fix: fall back to bundled TypeScript when typescript is not installed - #1346

Fixes #1264

• src/typescript.js: when there's no project-local typescript, fall back to require('./loaders/ts-loader.js').typescript. This is the same fallback dist/ncc/typescript.js had up to 0.24.1.
  • In dist/, this is the compiler bundled into loaders/ts-loader.js. Webpack has already loaded that module as the loader, so it isn't evaluated a second time.
  • From src/ (coverage runs), src/loaders/ts-loader.js re-exports the typescript devDependency, so behaviour there doesn't change.
• scripts/build.js: copy TypeScript's lib .d.ts files to dist/ncc/loaders/ instead of dist/ncc/loaders/typescript/lib/.
  • Since TypeScript 5.0, getDefaultLibFilePath() looks for them next to sys.getExecutingFilePath(), which for the bundled compiler is dist/ncc/loaders/ts-loader.js.
  • Without this, type-checking with the built-in compiler fails with TS6053: File '.../dist/ncc/loaders/lib.es6.d.ts' not found.
  • The files and the package size stay the same; only the directory changes.
• test/cli.test.js: a new test copies dist/ncc to a temp directory outside the repo, so typescript can't be resolved from ncc's location (as with a global install).
  • It builds test/integration/test.ts with TYPESCRIPT_LOOKUP_PATH pointing nowhere and expects the build to succeed with the built-in compiler.
  • The existing "ncc built-in" test can't catch this bug, because inside the repo require('typescript') finds the repo's own node_modules/typescript.
  • The new test is skipped under coverage, which runs from src/, where there is no bundle.

A project's own typescript is still used first. This only changes what happens when there isn't one.

Verification

Environment: macOS, Node 26.3.1. Setup: pnpm install --frozen-lockfile, pnpm build-test-binary, pnpm build.

Command: node --expose-gc --max_old_space_size=4096 node_modules/jest/bin/jest.js test/cli.test.js -t "built-in typescript when typescript is not installed"
Result:

• On main, the test fails with the issue's error (Could not load TypeScript compiler with NPM package name .../typescript.js).
• With only the src/typescript.js change, it fails with TS6053: File '.../loaders/lib.es6.d.ts' not found.
• With both changes, it passes (Tests: 23 skipped, 1 passed, 24 total).

Command: pnpm test
Result:

• This branch: Test Suites: 4 passed, 4 total, Tests: 122 passed, 122 total.
• main plus only the new test: Tests: 1 failed, 121 passed, 122 total. The only failure is the new test.
• An earlier full run on this branch reported Tests: 1 failed, 121 passed, 122 total. The failure was test/watcher.test.js › Should support custom watch API exceeding its 30 s timeout. That test watch-builds twilio, with no TypeScript involved. It passed when run alone (24.8 s) and in the run above. On main it took 23.7 s of its 30 s budget.

Command: node --expose-gc --max_old_space_size=4096 node_modules/jest/bin/jest.js --runInBand --coverage --globals '{"coverage":true}' test/cli.test.js (runs the CLI tests from src/)
Result: Tests: 23 passed, 23 total

Manual check of the reported scenario: I packed the build with npm pack and installed it with npm install -g --prefix <tmp>, in a directory tree with no typescript package anywhere.

• In a "type": "module" project (the issue's case), ncc run src/index.ts prints ncc: Using typescript@5.9.3 (ncc built-in) and runs the program. The published 0.45.0 fails in the same setup with the issue's error.
• Type errors are still reported (TS2322, exit code 1). -t still works, and --quiet still prints nothing.
• A project with its own typescript@5.4.5 still uses it (ncc: Using typescript@5.4.5 (local user-provided)).