Error on redeclarations of undefined

src/compiler/checker.ts

@@ -51,6 +51,7 @@ namespace ts {
         const emitResolver = createResolver();
 
         const undefinedSymbol = createSymbol(SymbolFlags.Property | SymbolFlags.Transient, "undefined");
+        undefinedSymbol.declarations = [];
         const argumentsSymbol = createSymbol(SymbolFlags.Property | SymbolFlags.Transient, "arguments");
 
         const checker: TypeChecker = {
@@ -234,6 +235,10 @@ namespace ts {
             ResolvedReturnType
         }
 
+        const builtinGlobals: SymbolTable = {
+            [undefinedSymbol.name]: undefinedSymbol
+        };
+
         initializeTypeChecker();
 
         return checker;
@@ -360,6 +365,24 @@ namespace ts {
             }
         }
 
+        function addToSymbolTable(target: SymbolTable, source: SymbolTable, message: DiagnosticMessage) {
+            for (const id in source) {
+                if (hasProperty(source, id)) {
+                    if (hasProperty(target, id)) {
+                        // Error on redeclarations
+                        forEach(target[id].declarations, addDeclarationDiagnostic(id, message));
+                    }
+                    else {
+                        target[id] = source[id];
+                    }
+                }
+            }
+
+            function addDeclarationDiagnostic(id: string, message: DiagnosticMessage) {
+                return (declaration: Declaration) => diagnostics.add(createDiagnosticForNode(declaration, message, id));
+            }
+        }
+
         function getSymbolLinks(symbol: Symbol): SymbolLinks {
             if (symbol.flags & SymbolFlags.Transient) return <TransientSymbol>symbol;
             const id = getSymbolId(symbol);
@@ -15331,10 +15354,12 @@ namespace ts {
                 }
             });
 
+            // Setup global builtins
+            addToSymbolTable(globals, builtinGlobals, Diagnostics.Declaration_name_conflicts_with_built_in_global_identifier_0);
+
             getSymbolLinks(undefinedSymbol).type = undefinedType;
             getSymbolLinks(argumentsSymbol).type = getGlobalType("IArguments");
             getSymbolLinks(unknownSymbol).type = unknownType;
-            globals[undefinedSymbol.name] = undefinedSymbol;
 
             // Initialize special types
             globalArrayType = <GenericType>getGlobalType("Array", /*arity*/ 1);

src/compiler/diagnosticMessages.json

@@ -1188,6 +1188,10 @@
         "category": "Error",
         "code": 2396
     },
+    "Declaration name conflicts with built-in global identifier '{0}'.": {
+        "category": "Error",
+        "code": 2397
+    },
     "Duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference.": {
         "category": "Error",
         "code": 2399

tests/baselines/reference/undefinedTypeAssignment1.errors.txt

@@ -0,0 +1,11 @@
+tests/cases/compiler/undefinedTypeAssignment1.ts(1,1): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+
+
+==== tests/cases/compiler/undefinedTypeAssignment1.ts (1 errors) ====
+    type undefined = string;
+    ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+    function p(undefined = "wat") {
+    	return undefined;
+    }
+

tests/baselines/reference/undefinedTypeAssignment1.js

@@ -0,0 +1,12 @@
+//// [undefinedTypeAssignment1.ts]
+type undefined = string;
+function p(undefined = "wat") {
+	return undefined;
+}
+
+
+//// [undefinedTypeAssignment1.js]
+function p(undefined) {
+    if (undefined === void 0) { undefined = "wat"; }
+    return undefined;
+}

tests/baselines/reference/undefinedTypeAssignment2.errors.txt

@@ -0,0 +1,8 @@
+tests/cases/compiler/undefinedTypeAssignment2.ts(1,5): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+
+
+==== tests/cases/compiler/undefinedTypeAssignment2.ts (1 errors) ====
+    var undefined = void 0;
+        ~~~~~~~~~
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+

tests/baselines/reference/undefinedTypeAssignment2.js

@@ -0,0 +1,6 @@
+//// [undefinedTypeAssignment2.ts]
+var undefined = void 0;
+
+
+//// [undefinedTypeAssignment2.js]
+var undefined = void 0;

tests/baselines/reference/undefinedTypeAssignment3.errors.txt

@@ -0,0 +1,8 @@
+tests/cases/compiler/undefinedTypeAssignment3.ts(1,5): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+
+
+==== tests/cases/compiler/undefinedTypeAssignment3.ts (1 errors) ====
+    var undefined = null;
+        ~~~~~~~~~
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+

tests/baselines/reference/undefinedTypeAssignment3.js

@@ -0,0 +1,6 @@
+//// [undefinedTypeAssignment3.ts]
+var undefined = null;
+
+
+//// [undefinedTypeAssignment3.js]
+var undefined = null;

tests/baselines/reference/undefinedTypeAssignment4.errors.txt

@@ -0,0 +1,24 @@
+tests/cases/compiler/undefinedTypeAssignment4.ts(1,7): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+tests/cases/compiler/undefinedTypeAssignment4.ts(4,11): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+tests/cases/compiler/undefinedTypeAssignment4.ts(7,11): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+
+
+==== tests/cases/compiler/undefinedTypeAssignment4.ts (3 errors) ====
+    class undefined {
+          ~~~~~~~~~
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+    	foo: string;
+    }
+    interface undefined {
+              ~~~~~~~~~
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+    	member: number;
+    }
+    namespace undefined {
+              ~~~~~~~~~
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+    	export var x = 42;
+    }
+    var x: undefined;
+    var y: typeof undefined;
+

tests/baselines/reference/undefinedTypeAssignment4.js

@@ -0,0 +1,26 @@
+//// [undefinedTypeAssignment4.ts]
+class undefined {
+	foo: string;
+}
+interface undefined {
+	member: number;
+}
+namespace undefined {
+	export var x = 42;
+}
+var x: undefined;
+var y: typeof undefined;
+
+
+//// [undefinedTypeAssignment4.js]
+var undefined = (function () {
+    function undefined() {
+    }
+    return undefined;
+})();
+var undefined;
+(function (undefined) {
+    undefined.x = 42;
+})(undefined || (undefined = {}));
+var x;
+var y;

tests/cases/compiler/undefinedTypeAssignment1.ts

@@ -0,0 +1,4 @@
+type undefined = string;
+function p(undefined = "wat") {
+	return undefined;
+}

tests/cases/compiler/undefinedTypeAssignment2.ts

@@ -0,0 +1 @@
+var undefined = void 0;

tests/cases/compiler/undefinedTypeAssignment3.ts

@@ -0,0 +1 @@
+var undefined = null;

tests/cases/compiler/undefinedTypeAssignment4.ts

@@ -0,0 +1,11 @@
+class undefined {
+	foo: string;
+}
+interface undefined {
+	member: number;
+}
+namespace undefined {
+	export var x = 42;
+}
+var x: undefined;
+var y: typeof undefined;