From: Robert Griesemer <gri@golang.org>
Date: Wed, 6 Oct 2021 16:33:55 +0000 (-0700)
Subject: [release-branch.go1.17] go/types: break cycles in invalid types
X-Git-Tag: go1.17.4~3
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=66007e5cfc9e151485791d440b7e67d44af1b29f;p=gostls13.git

[release-branch.go1.17] go/types: break cycles in invalid types

This is a partial port of CL 354329 from types2 to go/types.
It contains an adjustment to type.go to deal with possibly
invalid type bounds.

Fixes #48825.
For #48819.

Change-Id: I9efdcdbfa6432f3cee64d924a4c67ecc6793cf86
Reviewed-on: https://go-review.googlesource.com/c/go/+/354349
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/368456
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
---

diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 9211febc6d..ec173ad1cc 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -343,6 +343,7 @@ func (check *Checker) validType(typ Type, path []Object) typeInfo {
 				if tn == t.obj {
 					check.cycleError(path[i:])
 					t.info = invalid
+					t.underlying = Typ[Invalid]
 					return t.info
 				}
 			}
diff --git a/src/go/types/testdata/fixedbugs/issue48819.src b/src/go/types/testdata/fixedbugs/issue48819.src
new file mode 100644
index 0000000000..9262110ea0
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue48819.src
@@ -0,0 +1,15 @@
+// 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
+
+import "unsafe"
+
+type T /* ERROR illegal cycle in declaration of T */ struct {
+	T
+}
+
+func _(t T) {
+	_ = unsafe.Sizeof(t) // should not go into infinite recursion here
+}
diff --git a/src/go/types/type.go b/src/go/types/type.go
index 2660ce4408..20c4bec0bc 100644
--- a/src/go/types/type.go
+++ b/src/go/types/type.go
@@ -759,6 +759,9 @@ func (check *Checker) newTypeParam(obj *TypeName, index int, bound Type) *_TypeP
 
 func (t *_TypeParam) Bound() *Interface {
 	iface := asInterface(t.bound)
+	if iface == nil {
+		return &emptyInterface
+	}
 	// use the type bound position if we have one
 	pos := token.NoPos
 	if n, _ := t.bound.(*Named); n != nil {