go parser 源码
golang parser 代码
文件路径：/src/cmd/compile/internal/syntax/parser.go
// Copyright 2016 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 syntax
import (
"fmt"
"io"
"strconv"
"strings"
)
const debug = false
const trace = false
type parser struct {
file *PosBase
errh ErrorHandler
mode Mode
pragh PragmaHandler
scanner
base *PosBase // current position base
first error // first error encountered
errcnt int // number of errors encountered
pragma Pragma // pragmas
fnest int // function nesting level (for error handling)
xnest int // expression nesting level (for complit ambiguity resolution)
indent []byte // tracing support
}
func (p *parser) init(file *PosBase, r io.Reader, errh ErrorHandler, pragh PragmaHandler, mode Mode) {
p.file = file
p.errh = errh
p.mode = mode
p.pragh = pragh
p.scanner.init(
r,
// Error and directive handler for scanner.
// Because the (line, col) positions passed to the
// handler is always at or after the current reading
// position, it is safe to use the most recent position
// base to compute the corresponding Pos value.
func(line, col uint, msg string) {
if msg[0] != '/' {
p.errorAt(p.posAt(line, col), msg)
return
}
// otherwise it must be a comment containing a line or go: directive.
// //line directives must be at the start of the line (column colbase).
// /*line*/ directives can be anywhere in the line.
text := commentText(msg)
if (col == colbase || msg[1] == '*') && strings.HasPrefix(text, "line ") {
var pos Pos // position immediately following the comment
if msg[1] == '/' {
// line comment (newline is part of the comment)
pos = MakePos(p.file, line+1, colbase)
} else {
// regular comment
// (if the comment spans multiple lines it's not
// a valid line directive and will be discarded
// by updateBase)
pos = MakePos(p.file, line, col+uint(len(msg)))
}
p.updateBase(pos, line, col+2+5, text[5:]) // +2 to skip over // or /*
return
}
// go: directive (but be conservative and test)
if pragh != nil && strings.HasPrefix(text, "go:") {
p.pragma = pragh(p.posAt(line, col+2), p.scanner.blank, text, p.pragma) // +2 to skip over // or /*
}
},
directives,
)
p.base = file
p.first = nil
p.errcnt = 0
p.pragma = nil
p.fnest = 0
p.xnest = 0
p.indent = nil
}
// takePragma returns the current parsed pragmas
// and clears them from the parser state.
func (p *parser) takePragma() Pragma {
prag := p.pragma
p.pragma = nil
return prag
}
// clearPragma is called at the end of a statement or
// other Go form that does NOT accept a pragma.
// It sends the pragma back to the pragma handler
// to be reported as unused.
func (p *parser) clearPragma() {
if p.pragma != nil {
p.pragh(p.pos(), p.scanner.blank, "", p.pragma)
p.pragma = nil
}
}
// updateBase sets the current position base to a new line base at pos.
// The base's filename, line, and column values are extracted from text
// which is positioned at (tline, tcol) (only needed for error messages).
func (p *parser) updateBase(pos Pos, tline, tcol uint, text string) {
i, n, ok := trailingDigits(text)
if i == 0 {
return // ignore (not a line directive)
}
// i > 0
if !ok {
// text has a suffix :xxx but xxx is not a number
p.errorAt(p.posAt(tline, tcol+i), "invalid line number: "+text[i:])
return
}
var line, col uint
i2, n2, ok2 := trailingDigits(text[:i-1])
if ok2 {
//line filename:line:col
i, i2 = i2, i
line, col = n2, n
if col == 0 || col > PosMax {
p.errorAt(p.posAt(tline, tcol+i2), "invalid column number: "+text[i2:])
return
}
text = text[:i2-1] // lop off ":col"
} else {
//line filename:line
line = n
}
if line == 0 || line > PosMax {
p.errorAt(p.posAt(tline, tcol+i), "invalid line number: "+text[i:])
return
}
// If we have a column (//line filename:line:col form),
// an empty filename means to use the previous filename.
filename := text[:i-1] // lop off ":line"
trimmed := false
if filename == "" && ok2 {
filename = p.base.Filename()
trimmed = p.base.Trimmed()
}
p.base = NewLineBase(pos, filename, trimmed, line, col)
}
func commentText(s string) string {
if s[:2] == "/*" {
return s[2 : len(s)-2] // lop off /* and */
}
// line comment (does not include newline)
// (on Windows, the line comment may end in \r\n)
i := len(s)
if s[i-1] == '\r' {
i--
}
return s[2:i] // lop off //, and \r at end, if any
}
func trailingDigits(text string) (uint, uint, bool) {
// Want to use LastIndexByte below but it's not defined in Go1.4 and bootstrap fails.
i := strings.LastIndex(text, ":") // look from right (Windows filenames may contain ':')
if i < 0 {
return 0, 0, false // no ":"
}
// i >= 0
n, err := strconv.ParseUint(text[i+1:], 10, 0)
return uint(i + 1), uint(n), err == nil
}
func (p *parser) got(tok token) bool {
if p.tok == tok {
p.next()
return true
}
return false
}
func (p *parser) want(tok token) {
if !p.got(tok) {
p.syntaxError("expecting " + tokstring(tok))
p.advance()
}
}
// gotAssign is like got(_Assign) but it also accepts ":="
// (and reports an error) for better parser error recovery.
func (p *parser) gotAssign() bool {
switch p.tok {
case _Define:
p.syntaxError("expecting =")
fallthrough
case _Assign:
p.next()
return true
}
return false
}
// ----------------------------------------------------------------------------
// Error handling
// posAt returns the Pos value for (line, col) and the current position base.
func (p *parser) posAt(line, col uint) Pos {
return MakePos(p.base, line, col)
}
// error reports an error at the given position.
func (p *parser) errorAt(pos Pos, msg string) {
err := Error{pos, msg}
if p.first == nil {
p.first = err
}
p.errcnt++
if p.errh == nil {
panic(p.first)
}
p.errh(err)
}
// syntaxErrorAt reports a syntax error at the given position.
func (p *parser) syntaxErrorAt(pos Pos, msg string) {
if trace {
p.print("syntax error: " + msg)
}
if p.tok == _EOF && p.first != nil {
return // avoid meaningless follow-up errors
}
// add punctuation etc. as needed to msg
switch {
case msg == "":
// nothing to do
case strings.HasPrefix(msg, "in "), strings.HasPrefix(msg, "at "), strings.HasPrefix(msg, "after "):
msg = " " + msg
case strings.HasPrefix(msg, "expecting "):
msg = ", " + msg
default:
// plain error - we don't care about current token
p.errorAt(pos, "syntax error: "+msg)
return
}
// determine token string
var tok string
switch p.tok {
case _Name, _Semi:
tok = p.lit
case _Literal:
tok = "literal " + p.lit
case _Operator:
tok = p.op.String()
case _AssignOp:
tok = p.op.String() + "="
case _IncOp:
tok = p.op.String()
tok += tok
default:
tok = tokstring(p.tok)
}
p.errorAt(pos, "syntax error: unexpected "+tok+msg)
}
// tokstring returns the English word for selected punctuation tokens
// for more readable error messages. Use tokstring (not tok.String())
// for user-facing (error) messages; use tok.String() for debugging
// output.
func tokstring(tok token) string {
switch tok {
case _Comma:
return "comma"
case _Semi:
return "semicolon or newline"
}
return tok.String()
}
// Convenience methods using the current token position.
func (p *parser) pos() Pos { return p.posAt(p.line, p.col) }
func (p *parser) error(msg string) { p.errorAt(p.pos(), msg) }
func (p *parser) syntaxError(msg string) { p.syntaxErrorAt(p.pos(), msg) }
// The stopset contains keywords that start a statement.
// They are good synchronization points in case of syntax
// errors and (usually) shouldn't be skipped over.
const stopset uint64 = 1<<_Break |
1<<_Const |
1<<_Continue |
1<<_Defer |
1<<_Fallthrough |
1<<_For |
1<<_Go |
1<<_Goto |
1<<_If |
1<<_Return |
1<<_Select |
1<<_Switch |
1<<_Type |
1<<_Var
// Advance consumes tokens until it finds a token of the stopset or followlist.
// The stopset is only considered if we are inside a function (p.fnest > 0).
