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 1/4] 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;

From 0e47c67ee1b78aef0ac7d5ec63a1197e5499d688 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <t-weswig@microsoft.com>
Date: Wed, 28 Oct 2015 17:00:47 -0700
Subject: [PATCH 2/4] update error

---
 src/compiler/checker.ts                       |  2 +-
 src/compiler/diagnosticMessages.json          |  2 +-
 .../undefinedTypeAssignment.errors.txt        | 24 +++++++++----------
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ba0342596c1..fd86ff97c6a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -358,7 +358,7 @@ namespace ts {
             }
 
             function addDeclarationDiagnostic(id: string, declaration: Declaration) {
-                diagnostics.add(createDiagnosticForNode(declaration, Diagnostics.Declaration_duplicates_builtin_global_identifier_0, id));
+                diagnostics.add(createDiagnosticForNode(declaration, Diagnostics.Declaration_name_conflicts_with_built_in_global_identifier_0, id));
             }
         }
 
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index d6e7d8dd592..be0628e93dd 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1168,7 +1168,7 @@
         "category": "Error",
         "code": 2396
     },
-    "Declaration duplicates builtin global identifier '{0}'.": {
+    "Declaration name conflicts with built-in global identifier '{0}'.": {
         "category": "Error",
         "code": 2397
     },
diff --git a/tests/baselines/reference/undefinedTypeAssignment.errors.txt b/tests/baselines/reference/undefinedTypeAssignment.errors.txt
index a14b1191255..0b4a8eff874 100644
--- a/tests/baselines/reference/undefinedTypeAssignment.errors.txt
+++ b/tests/baselines/reference/undefinedTypeAssignment.errors.txt
@@ -1,39 +1,39 @@
-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/a.ts(1,1): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+tests/cases/compiler/a.ts(2,5): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+tests/cases/compiler/a.ts(3,5): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+tests/cases/compiler/b.ts(1,7): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+tests/cases/compiler/b.ts(4,11): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+tests/cases/compiler/b.ts(7,11): error TS2397: Declaration name conflicts with built-in 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'.
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
     var undefined = void 0;
         ~~~~~~~~~
-!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
     var undefined = null;
         ~~~~~~~~~
-!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+!!! error TS2397: Declaration name conflicts with built-in 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'.
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
     	foo: string;
     }
     interface undefined {
               ~~~~~~~~~
-!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
     	member: number;
     }
     namespace undefined {
               ~~~~~~~~~
-!!! error TS2397: Declaration duplicates builtin global identifier 'undefined'.
+!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
     	export var x = 42;
     }
     var x: undefined;

From 00576527bd78e095c2d074af4ee70304b58045db Mon Sep 17 00:00:00 2001
From: Wesley Wigham <t-weswig@microsoft.com>
Date: Fri, 4 Dec 2015 15:41:11 -0800
Subject: [PATCH 3/4] break down tests, make more clear whats doing done,
 remove specific logic from mergeSymbolTable

---
 src/compiler/checker.ts                       | 31 ++++++++++++-------
 .../cases/compiler/undefinedTypeAssignment.ts | 19 ------------
 .../compiler/undefinedTypeAssignment1.ts      |  4 +++
 .../compiler/undefinedTypeAssignment2.ts      |  1 +
 .../compiler/undefinedTypeAssignment3.ts      |  1 +
 .../compiler/undefinedTypeAssignment4.ts      | 11 +++++++
 6 files changed, 36 insertions(+), 31 deletions(-)
 delete mode 100644 tests/cases/compiler/undefinedTypeAssignment.ts
 create mode 100644 tests/cases/compiler/undefinedTypeAssignment1.ts
 create mode 100644 tests/cases/compiler/undefinedTypeAssignment2.ts
 create mode 100644 tests/cases/compiler/undefinedTypeAssignment3.ts
 create mode 100644 tests/cases/compiler/undefinedTypeAssignment4.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 18667e46733..8adb05f7a9c 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -355,13 +355,6 @@ 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);
@@ -370,9 +363,23 @@ namespace ts {
                     }
                 }
             }
+        }
 
