cmd/internal/gc: do not show computed value in type error

Fixes #9076.

Change-Id: Ib41a452fa9aa9fecf19f65c36d13715923548041
Reviewed-on: https://go-review.googlesource.com/1250Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Chris Manghane <cmang@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/gc/fmt.go

@@ -1261,14 +1261,14 @@ func exprfmt(n *Node, prec int) string {
 		return f
 
 	case OLITERAL: // this is a bit of a mess
-		if fmtmode == FErr && n.Sym != nil {
+		if n.Orig != nil && n.Orig != n {
 			var f string
-			f += fmt.Sprintf("%v", Sconv(n.Sym, 0))
+			f += exprfmt(n.Orig, prec)
 			return f
 		}
-		if n.Val.Ctype == CTNIL && n.Orig != nil && n.Orig != n {
+		if fmtmode == FErr && n.Sym != nil {
 			var f string
-			f += exprfmt(n.Orig, prec)
+			f += fmt.Sprintf("%v", Sconv(n.Sym, 0))
 			return f
 		}
 		if n.Type != nil && n.Type != Types[n.Type.Etype] && n.Type != idealbool && n.Type != idealstring {

test/fixedbugs/issue6964.go

@@ -7,5 +7,5 @@
 package main
 
 func main() {
-	_ = string(-4 + 2i + 2) // ERROR "-4\+2i"
+	_ = string(-4 + 2i + 2) // ERROR "-4 \+ 2i"
 }

test/fixedbugs/issue9076.go

+// errorcheck
+
+// Copyright 2014 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.
+
+// Issue 9076: cmd/gc shows computed values in error messages instead of original expression.
+
+package main
+
+import "unsafe"
+
+const Hundred = 100
+var _ int32 = 100/unsafe.Sizeof(int(0)) + 1 // GC_ERROR "100 \/ unsafe.Sizeof\(int\(0\)\) \+ 1"
+var _ int32 = Hundred/unsafe.Sizeof(int(0)) + 1 // GC_ERROR "Hundred \/ unsafe.Sizeof\(int\(0\)\) \+ 1"