go/types, types2: all interfaces implement comparable (add tests)

For #50646.

Change-Id: I7420545556e0df2659836364a62ce2c32ad7a8b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/380654
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/test/typeparam/issue50646.go b/test/typeparam/issue50646.go
new file mode 100644
index 0000000000..44bbe2ae6f
--- /dev/null
+++ b/test/typeparam/issue50646.go
@@ -0,0 +1,39 @@
+// run -gcflags=-G=3
+
+// Copyright 2022 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 main
+
+func eql[P comparable](x, y P) {
+	if x != y {
+		panic("not equal")
+	}
+}
+
+func expectPanic(f func()) {
+	defer func() {
+		if recover() == nil {
+			panic("function succeeded unexpectedly")
+		}
+	}()
+	f()
+}
+
+func main() {
+	eql[int](1, 1)
+	eql(1, 1)
+
+	// all interfaces implement comparable
+	var x, y any = 2, 2
+	eql[any](x, y)
+	eql(x, y)
+
+	// but we may get runtime panics
+	x, y = 1, 2 // x != y
+	expectPanic(func() { eql(x, y) })
+
+	x, y = main, main // functions are not comparable
+	expectPanic(func() { eql(x, y) })
+}