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Source file src/pkg/go/parser/parser.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	// Package parser implements a parser for Go source files. Input may be
     6	// provided in a variety of forms (see the various Parse* functions); the
     7	// output is an abstract syntax tree (AST) representing the Go source. The
     8	// parser is invoked through one of the Parse* functions.
     9	//
    10	package parser
    11	
    12	import (
    13		"fmt"
    14		"go/ast"
    15		"go/scanner"
    16		"go/token"
    17		"strconv"
    18		"strings"
    19		"unicode"
    20	)
    21	
    22	// The parser structure holds the parser's internal state.
    23	type parser struct {
    24		file    *token.File
    25		errors  scanner.ErrorList
    26		scanner scanner.Scanner
    27	
    28		// Tracing/debugging
    29		mode   Mode // parsing mode
    30		trace  bool // == (mode & Trace != 0)
    31		indent int  // indentation used for tracing output
    32	
    33		// Comments
    34		comments    []*ast.CommentGroup
    35		leadComment *ast.CommentGroup // last lead comment
    36		lineComment *ast.CommentGroup // last line comment
    37	
    38		// Next token
    39		pos token.Pos   // token position
    40		tok token.Token // one token look-ahead
    41		lit string      // token literal
    42	
    43		// Error recovery
    44		// (used to limit the number of calls to syncXXX functions
    45		// w/o making scanning progress - avoids potential endless
    46		// loops across multiple parser functions during error recovery)
    47		syncPos token.Pos // last synchronization position
    48		syncCnt int       // number of calls to syncXXX without progress
    49	
    50		// Non-syntactic parser control
    51		exprLev int  // < 0: in control clause, >= 0: in expression
    52		inRhs   bool // if set, the parser is parsing a rhs expression
    53	
    54		// Ordinary identifier scopes
    55		pkgScope   *ast.Scope        // pkgScope.Outer == nil
    56		topScope   *ast.Scope        // top-most scope; may be pkgScope
    57		unresolved []*ast.Ident      // unresolved identifiers
    58		imports    []*ast.ImportSpec // list of imports
    59	
    60		// Label scopes
    61		// (maintained by open/close LabelScope)
    62		labelScope  *ast.Scope     // label scope for current function
    63		targetStack [][]*ast.Ident // stack of unresolved labels
    64	}
    65	
    66	func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode Mode) {
    67		p.file = fset.AddFile(filename, -1, len(src))
    68		var m scanner.Mode
    69		if mode&ParseComments != 0 {
    70			m = scanner.ScanComments
    71		}
    72		eh := func(pos token.Position, msg string) { p.errors.Add(pos, msg) }
    73		p.scanner.Init(p.file, src, eh, m)
    74	
    75		p.mode = mode
    76		p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
    77	
    78		p.next()
    79	}
    80	
    81	// ----------------------------------------------------------------------------
    82	// Scoping support
    83	
    84	func (p *parser) openScope() {
    85		p.topScope = ast.NewScope(p.topScope)
    86	}
    87	
    88	func (p *parser) closeScope() {
    89		p.topScope = p.topScope.Outer
    90	}
    91	
    92	func (p *parser) openLabelScope() {
    93		p.labelScope = ast.NewScope(p.labelScope)
    94		p.targetStack = append(p.targetStack, nil)
    95	}
    96	
    97	func (p *parser) closeLabelScope() {
    98		// resolve labels
    99		n := len(p.targetStack) - 1
   100		scope := p.labelScope
   101		for _, ident := range p.targetStack[n] {
   102			ident.Obj = scope.Lookup(ident.Name)
   103			if ident.Obj == nil && p.mode&DeclarationErrors != 0 {
   104				p.error(ident.Pos(), fmt.Sprintf("label %s undefined", ident.Name))
   105			}
   106		}
   107		// pop label scope
   108		p.targetStack = p.targetStack[0:n]
   109		p.labelScope = p.labelScope.Outer
   110	}
   111	
   112	func (p *parser) declare(decl, data interface{}, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
   113		for _, ident := range idents {
   114			assert(ident.Obj == nil, "identifier already declared or resolved")
   115			obj := ast.NewObj(kind, ident.Name)
   116			// remember the corresponding declaration for redeclaration
   117			// errors and global variable resolution/typechecking phase
   118			obj.Decl = decl
   119			obj.Data = data
   120			ident.Obj = obj
   121			if ident.Name != "_" {
   122				if alt := scope.Insert(obj); alt != nil && p.mode&DeclarationErrors != 0 {
   123					prevDecl := ""
   124					if pos := alt.Pos(); pos.IsValid() {
   125						prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.file.Position(pos))
   126					}
   127					p.error(ident.Pos(), fmt.Sprintf("%s redeclared in this block%s", ident.Name, prevDecl))
   128				}
   129			}
   130		}
   131	}
   132	
   133	func (p *parser) shortVarDecl(decl *ast.AssignStmt, list []ast.Expr) {
   134		// Go spec: A short variable declaration may redeclare variables
   135		// provided they were originally declared in the same block with
   136		// the same type, and at least one of the non-blank variables is new.
   137		n := 0 // number of new variables
   138		for _, x := range list {
   139			if ident, isIdent := x.(*ast.Ident); isIdent {
   140				assert(ident.Obj == nil, "identifier already declared or resolved")
   141				obj := ast.NewObj(ast.Var, ident.Name)
   142				// remember corresponding assignment for other tools
   143				obj.Decl = decl
   144				ident.Obj = obj
   145				if ident.Name != "_" {
   146					if alt := p.topScope.Insert(obj); alt != nil {
   147						ident.Obj = alt // redeclaration
   148					} else {
   149						n++ // new declaration
   150					}
   151				}
   152			} else {
   153				p.errorExpected(x.Pos(), "identifier on left side of :=")
   154			}
   155		}
   156		if n == 0 && p.mode&DeclarationErrors != 0 {
   157			p.error(list[0].Pos(), "no new variables on left side of :=")
   158		}
   159	}
   160	
   161	// The unresolved object is a sentinel to mark identifiers that have been added
   162	// to the list of unresolved identifiers. The sentinel is only used for verifying
   163	// internal consistency.
   164	var unresolved = new(ast.Object)
   165	
   166	// If x is an identifier, tryResolve attempts to resolve x by looking up
   167	// the object it denotes. If no object is found and collectUnresolved is
   168	// set, x is marked as unresolved and collected in the list of unresolved
   169	// identifiers.
   170	//
   171	func (p *parser) tryResolve(x ast.Expr, collectUnresolved bool) {
   172		// nothing to do if x is not an identifier or the blank identifier
   173		ident, _ := x.(*ast.Ident)
   174		if ident == nil {
   175			return
   176		}
   177		assert(ident.Obj == nil, "identifier already declared or resolved")
   178		if ident.Name == "_" {
   179			return
   180		}
   181		// try to resolve the identifier
   182		for s := p.topScope; s != nil; s = s.Outer {
   183			if obj := s.Lookup(ident.Name); obj != nil {
   184				ident.Obj = obj
   185				return
   186			}
   187		}
   188		// all local scopes are known, so any unresolved identifier
   189		// must be found either in the file scope, package scope
   190		// (perhaps in another file), or universe scope --- collect
   191		// them so that they can be resolved later
   192		if collectUnresolved {
   193			ident.Obj = unresolved
   194			p.unresolved = append(p.unresolved, ident)
   195		}
   196	}
   197	
   198	func (p *parser) resolve(x ast.Expr) {
   199		p.tryResolve(x, true)
   200	}
   201	
   202	// ----------------------------------------------------------------------------
   203	// Parsing support
   204	
   205	func (p *parser) printTrace(a ...interface{}) {
   206		const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
   207		const n = len(dots)
   208		pos := p.file.Position(p.pos)
   209		fmt.Printf("%5d:%3d: ", pos.Line, pos.Column)
   210		i := 2 * p.indent
   211		for i > n {
   212			fmt.Print(dots)
   213			i -= n
   214		}
   215		// i <= n
   216		fmt.Print(dots[0:i])
   217		fmt.Println(a...)
   218	}
   219	
   220	func trace(p *parser, msg string) *parser {
   221		p.printTrace(msg, "(")
   222		p.indent++
   223		return p
   224	}
   225	
   226	// Usage pattern: defer un(trace(p, "..."))
   227	func un(p *parser) {
   228		p.indent--
   229		p.printTrace(")")
   230	}
   231	
   232	// Advance to the next token.
   233	func (p *parser) next0() {
   234		// Because of one-token look-ahead, print the previous token
   235		// when tracing as it provides a more readable output. The
   236		// very first token (!p.pos.IsValid()) is not initialized
   237		// (it is token.ILLEGAL), so don't print it .
   238		if p.trace && p.pos.IsValid() {
   239			s := p.tok.String()
   240			switch {
   241			case p.tok.IsLiteral():
   242				p.printTrace(s, p.lit)
   243			case p.tok.IsOperator(), p.tok.IsKeyword():
   244				p.printTrace("\"" + s + "\"")
   245			default:
   246				p.printTrace(s)
   247			}
   248		}
   249	
   250		p.pos, p.tok, p.lit = p.scanner.Scan()
   251	}
   252	
   253	// Consume a comment and return it and the line on which it ends.
   254	func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
   255		// /*-style comments may end on a different line than where they start.
   256		// Scan the comment for '\n' chars and adjust endline accordingly.
   257		endline = p.file.Line(p.pos)
   258		if p.lit[1] == '*' {
   259			// don't use range here - no need to decode Unicode code points
   260			for i := 0; i < len(p.lit); i++ {
   261				if p.lit[i] == '\n' {
   262					endline++
   263				}
   264			}
   265		}
   266	
   267		comment = &ast.Comment{Slash: p.pos, Text: p.lit}
   268		p.next0()
   269	
   270		return
   271	}
   272	
   273	// Consume a group of adjacent comments, add it to the parser's
   274	// comments list, and return it together with the line at which
   275	// the last comment in the group ends. A non-comment token or n
   276	// empty lines terminate a comment group.
   277	//
   278	func (p *parser) consumeCommentGroup(n int) (comments *ast.CommentGroup, endline int) {
   279		var list []*ast.Comment
   280		endline = p.file.Line(p.pos)
   281		for p.tok == token.COMMENT && p.file.Line(p.pos) <= endline+n {
   282			var comment *ast.Comment
   283			comment, endline = p.consumeComment()
   284			list = append(list, comment)
   285		}
   286	
   287		// add comment group to the comments list
   288		comments = &ast.CommentGroup{List: list}
   289		p.comments = append(p.comments, comments)
   290	
   291		return
   292	}
   293	
   294	// Advance to the next non-comment token. In the process, collect
   295	// any comment groups encountered, and remember the last lead and
   296	// and line comments.
   297	//
   298	// A lead comment is a comment group that starts and ends in a
   299	// line without any other tokens and that is followed by a non-comment
   300	// token on the line immediately after the comment group.
   301	//
   302	// A line comment is a comment group that follows a non-comment
   303	// token on the same line, and that has no tokens after it on the line
   304	// where it ends.
