tsup-sourcemaps-demo

This repository is intended to demo an existing issue in tsup related to sourcemap generation.

If the target sourcemap (dist/index.js.map) exists, tsup will not generate correct sourcemaps when building/bundling code. It will instead use the sourcesContent from the existing file.

To workaround this issue, you need to use clean option in tsup.

Steps to Reproduce

1. Run npm run build to build an initial dist/index.js and dist/index.js.map
2. Make some changes in index.ts
3. Run npm run build again.
4. Note that dist/index.js has the updated changes, but dist/index.js.map does NOT have the correct sourcesContent.

The same can be observed with running npm run watch.

clean=True workaround

Following the same steps as above, if the scripts build:clean or watch:clean are used, the dist folder contents are deleted and tsup generates fresh .js.map files correctly.

Extra Notes

1. This issue does not exist in swc, can be tested using the same steps as above and build:swc script instead of build.
2. Also tested with esbuild using build:esbuild script, and the issue does NOT exist with esbuild either.
3. If the existing .js.map file is invalidated in some way (syntax errors, invalid characters) it will discard it and generate a fresh, correct map file as expected.