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cmd/compile: suppress errors after "cannot assign to X"

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If the LHS is unassignable, there's no point in trying to make sure
the RHS can be assigned to it or making sure they're realizable
types. This is consistent with go/types.

In particular, this prevents "1 = 2" from causing a panic when "1"
still ends up with the type "untyped int", which is not realizable.

Fixes #20813.

Change-Id: I4710bdaac2e375ef12ec29b888b8ac84fb640e56
Reviewed-on: https://go-review.googlesource.com/46835
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Matthew Dempsky 2017-06-27 12:58:32 -07:00
parent ae238688d2
commit f62c608abb
2 changed files with 14 additions and 3 deletions
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6
src/cmd/compile/internal/gc/typecheck.go
View File

@ -3288,10 +3288,10 @@ func checkassign(stmt *Node, n *Node) {
if n.Op == ODOT && n.Left.Op == OINDEXMAP {
yyerror("cannot assign to struct field %v in map", n)
return
} else {
yyerror("cannot assign to %v", n)
}
yyerror("cannot assign to %v", n)
n.Type = nil
}
func checkassignlist(stmt *Node, l Nodes) {

11
test/fixedbugs/issue20813.go Normal file
View File

@ -0,0 +1,11 @@
// errorcheck
// Copyright 2017 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 p
func f() {
1 = 2 // ERROR "cannot assign to 1"
}