   305	//
   306	// Lead and line comments may be considered documentation that is
   307	// stored in the AST.
   308	//
   309	func (p *parser) next() {
   310		p.leadComment = nil
   311		p.lineComment = nil
   312		prev := p.pos
   313		p.next0()
   314	
   315		if p.tok == token.COMMENT {
   316			var comment *ast.CommentGroup
   317			var endline int
   318	
   319			if p.file.Line(p.pos) == p.file.Line(prev) {
   320				// The comment is on same line as the previous token; it
   321				// cannot be a lead comment but may be a line comment.
   322				comment, endline = p.consumeCommentGroup(0)
   323				if p.file.Line(p.pos) != endline {
   324					// The next token is on a different line, thus
   325					// the last comment group is a line comment.
   326					p.lineComment = comment
   327				}
   328			}
   329	
   330			// consume successor comments, if any
   331			endline = -1
   332			for p.tok == token.COMMENT {
   333				comment, endline = p.consumeCommentGroup(1)
   334			}
   335	
   336			if endline+1 == p.file.Line(p.pos) {
   337				// The next token is following on the line immediately after the
   338				// comment group, thus the last comment group is a lead comment.
   339				p.leadComment = comment
   340			}
   341		}
   342	}
   343	
   344	// A bailout panic is raised to indicate early termination.
   345	type bailout struct{}
   346	
   347	func (p *parser) error(pos token.Pos, msg string) {
   348		epos := p.file.Position(pos)
   349	
   350		// If AllErrors is not set, discard errors reported on the same line
   351		// as the last recorded error and stop parsing if there are more than
   352		// 10 errors.
   353		if p.mode&AllErrors == 0 {
   354			n := len(p.errors)
   355			if n > 0 && p.errors[n-1].Pos.Line == epos.Line {
   356				return // discard - likely a spurious error
   357			}
   358			if n > 10 {
   359				panic(bailout{})
   360			}
   361		}
   362	
   363		p.errors.Add(epos, msg)
   364	}
   365	
   366	func (p *parser) errorExpected(pos token.Pos, msg string) {
   367		msg = "expected " + msg
   368		if pos == p.pos {
   369			// the error happened at the current position;
   370			// make the error message more specific
   371			if p.tok == token.SEMICOLON && p.lit == "\n" {
   372				msg += ", found newline"
   373			} else {
   374				msg += ", found '" + p.tok.String() + "'"
   375				if p.tok.IsLiteral() {
   376					msg += " " + p.lit
   377				}
   378			}
   379		}
   380		p.error(pos, msg)
   381	}
   382	
   383	func (p *parser) expect(tok token.Token) token.Pos {
   384		pos := p.pos
   385		if p.tok != tok {
   386			p.errorExpected(pos, "'"+tok.String()+"'")
   387		}
   388		p.next() // make progress
   389		return pos
   390	}
   391	
   392	// expectClosing is like expect but provides a better error message
   393	// for the common case of a missing comma before a newline.
   394	//
   395	func (p *parser) expectClosing(tok token.Token, context string) token.Pos {
   396		if p.tok != tok && p.tok == token.SEMICOLON && p.lit == "\n" {
   397			p.error(p.pos, "missing ',' before newline in "+context)
   398			p.next()
   399		}
   400		return p.expect(tok)
   401	}
   402	
   403	func (p *parser) expectSemi() {
   404		// semicolon is optional before a closing ')' or '}'
   405		if p.tok != token.RPAREN && p.tok != token.RBRACE {
   406			if p.tok == token.SEMICOLON {
   407				p.next()
   408			} else {
   409				p.errorExpected(p.pos, "';'")
   410				syncStmt(p)
   411			}
   412		}
   413	}
   414	
   415	func (p *parser) atComma(context string) bool {
   416		if p.tok == token.COMMA {
   417			return true
   418		}
   419		if p.tok == token.SEMICOLON && p.lit == "\n" {
   420			p.error(p.pos, "missing ',' before newline in "+context)
   421			return true // "insert" the comma and continue
   422	
   423		}
   424		return false
   425	}
   426	
   427	func assert(cond bool, msg string) {
   428		if !cond {
   429			panic("go/parser internal error: " + msg)
   430		}
   431	}
   432	
   433	// syncStmt advances to the next statement.
   434	// Used for synchronization after an error.
   435	//
   436	func syncStmt(p *parser) {
   437		for {
   438			switch p.tok {
   439			case token.BREAK, token.CONST, token.CONTINUE, token.DEFER,
   440				token.FALLTHROUGH, token.FOR, token.GO, token.GOTO,
   441				token.IF, token.RETURN, token.SELECT, token.SWITCH,
   442				token.TYPE, token.VAR:
   443				// Return only if parser made some progress since last
   444				// sync or if it has not reached 10 sync calls without
   445				// progress. Otherwise consume at least one token to
   446				// avoid an endless parser loop (it is possible that
   447				// both parseOperand and parseStmt call syncStmt and
   448				// correctly do not advance, thus the need for the
   449				// invocation limit p.syncCnt).
   450				if p.pos == p.syncPos && p.syncCnt < 10 {
   451					p.syncCnt++
   452					return
   453				}
   454				if p.pos > p.syncPos {
   455					p.syncPos = p.pos
   456					p.syncCnt = 0
   457					return
   458				}
   459				// Reaching here indicates a parser bug, likely an
   460				// incorrect token list in this function, but it only
   461				// leads to skipping of possibly correct code if a
   462				// previous error is present, and thus is preferred
   463				// over a non-terminating parse.
   464			case token.EOF:
   465				return
   466			}
   467			p.next()
   468		}
   469	}
   470	
   471	// syncDecl advances to the next declaration.
   472	// Used for synchronization after an error.
   473	//
   474	func syncDecl(p *parser) {
   475		for {
   476			switch p.tok {
   477			case token.CONST, token.TYPE, token.VAR:
   478				// see comments in syncStmt
   479				if p.pos == p.syncPos && p.syncCnt < 10 {
   480					p.syncCnt++
   481					return
   482				}
   483				if p.pos > p.syncPos {
   484					p.syncPos = p.pos
   485					p.syncCnt = 0
   486					return
   487				}
   488			case token.EOF:
   489				return
   490			}
   491			p.next()
   492		}
   493	}
   494	
   495	// ----------------------------------------------------------------------------
   496	// Identifiers
   497	
   498	func (p *parser) parseIdent() *ast.Ident {
   499		pos := p.pos
   500		name := "_"
   501		if p.tok == token.IDENT {
   502			name = p.lit
   503			p.next()
   504		} else {
   505			p.expect(token.IDENT) // use expect() error handling
   506		}
   507		return &ast.Ident{NamePos: pos, Name: name}
   508	}
   509	
   510	func (p *parser) parseIdentList() (list []*ast.Ident) {
   511		if p.trace {
   512			defer un(trace(p, "IdentList"))
   513		}
   514	
   515		list = append(list, p.parseIdent())
   516		for p.tok == token.COMMA {
   517			p.next()
   518			list = append(list, p.parseIdent())
   519		}
   520	
   521		return
   522	}
   523	
   524	// ----------------------------------------------------------------------------
   525	// Common productions
   526	
   527	// If lhs is set, result list elements which are identifiers are not resolved.
   528	func (p *parser) parseExprList(lhs bool) (list []ast.Expr) {
   529		if p.trace {
   530			defer un(trace(p, "ExpressionList"))
   531		}
   532	
   533		list = append(list, p.checkExpr(p.parseExpr(lhs)))
   534		for p.tok == token.COMMA {
   535			p.next()
   536			list = append(list, p.checkExpr(p.parseExpr(lhs)))
   537		}
   538	
   539		return
   540	}
   541	
   542	func (p *parser) parseLhsList() []ast.Expr {
   543		old := p.inRhs
   544		p.inRhs = false
   545		list := p.parseExprList(true)
   546		switch p.tok {
   547		case token.DEFINE:
   548			// lhs of a short variable declaration
   549			// but doesn't enter scope until later:
   550			// caller must call p.shortVarDecl(p.makeIdentList(list))
   551			// at appropriate time.
   552		case token.COLON:
   553			// lhs of a label declaration or a communication clause of a select
   554			// statement (parseLhsList is not called when parsing the case clause
   555			// of a switch statement):
   556			// - labels are declared by the caller of parseLhsList
   557			// - for communication clauses, if there is a stand-alone identifier
   558			//   followed by a colon, we have a syntax error; there is no need
   559			//   to resolve the identifier in that case
   560		default:
   561			// identifiers must be declared elsewhere
   562			for _, x := range list {
   563				p.resolve(x)
   564			}
   565		}
   566		p.inRhs = old
   567		return list
   568	}
   569	
   570	func (p *parser) parseRhsList() []ast.Expr {
   571		old := p.inRhs
   572		p.inRhs = true
   573		list := p.parseExprList(false)
   574		p.inRhs = old
   575		return list
   576	}
   577	
   578	// ----------------------------------------------------------------------------
   579	// Types
   580	
   581	func (p *parser) parseType() ast.Expr {
   582		if p.trace {
   583			defer un(trace(p, "Type"))
   584		}
   585	
   586		typ := p.tryType()
   587	
   588		if typ == nil {
   589			pos := p.pos
   590			p.errorExpected(pos, "type")
   591			p.next() // make progress
   592			return &ast.BadExpr{From: pos, To: p.pos}
   593		}
   594	
   595		return typ
   596	}
   597	
   598	// If the result is an identifier, it is not resolved.