-            function addDeclarationDiagnostic(id: string, declaration: Declaration) {
-                diagnostics.add(createDiagnosticForNode(declaration, Diagnostics.Declaration_name_conflicts_with_built_in_global_identifier_0, id));
+        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));
             }
         }
 
@@ -15340,9 +15347,6 @@ namespace ts {
                 bindSourceFile(file, compilerOptions);
             });
 
-            // Setup global builtins
-            mergeSymbolTable(globals, builtinGlobals);
-
             // Initialize global symbol table
             forEach(host.getSourceFiles(), file => {
                 if (!isExternalOrCommonJsModule(file)) {
@@ -15350,6 +15354,9 @@ 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;
diff --git a/tests/cases/compiler/undefinedTypeAssignment.ts b/tests/cases/compiler/undefinedTypeAssignment.ts
deleted file mode 100644
index d8a128a49e7..00000000000
--- a/tests/cases/compiler/undefinedTypeAssignment.ts
+++ /dev/null
@@ -1,19 +0,0 @@
-// @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;
diff --git a/tests/cases/compiler/undefinedTypeAssignment1.ts b/tests/cases/compiler/undefinedTypeAssignment1.ts
new file mode 100644
index 00000000000..7d340daba69
--- /dev/null
+++ b/tests/cases/compiler/undefinedTypeAssignment1.ts
@@ -0,0 +1,4 @@
+type undefined = string;
+function p(undefined = "wat") {
+	return undefined;
+}
diff --git a/tests/cases/compiler/undefinedTypeAssignment2.ts b/tests/cases/compiler/undefinedTypeAssignment2.ts
new file mode 100644
index 00000000000..3f42068e24e
--- /dev/null
+++ b/tests/cases/compiler/undefinedTypeAssignment2.ts
@@ -0,0 +1 @@
+var undefined = void 0;
diff --git a/tests/cases/compiler/undefinedTypeAssignment3.ts b/tests/cases/compiler/undefinedTypeAssignment3.ts
new file mode 100644
index 00000000000..8bada4f946c
--- /dev/null
+++ b/tests/cases/compiler/undefinedTypeAssignment3.ts
@@ -0,0 +1 @@
+var undefined = null;
diff --git a/tests/cases/compiler/undefinedTypeAssignment4.ts b/tests/cases/compiler/undefinedTypeAssignment4.ts
new file mode 100644
index 00000000000..fc0dc155acd
--- /dev/null
+++ b/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;

From cb4a40867ee7b76500ebe3f4fcff582b6e1894af Mon Sep 17 00:00:00 2001
From: Wesley Wigham <t-weswig@microsoft.com>
Date: Fri, 4 Dec 2015 15:44:35 -0800
Subject: [PATCH 4/4] add baselines

---
 .../undefinedTypeAssignment.errors.txt        | 43 -------------------
 .../reference/undefinedTypeAssignment.js      | 42 ------------------
 .../undefinedTypeAssignment1.errors.txt       | 11 +++++
 .../reference/undefinedTypeAssignment1.js     | 12 ++++++
 .../undefinedTypeAssignment2.errors.txt       |  8 ++++
 .../reference/undefinedTypeAssignment2.js     |  6 +++
 .../undefinedTypeAssignment3.errors.txt       |  8 ++++
 .../reference/undefinedTypeAssignment3.js     |  6 +++
 .../undefinedTypeAssignment4.errors.txt       | 24 +++++++++++
 .../reference/undefinedTypeAssignment4.js     | 26 +++++++++++
 10 files changed, 101 insertions(+), 85 deletions(-)
 delete mode 100644 tests/baselines/reference/undefinedTypeAssignment.errors.txt
 delete mode 100644 tests/baselines/reference/undefinedTypeAssignment.js
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment1.errors.txt
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment1.js
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment2.errors.txt
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment2.js
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment3.errors.txt
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment3.js
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment4.errors.txt
 create mode 100644 tests/baselines/reference/undefinedTypeAssignment4.js

