
+	}
+	return typ
+}
+
+func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params []*ast.Field) {
+	if p.trace {
+		defer un(trace(p, "ParameterList"))
+	}
+
+	// 1st ParameterDecl
+	// A list of identifiers looks like a list of type names.
+	var list []ast.Expr
+	for {
+		list = append(list, p.parseVarType(ellipsisOk))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+		if p.tok == token.RPAREN {
+			break
+		}
+	}
+
+	// analyze case
+	if typ := p.tryVarType(ellipsisOk); typ != nil {
+		// IdentifierList Type
+		idents := p.makeIdentList(list)
+		field := &ast.Field{Names: idents, Type: typ}
+		params = append(params, field)
+		// Go spec: The scope of an identifier denoting a function
+		// parameter or result variable is the function body.
+		p.declare(field, nil, scope, ast.Var, idents...)
+		p.resolve(typ)
+		if !p.atComma("parameter list", token.RPAREN) {
+			return
+		}
+		p.next()
+		for p.tok != token.RPAREN && p.tok != token.EOF {
+			idents := p.parseIdentList()
+			typ := p.parseVarType(ellipsisOk)
+			field := &ast.Field{Names: idents, Type: typ}
+			params = append(params, field)
+			// Go spec: The scope of an identifier denoting a function
+			// parameter or result variable is the function body.
+			p.declare(field, nil, scope, ast.Var, idents...)
+			p.resolve(typ)
+			if !p.atComma("parameter list", token.RPAREN) {
+				break
+			}
+			p.next()
+		}
+		return
+	}
+
+	// Type { "," Type } (anonymous parameters)
+	params = make([]*ast.Field, len(list))
+	for i, typ := range list {
+		p.resolve(typ)
+		params[i] = &ast.Field{Type: typ}
+	}
+	return
+}
+
+func (p *parser) parseParameters(scope *ast.Scope, ellipsisOk bool) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Parameters"))
+	}
+
+	var params []*ast.Field
+	lparen := p.expect(token.LPAREN)
+	if p.tok != token.RPAREN {
+		params = p.parseParameterList(scope, ellipsisOk)
+	}
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.FieldList{Opening: lparen, List: params, Closing: rparen}
+}
+
+func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Result"))
+	}
+
+	if p.tok == token.LPAREN {
+		return p.parseParameters(scope, false)
+	}
+
+	typ := p.tryType()
+	if typ != nil {
+		list := make([]*ast.Field, 1)
+		list[0] = &ast.Field{Type: typ}
+		return &ast.FieldList{List: list}
+	}
+
+	return nil
+}
+
+func (p *parser) parseSignature(scope *ast.Scope) (params, results *ast.FieldList) {
+	if p.trace {
+		defer un(trace(p, "Signature"))
+	}
+
+	params = p.parseParameters(scope, true)
+	results = p.parseResult(scope)
+
+	return
+}
+
+func (p *parser) parseFuncType() (*ast.FuncType, *ast.Scope) {
+	if p.trace {
+		defer un(trace(p, "FuncType"))
+	}
+
+	pos := p.expect(token.FUNC)
+	scope := ast.NewScope(p.topScope) // function scope
+	params, results := p.parseSignature(scope)
+
+	return &ast.FuncType{Func: pos, Params: params, Results: results}, scope
+}
+
+func (p *parser) parseMethodSpec(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "MethodSpec"))
+	}
+
+	doc := p.leadComment
+	var idents []*ast.Ident
+	var typ ast.Expr
+	x := p.parseTypeName()
+	if ident, isIdent := x.(*ast.Ident); isIdent && p.tok == token.LPAREN {
+		// method
+		idents = []*ast.Ident{ident}
+		scope := ast.NewScope(nil) // method scope
+		params, results := p.parseSignature(scope)
+		typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
+	} else {
+		// embedded interface
+		typ = x
+		p.resolve(typ)
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	spec := &ast.Field{Doc: doc, Names: idents, Type: typ, Comment: p.lineComment}
+	p.declare(spec, nil, scope, ast.Fun, idents...)
