cmd/compile: fix recursive generic interface instantiation

When shapifying recursive instantiated types, the compiler ends up
leaving the type as-is if it already has been a shape type. However, if
both of type arguments are interfaces, and one of them is a recursive
one, it ends up being shaped as-is, while the other is shaped to its
underlying, causing mismatch in function signature.

Fixing this by shapifying an interface type as-is, if it is fully
instantiated and already been a shape type.

Fixes #65362
Fixes #66663

Change-Id: I839d266e0443b41238b1b7362aca09adc0177362
Reviewed-on: https://go-review.googlesource.com/c/go/+/559656
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -903,6 +903,11 @@ func shapify(targ *types.Type, basic bool) *types.Type {
 			base.Fatalf("%v is missing its underlying type", targ)
 		}
 	}
+	// For fully instantiated shape interface type, use it as-is. Otherwise, the instantiation
+	// involved recursive generic interface may cause mismatching in function signature, see issue #65362.
+	if targ.Kind() == types.TINTER && targ.IsFullyInstantiated() && targ.HasShape() {
+		return targ
+	}
 
 	// When a pointer type is used to instantiate a type parameter
 	// constrained by a basic interface, we know the pointer's element

test/fixedbugs/issue65362.go

@@ -0,0 +1,31 @@
+// compile
+
+// Copyright 2024 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
+
+type Vector[V any] interface {
+	ReadVector[V]
+}
+
+type ReadVector[V any] interface {
+	Comparisons[ReadVector[V], Vector[V]]
+}
+
+type Comparisons[RV, V any] interface {
+	Diff(RV) V
+}
+
+type VectorImpl[V any] struct{}
+
+func (*VectorImpl[V]) Diff(ReadVector[V]) (_ Vector[V]) {
+	return
+}
+
+func main() {
+	var v1 VectorImpl[int]
+	var v2 Vector[int]
+	_ = v1.Diff(v2)
+}

test/fixedbugs/issue66663.go

@@ -0,0 +1,34 @@
+// compile
+
+// Copyright 2024 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 Iterator[A any] func() (bool, A)
+
+type Range[A any] interface {
+	Blocks() Iterator[Block[A]]
+}
+
+type Block[A any] interface {
+	Range[A]
+}
+
+type rangeImpl[A any] struct{}
+
+func (r *rangeImpl[A]) Blocks() Iterator[Block[A]] {
+	return func() (bool, Block[A]) {
+		var a Block[A]
+		return false, a
+	}
+}
+
+func NewRange[A any]() Range[A] {
+	return &rangeImpl[A]{}
+}
+
+type AddrImpl struct{}
+
+var _ = NewRange[AddrImpl]()