// The followlist is the list of valid tokens that can follow a production;
// if it is empty, exactly one (non-EOF) token is consumed to ensure progress.
func (p *parser) advance(followlist ...token) {
if trace {
p.print(fmt.Sprintf("advance %s", followlist))
}
// compute follow set
// (not speed critical, advance is only called in error situations)
var followset uint64 = 1 << _EOF // don't skip over EOF
if len(followlist) > 0 {
if p.fnest > 0 {
followset |= stopset
}
for _, tok := range followlist {
followset |= 1 << tok
}
}
for !contains(followset, p.tok) {
if trace {
p.print("skip " + p.tok.String())
}
p.next()
if len(followlist) == 0 {
break
}
}
if trace {
p.print("next " + p.tok.String())
}
}
// usage: defer p.trace(msg)()
func (p *parser) trace(msg string) func() {
p.print(msg + " (")
const tab = ". "
p.indent = append(p.indent, tab...)
return func() {
p.indent = p.indent[:len(p.indent)-len(tab)]
if x := recover(); x != nil {
panic(x) // skip print_trace
}
p.print(")")
}
}
func (p *parser) print(msg string) {
fmt.Printf("%5d: %s%s\n", p.line, p.indent, msg)
}
// ----------------------------------------------------------------------------
// Package files
//
// Parse methods are annotated with matching Go productions as appropriate.
// The annotations are intended as guidelines only since a single Go grammar
// rule may be covered by multiple parse methods and vice versa.
//
// Excluding methods returning slices, parse methods named xOrNil may return
// nil; all others are expected to return a valid non-nil node.
// SourceFile = PackageClause ";" { ImportDecl ";" } { TopLevelDecl ";" } .
func (p *parser) fileOrNil() *File {
if trace {
defer p.trace("file")()
}
f := new(File)
f.pos = p.pos()
// PackageClause
if !p.got(_Package) {
p.syntaxError("package statement must be first")
return nil
}
f.Pragma = p.takePragma()
f.PkgName = p.name()
p.want(_Semi)
// don't bother continuing if package clause has errors
if p.first != nil {
return nil
}
// { ImportDecl ";" }
for p.got(_Import) {
f.DeclList = p.appendGroup(f.DeclList, p.importDecl)
p.want(_Semi)
}
// { TopLevelDecl ";" }
for p.tok != _EOF {
switch p.tok {
case _Const:
p.next()
f.DeclList = p.appendGroup(f.DeclList, p.constDecl)
case _Type:
p.next()
f.DeclList = p.appendGroup(f.DeclList, p.typeDecl)
case _Var:
p.next()
f.DeclList = p.appendGroup(f.DeclList, p.varDecl)
case _Func:
p.next()
if d := p.funcDeclOrNil(); d != nil {
f.DeclList = append(f.DeclList, d)
}
default:
if p.tok == _Lbrace && len(f.DeclList) > 0 && isEmptyFuncDecl(f.DeclList[len(f.DeclList)-1]) {
// opening { of function declaration on next line
p.syntaxError("unexpected semicolon or newline before {")
} else {
p.syntaxError("non-declaration statement outside function body")
}
p.advance(_Const, _Type, _Var, _Func)
continue
}
// Reset p.pragma BEFORE advancing to the next token (consuming ';')
// since comments before may set pragmas for the next function decl.
p.clearPragma()
if p.tok != _EOF && !p.got(_Semi) {
p.syntaxError("after top level declaration")
p.advance(_Const, _Type, _Var, _Func)
}
}
// p.tok == _EOF
p.clearPragma()
f.EOF = p.pos()
return f
}
func isEmptyFuncDecl(dcl Decl) bool {
f, ok := dcl.(*FuncDecl)
return ok && f.Body == nil
}
// ----------------------------------------------------------------------------
// Declarations
// list parses a possibly empty, sep-separated list of elements, optionally
// followed by sep, and closed by close (or EOF). sep must be one of _Comma
// or _Semi, and close must be one of _Rparen, _Rbrace, or _Rbrack.
//
// For each list element, f is called. Specifically, unless we're at close
// (or EOF), f is called at least once. After f returns true, no more list
// elements are accepted. list returns the position of the closing token.
//
// list = [ f { sep f } [sep] ] close .
func (p *parser) list(context string, sep, close token, f func() bool) Pos {
if debug && (sep != _Comma && sep != _Semi || close != _Rparen && close != _Rbrace && close != _Rbrack) {
panic("invalid sep or close argument for list")
}
done := false
for p.tok != _EOF && p.tok != close && !done {
done = f()
// sep is optional before close
if !p.got(sep) && p.tok != close {
p.syntaxError(fmt.Sprintf("in %s; possibly missing %s or %s", context, tokstring(sep), tokstring(close)))
p.advance(_Rparen, _Rbrack, _Rbrace)
if p.tok != close {
// position could be better but we had an error so we don't care
return p.pos()
}
}
}
pos := p.pos()
p.want(close)
return pos
}
// appendGroup(f) = f | "(" { f ";" } ")" . // ";" is optional before ")"
func (p *parser) appendGroup(list []Decl, f func(*Group) Decl) []Decl {
if p.tok == _Lparen {
g := new(Group)
p.clearPragma()
p.next() // must consume "(" after calling clearPragma!
p.list("grouped declaration", _Semi, _Rparen, func() bool {
if x := f(g); x != nil {
list = append(list, x)
}
return false
})
} else {
if x := f(nil); x != nil {
list = append(list, x)
}
}
return list
}
// ImportSpec = [ "." | PackageName ] ImportPath .
// ImportPath = string_lit .
func (p *parser) importDecl(group *Group) Decl {
if trace {
defer p.trace("importDecl")()
}
d := new(ImportDecl)
d.pos = p.pos()
d.Group = group
d.Pragma = p.takePragma()
switch p.tok {
case _Name:
d.LocalPkgName = p.name()
case _Dot:
d.LocalPkgName = NewName(p.pos(), ".")
p.next()
}
d.Path = p.oliteral()
if d.Path == nil {
p.syntaxError("missing import path")
p.advance(_Semi, _Rparen)
return d
}
if !d.Path.Bad && d.Path.Kind != StringLit {
p.syntaxError("import path must be a string")
d.Path.Bad = true
}
// d.Path.Bad || d.Path.Kind == StringLit
return d
}
// ConstSpec = IdentifierList [ [ Type ] "=" ExpressionList ] .
func (p *parser) constDecl(group *Group) Decl {
if trace {
defer p.trace("constDecl")()
}
d := new(ConstDecl)
d.pos = p.pos()
d.Group = group
d.Pragma = p.takePragma()
d.NameList = p.nameList(p.name())
if p.tok != _EOF && p.tok != _Semi && p.tok != _Rparen {
d.Type = p.typeOrNil()
if p.gotAssign() {
d.Values = p.exprList()
}
}
return d
}
// TypeSpec = identifier [ TypeParams ] [ "=" ] Type .
func (p *parser) typeDecl(group *Group) Decl {
if trace {
defer p.trace("typeDecl")()
}
d := new(TypeDecl)
d.pos = p.pos()
d.Group = group
d.Pragma = p.takePragma()
d.Name = p.name()
if p.tok == _Lbrack {
// d.Name "[" ...
// array/slice type or type parameter list
pos := p.pos()
p.next()
switch p.tok {
case _Name:
// 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 Expr = p.name()
if p.tok != _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 parser.pexpr.
p.xnest++
x = p.binaryExpr(p.pexpr(x, false), 0)
p.xnest--
}
// 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 == _Comma); pname != nil && (ptype != nil || p.tok != _Rbrack) {
// d.Name "[" pname ...
// d.Name "[" pname ptype ...
// d.Name "[" pname ptype "," ...
d.TParamList = p.paramList(pname, ptype, _Rbrack, true) // ptype may be nil
d.Alias = p.gotAssign()
d.Type = p.typeOrNil()
} else {
// d.Name "[" pname "]" ...
