[cramforce]

Stacked on #1558.

Summary

tsc's interop helpers around builtin modules. tsc wraps every CommonJS import in its helpers: const events_1 = __importDefault(require("events")), const path = __importStar(require("path")). For program modules, cjs-tsc-interop.ts reads such a binding as a plain require binding, so the helper declarations go dead. A builtin module is not a program module, though, so its binding kept the helpers live. Their probe of the module's top-level this, var __importDefault = (this && this.__importDefault) || …, then failed at load ("property access through top-level 'this'"). That shape appears in hundreds of tsc-compiled files in a typical dependency tree. A builtin carries no __esModule, so events_1.default is the module and the namespace copy reads the module's members. When every reference has that form, a package-file stage now respells the binding as the plain require() of the builtin and x.default as x. (Dropping the probe instead would be wrong: cjs-tsc-interop.ts recognizes the helpers by that probe.)

Star re-exports of empty namespaces. A bundled module that exports only types keeps var x_exports = {} with no __export call. Its star re-export into the entry, __reExport(main, (init_x(), __toCommonJS(x_exports)), module.exports), was left in place because the rewrite only knew namespaces that have an export table. It then failed at load on the module.exports argument ("the CommonJS 'module' object in this position"). Such a namespace is now an empty table: the re-export runs the initializer and adds nothing.

Two silent results on the same paths:

• A member read of a name a module doesn't export now answers undefined (__esModule answers true), where it was refused.
• A read through the bundle's own entry namespace inside the bundle ((init_index(), __toCommonJS(index_exports)).KIND) answered undefined. It now reads the entry's export table.

Evidence

• New npm case tsc-builtin-interop: real tsc 5.6 output (module: commonjs, esModuleInterop) of a class extending events.default.EventEmitter and a namespace import of path. Output is byte-identical to Node's; before, it failed at load.
• New npm-static case 2595-bundled-entry-namespace: real esbuild 0.27 output where a bundled module reads the entry's own namespace and an empty one. On Load bundled CommonJS dependencies: settled exports, merged requires, semver's tokens, fs.realpath, whole-export members #1558 it printed undefined where Node prints lambda.
• Unit tests:
  • npm-static-tsc-helpers.test.ts runs rewritten modules against their originals under Node, and checks which shapes keep their text;
  • npm-static-bundled-esm.test.ts covers the empty namespace, the types-only star re-export into the entry, and entry namespace reads.
• On the published @vercel/build-utils 14.21.0, the module fence at dist/index.js:119 is gone.
• Zero-cost gate against Load bundled CommonJS dependencies: settled exports, merged requires, semver's tokens, fs.realpath, whole-export members #1558 with the full corpus: all 3434 programs identical except fs-extra-package (the fs-extra shim's absolute checkout path only).
• The self-hosted compiler builds, and self-hosting-native-driver.test.ts passes (1118 s).
• pnpm lint, pnpm format:check and test:ts7 --baselines-only pass; only the new fixtures' baselines were added.
• The npm, npm-static and package-shims suites and the frontend unit tests pass 1143 of 1144. The one failure, node24-url-authority, comes from the sandbox's Node 24.15.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
scriptc	Ready	Preview, v0	Oct 21, 2026 12:22am UTC