cmd/gc: ensure unique parameter and result names in function types

In addition to fixing the bug, the check is now linear instead of quadratic.

Fixes issue 4469.

R=ken2
CC=golang-dev
https://codereview.appspot.com/7773047

1 files changed, 17 insertions, 0 deletions

diff --git a/test/funcdup2.go b/test/funcdup2.go
new file mode 100644
index 000000000..aeb5f7eb6
--- /dev/null
+++ b/test/funcdup2.go
@@ -0,0 +1,17 @@
+// errorcheck
+
+// Copyright 2013 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
+
+var T interface {
+	F1(i int) (i int) // ERROR "duplicate argument i"
+	F2(i, i int) // ERROR "duplicate argument i"
+	F3() (i, i int) // ERROR "duplicate argument i"
+}
+
+var T1 func(i, i int) // ERROR "duplicate argument i"
+var T2 func(i int) (i int) // ERROR "duplicate argument i"
+var T3 func() (i, i int) // ERROR "duplicate argument i"