break down tests, make more clear whats doing done, remove specific logic from mergeSymbolTable

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;

tests/cases/compiler/undefinedTypeAssignment.ts

@@ -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;

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;