// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package parser implements a parser for Go source files. Input may be
// provided in a variety of forms (see the various Parse* functions); the
// output is an abstract syntax tree (AST) representing the Go source. The
// parser is invoked through one of the Parse* functions.
//
// The parser accepts a larger language than is syntactically permitted by
// the Go spec, for simplicity, and for improved robustness in the presence
// of syntax errors. For instance, in method declarations, the receiver is
// treated like an ordinary parameter list and thus may contain multiple
// entries where the spec permits exactly one. Consequently, the corresponding
// field in the AST (ast.FuncDecl.Recv) field is not restricted to one entry.
package parser
import (
"fmt"
"go/ast"
"go/build/constraint"
"go/scanner"
"go/token"
"strings"
)
// The parser structure holds the parser's internal state.
type parser struct {
file *token.File
errors scanner.ErrorList
scanner scanner.Scanner
// Tracing/debugging
mode Mode // parsing mode
trace bool // == (mode&Trace != 0)
indent int // indentation used for tracing output
// Comments
comments []*ast.CommentGroup
leadComment *ast.CommentGroup // last lead comment
lineComment *ast.CommentGroup // last line comment
top bool // in top of file (before package clause)
goVersion string // minimum Go version found in //go:build comment
// Next token
pos token.Pos // token position
tok token.Token // one token look-ahead
lit string // token literal
// Error recovery
// (used to limit the number of calls to parser.advance
// w/o making scanning progress - avoids potential endless
// loops across multiple parser functions during error recovery)
syncPos token.Pos // last synchronization position
syncCnt int // number of parser.advance calls without progress
// Non-syntactic parser control
exprLev int // < 0: in control clause, >= 0: in expression
inRhs bool // if set, the parser is parsing a rhs expression
imports []*ast.ImportSpec // list of imports
// nestLev is used to track and limit the recursion depth
// during parsing.
nestLev int
}
func (p *parser) init(file *token.File, src []byte, mode Mode) {
p.file = file
eh := func(pos token.Position, msg string) { p.errors.Add(pos, msg) }
p.scanner.Init(p.file, src, eh, scanner.ScanComments)
p.top = true
p.mode = mode
p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
p.next()
}
// ----------------------------------------------------------------------------
// Parsing support
func (p *parser) printTrace(a ...any) {
const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
const n = len(dots)
pos := p.file.Position(p.pos)
fmt.Printf("%5d:%3d: ", pos.Line, pos.Column)
i := 2 * p.indent
for i > n {
fmt.Print(dots)
i -= n
}
// i <= n
fmt.Print(dots[0:i])
fmt.Println(a...)
}
func trace(p *parser, msg string) *parser {
p.printTrace(msg, "(")
p.indent++
return p
}
// Usage pattern: defer un(trace(p, "..."))
func un(p *parser) {
p.indent--
p.printTrace(")")
}
// maxNestLev is the deepest we're willing to recurse during parsing
const maxNestLev int = 1e5
func incNestLev(p *parser) *parser {
p.nestLev++
if p.nestLev > maxNestLev {
p.error(p.pos, "exceeded max nesting depth")
panic(bailout{})
}
return p
}
// decNestLev is used to track nesting depth during parsing to prevent stack exhaustion.
// It is used along with incNestLev in a similar fashion to how un and trace are used.
func decNestLev(p *parser) {
p.nestLev--
}
// Advance to the next token.
func (p *parser) next0() {
// Because of one-token look-ahead, print the previous token
// when tracing as it provides a more readable output. The
// very first token (!p.pos.IsValid()) is not initialized
// (it is token.ILLEGAL), so don't print it.
if p.trace && p.pos.IsValid() {
s := p.tok.String()
switch {
case p.tok.IsLiteral():
p.printTrace(s, p.lit)
case p.tok.IsOperator(), p.tok.IsKeyword():
p.printTrace("\"" + s + "\"")
default:
p.printTrace(s)
}
}
for {
p.pos, p.tok, p.lit = p.scanner.Scan()
if p.tok == token.COMMENT {
if p.top && strings.HasPrefix(p.lit, "//go:build") {
if x, err := constraint.Parse(p.lit); err == nil {
p.goVersion = constraint.GoVersion(x)
}
}
if p.mode&ParseComments == 0 {
continue
}
} else {
// Found a non-comment; top of file is over.
p.top = false
}
break
}
}
// Consume a comment and return it and the line on which it ends.
func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
// /*-style comments may end on a different line than where they start.
// Scan the comment for '\n' chars and adjust endline accordingly.
endline = p.file.Line(p.pos)
if p.lit[1] == '*' {
// don't use range here - no need to decode Unicode code points
for i := 0; i < len(p.lit); i++ {
if p.lit[i] == '\n' {
endline++
}
}
}
comment = &ast.Comment{Slash: p.pos, Text: p.lit}
p.next0()
return
}
// Consume a group of adjacent comments, add it to the parser's
// comments list, and return it together with the line at which
// the last comment in the group ends. A non-comment token or n
// empty lines terminate a comment group.
func (p *parser) consumeCommentGroup(n int) (comments *ast.CommentGroup, endline int) {
var list []*ast.Comment
endline = p.file.Line(p.pos)
for p.tok == token.COMMENT && p.file.Line(p.pos) <= endline+n {
var comment *ast.Comment
comment, endline = p.consumeComment()
list = append(list, comment)
}
// add comment group to the comments list
comments = &ast.CommentGroup{List: list}
p.comments = append(p.comments, comments)
return
}
// Advance to the next non-comment token. In the process, collect
// any comment groups encountered, and remember the last lead and
// line comments.
//
// A lead comment is a comment group that starts and ends in a
// line without any other tokens and that is followed by a non-comment
// token on the line immediately after the comment group.
//
// A line comment is a comment group that follows a non-comment
// token on the same line, and that has no tokens after it on the line
// where it ends.
//
// Lead and line comments may be considered documentation that is
// stored in the AST.
func (p *parser) next() {
p.leadComment = nil
p.lineComment = nil
prev := p.pos
p.next0()
if p.tok == token.COMMENT {
var comment *ast.CommentGroup
var endline int
if p.file.Line(p.pos) == p.file.Line(prev) {
// The comment is on same line as the previous token; it
// cannot be a lead comment but may be a line comment.
comment, endline = p.consumeCommentGroup(0)
if p.file.Line(p.pos) != endline || p.tok == token.SEMICOLON || p.tok == token.EOF {
// The next token is on a different line, thus
// the last comment group is a line comment.
p.lineComment = comment
}
}
// consume successor comments, if any
endline = -1
for p.tok == token.COMMENT {
comment, endline = p.consumeCommentGroup(1)
}
if endline+1 == p.file.Line(p.pos) {
// The next token is following on the line immediately after the
// comment group, thus the last comment group is a lead comment.
p.leadComment = comment
}
}
}
// A bailout panic is raised to indicate early termination. pos and msg are
// only populated when bailing out of object resolution.
type bailout struct {
pos token.Pos
msg string
}
func (p *parser) error(pos token.Pos, msg string) {
if p.trace {
defer un(trace(p, "error: "+msg))
}
epos := p.file.Position(pos)
// If AllErrors is not set, discard errors reported on the same line
// as the last recorded error and stop parsing if there are more than
// 10 errors.
if p.mode&AllErrors == 0 {
n := len(p.errors)
if n > 0 && p.errors[n-1].Pos.Line == epos.Line {
return // discard - likely a spurious error
}
if n > 10 {
panic(bailout{})
}
}
p.errors.Add(epos, msg)
}
func (p *parser) errorExpected(pos token.Pos, msg string) {
msg = "expected " + msg
if pos == p.pos {
// the error happened at the current position;
// make the error message more specific
switch {
case p.tok == token.SEMICOLON && p.lit == "\n":
msg += ", found newline"
case p.tok.IsLiteral():
// print 123 rather than 'INT', etc.
msg += ", found " + p.lit
default:
msg += ", found '" + p.tok.String() + "'"
}
}
p.error(pos, msg)
}
func (p *parser) expect(tok token.Token) token.Pos {
pos := p.pos
if p.tok != tok {
p.errorExpected(pos, "'"+tok.String()+"'")
}
p.next() // make progress
return pos
}
// expect2 is like expect, but it returns an invalid position
// if the expected token is not found.
func (p *parser) expect2(tok token.Token) (pos token.Pos) {
if p.tok == tok {
pos = p.pos
} else {
p.errorExpected(p.pos, "'"+tok.String()+"'")
}
p.next() // make progress
return
}
// expectClosing is like expect but provides a better error message
// for the common case of a missing comma before a newline.
func (p *parser) expectClosing(tok token.Token, context string) token.Pos {
if p.tok != tok && p.tok == token.SEMICOLON && p.lit == "\n" {
p.error(p.pos, "missing ',' before newline in "+context)
p.next()
}
return p.expect(tok)
}
// expectSemi consumes a semicolon and returns the applicable line comment.
func (p *parser) expectSemi() (comment *ast.CommentGroup) {
// semicolon is optional before a closing ')' or '}'
if p.tok != token.RPAREN && p.tok != token.RBRACE {
switch p.tok {
case token.COMMA:
// permit a ',' instead of a ';' but complain
p.errorExpected(p.pos, "';'")
fallthrough
case token.SEMICOLON:
if p.lit == ";" {
// explicit semicolon
p.next()
comment = p.lineComment // use following comments
} else {
// artificial semicolon
comment = p.lineComment // use preceding comments
p.next()
}
return comment
default:
p.errorExpected(p.pos, "';'")
p.advance(stmtStart)
}
}
return nil
}
func (p *parser) atComma(context string, follow token.Token) bool {
if p.tok == token.COMMA {
return true
}
if p.tok != follow {
msg := "missing ','"
if p.tok == token.SEMICOLON && p.lit == "\n" {
msg += " before newline"
}
p.error(p.pos, msg+" in "+context)
return true // "insert" comma and continue
}
return false
}
func assert(cond bool, msg string) {
if !cond {
panic("go/parser internal error: " + msg)
}
}
// advance consumes tokens until the current token p.tok
// is in the 'to' set, or token.EOF. For error recovery.
func (p *parser) advance(to map[token.Token]bool) {
for ; p.tok != token.EOF; p.next() {
if to[p.tok] {
// Return only if parser made some progress since last
// sync or if it has not reached 10 advance calls without
// progress. Otherwise consume at least one token to
// avoid an endless parser loop (it is possible that
// both parseOperand and parseStmt call advance and
// correctly do not advance, thus the need for the
// invocation limit p.syncCnt).
if p.pos == p.syncPos && p.syncCnt < 10 {
p.syncCnt++
return
}
if p.pos > p.syncPos {
p.syncPos = p.pos
p.syncCnt = 0
return
}
// Reaching here indicates a parser bug, likely an
// incorrect token list in this function, but it only
// leads to skipping of possibly correct code if a
// previous error is present, and thus is preferred
// over a non-terminating parse.
