test: add test that required algs get generated

This is a follow-up to CLs 19769 and 19770.

Change-Id: Ia9b71055613b80df4ce62b34fcc4f479f04f72fd
Reviewed-on: https://go-review.googlesource.com/22399
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

test/alg.go

@@ -0,0 +1,46 @@
+// build
+
+// Copyright 2016 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.
+
+// This file tests that required algs are generated,
+// even when similar types have been marked elsewhere
+// as not needing algs. See CLs 19769 and 19770.
+
+package main
+
+import "fmt"
+
+//go:noinline
+func f(m map[[8]string]int) int {
+	var k [8]string
+	return m[k]
+}
+
+//go:noinline
+func g(m map[[8]interface{}]int) int {
+	var k [8]interface{}
+	return m[k]
+}
+
+//go:noinline
+func h(m map[[2]string]int) int {
+	var k [2]string
+	return m[k]
+}
+
+type T map[string]interface{}
+
+func v(x ...string) string {
+	return x[0] + x[1]
+}
+
+func main() {
+	fmt.Println(
+		f(map[[8]string]int{}),
+		g(map[[8]interface{}]int{}),
+		h(map[[2]string]int{}),
+		v("a", "b"),
+	)
+}