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parser.go
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2148 lines (1844 loc) · 50.6 KB
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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.
package parser
import (
"fmt"
"go/ast"
"go/scanner"
"go/token"
)
// The mode parameter to the Parse* functions is a set of flags (or 0).
// They control the amount of source code parsed and other optional
// parser functionality.
const (
PackageClauseOnly uint = 1 << iota // parsing stops after package clause
ImportsOnly // parsing stops after import declarations
ParseComments // parse comments and add them to AST
Trace // print a trace of parsed productions
DeclarationErrors // report declaration errors
)
// The parser structure holds the parser's internal state.
type parser struct {
file *token.File
scanner.ErrorVector
scanner scanner.Scanner
// Tracing/debugging
mode uint // parsing mode
trace bool // == (mode & Trace != 0)
indent uint // 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
// Non-syntactic parser control
exprLev int // < 0: in control clause, >= 0: in 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 scope
// (maintained by open/close LabelScope)
labelScope *ast.Scope // label scope for current function
targetStack [][]*ast.Ident // stack of unresolved labels
}
// scannerMode returns the scanner mode bits given the parser's mode bits.
func scannerMode(mode uint) uint {
var m uint = scanner.InsertSemis
if mode&ParseComments != 0 {
m |= scanner.ScanComments
}
return m
}
func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode uint) {
p.file = fset.AddFile(filename, fset.Base(), len(src))
p.scanner.Init(p.file, src, p, scannerMode(mode))
p.mode = mode
p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
p.next()
// set up the pkgScope here (as opposed to in parseFile) because
// there are other parser entry points (ParseExpr, etc.)
p.openScope()
p.pkgScope = p.topScope
// for the same reason, set up a label scope
p.openLabelScope()
}
// ----------------------------------------------------------------------------
// 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 any, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
for _, ident := range idents {
assert(ident.Obj == nil, "identifier already declared or resolved")
if ident.Name != "_" {
obj := ast.NewObj(kind, ident.Name)
// remember the corresponding declaration for redeclaration
// errors and global variable resolution/typechecking phase
obj.Decl = decl
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))
}
ident.Obj = obj
}
}
}
func (p *parser) shortVarDecl(idents []*ast.Ident) {
// 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 _, ident := range idents {
assert(ident.Obj == nil, "identifier already declared or resolved")
if ident.Name != "_" {
obj := ast.NewObj(ast.Var, ident.Name)
// short var declarations cannot have redeclaration errors
// and are not global => no need to remember the respective
// declaration
alt := p.topScope.Insert(obj)
if alt == nil {
n++ // new declaration
alt = obj
}
ident.Obj = alt
}
}
if n == 0 && p.mode&DeclarationErrors != 0 {
p.error(idents[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)
func (p *parser) resolve(x ast.Expr) {
// 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
ident.Obj = unresolved
p.unresolved = append(p.unresolved, ident)
}
// ----------------------------------------------------------------------------
// Parsing support
func (p *parser) printTrace(a ...any) {
const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " +
". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
const n = uint(len(dots))
pos := p.file.Position(p.pos)
fmt.Printf("%5d:%3d: ", pos.Line, pos.Column)
i := 2 * p.indent
for ; i > n; i -= n {
fmt.Print(dots)
}
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{p.pos, 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. An empty line or non-comment
// token terminates a comment group.
func (p *parser) consumeCommentGroup() (comments *ast.CommentGroup, endline int) {
var list []*ast.Comment
endline = p.file.Line(p.pos)
for p.tok == token.COMMENT && endline+1 >= p.file.Line(p.pos) {
var comment *ast.Comment
comment, endline = p.consumeComment()
list = append(list, comment)
}
// add comment group to the comments list
comments = &ast.CommentGroup{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
line := p.file.Line(p.pos) // current line
p.next0()
if p.tok == token.COMMENT {
var comment *ast.CommentGroup
var endline int
if p.file.Line(p.pos) == line {
// 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()
if p.file.Line(p.pos) != endline {
// 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()
}
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
}
}
}
func (p *parser) error(pos token.Pos, msg string) {
p.Error(p.file.Position(pos), 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
if p.tok == token.SEMICOLON && p.lit[0] == '\n' {
msg += ", found newline"
} else {
msg += ", found '" + p.tok.String() + "'"
if p.tok.IsLiteral() {
msg += " " + p.lit
}
}
}
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
}
func (p *parser) expectSemi() {
if p.tok != token.RPAREN && p.tok != token.RBRACE {
p.expect(token.SEMICOLON)
}
}
func assert(cond bool, msg string) {
if !cond {
panic("go/parser internal error: " + msg)
}
}
// ----------------------------------------------------------------------------
// 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{pos, name, nil}
}
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.parseExpr(lhs))
for p.tok == token.COMMA {
p.next()
list = append(list, p.parseExpr(lhs))
}
return
}
func (p *parser) parseLhsList() []ast.Expr {
list := p.parseExprList(true)
switch p.tok {
case token.DEFINE:
// lhs of a short variable declaration
p.shortVarDecl(p.makeIdentList(list))
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)
}
}
return list
}
func (p *parser) parseRhsList() []ast.Expr {
return p.parseExprList(false)
}
// ----------------------------------------------------------------------------
// 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.next() // make progress
return &ast.BadExpr{pos, 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{ident, sel}
}
return ident
}
func (p *parser) parseArrayType(ellipsisOk bool) ast.Expr {
if p.trace {
defer un(trace(p, "ArrayType"))
}
lbrack := p.expect(token.LBRACK)
var len ast.Expr
if ellipsisOk && p.tok == token.ELLIPSIS {
len = &ast.Ellipsis{p.pos, nil}
p.next()
} else if p.tok != token.RBRACK {
len = p.parseRhs()
}
p.expect(token.RBRACK)
elt := p.parseType()
return &ast.ArrayType{lbrack, len, 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 {
pos := x.(ast.Expr).Pos()
p.errorExpected(pos, "identifier")
ident = &ast.Ident{pos, "_", nil}
}
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
// fields
list, typ := p.parseVarList(false)
// optional tag
var tag *ast.BasicLit
if p.tok == token.STRING {
tag = &ast.BasicLit{p.pos, p.tok, p.lit}
p.next()
}
// 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
p.resolve(typ)
if n := len(list); n > 1 || !isTypeName(deref(typ)) {
pos := typ.Pos()
p.errorExpected(pos, "anonymous field")
typ = &ast.BadExpr{pos, list[n-1].End()}
}
}
p.expectSemi() // call before accessing p.linecomment
field := &ast.Field{doc, idents, typ, tag, p.lineComment}
p.declare(field, scope, ast.Var, idents...)
