Error on types named "undefined"

src/compiler/checker.ts

@@ -2255,9 +2255,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     var identityRelation = new Map<string, RelationComparisonResult>();
     var enumRelation = new Map<string, RelationComparisonResult>();
 
-    var builtinGlobals = createSymbolTable();
-    builtinGlobals.set(undefinedSymbol.escapedName, undefinedSymbol);
-
     // Extensions suggested for path imports when module resolution is node16 or higher.
     // The first element of each tuple is the extension a file has.
     // The second element of each tuple is the extension that should be used in a path import.
@@ -2720,20 +2717,19 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
     }
 
-    function addToSymbolTable(target: SymbolTable, source: SymbolTable, message: DiagnosticMessage) {
-        source.forEach((sourceSymbol, id) => {
-            const targetSymbol = target.get(id);
-            if (targetSymbol) {
-                // Error on redeclarations
-                forEach(targetSymbol.declarations, addDeclarationDiagnostic(unescapeLeadingUnderscores(id), message));
-            }
-            else {
-                target.set(id, sourceSymbol);
-            }
-        });
-
-        function addDeclarationDiagnostic(id: string, message: DiagnosticMessage) {
-            return (declaration: Declaration) => diagnostics.add(createDiagnosticForNode(declaration, message, id));
+    function addUndefinedToGlobalsOrErrorOnRedeclaration() {
+        const name = undefinedSymbol.escapedName;
+        const targetSymbol = globals.get(name);
+        if (targetSymbol) {
+            forEach(targetSymbol.declarations, declaration => {
+                // checkTypeNameIsReserved will have added better diagnostics for undefined.
+                if (!isTypeDeclaration(declaration)) {
+                    diagnostics.add(createDiagnosticForNode(declaration, Diagnostics.Declaration_name_conflicts_with_built_in_global_identifier_0, unescapeLeadingUnderscores(name)));
+                }
+            });
+        }
+        else {
+            globals.set(name, undefinedSymbol);
         }
     }
 
@@ -44320,6 +44316,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             case "symbol":
             case "void":
             case "object":
+            case "undefined":
                 error(name, message, name.escapedText as string);
         }
     }
@@ -48749,7 +48746,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
             if (!isExternalOrCommonJsModule(file)) {
                 // It is an error for a non-external-module (i.e. script) to declare its own `globalThis`.
-                // We can't use `builtinGlobals` for this due to synthetic expando-namespace generation in JS files.
                 const fileGlobalThisSymbol = file.locals!.get("globalThis" as __String);
                 if (fileGlobalThisSymbol?.declarations) {
                     for (const declaration of fileGlobalThisSymbol.declarations) {
@@ -48795,8 +48791,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
         }
 
-        // Setup global builtins
-        addToSymbolTable(globals, builtinGlobals, Diagnostics.Declaration_name_conflicts_with_built_in_global_identifier_0);
+        addUndefinedToGlobalsOrErrorOnRedeclaration();
 
         getSymbolLinks(undefinedSymbol).type = undefinedWideningType;
         getSymbolLinks(argumentsSymbol).type = getGlobalType("IArguments" as __String, /*arity*/ 0, /*reportErrors*/ true);

tests/baselines/reference/typeNamedUndefined1.errors.txt

@@ -0,0 +1,23 @@
+typeNamedUndefined1.ts(3,17): error TS2457: Type alias name cannot be 'undefined'.
+typeNamedUndefined1.ts(13,13): error TS2457: Type alias name cannot be 'undefined'.
+
+
+==== typeNamedUndefined1.ts (2 errors) ====
+    export namespace ns {
+        const s = Symbol();
+        export type undefined = typeof s;
+                    ~~~~~~~~~
+!!! error TS2457: Type alias name cannot be 'undefined'.
+        export function x(p: undefined): undefined { // global undefined
+            return p;
+        }
+    }
+
+    export function x(p: ns.undefined) { // undefined from the namespace
+        return p;
+    }
+
+    export type undefined = "";
+                ~~~~~~~~~
+!!! error TS2457: Type alias name cannot be 'undefined'.
+

tests/baselines/reference/typeNamedUndefined1.js

@@ -0,0 +1,30 @@
+//// [tests/cases/compiler/typeNamedUndefined1.ts] ////
+
+//// [typeNamedUndefined1.ts]
+export namespace ns {
+    const s = Symbol();
+    export type undefined = typeof s;
+    export function x(p: undefined): undefined { // global undefined
+        return p;
+    }
+}
+
+export function x(p: ns.undefined) { // undefined from the namespace
+    return p;
+}
+
+export type undefined = "";
+
+
+//// [typeNamedUndefined1.js]
+export var ns;
+(function (ns) {
+    const s = Symbol();
+    function x(p) {
+        return p;
+    }
+    ns.x = x;
+})(ns || (ns = {}));
+export function x(p) {
+    return p;
+}

