test: add compiler regress tests for #46461

gri@ reports that types2 now correctly handles when type parameters
recursively refer back to the parameterized type, so we might as well
add tests to exercise that. Unified IR also correctly handles
importing and exporting these types, but -G=3 currently does not.

Updates #46461.

Change-Id: I272102aa08c40c980b9aeeca9f834291dfbbcc3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/348738
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/internal/gcimporter/gcimporter_test.go

@@ -167,6 +167,8 @@ func TestImportTypeparamTests(t *testing.T) {
 	skip := map[string]string{
 		"equal.go":  "inconsistent embedded sorting", // TODO(rfindley): investigate this.
 		"nested.go": "fails to compile",              // TODO(rfindley): investigate this.
+
+		"issue46461.go": "known issue with type parameter constraints referring back to parameterized type",
 	}
 
 	for _, entry := range list {

test/run.go

@@ -2188,6 +2188,8 @@ var g3Failures = setOf(
 
 	"typeparam/nested.go", // -G=3 doesn't support function-local types with generics
 
+	"typeparam/issue46461b.go", // -G=3 fails when type parameters refer back to the parameterized type itself
+
 	"typeparam/mdempsky/4.go", // -G=3 can't export functions with labeled breaks in loops
 )
 

test/typeparam/issue46461.go

@@ -0,0 +1,13 @@
+// compile -G=3
+
+// Copyright 2021 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[U interface{ M() T[U] }] int
+
+type X int
+
+func (X) M() T[X] { return 0 }

test/typeparam/issue46461b.dir/a.go

@@ -0,0 +1,7 @@
+// Copyright 2021 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 a
+
+type T[U interface{ M() T[U] }] int

test/typeparam/issue46461b.dir/b.go

@@ -0,0 +1,11 @@
+// Copyright 2021 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 b
+
+import "./a"
+
+type X int
+
+func (X) M() a.T[X] { return 0 }

test/typeparam/issue46461b.go

@@ -0,0 +1,7 @@
+// compiledir -G=3
+
+// Copyright 2021 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 ignored