From c4db5cc6b590bac31d0379b6db0caf3700b76d00 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <t-weswig@microsoft.com>
Date: Tue, 27 Oct 2015 12:47:35 -0700
Subject: [PATCH] Error on redeclarations of undefined

---
 src/compiler/checker.ts                       | 20 ++++++++-
 src/compiler/diagnosticMessages.json          |  4 ++
 .../undefinedTypeAssignment.errors.txt        | 43 +++++++++++++++++++
 .../reference/undefinedTypeAssignment.js      | 42 ++++++++++++++++++
 .../cases/compiler/undefinedTypeAssignment.ts | 19 ++++++++
 5 files changed, 127 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment.errors.txt
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment.js
 create mode 100644 tests/cases/compiler/undefinedTypeAssignment.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 5370e7c4f02..ba0342596c1 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -50,6 +50,7 @@ namespace ts {
         let emitResolver = createResolver();
 
         let undefinedSymbol = createSymbol(SymbolFlags.Property | SymbolFlags.Transient, "undefined");
+        undefinedSymbol.declarations = [];
         let argumentsSymbol = createSymbol(SymbolFlags.Property | SymbolFlags.Transient, "arguments");
 
         let checker: TypeChecker = {
@@ -225,6 +226,10 @@ namespace ts {
             ResolvedReturnType
         }
 
+        const builtinGlobals: SymbolTable = {
+            [undefinedSymbol.name]: undefinedSymbol
+        };
+
         initializeTypeChecker();
 
         return checker;
@@ -336,6 +341,13 @@ namespace ts {
                         target[id] = source[id];
                     }
                     else {
+                        if (target === globals && source !== builtinGlobals) {
+                            if (hasProperty(builtinGlobals, id) && source[id].declarations && source[id].declarations.length) {
+                                // Error on builtin redeclarations
+                                forEach(source[id].declarations, addDeclarationDiagnostic.bind(undefined, id));
+                                continue;
+                            }
+                        }
                         let symbol = target[id];
                         if (!(symbol.flags & SymbolFlags.Merged)) {
                             target[id] = symbol = cloneSymbol(symbol);
@@ -344,6 +356,10 @@ namespace ts {
                     }
                 }
             }
+
+            function addDeclarationDiagnostic(id: string, declaration: Declaration) {
+                diagnostics.add(createDiagnosticForNode(declaration, Diagnostics.Declaration_duplicates_builtin_global_identifier_0, id));
+            }
         }
 
         function getSymbolLinks(symbol: Symbol): SymbolLinks {
@@ -14909,6 +14925,9 @@ namespace ts {
                 bindSourceFile(file);
             });
 
+            // Setup global builtins
+            mergeSymbolTable(globals, builtinGlobals);
+
             // Initialize global symbol table
             forEach(host.getSourceFiles(), file => {
                 if (!isExternalModule(file)) {
@@ -14920,7 +14939,6 @@ namespace ts {
             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);
             globalObjectType = getGlobalType("Object");
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index b799c2addba..d6e7d8dd592 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1168,6 +1168,10 @@
         "category": "Error",
         "code": 2396
     },
+    "Declaration duplicates builtin global identifier '{0}'.": {
+        "category": "Error",
+        "code": 2397
+    },
     "Duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference.": {
         "category": "Error",
         "code": 2399
diff --git a/tests/baselines/reference/undefinedTypeAssignment.errors.txt b/tests/baselines/reference/undefinedTypeAssignment.errors.txt
new file mode 100644
index 00000000000..a14b1191255
--- /dev/null
+++ b/tests/baselines/reference/undefinedTypeAssignment.errors.txt
@@ -0,0 +1,43 @@
+tests/cases/compiler/a.ts(1,1): error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+tests/cases/compiler/a.ts(2,5): error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+tests/cases/compiler/a.ts(3,5): error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+tests/cases/compiler/b.ts(1,7): error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+tests/cases/compiler/b.ts(4,11): error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+tests/cases/compiler/b.ts(7,11): error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+tests/cases/compiler/b.ts(10,8): error TS2304: Cannot find name 'undefined'.
+
+
+==== tests/cases/compiler/a.ts (3 errors) ====
+    type undefined = string;
+    ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+    var undefined = void 0;
+        ~~~~~~~~~
+!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+    var undefined = null;
+        ~~~~~~~~~
+!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+    function p(undefined = 42) {
+    	return undefined;
+    }
+==== tests/cases/compiler/b.ts (4 errors) ====
+    class undefined {
+          ~~~~~~~~~
+!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+    	foo: string;
+    }
+    interface undefined {
+              ~~~~~~~~~
+!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+    	member: number;
+    }
+    namespace undefined {
+              ~~~~~~~~~
+!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+    	export var x = 42;
+    }
+    var x: undefined;
+           ~~~~~~~~~
+!!! error TS2304: Cannot find name 'undefined'.
+    var x: typeof undefined;
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/undefinedTypeAssignment.js b/tests/baselines/reference/undefinedTypeAssignment.js
new file mode 100644
index 00000000000..9b4106c18ea
--- /dev/null
+++ b/tests/baselines/reference/undefinedTypeAssignment.js
@@ -0,0 +1,42 @@
+//// [tests/cases/compiler/undefinedTypeAssignment.ts] ////
+
+//// [a.ts]
+type undefined = string;
+var undefined = void 0;
+var undefined = null;
+function p(undefined = 42) {
+	return undefined;
+}
+//// [b.ts]
+class undefined {
+	foo: string;
+}
+interface undefined {
+	member: number;
+}
+namespace undefined {
+	export var x = 42;
+}
+var x: undefined;
+var x: typeof undefined;
+
+
+//// [a.js]
+var undefined = void 0;
+var undefined = null;
+function p(undefined) {
+    if (undefined === void 0) { undefined = 42; }
+    return undefined;
+}
+//// [b.js]
+var undefined = (function () {
+    function undefined() {
+    }
+    return undefined;
+})();
+var undefined;
+(function (undefined) {
+    undefined.x = 42;
+})(undefined || (undefined = {}));
+var x;
+var x;
diff --git a/tests/cases/compiler/undefinedTypeAssignment.ts b/tests/cases/compiler/undefinedTypeAssignment.ts
new file mode 100644
index 00000000000..d8a128a49e7
--- /dev/null
+++ b/tests/cases/compiler/undefinedTypeAssignment.ts
@@ -0,0 +1,19 @@
+// @filename: a.ts
+type undefined = string;
+var undefined = void 0;
+var undefined = null;
+function p(undefined = 42) {
+	return undefined;
+}
+// @filename: b.ts
+class undefined {
+	foo: string;
+}
+interface undefined {
+	member: number;
+}
+namespace undefined {
+	export var x = 42;
+}
+var x: undefined;
+var x: typeof undefined;