}
}
}
var stmtStart = map[token.Token]bool{
token.BREAK: true,
token.CONST: true,
token.CONTINUE: true,
token.DEFER: true,
token.FALLTHROUGH: true,
token.FOR: true,
token.GO: true,
token.GOTO: true,
token.IF: true,
token.RETURN: true,
token.SELECT: true,
token.SWITCH: true,
token.TYPE: true,
token.VAR: true,
}
var declStart = map[token.Token]bool{
token.IMPORT: true,
token.CONST: true,
token.TYPE: true,
token.VAR: true,
}
var exprEnd = map[token.Token]bool{
token.COMMA: true,
token.COLON: true,
token.SEMICOLON: true,
token.RPAREN: true,
token.RBRACK: true,
token.RBRACE: true,
}
// safePos returns a valid file position for a given position: If pos
// is valid to begin with, safePos returns pos. If pos is out-of-range,
// safePos returns the EOF position.
//
// This is hack to work around "artificial" end positions in the AST which
// are computed by adding 1 to (presumably valid) token positions. If the
// token positions are invalid due to parse errors, the resulting end position
// may be past the file's EOF position, which would lead to panics if used
// later on.
func (p *parser) safePos(pos token.Pos) (res token.Pos) {
defer func() {
if recover() != nil {
res = token.Pos(p.file.Base() + p.file.Size()) // EOF position
}
}()
_ = p.file.Offset(pos) // trigger a panic if position is out-of-range
return pos
}
// ----------------------------------------------------------------------------
// Identifiers
func (p *parser) parseIdent() *ast.Ident {
pos := p.pos
name := "_"
if p.tok == token.IDENT {
name = p.lit
p.next()
} else {
p.expect(token.IDENT) // use expect() error handling
}
return &ast.Ident{NamePos: pos, Name: name}
}
func (p *parser) parseIdentList() (list []*ast.Ident) {
if p.trace {
defer un(trace(p, "IdentList"))
}
list = append(list, p.parseIdent())
for p.tok == token.COMMA {
p.next()
list = append(list, p.parseIdent())
}
return
}
// ----------------------------------------------------------------------------
// Common productions
// If lhs is set, result list elements which are identifiers are not resolved.
func (p *parser) parseExprList() (list []ast.Expr) {
if p.trace {
defer un(trace(p, "ExpressionList"))
}
list = append(list, p.parseExpr())
for p.tok == token.COMMA {
p.next()
list = append(list, p.parseExpr())
}
return
}
func (p *parser) parseList(inRhs bool) []ast.Expr {
old := p.inRhs
p.inRhs = inRhs
list := p.parseExprList()
p.inRhs = old
return list
}
// ----------------------------------------------------------------------------
// Types
func (p *parser) parseType() ast.Expr {
if p.trace {
defer un(trace(p, "Type"))
}
typ := p.tryIdentOrType()
if typ == nil {
pos := p.pos
p.errorExpected(pos, "type")
p.advance(exprEnd)
return &ast.BadExpr{From: pos, To: p.pos}
}
return typ
}
func (p *parser) parseQualifiedIdent(ident *ast.Ident) ast.Expr {
if p.trace {
defer un(trace(p, "QualifiedIdent"))
}
typ := p.parseTypeName(ident)
if p.tok == token.LBRACK {
typ = p.parseTypeInstance(typ)
}
return typ
}
// If the result is an identifier, it is not resolved.
func (p *parser) parseTypeName(ident *ast.Ident) ast.Expr {
if p.trace {
defer un(trace(p, "TypeName"))
}
if ident == nil {
ident = p.parseIdent()
}
if p.tok == token.PERIOD {
// ident is a package name
p.next()
sel := p.parseIdent()
return &ast.SelectorExpr{X: ident, Sel: sel}
}
return ident
}
// "[" has already been consumed, and lbrack is its position.
// If len != nil it is the already consumed array length.
func (p *parser) parseArrayType(lbrack token.Pos, len ast.Expr) *ast.ArrayType {
if p.trace {
defer un(trace(p, "ArrayType"))
}
if len == nil {
p.exprLev++
// always permit ellipsis for more fault-tolerant parsing
if p.tok == token.ELLIPSIS {
len = &ast.Ellipsis{Ellipsis: p.pos}
p.next()
} else if p.tok != token.RBRACK {
len = p.parseRhs()
}
p.exprLev--
}
if p.tok == token.COMMA {
// Trailing commas are accepted in type parameter
// lists but not in array type declarations.
// Accept for better error handling but complain.
p.error(p.pos, "unexpected comma; expecting ]")
p.next()
}
p.expect(token.RBRACK)
elt := p.parseType()
return &ast.ArrayType{Lbrack: lbrack, Len: len, Elt: elt}
}
func (p *parser) parseArrayFieldOrTypeInstance(x *ast.Ident) (*ast.Ident, ast.Expr) {
if p.trace {
defer un(trace(p, "ArrayFieldOrTypeInstance"))
}
lbrack := p.expect(token.LBRACK)
trailingComma := token.NoPos // if valid, the position of a trailing comma preceding the ']'
var args []ast.Expr
if p.tok != token.RBRACK {
p.exprLev++
args = append(args, p.parseRhs())
for p.tok == token.COMMA {
comma := p.pos
p.next()
if p.tok == token.RBRACK {
trailingComma = comma
break
}
args = append(args, p.parseRhs())
}
p.exprLev--
}
rbrack := p.expect(token.RBRACK)
if len(args) == 0 {
// x []E
elt := p.parseType()
return x, &ast.ArrayType{Lbrack: lbrack, Elt: elt}
}
// x [P]E or x[P]
if len(args) == 1 {
elt := p.tryIdentOrType()
if elt != nil {
// x [P]E
if trailingComma.IsValid() {
// Trailing commas are invalid in array type fields.
p.error(trailingComma, "unexpected comma; expecting ]")
}
return x, &ast.ArrayType{Lbrack: lbrack, Len: args[0], Elt: elt}
}
}
// x[P], x[P1, P2], ...
return nil, packIndexExpr(x, lbrack, args, rbrack)
}
func (p *parser) parseFieldDecl() *ast.Field {
if p.trace {
defer un(trace(p, "FieldDecl"))
}
doc := p.leadComment
var names []*ast.Ident
var typ ast.Expr
switch p.tok {
case token.IDENT:
name := p.parseIdent()
if p.tok == token.PERIOD || p.tok == token.STRING || p.tok == token.SEMICOLON || p.tok == token.RBRACE {
// embedded type
typ = name
if p.tok == token.PERIOD {
typ = p.parseQualifiedIdent(name)
}
} else {
// name1, name2, ... T
names = []*ast.Ident{name}
for p.tok == token.COMMA {
p.next()
names = append(names, p.parseIdent())
}
// Careful dance: We don't know if we have an embedded instantiated
// type T[P1, P2, ...] or a field T of array type []E or [P]E.
if len(names) == 1 && p.tok == token.LBRACK {
name, typ = p.parseArrayFieldOrTypeInstance(name)
if name == nil {
names = nil
}
} else {
// T P
typ = p.parseType()
}
}
case token.MUL:
star := p.pos
p.next()
if p.tok == token.LPAREN {
// *(T)
p.error(p.pos, "cannot parenthesize embedded type")
p.next()
typ = p.parseQualifiedIdent(nil)
// expect closing ')' but no need to complain if missing
if p.tok == token.RPAREN {
p.next()
}
} else {
// *T
typ = p.parseQualifiedIdent(nil)
}
typ = &ast.StarExpr{Star: star, X: typ}
case token.LPAREN:
p.error(p.pos, "cannot parenthesize embedded type")
p.next()
if p.tok == token.MUL {
// (*T)
star := p.pos
p.next()
typ = &ast.StarExpr{Star: star, X: p.parseQualifiedIdent(nil)}
} else {
// (T)
typ = p.parseQualifiedIdent(nil)
}
// expect closing ')' but no need to complain if missing
if p.tok == token.RPAREN {
p.next()
}
default:
pos := p.pos
p.errorExpected(pos, "field name or embedded type")
p.advance(exprEnd)
typ = &ast.BadExpr{From: pos, To: p.pos}
}
var tag *ast.BasicLit
if p.tok == token.STRING {
tag = &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
p.next()
}
comment := p.expectSemi()
field := &ast.Field{Doc: doc, Names: names, Type: typ, Tag: tag, Comment: comment}
return field
}
func (p *parser) parseStructType() *ast.StructType {
if p.trace {
defer un(trace(p, "StructType"))
}
pos := p.expect(token.STRUCT)
lbrace := p.expect(token.LBRACE)
var list []*ast.Field
for p.tok == token.IDENT || p.tok == token.MUL || p.tok == token.LPAREN {
// a field declaration cannot start with a '(' but we accept
// it here for more robust parsing and better error messages
// (parseFieldDecl will check and complain if necessary)
list = append(list, p.parseFieldDecl())
}
rbrace := p.expect(token.RBRACE)
return &ast.StructType{
Struct: pos,
Fields: &ast.FieldList{
Opening: lbrace,
List: list,
Closing: rbrace,
},
}
}
func (p *parser) parsePointerType() *ast.StarExpr {
if p.trace {
defer un(trace(p, "PointerType"))
}
star := p.expect(token.MUL)
base := p.parseType()
return &ast.StarExpr{Star: star, X: base}
}
func (p *parser) parseDotsType() *ast.Ellipsis {
if p.trace {
defer un(trace(p, "DotsType"))
}
pos := p.expect(token.ELLIPSIS)
elt := p.parseType()
return &ast.Ellipsis{Ellipsis: pos, Elt: elt}
}
type field struct {
name *ast.Ident
typ ast.Expr
}
func (p *parser) parseParamDecl(name *ast.Ident, typeSetsOK bool) (f field) {
// TODO(rFindley) refactor to be more similar to paramDeclOrNil in the syntax
// package
if p.trace {
defer un(trace(p, "ParamDecl"))
}
ptok := p.tok
if name != nil {
p.tok = token.IDENT // force token.IDENT case in switch below
} else if typeSetsOK && p.tok == token.TILDE {
// "~" ...