// d.Name "[" x ...
d.Type = p.arrayType(pos, x)
}
case _Rbrack:
// d.Name "[" "]" ...
p.next()
d.Type = p.sliceType(pos)
default:
// d.Name "[" ...
d.Type = p.arrayType(pos, nil)
}
} else {
d.Alias = p.gotAssign()
d.Type = p.typeOrNil()
}
if d.Type == nil {
d.Type = p.badExpr()
p.syntaxError("in type declaration")
p.advance(_Semi, _Rparen)
}
return d
}
// 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 Expr, force bool) (*Name, Expr) {
switch x := x.(type) {
case *Name:
return x, nil
case *Operation:
if x.Y == nil {
break // unary expr
}
switch x.Op {
case Mul:
if name, _ := x.X.(*Name); name != nil && (force || isTypeElem(x.Y)) {
// x = name *x.Y
op := *x
op.X, op.Y = op.Y, nil // change op into unary *op.Y
return name, &op
}
case 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 *CallExpr:
if name, _ := x.Fun.(*Name); name != nil {
if len(x.ArgList) == 1 && !x.HasDots && (force || isTypeElem(x.ArgList[0])) {
// x = name "(" x.ArgList[0] ")"
return name, x.ArgList[0]
}
}
}
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 Expr) bool {
switch x := x.(type) {
case *ArrayType, *StructType, *FuncType, *InterfaceType, *SliceType, *MapType, *ChanType:
return true
case *Operation:
return isTypeElem(x.X) || (x.Y != nil && isTypeElem(x.Y)) || x.Op == Tilde
case *ParenExpr:
return isTypeElem(x.X)
}
return false
}
// VarSpec = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) .
func (p *parser) varDecl(group *Group) Decl {
if trace {
defer p.trace("varDecl")()
}
d := new(VarDecl)
d.pos = p.pos()
d.Group = group
d.Pragma = p.takePragma()
d.NameList = p.nameList(p.name())
if p.gotAssign() {
d.Values = p.exprList()
} else {
d.Type = p.type_()
if p.gotAssign() {
d.Values = p.exprList()
}
}
return d
}
// FunctionDecl = "func" FunctionName [ TypeParams ] ( Function | Signature ) .
// FunctionName = identifier .
// Function = Signature FunctionBody .
// MethodDecl = "func" Receiver MethodName ( Function | Signature ) .
// Receiver = Parameters .
func (p *parser) funcDeclOrNil() *FuncDecl {
if trace {
defer p.trace("funcDecl")()
}
f := new(FuncDecl)
f.pos = p.pos()
f.Pragma = p.takePragma()
if p.got(_Lparen) {
rcvr := p.paramList(nil, nil, _Rparen, false)
switch len(rcvr) {
case 0:
p.error("method has no receiver")
default:
p.error("method has multiple receivers")
fallthrough
case 1:
f.Recv = rcvr[0]
}
}
if p.tok != _Name {
p.syntaxError("expecting name or (")
p.advance(_Lbrace, _Semi)
return nil
}
f.Name = p.name()
context := ""
if f.Recv != nil {
context = "method" // don't permit (method) type parameters in funcType
}
f.TParamList, f.Type = p.funcType(context)
if p.tok == _Lbrace {
f.Body = p.funcBody()
}
return f
}
func (p *parser) funcBody() *BlockStmt {
p.fnest++
errcnt := p.errcnt
body := p.blockStmt("")
p.fnest--
// Don't check branches if there were syntax errors in the function
// as it may lead to spurious errors (e.g., see test/switch2.go) or
// possibly crashes due to incomplete syntax trees.
if p.mode&CheckBranches != 0 && errcnt == p.errcnt {
checkBranches(body, p.errh)
}
return body
}
// ----------------------------------------------------------------------------
// Expressions
func (p *parser) expr() Expr {
if trace {
defer p.trace("expr")()
}
return p.binaryExpr(nil, 0)
}
// Expression = UnaryExpr | Expression binary_op Expression .
func (p *parser) binaryExpr(x Expr, prec int) Expr {
// don't trace binaryExpr - only leads to overly nested trace output
if x == nil {
x = p.unaryExpr()
}
for (p.tok == _Operator || p.tok == _Star) && p.prec > prec {
t := new(Operation)
t.pos = p.pos()
t.Op = p.op
tprec := p.prec
p.next()
t.X = x
t.Y = p.binaryExpr(nil, tprec)
x = t
}
return x
}
// UnaryExpr = PrimaryExpr | unary_op UnaryExpr .
func (p *parser) unaryExpr() Expr {
if trace {
defer p.trace("unaryExpr")()
}
switch p.tok {
case _Operator, _Star:
switch p.op {
case Mul, Add, Sub, Not, Xor, Tilde:
x := new(Operation)
x.pos = p.pos()
x.Op = p.op
p.next()
x.X = p.unaryExpr()
return x
case And:
x := new(Operation)
x.pos = p.pos()
x.Op = And
p.next()
// unaryExpr may have returned a parenthesized composite literal
// (see comment in operand) - remove parentheses if any
x.X = unparen(p.unaryExpr())
return x
}
case _Arrow:
// receive op (<-x) or receive-only channel (<-chan E)
pos := p.pos()
p.next()
// If the next token is _Chan we still don't know if it is
// a channel (<-chan int) or a receive op (<-chan int(ch)).
// We only know once we have found the end of the unaryExpr.
x := p.unaryExpr()
// There are two cases:
//
// <-chan... => <-x is a channel type
// <-x => <-x is a receive operation
//
// In the first case, <- must be re-associated with
// the channel type parsed already:
//
// <-(chan E) => (<-chan E)
// <-(chan<-E) => (<-chan (<-E))
if _, ok := x.(*ChanType); ok {
// x is a channel type => re-associate <-
dir := SendOnly
t := x
for dir == SendOnly {
c, ok := t.(*ChanType)
if !ok {
break
}
dir = c.Dir
if dir == RecvOnly {
// t is type <-chan E but <-<-chan E is not permitted
// (report same error as for "type _ <-<-chan E")
p.syntaxError("unexpected <-, expecting chan")
// already progressed, no need to advance
}
c.Dir = RecvOnly
t = c.Elem
}
if dir == SendOnly {
// channel dir is <- but channel element E is not a channel
// (report same error as for "type _ <-chan<-E")
p.syntaxError(fmt.Sprintf("unexpected %s, expecting chan", String(t)))
// already progressed, no need to advance
}
return x
}
// x is not a channel type => we have a receive op
o := new(Operation)
o.pos = pos
o.Op = Recv
o.X = x
return o
}
// TODO(mdempsky): We need parens here so we can report an
// error for "(x) := true". It should be possible to detect
// and reject that more efficiently though.
return p.pexpr(nil, true)
}
// callStmt parses call-like statements that can be preceded by 'defer' and 'go'.
func (p *parser) callStmt() *CallStmt {
if trace {
defer p.trace("callStmt")()
}
s := new(CallStmt)
s.pos = p.pos()
s.Tok = p.tok // _Defer or _Go
p.next()
x := p.pexpr(nil, p.tok == _Lparen) // keep_parens so we can report error below
if t := unparen(x); t != x {
p.errorAt(x.Pos(), fmt.Sprintf("expression in %s must not be parenthesized", s.Tok))
// already progressed, no need to advance
x = t
}
cx, ok := x.(*CallExpr)
if !ok {
p.errorAt(x.Pos(), fmt.Sprintf("expression in %s must be function call", s.Tok))
// already progressed, no need to advance
cx = new(CallExpr)
cx.pos = x.Pos()
cx.Fun = x // assume common error of missing parentheses (function invocation)
}
s.Call = cx
return s
}
// Operand = Literal | OperandName | MethodExpr | "(" Expression ")" .
// Literal = BasicLit | CompositeLit | FunctionLit .
// BasicLit = int_lit | float_lit | imaginary_lit | rune_lit | string_lit .
// OperandName = identifier | QualifiedIdent.
func (p *parser) operand(keep_parens bool) Expr {
if trace {
defer p.trace("operand " + p.tok.String())()
}
switch p.tok {
case _Name:
return p.name()
case _Literal:
return p.oliteral()
case _Lparen:
pos := p.pos()
p.next()
p.xnest++
x := p.expr()
p.xnest--
p.want(_Rparen)
// Optimization: Record presence of ()'s only where needed
// for error reporting. Don't bother in other cases; it is
// just a waste of memory and time.
