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cmd/compile: better recovery after := (rather than =) in declarations

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Before this fix, a mistaken := in a (const/type/var) declaration
ended that declaration with an error from which the parser didn't
recover well. This low-cost change will provide a better error
message and lets the parser recover perfectly.

Fixes #31092.

Change-Id: Ic4f94dc5e29dd00b7ef6d53a80dded638e3cea80
Reviewed-on: https://go-review.googlesource.com/c/go/+/169958
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Robert Griesemer 2019-03-28 13:32:31 -07:00
parent 9da6530faa
commit 4145c5da1f
2 changed files with 34 additions and 4 deletions
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22
src/cmd/compile/internal/syntax/parser.go
View file

@ -170,6 +170,20 @@ func (p *parser) want(tok token) {
}
}
// 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
@ -514,7 +528,7 @@ func (p *parser) constDecl(group *Group) Decl {
d.NameList = p.nameList(p.name())
if p.tok != _EOF && p.tok != _Semi && p.tok != _Rparen {
d.Type = p.typeOrNil()
if p.got(_Assign) {
if p.gotAssign() {
d.Values = p.exprList()
}
}
@ -533,7 +547,7 @@ func (p *parser) typeDecl(group *Group) Decl {
d.pos = p.pos()
d.Name = p.name()
d.Alias = p.got(_Assign)
d.Alias = p.gotAssign()
d.Type = p.typeOrNil()
if d.Type == nil {
d.Type = p.bad()
@ -556,11 +570,11 @@ func (p *parser) varDecl(group *Group) Decl {
d.pos = p.pos()
d.NameList = p.nameList(p.name())
if p.got(_Assign) {
if p.gotAssign() {
d.Values = p.exprList()
} else {
d.Type = p.type_()
if p.got(_Assign) {
if p.gotAssign() {
d.Values = p.exprList()
}
}