return field{nil, p.embeddedElem(nil)}
}
switch p.tok {
case token.IDENT:
// name
if name != nil {
f.name = name
p.tok = ptok
} else {
f.name = p.parseIdent()
}
switch p.tok {
case token.IDENT, token.MUL, token.ARROW, token.FUNC, token.CHAN, token.MAP, token.STRUCT, token.INTERFACE, token.LPAREN:
// name type
f.typ = p.parseType()
case token.LBRACK:
// name "[" type1, ..., typeN "]" or name "[" n "]" type
f.name, f.typ = p.parseArrayFieldOrTypeInstance(f.name)
case token.ELLIPSIS:
// name "..." type
f.typ = p.parseDotsType()
return // don't allow ...type "|" ...
case token.PERIOD:
// name "." ...
f.typ = p.parseQualifiedIdent(f.name)
f.name = nil
case token.TILDE:
if typeSetsOK {
f.typ = p.embeddedElem(nil)
return
}
case token.OR:
if typeSetsOK {
// name "|" typeset
f.typ = p.embeddedElem(f.name)
f.name = nil
return
}
}
case token.MUL, token.ARROW, token.FUNC, token.LBRACK, token.CHAN, token.MAP, token.STRUCT, token.INTERFACE, token.LPAREN:
// type
f.typ = p.parseType()
case token.ELLIPSIS:
// "..." type
// (always accepted)
f.typ = p.parseDotsType()
return // don't allow ...type "|" ...
default:
// TODO(rfindley): this is incorrect in the case of type parameter lists
// (should be "']'" in that case)
p.errorExpected(p.pos, "')'")
p.advance(exprEnd)
}
// [name] type "|"
if typeSetsOK && p.tok == token.OR && f.typ != nil {
f.typ = p.embeddedElem(f.typ)
}
return
}
func (p *parser) parseParameterList(name0 *ast.Ident, typ0 ast.Expr, closing token.Token) (params []*ast.Field) {
if p.trace {
defer un(trace(p, "ParameterList"))
}
// Type parameters are the only parameter list closed by ']'.
tparams := closing == token.RBRACK
pos0 := p.pos
if name0 != nil {
pos0 = name0.Pos()
} else if typ0 != nil {
pos0 = typ0.Pos()
}
// Note: The code below matches the corresponding code in the syntax
// parser closely. Changes must be reflected in either parser.
// For the code to match, we use the local []field list that
// corresponds to []syntax.Field. At the end, the list must be
// converted into an []*ast.Field.
var list []field
var named int // number of parameters that have an explicit name and type
var typed int // number of parameters that have an explicit type
for name0 != nil || p.tok != closing && p.tok != token.EOF {
var par field
if typ0 != nil {
if tparams {
typ0 = p.embeddedElem(typ0)
}
par = field{name0, typ0}
} else {
par = p.parseParamDecl(name0, tparams)
}
name0 = nil // 1st name was consumed if present
typ0 = nil // 1st typ was consumed if present
if par.name != nil || par.typ != nil {
list = append(list, par)
if par.name != nil && par.typ != nil {
named++
}
if par.typ != nil {
typed++
}
}
if !p.atComma("parameter list", closing) {
break
}
p.next()
}
if len(list) == 0 {
return // not uncommon
}
// distribute parameter types (len(list) > 0)
if named == 0 {
// all unnamed => found names are type names
for i := 0; i < len(list); i++ {
par := &list[i]
if typ := par.name; typ != nil {
par.typ = typ
par.name = nil
}
}
if tparams {
// This is the same error handling as below, adjusted for type parameters only.
// See comment below for details. (go.dev/issue/64534)
var errPos token.Pos
var msg string
if named == typed /* same as typed == 0 */ {
errPos = p.pos // position error at closing ]
msg = "missing type constraint"
} else {
errPos = pos0 // position at opening [ or first name
msg = "missing type parameter name"
if len(list) == 1 {
msg += " or invalid array length"
}
}
p.error(errPos, msg)
}
} else if named != len(list) {
// some named or we're in a type parameter list => all must be named
var errPos token.Pos // left-most error position (or invalid)
var typ ast.Expr // current type (from right to left)
for i := len(list) - 1; i >= 0; i-- {
if par := &list[i]; par.typ != nil {
typ = par.typ
if par.name == nil {
errPos = typ.Pos()
n := ast.NewIdent("_")
n.NamePos = errPos // correct position
par.name = n
}
} else if typ != nil {
par.typ = typ
} else {
// par.typ == nil && typ == nil => we only have a par.name
errPos = par.name.Pos()
par.typ = &ast.BadExpr{From: errPos, To: p.pos}
}
}
if errPos.IsValid() {
// Not all parameters are named because named != len(list).
// If named == typed, there must be parameters that have no types.
// They must be at the end of the parameter list, otherwise types
// would have been filled in by the right-to-left sweep above and
// there would be no error.
// If tparams is set, the parameter list is a type parameter list.
var msg string
if named == typed {
errPos = p.pos // position error at closing token ) or ]
if tparams {
msg = "missing type constraint"
} else {
msg = "missing parameter type"
}
} else {
if tparams {
msg = "missing type parameter name"
// go.dev/issue/60812
if len(list) == 1 {
msg += " or invalid array length"
}
} else {
msg = "missing parameter name"
}
}
p.error(errPos, msg)
}
}
// Convert list to []*ast.Field.
// If list contains types only, each type gets its own ast.Field.
if named == 0 {
// parameter list consists of types only
for _, par := range list {
assert(par.typ != nil, "nil type in unnamed parameter list")
params = append(params, &ast.Field{Type: par.typ})
}
return
}
// If the parameter list consists of named parameters with types,
// collect all names with the same types into a single ast.Field.
var names []*ast.Ident
var typ ast.Expr
addParams := func() {
assert(typ != nil, "nil type in named parameter list")
field := &ast.Field{Names: names, Type: typ}
params = append(params, field)
names = nil
}
for _, par := range list {
if par.typ != typ {
if len(names) > 0 {
addParams()
}
typ = par.typ
}
names = append(names, par.name)
}
if len(names) > 0 {
addParams()
}
return
}
func (p *parser) parseParameters(acceptTParams bool) (tparams, params *ast.FieldList) {
if p.trace {
defer un(trace(p, "Parameters"))
}
if acceptTParams && p.tok == token.LBRACK {
opening := p.pos
p.next()
// [T any](params) syntax
list := p.parseParameterList(nil, nil, token.RBRACK)
rbrack := p.expect(token.RBRACK)
tparams = &ast.FieldList{Opening: opening, List: list, Closing: rbrack}
// Type parameter lists must not be empty.
if tparams.NumFields() == 0 {
p.error(tparams.Closing, "empty type parameter list")
tparams = nil // avoid follow-on errors
}
}
opening := p.expect(token.LPAREN)
var fields []*ast.Field
if p.tok != token.RPAREN {
fields = p.parseParameterList(nil, nil, token.RPAREN)
}
rparen := p.expect(token.RPAREN)
params = &ast.FieldList{Opening: opening, List: fields, Closing: rparen}
return
}
func (p *parser) parseResult() *ast.FieldList {
if p.trace {
defer un(trace(p, "Result"))
}
if p.tok == token.LPAREN {
_, results := p.parseParameters(false)
return results
}
typ := p.tryIdentOrType()
if typ != nil {
list := make([]*ast.Field, 1)
list[0] = &ast.Field{Type: typ}
return &ast.FieldList{List: list}
}
return nil
}
func (p *parser) parseFuncType() *ast.FuncType {
if p.trace {
defer un(trace(p, "FuncType"))
}
pos := p.expect(token.FUNC)
tparams, params := p.parseParameters(true)
if tparams != nil {
p.error(tparams.Pos(), "function type must have no type parameters")
}
results := p.parseResult()
return &ast.FuncType{Func: pos, Params: params, Results: results}
}
func (p *parser) parseMethodSpec() *ast.Field {
if p.trace {
defer un(trace(p, "MethodSpec"))
}
doc := p.leadComment
var idents []*ast.Ident
var typ ast.Expr
x := p.parseTypeName(nil)
if ident, _ := x.(*ast.Ident); ident != nil {
switch {
case p.tok == token.LBRACK:
// generic method or embedded instantiated type
lbrack := p.pos
p.next()
p.exprLev++
x := p.parseExpr()
p.exprLev--
if name0, _ := x.(*ast.Ident); name0 != nil && p.tok != token.COMMA && p.tok != token.RBRACK {
// generic method m[T any]
//
// Interface methods do not have type parameters. We parse them for a
// better error message and improved error recovery.