tests/baselines/reference/typeNamedUndefined1.symbols

@@ -0,0 +1,36 @@
+//// [tests/cases/compiler/typeNamedUndefined1.ts] ////
+
+=== typeNamedUndefined1.ts ===
+export namespace ns {
+>ns : Symbol(ns, Decl(typeNamedUndefined1.ts, 0, 0))
+
+    const s = Symbol();
+>s : Symbol(s, Decl(typeNamedUndefined1.ts, 1, 9))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2019.symbol.d.ts, --, --))
+
+    export type undefined = typeof s;
+>undefined : Symbol(undefined, Decl(typeNamedUndefined1.ts, 1, 23))
+>s : Symbol(s, Decl(typeNamedUndefined1.ts, 1, 9))
+
+    export function x(p: undefined): undefined { // global undefined
+>x : Symbol(x, Decl(typeNamedUndefined1.ts, 2, 37))
+>p : Symbol(p, Decl(typeNamedUndefined1.ts, 3, 22))
+
+        return p;
+>p : Symbol(p, Decl(typeNamedUndefined1.ts, 3, 22))
+    }
+}
+
+export function x(p: ns.undefined) { // undefined from the namespace
+>x : Symbol(x, Decl(typeNamedUndefined1.ts, 6, 1))
+>p : Symbol(p, Decl(typeNamedUndefined1.ts, 8, 18))
+>ns : Symbol(ns, Decl(typeNamedUndefined1.ts, 0, 0))
+>undefined : Symbol(ns.undefined, Decl(typeNamedUndefined1.ts, 1, 23))
+
+    return p;
+>p : Symbol(p, Decl(typeNamedUndefined1.ts, 8, 18))
+}
+
+export type undefined = "";
+>undefined : Symbol(undefined, Decl(typeNamedUndefined1.ts, 10, 1))
+

tests/baselines/reference/typeNamedUndefined1.types

@@ -0,0 +1,36 @@
+//// [tests/cases/compiler/typeNamedUndefined1.ts] ////
+
+=== typeNamedUndefined1.ts ===
+export namespace ns {
+>ns : typeof ns
+
+    const s = Symbol();
+>s : unique symbol
+>Symbol() : unique symbol
+>Symbol : SymbolConstructor
+
+    export type undefined = typeof s;
+>undefined : unique symbol
+>s : unique symbol
+
+    export function x(p: undefined): undefined { // global undefined
+>x : (p: undefined) => undefined
+>p : undefined
+
+        return p;
+>p : undefined
+    }
+}
+
+export function x(p: ns.undefined) { // undefined from the namespace
+>x : (p: ns.undefined) => symbol
+>p : unique symbol
+>ns : any
+
+    return p;
+>p : unique symbol
+}
+
+export type undefined = "";
+>undefined : ""
+

tests/baselines/reference/typeNamedUndefined2.errors.txt

@@ -0,0 +1,28 @@
+typeNamedUndefined2.ts(4,21): error TS2457: Type alias name cannot be 'undefined'.
+typeNamedUndefined2.ts(17,17): error TS2457: Type alias name cannot be 'undefined'.
+
+
+==== typeNamedUndefined2.ts (2 errors) ====
+    export namespace ns {
+        export namespace undefined {
+            export const s = Symbol();
+            export type undefined = typeof s;
+                        ~~~~~~~~~
+!!! error TS2457: Type alias name cannot be 'undefined'.
+        };
+        export function x(p: undefined): undefined {
+            return p;
+        }
+    }
+
+    export function x(p: ns.undefined.undefined) {
+        return p;
+    }
+
+    export namespace undefined {
+        export const s = Symbol();
+        export type undefined = typeof s;
+                    ~~~~~~~~~
+!!! error TS2457: Type alias name cannot be 'undefined'.
+    };
+

tests/baselines/reference/typeNamedUndefined2.js

@@ -0,0 +1,44 @@
+//// [tests/cases/compiler/typeNamedUndefined2.ts] ////
+
+//// [typeNamedUndefined2.ts]
+export namespace ns {
+    export namespace undefined {
+        export const s = Symbol();
+        export type undefined = typeof s;
+    };
+    export function x(p: undefined): undefined {
+        return p;
+    }
+}
+
+export function x(p: ns.undefined.undefined) {
+    return p;
+}
+
+export namespace undefined {
+    export const s = Symbol();
+    export type undefined = typeof s;
+};
+
+
+//// [typeNamedUndefined2.js]
+export var ns;
+(function (ns) {
+    let undefined;
+    (function (undefined) {
+        undefined.s = Symbol();
+    })(undefined = ns.undefined || (ns.undefined = {}));
+    ;
+    function x(p) {
+        return p;
+    }
+    ns.x = x;
+})(ns || (ns = {}));
+export function x(p) {
+    return p;
+}
+export var undefined;
+(function (undefined) {
+    undefined.s = Symbol();
+})(undefined || (undefined = {}));
+;

