From 13f3c57cefef59e5d94f678483aff527807fb33b Mon Sep 17 00:00:00 2001
From: Robert Findley <rfindley@google.com>
Date: Thu, 23 Sep 2021 12:19:05 -0400
Subject: [PATCH] go/types,types2: disallow illegal cycles through Unions

Checker.validType was not considering Unions when looking for illegal
cycles.

Fixes #48582

Change-Id: I11ad0279eeaaa56bb6d5731b0572c1c3a0c459eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/351829
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
---
 src/cmd/compile/internal/types2/decl.go       |  7 +++++
 .../types2/testdata/fixedbugs/issue41124.go2  |  2 +-
 .../types2/testdata/fixedbugs/issue48582.go2  | 29 +++++++++++++++++++
 src/go/types/decl.go                          |  7 +++++
 .../types/testdata/fixedbugs/issue41124.go2   |  4 +--
 .../types/testdata/fixedbugs/issue48582.go2   | 29 +++++++++++++++++++
 6 files changed, 75 insertions(+), 3 deletions(-)
 create mode 100644 src/cmd/compile/internal/types2/testdata/fixedbugs/issue48582.go2
 create mode 100644 src/go/types/testdata/fixedbugs/issue48582.go2

diff --git a/src/cmd/compile/internal/types2/decl.go b/src/cmd/compile/internal/types2/decl.go
index 994c19ea30a..ab2e3b875f0 100644
--- a/src/cmd/compile/internal/types2/decl.go
+++ b/src/cmd/compile/internal/types2/decl.go
@@ -315,6 +315,13 @@ func (check *Checker) validType(typ Type, path []Object) typeInfo {
 			}
 		}
 
+	case *Union:
+		for _, t := range t.terms {
+			if check.validType(t.typ, path) == invalid {
+				return invalid
+			}
+		}
+
 	case *Interface:
 		for _, etyp := range t.embeddeds {
 			if check.validType(etyp, path) == invalid {
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue41124.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue41124.go2
index 4642ab60fc8..cef24bd2379 100644
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue41124.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue41124.go2
@@ -6,7 +6,7 @@ package p
 
 // Test case from issue.
 
-type Nat interface {
+type Nat /* ERROR cycle */ interface {
 	Zero|Succ
 }
 
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue48582.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue48582.go2
new file mode 100644
index 00000000000..c12091be790
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue48582.go2
@@ -0,0 +1,29 @@
+// 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 N /* ERROR cycle */ interface {
+	int | N
+}
+
+type A /* ERROR cycle */ interface {
+	int | B
+}
+
+type B interface {
+	int | A
+}
+
+type S /* ERROR cycle */ struct {
+	I // ERROR interface contains type constraints
+}
+
+type I interface {
+	int | S
+}
+
+type P interface {
+	*P // ERROR interface contains type constraints
+}
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 061fc018296..77914dd1af9 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -314,6 +314,13 @@ func (check *Checker) validType(typ Type, path []Object) typeInfo {
 			}
 		}
 
+	case *Union:
+		for _, t := range t.terms {
+			if check.validType(t.typ, path) == invalid {
+				return invalid
+			}
+		}
+
 	case *Interface:
 		for _, etyp := range t.embeddeds {
 			if check.validType(etyp, path) == invalid {
diff --git a/src/go/types/testdata/fixedbugs/issue41124.go2 b/src/go/types/testdata/fixedbugs/issue41124.go2
index 4642ab60fc8..ac336a2eceb 100644
--- a/src/go/types/testdata/fixedbugs/issue41124.go2
+++ b/src/go/types/testdata/fixedbugs/issue41124.go2
@@ -6,13 +6,13 @@ package p
 
 // Test case from issue.
 
-type Nat interface {
+type Nat /* ERROR cycle */ interface {
 	Zero|Succ
 }
 
 type Zero struct{}
 type Succ struct{
-	Nat // ERROR interface contains type constraints
+	Nat /* ERROR interface contains type constraints */
 }
 
 // Struct tests.
diff --git a/src/go/types/testdata/fixedbugs/issue48582.go2 b/src/go/types/testdata/fixedbugs/issue48582.go2
new file mode 100644
index 00000000000..c12091be790
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue48582.go2
@@ -0,0 +1,29 @@
+// 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 N /* ERROR cycle */ interface {
+	int | N
+}
+
+type A /* ERROR cycle */ interface {
+	int | B
+}
+
+type B interface {
+	int | A
+}
+
+type S /* ERROR cycle */ struct {
+	I // ERROR interface contains type constraints
+}
+
+type I interface {
+	int | S
+}
+
+type P interface {
+	*P // ERROR interface contains type constraints
+}