//
// Parentheses are not permitted around T in a composite
// literal T{}. If the next token is a {, assume x is a
// composite literal type T (it may not be, { could be
// the opening brace of a block, but we don't know yet).
if p.tok == _Lbrace {
keep_parens = true
}
// Parentheses are also not permitted around the expression
// in a go/defer statement. In that case, operand is called
// with keep_parens set.
if keep_parens {
px := new(ParenExpr)
px.pos = pos
px.X = x
x = px
}
return x
case _Func:
pos := p.pos()
p.next()
_, ftyp := p.funcType("function type")
if p.tok == _Lbrace {
p.xnest++
f := new(FuncLit)
f.pos = pos
f.Type = ftyp
f.Body = p.funcBody()
p.xnest--
return f
}
return ftyp
case _Lbrack, _Chan, _Map, _Struct, _Interface:
return p.type_() // othertype
default:
x := p.badExpr()
p.syntaxError("expecting expression")
p.advance(_Rparen, _Rbrack, _Rbrace)
return x
}
// Syntactically, composite literals are operands. Because a complit
// type may be a qualified identifier which is handled by pexpr
// (together with selector expressions), complits are parsed there
// as well (operand is only called from pexpr).
}
// pexpr parses a PrimaryExpr.
//
// PrimaryExpr =
// Operand |
// Conversion |
// PrimaryExpr Selector |
// PrimaryExpr Index |
// PrimaryExpr Slice |
// PrimaryExpr TypeAssertion |
// PrimaryExpr Arguments .
//
// Selector = "." identifier .
// Index = "[" Expression "]" .
// Slice = "[" ( [ Expression ] ":" [ Expression ] ) |
// ( [ Expression ] ":" Expression ":" Expression )
// "]" .
// TypeAssertion = "." "(" Type ")" .
// Arguments = "(" [ ( ExpressionList | Type [ "," ExpressionList ] ) [ "..." ] [ "," ] ] ")" .
func (p *parser) pexpr(x Expr, keep_parens bool) Expr {
if trace {
defer p.trace("pexpr")()
}
if x == nil {
x = p.operand(keep_parens)
}
loop:
for {
pos := p.pos()
switch p.tok {
case _Dot:
p.next()
switch p.tok {
case _Name:
// pexpr '.' sym
t := new(SelectorExpr)
t.pos = pos
t.X = x
t.Sel = p.name()
x = t
case _Lparen:
p.next()
if p.got(_Type) {
t := new(TypeSwitchGuard)
// t.Lhs is filled in by parser.simpleStmt
t.pos = pos
t.X = x
x = t
} else {
t := new(AssertExpr)
t.pos = pos
t.X = x
t.Type = p.type_()
x = t
}
p.want(_Rparen)
default:
p.syntaxError("expecting name or (")
p.advance(_Semi, _Rparen)
}
case _Lbrack:
p.next()
if p.tok == _Rbrack {
// invalid empty instance, slice or index expression; accept but complain
p.syntaxError("expecting operand")
p.next()
break
}
var i Expr
if p.tok != _Colon {
var comma bool
i, comma = p.typeList()
if comma || p.tok == _Rbrack {
p.want(_Rbrack)
// x[i,] or x[i, j, ...]
t := new(IndexExpr)
t.pos = pos
t.X = x
t.Index = i
x = t
break
}
}
// x[i:...
// For better error message, don't simply use p.want(_Colon) here (issue #47704).
if !p.got(_Colon) {
p.syntaxError("expecting comma, : or ]")
p.advance(_Comma, _Colon, _Rbrack)
}
p.xnest++
t := new(SliceExpr)
t.pos = pos
t.X = x
t.Index[0] = i
if p.tok != _Colon && p.tok != _Rbrack {
// x[i:j...
t.Index[1] = p.expr()
}
if p.tok == _Colon {
t.Full = true
// x[i:j:...]
if t.Index[1] == nil {
p.error("middle index required in 3-index slice")
t.Index[1] = p.badExpr()
}
p.next()
if p.tok != _Rbrack {
// x[i:j:k...
t.Index[2] = p.expr()
} else {
p.error("final index required in 3-index slice")
t.Index[2] = p.badExpr()
}
}
p.xnest--
p.want(_Rbrack)
x = t
case _Lparen:
t := new(CallExpr)
t.pos = pos
p.next()
t.Fun = x
t.ArgList, t.HasDots = p.argList()
x = t
case _Lbrace:
// operand may have returned a parenthesized complit
// type; accept it but complain if we have a complit
t := unparen(x)
// determine if '{' belongs to a composite literal or a block statement
complit_ok := false
switch t.(type) {
case *Name, *SelectorExpr:
if p.xnest >= 0 {
// x is possibly a composite literal type
complit_ok = true
}
case *IndexExpr:
if p.xnest >= 0 && !isValue(t) {
// x is possibly a composite literal type
complit_ok = true
}
case *ArrayType, *SliceType, *StructType, *MapType:
// x is a comptype
complit_ok = true
}
if !complit_ok {
break loop
}
if t != x {
p.syntaxError("cannot parenthesize type in composite literal")
// already progressed, no need to advance
}
n := p.complitexpr()
n.Type = x
x = n
default:
break loop
}
}
return x
}
// isValue reports whether x syntactically must be a value (and not a type) expression.
func isValue(x Expr) bool {
switch x := x.(type) {
case *BasicLit, *CompositeLit, *FuncLit, *SliceExpr, *AssertExpr, *TypeSwitchGuard, *CallExpr:
return true
case *Operation:
return x.Op != Mul || x.Y != nil // *T may be a type
case *ParenExpr:
return isValue(x.X)
case *IndexExpr:
return isValue(x.X) || isValue(x.Index)
}
return false
}
// Element = Expression | LiteralValue .
func (p *parser) bare_complitexpr() Expr {
if trace {
defer p.trace("bare_complitexpr")()
}
if p.tok == _Lbrace {
// '{' start_complit braced_keyval_list '}'
return p.complitexpr()
}
return p.expr()
}
// LiteralValue = "{" [ ElementList [ "," ] ] "}" .
func (p *parser) complitexpr() *CompositeLit {
if trace {
defer p.trace("complitexpr")()
}
x := new(CompositeLit)
x.pos = p.pos()
p.xnest++
p.want(_Lbrace)
x.Rbrace = p.list("composite literal", _Comma, _Rbrace, func() bool {
// value
e := p.bare_complitexpr()
if p.tok == _Colon {
// key ':' value
l := new(KeyValueExpr)
l.pos = p.pos()
p.next()
l.Key = e
l.Value = p.bare_complitexpr()
e = l
x.NKeys++
}
x.ElemList = append(x.ElemList, e)
return false
})
p.xnest--
return x
}
// ----------------------------------------------------------------------------
// Types
func (p *parser) type_() Expr {
if trace {
defer p.trace("type_")()
}
typ := p.typeOrNil()
if typ == nil {
typ = p.badExpr()
p.syntaxError("expecting type")
p.advance(_Comma, _Colon, _Semi, _Rparen, _Rbrack, _Rbrace)
}
return typ
}
func newIndirect(pos Pos, typ Expr) Expr {
o := new(Operation)
o.pos = pos
o.Op = Mul
o.X = typ
return o
}
// typeOrNil is like type_ but it returns nil if there was no type
// instead of reporting an error.
//
// Type = TypeName | TypeLit | "(" Type ")" .
// TypeName = identifier | QualifiedIdent .
// TypeLit = ArrayType | StructType | PointerType | FunctionType | InterfaceType |
// SliceType | MapType | Channel_Type .
func (p *parser) typeOrNil() Expr {
if trace {
defer p.trace("typeOrNil")()
}
pos := p.pos()
switch p.tok {
case _Star:
// ptrtype
p.next()
return newIndirect(pos, p.type_())
case _Arrow:
// recvchantype
p.next()
p.want(_Chan)
t := new(ChanType)
t.pos = pos
t.Dir = RecvOnly
t.Elem = p.chanElem()
return t
case _Func:
// fntype
p.next()
_, t := p.funcType("function type")
return t
case _Lbrack:
// '[' oexpr ']' ntype
// '[' _DotDotDot ']' ntype
p.next()
if p.got(_Rbrack) {
return p.sliceType(pos)
}
return p.arrayType(pos, nil)
case _Chan:
// _Chan non_recvchantype
// _Chan _Comm ntype
p.next()
t := new(ChanType)
t.pos = pos
if p.got(_Arrow) {
t.Dir = SendOnly
}
t.Elem = p.chanElem()
return t
case _Map:
// _Map '[' ntype ']' ntype
p.next()
p.want(_Lbrack)
t := new(MapType)
t.pos = pos
t.Key = p.type_()
p.want(_Rbrack)
t.Value = p.type_()
return t
case _Struct:
return p.structType()
case _Interface:
return p.interfaceType()
case _Name:
return p.qualifiedName(nil)
case _Lparen:
p.next()
t := p.type_()
p.want(_Rparen)
return t
}
return nil
}
func (p *parser) typeInstance(typ Expr) Expr {
if trace {
defer p.trace("typeInstance")()
}
pos := p.pos()
p.want(_Lbrack)
x := new(IndexExpr)
x.pos = pos
x.X = typ
if p.tok == _Rbrack {
p.syntaxError("expecting type")
x.Index = p.badExpr()
} else {
x.Index, _ = p.typeList()
}
p.want(_Rbrack)
return x
}
// If context != "", type parameters are not permitted.