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)
// TODO(gri): store struct scope in AST
return &ast.StructType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
}
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, base}
}
func (p *parser) tryVarType(isParam bool) ast.Expr {
if isParam && p.tok == token.ELLIPSIS {
pos := p.pos
p.next()
typ := p.tryIdentOrType(isParam) // don't use parseType so we can provide better error message
if typ == nil {
p.error(pos, "'...' parameter is missing type")
typ = &ast.BadExpr{pos, p.pos}
}
if p.tok != token.RPAREN {
p.error(pos, "can use '...' with last parameter type only")
}
return &ast.Ellipsis{pos, typ}
}
return p.tryIdentOrType(false)
}
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{pos, p.pos}
}
return typ
}
func (p *parser) parseVarList(isParam bool) (list []ast.Expr, typ ast.Expr) {
if p.trace {
defer un(trace(p, "VarList"))
}
// a list of identifiers looks like a list of type names
for {
// parseVarType accepts any type (including parenthesized ones)
// even though the syntax does not permit them here: we
// accept them all for more robust parsing and complain
// afterwards
list = append(list, p.parseVarType(isParam))
if p.tok != token.COMMA {
break
}
p.next()
}
// if we had a list of identifiers, it must be followed by a type
typ = p.tryVarType(isParam)
if typ != nil {
p.resolve(typ)
}
return
}
func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params []*ast.Field) {
if p.trace {
defer un(trace(p, "ParameterList"))
}
list, typ := p.parseVarList(ellipsisOk)
if typ != nil {
// IdentifierList Type
idents := p.makeIdentList(list)
field := &ast.Field{nil, idents, typ, nil, nil}
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, scope, ast.Var, idents...)
if p.tok == token.COMMA {
p.next()
}
for p.tok != token.RPAREN && p.tok != token.EOF {
idents := p.parseIdentList()
typ := p.parseVarType(ellipsisOk)
field := &ast.Field{nil, idents, typ, nil, nil}
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, scope, ast.Var, idents...)
if p.tok != token.COMMA {
break
}
p.next()
}
} else {
// Type { "," Type } (anonymous parameters)
params = make([]*ast.Field, len(list))
for i, x := range list {
p.resolve(x)
params[i] = &ast.Field{Type: x}
}
}
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{lparen, params, 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{pos, params, 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{token.NoPos, params, results}
} else {
// embedded interface
typ = x
}
p.expectSemi() // call before accessing p.linecomment
spec := &ast.Field{doc, idents, typ, nil, p.lineComment}
p.declare(spec, 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)
// TODO(gri): store interface scope in AST
return &ast.InterfaceType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
}
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{pos, key, value}
}
func (p *parser) parseChanType() *ast.ChanType {
if p.trace {
defer un(trace(p, "ChanType"))
}
pos := p.pos
dir := ast.SEND | ast.RECV
if p.tok == token.CHAN {
p.next()
if p.tok == token.ARROW {
p.next()
dir = ast.SEND
}
} else {
p.expect(token.ARROW)
p.expect(token.CHAN)
dir = ast.RECV
}
value := p.parseType()
return &ast.ChanType{pos, dir, value}
}
// If the result is an identifier, it is not resolved.
func (p *parser) tryIdentOrType(ellipsisOk bool) ast.Expr {
switch p.tok {
case token.IDENT:
return p.parseTypeName()
case token.LBRACK:
return p.parseArrayType(ellipsisOk)
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, typ, rparen}
}
// no type found
return nil
}
func (p *parser) tryType() ast.Expr {
typ := p.tryIdentOrType(false)
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.expect(token.RBRACE)
return &ast.BlockStmt{lbrace, list, 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.expect(token.RBRACE)
return &ast.BlockStmt{lbrace, list, 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{typ, 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{p.pos, p.tok, p.lit}
p.next()
return x
case token.LPAREN:
lparen := p.pos
p.next()
p.exprLev++
x := p.parseRhs()
p.exprLev--
rparen := p.expect(token.RPAREN)
return &ast.ParenExpr{lparen, x, rparen}
case token.FUNC:
return p.parseFuncTypeOrLit()
default:
if typ := p.tryIdentOrType(true); typ != nil {
// could be type for composite literal or conversion
_, isIdent := typ.(*ast.Ident)
assert(!isIdent, "type cannot be identifier")
return typ
}
}
pos := p.pos
p.errorExpected(pos, "operand")
p.next() // make progress
return &ast.BadExpr{pos, 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, sel}
}