cmd/gc: fix computation of equality class of types.
A struct with a single field was considered as equivalent to the
field type, which is incorrect is the field is blank.
Fields with padding could make the compiler think some
types are comparable when they are not.
Fixes #5698.
R=rsc, golang-dev, daniel.morsing, bradfitz, gri, r
CC=golang-dev
https://golang.org/cl/10271046
diff --git a/test/fixedbugs/issue5698.go b/test/fixedbugs/issue5698.go
new file mode 100644
index 0000000..035bbd3
--- /dev/null
+++ b/test/fixedbugs/issue5698.go
@@ -0,0 +1,18 @@
+// 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.
+
+// Issue 5698: can define a key type with slices.
+
+package main
+
+type Key struct {
+ a int16 // the compiler was confused by the padding.
+ b []int
+}
+
+type Val struct{}
+
+type Map map[Key]Val // ERROR "invalid map key type"