   599	func (p *parser) parseTypeName() ast.Expr {
   600		if p.trace {
   601			defer un(trace(p, "TypeName"))
   602		}
   603	
   604		ident := p.parseIdent()
   605		// don't resolve ident yet - it may be a parameter or field name
   606	
   607		if p.tok == token.PERIOD {
   608			// ident is a package name
   609			p.next()
   610			p.resolve(ident)
   611			sel := p.parseIdent()
   612			return &ast.SelectorExpr{X: ident, Sel: sel}
   613		}
   614	
   615		return ident
   616	}
   617	
   618	func (p *parser) parseArrayType() ast.Expr {
   619		if p.trace {
   620			defer un(trace(p, "ArrayType"))
   621		}
   622	
   623		lbrack := p.expect(token.LBRACK)
   624		var len ast.Expr
   625		// always permit ellipsis for more fault-tolerant parsing
   626		if p.tok == token.ELLIPSIS {
   627			len = &ast.Ellipsis{Ellipsis: p.pos}
   628			p.next()
   629		} else if p.tok != token.RBRACK {
   630			len = p.parseRhs()
   631		}
   632		p.expect(token.RBRACK)
   633		elt := p.parseType()
   634	
   635		return &ast.ArrayType{Lbrack: lbrack, Len: len, Elt: elt}
   636	}
   637	
   638	func (p *parser) makeIdentList(list []ast.Expr) []*ast.Ident {
   639		idents := make([]*ast.Ident, len(list))
   640		for i, x := range list {
   641			ident, isIdent := x.(*ast.Ident)
   642			if !isIdent {
   643				if _, isBad := x.(*ast.BadExpr); !isBad {
   644					// only report error if it's a new one
   645					p.errorExpected(x.Pos(), "identifier")
   646				}
   647				ident = &ast.Ident{NamePos: x.Pos(), Name: "_"}
   648			}
   649			idents[i] = ident
   650		}
   651		return idents
   652	}
   653	
   654	func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
   655		if p.trace {
   656			defer un(trace(p, "FieldDecl"))
   657		}
   658	
   659		doc := p.leadComment
   660	
   661		// FieldDecl
   662		list, typ := p.parseVarList(false)
   663	
   664		// Tag
   665		var tag *ast.BasicLit
   666		if p.tok == token.STRING {
   667			tag = &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
   668			p.next()
   669		}
   670	
   671		// analyze case
   672		var idents []*ast.Ident
   673		if typ != nil {
   674			// IdentifierList Type
   675			idents = p.makeIdentList(list)
   676		} else {
   677			// ["*"] TypeName (AnonymousField)
   678			typ = list[0] // we always have at least one element
   679			if n := len(list); n > 1 || !isTypeName(deref(typ)) {
   680				pos := typ.Pos()
   681				p.errorExpected(pos, "anonymous field")
   682				typ = &ast.BadExpr{From: pos, To: list[n-1].End()}
   683			}
   684		}
   685	
   686		p.expectSemi() // call before accessing p.linecomment
   687	
   688		field := &ast.Field{Doc: doc, Names: idents, Type: typ, Tag: tag, Comment: p.lineComment}
   689		p.declare(field, nil, scope, ast.Var, idents...)
   690		p.resolve(typ)
   691	
   692		return field
   693	}
   694	
   695	func (p *parser) parseStructType() *ast.StructType {
   696		if p.trace {
   697			defer un(trace(p, "StructType"))
   698		}
   699	
   700		pos := p.expect(token.STRUCT)
   701		lbrace := p.expect(token.LBRACE)
   702		scope := ast.NewScope(nil) // struct scope
   703		var list []*ast.Field
   704		for p.tok == token.IDENT || p.tok == token.MUL || p.tok == token.LPAREN {
   705			// a field declaration cannot start with a '(' but we accept
   706			// it here for more robust parsing and better error messages
   707			// (parseFieldDecl will check and complain if necessary)
   708			list = append(list, p.parseFieldDecl(scope))
   709		}
   710		rbrace := p.expect(token.RBRACE)
   711	
   712		return &ast.StructType{
   713			Struct: pos,
   714			Fields: &ast.FieldList{
   715				Opening: lbrace,
   716				List:    list,
   717				Closing: rbrace,
   718			},
   719		}
   720	}
   721	
   722	func (p *parser) parsePointerType() *ast.StarExpr {
   723		if p.trace {
   724			defer un(trace(p, "PointerType"))
   725		}
   726	
   727		star := p.expect(token.MUL)
   728		base := p.parseType()
   729	
   730		return &ast.StarExpr{Star: star, X: base}
   731	}
   732	
   733	// If the result is an identifier, it is not resolved.
   734	func (p *parser) tryVarType(isParam bool) ast.Expr {
   735		if isParam && p.tok == token.ELLIPSIS {
   736			pos := p.pos
   737			p.next()
   738			typ := p.tryIdentOrType() // don't use parseType so we can provide better error message
   739			if typ != nil {
   740				p.resolve(typ)
   741			} else {
   742				p.error(pos, "'...' parameter is missing type")
   743				typ = &ast.BadExpr{From: pos, To: p.pos}
   744			}
   745			return &ast.Ellipsis{Ellipsis: pos, Elt: typ}
   746		}
   747		return p.tryIdentOrType()
   748	}
   749	
   750	// If the result is an identifier, it is not resolved.
   751	func (p *parser) parseVarType(isParam bool) ast.Expr {
   752		typ := p.tryVarType(isParam)
   753		if typ == nil {
   754			pos := p.pos
   755			p.errorExpected(pos, "type")
   756			p.next() // make progress
   757			typ = &ast.BadExpr{From: pos, To: p.pos}
   758		}
   759		return typ
   760	}
   761	
   762	// If any of the results are identifiers, they are not resolved.
   763	func (p *parser) parseVarList(isParam bool) (list []ast.Expr, typ ast.Expr) {
   764		if p.trace {
   765			defer un(trace(p, "VarList"))
   766		}
   767	
   768		// a list of identifiers looks like a list of type names
   769		//
   770		// parse/tryVarType accepts any type (including parenthesized
   771		// ones) even though the syntax does not permit them here: we
   772		// accept them all for more robust parsing and complain later
   773		for typ := p.parseVarType(isParam); typ != nil; {
   774			list = append(list, typ)
   775			if p.tok != token.COMMA {
   776				break
   777			}
   778			p.next()
   779			typ = p.tryVarType(isParam) // maybe nil as in: func f(int,) {}
   780		}
   781	
   782		// if we had a list of identifiers, it must be followed by a type
   783		typ = p.tryVarType(isParam)
   784	
   785		return
   786	}
   787	
   788	func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params []*ast.Field) {
   789		if p.trace {
   790			defer un(trace(p, "ParameterList"))
   791		}
   792	
   793		// ParameterDecl
   794		list, typ := p.parseVarList(ellipsisOk)
   795	
   796		// analyze case
   797		if typ != nil {
   798			// IdentifierList Type
   799			idents := p.makeIdentList(list)
   800			field := &ast.Field{Names: idents, Type: typ}
   801			params = append(params, field)
   802			// Go spec: The scope of an identifier denoting a function
   803			// parameter or result variable is the function body.
   804			p.declare(field, nil, scope, ast.Var, idents...)
   805			p.resolve(typ)
   806			if p.tok == token.COMMA {
   807				p.next()
   808			}
   809			for p.tok != token.RPAREN && p.tok != token.EOF {
   810				idents := p.parseIdentList()
   811				typ := p.parseVarType(ellipsisOk)
   812				field := &ast.Field{Names: idents, Type: typ}
   813				params = append(params, field)
   814				// Go spec: The scope of an identifier denoting a function
   815				// parameter or result variable is the function body.
   816				p.declare(field, nil, scope, ast.Var, idents...)
   817				p.resolve(typ)
   818				if !p.atComma("parameter list") {
   819					break
   820				}
   821				p.next()
   822			}
   823		} else {
   824			// Type { "," Type } (anonymous parameters)
   825			params = make([]*ast.Field, len(list))
   826			for i, typ := range list {
   827				p.resolve(typ)
   828				params[i] = &ast.Field{Type: typ}
   829			}
   830		}
   831	
   832		return
   833	}
   834	
   835	func (p *parser) parseParameters(scope *ast.Scope, ellipsisOk bool) *ast.FieldList {
   836		if p.trace {
   837			defer un(trace(p, "Parameters"))
   838		}
   839	
   840		var params []*ast.Field
   841		lparen := p.expect(token.LPAREN)
   842		if p.tok != token.RPAREN {
   843			params = p.parseParameterList(scope, ellipsisOk)
   844		}
   845		rparen := p.expect(token.RPAREN)
   846	
   847		return &ast.FieldList{Opening: lparen, List: params, Closing: rparen}
   848	}
   849	
   850	func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
   851		if p.trace {
   852			defer un(trace(p, "Result"))
   853		}
   854	
   855		if p.tok == token.LPAREN {
   856			return p.parseParameters(scope, false)
   857		}
   858	
   859		typ := p.tryType()
   860		if typ != nil {
   861			list := make([]*ast.Field, 1)
   862			list[0] = &ast.Field{Type: typ}
   863			return &ast.FieldList{List: list}
   864		}
   865	
   866		return nil
   867	}
   868	
   869	func (p *parser) parseSignature(scope *ast.Scope) (params, results *ast.FieldList) {
   870		if p.trace {
   871			defer un(trace(p, "Signature"))
   872		}
   873	
   874		params = p.parseParameters(scope, true)
   875		results = p.parseResult(scope)
   876	
   877		return
   878	}
   879	
   880	func (p *parser) parseFuncType() (*ast.FuncType, *ast.Scope) {
   881		if p.trace {
   882			defer un(trace(p, "FuncType"))
   883		}
   884	
   885		pos := p.expect(token.FUNC)
   886		scope := ast.NewScope(p.topScope) // function scope
   887		params, results := p.parseSignature(scope)
   888	
   889		return &ast.FuncType{Func: pos, Params: params, Results: results}, scope
   890	}
   891	
   892	func (p *parser) parseMethodSpec(scope *ast.Scope) *ast.Field {
   893		if p.trace {
   894			defer un(trace(p, "MethodSpec"))
   895		}
   896	
   897		doc := p.leadComment
   898		var idents []*ast.Ident
   899		var typ ast.Expr
   900		x := p.parseTypeName()
   901		if ident, isIdent := x.(*ast.Ident); isIdent && p.tok == token.LPAREN {
   902			// method
   903			idents = []*ast.Ident{ident}
   904			scope := ast.NewScope(nil) // method scope
   905			params, results := p.parseSignature(scope)
   906			typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
   907		} else {
   908			// embedded interface
   909			typ = x
   910			p.resolve(typ)
   911		}
   912		p.expectSemi() // call before accessing p.linecomment
   913	
   914		spec := &ast.Field{Doc: doc, Names: idents, Type: typ, Comment: p.lineComment}
   915		p.declare(spec, nil, scope, ast.Fun, idents...)
   916	
   917		return spec
   918	}
   919	
   920	func (p *parser) parseInterfaceType() *ast.InterfaceType {
   921		if p.trace {
   922			defer un(trace(p, "InterfaceType"))
   923		}
   924	
   925		pos := p.expect(token.INTERFACE)
   926		lbrace := p.expect(token.LBRACE)
   927		scope := ast.NewScope(nil) // interface scope
   928		var list []*ast.Field
   929		for p.tok == token.IDENT {
   930			list = append(list, p.parseMethodSpec(scope))
   931		}
   932		rbrace := p.expect(token.RBRACE)
   933	
   934		return &ast.InterfaceType{
   935			Interface: pos,
   936			Methods: &ast.FieldList{
   937				Opening: lbrace,
   938				List:    list,
   939				Closing: rbrace,
   940			},
   941		}
   942	}
   943	
   944	func (p *parser) parseMapType() *ast.MapType {
   945		if p.trace {
   946			defer un(trace(p, "MapType"))
   947		}
   948	
   949		pos := p.expect(token.MAP)
   950		p.expect(token.LBRACK)
   951		key := p.parseType()
   952		p.expect(token.RBRACK)
   953		value := p.parseType()
   954	
   955		return &ast.MapType{Map: pos, Key: key, Value: value}
   956	}
   957	
   958	func (p *parser) parseChanType() *ast.ChanType {
   959		if p.trace {
   960			defer un(trace(p, "ChanType"))
   961		}
   962	
   963		pos := p.pos
   964		dir := ast.SEND | ast.RECV
   965		var arrow token.Pos
   966		if p.tok == token.CHAN {
   967			p.next()
   968			if p.tok == token.ARROW {
   969				arrow = p.pos
   970				p.next()
   971				dir = ast.SEND
   972			}
   973		} else {
   974			arrow = p.expect(token.ARROW)
   975			p.expect(token.CHAN)
   976			dir = ast.RECV
   977		}
   978		value := p.parseType()
   979	
   980		return &ast.ChanType{Begin: pos, Arrow: arrow, Dir: dir, Value: value}
   981	}
   982	
   983	// If the result is an identifier, it is not resolved.
