Disallow merging for default export declarations

src/compiler/checker.ts

@@ -4363,11 +4363,11 @@ namespace ts {
                         return getInferredType(context, i);
                     }
                 }
-                return t;
+                return t;
             };
 
             mapper.context = context;
-            return mapper;
+            return mapper;
         }
 
         function identityMapper(type: Type): Type {
@@ -10849,9 +10849,6 @@ namespace ts {
                 return;
             }
 
-            // Exports should be checked only if enclosing module contains both exported and non exported declarations.
-            // In case if all declarations are non-exported check is unnecessary.
-
             // if localSymbol is defined on node then node itself is exported - check is required
             let symbol = node.localSymbol;
             if (!symbol) {
@@ -10871,27 +10868,45 @@ namespace ts {
 
             // we use SymbolFlags.ExportValue, SymbolFlags.ExportType and SymbolFlags.ExportNamespace
             // to denote disjoint declarationSpaces (without making new enum type).
-            let exportedDeclarationSpaces: SymbolFlags = 0;
-            let nonExportedDeclarationSpaces: SymbolFlags = 0;
-            forEach(symbol.declarations, d => {
+            let exportedDeclarationSpaces = SymbolFlags.None;
+            let nonExportedDeclarationSpaces = SymbolFlags.None;
+            let defaultExportedDeclarationSpaces = SymbolFlags.None;
+            for (let d of symbol.declarations) {
                 let declarationSpaces = getDeclarationSpaces(d);
-                if (getEffectiveDeclarationFlags(d, NodeFlags.Export)) {
-                    exportedDeclarationSpaces |= declarationSpaces;
+                let effectiveDeclarationFlags = getEffectiveDeclarationFlags(d, NodeFlags.Export | NodeFlags.Default);
+
+                if (effectiveDeclarationFlags & NodeFlags.Export) {
+                    if (effectiveDeclarationFlags & NodeFlags.Default) {
+                        defaultExportedDeclarationSpaces |= declarationSpaces;
+                    }
+                    else {
+                        exportedDeclarationSpaces |= declarationSpaces;
+                    }
                 }
                 else {
                     nonExportedDeclarationSpaces |= declarationSpaces;
                 }
-            });
+            }
 
-            let commonDeclarationSpace = exportedDeclarationSpaces & nonExportedDeclarationSpaces;
+            // Spaces for anyting not declared a 'default export'.
+            let nonDefaultExportedDeclarationSpaces = exportedDeclarationSpaces | nonExportedDeclarationSpaces;
+
+            let commonDeclarationSpacesForExportsAndLocals = exportedDeclarationSpaces & nonExportedDeclarationSpaces;
+            let commonDeclarationSpacesForDefaultAndNonDefault = defaultExportedDeclarationSpaces & nonDefaultExportedDeclarationSpaces;
 
-            if (commonDeclarationSpace) {
+            if (commonDeclarationSpacesForExportsAndLocals || commonDeclarationSpacesForDefaultAndNonDefault) {
                 // declaration spaces for exported and non-exported declarations intersect
-                forEach(symbol.declarations, d => {
-                    if (getDeclarationSpaces(d) & commonDeclarationSpace) {
+                for (let d of symbol.declarations) {
+                    let declarationSpaces = getDeclarationSpaces(d);
+
+                    // Only error on the declarations that conributed to the intersecting spaces.
+                    if (declarationSpaces & commonDeclarationSpacesForDefaultAndNonDefault) {
+                        error(d.name, Diagnostics.Merged_declaration_0_cannot_include_a_default_export_declaration_Consider_adding_a_separate_export_default_0_declaration_instead, declarationNameToString(d.name));
+                    }
+                    else if (declarationSpaces & commonDeclarationSpacesForExportsAndLocals) {
                         error(d.name, Diagnostics.Individual_declarations_in_merged_declaration_0_must_be_all_exported_or_all_local, declarationNameToString(d.name));
                     }
-                });
+                }
             }
 