+
+	return spec
+}
+
+func (p *parser) parseInterfaceType() *ast.InterfaceType {
+	if p.trace {
+		defer un(trace(p, "InterfaceType"))
+	}
+
+	pos := p.expect(token.INTERFACE)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // interface scope
+	var list []*ast.Field
+	for p.tok == token.IDENT {
+		list = append(list, p.parseMethodSpec(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	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}
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) tryIdentOrType() ast.Expr {
+	switch p.tok {
+	case token.IDENT:
+		return p.parseTypeName()
+	case token.LBRACK:
+		return p.parseArrayType()
+	case token.STRUCT:
+		return p.parseStructType()
+	case token.MUL:
+		return p.parsePointerType()
+	case token.FUNC:
+		typ, _ := p.parseFuncType()
+		return typ
+	case token.INTERFACE:
+		return p.parseInterfaceType()
+	case token.MAP:
+		return p.parseMapType()
+	case token.CHAN, token.ARROW:
+		return p.parseChanType()
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		typ := p.parseType()
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{Lparen: lparen, X: typ, Rparen: rparen}
+	}
+
+	// no type found
+	return nil
+}
+
+func (p *parser) tryType() ast.Expr {
+	typ := p.tryIdentOrType()
+	if typ != nil {
+		p.resolve(typ)
+	}
+	return typ
+}
+
+// ----------------------------------------------------------------------------
+// Blocks
+
+func (p *parser) parseStmtList() (list []ast.Stmt) {
+	if p.trace {
+		defer un(trace(p, "StatementList"))
+	}
+
+	for p.tok != token.CASE && p.tok != token.DEFAULT && p.tok != token.RBRACE && p.tok != token.EOF {
+		list = append(list, p.parseStmt())
+	}
+
+	return
+}
+
+func (p *parser) parseBody(scope *ast.Scope) *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "Body"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	p.topScope = scope // open function scope
+	p.openLabelScope()
+	list := p.parseStmtList()
+	p.closeLabelScope()
+	p.closeScope()
+	rbrace := p.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)
+	p.openScope()
+	list := p.parseStmtList()
+	p.closeScope()
+	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, scope := p.parseFuncType()
+	if p.tok != token.LBRACE {
+		// function type only
+		return typ
+	}
+
+	p.exprLev++
+	body := p.parseBody(scope)
+	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.
+// If lhs is set and the result is an identifier, it is not resolved.
+//
+func (p *parser) parseOperand(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Operand"))
+	}
+
+	switch p.tok {
+	case token.IDENT:
+		x := p.parseIdent()
+		if !lhs {
+			p.resolve(x)
+		}
+		return x
+
+	case token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING:
+		x := &ast.BasicLit{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.parseRhsOrType() // 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 {
+		// 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) parseIndexOrSlice(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "IndexOrSlice"))
+	}
+
+	const N = 3 // change the 3 to 2 to disable 3-index slices
+	lbrack := p.expect(token.LBRACK)
+	p.exprLev++
+	var index [N]ast.Expr
+	var colons [N - 1]token.Pos
+	if p.tok != token.COLON {
+		index[0] = p.parseRhs()
+	}
+	ncolons := 0
+	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()
+		}
+	}
+	p.exprLev--
+	rbrack := p.expect(token.RBRACK)
+
+	if ncolons > 0 {
+		// slice expression
+		slice3 := false
+		if ncolons == 2 {
+			slice3 = true
+			// Check presence of 2nd and 3rd 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], "2nd 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], "3rd 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}
+	}
+
+	return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: 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.parseRhsOrType()) // 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(keyOk bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Element"))
+	}
+
+	if p.tok == token.LBRACE {
+		return p.parseLiteralValue(nil)
+	}
+
+	// Because the parser doesn't know the composite literal type, it cannot
+	// know if a key that's an identifier is a struct field name or a name
+	// denoting a value. The former is not resolved by the parser or the
+	// resolver.
+	//
+	// Instead, _try_ to resolve such a key if possible. If it resolves,
+	// it a) has correctly resolved, or b) incorrectly resolved because
+	// the key is a struct field with a name matching another identifier.
+	// In the former case we are done, and in the latter case we don't
+	// care because the type checker will do a separate field lookup.
+	//
+	// If the key does not resolve, it a) must be defined at the top
+	// level in another file of the same package, the universe scope, or be
+	// undeclared; or b) it is a struct field. In the former case, the type
+	// checker can do a top-level lookup, and in the latter case it will do
+	// a separate field lookup.