tests/baselines/reference/typeNamedUndefined2.symbols

@@ -0,0 +1,51 @@
+//// [tests/cases/compiler/typeNamedUndefined2.ts] ////
+
+=== typeNamedUndefined2.ts ===
+export namespace ns {
+>ns : Symbol(ns, Decl(typeNamedUndefined2.ts, 0, 0))
+
+    export namespace undefined {
+>undefined : Symbol(undefined, Decl(typeNamedUndefined2.ts, 0, 21))
+
+        export const s = Symbol();
+>s : Symbol(s, Decl(typeNamedUndefined2.ts, 2, 20))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2019.symbol.d.ts, --, --))
+
+        export type undefined = typeof s;
+>undefined : Symbol(undefined, Decl(typeNamedUndefined2.ts, 2, 34))
+>s : Symbol(s, Decl(typeNamedUndefined2.ts, 2, 20))
+
+    };
+    export function x(p: undefined): undefined {
+>x : Symbol(x, Decl(typeNamedUndefined2.ts, 4, 6))
+>p : Symbol(p, Decl(typeNamedUndefined2.ts, 5, 22))
+
+        return p;
+>p : Symbol(p, Decl(typeNamedUndefined2.ts, 5, 22))
+    }
+}
+
+export function x(p: ns.undefined.undefined) {
+>x : Symbol(x, Decl(typeNamedUndefined2.ts, 8, 1))
+>p : Symbol(p, Decl(typeNamedUndefined2.ts, 10, 18))
+>ns : Symbol(ns, Decl(typeNamedUndefined2.ts, 0, 0))
+>undefined : Symbol(ns.undefined, Decl(typeNamedUndefined2.ts, 0, 21))
+>undefined : Symbol(ns.undefined.undefined, Decl(typeNamedUndefined2.ts, 2, 34))
+
+    return p;
+>p : Symbol(p, Decl(typeNamedUndefined2.ts, 10, 18))
+}
+
+export namespace undefined {
+>undefined : Symbol(undefined, Decl(typeNamedUndefined2.ts, 12, 1))
+
+    export const s = Symbol();
+>s : Symbol(s, Decl(typeNamedUndefined2.ts, 15, 16))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2019.symbol.d.ts, --, --))
+
+    export type undefined = typeof s;
+>undefined : Symbol(undefined, Decl(typeNamedUndefined2.ts, 15, 30))
+>s : Symbol(s, Decl(typeNamedUndefined2.ts, 15, 16))
+
+};
+

tests/baselines/reference/typeNamedUndefined2.types

@@ -0,0 +1,52 @@
+//// [tests/cases/compiler/typeNamedUndefined2.ts] ////
+
+=== typeNamedUndefined2.ts ===
+export namespace ns {
+>ns : typeof ns
+
+    export namespace undefined {
+>undefined : typeof undefined
+
+        export const s = Symbol();
+>s : unique symbol
+>Symbol() : unique symbol
+>Symbol : SymbolConstructor
+
+        export type undefined = typeof s;
+>undefined : unique symbol
+>s : unique symbol
+
+    };
+    export function x(p: undefined): undefined {
+>x : (p: undefined) => undefined
+>p : undefined
+
+        return p;
+>p : undefined
+    }
+}
+
+export function x(p: ns.undefined.undefined) {
+>x : (p: ns.undefined.undefined) => symbol
+>p : unique symbol
+>ns : any
+>undefined : any
+
+    return p;
+>p : unique symbol
+}
+
+export namespace undefined {
+>undefined : typeof undefined
+
+    export const s = Symbol();
+>s : unique symbol
+>Symbol() : unique symbol
+>Symbol : SymbolConstructor
+
+    export type undefined = typeof s;
+>undefined : unique symbol
+>s : unique symbol
+
+};
+

tests/baselines/reference/undefinedTypeAssignment1.errors.txt

@@ -1,10 +1,10 @@
-undefinedTypeAssignment1.ts(1,6): error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+undefinedTypeAssignment1.ts(1,6): error TS2457: Type alias name cannot be 'undefined'.
 
 
 ==== undefinedTypeAssignment1.ts (1 errors) ====
     type undefined = string;
          ~~~~~~~~~
-!!! error TS2397: Declaration name conflicts with built-in global identifier 'undefined'.
+!!! error TS2457: Type alias name cannot be 'undefined'.
     function p(undefined = "wat") {
     	return undefined;
     }