func (p *parser) funcType(context string) ([]*Field, *FuncType) {
if trace {
defer p.trace("funcType")()
}
typ := new(FuncType)
typ.pos = p.pos()
var tparamList []*Field
if p.got(_Lbrack) {
if context != "" {
// accept but complain
p.syntaxErrorAt(typ.pos, context+" must have no type parameters")
}
if p.tok == _Rbrack {
p.syntaxError("empty type parameter list")
p.next()
} else {
tparamList = p.paramList(nil, nil, _Rbrack, true)
}
}
p.want(_Lparen)
typ.ParamList = p.paramList(nil, nil, _Rparen, false)
typ.ResultList = p.funcResult()
return tparamList, typ
}
// "[" has already been consumed, and pos is its position.
// If len != nil it is the already consumed array length.
func (p *parser) arrayType(pos Pos, len Expr) Expr {
if trace {
defer p.trace("arrayType")()
}
if len == nil && !p.got(_DotDotDot) {
p.xnest++
len = p.expr()
p.xnest--
}
if p.tok == _Comma {
// Trailing commas are accepted in type parameter
// lists but not in array type declarations.
// Accept for better error handling but complain.
p.syntaxError("unexpected comma; expecting ]")
p.next()
}
p.want(_Rbrack)
t := new(ArrayType)
t.pos = pos
t.Len = len
t.Elem = p.type_()
return t
}
// "[" and "]" have already been consumed, and pos is the position of "[".
func (p *parser) sliceType(pos Pos) Expr {
t := new(SliceType)
t.pos = pos
t.Elem = p.type_()
return t
}
func (p *parser) chanElem() Expr {
if trace {
defer p.trace("chanElem")()
}
typ := p.typeOrNil()
if typ == nil {
typ = p.badExpr()
p.syntaxError("missing channel element type")
// assume element type is simply absent - don't advance
}
return typ
}
// StructType = "struct" "{" { FieldDecl ";" } "}" .
func (p *parser) structType() *StructType {
if trace {
defer p.trace("structType")()
}
typ := new(StructType)
typ.pos = p.pos()
p.want(_Struct)
p.want(_Lbrace)
p.list("struct type", _Semi, _Rbrace, func() bool {
p.fieldDecl(typ)
return false
})
return typ
}
// InterfaceType = "interface" "{" { ( MethodDecl | EmbeddedElem | TypeList ) ";" } "}" .
// TypeList = "type" Type { "," Type } .
func (p *parser) interfaceType() *InterfaceType {
if trace {
defer p.trace("interfaceType")()
}
typ := new(InterfaceType)
typ.pos = p.pos()
p.want(_Interface)
p.want(_Lbrace)
p.list("interface type", _Semi, _Rbrace, func() bool {
var f *Field
if p.tok == _Name {
f = p.methodDecl()
}
if f == nil || f.Name == nil {
f = p.embeddedElem(f)
}
typ.MethodList = append(typ.MethodList, f)
return false
})
return typ
}
// Result = Parameters | Type .
func (p *parser) funcResult() []*Field {
if trace {
defer p.trace("funcResult")()
}
if p.got(_Lparen) {
return p.paramList(nil, nil, _Rparen, false)
}
pos := p.pos()
if typ := p.typeOrNil(); typ != nil {
f := new(Field)
f.pos = pos
f.Type = typ
return []*Field{f}
}
return nil
}
func (p *parser) addField(styp *StructType, pos Pos, name *Name, typ Expr, tag *BasicLit) {
if tag != nil {
for i := len(styp.FieldList) - len(styp.TagList); i > 0; i-- {
styp.TagList = append(styp.TagList, nil)
}
styp.TagList = append(styp.TagList, tag)
}
f := new(Field)
f.pos = pos
f.Name = name
f.Type = typ
styp.FieldList = append(styp.FieldList, f)
if debug && tag != nil && len(styp.FieldList) != len(styp.TagList) {
panic("inconsistent struct field list")
}
}
// FieldDecl = (IdentifierList Type | AnonymousField) [ Tag ] .
// AnonymousField = [ "*" ] TypeName .
// Tag = string_lit .
func (p *parser) fieldDecl(styp *StructType) {
if trace {
defer p.trace("fieldDecl")()
}
pos := p.pos()
switch p.tok {
case _Name:
name := p.name()
if p.tok == _Dot || p.tok == _Literal || p.tok == _Semi || p.tok == _Rbrace {
// embedded type
typ := p.qualifiedName(name)
tag := p.oliteral()
p.addField(styp, pos, nil, typ, tag)
break
}
// name1, name2, ... Type [ tag ]
names := p.nameList(name)
var typ Expr
// Careful dance: We don't know if we have an embedded instantiated
// type T[P1, P2, ...] or a field T of array/slice type [P]E or []E.
if len(names) == 1 && p.tok == _Lbrack {
typ = p.arrayOrTArgs()
if typ, ok := typ.(*IndexExpr); ok {
// embedded type T[P1, P2, ...]
typ.X = name // name == names[0]
tag := p.oliteral()
p.addField(styp, pos, nil, typ, tag)
break
}
} else {
// T P
typ = p.type_()
}
tag := p.oliteral()
for _, name := range names {
p.addField(styp, name.Pos(), name, typ, tag)
}
case _Star:
p.next()
var typ Expr
if p.tok == _Lparen {
// *(T)
p.syntaxError("cannot parenthesize embedded type")
p.next()
typ = p.qualifiedName(nil)
p.got(_Rparen) // no need to complain if missing
} else {
// *T
typ = p.qualifiedName(nil)
}
tag := p.oliteral()
p.addField(styp, pos, nil, newIndirect(pos, typ), tag)
case _Lparen:
p.syntaxError("cannot parenthesize embedded type")
p.next()
var typ Expr
if p.tok == _Star {
// (*T)
pos := p.pos()
p.next()
typ = newIndirect(pos, p.qualifiedName(nil))
} else {
// (T)
typ = p.qualifiedName(nil)
}
p.got(_Rparen) // no need to complain if missing
tag := p.oliteral()
p.addField(styp, pos, nil, typ, tag)
default:
p.syntaxError("expecting field name or embedded type")
p.advance(_Semi, _Rbrace)
}
}
func (p *parser) arrayOrTArgs() Expr {
if trace {
defer p.trace("arrayOrTArgs")()
}
pos := p.pos()
p.want(_Lbrack)
if p.got(_Rbrack) {
return p.sliceType(pos)
}
// x [n]E or x[n,], x[n1, n2], ...
n, comma := p.typeList()
p.want(_Rbrack)
if !comma {
if elem := p.typeOrNil(); elem != nil {
// x [n]E
t := new(ArrayType)
t.pos = pos
t.Len = n
t.Elem = elem
return t
}
}
// x[n,], x[n1, n2], ...
t := new(IndexExpr)
t.pos = pos
// t.X will be filled in by caller
t.Index = n
return t
}
func (p *parser) oliteral() *BasicLit {
if p.tok == _Literal {
b := new(BasicLit)
b.pos = p.pos()
b.Value = p.lit
b.Kind = p.kind
b.Bad = p.bad
p.next()
return b
}
return nil
}
// MethodSpec = MethodName Signature | InterfaceTypeName .
// MethodName = identifier .
// InterfaceTypeName = TypeName .
func (p *parser) methodDecl() *Field {
if trace {
defer p.trace("methodDecl")()
}
f := new(Field)
f.pos = p.pos()
name := p.name()
const context = "interface method"
switch p.tok {
case _Lparen:
// method
f.Name = name
_, f.Type = p.funcType(context)
case _Lbrack:
// Careful dance: We don't know if we have a generic method m[T C](x T)
// or an embedded instantiated type T[P1, P2] (we accept generic methods
// for generality and robustness of parsing but complain with an error).
pos := p.pos()
p.next()
// Empty type parameter or argument lists are not permitted.