+	x := p.checkExpr(p.parseExpr(keyOk))
+	if keyOk {
+		if p.tok == token.COLON {
+			// Try to resolve the key but don't collect it
+			// as unresolved identifier if it fails so that
+			// we don't get (possibly false) errors about
+			// undeclared names.
+			p.tryResolve(x, false)
+		} else {
+			// not a key
+			p.resolve(x)
+		}
+	}
+
+	return x
+}
+
+func (p *parser) parseElement() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Element"))
+	}
+
+	x := p.parseValue(true)
+	if p.tok == token.COLON {
+		colon := p.pos
+		p.next()
+		x = &ast.KeyValueExpr{Key: x, Colon: colon, Value: p.parseValue(false)}
+	}
+
+	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}
+}
+
+// checkExpr checks that x is an expression (and not a type).
+func (p *parser) checkExpr(x ast.Expr) ast.Expr {
+	switch unparen(x).(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.BasicLit:
+	case *ast.FuncLit:
+	case *ast.CompositeLit:
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.SelectorExpr:
+	case *ast.IndexExpr:
+	case *ast.SliceExpr:
+	case *ast.TypeAssertExpr:
+		// If t.Type == nil we have a type assertion of the form
+		// y.(type), which is only allowed in type switch expressions.
+		// It's hard to exclude those but for the case where we are in
+		// a type switch. Instead be lenient and test this in the type
+		// checker.
+	case *ast.CallExpr:
+	case *ast.StarExpr:
+	case *ast.UnaryExpr:
+	case *ast.BinaryExpr:
+	default:
+		// all other nodes are not proper expressions
+		p.errorExpected(x.Pos(), "expression")
+		x = &ast.BadExpr{From: x.Pos(), To: p.safePos(x.End())}
+	}
+	return x
+}
+
+// isTypeName reports whether x is a (qualified) TypeName.
+func isTypeName(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	default:
+		return false // all other nodes are not type names
+	}
+	return true
+}
+
+// isLiteralType reports whether x is a legal composite literal type.
+func isLiteralType(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	case *ast.ArrayType:
+	case *ast.StructType:
+	case *ast.MapType:
+	default:
+		return false // all other nodes are not legal composite literal types
+	}
+	return true
+}
+
+// If x is of the form *T, deref returns T, otherwise it returns x.
+func deref(x ast.Expr) ast.Expr {
+	if p, isPtr := x.(*ast.StarExpr); isPtr {
+		x = p.X
+	}
+	return x
+}
+
+// If x is of the form (T), unparen returns unparen(T), otherwise it returns x.
+func unparen(x ast.Expr) ast.Expr {
+	if p, isParen := x.(*ast.ParenExpr); isParen {
+		x = unparen(p.X)
+	}
+	return x
+}
+
+// checkExprOrType checks that x is an expression or a type
+// (and not a raw type such as [...]T).
+//
+func (p *parser) checkExprOrType(x ast.Expr) ast.Expr {
+	switch t := unparen(x).(type) {
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.ArrayType:
+		if len, isEllipsis := t.Len.(*ast.Ellipsis); isEllipsis {
+			p.error(len.Pos(), "expected array length, found '...'")
+			x = &ast.BadExpr{From: x.Pos(), To: p.safePos(x.End())}
+		}
+	}
+
+	// all other nodes are expressions or types
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parsePrimaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "PrimaryExpr"))
+	}
+
+	x := p.parseOperand(lhs)
+L:
+	for {
+		switch p.tok {
+		case token.PERIOD:
+			p.next()
+			if lhs {
+				p.resolve(x)
+			}
+			switch p.tok {
+			case token.IDENT:
+				x = p.parseSelector(p.checkExprOrType(x))
+			case token.LPAREN:
+				x = p.parseTypeAssertion(p.checkExpr(x))
+			default:
+				pos := p.pos
+				p.errorExpected(pos, "selector or type assertion")
+				p.next() // make progress
+				sel := &ast.Ident{NamePos: pos, Name: "_"}
+				x = &ast.SelectorExpr{X: x, Sel: sel}
+			}
+		case token.LBRACK:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseIndexOrSlice(p.checkExpr(x))
+		case token.LPAREN:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseCallOrConversion(p.checkExprOrType(x))
+		case token.LBRACE:
+			if isLiteralType(x) && (p.exprLev >= 0 || !isTypeName(x)) {
+				if lhs {
+					p.resolve(x)
+				}
+				x = p.parseLiteralValue(x)
+			} else {
+				break L
+			}
+		default:
+			break L
+		}
+		lhs = false // no need to try to resolve again
+	}
+
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseUnaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "UnaryExpr"))
+	}
+
+	switch p.tok {