             function getDeclarationSpaces(d: Declaration): SymbolFlags {

src/compiler/diagnosticInformationMap.generated.ts

@@ -294,7 +294,7 @@ namespace ts {
         Multiple_constructor_implementations_are_not_allowed: { code: 2392, category: DiagnosticCategory.Error, key: "Multiple constructor implementations are not allowed." },
         Duplicate_function_implementation: { code: 2393, category: DiagnosticCategory.Error, key: "Duplicate function implementation." },
         Overload_signature_is_not_compatible_with_function_implementation: { code: 2394, category: DiagnosticCategory.Error, key: "Overload signature is not compatible with function implementation." },
-        Individual_declarations_in_merged_declaration_0_must_be_all_exported_or_all_local: { code: 2395, category: DiagnosticCategory.Error, key: "Individual declarations in merged declaration {0} must be all exported or all local." },
+        Individual_declarations_in_merged_declaration_0_must_be_all_exported_or_all_local: { code: 2395, category: DiagnosticCategory.Error, key: "Individual declarations in merged declaration '{0}' must be all exported or all local." },
         Duplicate_identifier_arguments_Compiler_uses_arguments_to_initialize_rest_parameters: { code: 2396, category: DiagnosticCategory.Error, key: "Duplicate identifier 'arguments'. Compiler uses 'arguments' to initialize rest parameters." },
         Duplicate_identifier_this_Compiler_uses_variable_declaration_this_to_capture_this_reference: { code: 2399, category: DiagnosticCategory.Error, key: "Duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference." },
         Expression_resolves_to_variable_declaration_this_that_compiler_uses_to_capture_this_reference: { code: 2400, category: DiagnosticCategory.Error, key: "Expression resolves to variable declaration '_this' that compiler uses to capture 'this' reference." },
@@ -425,6 +425,7 @@ namespace ts {
         JSX_element_class_does_not_support_attributes_because_it_does_not_have_a_0_property: { code: 2607, category: DiagnosticCategory.Error, key: "JSX element class does not support attributes because it does not have a '{0}' property" },
         The_global_type_JSX_0_may_not_have_more_than_one_property: { code: 2608, category: DiagnosticCategory.Error, key: "The global type 'JSX.{0}' may not have more than one property" },
         Cannot_emit_namespaced_JSX_elements_in_React: { code: 2650, category: DiagnosticCategory.Error, key: "Cannot emit namespaced JSX elements in React" },
+        Merged_declaration_0_cannot_include_a_default_export_declaration_Consider_adding_a_separate_export_default_0_declaration_instead: { code: 2651, category: DiagnosticCategory.Error, key: "Merged declaration '{0}' cannot include a default export declaration. Consider adding a separate 'export default {0}' declaration instead." },
         Import_declaration_0_is_using_private_name_1: { code: 4000, category: DiagnosticCategory.Error, key: "Import declaration '{0}' is using private name '{1}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_private_name_1: { code: 4002, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using private name '{1}'." },
         Type_parameter_0_of_exported_interface_has_or_is_using_private_name_1: { code: 4004, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported interface has or is using private name '{1}'." },

src/compiler/diagnosticMessages.json

@@ -1165,7 +1165,7 @@
         "category": "Error",
         "code": 2394
     },
-    "Individual declarations in merged declaration {0} must be all exported or all local.": {
+    "Individual declarations in merged declaration '{0}' must be all exported or all local.": {
         "category": "Error",
         "code": 2395
     },
@@ -1689,6 +1689,10 @@
         "category": "Error",
         "code": 2650
     },
+    "Merged declaration '{0}' cannot include a default export declaration. Consider adding a separate 'export default {0}' declaration instead.": {
+        "category": "Error",
+        "code": 2651
+    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000

tests/baselines/reference/defaultExportsCannotMerge01.errors.txt

@@ -0,0 +1,49 @@
+tests/cases/conformance/es6/modules/m1.ts(2,25): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m1.ts(11,18): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m2.ts(5,8): error TS2304: Cannot find name 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(6,8): error TS2503: Cannot find namespace 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(8,8): error TS2339: Property 'x' does not exist on type '() => number'.
+tests/cases/conformance/es6/modules/m2.ts(9,8): error TS2339: Property 'y' does not exist on type '() => number'.
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (2 errors) ====
+
+    export default function Decl() {
+                            ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        return 0;
+    }
+
+    export interface Decl {
+        p1: number;
+        p2: number;
+    }
+
+    export namespace Decl {
+                     ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        export var x = 10;
+        export var y = 20;
+
+        interface I {
+        }
+    }
+
+==== tests/cases/conformance/es6/modules/m2.ts (4 errors) ====
+    import Entity from "m1"
+
+    Entity();
+
+    var x: Entity;
+           ~~~~~~
+!!! error TS2304: Cannot find name 'Entity'.
+    var y: Entity.I;
+           ~~~~~~
+!!! error TS2503: Cannot find namespace 'Entity'.
+
+    Entity.x;
+           ~
+!!! error TS2339: Property 'x' does not exist on type '() => number'.
+    Entity.y;
+           ~
+!!! error TS2339: Property 'y' does not exist on type '() => number'.

