From: Kashav Madan <kshvmdn@gmail.com>
Date: Tue, 27 Jun 2017 23:29:59 +0000 (-0400)
Subject: cmd/compile: avoid duplicate cast error
X-Git-Tag: go1.10beta1~1421
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=d05a1238d6811aa11abf117e668cd9c4f4c15e6a;p=gostls13.git

cmd/compile: avoid duplicate cast error

If an error was already printed during LHS conversion step, we don't reprint
the "cannot convert" error.

In particular, this prevents `_ = int("1")` (and all similar casts) from
resulting in multiple identical error messages being printed.

Fixes #20812.

Change-Id: If6e52c59eab438599d641ecf6f110ebafca740a9
Reviewed-on: https://go-review.googlesource.com/46912
Reviewed-by: Robert Griesemer <gri@golang.org>
---

diff --git a/src/cmd/compile/internal/gc/const.go b/src/cmd/compile/internal/gc/const.go
index a465d4a7bb..c6a679ed78 100644
--- a/src/cmd/compile/internal/gc/const.go
+++ b/src/cmd/compile/internal/gc/const.go
@@ -408,7 +408,7 @@ func convlit1(n *Node, t *types.Type, explicit bool, reuse canReuseNode) *Node {
 bad:
 	if !n.Diag() {
 		if !t.Broke() {
-			yyerror("cannot convert %v to type %v", n, t)
+			yyerror("cannot convert %L to type %v", n, t)
 		}
 		n.SetDiag(true)
 	}
diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index b809a8bee7..2f30581cb8 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -1760,7 +1760,7 @@ OpSwitch:
 		var why string
 		n.Op = convertop(t, n.Type, &why)
 		if n.Op == 0 {
-			if !n.Diag() && !n.Type.Broke() {
+			if !n.Diag() && !n.Type.Broke() && !n.Left.Diag() {
 				yyerror("cannot convert %L to type %v%s", n.Left, n.Type, why)
 				n.SetDiag(true)
 			}
diff --git a/test/fixedbugs/issue20812.go b/test/fixedbugs/issue20812.go
new file mode 100644
index 0000000000..0175eede17
--- /dev/null
+++ b/test/fixedbugs/issue20812.go
@@ -0,0 +1,15 @@
+// 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() {
+	_ = int("1")      // ERROR "cannot convert"
+	_ = bool(0)       // ERROR "cannot convert"
+	_ = bool("false") // ERROR "cannot convert"
+	_ = int(false)    // ERROR "cannot convert"
+	_ = string(true)  // ERROR "cannot convert"
+}
diff --git a/test/rename1.go b/test/rename1.go
index a71e5b2e53..568aa13d44 100644
--- a/test/rename1.go
+++ b/test/rename1.go
@@ -10,10 +10,10 @@
 package main
 
 func main() {
-	var n byte       // ERROR "not a type|expected type"
+	var n byte         // ERROR "not a type|expected type"
 	var y = float32(0) // ERROR "cannot call|expected function"
 	const (
-		a = 1 + iota // ERROR "string|incompatible types" "convert iota"
+		a = 1 + iota // ERROR "invalid operation|incompatible types" "cannot convert iota"
 	)
 
 }