+	case token.ADD, token.SUB, token.NOT, token.XOR, token.AND:
+		pos, op := p.pos, p.tok
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.UnaryExpr{OpPos: pos, Op: op, X: p.checkExpr(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(false)
+
+		// 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: p.checkExpr(x)}
+
+	case token.MUL:
+		// pointer type or unary "*" expression
+		pos := p.pos
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.StarExpr{Star: pos, X: p.checkExprOrType(x)}
+	}
+
+	return p.parsePrimaryExpr(lhs)
+}
+
+func (p *parser) tokPrec() (token.Token, int) {
+	tok := p.tok
+	if p.inRhs && tok == token.ASSIGN {
+		tok = token.EQL
+	}
+	return tok, tok.Precedence()
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseBinaryExpr(lhs bool, prec1 int) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "BinaryExpr"))
+	}
+
+	x := p.parseUnaryExpr(lhs)
+	for {
+		op, oprec := p.tokPrec()
+		if oprec < prec1 {
+			return x
+		}
+		pos := p.expect(op)
+		if lhs {
+			p.resolve(x)
+			lhs = false
+		}
+		y := p.parseBinaryExpr(false, oprec+1)
+		x = &ast.BinaryExpr{X: p.checkExpr(x), OpPos: pos, Op: op, Y: p.checkExpr(y)}
+	}
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+// The result may be a type or even a raw type ([...]int). Callers must
+// check the result (using checkExpr or checkExprOrType), depending on
+// context.
+func (p *parser) parseExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Expression"))
+	}
+
+	return p.parseBinaryExpr(lhs, token.LowestPrec+1)
+}
+
+func (p *parser) parseRhs() ast.Expr {
+	old := p.inRhs
+	p.inRhs = true
+	x := p.checkExpr(p.parseExpr(false))
+	p.inRhs = old
+	return x
+}
+
+func (p *parser) parseRhsOrType() ast.Expr {
+	old := p.inRhs
+	p.inRhs = true
+	x := p.checkExprOrType(p.parseExpr(false))
+	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.parseLhsList()
+
+	switch p.tok {
+	case
+		token.DEFINE, token.ASSIGN, token.ADD_ASSIGN,
+		token.SUB_ASSIGN, token.MUL_ASSIGN, token.QUO_ASSIGN,
+		token.REM_ASSIGN, token.AND_ASSIGN, token.OR_ASSIGN,
+		token.XOR_ASSIGN, token.SHL_ASSIGN, token.SHR_ASSIGN, token.AND_NOT_ASSIGN:
+		// assignment statement, 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.parseRhsList()
+		}
+		as := &ast.AssignStmt{Lhs: x, TokPos: pos, Tok: tok, Rhs: y}
+		if tok == token.DEFINE {
+			p.shortVarDecl(as, x)
+		}
+		return as, 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()}
+			p.declare(stmt, nil, p.labelScope, ast.Lbl, label)
+			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.parseRhsOrType() // could be a conversion: (some type)(x)
+	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("function must be invoked in %s statement", 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.parseRhsList()
+	}
+	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()
+		// add to list of unresolved targets
+		n := len(p.targetStack) - 1
+		p.targetStack[n] = append(p.targetStack[n], label)
+	}
+	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 p.checkExpr(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
+
+	outer := 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, fmt.Sprintf("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 = outer
+	return
+}
+
+func (p *parser) parseIfStmt() *ast.IfStmt {
+	if p.trace {
+		defer un(trace(p, "IfStmt"))
+	}
+
+	pos := p.expect(token.IF)
+	p.openScope()
+	defer p.closeScope()
+
+	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) parseTypeList() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "TypeList"))
+	}
+
+	list = append(list, p.parseType())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseType())
+	}
+
+	return
+}
+
+func (p *parser) parseCaseClause(typeSwitch bool) *ast.CaseClause {
+	if p.trace {
+		defer un(trace(p, "CaseClause"))
+	}
+
+	pos := p.pos
+	var list []ast.Expr
+	if p.tok == token.CASE {
+		p.next()
+		if typeSwitch {
+			list = p.parseTypeList()
+		} else {
+			list = p.parseRhsList()
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	p.openScope()
+	body := p.parseStmtList()
+	p.closeScope()
+
+	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)
+	p.openScope()
+	defer p.closeScope()
+
+	var s1, s2 ast.Stmt
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2, _ = p.parseSimpleStmt(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.