_ = p.parseParameterList(name0, nil, token.RBRACK)
_ = p.expect(token.RBRACK)
p.error(lbrack, "interface method must have no type parameters")
// TODO(rfindley) refactor to share code with parseFuncType.
_, params := p.parseParameters(false)
results := p.parseResult()
idents = []*ast.Ident{ident}
typ = &ast.FuncType{
Func: token.NoPos,
Params: params,
Results: results,
}
} else {
// embedded instantiated type
// TODO(rfindley) should resolve all identifiers in x.
list := []ast.Expr{x}
if p.atComma("type argument list", token.RBRACK) {
p.exprLev++
p.next()
for p.tok != token.RBRACK && p.tok != token.EOF {
list = append(list, p.parseType())
if !p.atComma("type argument list", token.RBRACK) {
break
}
p.next()
}
p.exprLev--
}
rbrack := p.expectClosing(token.RBRACK, "type argument list")
typ = packIndexExpr(ident, lbrack, list, rbrack)
}
case p.tok == token.LPAREN:
// ordinary method
// TODO(rfindley) refactor to share code with parseFuncType.
_, params := p.parseParameters(false)
results := p.parseResult()
idents = []*ast.Ident{ident}
typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
default:
// embedded type
typ = x
}
} else {
// embedded, possibly instantiated type
typ = x
if p.tok == token.LBRACK {
// embedded instantiated interface
typ = p.parseTypeInstance(typ)
}
}
// Comment is added at the callsite: the field below may joined with
// additional type specs using '|'.
// TODO(rfindley) this should be refactored.
// TODO(rfindley) add more tests for comment handling.
return &ast.Field{Doc: doc, Names: idents, Type: typ}
}
func (p *parser) embeddedElem(x ast.Expr) ast.Expr {
if p.trace {
defer un(trace(p, "EmbeddedElem"))
}
if x == nil {
x = p.embeddedTerm()
}
for p.tok == token.OR {
t := new(ast.BinaryExpr)
t.OpPos = p.pos
t.Op = token.OR
p.next()
t.X = x
t.Y = p.embeddedTerm()
x = t
}
return x
}
func (p *parser) embeddedTerm() ast.Expr {
if p.trace {
defer un(trace(p, "EmbeddedTerm"))
}
if p.tok == token.TILDE {
t := new(ast.UnaryExpr)
t.OpPos = p.pos
t.Op = token.TILDE
p.next()
t.X = p.parseType()
return t
}
t := p.tryIdentOrType()
if t == nil {
pos := p.pos
p.errorExpected(pos, "~ term or type")
p.advance(exprEnd)
return &ast.BadExpr{From: pos, To: p.pos}
}
return t
}
func (p *parser) parseInterfaceType() *ast.InterfaceType {
if p.trace {
defer un(trace(p, "InterfaceType"))
}
pos := p.expect(token.INTERFACE)
lbrace := p.expect(token.LBRACE)
var list []*ast.Field
parseElements:
for {
switch {
case p.tok == token.IDENT:
f := p.parseMethodSpec()
if f.Names == nil {
f.Type = p.embeddedElem(f.Type)
}
f.Comment = p.expectSemi()
list = append(list, f)
case p.tok == token.TILDE:
typ := p.embeddedElem(nil)
comment := p.expectSemi()
list = append(list, &ast.Field{Type: typ, Comment: comment})
default:
if t := p.tryIdentOrType(); t != nil {
typ := p.embeddedElem(t)
comment := p.expectSemi()
list = append(list, &ast.Field{Type: typ, Comment: comment})
} else {
break parseElements
}
}
}
// TODO(rfindley): the error produced here could be improved, since we could
// accept an identifier, 'type', or a '}' at this point.
rbrace := p.expect(token.RBRACE)
return &ast.InterfaceType{
Interface: pos,
Methods: &ast.FieldList{
Opening: lbrace,
List: list,
Closing: rbrace,
},
}
}
func (p *parser) parseMapType() *ast.MapType {
if p.trace {
defer un(trace(p, "MapType"))
}
pos := p.expect(token.MAP)
p.expect(token.LBRACK)
key := p.parseType()
p.expect(token.RBRACK)
value := p.parseType()
return &ast.MapType{Map: pos, Key: key, Value: value}
}
func (p *parser) parseChanType() *ast.ChanType {
if p.trace {
defer un(trace(p, "ChanType"))
}
pos := p.pos
dir := ast.SEND | ast.RECV
var arrow token.Pos
if p.tok == token.CHAN {
p.next()
if p.tok == token.ARROW {
arrow = p.pos
p.next()
dir = ast.SEND
}
} else {
arrow = p.expect(token.ARROW)
p.expect(token.CHAN)
dir = ast.RECV
}
value := p.parseType()
return &ast.ChanType{Begin: pos, Arrow: arrow, Dir: dir, Value: value}
}
func (p *parser) parseTypeInstance(typ ast.Expr) ast.Expr {
if p.trace {
defer un(trace(p, "TypeInstance"))
}
opening := p.expect(token.LBRACK)
p.exprLev++
var list []ast.Expr
for p.tok != token.RBRACK && p.tok != token.EOF {
list = append(list, p.parseType())
if !p.atComma("type argument list", token.RBRACK) {
break
}
p.next()
}
p.exprLev--
closing := p.expectClosing(token.RBRACK, "type argument list")
if len(list) == 0 {
p.errorExpected(closing, "type argument list")
return &ast.IndexExpr{
X: typ,
Lbrack: opening,
Index: &ast.BadExpr{From: opening + 1, To: closing},
Rbrack: closing,
}
}
return packIndexExpr(typ, opening, list, closing)
}
func (p *parser) tryIdentOrType() ast.Expr {
defer decNestLev(incNestLev(p))
switch p.tok {
case token.IDENT:
typ := p.parseTypeName(nil)
if p.tok == token.LBRACK {
typ = p.parseTypeInstance(typ)
}
return typ
case token.LBRACK:
lbrack := p.expect(token.LBRACK)
return p.parseArrayType(lbrack, nil)
case token.STRUCT:
return p.parseStructType()
case token.MUL:
return p.parsePointerType()
case token.FUNC:
return p.parseFuncType()
case token.INTERFACE:
return p.parseInterfaceType()
case token.MAP:
return p.parseMapType()
case token.CHAN, token.ARROW:
return p.parseChanType()
case token.LPAREN:
lparen := p.pos
p.next()
typ := p.parseType()
rparen := p.expect(token.RPAREN)
return &ast.ParenExpr{Lparen: lparen, X: typ, Rparen: rparen}
}
// no type found
return nil
}
// ----------------------------------------------------------------------------
// Blocks
func (p *parser) parseStmtList() (list []ast.Stmt) {
if p.trace {
defer un(trace(p, "StatementList"))
}
for p.tok != token.CASE && p.tok != token.DEFAULT && p.tok != token.RBRACE && p.tok != token.EOF {
list = append(list, p.parseStmt())
}
return
}
func (p *parser) parseBody() *ast.BlockStmt {
if p.trace {
defer un(trace(p, "Body"))
}
lbrace := p.expect(token.LBRACE)
list := p.parseStmtList()
rbrace := p.expect2(token.RBRACE)
return &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
}
func (p *parser) parseBlockStmt() *ast.BlockStmt {
if p.trace {
defer un(trace(p, "BlockStmt"))
}
lbrace := p.expect(token.LBRACE)
list := p.parseStmtList()
rbrace := p.expect2(token.RBRACE)
return &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
}
// ----------------------------------------------------------------------------
// Expressions
func (p *parser) parseFuncTypeOrLit() ast.Expr {
if p.trace {
defer un(trace(p, "FuncTypeOrLit"))
}
typ := p.parseFuncType()
if p.tok != token.LBRACE {
// function type only
return typ
}
p.exprLev++
body := p.parseBody()
p.exprLev--
return &ast.FuncLit{Type: typ, Body: body}
}
// parseOperand may return an expression or a raw type (incl. array
// types of the form [...]T). Callers must verify the result.
func (p *parser) parseOperand() ast.Expr {
if p.trace {
defer un(trace(p, "Operand"))
}
switch p.tok {
case token.IDENT:
x := p.parseIdent()
return x
case token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING:
x := &ast.BasicLit{ValuePos: p.pos, Kind: p.tok, Value: p.lit}
p.next()
return x
case token.LPAREN:
lparen := p.pos
p.next()
p.exprLev++
x := p.parseRhs() // types may be parenthesized: (some type)
p.exprLev--
rparen := p.expect(token.RPAREN)
return &ast.ParenExpr{Lparen: lparen, X: x, Rparen: rparen}
case token.FUNC:
return p.parseFuncTypeOrLit()
}
if typ := p.tryIdentOrType(); typ != nil { // do not consume trailing type parameters
// could be type for composite literal or conversion
_, isIdent := typ.(*ast.Ident)
assert(!isIdent, "type cannot be identifier")
return typ
}
// we have an error
pos := p.pos
p.errorExpected(pos, "operand")
p.advance(stmtStart)
return &ast.BadExpr{From: pos, To: p.pos}
}
func (p *parser) parseSelector(x ast.Expr) ast.Expr {
if p.trace {
defer un(trace(p, "Selector"))
}
sel := p.parseIdent()
return &ast.SelectorExpr{X: x, Sel: sel}
}
func (p *parser) parseTypeAssertion(x ast.Expr) ast.Expr {
if p.trace {
defer un(trace(p, "TypeAssertion"))
}
lparen := p.expect(token.LPAREN)
var typ ast.Expr
if p.tok == token.TYPE {
// type switch: typ == nil
p.next()
} else {
typ = p.parseType()
}
rparen := p.expect(token.RPAREN)
return &ast.TypeAssertExpr{X: x, Type: typ, Lparen: lparen, Rparen: rparen}
}
func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
if p.trace {
defer un(trace(p, "parseIndexOrSliceOrInstance"))
}
lbrack := p.expect(token.LBRACK)
if p.tok == token.RBRACK {
// empty index, slice or index expressions are not permitted;
// accept them for parsing tolerance, but complain
p.errorExpected(p.pos, "operand")
rbrack := p.pos
p.next()
return &ast.IndexExpr{
X: x,
Lbrack: lbrack,
Index: &ast.BadExpr{From: rbrack, To: rbrack},
Rbrack: rbrack,
}
}
p.exprLev++
const N = 3 // change the 3 to 2 to disable 3-index slices
var args []ast.Expr
var index [N]ast.Expr
var colons [N - 1]token.Pos
if p.tok != token.COLON {
// We can't know if we have an index expression or a type instantiation;
// so even if we see a (named) type we are not going to be in type context.