   984	func (p *parser) tryIdentOrType() ast.Expr {
   985		switch p.tok {
   986		case token.IDENT:
   987			return p.parseTypeName()
   988		case token.LBRACK:
   989			return p.parseArrayType()
   990		case token.STRUCT:
   991			return p.parseStructType()
   992		case token.MUL:
   993			return p.parsePointerType()
   994		case token.FUNC:
   995			typ, _ := p.parseFuncType()
   996			return typ
   997		case token.INTERFACE:
   998			return p.parseInterfaceType()
   999		case token.MAP:
  1000			return p.parseMapType()
  1001		case token.CHAN, token.ARROW:
  1002			return p.parseChanType()
  1003		case token.LPAREN:
  1004			lparen := p.pos
  1005			p.next()
  1006			typ := p.parseType()
  1007			rparen := p.expect(token.RPAREN)
  1008			return &ast.ParenExpr{Lparen: lparen, X: typ, Rparen: rparen}
  1009		}
  1010	
  1011		// no type found
  1012		return nil
  1013	}
  1014	
  1015	func (p *parser) tryType() ast.Expr {
  1016		typ := p.tryIdentOrType()
  1017		if typ != nil {
  1018			p.resolve(typ)
  1019		}
  1020		return typ
  1021	}
  1022	
  1023	// ----------------------------------------------------------------------------
  1024	// Blocks
  1025	
  1026	func (p *parser) parseStmtList() (list []ast.Stmt) {
  1027		if p.trace {
  1028			defer un(trace(p, "StatementList"))
  1029		}
  1030	
  1031		for p.tok != token.CASE && p.tok != token.DEFAULT && p.tok != token.RBRACE && p.tok != token.EOF {
  1032			list = append(list, p.parseStmt())
  1033		}
  1034	
  1035		return
  1036	}
  1037	
  1038	func (p *parser) parseBody(scope *ast.Scope) *ast.BlockStmt {
  1039		if p.trace {
  1040			defer un(trace(p, "Body"))
  1041		}
  1042	
  1043		lbrace := p.expect(token.LBRACE)
  1044		p.topScope = scope // open function scope
  1045		p.openLabelScope()
  1046		list := p.parseStmtList()
  1047		p.closeLabelScope()
  1048		p.closeScope()
  1049		rbrace := p.expect(token.RBRACE)
  1050	
  1051		return &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
  1052	}
  1053	
  1054	func (p *parser) parseBlockStmt() *ast.BlockStmt {
  1055		if p.trace {
  1056			defer un(trace(p, "BlockStmt"))
  1057		}
  1058	
  1059		lbrace := p.expect(token.LBRACE)
  1060		p.openScope()
  1061		list := p.parseStmtList()
  1062		p.closeScope()
  1063		rbrace := p.expect(token.RBRACE)
  1064	
  1065		return &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
  1066	}
  1067	
  1068	// ----------------------------------------------------------------------------
  1069	// Expressions
  1070	
  1071	func (p *parser) parseFuncTypeOrLit() ast.Expr {
  1072		if p.trace {
  1073			defer un(trace(p, "FuncTypeOrLit"))
  1074		}
  1075	
  1076		typ, scope := p.parseFuncType()
  1077		if p.tok != token.LBRACE {
  1078			// function type only
  1079			return typ
  1080		}
  1081	
  1082		p.exprLev++
  1083		body := p.parseBody(scope)
  1084		p.exprLev--
  1085	
  1086		return &ast.FuncLit{Type: typ, Body: body}
  1087	}
  1088	
  1089	// parseOperand may return an expression or a raw type (incl. array
  1090	// types of the form [...]T. Callers must verify the result.
  1091	// If lhs is set and the result is an identifier, it is not resolved.
  1092	//
  1093	func (p *parser) parseOperand(lhs bool) ast.Expr {
  1094		if p.trace {
  1095			defer un(trace(p, "Operand"))
  1096		}
  1097	
  1098		switch p.tok {
  1099		case token.IDENT:
  1100			x := p.parseIdent()
  1101			if !lhs {
  1102				p.resolve(x)
  1103			}
  1104			return x
  1105	
  1106		case token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING:
  1107			x := &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
  1108			p.next()
  1109			return x
  1110	
  1111		case token.LPAREN:
  1112			lparen := p.pos
  1113			p.next()
  1114			p.exprLev++
  1115			x := p.parseRhsOrType() // types may be parenthesized: (some type)
  1116			p.exprLev--
  1117			rparen := p.expect(token.RPAREN)
  1118			return &ast.ParenExpr{Lparen: lparen, X: x, Rparen: rparen}
  1119	
  1120		case token.FUNC:
  1121			return p.parseFuncTypeOrLit()
  1122		}
  1123	
  1124		if typ := p.tryIdentOrType(); typ != nil {
  1125			// could be type for composite literal or conversion
  1126			_, isIdent := typ.(*ast.Ident)
  1127			assert(!isIdent, "type cannot be identifier")
  1128			return typ
  1129		}
  1130	
  1131		// we have an error
  1132		pos := p.pos
  1133		p.errorExpected(pos, "operand")
  1134		syncStmt(p)
  1135		return &ast.BadExpr{From: pos, To: p.pos}
  1136	}
  1137	
  1138	func (p *parser) parseSelector(x ast.Expr) ast.Expr {
  1139		if p.trace {
  1140			defer un(trace(p, "Selector"))
  1141		}
  1142	
  1143		sel := p.parseIdent()
  1144	
  1145		return &ast.SelectorExpr{X: x, Sel: sel}
  1146	}
  1147	
  1148	func (p *parser) parseTypeAssertion(x ast.Expr) ast.Expr {
  1149		if p.trace {
  1150			defer un(trace(p, "TypeAssertion"))
  1151		}
  1152	
  1153		lparen := p.expect(token.LPAREN)
  1154		var typ ast.Expr
  1155		if p.tok == token.TYPE {
  1156			// type switch: typ == nil
  1157			p.next()
  1158		} else {
  1159			typ = p.parseType()
  1160		}
  1161		rparen := p.expect(token.RPAREN)
  1162	
  1163		return &ast.TypeAssertExpr{X: x, Type: typ, Lparen: lparen, Rparen: rparen}
  1164	}
  1165	
  1166	func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
  1167		if p.trace {
  1168			defer un(trace(p, "IndexOrSlice"))
  1169		}
  1170	
  1171		lbrack := p.expect(token.LBRACK)
  1172		p.exprLev++
  1173		var index [3]ast.Expr // change the 3 to 2 to disable slice expressions w/ cap
  1174		if p.tok != token.COLON {
  1175			index[0] = p.parseRhs()
  1176		}
  1177		ncolons := 0
  1178		for p.tok == token.COLON && ncolons < len(index)-1 {
  1179			p.next()
  1180			ncolons++
  1181			if p.tok != token.COLON && p.tok != token.RBRACK && p.tok != token.EOF {
  1182				index[ncolons] = p.parseRhs()
  1183			}
  1184		}
  1185		p.exprLev--
  1186		rbrack := p.expect(token.RBRACK)
  1187	
  1188		if ncolons > 0 {
  1189			// slice expression
  1190			return &ast.SliceExpr{X: x, Lbrack: lbrack, Low: index[0], High: index[1], Max: index[2], Slice3: ncolons == 2, Rbrack: rbrack}
  1191		}
  1192	
  1193		return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: rbrack}
  1194	}
  1195	
  1196	func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
  1197		if p.trace {
  1198			defer un(trace(p, "CallOrConversion"))
  1199		}
  1200	
  1201		lparen := p.expect(token.LPAREN)
  1202		p.exprLev++
  1203		var list []ast.Expr
  1204		var ellipsis token.Pos
  1205		for p.tok != token.RPAREN && p.tok != token.EOF && !ellipsis.IsValid() {
  1206			list = append(list, p.parseRhsOrType()) // builtins may expect a type: make(some type, ...)
  1207			if p.tok == token.ELLIPSIS {
  1208				ellipsis = p.pos
  1209				p.next()
  1210			}
  1211			if !p.atComma("argument list") {
  1212				break
  1213			}
  1214			p.next()
  1215		}
  1216		p.exprLev--
  1217		rparen := p.expectClosing(token.RPAREN, "argument list")
  1218	
  1219		return &ast.CallExpr{Fun: fun, Lparen: lparen, Args: list, Ellipsis: ellipsis, Rparen: rparen}
  1220	}
  1221	
  1222	func (p *parser) parseElement(keyOk bool) ast.Expr {
  1223		if p.trace {
  1224			defer un(trace(p, "Element"))
  1225		}
  1226	
  1227		if p.tok == token.LBRACE {
  1228			return p.parseLiteralValue(nil)
  1229		}
  1230	
  1231		// Because the parser doesn't know the composite literal type, it cannot
  1232		// know if a key that's an identifier is a struct field name or a name
  1233		// denoting a value. The former is not resolved by the parser or the
  1234		// resolver.
  1235		//
  1236		// Instead, _try_ to resolve such a key if possible. If it resolves,
  1237		// it a) has correctly resolved, or b) incorrectly resolved because
  1238		// the key is a struct field with a name matching another identifier.
  1239		// In the former case we are done, and in the latter case we don't
  1240		// care because the type checker will do a separate field lookup.
  1241		//
  1242		// If the key does not resolve, it a) must be defined at the top
  1243		// level in another file of the same package, the universe scope, or be
  1244		// undeclared; or b) it is a struct field. In the former case, the type
  1245		// checker can do a top-level lookup, and in the latter case it will do
  1246		// a separate field lookup.
  1247		x := p.checkExpr(p.parseExpr(keyOk))
  1248		if keyOk {
  1249			if p.tok == token.COLON {
  1250				colon := p.pos
  1251				p.next()
  1252				// Try to resolve the key but don't collect it
  1253				// as unresolved identifier if it fails so that
  1254				// we don't get (possibly false) errors about
  1255				// undeclared names.
