src/resolver.ts

@@ -392,7 +392,7 @@ export class Resolver extends DiagnosticEmitter {
           break;
         }
         case ParameterKind.Rest: {
-          assert(i == numParameters);
+          assert(i == numParameters - 1);
           hasRest = true;
           break;
         }

tests/compiler/issues/2707.json

@@ -0,0 +1,7 @@
+{
+  "asc_flags": [],
+  "stderr": [
+    "AS100: Not implemented: Rest parameters",
+    "func(1, 2, 3, 4);"
+  ]
+}

tests/compiler/issues/2707.ts

@@ -0,0 +1,6 @@
+// should not crash
+let func: (...args: i32[]) => i32 = (...args: i32[]) => {
+  return 1;
+};
+
+func(1, 2, 3, 4);