From 1a90dcdaaf46d9dd0ee61781dcb9b6e05b80d926 Mon Sep 17 00:00:00 2001
From: Tim King <taking@google.com>
Date: Thu, 15 Aug 2024 16:48:42 -0700
Subject: [PATCH] go/types, types2: unalias tilde terms in underIs

Unalias the ~T terms during underIs. Before, if T was an alias
of U, it may pass T to the iteration function. The iterator
function expects an underlying type, under(U), to be passed.
This caused several bugs where underIs is used without
eventually taking the underlying type.

Updates #68935
Fixes #68903

Change-Id: Ie8691d8dddaea00e1dcba94d17c0f1b021fc49a2
Reviewed-on: https://go-review.googlesource.com/c/go/+/606075
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>
---
 src/cmd/compile/internal/types2/typeset.go    |  4 +--
 src/go/types/typeset.go                       |  4 +--
 .../types/testdata/fixedbugs/issue68903.go    | 24 +++++++++++++++++
 .../types/testdata/fixedbugs/issue68935.go    | 26 +++++++++++++++++++
 4 files changed, 54 insertions(+), 4 deletions(-)
 create mode 100644 src/internal/types/testdata/fixedbugs/issue68903.go
 create mode 100644 src/internal/types/testdata/fixedbugs/issue68935.go

diff --git a/src/cmd/compile/internal/types2/typeset.go b/src/cmd/compile/internal/types2/typeset.go
index 2577631a535425..01636ed379a090 100644
--- a/src/cmd/compile/internal/types2/typeset.go
+++ b/src/cmd/compile/internal/types2/typeset.go
@@ -131,8 +131,8 @@ func (s *_TypeSet) underIs(f func(Type) bool) bool {
 	}
 	for _, t := range s.terms {
 		assert(t.typ != nil)
-		// x == under(x) for ~x terms
-		u := t.typ
+		// Unalias(x) == under(x) for ~x terms
+		u := Unalias(t.typ)
 		if !t.tilde {
 			u = under(u)
 		}
diff --git a/src/go/types/typeset.go b/src/go/types/typeset.go
index 5981c8ae62b36f..a94d4fada46058 100644
--- a/src/go/types/typeset.go
+++ b/src/go/types/typeset.go
@@ -134,8 +134,8 @@ func (s *_TypeSet) underIs(f func(Type) bool) bool {
 	}
 	for _, t := range s.terms {
 		assert(t.typ != nil)
-		// x == under(x) for ~x terms
-		u := t.typ
+		// Unalias(x) == under(x) for ~x terms
+		u := Unalias(t.typ)
 		if !t.tilde {
 			u = under(u)
 		}
diff --git a/src/internal/types/testdata/fixedbugs/issue68903.go b/src/internal/types/testdata/fixedbugs/issue68903.go
new file mode 100644
index 00000000000000..b1369aa0f6faa7
--- /dev/null
+++ b/src/internal/types/testdata/fixedbugs/issue68903.go
@@ -0,0 +1,24 @@
+// 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 A = [4]int
+type B = map[string]interface{}
+
+func _[T ~A](x T) {
+	_ = len(x)
+}
+
+func _[U ~A](x U) {
+	_ = cap(x)
+}
+
+func _[V ~A]() {
+	_ = V{}
+}
+
+func _[W ~B](a interface{}) {
+	_ = a.(W)["key"]
+}
diff --git a/src/internal/types/testdata/fixedbugs/issue68935.go b/src/internal/types/testdata/fixedbugs/issue68935.go
new file mode 100644
index 00000000000000..2e72468f05eb0c
--- /dev/null
+++ b/src/internal/types/testdata/fixedbugs/issue68935.go
@@ -0,0 +1,26 @@
+// 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 A = struct {
+	F string
+	G int
+}
+
+func Make[T ~A]() T {
+	return T{
+		F: "blah",
+		G: 1234,
+	}
+}
+
+type N struct {
+	F string
+	G int
+}
+
+func _() {
+	_ = Make[N]()
+}