  1256				p.tryResolve(x, false)
  1257				return &ast.KeyValueExpr{Key: x, Colon: colon, Value: p.parseElement(false)}
  1258			}
  1259			p.resolve(x) // not a key
  1260		}
  1261	
  1262		return x
  1263	}
  1264	
  1265	func (p *parser) parseElementList() (list []ast.Expr) {
  1266		if p.trace {
  1267			defer un(trace(p, "ElementList"))
  1268		}
  1269	
  1270		for p.tok != token.RBRACE && p.tok != token.EOF {
  1271			list = append(list, p.parseElement(true))
  1272			if !p.atComma("composite literal") {
  1273				break
  1274			}
  1275			p.next()
  1276		}
  1277	
  1278		return
  1279	}
  1280	
  1281	func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
  1282		if p.trace {
  1283			defer un(trace(p, "LiteralValue"))
  1284		}
  1285	
  1286		lbrace := p.expect(token.LBRACE)
  1287		var elts []ast.Expr
  1288		p.exprLev++
  1289		if p.tok != token.RBRACE {
  1290			elts = p.parseElementList()
  1291		}
  1292		p.exprLev--
  1293		rbrace := p.expectClosing(token.RBRACE, "composite literal")
  1294		return &ast.CompositeLit{Type: typ, Lbrace: lbrace, Elts: elts, Rbrace: rbrace}
  1295	}
  1296	
  1297	// checkExpr checks that x is an expression (and not a type).
  1298	func (p *parser) checkExpr(x ast.Expr) ast.Expr {
  1299		switch unparen(x).(type) {
  1300		case *ast.BadExpr:
  1301		case *ast.Ident:
  1302		case *ast.BasicLit:
  1303		case *ast.FuncLit:
  1304		case *ast.CompositeLit:
  1305		case *ast.ParenExpr:
  1306			panic("unreachable")
  1307		case *ast.SelectorExpr:
  1308		case *ast.IndexExpr:
  1309		case *ast.SliceExpr:
  1310		case *ast.TypeAssertExpr:
  1311			// If t.Type == nil we have a type assertion of the form
  1312			// y.(type), which is only allowed in type switch expressions.
  1313			// It's hard to exclude those but for the case where we are in
  1314			// a type switch. Instead be lenient and test this in the type
  1315			// checker.
  1316		case *ast.CallExpr:
  1317		case *ast.StarExpr:
  1318		case *ast.UnaryExpr:
  1319		case *ast.BinaryExpr:
  1320		default:
  1321			// all other nodes are not proper expressions
  1322			p.errorExpected(x.Pos(), "expression")
  1323			x = &ast.BadExpr{From: x.Pos(), To: x.End()}
  1324		}
  1325		return x
  1326	}
  1327	
  1328	// isTypeName returns true iff x is a (qualified) TypeName.
  1329	func isTypeName(x ast.Expr) bool {
  1330		switch t := x.(type) {
  1331		case *ast.BadExpr:
  1332		case *ast.Ident:
  1333		case *ast.SelectorExpr:
  1334			_, isIdent := t.X.(*ast.Ident)
  1335			return isIdent
  1336		default:
  1337			return false // all other nodes are not type names
  1338		}
  1339		return true
  1340	}
  1341	
  1342	// isLiteralType returns true iff x is a legal composite literal type.
  1343	func isLiteralType(x ast.Expr) bool {
  1344		switch t := x.(type) {
  1345		case *ast.BadExpr:
  1346		case *ast.Ident:
  1347		case *ast.SelectorExpr:
  1348			_, isIdent := t.X.(*ast.Ident)
  1349			return isIdent
  1350		case *ast.ArrayType:
  1351		case *ast.StructType:
  1352		case *ast.MapType:
  1353		default:
  1354			return false // all other nodes are not legal composite literal types
  1355		}
  1356		return true
  1357	}
  1358	
  1359	// If x is of the form *T, deref returns T, otherwise it returns x.
  1360	func deref(x ast.Expr) ast.Expr {
  1361		if p, isPtr := x.(*ast.StarExpr); isPtr {
  1362			x = p.X
  1363		}
  1364		return x
  1365	}
  1366	
  1367	// If x is of the form (T), unparen returns unparen(T), otherwise it returns x.
  1368	func unparen(x ast.Expr) ast.Expr {
  1369		if p, isParen := x.(*ast.ParenExpr); isParen {
  1370			x = unparen(p.X)
  1371		}
  1372		return x
  1373	}
  1374	
  1375	// checkExprOrType checks that x is an expression or a type
  1376	// (and not a raw type such as [...]T).
  1377	//
  1378	func (p *parser) checkExprOrType(x ast.Expr) ast.Expr {
  1379		switch t := unparen(x).(type) {
  1380		case *ast.ParenExpr:
  1381			panic("unreachable")
  1382		case *ast.UnaryExpr:
  1383		case *ast.ArrayType:
  1384			if len, isEllipsis := t.Len.(*ast.Ellipsis); isEllipsis {
  1385				p.error(len.Pos(), "expected array length, found '...'")
  1386				x = &ast.BadExpr{From: x.Pos(), To: x.End()}
  1387			}
  1388		}
  1389	
  1390		// all other nodes are expressions or types
  1391		return x
  1392	}
  1393	
  1394	// If lhs is set and the result is an identifier, it is not resolved.
  1395	func (p *parser) parsePrimaryExpr(lhs bool) ast.Expr {
  1396		if p.trace {
  1397			defer un(trace(p, "PrimaryExpr"))
  1398		}
  1399	
  1400		x := p.parseOperand(lhs)
  1401	L:
  1402		for {
  1403			switch p.tok {
  1404			case token.PERIOD:
  1405				p.next()
  1406				if lhs {
  1407					p.resolve(x)
  1408				}
  1409				switch p.tok {
  1410				case token.IDENT:
  1411					x = p.parseSelector(p.checkExprOrType(x))
  1412				case token.LPAREN:
  1413					x = p.parseTypeAssertion(p.checkExpr(x))
  1414				default:
  1415					pos := p.pos
  1416					p.errorExpected(pos, "selector or type assertion")
  1417					p.next() // make progress
  1418					x = &ast.BadExpr{From: pos, To: p.pos}
  1419				}
  1420			case token.LBRACK:
  1421				if lhs {
  1422					p.resolve(x)
  1423				}
  1424				x = p.parseIndexOrSlice(p.checkExpr(x))
  1425			case token.LPAREN:
  1426				if lhs {
  1427					p.resolve(x)
  1428				}
  1429				x = p.parseCallOrConversion(p.checkExprOrType(x))
  1430			case token.LBRACE:
  1431				if isLiteralType(x) && (p.exprLev >= 0 || !isTypeName(x)) {
  1432					if lhs {
  1433						p.resolve(x)
  1434					}
  1435					x = p.parseLiteralValue(x)
  1436				} else {
  1437					break L
  1438				}
  1439			default:
  1440				break L
  1441			}
  1442			lhs = false // no need to try to resolve again
  1443		}
  1444	
  1445		return x
  1446	}
  1447	
  1448	// If lhs is set and the result is an identifier, it is not resolved.
  1449	func (p *parser) parseUnaryExpr(lhs bool) ast.Expr {
  1450		if p.trace {
  1451			defer un(trace(p, "UnaryExpr"))
  1452		}
  1453	
  1454		switch p.tok {
  1455		case token.ADD, token.SUB, token.NOT, token.XOR, token.AND:
  1456			pos, op := p.pos, p.tok
  1457			p.next()
  1458			x := p.parseUnaryExpr(false)
  1459			return &ast.UnaryExpr{OpPos: pos, Op: op, X: p.checkExpr(x)}
  1460	
  1461		case token.ARROW:
  1462			// channel type or receive expression
  1463			arrow := p.pos
  1464			p.next()
  1465	
  1466			// If the next token is token.CHAN we still don't know if it
  1467			// is a channel type or a receive operation - we only know
  1468			// once we have found the end of the unary expression. There
  1469			// are two cases:
  1470			//
  1471			//   <- type  => (<-type) must be channel type
  1472			//   <- expr  => <-(expr) is a receive from an expression
  1473			//
  1474			// In the first case, the arrow must be re-associated with
  1475			// the channel type parsed already:
  1476			//
  1477			//   <- (chan type)    =>  (<-chan type)
  1478			//   <- (chan<- type)  =>  (<-chan (<-type))
  1479	
  1480			x := p.parseUnaryExpr(false)
  1481	
  1482			// determine which case we have
  1483			if typ, ok := x.(*ast.ChanType); ok {
  1484				// (<-type)
  1485	
  1486				// re-associate position info and <-
  1487				dir := ast.SEND
  1488				for ok && dir == ast.SEND {
  1489					if typ.Dir == ast.RECV {
  1490						// error: (<-type) is (<-(<-chan T))
  1491						p.errorExpected(typ.Arrow, "'chan'")
  1492					}
  1493					arrow, typ.Begin, typ.Arrow = typ.Arrow, arrow, arrow
  1494					dir, typ.Dir = typ.Dir, ast.RECV
  1495					typ, ok = typ.Value.(*ast.ChanType)
  1496				}
  1497				if dir == ast.SEND {
  1498					p.errorExpected(arrow, "channel type")
  1499				}
  1500	
  1501				return x
  1502			}
  1503	
  1504			// <-(expr)
  1505			return &ast.UnaryExpr{OpPos: arrow, Op: token.ARROW, X: p.checkExpr(x)}
  1506	
  1507		case token.MUL:
  1508			// pointer type or unary "*" expression
  1509			pos := p.pos
  1510			p.next()
  1511			x := p.parseUnaryExpr(false)
  1512			return &ast.StarExpr{Star: pos, X: p.checkExprOrType(x)}
  1513		}
  1514	
  1515		return p.parsePrimaryExpr(lhs)
  1516	}
  1517	
  1518	func (p *parser) tokPrec() (token.Token, int) {
  1519		tok := p.tok
  1520		if p.inRhs && tok == token.ASSIGN {
  1521			tok = token.EQL
  1522		}
  1523		return tok, tok.Precedence()
  1524	}
  1525	
  1526	// If lhs is set and the result is an identifier, it is not resolved.
  1527	func (p *parser) parseBinaryExpr(lhs bool, prec1 int) ast.Expr {
  1528		if p.trace {
  1529			defer un(trace(p, "BinaryExpr"))
  1530		}
  1531	
  1532		x := p.parseUnaryExpr(lhs)
  1533		for _, prec := p.tokPrec(); prec >= prec1; prec-- {
  1534			for {
  1535				op, oprec := p.tokPrec()
  1536				if oprec != prec {
  1537					break
  1538				}
  1539				pos := p.expect(op)
  1540				if lhs {
  1541					p.resolve(x)
  1542					lhs = false
  1543				}
  1544				y := p.parseBinaryExpr(false, prec+1)
  1545				x = &ast.BinaryExpr{X: p.checkExpr(x), OpPos: pos, Op: op, Y: p.checkExpr(y)}
  1546			}
  1547		}
  1548	
  1549		return x
  1550	}
  1551	
  1552	// If lhs is set and the result is an identifier, it is not resolved.
  1553	// The result may be a type or even a raw type ([...]int). Callers must
  1554	// check the result (using checkExpr or checkExprOrType), depending on
  1555	// context.
