Add "A module cannot have multiple default exports." message for multiple "default" exports

src/compiler/binder.ts

@@ -185,8 +185,9 @@ namespace ts {
         function declareSymbol(symbolTable: SymbolTable, parent: Symbol, node: Declaration, includes: SymbolFlags, excludes: SymbolFlags): Symbol {
             Debug.assert(!hasDynamicName(node));
 
+            let isDefaultExport = node.flags & NodeFlags.Default;
             // The exported symbol for an export default function/class node is always named "default"
-            let name = node.flags & NodeFlags.Default && parent ? "default" : getDeclarationName(node);
+            let name = isDefaultExport && parent ? "default" : getDeclarationName(node);
 
             let symbol: Symbol;
             if (name !== undefined) {
@@ -227,6 +228,13 @@ namespace ts {
                     let message = symbol.flags & SymbolFlags.BlockScopedVariable
                         ? Diagnostics.Cannot_redeclare_block_scoped_variable_0
                         : Diagnostics.Duplicate_identifier_0;
+
+                    forEach(symbol.declarations, declaration => {
+                        if (declaration.flags & NodeFlags.Default) {
+                            message = Diagnostics.A_module_cannot_have_multiple_default_exports;
+                        }
+                    });
+
                     forEach(symbol.declarations, declaration => {
                         file.bindDiagnostics.push(createDiagnosticForNode(declaration.name || declaration, message, getDisplayName(declaration)));
                     });

src/compiler/diagnosticMessages.json

@@ -1656,6 +1656,10 @@
         "category": "Error",
         "code": 2527
     },
+    "A module cannot have multiple default exports.": {
+        "category": "Error",
+        "code": 2528
+    },
     "JSX element attributes type '{0}' must be an object type.": {
         "category": "Error",
         "code": 2600

tests/baselines/reference/defaultExportWithOverloads01.js

@@ -0,0 +1,16 @@
+//// [defaultExportWithOverloads01.ts]
+
+export default function f();
+export default function f(x: string);
+export default function f(...args: any[]) {
+}
+
+//// [defaultExportWithOverloads01.js]
+function f() {
+    var args = [];
+    for (var _i = 0; _i < arguments.length; _i++) {
+        args[_i - 0] = arguments[_i];
+    }
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = f;

tests/baselines/reference/defaultExportWithOverloads01.symbols

@@ -0,0 +1,13 @@
+=== tests/cases/conformance/es6/modules/defaultExportWithOverloads01.ts ===
+
+export default function f();
+>f : Symbol(f, Decl(defaultExportWithOverloads01.ts, 0, 0), Decl(defaultExportWithOverloads01.ts, 1, 28), Decl(defaultExportWithOverloads01.ts, 2, 37))
+
+export default function f(x: string);
+>f : Symbol(f, Decl(defaultExportWithOverloads01.ts, 0, 0), Decl(defaultExportWithOverloads01.ts, 1, 28), Decl(defaultExportWithOverloads01.ts, 2, 37))
+>x : Symbol(x, Decl(defaultExportWithOverloads01.ts, 2, 26))
+
+export default function f(...args: any[]) {
+>f : Symbol(f, Decl(defaultExportWithOverloads01.ts, 0, 0), Decl(defaultExportWithOverloads01.ts, 1, 28), Decl(defaultExportWithOverloads01.ts, 2, 37))
+>args : Symbol(args, Decl(defaultExportWithOverloads01.ts, 3, 26))
+}

tests/baselines/reference/defaultExportWithOverloads01.types

@@ -0,0 +1,13 @@
+=== tests/cases/conformance/es6/modules/defaultExportWithOverloads01.ts ===
+
+export default function f();
+>f : { (): any; (x: string): any; }
+
+export default function f(x: string);
+>f : { (): any; (x: string): any; }
+>x : string
+
+export default function f(...args: any[]) {
+>f : { (): any; (x: string): any; }
+>args : any[]
+}

tests/baselines/reference/multipleDefaultExports01.errors.txt

@@ -1,6 +1,6 @@
-tests/cases/conformance/es6/modules/m1.ts(2,22): error TS2300: Duplicate identifier 'foo'.
-tests/cases/conformance/es6/modules/m1.ts(6,25): error TS2300: Duplicate identifier 'bar'.
-tests/cases/conformance/es6/modules/m1.ts(11,1): error TS2300: Duplicate identifier 'default'.
+tests/cases/conformance/es6/modules/m1.ts(2,22): error TS2528: A module cannot have multiple default exports.
+tests/cases/conformance/es6/modules/m1.ts(6,25): error TS2528: A module cannot have multiple default exports.
+tests/cases/conformance/es6/modules/m1.ts(11,1): error TS2528: A module cannot have multiple default exports.
 tests/cases/conformance/es6/modules/m2.ts(3,1): error TS2348: Value of type 'typeof foo' is not callable. Did you mean to include 'new'?
 
