invariant: improve code that babel outputs (#2064)

Author: IvanGoncharov

resources/inline-invariant.js

@@ -15,9 +15,7 @@
  */
 module.exports = function inlineInvariant(context) {
   const replaceTemplate = context.template(`
-    if (!%%cond%%) {
-      invariant(0, %%args%%);
-    }
+    (%%cond%%) || invariant(0, %%args%%)
   `);
 
   return {
@@ -39,9 +37,9 @@ module.exports = function inlineInvariant(context) {
 
 function isAppropriateInvariantCall(node, parent) {
   return (
+    parent.type === 'ExpressionStatement' &&
     node.callee.type === 'Identifier' &&
     node.callee.name === 'invariant' &&
-    node.arguments.length > 0 &&
-    parent.type === 'ExpressionStatement'
+    node.arguments.length > 0
   );
 }

src/jsutils/invariant.js

@@ -1,9 +1,9 @@
 // @flow strict
 
-export default function invariant(condition: mixed, message: string) {
+/* istanbul ignore file */
+export default function invariant(condition: mixed, message?: string): void {
   const booleanCondition = Boolean(condition);
-  /* istanbul ignore else */
   if (!booleanCondition) {
-    throw new Error(message);
+    throw new Error(message || 'Unexpected invariant triggered');
   }
 }