+				p.openScope()
+				defer p.closeScope()
+				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(typeSwitch))
+	}
+	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"))
+	}
+
+	p.openScope()
+	pos := p.pos
+	var comm ast.Stmt
+	if p.tok == token.CASE {
+		p.next()
+		lhs := p.parseLhsList()
+		if p.tok == token.ARROW {
+			// SendStmt
+			if len(lhs) > 1 {
+				p.errorExpected(lhs[0].Pos(), "1 expression")
+				// continue with first expression
+			}
+			arrow := p.pos
+			p.next()
+			rhs := p.parseRhs()
+			comm = &ast.SendStmt{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()
+				as := &ast.AssignStmt{Lhs: lhs, TokPos: pos, Tok: tok, Rhs: []ast.Expr{rhs}}
+				if tok == token.DEFINE {
+					p.shortVarDecl(as, lhs)
+				}
+				comm = as
+			} 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()
+	p.closeScope()
+
+	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)
+	p.openScope()
+	defer p.closeScope()
+
+	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,
+			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) {
+	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 isValidImport(lit string) bool {
+	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
+	s, _ := strconv.Unquote(lit) // go/scanner returns a legal string literal
+	for _, r := range s {
+		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
+			return false
+		}
+	}
+	return s != ""
+}
+
+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.PERIOD:
+		ident = &ast.Ident{NamePos: p.pos, Name: "."}
+		p.next()
+	case token.IDENT:
+		ident = p.parseIdent()
+	}
+
+	pos := p.pos
+	var path string
+	if p.tok == token.STRING {
+		path = p.lit
+		if !isValidImport(path) {
+			p.error(pos, "invalid import path: "+path)
+		}
+		p.next()
+	} else {
+		p.expect(token.STRING) // use expect() error handling
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// collect imports
+	spec := &ast.ImportSpec{
+		Doc:     doc,
+		Name:    ident,
+		Path:    &ast.BasicLit{ValuePos: pos, Kind: token.STRING, Value: path},
+		Comment: p.lineComment,
+	}
+	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"))
+	}
+
+	pos := p.pos
+	idents := p.parseIdentList()
+	typ := p.tryType()
+	var values []ast.Expr
+	// always permit optional initialization for more tolerant parsing
+	if p.tok == token.ASSIGN {
+		p.next()
+		values = p.parseRhsList()
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	switch keyword {
+	case token.VAR:
+		if typ == nil && values == nil {
+			p.error(pos, "missing variable type or initialization")
+		}
+	case token.CONST:
+		if values == nil && (iota == 0 || typ != nil) {
+			p.error(pos, "missing constant value")
+		}
+	}
+
+	// Go spec: The scope of a constant or variable identifier declared inside
+	// a function begins at the end of the ConstSpec or VarSpec and ends at
+	// the end of the innermost containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.ValueSpec{
+		Doc:     doc,
+		Names:   idents,
+		Type:    typ,
+		Values:  values,
+		Comment: p.lineComment,
+	}
+	kind := ast.Con
+	if keyword == token.VAR {
+		kind = ast.Var
+	}
+	p.declare(spec, iota, p.topScope, kind, idents...)
