ensure export modifier is used before default modifier (#44570)

* ensure export modifier is used before default modifier

* gracefully handle `default function`

* Revert "gracefully handle `default function`"

This reverts commit 1d8e288754.

* give better error message on default without leading export

src/compiler/checker.ts

@@ -41139,6 +41139,9 @@ namespace ts {
                         if (container.kind === SyntaxKind.ModuleDeclaration && !isAmbientModule(container)) {
                             return grammarErrorOnNode(modifier, Diagnostics.A_default_export_can_only_be_used_in_an_ECMAScript_style_module);
                         }
+                        else if (!(flags & ModifierFlags.Export)) {
+                            return grammarErrorOnNode(modifier, Diagnostics._0_modifier_must_precede_1_modifier, "export", "default");
+                        }
 
                         flags |= ModifierFlags.Default;
                         break;

src/compiler/parser.ts

@@ -2429,7 +2429,10 @@ namespace ts {
 
         function parsingContextErrors(context: ParsingContext) {
             switch (context) {
-                case ParsingContext.SourceElements: return parseErrorAtCurrentToken(Diagnostics.Declaration_or_statement_expected);
+                case ParsingContext.SourceElements:
+                    return token() === SyntaxKind.DefaultKeyword
+                        ? parseErrorAtCurrentToken(Diagnostics._0_expected, tokenToString(SyntaxKind.ExportKeyword))
+                        : parseErrorAtCurrentToken(Diagnostics.Declaration_or_statement_expected);
                 case ParsingContext.BlockStatements: return parseErrorAtCurrentToken(Diagnostics.Declaration_or_statement_expected);
                 case ParsingContext.SwitchClauses: return parseErrorAtCurrentToken(Diagnostics.case_or_default_expected);
                 case ParsingContext.SwitchClauseStatements: return parseErrorAtCurrentToken(Diagnostics.Statement_expected);

tests/baselines/reference/classAbstractManyKeywords.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractManyKeywords.ts(3,1): error TS1128: Declaration or statement expected.
+tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractManyKeywords.ts(3,1): error TS1005: 'export' expected.
 tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractManyKeywords.ts(4,17): error TS1005: '=' expected.
 
 
@@ -7,7 +7,7 @@ tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbst
     export abstract class B {}
     default abstract class C {}
     ~~~~~~~
-!!! error TS1128: Declaration or statement expected.
+!!! error TS1005: 'export' expected.
     import abstract class D {}
                     ~~~~~
 !!! error TS1005: '=' expected.

tests/baselines/reference/defaultKeywordWithoutExport1.errors.txt

@@ -0,0 +1,10 @@
+tests/cases/compiler/defaultKeywordWithoutExport1.ts(4,1): error TS1029: 'export' modifier must precede 'default' modifier.
+
+
+==== tests/cases/compiler/defaultKeywordWithoutExport1.ts (1 errors) ====
+    declare function decorator(constructor: any): any;
+    
+    @decorator
+    default class {}
+    ~~~~~~~
+!!! error TS1029: 'export' modifier must precede 'default' modifier.

tests/baselines/reference/defaultKeywordWithoutExport1.js

@@ -0,0 +1,21 @@
+//// [defaultKeywordWithoutExport1.ts]
+declare function decorator(constructor: any): any;
+
+@decorator
+default class {}
+
+//// [defaultKeywordWithoutExport1.js]
+var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
+    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
+    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
+    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
+    return c > 3 && r && Object.defineProperty(target, key, r), r;
+};
+var default_1 = /** @class */ (function () {
+    function default_1() {
+    }
+    default_1 = __decorate([
+        decorator
+    ], default_1);
+    return default_1;
+}());

tests/baselines/reference/defaultKeywordWithoutExport1.symbols

@@ -0,0 +1,9 @@
+=== tests/cases/compiler/defaultKeywordWithoutExport1.ts ===
+declare function decorator(constructor: any): any;
+>decorator : Symbol(decorator, Decl(defaultKeywordWithoutExport1.ts, 0, 0))
+>constructor : Symbol(constructor, Decl(defaultKeywordWithoutExport1.ts, 0, 27))
+
+@decorator
+>decorator : Symbol(decorator, Decl(defaultKeywordWithoutExport1.ts, 0, 0))
+
+default class {}

tests/baselines/reference/defaultKeywordWithoutExport1.types

@@ -0,0 +1,9 @@
+=== tests/cases/compiler/defaultKeywordWithoutExport1.ts ===
+declare function decorator(constructor: any): any;
+>decorator : (constructor: any) => any
+>constructor : any
+
+@decorator
+>decorator : (constructor: any) => any
+
+default class {}

tests/baselines/reference/defaultKeywordWithoutExport2.errors.txt

@@ -0,0 +1,12 @@
+tests/cases/compiler/defaultKeywordWithoutExport2.ts(1,1): error TS1005: 'export' expected.
+tests/cases/compiler/defaultKeywordWithoutExport2.ts(1,18): error TS1003: Identifier expected.
+
+
+==== tests/cases/compiler/defaultKeywordWithoutExport2.ts (2 errors) ====
+    default function () {
+    ~~~~~~~
+!!! error TS1005: 'export' expected.
+                     ~
+!!! error TS1003: Identifier expected.
+    
+    }

tests/baselines/reference/defaultKeywordWithoutExport2.js

@@ -0,0 +1,8 @@
+//// [defaultKeywordWithoutExport2.ts]
+default function () {
+
+}
+
+//// [defaultKeywordWithoutExport2.js]
+function () {
+}

tests/baselines/reference/defaultKeywordWithoutExport2.symbols

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/defaultKeywordWithoutExport2.ts ===
+default function () {
+> : Symbol((Missing), Decl(defaultKeywordWithoutExport2.ts, 0, 7))
+
+}

tests/baselines/reference/defaultKeywordWithoutExport2.types

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/defaultKeywordWithoutExport2.ts ===
+default function () {
+> : () => void
+
+}

tests/cases/compiler/defaultKeywordWithoutExport1.ts

@@ -0,0 +1,6 @@
+// @experimentaldecorators: true
+
+declare function decorator(constructor: any): any;
+
+@decorator
+default class {}

tests/cases/compiler/defaultKeywordWithoutExport2.ts

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