From 907736e2fe94c8cd41d3016154f2093280065484 Mon Sep 17 00:00:00 2001
From: Jan Ziak <0xe2.0x9a.0x9b@gmail.com>
Date: Wed, 9 Apr 2014 08:34:17 +0200
Subject: [PATCH] cmd/gc: ignore blank (_) labels in label declarations

Fixes #7538

LGTM=rsc
R=gri, rsc
CC=golang-codereviews
https://golang.org/cl/85040045
---
 src/cmd/gc/gen.c             |  4 ++++
 test/fixedbugs/issue7538a.go | 15 +++++++++++++++
 test/fixedbugs/issue7538b.go | 13 +++++++++++++
 3 files changed, 32 insertions(+)
 create mode 100644 test/fixedbugs/issue7538a.go
 create mode 100644 test/fixedbugs/issue7538b.go

diff --git a/src/cmd/gc/gen.c b/src/cmd/gc/gen.c
index b7cc621792..5a5c1c24c1 100644
--- a/src/cmd/gc/gen.c
+++ b/src/cmd/gc/gen.c
@@ -301,6 +301,10 @@ gen(Node *n)
 		break;
 
 	case OLABEL:
+		if(isblanksym(n->left->sym)) {
+			break;
+		}
+		
 		lab = newlab(n);
 
 		// if there are pending gotos, resolve them all to the current pc.
diff --git a/test/fixedbugs/issue7538a.go b/test/fixedbugs/issue7538a.go
new file mode 100644
index 0000000000..283d9eb1ba
--- /dev/null
+++ b/test/fixedbugs/issue7538a.go
@@ -0,0 +1,15 @@
+// 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 7538: blank (_) labels handled incorrectly
+
+package p
+
+func f() {
+_:
+_:
+	goto _ // ERROR "not defined"
+}
diff --git a/test/fixedbugs/issue7538b.go b/test/fixedbugs/issue7538b.go
new file mode 100644
index 0000000000..28cef5d608
--- /dev/null
+++ b/test/fixedbugs/issue7538b.go
@@ -0,0 +1,13 @@
+// compile
+
+// 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 7538: blank (_) labels handled incorrectly
+
+package p
+
+func f() {
+_:
+}
-- 
2.50.0