+
+	return spec
+}
+
+func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "TypeSpec"))
+	}
+
+	ident := p.parseIdent()
+
+	// Go spec: The scope of a type identifier declared inside a function begins
+	// at the identifier in the TypeSpec and ends at the end of the innermost
+	// containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.TypeSpec{Doc: doc, Name: ident}
+	p.declare(spec, nil, p.topScope, ast.Typ, ident)
+	if p.tok == token.ASSIGN {
+		spec.Assign = p.pos
+		p.next()
+	}
+	spec.Type = p.parseType()
+	p.expectSemi() // call before accessing p.linecomment
+	spec.Comment = p.lineComment
+
+	return spec
+}
+
+func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
+	if p.trace {
+		defer un(trace(p, "GenDecl("+keyword.String()+")"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(keyword)
+	var lparen, rparen token.Pos
+	var list []ast.Spec
+	if p.tok == token.LPAREN {
+		lparen = p.pos
+		p.next()
+		for iota := 0; p.tok != token.RPAREN && p.tok != token.EOF; iota++ {
+			list = append(list, f(p.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)
+	scope := ast.NewScope(p.topScope) // function scope
+
+	var recv *ast.FieldList
+	if p.tok == token.LPAREN {
+		recv = p.parseParameters(scope, false)
+	}
+
+	ident := p.parseIdent()
+
+	params, results := p.parseSignature(scope)
+
+	var body *ast.BlockStmt
+	if p.tok == token.LBRACE {
+		body = p.parseBody(scope)
+		p.expectSemi()
+	} else if p.tok == 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(scope)
+			p.expectSemi()
+		}
+	} else {
+		p.expectSemi()
+	}
+
+	decl := &ast.FuncDecl{
+		Doc:  doc,
+		Recv: recv,
+		Name: ident,
+		Type: &ast.FuncType{
+			Func:    pos,
+			Params:  params,
+			Results: results,
+		},
+		Body: body,
+	}
+	if recv == nil {
+		// Go spec: The scope of an identifier denoting a constant, type,
+		// variable, or function (but not method) declared at top level
+		// (outside any function) is the package block.
+		//
+		// init() functions cannot be referred to and there may
+		// be more than one - don't put them in the pkgScope
+		if ident.Name != "init" {
+			p.declare(decl, nil, p.pkgScope, ast.Fun, ident)
+		}
+	}
+
+	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.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
+	}
+
+	p.openScope()
+	p.pkgScope = p.topScope
+	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
+			for p.tok != token.EOF {
+				decls = append(decls, p.parseDecl(declStart))
+			}
+		}
+	}
+	p.closeScope()
+	assert(p.topScope == nil, "unbalanced scopes")
+	assert(p.labelScope == nil, "unbalanced label scopes")
+
+	// resolve global identifiers within the same file
+	i := 0
+	for _, ident := range p.unresolved {
+		// i <= index for current ident
+		assert(ident.Obj == unresolved, "object already resolved")
+		ident.Obj = p.pkgScope.Lookup(ident.Name) // also removes unresolved sentinel
+		if ident.Obj == nil {
+			p.unresolved[i] = ident
+			i++
+		}
+	}
+
+	return &ast.File{
+		Doc:        doc,
+		Package:    pos,
+		Name:       ident,
+		Decls:      decls,
+		Scope:      p.pkgScope,
+		Imports:    p.imports,
+		Unresolved: p.unresolved[0:i],
+		Comments:   p.comments,
+	}
+}
diff --git a/src/go/parser/parser_test.go b/src/go/parser/parser_test.go
new file mode 100644
index 0000000..a4f882d
--- /dev/null
+++ b/src/go/parser/parser_test.go
@@ -0,0 +1,579 @@
+// 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 (
+	"bytes"
+	"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 bytes.Buffer
+	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)
+	}
+}
+
+var imports = map[string]bool{
+	`"a"`:        true,
+	"`a`":        true,
+	`"a/b"`:      true,
+	`"a.b"`:      true,
+	`"m\x61th"`:  true,
+	`"greek/αβ"`: true,
+	`""`:         false,
+
+	// Each of these pairs tests both `` vs "" strings
+	// and also use of invalid characters spelled out as
+	// escape sequences and written directly.
+	// For example `"\x00"` tests import "\x00"
+	// while "`\x00`" tests import `<actual-NUL-byte>`.