  1556	func (p *parser) parseExpr(lhs bool) ast.Expr {
  1557		if p.trace {
  1558			defer un(trace(p, "Expression"))
  1559		}
  1560	
  1561		return p.parseBinaryExpr(lhs, token.LowestPrec+1)
  1562	}
  1563	
  1564	func (p *parser) parseRhs() ast.Expr {
  1565		old := p.inRhs
  1566		p.inRhs = true
  1567		x := p.checkExpr(p.parseExpr(false))
  1568		p.inRhs = old
  1569		return x
  1570	}
  1571	
  1572	func (p *parser) parseRhsOrType() ast.Expr {
  1573		old := p.inRhs
  1574		p.inRhs = true
  1575		x := p.checkExprOrType(p.parseExpr(false))
  1576		p.inRhs = old
  1577		return x
  1578	}
  1579	
  1580	// ----------------------------------------------------------------------------
  1581	// Statements
  1582	
  1583	// Parsing modes for parseSimpleStmt.
  1584	const (
  1585		basic = iota
  1586		labelOk
  1587		rangeOk
  1588	)
  1589	
  1590	// parseSimpleStmt returns true as 2nd result if it parsed the assignment
  1591	// of a range clause (with mode == rangeOk). The returned statement is an
  1592	// assignment with a right-hand side that is a single unary expression of
  1593	// the form "range x". No guarantees are given for the left-hand side.
  1594	func (p *parser) parseSimpleStmt(mode int) (ast.Stmt, bool) {
  1595		if p.trace {
  1596			defer un(trace(p, "SimpleStmt"))
  1597		}
  1598	
  1599		x := p.parseLhsList()
  1600	
  1601		switch p.tok {
  1602		case
  1603			token.DEFINE, token.ASSIGN, token.ADD_ASSIGN,
  1604			token.SUB_ASSIGN, token.MUL_ASSIGN, token.QUO_ASSIGN,
  1605			token.REM_ASSIGN, token.AND_ASSIGN, token.OR_ASSIGN,
  1606			token.XOR_ASSIGN, token.SHL_ASSIGN, token.SHR_ASSIGN, token.AND_NOT_ASSIGN:
  1607			// assignment statement, possibly part of a range clause
  1608			pos, tok := p.pos, p.tok
  1609			p.next()
  1610			var y []ast.Expr
  1611			isRange := false
  1612			if mode == rangeOk && p.tok == token.RANGE && (tok == token.DEFINE || tok == token.ASSIGN) {
  1613				pos := p.pos
  1614				p.next()
  1615				y = []ast.Expr{&ast.UnaryExpr{OpPos: pos, Op: token.RANGE, X: p.parseRhs()}}
  1616				isRange = true
  1617			} else {
  1618				y = p.parseRhsList()
  1619			}
  1620			as := &ast.AssignStmt{Lhs: x, TokPos: pos, Tok: tok, Rhs: y}
  1621			if tok == token.DEFINE {
  1622				p.shortVarDecl(as, x)
  1623			}
  1624			return as, isRange
  1625		}
  1626	
  1627		if len(x) > 1 {
  1628			p.errorExpected(x[0].Pos(), "1 expression")
  1629			// continue with first expression
  1630		}
  1631	
  1632		switch p.tok {
  1633		case token.COLON:
  1634			// labeled statement
  1635			colon := p.pos
  1636			p.next()
  1637			if label, isIdent := x[0].(*ast.Ident); mode == labelOk && isIdent {
  1638				// Go spec: The scope of a label is the body of the function
  1639				// in which it is declared and excludes the body of any nested
  1640				// function.
  1641				stmt := &ast.LabeledStmt{Label: label, Colon: colon, Stmt: p.parseStmt()}
  1642				p.declare(stmt, nil, p.labelScope, ast.Lbl, label)
  1643				return stmt, false
  1644			}
  1645			// The label declaration typically starts at x[0].Pos(), but the label
  1646			// declaration may be erroneous due to a token after that position (and
  1647			// before the ':'). If SpuriousErrors is not set, the (only) error re-
  1648			// ported for the line is the illegal label error instead of the token
  1649			// before the ':' that caused the problem. Thus, use the (latest) colon
  1650			// position for error reporting.
  1651			p.error(colon, "illegal label declaration")
  1652			return &ast.BadStmt{From: x[0].Pos(), To: colon + 1}, false
  1653	
  1654		case token.ARROW:
  1655			// send statement
  1656			arrow := p.pos
  1657			p.next()
  1658			y := p.parseRhs()
  1659			return &ast.SendStmt{Chan: x[0], Arrow: arrow, Value: y}, false
  1660	
  1661		case token.INC, token.DEC:
  1662			// increment or decrement
  1663			s := &ast.IncDecStmt{X: x[0], TokPos: p.pos, Tok: p.tok}
  1664			p.next()
  1665			return s, false
  1666		}
  1667	
  1668		// expression
  1669		return &ast.ExprStmt{X: x[0]}, false
  1670	}
  1671	
  1672	func (p *parser) parseCallExpr() *ast.CallExpr {
  1673		x := p.parseRhsOrType() // could be a conversion: (some type)(x)
  1674		if call, isCall := x.(*ast.CallExpr); isCall {
  1675			return call
  1676		}
  1677		if _, isBad := x.(*ast.BadExpr); !isBad {
  1678			// only report error if it's a new one
  1679			p.errorExpected(x.Pos(), "function/method call")
  1680		}
  1681		return nil
  1682	}
  1683	
  1684	func (p *parser) parseGoStmt() ast.Stmt {
  1685		if p.trace {
  1686			defer un(trace(p, "GoStmt"))
  1687		}
  1688	
  1689		pos := p.expect(token.GO)
  1690		call := p.parseCallExpr()
  1691		p.expectSemi()
  1692		if call == nil {
  1693			return &ast.BadStmt{From: pos, To: pos + 2} // len("go")
  1694		}
  1695	
  1696		return &ast.GoStmt{Go: pos, Call: call}
  1697	}
  1698	
  1699	func (p *parser) parseDeferStmt() ast.Stmt {
  1700		if p.trace {
  1701			defer un(trace(p, "DeferStmt"))
  1702		}
  1703	
  1704		pos := p.expect(token.DEFER)
  1705		call := p.parseCallExpr()
  1706		p.expectSemi()
  1707		if call == nil {
  1708			return &ast.BadStmt{From: pos, To: pos + 5} // len("defer")
  1709		}
  1710	
  1711		return &ast.DeferStmt{Defer: pos, Call: call}
  1712	}
  1713	
  1714	func (p *parser) parseReturnStmt() *ast.ReturnStmt {
  1715		if p.trace {
  1716			defer un(trace(p, "ReturnStmt"))
  1717		}
  1718	
  1719		pos := p.pos
  1720		p.expect(token.RETURN)
  1721		var x []ast.Expr
  1722		if p.tok != token.SEMICOLON && p.tok != token.RBRACE {
  1723			x = p.parseRhsList()
  1724		}
  1725		p.expectSemi()
  1726	
  1727		return &ast.ReturnStmt{Return: pos, Results: x}
  1728	}
  1729	
  1730	func (p *parser) parseBranchStmt(tok token.Token) *ast.BranchStmt {
  1731		if p.trace {
  1732			defer un(trace(p, "BranchStmt"))
  1733		}
  1734	
  1735		pos := p.expect(tok)
  1736		var label *ast.Ident
  1737		if tok != token.FALLTHROUGH && p.tok == token.IDENT {
  1738			label = p.parseIdent()
  1739			// add to list of unresolved targets
  1740			n := len(p.targetStack) - 1
  1741			p.targetStack[n] = append(p.targetStack[n], label)
  1742		}
  1743		p.expectSemi()
  1744	
  1745		return &ast.BranchStmt{TokPos: pos, Tok: tok, Label: label}
  1746	}
  1747	
  1748	func (p *parser) makeExpr(s ast.Stmt) ast.Expr {
  1749		if s == nil {
  1750			return nil
  1751		}
  1752		if es, isExpr := s.(*ast.ExprStmt); isExpr {
  1753			return p.checkExpr(es.X)
  1754		}
  1755		p.error(s.Pos(), "expected condition, found simple statement")
  1756		return &ast.BadExpr{From: s.Pos(), To: s.End()}
  1757	}
  1758	
  1759	func (p *parser) parseIfStmt() *ast.IfStmt {
  1760		if p.trace {
  1761			defer un(trace(p, "IfStmt"))
  1762		}
  1763	
  1764		pos := p.expect(token.IF)
  1765		p.openScope()
  1766		defer p.closeScope()
  1767	
  1768		var s ast.Stmt
  1769		var x ast.Expr
  1770		{
  1771			prevLev := p.exprLev
  1772			p.exprLev = -1
  1773			if p.tok == token.SEMICOLON {
  1774				p.next()
  1775				x = p.parseRhs()
  1776			} else {
  1777				s, _ = p.parseSimpleStmt(basic)
  1778				if p.tok == token.SEMICOLON {
  1779					p.next()
  1780					x = p.parseRhs()
  1781				} else {
  1782					x = p.makeExpr(s)
  1783					s = nil
  1784				}
  1785			}
  1786			p.exprLev = prevLev
  1787		}
  1788	
  1789		body := p.parseBlockStmt()
  1790		var else_ ast.Stmt
  1791		if p.tok == token.ELSE {
  1792			p.next()
  1793			else_ = p.parseStmt()
  1794		} else {
  1795			p.expectSemi()
  1796		}
  1797	
  1798		return &ast.IfStmt{If: pos, Init: s, Cond: x, Body: body, Else: else_}
  1799	}
  1800	
  1801	func (p *parser) parseTypeList() (list []ast.Expr) {
  1802		if p.trace {
  1803			defer un(trace(p, "TypeList"))
  1804		}
  1805	
  1806		list = append(list, p.parseType())
  1807		for p.tok == token.COMMA {
  1808			p.next()
  1809			list = append(list, p.parseType())
  1810		}
  1811	
  1812		return
  1813	}
  1814	
  1815	func (p *parser) parseCaseClause(typeSwitch bool) *ast.CaseClause {
  1816		if p.trace {
  1817			defer un(trace(p, "CaseClause"))
  1818		}
  1819	
  1820		pos := p.pos
  1821		var list []ast.Expr
  1822		if p.tok == token.CASE {
  1823			p.next()
  1824			if typeSwitch {
  1825				list = p.parseTypeList()
  1826			} else {
  1827				list = p.parseRhsList()
  1828			}
  1829		} else {
  1830			p.expect(token.DEFAULT)
  1831		}
  1832	
  1833		colon := p.expect(token.COLON)
  1834		p.openScope()
  1835		body := p.parseStmtList()
  1836		p.closeScope()
  1837	
  1838		return &ast.CaseClause{Case: pos, List: list, Colon: colon, Body: body}
  1839	}
  1840	
  1841	func isTypeSwitchAssert(x ast.Expr) bool {
  1842		a, ok := x.(*ast.TypeAssertExpr)
  1843		return ok && a.Type == nil
  1844	}
  1845	
  1846	func isTypeSwitchGuard(s ast.Stmt) bool {
  1847		switch t := s.(type) {
  1848		case *ast.ExprStmt:
  1849			// x.(nil)
  1850			return isTypeSwitchAssert(t.X)
  1851		case *ast.AssignStmt:
  1852			// v := x.(nil)
  1853			return len(t.Lhs) == 1 && t.Tok == token.DEFINE && len(t.Rhs) == 1 && isTypeSwitchAssert(t.Rhs[0])
  1854		}
  1855		return false
  1856	}
  1857	
  1858	func (p *parser) parseSwitchStmt() ast.Stmt {
  1859		if p.trace {
  1860			defer un(trace(p, "SwitchStmt"))
  1861		}
  1862	
  1863		pos := p.expect(token.SWITCH)
  1864		p.openScope()
  1865		defer p.closeScope()
  1866	
  1867		var s1, s2 ast.Stmt
  1868		if p.tok != token.LBRACE {
  1869			prevLev := p.exprLev
  1870			p.exprLev = -1
  1871			if p.tok != token.SEMICOLON {
  1872				s2, _ = p.parseSimpleStmt(basic)
  1873			}
  1874			if p.tok == token.SEMICOLON {
  1875				p.next()
  1876				s1 = s2
  1877				s2 = nil
  1878				if p.tok != token.LBRACE {
  1879					// A TypeSwitchGuard may declare a variable in addition
  1880					// to the variable declared in the initial SimpleStmt.
