cmd/gc: do not display ~b identifiers in error messages

Instead of errors like:

./blank2.go:15: cannot use ~b1 (type []int) as type int in assignment

we now have:

./blank2.go:15: cannot use _ (type []int) as type int in assignment

Less confusing for users.

Fixes #9521

Change-Id: Ieab9859040e8e0df95deeaee7eeb408d3be61c0f
Reviewed-on: https://go-review.googlesource.com/9902
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/test/fixedbugs/issue9521.go b/test/fixedbugs/issue9521.go
new file mode 100644
index 0000000000..51b5204e7a
--- /dev/null
+++ b/test/fixedbugs/issue9521.go
@@ -0,0 +1,16 @@
+// errorcheck
+
+// Copyright 2015 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.
+
+// Test that an incorrect use of the blank identifer is caught.
+// Does not compile.
+
+package main
+
+func f() (_, _ []int) { return }
+
+func main() {
+	_ = append(f()) // ERROR "cannot use _"
+}