fix: handle frozen receivers in $methodVal

flimzy · flimzy · commit c74dd49a4278 · 2026-02-03T13:49:47.000-05:00
Fixes #1408
diff --git a/compiler/prelude/prelude.js b/compiler/prelude/prelude.js
@@ -118,7 +118,9 @@ var $mapDelete = (m, key) => {
 // standalone function. Bound function is cached for later reuse.
 var $methodVal = (recv, name) => {
     var vals = recv.$methodVals || {};
-    recv.$methodVals = vals; /* noop for primitives */
+    if (Object.isExtensible(recv)) {
+      recv.$methodVals = vals; /* noop for primitives */
+    }
     var f = vals[name];
     if (f !== undefined) {
         return f;
diff --git a/tests/frozenreceiver_test.go b/tests/frozenreceiver_test.go
@@ -0,0 +1,14 @@
+package tests
+
+import "testing"
+
+type mySlice []int
+
+func (s mySlice) Len() int { return len(s) }
+func TestMethodValueOnNilSlice(t *testing.T) {
+	var s mySlice
+	f := s.Len
+	if got := f(); got != 0 {
+		t.Errorf("got %d, want 0", got)
+	}
+}
