[dev.typeparams] cmd/compile/internal/types2: don't permit method calls on ptr to type parameter receivers

Simplify the implementation of asInterface while at it.

For #47031.

Change-Id: Ie7d4fbbab898d961ed3c0b7772ba9604641be13f
Reviewed-on: https://go-review.googlesource.com/c/go/+/332609
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

2 files changed, 24 insertions, 6 deletions

diff --git a/src/cmd/compile/internal/types2/testdata/check/issues.go2 b/src/cmd/compile/internal/types2/testdata/check/issues.go2
index 59dd4ae465..88ae294d7c 100644
--- a/src/cmd/compile/internal/types2/testdata/check/issues.go2
+++ b/src/cmd/compile/internal/types2/testdata/check/issues.go2
@@ -24,22 +24,20 @@ func _() {
 	eql[io.Reader](nil, nil)
 }
 
-// If we have a receiver of pointer type (below: *T) we must ignore
-// the pointer in the implementation of the method lookup because
-// the type bound of T is an interface and pointer to interface types
-// have no methods and then the lookup would fail.
+// If we have a receiver of pointer to type parameter type (below: *T)
+// we don't have any methods, like for interfaces.
 type C[T any] interface {
     m()
 }
 
 // using type bound C
 func _[T C[T]](x *T) {
-	x.m()
+	x.m /* ERROR x\.m undefined */ ()
 }
 
 // using an interface literal as bound
 func _[T interface{ m() }](x *T) {
-	x.m()
+	x.m /* ERROR x\.m undefined */ ()
 }
 
 func f2[_ interface{ m1(); m2() }]()
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47031.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47031.go2
new file mode 100644
index 0000000000..b184f9b5b7
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue47031.go2
@@ -0,0 +1,20 @@
+// 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 Mer interface { M() }
+
+func F[T Mer](p *T) {
+	p.M /* ERROR p\.M undefined */ ()
+}
+
+type MyMer int
+
+func (MyMer) M() {}
+
+func _() {
+	F(new(MyMer))
+	F[Mer](nil)
+}