sourceMappingURL missing in prod using sprockets and esbuild

[sedubois]

Thank you for this new gem! I'm trying to get source maps working, I apologize in advance if I misunderstood (I have a limited understanding of front-end tooling).

Source maps do seem to work in our Rails 7 app in development (using sprockets 4.0.2, sprockets-rails 3.4.2, jsbundling-rails 1.0.1 and esbuild 0.14.23): assets:precompile generates a JS bundle with a sourceMappingURL clause at the end. However they do not seem to work in production: the sourceMappingURL clause is absent in this case.

Because of this we do not have proper Javascript crash reports in our monitoring system.

We have this under package.json's scripts: "build": "esbuild app/javascript/*.* --bundle --sourcemap --target=es2016 --minify --outdir=app/assets/builds". I've tried with both config.assets.debug = false (as suggested) and config.assets.debug = true in application.rb, but this does not seem to change the situation. Some debug info below (point 3 is problematic).

1. When running that esbuild command, two files are generated as expected: app/assets/builds/application.js and app/assets/builds/application.js.map, where the last line of the JS file is //# sourceMappingURL=application.js.map.

2. When running RAILS_ENV=development bin/rails assets:precompile, two files are generated: public/assets/application-cc3245bb241eac905dc4ffd8a5abc8d3d42445e9e1986ea93ba7b267e583f1cf.js and public/assets/application.js-67cdc37aff88978cfa5a2cdba39ef49c3da8d9b6ff16f4c7eca581548009fe0c.map, and the last lines of the JS file are (which seem correct):

//# sourceMappingURL=/assets/application.js-67cdc37aff88978cfa5a2cdba39ef49c3da8d9b6ff16f4c7eca581548009fe0c.map
//!
;

3. When running RAILS_ENV=production bin/rails assets:precompile, two files are generated: public/assets/application-6c7fc839b49f22a88c3f45c04cde931d8a6801ad0312f478165ac605915c1d55.js and public/assets/application.js-67cdc37aff88978cfa5a2cdba39ef49c3da8d9b6ff16f4c7eca581548009fe0c.map. However the JS file has no sourceMappingURL statement at the end, it ends with //!.

Is there a way to make source maps work with jsbundling-rails and esbuild?

[silva96]

I found that removing: --public-path=assets in the package.json solves everything. I don't know why, I don't even know what is that for.

But it solves it.

[richardkmiller]

@silva96 See #58 for why --public-path=assets is desirable, but it indeed breaks sourcemaps. I've submitted rails/sprockets-rails#515 to fix this in Sprockets.