Source map resolution fails when :output-to points to non‑default directory in ClojureScript :advanced builds

Direct Answer

Set the :source-map compiler option to an explicit map-file path (e.g., :source-map "build/app.js.map") when :output-to points outside the default location. This option controls where the .map file is written and what sourceMappingURL is emitted in the generated JavaScript.

What Happens If You Omit It

If :source-map is enabled (truthy) but no explicit path is given, the compiler derives a default relative path/URL based on :output-to. That derived path is not guaranteed to match the deployed location, so stack traces and devtools may fail to fetch the map. If :source-map is nil or false, no map file is emitted and no sourceMappingURL comment appears—there is no fallback.

:source-map vs. :source-map-path

• :source-map – specifies the output map file path (or true to derive). This is the setting that moves the map file and sets the sourceMappingURL.
• :source-map-path – adjusts the sourceRoot and sources entries inside the map. It does not change where the map file is written or the emitted URL. Use it only if the internal source paths are wrong after the map file location is correct.

Version and :advanced Considerations

The :advanced optimization level does not by itself alter source-map path resolution. However, default derivation logic for :source-map can vary between ClojureScript releases. Always verify against the exact version in your project (check the changelog for source-map related changes).

Steps to Resolve

1. Add an explicit :source-map path next to your :output-to file, e.g.:
   

   {:output-to "target/custom/app.js"
    :source-map "target/custom/app.js.map"}

2. Rebuild and inspect the emitted JavaScript for the //# sourceMappingURL=... comment. Confirm the URL is correct relative to the deployed JS location.
3. Ensure the .map file is served at that exact URL in your deployment (static file server, CDN, etc.).
4. Open the generated .map and verify sources and sourceRoot point to your original source paths. If they are wrong, adjust :source-map-path.
5. Test stack traces in the target environment (browser, Node, etc.) to confirm resolution works.

Missing Diagnostic That Changes the Recommendation

Provide the exact sourceMappingURL value found in the deployed JavaScript and confirm whether the corresponding .map file exists at that path/URL. If no sourceMappingURL is present, source-map generation is disabled—enable it first before adjusting paths.

Verification Checklist

• Build with your installed ClojureScript version and grep the output JS for sourceMappingURL.
• Check that the .map file is present at the resolved URL.
• Validate internal sources/sourceRoot in the map file.
• Redeploy and test error stack traces.