diff --git a/tests/baselines/reference/undefinedTypeAssignment.errors.txt b/tests/baselines/reference/undefinedTypeAssignment.errors.txt
deleted file mode 100644
index 0b4a8eff874..00000000000
--- a/tests/baselines/reference/undefinedTypeAssignment.errors.txt
+++ /dev/null
@@ -1,43 +0,0 @@
-tests/cases/compiler/a.ts(1,1): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
-tests/cases/compiler/a.ts(2,5): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
-tests/cases/compiler/a.ts(3,5): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
-tests/cases/compiler/b.ts(1,7): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
-tests/cases/compiler/b.ts(4,11): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
-tests/cases/compiler/b.ts(7,11): error TS2397: Declaration name conflicts with built-in 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 name conflicts with built-in global identifier 'undefined'.
-    var undefined = void 0;
-        ~~~~~~~~~
-!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
-    var undefined = null;
-        ~~~~~~~~~
-!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
-    function p(undefined = 42) {
-    	return undefined;
-    }
-==== tests/cases/compiler/b.ts (4 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;
-           ~~~~~~~~~
-!!! 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
deleted file mode 100644
index 9b4106c18ea..00000000000
--- a/tests/baselines/reference/undefinedTypeAssignment.js
+++ /dev/null
@@ -1,42 +0,0 @@
-//// [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/baselines/reference/undefinedTypeAssignment1.errors.txt b/tests/baselines/reference/undefinedTypeAssignment1.errors.txt
new file mode 100644
index 00000000000..b8dd74a58a8
--- /dev/null
+++ b/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;
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/undefinedTypeAssignment1.js b/tests/baselines/reference/undefinedTypeAssignment1.js
new file mode 100644
index 00000000000..1f53c4f6c45
--- /dev/null
+++ b/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;
+}
diff --git a/tests/baselines/reference/undefinedTypeAssignment2.errors.txt b/tests/baselines/reference/undefinedTypeAssignment2.errors.txt
new file mode 100644
index 00000000000..55fdbf0fc1b
--- /dev/null
+++ b/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'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/undefinedTypeAssignment2.js b/tests/baselines/reference/undefinedTypeAssignment2.js
new file mode 100644
index 00000000000..040bc8c800d
--- /dev/null
+++ b/tests/baselines/reference/undefinedTypeAssignment2.js
@@ -0,0 +1,6 @@
+//// [undefinedTypeAssignment2.ts]
+var undefined = void 0;
+
+
+//// [undefinedTypeAssignment2.js]
+var undefined = void 0;
diff --git a/tests/baselines/reference/undefinedTypeAssignment3.errors.txt b/tests/baselines/reference/undefinedTypeAssignment3.errors.txt
new file mode 100644
index 00000000000..88df370940f
--- /dev/null
+++ b/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'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/undefinedTypeAssignment3.js b/tests/baselines/reference/undefinedTypeAssignment3.js
new file mode 100644
index 00000000000..4015d49e33a
--- /dev/null
+++ b/tests/baselines/reference/undefinedTypeAssignment3.js
@@ -0,0 +1,6 @@
+//// [undefinedTypeAssignment3.ts]
+var undefined = null;
+
+
+//// [undefinedTypeAssignment3.js]
+var undefined = null;
diff --git a/tests/baselines/reference/undefinedTypeAssignment4.errors.txt b/tests/baselines/reference/undefinedTypeAssignment4.errors.txt
new file mode 100644
index 00000000000..dab6ea2a880
--- /dev/null
+++ b/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;
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/undefinedTypeAssignment4.js b/tests/baselines/reference/undefinedTypeAssignment4.js
new file mode 100644
index 00000000000..186afd872c3
--- /dev/null
+++ b/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;