test: add regress test for issue 55101

This test case already works with GOEXPERIMENT=unified, and it never
worked with Go 1.18 or Go 1.19. So this CL simply adds a regress test
to make sure it continues working.

Fixes #55101.

Change-Id: I7e06bfdc136ce124f65cdcf02d20a1050b841d42
Reviewed-on: https://go-review.googlesource.com/c/go/+/431455
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/go/internal/gcimporter/gcimporter_test.go

@@ -179,6 +179,7 @@ func TestImportTypeparamTests(t *testing.T) {
 		"issue50417.go": "inconsistent interface member sorting",
 		"issue53419.go": "fails to compile",
 		"issue53477.go": "fails to compile",
+		"issue55101.go": "fails to compile",
 	}
 
 	for _, entry := range list {

test/run.go

@@ -1987,6 +1987,7 @@ var go118Failures = setOf(
 	"typeparam/issue51521.go",  // 1.18 compiler produces bad panic message and link error
 	"typeparam/issue54456.go",  // 1.18 compiler fails to distinguish local generic types
 	"typeparam/issue54497.go",  // 1.18 compiler is more conservative about inlining due to repeated issues
+	"typeparam/issue55101.go",  // 1.18 compiler ICEs writing export data
 	"typeparam/mdempsky/16.go", // 1.18 compiler uses interface shape type in failed type assertions
 	"typeparam/mdempsky/17.go", // 1.18 compiler mishandles implicit conversions from range loops
 	"typeparam/mdempsky/18.go", // 1.18 compiler mishandles implicit conversions in select statements

test/typeparam/issue55101.go

@@ -0,0 +1,16 @@
+// compile
+
+// 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 p
+
+func F() *Cache[error] { return nil }
+
+type Cache[T any] struct{ l *List[entry[T]] }
+type entry[T any] struct{ value T }
+type List[T any] struct{ len int }
+
+func (c *Cache[V]) Len() int { return c.l.Len() }
+func (l *List[T]) Len() int  { return l.len }