index[0] = p.parseRhs()
}
ncolons := 0
switch p.tok {
case token.COLON:
// slice expression
for p.tok == token.COLON && ncolons < len(colons) {
colons[ncolons] = p.pos
ncolons++
p.next()
if p.tok != token.COLON && p.tok != token.RBRACK && p.tok != token.EOF {
index[ncolons] = p.parseRhs()
}
}
case token.COMMA:
// instance expression
args = append(args, index[0])
for p.tok == token.COMMA {
p.next()
if p.tok != token.RBRACK && p.tok != token.EOF {
args = append(args, p.parseType())
}
}
}
p.exprLev--
rbrack := p.expect(token.RBRACK)
if ncolons > 0 {
// slice expression
slice3 := false
if ncolons == 2 {
slice3 = true
// Check presence of middle and final index here rather than during type-checking
// to prevent erroneous programs from passing through gofmt (was go.dev/issue/7305).
if index[1] == nil {
p.error(colons[0], "middle index required in 3-index slice")
index[1] = &ast.BadExpr{From: colons[0] + 1, To: colons[1]}
}
if index[2] == nil {
p.error(colons[1], "final index required in 3-index slice")
index[2] = &ast.BadExpr{From: colons[1] + 1, To: rbrack}
}
}
return &ast.SliceExpr{X: x, Lbrack: lbrack, Low: index[0], High: index[1], Max: index[2], Slice3: slice3, Rbrack: rbrack}
}
if len(args) == 0 {
// index expression
return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: rbrack}
}
// instance expression
return packIndexExpr(x, lbrack, args, rbrack)
}
func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
if p.trace {
defer un(trace(p, "CallOrConversion"))
}
lparen := p.expect(token.LPAREN)
p.exprLev++
var list []ast.Expr
var ellipsis token.Pos
for p.tok != token.RPAREN && p.tok != token.EOF && !ellipsis.IsValid() {
list = append(list, p.parseRhs()) // builtins may expect a type: make(some type, ...)
if p.tok == token.ELLIPSIS {
ellipsis = p.pos
p.next()
}
if !p.atComma("argument list", token.RPAREN) {
break
}
p.next()
}
p.exprLev--
rparen := p.expectClosing(token.RPAREN, "argument list")
return &ast.CallExpr{Fun: fun, Lparen: lparen, Args: list, Ellipsis: ellipsis, Rparen: rparen}
}
func (p *parser) parseValue() ast.Expr {
if p.trace {
defer un(trace(p, "Element"))
}
if p.tok == token.LBRACE {
return p.parseLiteralValue(nil)
}
x := p.parseExpr()
return x
}
func (p *parser) parseElement() ast.Expr {
if p.trace {
defer un(trace(p, "Element"))
}
x := p.parseValue()
if p.tok == token.COLON {
colon := p.pos
p.next()
x = &ast.KeyValueExpr{Key: x, Colon: colon, Value: p.parseValue()}
}
return x
}
func (p *parser) parseElementList() (list []ast.Expr) {
if p.trace {
defer un(trace(p, "ElementList"))
}
for p.tok != token.RBRACE && p.tok != token.EOF {
list = append(list, p.parseElement())
if !p.atComma("composite literal", token.RBRACE) {
break
}
p.next()
}
return
}
func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
defer decNestLev(incNestLev(p))
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}
}
func (p *parser) parsePrimaryExpr(x ast.Expr) ast.Expr {
if p.trace {
defer un(trace(p, "PrimaryExpr"))
}
if x == nil {
x = p.parseOperand()
}
// We track the nesting here rather than at the entry for the function,
// since it can iteratively produce a nested output, and we want to
// limit how deep a structure we generate.
var n int
defer func() { p.nestLev -= n }()
for n = 1; ; n++ {
incNestLev(p)
switch p.tok {
case token.PERIOD:
p.next()
switch p.tok {
case token.IDENT:
x = p.parseSelector(x)
case token.LPAREN:
x = p.parseTypeAssertion(x)
default:
pos := p.pos
p.errorExpected(pos, "selector or type assertion")
// TODO(rFindley) The check for token.RBRACE below is a targeted fix
// to error recovery sufficient to make the x/tools tests to
// pass with the new parsing logic introduced for type
// parameters. Remove this once error recovery has been
// more generally reconsidered.
if p.tok != token.RBRACE {
p.next() // make progress
}
sel := &ast.Ident{NamePos: pos, Name: "_"}
x = &ast.SelectorExpr{X: x, Sel: sel}
}
case token.LBRACK:
x = p.parseIndexOrSliceOrInstance(x)
case token.LPAREN:
x = p.parseCallOrConversion(x)
case token.LBRACE:
// operand may have returned a parenthesized complit
// type; accept it but complain if we have a complit
t := ast.Unparen(x)
// determine if '{' belongs to a composite literal or a block statement
switch t.(type) {
case *ast.BadExpr, *ast.Ident, *ast.SelectorExpr:
if p.exprLev < 0 {
return x
}
// x is possibly a composite literal type
case *ast.IndexExpr, *ast.IndexListExpr:
if p.exprLev < 0 {
return x
}
// x is possibly a composite literal type
case *ast.ArrayType, *ast.StructType, *ast.MapType:
// x is a composite literal type
default:
return x
}
if t != x {
p.error(t.Pos(), "cannot parenthesize type in composite literal")
// already progressed, no need to advance
}
x = p.parseLiteralValue(x)
default:
return x
}
}
}
func (p *parser) parseUnaryExpr() ast.Expr {
defer decNestLev(incNestLev(p))
if p.trace {
defer un(trace(p, "UnaryExpr"))
}
switch p.tok {
case token.ADD, token.SUB, token.NOT, token.XOR, token.AND, token.TILDE:
pos, op := p.pos, p.tok
p.next()
x := p.parseUnaryExpr()
return &ast.UnaryExpr{OpPos: pos, Op: op, X: x}
case token.ARROW:
// channel type or receive expression
arrow := p.pos
p.next()
// If the next token is token.CHAN we still don't know if it
// is a channel type or a receive operation - we only know
// once we have found the end of the unary expression. There
// are two cases:
//
// <- type => (<-type) must be channel type
// <- expr => <-(expr) is a receive from an expression
//
// In the first case, the arrow must be re-associated with
// the channel type parsed already:
//
// <- (chan type) => (<-chan type)
// <- (chan<- type) => (<-chan (<-type))
x := p.parseUnaryExpr()
// determine which case we have
if typ, ok := x.(*ast.ChanType); ok {
// (<-type)
// re-associate position info and <-
dir := ast.SEND
for ok && dir == ast.SEND {
if typ.Dir == ast.RECV {
// error: (<-type) is (<-(<-chan T))
p.errorExpected(typ.Arrow, "'chan'")
}
arrow, typ.Begin, typ.Arrow = typ.Arrow, arrow, arrow
dir, typ.Dir = typ.Dir, ast.RECV
typ, ok = typ.Value.(*ast.ChanType)
}
if dir == ast.SEND {
p.errorExpected(arrow, "channel type")
}
return x
}
// <-(expr)
return &ast.UnaryExpr{OpPos: arrow, Op: token.ARROW, X: x}
case token.MUL:
// pointer type or unary "*" expression
pos := p.pos
p.next()
x := p.parseUnaryExpr()
return &ast.StarExpr{Star: pos, X: x}
}
return p.parsePrimaryExpr(nil)
}
func (p *parser) tokPrec() (token.Token, int) {
tok := p.tok
if p.inRhs && tok == token.ASSIGN {
tok = token.EQL
}
return tok, tok.Precedence()
}
// parseBinaryExpr parses a (possibly) binary expression.
// If x is non-nil, it is used as the left operand.
//
// TODO(rfindley): parseBinaryExpr has become overloaded. Consider refactoring.
func (p *parser) parseBinaryExpr(x ast.Expr, prec1 int) ast.Expr {
if p.trace {
defer un(trace(p, "BinaryExpr"))
}
if x == nil {
x = p.parseUnaryExpr()
}
// We track the nesting here rather than at the entry for the function,
// since it can iteratively produce a nested output, and we want to
// limit how deep a structure we generate.
var n int
defer func() { p.nestLev -= n }()
for n = 1; ; n++ {
incNestLev(p)
op, oprec := p.tokPrec()
if oprec < prec1 {
return x
}
pos := p.expect(op)
y := p.parseBinaryExpr(nil, oprec+1)
x = &ast.BinaryExpr{X: x, OpPos: pos, Op: op, Y: y}
}
}
// The result may be a type or even a raw type ([...]int).
func (p *parser) parseExpr() ast.Expr {
if p.trace {
defer un(trace(p, "Expression"))
}
return p.parseBinaryExpr(nil, token.LowestPrec+1)
}
func (p *parser) parseRhs() ast.Expr {
old := p.inRhs
p.inRhs = true
x := p.parseExpr()
p.inRhs = old
return x
}
// ----------------------------------------------------------------------------
// Statements
// Parsing modes for parseSimpleStmt.
const (
basic = iota
labelOk
rangeOk
)
// parseSimpleStmt returns true as 2nd result if it parsed the assignment
// of a range clause (with mode == rangeOk). The returned statement is an
// assignment with a right-hand side that is a single unary expression of
// the form "range x". No guarantees are given for the left-hand side.
