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 #4469.
R=ken2
CC=golang-dev
https://golang.org/cl/7773047
diff --git a/test/funcdup.go b/test/funcdup.go
new file mode 100644
index 0000000..706dd63
--- /dev/null
+++ b/test/funcdup.go
@@ -0,0 +1,27 @@
+// 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
+
+type 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"
+}
+
+type T1 func(i, i int) // ERROR "duplicate argument i"
+type T2 func(i int) (i int) // ERROR "duplicate argument i"
+type T3 func() (i, i int) // ERROR "duplicate argument i"
+
+type R struct{}
+
+func (i *R) F1(i int) {} // ERROR "duplicate argument i"
+func (i *R) F2() (i int) {return 0} // ERROR "duplicate argument i"
+func (i *R) F3(j int) (j int) {return 0} // ERROR "duplicate argument j"
+
+func F1(i, i int) {} // ERROR "duplicate argument i"
+func F2(i int) (i int) {return 0} // ERROR "duplicate argument i"
+func F3() (i, i int) {return 0, 0} // ERROR "duplicate argument i"