  1881					// Introduce extra scope to avoid redeclaration errors:
  1882					//
  1883					//	switch t := 0; t := x.(T) { ... }
  1884					//
  1885					// (this code is not valid Go because the first t
  1886					// cannot be accessed and thus is never used, the extra
  1887					// scope is needed for the correct error message).
  1888					//
  1889					// If we don't have a type switch, s2 must be an expression.
  1890					// Having the extra nested but empty scope won't affect it.
  1891					p.openScope()
  1892					defer p.closeScope()
  1893					s2, _ = p.parseSimpleStmt(basic)
  1894				}
  1895			}
  1896			p.exprLev = prevLev
  1897		}
  1898	
  1899		typeSwitch := isTypeSwitchGuard(s2)
  1900		lbrace := p.expect(token.LBRACE)
  1901		var list []ast.Stmt
  1902		for p.tok == token.CASE || p.tok == token.DEFAULT {
  1903			list = append(list, p.parseCaseClause(typeSwitch))
  1904		}
  1905		rbrace := p.expect(token.RBRACE)
  1906		p.expectSemi()
  1907		body := &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
  1908	
  1909		if typeSwitch {
  1910			return &ast.TypeSwitchStmt{Switch: pos, Init: s1, Assign: s2, Body: body}
  1911		}
  1912	
  1913		return &ast.SwitchStmt{Switch: pos, Init: s1, Tag: p.makeExpr(s2), Body: body}
  1914	}
  1915	
  1916	func (p *parser) parseCommClause() *ast.CommClause {
  1917		if p.trace {
  1918			defer un(trace(p, "CommClause"))
  1919		}
  1920	
  1921		p.openScope()
  1922		pos := p.pos
  1923		var comm ast.Stmt
  1924		if p.tok == token.CASE {
  1925			p.next()
  1926			lhs := p.parseLhsList()
  1927			if p.tok == token.ARROW {
  1928				// SendStmt
  1929				if len(lhs) > 1 {
  1930					p.errorExpected(lhs[0].Pos(), "1 expression")
  1931					// continue with first expression
  1932				}
  1933				arrow := p.pos
  1934				p.next()
  1935				rhs := p.parseRhs()
  1936				comm = &ast.SendStmt{Chan: lhs[0], Arrow: arrow, Value: rhs}
  1937			} else {
  1938				// RecvStmt
  1939				if tok := p.tok; tok == token.ASSIGN || tok == token.DEFINE {
  1940					// RecvStmt with assignment
  1941					if len(lhs) > 2 {
  1942						p.errorExpected(lhs[0].Pos(), "1 or 2 expressions")
  1943						// continue with first two expressions
  1944						lhs = lhs[0:2]
  1945					}
  1946					pos := p.pos
  1947					p.next()
  1948					rhs := p.parseRhs()
  1949					as := &ast.AssignStmt{Lhs: lhs, TokPos: pos, Tok: tok, Rhs: []ast.Expr{rhs}}
  1950					if tok == token.DEFINE {
  1951						p.shortVarDecl(as, lhs)
  1952					}
  1953					comm = as
  1954				} else {
  1955					// lhs must be single receive operation
  1956					if len(lhs) > 1 {
  1957						p.errorExpected(lhs[0].Pos(), "1 expression")
  1958						// continue with first expression
  1959					}
  1960					comm = &ast.ExprStmt{X: lhs[0]}
  1961				}
  1962			}
  1963		} else {
  1964			p.expect(token.DEFAULT)
  1965		}
  1966	
  1967		colon := p.expect(token.COLON)
  1968		body := p.parseStmtList()
  1969		p.closeScope()
  1970	
  1971		return &ast.CommClause{Case: pos, Comm: comm, Colon: colon, Body: body}
  1972	}
  1973	
  1974	func (p *parser) parseSelectStmt() *ast.SelectStmt {
  1975		if p.trace {
  1976			defer un(trace(p, "SelectStmt"))
  1977		}
  1978	
  1979		pos := p.expect(token.SELECT)
  1980		lbrace := p.expect(token.LBRACE)
  1981		var list []ast.Stmt
  1982		for p.tok == token.CASE || p.tok == token.DEFAULT {
  1983			list = append(list, p.parseCommClause())
  1984		}
  1985		rbrace := p.expect(token.RBRACE)
  1986		p.expectSemi()
  1987		body := &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
  1988	
  1989		return &ast.SelectStmt{Select: pos, Body: body}
  1990	}
  1991	
  1992	func (p *parser) parseForStmt() ast.Stmt {
  1993		if p.trace {
  1994			defer un(trace(p, "ForStmt"))
  1995		}
  1996	
  1997		pos := p.expect(token.FOR)
  1998		p.openScope()
  1999		defer p.closeScope()
  2000	
  2001		var s1, s2, s3 ast.Stmt
  2002		var isRange bool
  2003		if p.tok != token.LBRACE {
  2004			prevLev := p.exprLev
  2005			p.exprLev = -1
  2006			if p.tok != token.SEMICOLON {
  2007				s2, isRange = p.parseSimpleStmt(rangeOk)
  2008			}
  2009			if !isRange && p.tok == token.SEMICOLON {
  2010				p.next()
  2011				s1 = s2
  2012				s2 = nil
  2013				if p.tok != token.SEMICOLON {
  2014					s2, _ = p.parseSimpleStmt(basic)
  2015				}
  2016				p.expectSemi()
  2017				if p.tok != token.LBRACE {
  2018					s3, _ = p.parseSimpleStmt(basic)
  2019				}
  2020			}
  2021			p.exprLev = prevLev
  2022		}
  2023	
  2024		body := p.parseBlockStmt()
  2025		p.expectSemi()
  2026	
  2027		if isRange {
  2028			as := s2.(*ast.AssignStmt)
  2029			// check lhs
  2030			var key, value ast.Expr
  2031			switch len(as.Lhs) {
  2032			case 2:
  2033				key, value = as.Lhs[0], as.Lhs[1]
  2034			case 1:
  2035				key = as.Lhs[0]
  2036			default:
  2037				p.errorExpected(as.Lhs[0].Pos(), "1 or 2 expressions")
  2038				return &ast.BadStmt{From: pos, To: body.End()}
  2039			}
  2040			// parseSimpleStmt returned a right-hand side that
  2041			// is a single unary expression of the form "range x"
  2042			x := as.Rhs[0].(*ast.UnaryExpr).X
  2043			return &ast.RangeStmt{
  2044				For:    pos,
  2045				Key:    key,
  2046				Value:  value,
  2047				TokPos: as.TokPos,
  2048				Tok:    as.Tok,
  2049				X:      x,
  2050				Body:   body,
  2051			}
  2052		}
  2053	
  2054		// regular for statement
  2055		return &ast.ForStmt{
  2056			For:  pos,
  2057			Init: s1,
  2058			Cond: p.makeExpr(s2),
  2059			Post: s3,
  2060			Body: body,
  2061		}
  2062	}
  2063	
  2064	func (p *parser) parseStmt() (s ast.Stmt) {
  2065		if p.trace {
  2066			defer un(trace(p, "Statement"))
  2067		}
  2068	
  2069		switch p.tok {
  2070		case token.CONST, token.TYPE, token.VAR:
  2071			s = &ast.DeclStmt{Decl: p.parseDecl(syncStmt)}
  2072		case
  2073			// tokens that may start an expression
  2074			token.IDENT, token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING, token.FUNC, token.LPAREN, // operands
  2075			token.LBRACK, token.STRUCT, // composite types
  2076			token.ADD, token.SUB, token.MUL, token.AND, token.XOR, token.ARROW, token.NOT: // unary operators
  2077			s, _ = p.parseSimpleStmt(labelOk)
  2078			// because of the required look-ahead, labeled statements are
  2079			// parsed by parseSimpleStmt - don't expect a semicolon after
  2080			// them
  2081			if _, isLabeledStmt := s.(*ast.LabeledStmt); !isLabeledStmt {
  2082				p.expectSemi()
  2083			}
  2084		case token.GO:
  2085			s = p.parseGoStmt()
  2086		case token.DEFER:
  2087			s = p.parseDeferStmt()
  2088		case token.RETURN:
  2089			s = p.parseReturnStmt()
  2090		case token.BREAK, token.CONTINUE, token.GOTO, token.FALLTHROUGH:
  2091			s = p.parseBranchStmt(p.tok)
  2092		case token.LBRACE:
  2093			s = p.parseBlockStmt()
  2094			p.expectSemi()
  2095		case token.IF:
  2096			s = p.parseIfStmt()
  2097		case token.SWITCH:
  2098			s = p.parseSwitchStmt()
  2099		case token.SELECT:
  2100			s = p.parseSelectStmt()
  2101		case token.FOR:
  2102			s = p.parseForStmt()
  2103		case token.SEMICOLON:
  2104			s = &ast.EmptyStmt{Semicolon: p.pos}
  2105			p.next()
  2106		case token.RBRACE:
  2107			// a semicolon may be omitted before a closing "}"
  2108			s = &ast.EmptyStmt{Semicolon: p.pos}
  2109		default:
  2110			// no statement found
  2111			pos := p.pos
  2112			p.errorExpected(pos, "statement")
  2113			syncStmt(p)
  2114			s = &ast.BadStmt{From: pos, To: p.pos}
  2115		}
  2116	
  2117		return
  2118	}
  2119	
  2120	// ----------------------------------------------------------------------------
  2121	// Declarations
  2122	
  2123	type parseSpecFunction func(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec
  2124	
  2125	func isValidImport(lit string) bool {
  2126		const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
  2127		s, _ := strconv.Unquote(lit) // go/scanner returns a legal string literal
  2128		for _, r := range s {
  2129			if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
  2130				return false
  2131			}
  2132		}
  2133		return s != ""
  2134	}
  2135	
  2136	func (p *parser) parseImportSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
  2137		if p.trace {
  2138			defer un(trace(p, "ImportSpec"))
  2139		}
  2140	
  2141		var ident *ast.Ident
  2142		switch p.tok {
  2143		case token.PERIOD:
  2144			ident = &ast.Ident{NamePos: p.pos, Name: "."}
  2145			p.next()
  2146		case token.IDENT:
  2147			ident = p.parseIdent()
  2148		}
  2149	
  2150		pos := p.pos
  2151		var path string
  2152		if p.tok == token.STRING {
  2153			path = p.lit
  2154			if !isValidImport(path) {
  2155				p.error(pos, "invalid import path: "+path)
  2156			}
  2157			p.next()
  2158		} else {
  2159			p.expect(token.STRING) // use expect() error handling
  2160		}
  2161		p.expectSemi() // call before accessing p.linecomment
  2162	
  2163		// collect imports
  2164		spec := &ast.ImportSpec{
  2165			Doc:     doc,
  2166			Name:    ident,
  2167			Path:    &ast.BasicLit{ValuePos: pos, Kind: token.STRING, Value: path},
  2168			Comment: p.lineComment,
  2169		}
  2170		p.imports = append(p.imports, spec)
  2171	
  2172		return spec
  2173	}
  2174	
  2175	func (p *parser) parseValueSpec(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec {
  2176		if p.trace {
  2177			defer un(trace(p, keyword.String()+"Spec"))
  2178		}
  2179	
  2180		idents := p.parseIdentList()
  2181		typ := p.tryType()
  2182		var values []ast.Expr
  2183		// always permit optional initialization for more tolerant parsing
  2184		if p.tok == token.ASSIGN {
  2185			p.next()
  2186			values = p.parseRhsList()
  2187		}
  2188		p.expectSemi() // call before accessing p.linecomment
  2189	
  2190		// Go spec: The scope of a constant or variable identifier declared inside
  2191		// a function begins at the end of the ConstSpec or VarSpec and ends at
  2192		// the end of the innermost containing block.
