test: add test cases for issue47892.

This issue has been fixed in https://golang.org/cl/345411

Fixes: #47892

Change-Id: I13dd3814650913da065e5f24a0c61d30adb0633a
Reviewed-on: https://go-review.googlesource.com/c/go/+/345229
Reviewed-by: Dan Scales <danscales@google.com>
Trust: Dan Scales <danscales@google.com>
Trust: Keith Randall <khr@golang.org>
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>

test/typeparam/issue47892.dir/a.go

@@ -0,0 +1,17 @@
+// 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 Index[T any] interface {
+	G() T
+}
+
+type I1[T any] struct {
+	a T
+}
+
+func (i *I1[T]) G() T {
+	return i.a
+}

test/typeparam/issue47892.dir/main.go

@@ -0,0 +1,21 @@
+// 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 main
+
+import "a"
+
+type Model[T any] struct {
+	index       a.Index[T]
+}
+
+func NewModel[T any](index a.Index[T]) Model[T] {
+	return Model[T]{
+		index:       index,
+	}
+}
+
+func main() {
+	_ = NewModel[int]((*a.I1[int])(nil))
+}

test/typeparam/issue47892.go

@@ -0,0 +1,7 @@
+// rundir -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

test/typeparam/issue47892b.dir/a.go

@@ -0,0 +1,29 @@
+// 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 struct{ p *int64 }
+
+type i struct{}
+
+func G() *T { return &T{nil} }
+
+func (j i) F(a, b *T) *T {
+	n := *a.p + *b.p
+	return &T{&n}
+}
+
+func (j i) G() *T {
+	return &T{}
+}
+
+type I[Idx any] interface {
+	G() Idx
+	F(a, b Idx) Idx
+}
+
+func Gen() I[*T] {
+	return i{}
+}

test/typeparam/issue47892b.dir/main.go

@@ -0,0 +1,17 @@
+// 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 main
+
+import "a"
+
+type S[Idx any] struct {
+	A string
+	B Idx
+}
+
+type O[Idx any] struct {
+	A int
+	B a.I[Idx]
+}

test/typeparam/issue47892b.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