func (p *parser) parseSimpleStmt(mode int) (ast.Stmt, bool) {
if p.trace {
defer un(trace(p, "SimpleStmt"))
}
x := p.parseList(false)
switch p.tok {
case
token.DEFINE, token.ASSIGN, token.ADD_ASSIGN,
token.SUB_ASSIGN, token.MUL_ASSIGN, token.QUO_ASSIGN,
token.REM_ASSIGN, token.AND_ASSIGN, token.OR_ASSIGN,
token.XOR_ASSIGN, token.SHL_ASSIGN, token.SHR_ASSIGN, token.AND_NOT_ASSIGN:
// assignment statement, possibly part of a range clause
pos, tok := p.pos, p.tok
p.next()
var y []ast.Expr
isRange := false
if mode == rangeOk && p.tok == token.RANGE && (tok == token.DEFINE || tok == token.ASSIGN) {
pos := p.pos
p.next()
y = []ast.Expr{&ast.UnaryExpr{OpPos: pos, Op: token.RANGE, X: p.parseRhs()}}
isRange = true
} else {
y = p.parseList(true)
}
return &ast.AssignStmt{Lhs: x, TokPos: pos, Tok: tok, Rhs: y}, isRange
}
if len(x) > 1 {
p.errorExpected(x[0].Pos(), "1 expression")
// continue with first expression
}
switch p.tok {
case token.COLON:
// labeled statement
colon := p.pos
p.next()
if label, isIdent := x[0].(*ast.Ident); mode == labelOk && isIdent {
// Go spec: The scope of a label is the body of the function
// in which it is declared and excludes the body of any nested
// function.
stmt := &ast.LabeledStmt{Label: label, Colon: colon, Stmt: p.parseStmt()}
return stmt, false
}
// The label declaration typically starts at x[0].Pos(), but the label
// declaration may be erroneous due to a token after that position (and
// before the ':'). If SpuriousErrors is not set, the (only) error
// reported for the line is the illegal label error instead of the token
// before the ':' that caused the problem. Thus, use the (latest) colon
// position for error reporting.
p.error(colon, "illegal label declaration")
return &ast.BadStmt{From: x[0].Pos(), To: colon + 1}, false
case token.ARROW:
// send statement
arrow := p.pos
p.next()
y := p.parseRhs()
return &ast.SendStmt{Chan: x[0], Arrow: arrow, Value: y}, false
case token.INC, token.DEC:
// increment or decrement
s := &ast.IncDecStmt{X: x[0], TokPos: p.pos, Tok: p.tok}
p.next()
return s, false
}
// expression
return &ast.ExprStmt{X: x[0]}, false
}
func (p *parser) parseCallExpr(callType string) *ast.CallExpr {
x := p.parseRhs() // could be a conversion: (some type)(x)
if t := ast.Unparen(x); t != x {
p.error(x.Pos(), fmt.Sprintf("expression in %s must not be parenthesized", callType))
x = t
}
if call, isCall := x.(*ast.CallExpr); isCall {
return call
}
if _, isBad := x.(*ast.BadExpr); !isBad {
// only report error if it's a new one
p.error(p.safePos(x.End()), fmt.Sprintf("expression in %s must be function call", callType))
}
return nil
}
func (p *parser) parseGoStmt() ast.Stmt {
if p.trace {
defer un(trace(p, "GoStmt"))
}
pos := p.expect(token.GO)
call := p.parseCallExpr("go")
p.expectSemi()
if call == nil {
return &ast.BadStmt{From: pos, To: pos + 2} // len("go")
}
return &ast.GoStmt{Go: pos, Call: call}
}
func (p *parser) parseDeferStmt() ast.Stmt {
if p.trace {
defer un(trace(p, "DeferStmt"))
}
pos := p.expect(token.DEFER)
call := p.parseCallExpr("defer")
p.expectSemi()
if call == nil {
return &ast.BadStmt{From: pos, To: pos + 5} // len("defer")
}
return &ast.DeferStmt{Defer: pos, Call: call}
}
func (p *parser) parseReturnStmt() *ast.ReturnStmt {
if p.trace {
defer un(trace(p, "ReturnStmt"))
}
pos := p.pos
p.expect(token.RETURN)
var x []ast.Expr
if p.tok != token.SEMICOLON && p.tok != token.RBRACE {
x = p.parseList(true)
}
p.expectSemi()
return &ast.ReturnStmt{Return: pos, Results: x}
}
func (p *parser) parseBranchStmt(tok token.Token) *ast.BranchStmt {
if p.trace {
defer un(trace(p, "BranchStmt"))
}
pos := p.expect(tok)
var label *ast.Ident
if tok != token.FALLTHROUGH && p.tok == token.IDENT {
label = p.parseIdent()
}
p.expectSemi()
return &ast.BranchStmt{TokPos: pos, Tok: tok, Label: label}
}
func (p *parser) makeExpr(s ast.Stmt, want string) ast.Expr {
if s == nil {
return nil
}
if es, isExpr := s.(*ast.ExprStmt); isExpr {
return es.X
}
found := "simple statement"
if _, isAss := s.(*ast.AssignStmt); isAss {
found = "assignment"
}
p.error(s.Pos(), fmt.Sprintf("expected %s, found %s (missing parentheses around composite literal?)", want, found))
return &ast.BadExpr{From: s.Pos(), To: p.safePos(s.End())}
}
// parseIfHeader is an adjusted version of parser.header
// in cmd/compile/internal/syntax/parser.go, which has
// been tuned for better error handling.
func (p *parser) parseIfHeader() (init ast.Stmt, cond ast.Expr) {
if p.tok == token.LBRACE {
p.error(p.pos, "missing condition in if statement")
cond = &ast.BadExpr{From: p.pos, To: p.pos}
return
}
// p.tok != token.LBRACE
prevLev := p.exprLev
p.exprLev = -1
if p.tok != token.SEMICOLON {
// accept potential variable declaration but complain
if p.tok == token.VAR {
p.next()
p.error(p.pos, "var declaration not allowed in if initializer")
}
init, _ = p.parseSimpleStmt(basic)
}
var condStmt ast.Stmt
var semi struct {
pos token.Pos
lit string // ";" or "\n"; valid if pos.IsValid()
}
if p.tok != token.LBRACE {
if p.tok == token.SEMICOLON {
semi.pos = p.pos
semi.lit = p.lit
p.next()
} else {
p.expect(token.SEMICOLON)
}
if p.tok != token.LBRACE {
condStmt, _ = p.parseSimpleStmt(basic)
}
} else {
condStmt = init
init = nil
}
if condStmt != nil {
cond = p.makeExpr(condStmt, "boolean expression")
} else if semi.pos.IsValid() {
if semi.lit == "\n" {
p.error(semi.pos, "unexpected newline, expecting { after if clause")
} else {
p.error(semi.pos, "missing condition in if statement")
}
}
// make sure we have a valid AST
if cond == nil {
cond = &ast.BadExpr{From: p.pos, To: p.pos}
}
p.exprLev = prevLev
return
}
func (p *parser) parseIfStmt() *ast.IfStmt {
defer decNestLev(incNestLev(p))
if p.trace {
defer un(trace(p, "IfStmt"))
}
pos := p.expect(token.IF)
init, cond := p.parseIfHeader()
body := p.parseBlockStmt()
var else_ ast.Stmt
if p.tok == token.ELSE {
p.next()
switch p.tok {
case token.IF:
else_ = p.parseIfStmt()
case token.LBRACE:
else_ = p.parseBlockStmt()
p.expectSemi()
default:
p.errorExpected(p.pos, "if statement or block")
else_ = &ast.BadStmt{From: p.pos, To: p.pos}
}
} else {
p.expectSemi()
}
return &ast.IfStmt{If: pos, Init: init, Cond: cond, Body: body, Else: else_}
}
func (p *parser) parseCaseClause() *ast.CaseClause {
if p.trace {
defer un(trace(p, "CaseClause"))
}
pos := p.pos
var list []ast.Expr
if p.tok == token.CASE {
p.next()
list = p.parseList(true)
} else {
p.expect(token.DEFAULT)
}
colon := p.expect(token.COLON)
body := p.parseStmtList()
return &ast.CaseClause{Case: pos, List: list, Colon: colon, Body: body}
}
func isTypeSwitchAssert(x ast.Expr) bool {
a, ok := x.(*ast.TypeAssertExpr)
return ok && a.Type == nil
}
func (p *parser) isTypeSwitchGuard(s ast.Stmt) bool {
switch t := s.(type) {
case *ast.ExprStmt:
// x.(type)
return isTypeSwitchAssert(t.X)
case *ast.AssignStmt:
// v := x.(type)
if len(t.Lhs) == 1 && len(t.Rhs) == 1 && isTypeSwitchAssert(t.Rhs[0]) {
switch t.Tok {
case token.ASSIGN:
// permit v = x.(type) but complain
p.error(t.TokPos, "expected ':=', found '='")
fallthrough
case token.DEFINE:
return true
}
}
}
return false
}
func (p *parser) parseSwitchStmt() ast.Stmt {
if p.trace {
defer un(trace(p, "SwitchStmt"))
}
pos := p.expect(token.SWITCH)
var s1, s2 ast.Stmt
if p.tok != token.LBRACE {
prevLev := p.exprLev
p.exprLev = -1
if p.tok != token.SEMICOLON {
s2, _ = p.parseSimpleStmt(basic)
}
if p.tok == token.SEMICOLON {
p.next()
s1 = s2
s2 = nil
if p.tok != token.LBRACE {
// A TypeSwitchGuard may declare a variable in addition
// to the variable declared in the initial SimpleStmt.
// Introduce extra scope to avoid redeclaration errors:
//
// switch t := 0; t := x.(T) { ... }
//
// (this code is not valid Go because the first t
// cannot be accessed and thus is never used, the extra
// scope is needed for the correct error message).
