go/types, types2: delay receiver type validation

Delay validation of receiver type as it may cause premature expansion
of types the receiver type is dependent on. This was actually a TODO.

While the diff looks large-ish, the actual change is small: all the
receiver validation code has been moved inside the delayed function
body, and a couple of comments have been adjusted.

Fixes #51232.
Fixes #51233.

Change-Id: I44edf0ba615996266791724b832d81b9ccb8b435
Reviewed-on: https://go-review.googlesource.com/c/go/+/387918
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

2 files changed, 53 insertions, 0 deletions

diff --git a/test/typeparam/issue51232.go b/test/typeparam/issue51232.go
new file mode 100644
index 0000000000..2272dcdfcd
--- /dev/null
+++ b/test/typeparam/issue51232.go
@@ -0,0 +1,31 @@
+// compile -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 p
+
+type RC[RG any] interface {
+	~[]RG
+}
+
+type Fn[RCT RC[RG], RG any] func(RCT)
+
+type F[RCT RC[RG], RG any] interface {
+	Fn() Fn[RCT]
+}
+
+type concreteF[RCT RC[RG], RG any] struct {
+	makeFn func() Fn[RCT]
+}
+
+func (c *concreteF[RCT, RG]) Fn() Fn[RCT] {
+	return c.makeFn()
+}
+
+func NewConcrete[RCT RC[RG], RG any](Rc RCT) F[RCT] {
+	return &concreteF[RCT]{
+		makeFn: nil,
+	}
+}
diff --git a/test/typeparam/issue51233.go b/test/typeparam/issue51233.go
new file mode 100644
index 0000000000..523f0b34d6
--- /dev/null
+++ b/test/typeparam/issue51233.go
@@ -0,0 +1,22 @@
+// compile -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 p
+
+type RC[RG any] interface {
+	~[]RG
+}
+type Fn[RCT RC[RG], RG any] func(RCT)
+type FFn[RCT RC[RG], RG any] func() Fn[RCT]
+type F[RCT RC[RG], RG any] interface {
+	Fn() Fn[RCT]
+}
+type concreteF[RCT RC[RG], RG any] struct {
+	makeFn FFn[RCT]
+}
+
+func (c *concreteF[RCT, RG]) Fn() Fn[RCT] {
+	return c.makeFn()
+}