[[FIX]] Allow empty export and trailing comma

Now JSHint correctly parses this code:
  export { a, };
  export {};
but warns `Empty export.` at line 2

This commit fixes #2567

src/jshint.js

@@ -3412,7 +3412,7 @@ var JSHINT = (function() {
         advance("[");
       }
       if (checkPunctuator(state.tokens.next, "]")) {
-        warning("W137", state.tokens.curr);
+        warning("W137", state.tokens.curr, "destructuring");
       }
       var element_after_rest = false;
       while (!checkPunctuator(state.tokens.next, "]")) {
@@ -3444,7 +3444,7 @@ var JSHINT = (function() {
         advance("{");
       }
       if (checkPunctuator(state.tokens.next, "}")) {
-        warning("W137", state.tokens.curr);
+        warning("W137", state.tokens.curr, "destructuring");
       }
       while (!checkPunctuator(state.tokens.next, "}")) {
         assignmentProperty();
@@ -4634,6 +4634,10 @@ var JSHINT = (function() {
     } else {
       // ImportClause :: NamedImports
       advance("{");
+      // Breaking change
+      // if (checkPunctuator(state.tokens.next, "}")) {
+      //   warning("W137", state.tokens.next, "import");
+      // }
       for (;;) {
         if (state.tokens.next.value === "}") {
           advance("}");
@@ -4731,8 +4735,11 @@ var JSHINT = (function() {
     if (state.tokens.next.value === "{") {
       // ExportDeclaration :: export ExportClause
       advance("{");
+      if (checkPunctuator(state.tokens.next, "}")) {
+        warning("W137", state.tokens.next, "export");
+      }
       var exportedTokens = [];
-      for (;;) {
+      while (!checkPunctuator(state.tokens.next, "}")) {
         if (!state.tokens.next.identifier) {
           error("E030", state.tokens.next, state.tokens.next.value);
         }
@@ -4748,16 +4755,11 @@ var JSHINT = (function() {
           advance();
         }
 
-        if (state.tokens.next.value === ",") {
+        if (!checkPunctuator(state.tokens.next, "}")) {
           advance(",");
-        } else if (state.tokens.next.value === "}") {
-          advance("}");
-          break;
-        } else {
-          error("E024", state.tokens.next, state.tokens.next.value);
-          break;
         }
       }
+      advance("}");
       if (state.tokens.next.value === "from") {
         // ExportDeclaration :: export ExportClause FromClause
         advance("from");

src/messages.js

@@ -222,7 +222,7 @@ var warnings = {
   W134: "The '{a}' option is only available when linting ECMAScript {b} code.",
   W135: "{a} may not be supported by non-browser environments.",
   W136: "'{a}' must be in function scope.",
-  W137: "Empty destructuring.",
+  W137: "Empty {a}.",
   W138: "Regular parameters should not come after default parameters.",
   W139: "Function expressions should not be used as the second operand to instanceof.",
   W140: "Missing comma."

tests/test262/expectations.txt

@@ -410,12 +410,7 @@ language/module-code/early-dup-export-id.js
 language/module-code/early-export-global.js
 language/module-code/early-export-unresolvable.js
 language/module-code/early-super.js
-language/module-code/eval-rqstd-once.js
-language/module-code/eval-rqstd-order.js
-language/module-code/eval-self-once.js
-language/module-code/instn-iee-trlng-comma.js
 language/module-code/instn-named-id-name.js
-language/module-code/instn-once.js
 language/module-code/instn-resolve-empty-import.js
 language/module-code/instn-resolve-err-reference.js
 language/module-code/instn-resolve-err-syntax.js
@@ -433,7 +428,6 @@ language/module-code/parse-err-invoke-anon-fun-decl.js
 language/module-code/parse-err-invoke-anon-gen-decl.js
 language/module-code/parse-err-reference.js
 language/module-code/parse-err-return.js
-language/module-code/parse-export-empty.js
 language/expressions/async-arrow-function/arrow-returns-promise.js
 language/expressions/async-function/expression-returns-promise.js
 language/expressions/async-function/syntax-expression-is-PrimaryExpression.js
@@ -4619,3 +4613,7 @@ language/statements/class/meth-static-dflt-params-ref-self.js
 language/statements/class/meth-static-dflt-params-trailing-comma.js
 language/statements/class/meth-static-params-trailing-comma-multiple.js
 language/statements/class/meth-static-params-trailing-comma-single.js
+
+# JSHint currently makes no attempt to resolve module references, so it is
+# incapable of detecting early errors across modules.
+language/module-code/instn-resolve-empty-export.js

tests/unit/core.js

@@ -827,11 +827,12 @@ exports.testES6Modules = function (test) {
     [60, 13, "'ember2' has already been declared."]
   ];
 
-  var testRun = TestRun(test);
+  var testRun = TestRun(test)
+    .addError(74, 9, "Empty export.");
   importConstErrors.forEach(function(error) { testRun.addError.apply(testRun, error); });
   testRun.test(src, {esnext: true});
 
-  testRun = TestRun(test)
+  testRun
     .addError(3, 1, "'import' is only available in ES6 (use 'esversion: 6').")
     .addError(4, 1, "'import' is only available in ES6 (use 'esversion: 6').")
     .addError(5, 1, "'import' is only available in ES6 (use 'esversion: 6').")
@@ -862,9 +863,12 @@ exports.testES6Modules = function (test) {
     .addError(65, 1, "'import' is only available in ES6 (use 'esversion: 6').")
     .addError(67, 1, "'export' is only available in ES6 (use 'esversion: 6').")
     .addError(67, 16, "'function*' is only available in ES6 (use 'esversion: 6').")
-    .addError(67, 26, "'yield' is available in ES6 (use 'esversion: 6') or Mozilla JS extensions (use moz).");
-  importConstErrors.forEach(function(error) { testRun.addError.apply(testRun, error); });
-  testRun.test(src, {});
+    .addError(67, 26, "'yield' is available in ES6 (use 'esversion: 6') or Mozilla JS extensions (use moz).")
+    .addError(70, 1, "'export' is only available in ES6 (use 'esversion: 6').")
+    .addError(71, 1, "'import' is only available in ES6 (use 'esversion: 6').")
+    .addError(74, 1, "'export' is only available in ES6 (use 'esversion: 6').")
+    .addError(75, 1, "'import' is only available in ES6 (use 'esversion: 6').")
+    .test(src);
 
   var src2 = [
     "var a = {",

tests/unit/fixtures/es6-import-export.js

@@ -65,3 +65,11 @@ if (newImport) {
 import newImport from 'newImport';
 
 export function* gen() { yield 1; }
+
+// Trailing comma
+export { a, };
+import { x, } from "source";
+
+// Empty
+export {};
+import {} from "source";