//
// If we don't have a type switch, s2 must be an expression.
// Having the extra nested but empty scope won't affect it.
s2, _ = p.parseSimpleStmt(basic)
}
}
p.exprLev = prevLev
}
typeSwitch := p.isTypeSwitchGuard(s2)
lbrace := p.expect(token.LBRACE)
var list []ast.Stmt
for p.tok == token.CASE || p.tok == token.DEFAULT {
list = append(list, p.parseCaseClause())
}
rbrace := p.expect(token.RBRACE)
p.expectSemi()
body := &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
if typeSwitch {
return &ast.TypeSwitchStmt{Switch: pos, Init: s1, Assign: s2, Body: body}
}
return &ast.SwitchStmt{Switch: pos, Init: s1, Tag: p.makeExpr(s2, "switch expression"), Body: body}
}
func (p *parser) parseCommClause() *ast.CommClause {
if p.trace {
defer un(trace(p, "CommClause"))
}
pos := p.pos
var comm ast.Stmt
if p.tok == token.CASE {
p.next()
lhs := p.parseList(false)
if p.tok == token.ARROW {
// SendStmt
if len(lhs) > 1 {
p.errorExpected(lhs[0].Pos(), "1 expression")
// continue with first expression
}
arrow := p.pos
p.next()
rhs := p.parseRhs()
comm = &ast.SendStmt{Chan: lhs[0], Arrow: arrow, Value: rhs}
} else {
// RecvStmt
if tok := p.tok; tok == token.ASSIGN || tok == token.DEFINE {
// RecvStmt with assignment
if len(lhs) > 2 {
p.errorExpected(lhs[0].Pos(), "1 or 2 expressions")
// continue with first two expressions
lhs = lhs[0:2]
}
pos := p.pos
p.next()
rhs := p.parseRhs()
comm = &ast.AssignStmt{Lhs: lhs, TokPos: pos, Tok: tok, Rhs: []ast.Expr{rhs}}
} else {
// lhs must be single receive operation
if len(lhs) > 1 {
p.errorExpected(lhs[0].Pos(), "1 expression")
// continue with first expression
}
comm = &ast.ExprStmt{X: lhs[0]}
}
}
} else {
p.expect(token.DEFAULT)
}
colon := p.expect(token.COLON)
body := p.parseStmtList()
return &ast.CommClause{Case: pos, Comm: comm, Colon: colon, Body: body}
}
func (p *parser) parseSelectStmt() *ast.SelectStmt {
if p.trace {
defer un(trace(p, "SelectStmt"))
}
pos := p.expect(token.SELECT)
lbrace := p.expect(token.LBRACE)
var list []ast.Stmt
for p.tok == token.CASE || p.tok == token.DEFAULT {
list = append(list, p.parseCommClause())
}
rbrace := p.expect(token.RBRACE)
p.expectSemi()
body := &ast.BlockStmt{Lbrace: lbrace, List: list, Rbrace: rbrace}
return &ast.SelectStmt{Select: pos, Body: body}
}
func (p *parser) parseForStmt() ast.Stmt {
if p.trace {
defer un(trace(p, "ForStmt"))
}
pos := p.expect(token.FOR)
var s1, s2, s3 ast.Stmt
var isRange bool
if p.tok != token.LBRACE {
prevLev := p.exprLev
p.exprLev = -1
if p.tok != token.SEMICOLON {
if p.tok == token.RANGE {
// "for range x" (nil lhs in assignment)
pos := p.pos
p.next()
y := []ast.Expr{&ast.UnaryExpr{OpPos: pos, Op: token.RANGE, X: p.parseRhs()}}
s2 = &ast.AssignStmt{Rhs: y}
isRange = true
} else {
s2, isRange = p.parseSimpleStmt(rangeOk)
}
}
if !isRange && p.tok == token.SEMICOLON {
p.next()
s1 = s2
s2 = nil
if p.tok != token.SEMICOLON {
s2, _ = p.parseSimpleStmt(basic)
}
p.expectSemi()
if p.tok != token.LBRACE {
s3, _ = p.parseSimpleStmt(basic)
}
}
p.exprLev = prevLev
}
body := p.parseBlockStmt()
p.expectSemi()
if isRange {
as := s2.(*ast.AssignStmt)
// check lhs
var key, value ast.Expr
switch len(as.Lhs) {
case 0:
// nothing to do
case 1:
key = as.Lhs[0]
case 2:
key, value = as.Lhs[0], as.Lhs[1]
default:
p.errorExpected(as.Lhs[len(as.Lhs)-1].Pos(), "at most 2 expressions")
return &ast.BadStmt{From: pos, To: p.safePos(body.End())}
}
// parseSimpleStmt returned a right-hand side that
// is a single unary expression of the form "range x"
x := as.Rhs[0].(*ast.UnaryExpr).X
return &ast.RangeStmt{
For: pos,
Key: key,
Value: value,
TokPos: as.TokPos,
Tok: as.Tok,
Range: as.Rhs[0].Pos(),
X: x,
Body: body,
}
}
// regular for statement
return &ast.ForStmt{
For: pos,
Init: s1,
Cond: p.makeExpr(s2, "boolean or range expression"),
Post: s3,
Body: body,
}
}
func (p *parser) parseStmt() (s ast.Stmt) {
defer decNestLev(incNestLev(p))
if p.trace {
defer un(trace(p, "Statement"))
}
switch p.tok {
case token.CONST, token.TYPE, token.VAR:
s = &ast.DeclStmt{Decl: p.parseDecl(stmtStart)}
case
// tokens that may start an expression
token.IDENT, token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING, token.FUNC, token.LPAREN, // operands
token.LBRACK, token.STRUCT, token.MAP, token.CHAN, token.INTERFACE, // composite types
token.ADD, token.SUB, token.MUL, token.AND, token.XOR, token.ARROW, token.NOT: // unary operators
s, _ = p.parseSimpleStmt(labelOk)
// because of the required look-ahead, labeled statements are
// parsed by parseSimpleStmt - don't expect a semicolon after
// them
if _, isLabeledStmt := s.(*ast.LabeledStmt); !isLabeledStmt {
p.expectSemi()
}
case token.GO:
s = p.parseGoStmt()
case token.DEFER:
s = p.parseDeferStmt()
case token.RETURN:
s = p.parseReturnStmt()
case token.BREAK, token.CONTINUE, token.GOTO, token.FALLTHROUGH:
s = p.parseBranchStmt(p.tok)
case token.LBRACE:
s = p.parseBlockStmt()
p.expectSemi()
case token.IF:
s = p.parseIfStmt()
case token.SWITCH:
s = p.parseSwitchStmt()
case token.SELECT:
s = p.parseSelectStmt()
case token.FOR:
s = p.parseForStmt()
case token.SEMICOLON:
// Is it ever possible to have an implicit semicolon
// producing an empty statement in a valid program?
// (handle correctly anyway)
s = &ast.EmptyStmt{Semicolon: p.pos, Implicit: p.lit == "\n"}
p.next()
case token.RBRACE:
// a semicolon may be omitted before a closing "}"
s = &ast.EmptyStmt{Semicolon: p.pos, Implicit: true}
default:
// no statement found
pos := p.pos
p.errorExpected(pos, "statement")
p.advance(stmtStart)
s = &ast.BadStmt{From: pos, To: p.pos}
}
return
}
// ----------------------------------------------------------------------------
// Declarations
type parseSpecFunction func(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec
func (p *parser) parseImportSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
if p.trace {
defer un(trace(p, "ImportSpec"))
}
var ident *ast.Ident
switch p.tok {
case token.IDENT:
ident = p.parseIdent()
case token.PERIOD:
ident = &ast.Ident{NamePos: p.pos, Name: "."}
p.next()
}
pos := p.pos
var path string
if p.tok == token.STRING {
path = p.lit
p.next()
} else if p.tok.IsLiteral() {
p.error(pos, "import path must be a string")
p.next()
} else {
p.error(pos, "missing import path")
p.advance(exprEnd)
}
comment := p.expectSemi()
// collect imports
spec := &ast.ImportSpec{
Doc: doc,
Name: ident,
Path: &ast.BasicLit{ValuePos: pos, Kind: token.STRING, Value: path},
Comment: comment,
}
p.imports = append(p.imports, spec)
return spec
}
func (p *parser) parseValueSpec(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec {
if p.trace {
defer un(trace(p, keyword.String()+"Spec"))
}
idents := p.parseIdentList()
var typ ast.Expr
var values []ast.Expr
switch keyword {
case token.CONST:
// always permit optional type and initialization for more tolerant parsing
if p.tok != token.EOF && p.tok != token.SEMICOLON && p.tok != token.RPAREN {
typ = p.tryIdentOrType()
if p.tok == token.ASSIGN {
p.next()
values = p.parseList(true)
}
}
case token.VAR:
if p.tok != token.ASSIGN {
typ = p.parseType()
}
if p.tok == token.ASSIGN {
p.next()
values = p.parseList(true)
}
default:
panic("unreachable")
}
comment := p.expectSemi()
spec := &ast.ValueSpec{
Doc: doc,
Names: idents,
Type: typ,
Values: values,
Comment: comment,
}
return spec
}
func (p *parser) parseGenericType(spec *ast.TypeSpec, openPos token.Pos, name0 *ast.Ident, typ0 ast.Expr) {
if p.trace {
defer un(trace(p, "parseGenericType"))
}
list := p.parseParameterList(name0, typ0, token.RBRACK)
closePos := p.expect(token.RBRACK)
spec.TypeParams = &ast.FieldList{Opening: openPos, List: list, Closing: closePos}
// Let the type checker decide whether to accept type parameters on aliases:
// see go.dev/issue/46477.
if p.tok == token.ASSIGN {
// type alias
spec.Assign = p.pos
p.next()
}
spec.Type = p.parseType()
}
func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
if p.trace {
defer un(trace(p, "TypeSpec"))
}
name := p.parseIdent()
spec := &ast.TypeSpec{Doc: doc, Name: name}
if p.tok == token.LBRACK {
// spec.Name "[" ...
