Building with mtc

pnpm build runs one command: mtc -p tsconfig.tags.json. Same mtc you met in chapter one — but there it only checked. Two fields in this tsconfig turn the checker into a builder: noEmit: false and declaration: true. That’s the whole switch.

A published .marko is not the one you wrote. Run pnpm build, then:

cat dist/tags/fancy-badge/index.marko

Your export interface Input is gone. And the import changed: "./options" became "./options.js". Then look at what it left behind:

cat dist/tags/fancy-badge/index.d.marko

There’s your interface. The build strips the TypeScript out of the template and moves it into a declaration twin — a .d.marko, the template equivalent of a .d.ts. Consumers get a plain template their compiler can read without knowing any TypeScript, plus a types file their editor reads. options.ts gets the same treatment: options.js and options.d.ts.

That’s why .marko is the shippable artifact and there’s no index.js anywhere. A Marko tag is compiled by the app that uses it — one template becomes server code in their server bundle and DOM code in their client bundle. The library can’t do that; only the consumer’s compiler knows which is needed.

Now the bug this lesson exists for. Look at tsBuildInfoFile in the tsconfig. That’s mtc’s incremental cache, and it currently sits in the project root.

1. Run pnpm build, then ls dist/tags/fancy-badge — four files. Fine.
2. Now do what every build script does before a build: rm -rf dist.
3. Run pnpm build again. It exits 0. Now run ls dist — nothing. It emitted nothing at all and told you it succeeded.
4. Fix it: change tsBuildInfoFile to "./dist/tsconfig.tags.tsbuildinfo".
5. rm -rf dist, pnpm build, ls dist/tags/fancy-badge. Four files again.

The cache said “already built” — and it was right, from its point of view. It never noticed dist had been deleted, because it wasn’t in dist. Put the cache inside the directory that gets cleaned, and any clean cleans the cache too.

You should now see four files per tag in dist. Next: someone installs it.