+	`"\x00"`:     false,
+	"`\x00`":     false,
+	`"\x7f"`:     false,
+	"`\x7f`":     false,
+	`"a!"`:       false,
+	"`a!`":       false,
+	`"a b"`:      false,
+	"`a b`":      false,
+	`"a\\b"`:     false,
+	"`a\\b`":     false,
+	"\"`a`\"":    false,
+	"`\"a\"`":    false,
+	`"\x80\x80"`: false,
+	"`\x80\x80`": false,
+	`"\xFFFD"`:   false,
+	"`\xFFFD`":   false,
+}
+
+func TestImports(t *testing.T) {
+	for path, isValid := range imports {
+		src := fmt.Sprintf("package p; import %s", path)
+		_, err := ParseFile(token.NewFileSet(), "", src, 0)
+		switch {
+		case err != nil && isValid:
+			t.Errorf("ParseFile(%s): got %v; expected no error", src, err)
+		case err == nil && !isValid:
+			t.Errorf("ParseFile(%s): got no error; expected one", src)
+		}
+	}
+}
+
+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 bytes.Buffer
+	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
+}
+`, 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")
+	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
+		})
+	}
+}
+
+// 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")
+	}
+}
diff --git a/src/go/parser/performance_test.go b/src/go/parser/performance_test.go
new file mode 100644
index 0000000..f81bcee
--- /dev/null
+++ b/src/go/parser/performance_test.go
@@ -0,0 +1,30 @@
+// 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("parser.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)
+		}
+	}
+}
diff --git a/src/go/parser/short_test.go b/src/go/parser/short_test.go
new file mode 100644
index 0000000..49bb681
--- /dev/null
+++ b/src/go/parser/short_test.go
@@ -0,0 +1,136 @@
+// 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)`,
+}
+
+func TestValid(t *testing.T) {
+	for _, src := range valids {
+		checkErrors(t, src, src)
+	}
+}
+
+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; var a = [ /* ERROR "expected expression" */ 1]int;`,
+	`package p; var a = [ /* ERROR "expected expression" */ ...]int;`,
+	`package p; var a = struct /* ERROR "expected expression" */ {}`,
+	`package p; var a = func /* ERROR "expected expression" */ ();`,
+	`package p; var a = interface /* ERROR "expected expression" */ {}`,
+	`package p; var a = [ /* ERROR "expected expression" */ ]int`,
+	`package p; var a = map /* ERROR "expected expression" */ [int]int`,
+	`package p; var a = chan /* ERROR "expected expression" */ int;`,
+	`package p; var a = []int{[ /* ERROR "expected expression" */ ]int};`,
+	`package p; var a = ( /* ERROR "expected expression" */ []int);`,
+	`package p; var a = a[[ /* ERROR "expected expression" */ ]int:[]int];`,
+	`package p; var a = <- /* ERROR "expected expression" */ chan int;`,
+	`package p; func f() { select { case _ <- chan /* ERROR "expected expression" */ int: } };`,
+	`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() { var t []int; t /* ERROR "expected identifier on left side of :=" */ [0] := 0 };`,
+	`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 "3rd index required" */ ] };`,
+	`package p; func f() { var s []int; _ = s[i: /* ERROR "2nd index required" */ :k] };`,
+	`package p; func f() { var s []int; _ = s[i: /* ERROR "2nd index required" */ :] };`,
+	`package p; func f() { var s []int; _ = s[: /* ERROR "2nd index required" */ :] };`,
+	`package p; func f() { var s []int; _ = s[: /* ERROR "2nd 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 "function must be invoked" */ }`,
+	`package p; func f() { defer func() {} /* ERROR HERE "function must be invoked" */ }`,
+	`package p; func f() { go func() { func() { f(x func /* ERROR "missing ','" */ (){}) } } }`,
+	`package p; func f(x func(), u v func /* ERROR "missing ','" */ ()){}`,
+
+	// issue 8656
+	`package p; func f() (a b string /* ERROR "missing ','" */ , ok bool)`,
+
+	// issue 9639
+	`package p; var x /* ERROR "missing variable type or initialization" */ , y, z;`,
+	`package p; const x /* ERROR "missing constant value" */ ;`,
+	`package p; const x /* ERROR "missing constant value" */ int;`,
+	`package p; const (x = 0; y; z /* ERROR "missing constant value" */ int);`,
+
+	// 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 type, found '}'" */ ;`,
+	`package p; type _ struct { int, float } /* ERROR "expected type, found '}'" */ ;`,
+	`package p; type _ struct { ( /* ERROR "expected anonymous field" */ int) };`,
+	`package p; func _()(x, y, z ... /* ERROR "expected '\)', found '...'" */ int){}`,
+	`package p; func _()(... /* ERROR "expected type, found '...'" */ int){}`,
+
+	// 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() }`,
+}
+
+func TestInvalid(t *testing.T) {
+	for _, src := range invalids {
+		checkErrors(t, src, src)
+	}
+}
diff --git a/src/go/parser/testdata/commas.src b/src/go/parser/testdata/commas.src
new file mode 100644
index 0000000..e0603cf
--- /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 HERE "missing ','" */
+}
+
+var _ = []int{
+	0,
+	1,
+	2,
+	3/* ERROR HERE "missing ','" */
+}
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.