handle call expressions of uncallable things more gracefully (#1257)

src/ast/nodes/shared/callHasEffects.js

@@ -96,12 +96,14 @@ export default function callHasEffects ( scope, callee, isNew ) {
 			}
 		}
 
-		else {
-			if ( !node.gatherPossibleValues ) {
-				throw new Error( 'TODO' );
-			}
+		else if ( node.gatherPossibleValues ) {
 			node.gatherPossibleValues( values );
 		}
+
+		else {
+			// probably an error in the user's code — err on side of caution
+			return true;
+		}
 	}
 
 	return false;

test/function/handle-calling-uncallable/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'does not give cryptic error when calling uncallable things (#1257)'
+};

test/function/handle-calling-uncallable/foo.js

@@ -0,0 +1,3 @@
+function foo() {}
+
+export default { foo };

test/function/handle-calling-uncallable/main.js

@@ -0,0 +1,5 @@
+import foo from './foo.js';
+
+assert.throws( function () {
+	foo();
+}, /is not a function/ );