// array/slice type or type parameter list
lbrack := p.pos
p.next()
if p.tok == token.IDENT {
// We may have an array type or a type parameter list.
// In either case we expect an expression x (which may
// just be a name, or a more complex expression) which
// we can analyze further.
//
// A type parameter list may have a type bound starting
// with a "[" as in: P []E. In that case, simply parsing
// an expression would lead to an error: P[] is invalid.
// But since index or slice expressions are never constant
// and thus invalid array length expressions, if the name
// is followed by "[" it must be the start of an array or
// slice constraint. Only if we don't see a "[" do we
// need to parse a full expression. Notably, name <- x
// is not a concern because name <- x is a statement and
// not an expression.
var x ast.Expr = p.parseIdent()
if p.tok != token.LBRACK {
// To parse the expression starting with name, expand
// the call sequence we would get by passing in name
// to parser.expr, and pass in name to parsePrimaryExpr.
p.exprLev++
lhs := p.parsePrimaryExpr(x)
x = p.parseBinaryExpr(lhs, token.LowestPrec+1)
p.exprLev--
}
// Analyze expression x. If we can split x into a type parameter
// name, possibly followed by a type parameter type, we consider
// this the start of a type parameter list, with some caveats:
// a single name followed by "]" tilts the decision towards an
// array declaration; a type parameter type that could also be
// an ordinary expression but which is followed by a comma tilts
// the decision towards a type parameter list.
if pname, ptype := extractName(x, p.tok == token.COMMA); pname != nil && (ptype != nil || p.tok != token.RBRACK) {
// spec.Name "[" pname ...
// spec.Name "[" pname ptype ...
// spec.Name "[" pname ptype "," ...
p.parseGenericType(spec, lbrack, pname, ptype) // ptype may be nil
} else {
// spec.Name "[" pname "]" ...
// spec.Name "[" x ...
spec.Type = p.parseArrayType(lbrack, x)
}
} else {
// array type
spec.Type = p.parseArrayType(lbrack, nil)
}
} else {
// no type parameters
if p.tok == token.ASSIGN {
// type alias
spec.Assign = p.pos
p.next()
}
spec.Type = p.parseType()
}
spec.Comment = p.expectSemi()
return spec
}
// extractName splits the expression x into (name, expr) if syntactically
// x can be written as name expr. The split only happens if expr is a type
// element (per the isTypeElem predicate) or if force is set.
// If x is just a name, the result is (name, nil). If the split succeeds,
// the result is (name, expr). Otherwise the result is (nil, x).
// Examples:
//
// x force name expr
// ------------------------------------
// P*[]int T/F P *[]int
// P*E T P *E
// P*E F nil P*E
// P([]int) T/F P ([]int)
// P(E) T P (E)
// P(E) F nil P(E)
// P*E|F|~G T/F P *E|F|~G
// P*E|F|G T P *E|F|G
// P*E|F|G F nil P*E|F|G
func extractName(x ast.Expr, force bool) (*ast.Ident, ast.Expr) {
switch x := x.(type) {
case *ast.Ident:
return x, nil
case *ast.BinaryExpr:
switch x.Op {
case token.MUL:
if name, _ := x.X.(*ast.Ident); name != nil && (force || isTypeElem(x.Y)) {
// x = name *x.Y
return name, &ast.StarExpr{Star: x.OpPos, X: x.Y}
}
case token.OR:
if name, lhs := extractName(x.X, force || isTypeElem(x.Y)); name != nil && lhs != nil {
// x = name lhs|x.Y
op := *x
op.X = lhs
return name, &op
}
}
case *ast.CallExpr:
if name, _ := x.Fun.(*ast.Ident); name != nil {
if len(x.Args) == 1 && x.Ellipsis == token.NoPos && (force || isTypeElem(x.Args[0])) {
// x = name (x.Args[0])
// (Note that the cmd/compile/internal/syntax parser does not care
// about syntax tree fidelity and does not preserve parentheses here.)
return name, &ast.ParenExpr{
Lparen: x.Lparen,
X: x.Args[0],
Rparen: x.Rparen,
}
}
}
}
return nil, x
}
// isTypeElem reports whether x is a (possibly parenthesized) type element expression.
// The result is false if x could be a type element OR an ordinary (value) expression.
func isTypeElem(x ast.Expr) bool {
switch x := x.(type) {
case *ast.ArrayType, *ast.StructType, *ast.FuncType, *ast.InterfaceType, *ast.MapType, *ast.ChanType:
return true
case *ast.BinaryExpr:
return isTypeElem(x.X) || isTypeElem(x.Y)
case *ast.UnaryExpr:
return x.Op == token.TILDE
case *ast.ParenExpr:
return isTypeElem(x.X)
}
return false
}
func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
if p.trace {
defer un(trace(p, "GenDecl("+keyword.String()+")"))
}
doc := p.leadComment
pos := p.expect(keyword)
var lparen, rparen token.Pos
var list []ast.Spec
if p.tok == token.LPAREN {
lparen = p.pos
p.next()
for iota := 0; p.tok != token.RPAREN && p.tok != token.EOF; iota++ {
list = append(list, f(p.leadComment, keyword, iota))
}
rparen = p.expect(token.RPAREN)
p.expectSemi()
} else {
list = append(list, f(nil, keyword, 0))
}
return &ast.GenDecl{
Doc: doc,
TokPos: pos,
Tok: keyword,
Lparen: lparen,
Specs: list,
Rparen: rparen,
}
}
func (p *parser) parseFuncDecl() *ast.FuncDecl {
if p.trace {
defer un(trace(p, "FunctionDecl"))
}
doc := p.leadComment
pos := p.expect(token.FUNC)
var recv *ast.FieldList
if p.tok == token.LPAREN {
_, recv = p.parseParameters(false)
}
ident := p.parseIdent()
tparams, params := p.parseParameters(true)
if recv != nil && tparams != nil {
// Method declarations do not have type parameters. We parse them for a
// better error message and improved error recovery.
p.error(tparams.Opening, "method must have no type parameters")
tparams = nil
}
results := p.parseResult()
var body *ast.BlockStmt
switch p.tok {
case token.LBRACE:
body = p.parseBody()
p.expectSemi()
case token.SEMICOLON:
p.next()
if p.tok == token.LBRACE {
// opening { of function declaration on next line
p.error(p.pos, "unexpected semicolon or newline before {")
body = p.parseBody()
p.expectSemi()
}
default:
p.expectSemi()
}
decl := &ast.FuncDecl{
Doc: doc,
Recv: recv,
Name: ident,
Type: &ast.FuncType{
Func: pos,
TypeParams: tparams,
Params: params,
Results: results,
},
Body: body,
}
return decl
}
func (p *parser) parseDecl(sync map[token.Token]bool) ast.Decl {
if p.trace {
defer un(trace(p, "Declaration"))
}
var f parseSpecFunction
switch p.tok {
case token.IMPORT:
f = p.parseImportSpec
case token.CONST, token.VAR:
f = p.parseValueSpec
case token.TYPE:
f = p.parseTypeSpec
case token.FUNC:
return p.parseFuncDecl()
default:
pos := p.pos
p.errorExpected(pos, "declaration")
p.advance(sync)
return &ast.BadDecl{From: pos, To: p.pos}
}
return p.parseGenDecl(p.tok, f)
}
// ----------------------------------------------------------------------------
// Source files
func (p *parser) parseFile() *ast.File {
if p.trace {
defer un(trace(p, "File"))
}
// Don't bother parsing the rest if we had errors scanning the first token.
// Likely not a Go source file at all.
if p.errors.Len() != 0 {
return nil
}
// package clause
doc := p.leadComment
pos := p.expect(token.PACKAGE)
// Go spec: The package clause is not a declaration;
// the package name does not appear in any scope.
ident := p.parseIdent()
if ident.Name == "_" && p.mode&DeclarationErrors != 0 {
p.error(p.pos, "invalid package name _")
}
p.expectSemi()
// Don't bother parsing the rest if we had errors parsing the package clause.
// Likely not a Go source file at all.
if p.errors.Len() != 0 {
return nil
}
var decls []ast.Decl
if p.mode&PackageClauseOnly == 0 {
// import decls
for p.tok == token.IMPORT {
decls = append(decls, p.parseGenDecl(token.IMPORT, p.parseImportSpec))
}
if p.mode&ImportsOnly == 0 {
// rest of package body
prev := token.IMPORT
for p.tok != token.EOF {
// Continue to accept import declarations for error tolerance, but complain.
if p.tok == token.IMPORT && prev != token.IMPORT {
p.error(p.pos, "imports must appear before other declarations")
}
prev = p.tok
decls = append(decls, p.parseDecl(declStart))
}
}
}
f := &ast.File{
Doc: doc,
Package: pos,
Name: ident,
Decls: decls,
// File{Start,End} are set by the defer in the caller.
Imports: p.imports,
Comments: p.comments,
GoVersion: p.goVersion,
}
var declErr func(token.Pos, string)
if p.mode&DeclarationErrors != 0 {
declErr = p.error
}
if p.mode&SkipObjectResolution == 0 {
resolveFile(f, p.file, declErr)
}
return f
}
// packIndexExpr returns an IndexExpr x[expr0] or IndexListExpr x[expr0, ...].
func packIndexExpr(x ast.Expr, lbrack token.Pos, exprs []ast.Expr, rbrack token.Pos) ast.Expr {
switch len(exprs) {
case 0:
panic("internal error: packIndexExpr with empty expr slice")
case 1:
return &ast.IndexExpr{
X: x,
Lbrack: lbrack,
Index: exprs[0],
Rbrack: rbrack,
}
default:
return &ast.IndexListExpr{
X: x,
Lbrack: lbrack,
Indices: exprs,
Rbrack: rbrack,
}
}
}