From 41b75a7dfb0cca9fa8cfeaec08f61d4086aefecc Mon Sep 17 00:00:00 2001
From: Tristan Swadell <tswadell@google.com>
Date: Fri, 23 Aug 2019 13:59:00 -0700
Subject: [PATCH] Add a base case for type assignability to prevent infinite
 recursion.

---
 checker/types.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/checker/types.go b/checker/types.go
index 63efa202..2d716e0b 100644
--- a/checker/types.go
+++ b/checker/types.go
@@ -179,6 +179,11 @@ func isEqualOrLessSpecific(t1 *exprpb.Type, t2 *exprpb.Type) bool {
 
 /// internalIsAssignable returns true if t1 is assignable to t2.
 func internalIsAssignable(m *mapping, t1 *exprpb.Type, t2 *exprpb.Type) bool {
+	// A type is always assignable to itself.
+	// Early terminate the call to avoid cases of infinite recursion.
+	if proto.Equal(t1, t2) {
+		return true
+	}
 	// Process type parameters.
 	kind1, kind2 := kindOf(t1), kindOf(t2)
 	if kind2 == kindTypeParam {