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cmd/compile/internal/syntax: better errors for syntax errors in lists

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For syntax errors in various (syntactic) lists, instead of reporting
a set of "expected" tokens (which may be incomplete), provide context
and mention "possibly missing" tokens. The result is a friendlier and
more accurate error message.

Fixes #49205.

Change-Id: I38ae7bf62febfe790075e62deb33ec8c17d64476
Reviewed-on: https://go-review.googlesource.com/c/go/+/396914
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Robert Griesemer 2022-03-30 13:23:37 -07:00
parent 3b7fce24cd
commit 0775730180
4 changed files with 38 additions and 11 deletions
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16
src/cmd/compile/internal/syntax/parser.go
View file

@ -472,7 +472,7 @@ func isEmptyFuncDecl(dcl Decl) bool {
//
// list = [ f { sep f } [sep] ] close .
//
func (p *parser) list(sep, close token, f func() bool) Pos {
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")
}
@ -482,7 +482,7 @@ func (p *parser) list(sep, close token, f func() bool) Pos {
done = f()
// sep is optional before close
if !p.got(sep) && p.tok != close {
p.syntaxError(fmt.Sprintf("expecting %s or %s", tokstring(sep), tokstring(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
@ -502,7 +502,7 @@ func (p *parser) appendGroup(list []Decl, f func(*Group) Decl) []Decl {
g := new(Group)
p.clearPragma()
p.next() // must consume "(" after calling clearPragma!
p.list(_Semi, _Rparen, func() bool {
p.list("grouped declaration", _Semi, _Rparen, func() bool {
if x := f(g); x != nil {
list = append(list, x)
}
@ -1233,7 +1233,7 @@ func (p *parser) complitexpr() *CompositeLit {
p.xnest++
p.want(_Lbrace)
x.Rbrace = p.list(_Comma, _Rbrace, func() bool {
x.Rbrace = p.list("composite literal", _Comma, _Rbrace, func() bool {
// value
e := p.bare_complitexpr()
if p.tok == _Colon {
@ -1477,7 +1477,7 @@ func (p *parser) structType() *StructType {
p.want(_Struct)
p.want(_Lbrace)
p.list(_Semi, _Rbrace, func() bool {
p.list("struct type", _Semi, _Rbrace, func() bool {
p.fieldDecl(typ)
return false
})
@ -1497,7 +1497,7 @@ func (p *parser) interfaceType() *InterfaceType {
p.want(_Interface)
p.want(_Lbrace)
p.list(_Semi, _Rbrace, func() bool {
p.list("interface type", _Semi, _Rbrace, func() bool {
switch p.tok {
case _Name:
f := p.methodDecl()
@ -1980,7 +1980,7 @@ func (p *parser) paramList(name *Name, typ Expr, close token, requireNames bool)
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(_Comma, close, func() bool {
end := p.list("parameter list", _Comma, close, func() bool {
var par *Field
if typ != nil {
if debug && name == nil {
@ -2660,7 +2660,7 @@ func (p *parser) argList() (list []Expr, hasDots bool) {
}
p.xnest++
p.list(_Comma, _Rparen, func() bool {
p.list("argument list", _Comma, _Rparen, func() bool {
list = append(list, p.expr())
hasDots = p.got(_DotDotDot)
return hasDots