 
@@ -8,20 +8,20 @@ tests/cases/conformance/es6/modules/m2.ts(3,1): error TS2348: Value of type 'typ
     
     export default class foo {
                          ~~~
-!!! error TS2300: Duplicate identifier 'foo'.
+!!! error TS2528: A module cannot have multiple default exports.
     
     }
     
     export default function bar() {
                             ~~~
-!!! error TS2300: Duplicate identifier 'bar'.
+!!! error TS2528: A module cannot have multiple default exports.
     
     }
     
     var x = 10;
     export default x;
     ~~~~~~~~~~~~~~~~~
-!!! error TS2300: Duplicate identifier 'default'.
+!!! error TS2528: A module cannot have multiple default exports.
     
 ==== tests/cases/conformance/es6/modules/m2.ts (1 errors) ====
     import Entity from "./m1"

tests/baselines/reference/multipleDefaultExports03.errors.txt

@@ -0,0 +1,15 @@
+tests/cases/conformance/es6/modules/multipleDefaultExports03.ts(2,22): error TS2528: A module cannot have multiple default exports.
+tests/cases/conformance/es6/modules/multipleDefaultExports03.ts(5,22): error TS2528: A module cannot have multiple default exports.
+
+
+==== tests/cases/conformance/es6/modules/multipleDefaultExports03.ts (2 errors) ====
+    
+    export default class C {
+                         ~
+!!! error TS2528: A module cannot have multiple default exports.
+    }
+    
+    export default class C {
+                         ~
+!!! error TS2528: A module cannot have multiple default exports.
+    }

tests/baselines/reference/multipleDefaultExports03.js

@@ -0,0 +1,23 @@
+//// [multipleDefaultExports03.ts]
+
+export default class C {
+}
+
+export default class C {
+}
+
+//// [multipleDefaultExports03.js]
+var C = (function () {
+    function C() {
+    }
+    return C;
+})();
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = C;
+var C = (function () {
+    function C() {
+    }
+    return C;
+})();
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = C;

tests/baselines/reference/multipleDefaultExports04.errors.txt

@@ -0,0 +1,15 @@
+tests/cases/conformance/es6/modules/multipleDefaultExports04.ts(2,25): error TS2393: Duplicate function implementation.
+tests/cases/conformance/es6/modules/multipleDefaultExports04.ts(5,25): error TS2393: Duplicate function implementation.
+
+
+==== tests/cases/conformance/es6/modules/multipleDefaultExports04.ts (2 errors) ====
+    
+    export default function f() {
+                            ~
+!!! error TS2393: Duplicate function implementation.
+    }
+    
+    export default function f() {
+                            ~
+!!! error TS2393: Duplicate function implementation.
+    }

tests/baselines/reference/multipleDefaultExports04.js

@@ -0,0 +1,17 @@
+//// [multipleDefaultExports04.ts]
+
+export default function f() {
+}
+
+export default function f() {
+}
+
+//// [multipleDefaultExports04.js]
+function f() {
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = f;
+function f() {
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = f;

tests/cases/conformance/es6/modules/defaultExportWithOverloads01.ts

@@ -0,0 +1,7 @@
+// @module: commonjs
+// @target: ES5
+
+export default function f();
+export default function f(x: string);
+export default function f(...args: any[]) {
+}

tests/cases/conformance/es6/modules/multipleDefaultExports03.ts

@@ -0,0 +1,8 @@
+// @module: commonjs
+// @target: ES5
+
+export default class C {
+}
+
+export default class C {
+}

tests/cases/conformance/es6/modules/multipleDefaultExports04.ts

@@ -0,0 +1,8 @@
+// @module: commonjs
+// @target: ES5
+
+export default function f() {
+}
+
+export default function f() {
+}