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// 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,
}
}
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