Build JavaScript default-export objects that hold class values

`export default { parse, stringify, DateType, ParseError }` failed at
module initialization: the literal's width check against the default
binding's type found class members missing.

- A class name in a shorthand property (`{ ParseError }`) now evaluates
  to the class object, exactly like the long form `{ ParseError:
  ParseError }`; it had no lowering, so the JavaScript literal dropped
  the member.
- A class the program could not lower (one extending Date) is still
  dropped from the literal, its diagnostic deferred to the reads that
  reach it. The default binding of a JavaScript object literal now
  registers its type without such members, so the module initializes
  and the named exports work.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/compiler/src/frontend/lowering/expressions/object-literals.ts

@@ -3193,6 +3193,22 @@ export function lowerShorthandValue(
         `generic functions as values (call '${propName.text}' directly)`,
       );
     }
+    // A program class name (`{ parse, TomlError }`, an imported class
+    // included): the class object, exactly the long form `{ C: C }`.
+    // Generic classes keep the identifier path's contextual pinning.
+    const classInfo = lowerer.classBySymbol.get(resolved);
+    if (classInfo && !classInfo.generic) {
+      const decoratedGlobal = classInfo.classDecorators?.valueGlobalId;
+      if (decoratedGlobal !== undefined) {
+        return {
+          kind: "varRef",
+          localId: decoratedGlobal,
+          type: { kind: "classval", className: classInfo.def.name },
+          loc,
+        };
+      }
+      return lowerer.classValueRef(classInfo, propName);
+    }
   }
   lowerer.rejectUnresolvedSymbol(
     symbol

packages/compiler/src/frontend/lowering/lower-modules.ts

@@ -1229,6 +1229,36 @@ function jsDynHoldableInitializer(lowerer: Lowerer, init: ts.Expression | undefi
   return false;
 }
 
+/** A JavaScript default-export object literal holding a class the program
+ * could not lower (`export default { parse, TomlDate }` where TomlDate
+ * extends an unsupported base): the literal narrows that member away, its
+ * diagnostics deferred to the reads that reach it, so the binding's type
+ * drops it too. Otherwise the module's own initialization would fail the
+ * width check against members no build can supply. */
+function withoutRejectedClassMembers(
+  lowerer: Lowerer,
+  expression: ts.Expression,
+  type: IrType,
+): IrType {
+  let literal = expression;
+  while (ts.isParenthesizedExpression(literal)) literal = literal.expression;
+  if (!ts.isObjectLiteralExpression(literal) || type.kind !== "record") return type;
+  const shape = lowerer.shapes.get(type.shapeId);
+  if (!shape || shape.tuple) return type;
+  const rejected = (t: IrType): boolean =>
+    t.kind === "classval" &&
+    !lowerer.classes.has(t.className) &&
+    lowerer.deferredClassByName.has(t.className);
+  if (!shape.fields.some((f) => rejected(f.type))) return type;
+  const kept = shape.fields.filter((f) => !rejected(f.type));
+  const shapeId = lowerer.shapes.intern(
+    kept.map((f) => ({ name: f.name, type: f.type })),
+    false,
+    shape.indexValue,
+  );
+  return { kind: "record", shapeId };
+}
+
 export function collectGlobals(
   lowerer: Lowerer,
   sf: ts.SourceFile,
@@ -1331,6 +1361,7 @@ export function collectGlobals(
           type = unitOnlyUnion(lowerer.unions);
         }
         if (type.kind === "void") lowerer.badType(stmt.expression, tsType);
+        if (isJsSourceFile(sf)) type = withoutRejectedClassMembers(lowerer, stmt.expression, type);
         const g: IrGlobal = { id: `%g.${tag}default`, name: "default", type, mutable: false };
         lowerer.globalsBySymbol.set(symbol, g);
         lowerer.globalsList.push(g);

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6494-default-export-class-members/main.ts.json

@@ -0,0 +1,9 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6494-default-export-class-members/lib/date.js",
+  "<repo>/tests/corpus/6494-default-export-class-members/lib/error.js",
+  "<repo>/tests/corpus/6494-default-export-class-members/lib/index.js",
+  "<repo>/tests/corpus/6494-default-export-class-members/main.ts"
+ ],
+ "diags": []
+}

tests/corpus/6494-default-export-class-members/lib/date.js

@@ -0,0 +1,8 @@
+// A class whose base scriptc cannot extend yet: the default export object
+// below narrows this member away, and only reads of it would fence.
+export class StampDate extends Date {
+  constructor(text) {
+    super(text);
+    this.label = "stamp:" + text;
+  }
+}

tests/corpus/6494-default-export-class-members/lib/error.js

@@ -0,0 +1,7 @@
+export class ParseError extends Error {
+  constructor(message, line) {
+    super(message);
+    this.name = "ParseError";
+    this.line = line;
+  }
+}

tests/corpus/6494-default-export-class-members/lib/index.js

@@ -0,0 +1,14 @@
+import { StampDate } from "./date.js";
+import { ParseError } from "./error.js";
+function parse(text) {
+  if (text === "") throw new ParseError("empty document", 1);
+  const [key, value] = text.split("=").map((part) => part.trim());
+  return { key, value };
+}
+function stringify(value) {
+  return JSON.stringify(value);
+}
+// A default export object of functions and class values (the shorthand
+// spelling of `{ ParseError: ParseError }`).
+export default { parse, stringify, StampDate, ParseError };
+export { parse, stringify, StampDate, ParseError };

tests/corpus/6494-default-export-class-members/main.ts

@@ -0,0 +1,15 @@
+// A JavaScript module's default export object holding functions and class
+// values builds at module initialization, and its members work through
+// both the default object and the named exports.
+import lib, { parse, ParseError } from "./lib/index.js";
+
+console.log(JSON.stringify(parse("a = 1")));
+console.log(lib.stringify(lib.parse("b = 2")));
+try {
+  lib.parse("");
+} catch (e) {
+  if (e instanceof ParseError) console.log(e.name, e.message, e.line);
+}
+const Ctor = lib.ParseError;
+const made = new Ctor("built through the default object", 7);
+console.log(made instanceof ParseError, made.message, made.line, Ctor === ParseError);

tests/corpus/6494-default-export-class-members/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "default-export-class-members-corpus",
+  "private": true,
+  "type": "module"
+}