  2193		// (Global identifiers are resolved in a separate phase after parsing.)
  2194		spec := &ast.ValueSpec{
  2195			Doc:     doc,
  2196			Names:   idents,
  2197			Type:    typ,
  2198			Values:  values,
  2199			Comment: p.lineComment,
  2200		}
  2201		kind := ast.Con
  2202		if keyword == token.VAR {
  2203			kind = ast.Var
  2204		}
  2205		p.declare(spec, iota, p.topScope, kind, idents...)
  2206	
  2207		return spec
  2208	}
  2209	
  2210	func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
  2211		if p.trace {
  2212			defer un(trace(p, "TypeSpec"))
  2213		}
  2214	
  2215		ident := p.parseIdent()
  2216	
  2217		// Go spec: The scope of a type identifier declared inside a function begins
  2218		// at the identifier in the TypeSpec and ends at the end of the innermost
  2219		// containing block.
  2220		// (Global identifiers are resolved in a separate phase after parsing.)
  2221		spec := &ast.TypeSpec{Doc: doc, Name: ident}
  2222		p.declare(spec, nil, p.topScope, ast.Typ, ident)
  2223	
  2224		spec.Type = p.parseType()
  2225		p.expectSemi() // call before accessing p.linecomment
  2226		spec.Comment = p.lineComment
  2227	
  2228		return spec
  2229	}
  2230	
  2231	func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
  2232		if p.trace {
  2233			defer un(trace(p, "GenDecl("+keyword.String()+")"))
  2234		}
  2235	
  2236		doc := p.leadComment
  2237		pos := p.expect(keyword)
  2238		var lparen, rparen token.Pos
  2239		var list []ast.Spec
  2240		if p.tok == token.LPAREN {
  2241			lparen = p.pos
  2242			p.next()
  2243			for iota := 0; p.tok != token.RPAREN && p.tok != token.EOF; iota++ {
  2244				list = append(list, f(p.leadComment, keyword, iota))
  2245			}
  2246			rparen = p.expect(token.RPAREN)
  2247			p.expectSemi()
  2248		} else {
  2249			list = append(list, f(nil, keyword, 0))
  2250		}
  2251	
  2252		return &ast.GenDecl{
  2253			Doc:    doc,
  2254			TokPos: pos,
  2255			Tok:    keyword,
  2256			Lparen: lparen,
  2257			Specs:  list,
  2258			Rparen: rparen,
  2259		}
  2260	}
  2261	
  2262	func (p *parser) parseReceiver(scope *ast.Scope) *ast.FieldList {
  2263		if p.trace {
  2264			defer un(trace(p, "Receiver"))
  2265		}
  2266	
  2267		par := p.parseParameters(scope, false)
  2268	
  2269		// must have exactly one receiver
  2270		if par.NumFields() != 1 {
  2271			p.errorExpected(par.Opening, "exactly one receiver")
  2272			par.List = []*ast.Field{{Type: &ast.BadExpr{From: par.Opening, To: par.Closing + 1}}}
  2273			return par
  2274		}
  2275	
  2276		// recv type must be of the form ["*"] identifier
  2277		recv := par.List[0]
  2278		base := deref(recv.Type)
  2279		if _, isIdent := base.(*ast.Ident); !isIdent {
  2280			if _, isBad := base.(*ast.BadExpr); !isBad {
  2281				// only report error if it's a new one
  2282				p.errorExpected(base.Pos(), "(unqualified) identifier")
  2283			}
  2284			par.List = []*ast.Field{
  2285				{Type: &ast.BadExpr{From: recv.Pos(), To: recv.End()}},
  2286			}
  2287		}
  2288	
  2289		return par
  2290	}
  2291	
  2292	func (p *parser) parseFuncDecl() *ast.FuncDecl {
  2293		if p.trace {
  2294			defer un(trace(p, "FunctionDecl"))
  2295		}
  2296	
  2297		doc := p.leadComment
  2298		pos := p.expect(token.FUNC)
  2299		scope := ast.NewScope(p.topScope) // function scope
  2300	
  2301		var recv *ast.FieldList
  2302		if p.tok == token.LPAREN {
  2303			recv = p.parseReceiver(scope)
  2304		}
  2305	
  2306		ident := p.parseIdent()
  2307	
  2308		params, results := p.parseSignature(scope)
  2309	
  2310		var body *ast.BlockStmt
  2311		if p.tok == token.LBRACE {
  2312			body = p.parseBody(scope)
  2313		}
  2314		p.expectSemi()
  2315	
  2316		decl := &ast.FuncDecl{
  2317			Doc:  doc,
  2318			Recv: recv,
  2319			Name: ident,
  2320			Type: &ast.FuncType{
  2321				Func:    pos,
  2322				Params:  params,
  2323				Results: results,
  2324			},
  2325			Body: body,
  2326		}
  2327		if recv == nil {
  2328			// Go spec: The scope of an identifier denoting a constant, type,
  2329			// variable, or function (but not method) declared at top level
  2330			// (outside any function) is the package block.
  2331			//
  2332			// init() functions cannot be referred to and there may
  2333			// be more than one - don't put them in the pkgScope
  2334			if ident.Name != "init" {
  2335				p.declare(decl, nil, p.pkgScope, ast.Fun, ident)
  2336			}
  2337		}
  2338	
  2339		return decl
  2340	}
  2341	
  2342	func (p *parser) parseDecl(sync func(*parser)) ast.Decl {
  2343		if p.trace {
  2344			defer un(trace(p, "Declaration"))
  2345		}
  2346	
  2347		var f parseSpecFunction
  2348		switch p.tok {
  2349		case token.CONST, token.VAR:
  2350			f = p.parseValueSpec
  2351	
  2352		case token.TYPE:
  2353			f = p.parseTypeSpec
  2354	
  2355		case token.FUNC:
  2356			return p.parseFuncDecl()
  2357	
  2358		default:
  2359			pos := p.pos
  2360			p.errorExpected(pos, "declaration")
  2361			sync(p)
  2362			return &ast.BadDecl{From: pos, To: p.pos}
  2363		}
  2364	
  2365		return p.parseGenDecl(p.tok, f)
  2366	}
  2367	
  2368	// ----------------------------------------------------------------------------
  2369	// Source files
  2370	
  2371	func (p *parser) parseFile() *ast.File {
  2372		if p.trace {
  2373			defer un(trace(p, "File"))
  2374		}
  2375	
  2376		// Don't bother parsing the rest if we had errors scanning the first token.
  2377		// Likely not a Go source file at all.
  2378		if p.errors.Len() != 0 {
  2379			return nil
  2380		}
  2381	
  2382		// package clause
  2383		doc := p.leadComment
  2384		pos := p.expect(token.PACKAGE)
  2385		// Go spec: The package clause is not a declaration;
  2386		// the package name does not appear in any scope.
  2387		ident := p.parseIdent()
  2388		if ident.Name == "_" && p.mode&DeclarationErrors != 0 {
  2389			p.error(p.pos, "invalid package name _")
  2390		}
  2391		p.expectSemi()
  2392	
  2393		// Don't bother parsing the rest if we had errors parsing the package clause.
  2394		// Likely not a Go source file at all.
  2395		if p.errors.Len() != 0 {
  2396			return nil
  2397		}
  2398	
  2399		p.openScope()
  2400		p.pkgScope = p.topScope
  2401		var decls []ast.Decl
  2402		if p.mode&PackageClauseOnly == 0 {
  2403			// import decls
  2404			for p.tok == token.IMPORT {
  2405				decls = append(decls, p.parseGenDecl(token.IMPORT, p.parseImportSpec))
  2406			}
  2407	
  2408			if p.mode&ImportsOnly == 0 {
  2409				// rest of package body
  2410				for p.tok != token.EOF {
  2411					decls = append(decls, p.parseDecl(syncDecl))
  2412				}
  2413			}
  2414		}
  2415		p.closeScope()
  2416		assert(p.topScope == nil, "unbalanced scopes")
  2417		assert(p.labelScope == nil, "unbalanced label scopes")
  2418	
  2419		// resolve global identifiers within the same file
  2420		i := 0
  2421		for _, ident := range p.unresolved {
  2422			// i <= index for current ident
  2423			assert(ident.Obj == unresolved, "object already resolved")
  2424			ident.Obj = p.pkgScope.Lookup(ident.Name) // also removes unresolved sentinel
  2425			if ident.Obj == nil {
  2426				p.unresolved[i] = ident
  2427				i++
  2428			}
  2429		}
  2430	
  2431		return &ast.File{
  2432			Doc:        doc,
  2433			Package:    pos,
  2434			Name:       ident,
  2435			Decls:      decls,
  2436			Scope:      p.pkgScope,
  2437			Imports:    p.imports,
  2438			Unresolved: p.unresolved[0:i],
  2439			Comments:   p.comments,
  2440		}
  2441	}

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