// Treat as if [] were absent.
if p.tok == _Rbrack {
// name[]
pos := p.pos()
p.next()
if p.tok == _Lparen {
// name[](
p.errorAt(pos, "empty type parameter list")
f.Name = name
_, f.Type = p.funcType(context)
} else {
p.errorAt(pos, "empty type argument list")
f.Type = name
}
break
}
// A type argument list looks like a parameter list with only
// types. Parse a parameter list and decide afterwards.
list := p.paramList(nil, nil, _Rbrack, false)
if len(list) == 0 {
// The type parameter list is not [] but we got nothing
// due to other errors (reported by paramList). Treat
// as if [] were absent.
if p.tok == _Lparen {
f.Name = name
_, f.Type = p.funcType(context)
} else {
f.Type = name
}
break
}
// len(list) > 0
if list[0].Name != nil {
// generic method
f.Name = name
_, f.Type = p.funcType(context)
p.errorAt(pos, "interface method must have no type parameters")
break
}
// embedded instantiated type
t := new(IndexExpr)
t.pos = pos
t.X = name
if len(list) == 1 {
t.Index = list[0].Type
} else {
// len(list) > 1
l := new(ListExpr)
l.pos = list[0].Pos()
l.ElemList = make([]Expr, len(list))
for i := range list {
l.ElemList[i] = list[i].Type
}
t.Index = l
}
f.Type = t
default:
// embedded type
f.Type = p.qualifiedName(name)
}
return f
}
// EmbeddedElem = MethodSpec | EmbeddedTerm { "|" EmbeddedTerm } .
func (p *parser) embeddedElem(f *Field) *Field {
if trace {
defer p.trace("embeddedElem")()
}
if f == nil {
f = new(Field)
f.pos = p.pos()
f.Type = p.embeddedTerm()
}
for p.tok == _Operator && p.op == Or {
t := new(Operation)
t.pos = p.pos()
t.Op = Or
p.next()
t.X = f.Type
t.Y = p.embeddedTerm()
f.Type = t
}
return f
}
// EmbeddedTerm = [ "~" ] Type .
func (p *parser) embeddedTerm() Expr {
if trace {
defer p.trace("embeddedTerm")()
}
if p.tok == _Operator && p.op == Tilde {
t := new(Operation)
t.pos = p.pos()
t.Op = Tilde
p.next()
t.X = p.type_()
return t
}
t := p.typeOrNil()
if t == nil {
t = p.badExpr()
p.syntaxError("expecting ~ term or type")
p.advance(_Operator, _Semi, _Rparen, _Rbrack, _Rbrace)
}
return t
}
// ParameterDecl = [ IdentifierList ] [ "..." ] Type .
func (p *parser) paramDeclOrNil(name *Name, follow token) *Field {
if trace {
defer p.trace("paramDeclOrNil")()
}
// type set notation is ok in type parameter lists
typeSetsOk := follow == _Rbrack
pos := p.pos()
if name != nil {
pos = name.pos
} else if typeSetsOk && p.tok == _Operator && p.op == Tilde {
// "~" ...
return p.embeddedElem(nil)
}
f := new(Field)
f.pos = pos
if p.tok == _Name || name != nil {
// name
if name == nil {
name = p.name()
}
if p.tok == _Lbrack {
// name "[" ...
f.Type = p.arrayOrTArgs()
if typ, ok := f.Type.(*IndexExpr); ok {
// name "[" ... "]"
typ.X = name
} else {
// name "[" n "]" E
f.Name = name
}
if typeSetsOk && p.tok == _Operator && p.op == Or {
// name "[" ... "]" "|" ...
// name "[" n "]" E "|" ...
f = p.embeddedElem(f)
}
return f
}
if p.tok == _Dot {
// name "." ...
f.Type = p.qualifiedName(name)
if typeSetsOk && p.tok == _Operator && p.op == Or {
// name "." name "|" ...
f = p.embeddedElem(f)
}
return f
}
if typeSetsOk && p.tok == _Operator && p.op == Or {
// name "|" ...
f.Type = name
return p.embeddedElem(f)
}
f.Name = name
}
if p.tok == _DotDotDot {
// [name] "..." ...
t := new(DotsType)
t.pos = p.pos()
p.next()
t.Elem = p.typeOrNil()
if t.Elem == nil {
t.Elem = p.badExpr()
p.syntaxError("... is missing type")
}
f.Type = t
return f
}
if typeSetsOk && p.tok == _Operator && p.op == Tilde {
// [name] "~" ...
f.Type = p.embeddedElem(nil).Type
return f
}
f.Type = p.typeOrNil()
if typeSetsOk && p.tok == _Operator && p.op == Or && f.Type != nil {
// [name] type "|"
f = p.embeddedElem(f)
}
if f.Name != nil || f.Type != nil {
return f
}
p.syntaxError("expecting " + tokstring(follow))
p.advance(_Comma, follow)
return nil
}
// Parameters = "(" [ ParameterList [ "," ] ] ")" .
// ParameterList = ParameterDecl { "," ParameterDecl } .
// "(" or "[" has already been consumed.
// If name != nil, it is the first name after "(" or "[".
// If typ != nil, name must be != nil, and (name, typ) is the first field in the list.
// In the result list, either all fields have a name, or no field has a name.
func (p *parser) paramList(name *Name, typ Expr, close token, requireNames bool) (list []*Field) {
if trace {
defer p.trace("paramList")()
}
// p.list won't invoke its function argument if we're at the end of the
// parameter list. If we have a complete field, handle this case here.
if name != nil && typ != nil && p.tok == close {
p.next()
par := new(Field)
par.pos = name.pos
par.Name = name
par.Type = typ
return []*Field{par}
}
var named int // number of parameters that have an explicit name and type
var typed int // number of parameters that have an explicit type
end := p.list("parameter list", _Comma, close, func() bool {
var par *Field
if typ != nil {
if debug && name == nil {
panic("initial type provided without name")
}
par = new(Field)
par.pos = name.pos
par.Name = name
par.Type = typ
} else {
par = p.paramDeclOrNil(name, close)
}
name = nil // 1st name was consumed if present
typ = nil // 1st type was consumed if present
if par != nil {
if debug && par.Name == nil && par.Type == nil {
panic("parameter without name or type")
}
if par.Name != nil && par.Type != nil {
named++
}
if par.Type != nil {
typed++
}
list = append(list, par)
}
return false
})
if len(list) == 0 {
return
}
// distribute parameter types (len(list) > 0)
if named == 0 && !requireNames {
// all unnamed => found names are named types
for _, par := range list {
if typ := par.Name; typ != nil {
par.Type = typ
par.Name = nil
}
}
} else if named != len(list) {
// some named => all must have names and types
var pos Pos // left-most error position (or unknown)
var typ Expr // current type (from right to left)
for i := len(list) - 1; i >= 0; i-- {
par := list[i]
if par.Type != nil {
typ = par.Type
if par.Name == nil {
pos = StartPos(typ)
par.Name = NewName(pos, "_")
}
} else if typ != nil {
par.Type = typ
} else {
// par.Type == nil && typ == nil => we only have a par.Name
pos = par.Name.Pos()
t := p.badExpr()
t.pos = pos // correct position
par.Type = t
}
}
if pos.IsKnown() {
var msg string
if requireNames {
if named == typed {
pos = end // position error at closing ]
msg = "missing type constraint"
} else {
msg = "type parameters must be named"
}
} else {
msg = "mixed named and unnamed parameters"
}
p.syntaxErrorAt(pos, msg)
}
}
return
}
func (p *parser) badExpr() *BadExpr {
b := new(BadExpr)
b.pos = p.pos()
return b
}
// ----------------------------------------------------------------------------
// Statements
// SimpleStmt = EmptyStmt | ExpressionStmt | SendStmt | IncDecStmt | Assignment | ShortVarDecl .
