cmd/compile: relax overly strict assertion

The assertion here was to make sure the newly constructed and
typechecked expression selected the same receiver-qualified method,
but in the case of anonymous receiver types we can actually end up
with separate types.Field instances corresponding to each types.Type
instance. In that case, the assertion spuriously failed.

The fix here is to relax and assertion and just compare the method's
name and type (including receiver type).

Fixes #58563.

Change-Id: I67d51ddb020e6ed52671473c93fc08f283a40886
Reviewed-on: https://go-review.googlesource.com/c/go/+/471676
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/noder/reader.go

@@ -2184,7 +2184,18 @@ func (r *reader) expr() (res ir.Node) {
 			}
 
 			n := typecheck.Expr(ir.NewSelectorExpr(pos, ir.OXDOT, recv, wrapperFn.Sel)).(*ir.SelectorExpr)
-			assert(n.Selection == wrapperFn.Selection)
+
+			// As a consistency check here, we make sure "n" selected the
+			// same method (represented by a types.Field) that wrapperFn
+			// selected. However, for anonymous receiver types, there can be
+			// multiple such types.Field instances (#58563). So we may need
+			// to fallback to making sure Sym and Type (including the
+			// receiver parameter's type) match.
+			if n.Selection != wrapperFn.Selection {
+				assert(n.Selection.Sym == wrapperFn.Selection.Sym)
+				assert(types.Identical(n.Selection.Type, wrapperFn.Selection.Type))
+				assert(types.Identical(n.Selection.Type.Recv().Type, wrapperFn.Selection.Type.Recv().Type))
+			}
 
 			wrapper := methodValueWrapper{
 				rcvr:   n.X.Type(),

test/fixedbugs/issue58563.dir/a.go

@@ -0,0 +1,13 @@
+// Copyright 2023 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
+
+func Start() interface{ Stop() } {
+	return new(Stopper)
+}
+
+type Stopper struct{}
+
+func (s *Stopper) Stop() {}

test/fixedbugs/issue58563.dir/main.go

@@ -0,0 +1,16 @@
+// Copyright 2023 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 "test/a"
+
+func main() {
+	stop := start()
+	defer stop()
+}
+
+func start() func() {
+	return a.Start().Stop
+}

test/fixedbugs/issue58563.go

@@ -0,0 +1,7 @@
+// compiledir
+
+// Copyright 2023 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