tests/baselines/reference/defaultExportsCannotMerge01.js

@@ -0,0 +1,50 @@
+//// [tests/cases/conformance/es6/modules/defaultExportsCannotMerge01.ts] ////
+
+//// [m1.ts]
+
+export default function Decl() {
+    return 0;
+}
+
+export interface Decl {
+    p1: number;
+    p2: number;
+}
+
+export namespace Decl {
+    export var x = 10;
+    export var y = 20;
+
+    interface I {
+    }
+}
+
+//// [m2.ts]
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+
+Entity.x;
+Entity.y;
+
+//// [m1.js]
+function Decl() {
+    return 0;
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = Decl;
+var Decl;
+(function (Decl) {
+    Decl.x = 10;
+    Decl.y = 20;
+})(Decl = exports.Decl || (exports.Decl = {}));
+//// [m2.js]
+var m1_1 = require("m1");
+m1_1.default();
+var x;
+var y;
+m1_1.default.x;
+m1_1.default.y;

tests/baselines/reference/defaultExportsCannotMerge02.errors.txt

@@ -0,0 +1,44 @@
+tests/cases/conformance/es6/modules/m1.ts(2,22): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m1.ts(5,18): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m2.ts(3,1): error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+tests/cases/conformance/es6/modules/m2.ts(6,8): error TS2503: Cannot find namespace 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(8,13): error TS2339: Property 'p1' does not exist on type 'Decl'.
+tests/cases/conformance/es6/modules/m2.ts(8,20): error TS2339: Property 'p2' does not exist on type 'Decl'.
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (2 errors) ====
+
+    export default class Decl {
+                         ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+    }
+
+    export interface Decl {
+                     ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        p1: number;
+        p2: number;
+    }
+
+    export namespace Decl {
+        interface I {
+        }
+    }
+
+==== tests/cases/conformance/es6/modules/m2.ts (4 errors) ====
+    import Entity from "m1"
+
+    Entity();
+    ~~~~~~~~
+!!! error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+
+    var x: Entity;
+    var y: Entity.I;
+           ~~~~~~
+!!! error TS2503: Cannot find namespace 'Entity'.
+    var z = new Entity();
+    var sum = z.p1 + z.p2
+                ~~
+!!! error TS2339: Property 'p1' does not exist on type 'Decl'.
+                       ~~
+!!! error TS2339: Property 'p2' does not exist on type 'Decl'.

tests/baselines/reference/defaultExportsCannotMerge02.js

@@ -0,0 +1,42 @@
+//// [tests/cases/conformance/es6/modules/defaultExportsCannotMerge02.ts] ////
+
+//// [m1.ts]
+
+export default class Decl {
+}
+
+export interface Decl {
+    p1: number;
+    p2: number;
+}
+
+export namespace Decl {
+    interface I {
+    }
+}
+
+//// [m2.ts]
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+var z = new Entity();
+var sum = z.p1 + z.p2
+
+//// [m1.js]
+var Decl = (function () {
+    function Decl() {
+    }
+    return Decl;
+})();
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = Decl;
+//// [m2.js]
+var m1_1 = require("m1");
+m1_1.default();
+var x;
+var y;
+var z = new m1_1.default();
+var sum = z.p1 + z.p2;

tests/baselines/reference/defaultExportsCannotMerge03.errors.txt

@@ -0,0 +1,47 @@
+tests/cases/conformance/es6/modules/m1.ts(2,22): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m1.ts(5,11): error TS2518: Only an ambient class can be merged with an interface.
+tests/cases/conformance/es6/modules/m1.ts(5,11): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m2.ts(3,1): error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+tests/cases/conformance/es6/modules/m2.ts(6,8): error TS2503: Cannot find namespace 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(8,13): error TS2339: Property 'p1' does not exist on type 'Decl'.
+tests/cases/conformance/es6/modules/m2.ts(8,20): error TS2339: Property 'p2' does not exist on type 'Decl'.
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (3 errors) ====
+
+    export default class Decl {
+                         ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+    }
+
+    interface Decl {
+              ~~~~
+!!! error TS2518: Only an ambient class can be merged with an interface.
+              ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        p1: number;
+        p2: number;
+    }
+
+    namespace Decl {
+        interface I {
+        }
+    }
+
+==== tests/cases/conformance/es6/modules/m2.ts (4 errors) ====
+    import Entity from "m1"
+
+    Entity();
+    ~~~~~~~~
+!!! error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+
+    var x: Entity;
+    var y: Entity.I;
+           ~~~~~~
+!!! error TS2503: Cannot find namespace 'Entity'.
+    var z = new Entity();
+    var sum = z.p1 + z.p2
+                ~~
+!!! error TS2339: Property 'p1' does not exist on type 'Decl'.
+                       ~~
+!!! error TS2339: Property 'p2' does not exist on type 'Decl'.