func (p *parser) simpleStmt(lhs Expr, keyword token) SimpleStmt {
if trace {
defer p.trace("simpleStmt")()
}
if keyword == _For && p.tok == _Range {
// _Range expr
if debug && lhs != nil {
panic("invalid call of simpleStmt")
}
return p.newRangeClause(nil, false)
}
if lhs == nil {
lhs = p.exprList()
}
if _, ok := lhs.(*ListExpr); !ok && p.tok != _Assign && p.tok != _Define {
// expr
pos := p.pos()
switch p.tok {
case _AssignOp:
// lhs op= rhs
op := p.op
p.next()
return p.newAssignStmt(pos, op, lhs, p.expr())
case _IncOp:
// lhs++ or lhs--
op := p.op
p.next()
return p.newAssignStmt(pos, op, lhs, nil)
case _Arrow:
// lhs <- rhs
s := new(SendStmt)
s.pos = pos
p.next()
s.Chan = lhs
s.Value = p.expr()
return s
default:
// expr
s := new(ExprStmt)
s.pos = lhs.Pos()
s.X = lhs
return s
}
}
// expr_list
switch p.tok {
case _Assign, _Define:
pos := p.pos()
var op Operator
if p.tok == _Define {
op = Def
}
p.next()
if keyword == _For && p.tok == _Range {
// expr_list op= _Range expr
return p.newRangeClause(lhs, op == Def)
}
// expr_list op= expr_list
rhs := p.exprList()
if x, ok := rhs.(*TypeSwitchGuard); ok && keyword == _Switch && op == Def {
if lhs, ok := lhs.(*Name); ok {
// switch … lhs := rhs.(type)
x.Lhs = lhs
s := new(ExprStmt)
s.pos = x.Pos()
s.X = x
return s
}
}
return p.newAssignStmt(pos, op, lhs, rhs)
default:
p.syntaxError("expecting := or = or comma")
p.advance(_Semi, _Rbrace)
// make the best of what we have
if x, ok := lhs.(*ListExpr); ok {
lhs = x.ElemList[0]
}
s := new(ExprStmt)
s.pos = lhs.Pos()
s.X = lhs
return s
}
}
func (p *parser) newRangeClause(lhs Expr, def bool) *RangeClause {
r := new(RangeClause)
r.pos = p.pos()
p.next() // consume _Range
r.Lhs = lhs
r.Def = def
r.X = p.expr()
return r
}
func (p *parser) newAssignStmt(pos Pos, op Operator, lhs, rhs Expr) *AssignStmt {
a := new(AssignStmt)
a.pos = pos
a.Op = op
a.Lhs = lhs
a.Rhs = rhs
return a
}
func (p *parser) labeledStmtOrNil(label *Name) Stmt {
if trace {
defer p.trace("labeledStmt")()
}
s := new(LabeledStmt)
s.pos = p.pos()
s.Label = label
p.want(_Colon)
if p.tok == _Rbrace {
// We expect a statement (incl. an empty statement), which must be
// terminated by a semicolon. Because semicolons may be omitted before
// an _Rbrace, seeing an _Rbrace implies an empty statement.
e := new(EmptyStmt)
e.pos = p.pos()
s.Stmt = e
return s
}
s.Stmt = p.stmtOrNil()
if s.Stmt != nil {
return s
}
// report error at line of ':' token
p.syntaxErrorAt(s.pos, "missing statement after label")
// we are already at the end of the labeled statement - no need to advance
return nil // avoids follow-on errors (see e.g., fixedbugs/bug274.go)
}
// context must be a non-empty string unless we know that p.tok == _Lbrace.
func (p *parser) blockStmt(context string) *BlockStmt {
if trace {
defer p.trace("blockStmt")()
}
s := new(BlockStmt)
s.pos = p.pos()
// people coming from C may forget that braces are mandatory in Go
if !p.got(_Lbrace) {
p.syntaxError("expecting { after " + context)
p.advance(_Name, _Rbrace)
s.Rbrace = p.pos() // in case we found "}"
if p.got(_Rbrace) {
return s
}
}
s.List = p.stmtList()
s.Rbrace = p.pos()
p.want(_Rbrace)
return s
}
func (p *parser) declStmt(f func(*Group) Decl) *DeclStmt {
if trace {
defer p.trace("declStmt")()
}
s := new(DeclStmt)
s.pos = p.pos()
p.next() // _Const, _Type, or _Var
s.DeclList = p.appendGroup(nil, f)
return s
}
func (p *parser) forStmt() Stmt {
if trace {
defer p.trace("forStmt")()
}
s := new(ForStmt)
s.pos = p.pos()
s.Init, s.Cond, s.Post = p.header(_For)
s.Body = p.blockStmt("for clause")
return s
}
func (p *parser) header(keyword token) (init SimpleStmt, cond Expr, post SimpleStmt) {
p.want(keyword)
if p.tok == _Lbrace {
if keyword == _If {
p.syntaxError("missing condition in if statement")
cond = p.badExpr()
}
return
}
// p.tok != _Lbrace
outer := p.xnest
p.xnest = -1
if p.tok != _Semi {
// accept potential varDecl but complain
if p.got(_Var) {
p.syntaxError(fmt.Sprintf("var declaration not allowed in %s initializer", tokstring(keyword)))
}
init = p.simpleStmt(nil, keyword)
// If we have a range clause, we are done (can only happen for keyword == _For).
if _, ok := init.(*RangeClause); ok {
p.xnest = outer
return
}
}
var condStmt SimpleStmt
var semi struct {
pos Pos
lit string // valid if pos.IsKnown()
}
if p.tok != _Lbrace {
if p.tok == _Semi {
semi.pos = p.pos()
semi.lit = p.lit
p.next()
} else {
// asking for a '{' rather than a ';' here leads to a better error message
p.want(_Lbrace)
if p.tok != _Lbrace {
p.advance(_Lbrace, _Rbrace) // for better synchronization (e.g., issue #22581)
}
}
if keyword == _For {
if p.tok != _Semi {
if p.tok == _Lbrace {
p.syntaxError("expecting for loop condition")
goto done
}
condStmt = p.simpleStmt(nil, 0 /* range not permitted */)
}
p.want(_Semi)
if p.tok != _Lbrace {
post = p.simpleStmt(nil, 0 /* range not permitted */)
if a, _ := post.(*AssignStmt); a != nil && a.Op == Def {
p.syntaxErrorAt(a.Pos(), "cannot declare in post statement of for loop")
}
}
} else if p.tok != _Lbrace {
condStmt = p.simpleStmt(nil, keyword)
}
} else {
condStmt = init
init = nil
}
done:
// unpack condStmt
switch s := condStmt.(type) {
case nil:
if keyword == _If && semi.pos.IsKnown() {
if semi.lit != "semicolon" {
p.syntaxErrorAt(semi.pos, fmt.Sprintf("unexpected %s, expecting { after if clause", semi.lit))
} else {
p.syntaxErrorAt(semi.pos, "missing condition in if statement")
}
b := new(BadExpr)
b.pos = semi.pos
cond = b
}
case *ExprStmt:
cond = s.X
default:
// A common syntax error is to write '=' instead of '==',
// which turns an expression into an assignment. Provide
// a more explicit error message in that case to prevent
// further confusion.
var str string
if as, ok := s.(*AssignStmt); ok && as.Op == 0 {
// Emphasize Lhs and Rhs of assignment with parentheses to highlight '='.
// Do it always - it's not worth going through the trouble of doing it
// only for "complex" left and right sides.
str = "assignment (" + String(as.Lhs) + ") = (" + String(as.Rhs) + ")"
} else {
str = String(s)
}
p.syntaxErrorAt(s.Pos(), fmt.Sprintf("cannot use %s as value", str))
}
p.xnest = outer
return
}
func (p *parser) ifStmt() *IfStmt {
if trace {
defer p.trace("ifStmt")()
}
s := new(IfStmt)
s.pos = p.pos()
s.Init, s.Cond, _ = p.header(_If)
s.Then = p.blockStmt("if clause")
if p.got(_Else) {
switch p.tok {
case _If:
s.Else = p.ifStmt()
case _Lbrace:
s.Else = p.blockStmt("")
default:
p.syntaxError("else must be followed by if or statement block")
p.advance(_Name, _Rbrace)
}
}
return s
}
func (p *parser) switchStmt() *SwitchStmt {
if trace {
defer p.trace("switchStmt")()
}
s := new(SwitchStmt)
s.pos = p.pos()
s.Init, s.Tag, _ = p.header(_Switch)
if !p.got(_Lbrace) {
p.syntaxError("missing { after switch clause")
p.advance(_Case, _Default, _Rbrace)
}
for p.tok != _EOF && p.tok != _Rbrace {
s.Body = append(s.Body, p.caseClause())
}
s.Rbrace = p.pos()
p.want(_Rbrace)
return s
}
func (p *parser) selectStmt() *SelectStmt {
if trace {
defer p.trace("selectStmt")()
}
s := new(SelectStmt)
s.pos = p.pos()
p.want(_Select)
if !p.got(_Lbrace) {
p.syntaxError("missing { after select clause")
p.advance(_Case, _Default, _Rbrace)
}
for p.tok != _EOF && p.tok != _Rbrace {
s.Body = append(s.Body, p.commClause())
}
s.Rbrace = p.pos()
p.want(_Rbrace)
return s
}
func (p *parser) caseClause() *CaseClause {
if trace {
defer p.trace("caseClause")()
}
c := new(CaseClause)
c.pos = p.pos()
switch p.tok {
case _Case:
p.next()
c.Cases = p.exprList()
case _Default:
p.next()
default:
p.syntaxError("expecting case or default or }")
p.advance(_Colon, _Case, _Default, _Rbrace)
}
c.Colon = p.pos()
p.want(_Colon)
c.Body = p.stmtList()
return c
}
func (p *parser) commClause() *CommClause {
if trace {
defer p.trace("commClause")()
}
c := new(CommClause)
c.pos = p.pos()
switch p.tok {
case _Case:
p.next()
c.Comm = p.simpleStmt(nil, 0)
// The syntax restricts the possible simple statements here to:
//
// lhs <- x (send statement)
// <-x
// lhs = <-x
// lhs := <-x
//
// All these (and more) are recognized by simpleStmt and invalid
// syntax trees are flagged later, during type checking.
// TODO(gri) eventually may want to restrict valid syntax trees
// here.
case _Default:
p.next()
default:
p.syntaxError("expecting case or default or }")
p.advance(_Colon, _Case, _Default, _Rbrace)
}
c.Colon = p.pos()
p.want(_Colon)
c.Body = p.stmtList()
return c
}
// stmtOrNil parses a statement if one is present, or else returns nil.
//
// Statement =
// Declaration | LabeledStmt | SimpleStmt |
// GoStmt | ReturnStmt | BreakStmt | ContinueStmt | GotoStmt |
// FallthroughStmt | Block | IfStmt | SwitchStmt | SelectStmt | ForStmt |
// DeferStmt .
func (p *parser) stmtOrNil() Stmt {
if trace {
defer p.trace("stmt " + p.tok.String())()
}
// Most statements (assignments) start with an identifier;
// look for it first before doing anything more expensive.
if p.tok == _Name {
p.clearPragma()
lhs := p.exprList()
if label, ok := lhs.(*Name); ok && p.tok == _Colon {
return p.labeledStmtOrNil(label)
}
return p.simpleStmt(lhs, 0)
}
switch p.tok {
case _Var:
return p.declStmt(p.varDecl)
case _Const:
return p.declStmt(p.constDecl)
case _Type:
return p.declStmt(p.typeDecl)
}
p.clearPragma()
switch p.tok {
case _Lbrace:
return p.blockStmt("")
case _Operator, _Star:
switch p.op {
case Add, Sub, Mul, And, Xor, Not:
return p.simpleStmt(nil, 0) // unary operators
}
case _Literal, _Func, _Lparen, // operands
_Lbrack, _Struct, _Map, _Chan, _Interface, // composite types
_Arrow: // receive operator
return p.simpleStmt(nil, 0)
case _For:
return p.forStmt()
case _Switch:
return p.switchStmt()
case _Select:
return p.selectStmt()
case _If:
return p.ifStmt()
case _Fallthrough:
s := new(BranchStmt)
s.pos = p.pos()
p.next()
s.Tok = _Fallthrough
return s
case _Break, _Continue:
s := new(BranchStmt)
s.pos = p.pos()
s.Tok = p.tok
p.next()
if p.tok == _Name {
s.Label = p.name()
}
return s
case _Go, _Defer:
return p.callStmt()
case _Goto:
s := new(BranchStmt)
s.pos = p.pos()
s.Tok = _Goto
p.next()
s.Label = p.name()
return s
case _Return:
s := new(ReturnStmt)
s.pos = p.pos()
p.next()
if p.tok != _Semi && p.tok != _Rbrace {
s.Results = p.exprList()
}
return s
case _Semi:
s := new(EmptyStmt)
s.pos = p.pos()
return s
}
return nil
}
// StatementList = { Statement ";" } .
func (p *parser) stmtList() (l []Stmt) {
if trace {
defer p.trace("stmtList")()
}
for p.tok != _EOF && p.tok != _Rbrace && p.tok != _Case && p.tok != _Default {
s := p.stmtOrNil()
p.clearPragma()
if s == nil {
break
}
l = append(l, s)
// ";" is optional before "}"
if !p.got(_Semi) && p.tok != _Rbrace {
p.syntaxError("at end of statement")
p.advance(_Semi, _Rbrace, _Case, _Default)
p.got(_Semi) // avoid spurious empty statement
}
}
return
}
// argList parses a possibly empty, comma-separated list of arguments,
// optionally followed by a comma (if not empty), and closed by ")".
// The last argument may be followed by "...".
//
// argList = [ arg { "," arg } [ "..." ] [ "," ] ] ")" .
func (p *parser) argList() (list []Expr, hasDots bool) {
if trace {
defer p.trace("argList")()
}
p.xnest++
p.list("argument list", _Comma, _Rparen, func() bool {
list = append(list, p.expr())
hasDots = p.got(_DotDotDot)
return hasDots
})
p.xnest--
return
}
// ----------------------------------------------------------------------------
// Common productions
func (p *parser) name() *Name {
// no tracing to avoid overly verbose output
if p.tok == _Name {
n := NewName(p.pos(), p.lit)
p.next()
return n
}
n := NewName(p.pos(), "_")
p.syntaxError("expecting name")
p.advance()
return n
}
// IdentifierList = identifier { "," identifier } .
// The first name must be provided.
func (p *parser) nameList(first *Name) []*Name {
if trace {
defer p.trace("nameList")()
}
if debug && first == nil {
panic("first name not provided")
}
l := []*Name{first}
for p.got(_Comma) {
l = append(l, p.name())
}
return l
}
// The first name may be provided, or nil.
func (p *parser) qualifiedName(name *Name) Expr {
if trace {
defer p.trace("qualifiedName")()
}
var x Expr
switch {
case name != nil:
x = name
case p.tok == _Name:
x = p.name()
default:
x = NewName(p.pos(), "_")
p.syntaxError("expecting name")
p.advance(_Dot, _Semi, _Rbrace)
}
if p.tok == _Dot {
s := new(SelectorExpr)
s.pos = p.pos()
p.next()
s.X = x
s.Sel = p.name()
x = s
}
if p.tok == _Lbrack {
x = p.typeInstance(x)
}
return x
}
// ExpressionList = Expression { "," Expression } .
func (p *parser) exprList() Expr {
if trace {
defer p.trace("exprList")()
}
x := p.expr()
if p.got(_Comma) {
list := []Expr{x, p.expr()}
for p.got(_Comma) {
list = append(list, p.expr())
}
t := new(ListExpr)
t.pos = x.Pos()
t.ElemList = list
x = t
}
return x
}
// typeList parses a non-empty, comma-separated list of expressions,
// optionally followed by a comma. The first list element may be any
// expression, all other list elements must be type expressions.
// If there is more than one argument, the result is a *ListExpr.
// The comma result indicates whether there was a (separating or
// trailing) comma.
//
// typeList = arg { "," arg } [ "," ] .
func (p *parser) typeList() (x Expr, comma bool) {
if trace {
defer p.trace("typeList")()
}
p.xnest++
x = p.expr()
if p.got(_Comma) {
comma = true
if t := p.typeOrNil(); t != nil {
list := []Expr{x, t}
for p.got(_Comma) {
if t = p.typeOrNil(); t == nil {
break
}
list = append(list, t)
}
l := new(ListExpr)
l.pos = x.Pos() // == list[0].Pos()
l.ElemList = list
x = l
}
}
p.xnest--
return
}
// unparen removes all parentheses around an expression.
func unparen(x Expr) Expr {
for {
p, ok := x.(*ParenExpr)
if !ok {
break
}
x = p.X
}
return x
}
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