[@rollup/plugin-typescript]: Source-map source paths break if "sourceRoot" is specified

[Haringat]

• Rollup Plugin Name: Typescript
• Rollup Plugin Version: 12.3.0
• Rollup Version: 4.53.3
• Operating System (or Browser): Archlinux kernel 6.17.9
• Node Version: 22.21.1
• Link to reproduction (⚠️ read below): https://stackblitz.com/edit/rollup-repro-sxnmzqs2?file=tsconfig.json

Expected Behavior

Each path reference inside the source map leads to a source file inside the source root.

Actual Behavior

The paths are invalid if a source root is specified and repeat the path to the source file after the path to the directory containing the source file (see dist/index.js.map inside the stackblitz)

Additional Information

If the sourceRoot option is removed from the compilerOptions, it works as expected.

[shellscape]

@CharlieHelps using the reproduction link and the issue description, please do a best-effort triage of this issue and recommend a reasonable fix. If you have questions, please ask them first and provide 1-4 suggested answers in a b c d format. this has come up in issues in this repo in the past and there are commits around this subject, be sure to research and consider those.

[charliecreates]

Thanks for the ping — I did a best-effort triage and looked at prior related work.

I can reproduce this on master with a local fixture mirroring the report (sourceRoot: "./src"): final map.sources entries get duplicated path segments (examples: .../src/foo/src/foo/foo.ts, .../src/src/index.ts). Removing sourceRoot produces correct paths.

Likely root cause:

• packages/typescript/src/outputFile.ts (findTypescriptOutput) currently passes the emitted TS .map through unchanged.
• packages/typescript/src/index.ts returns that map directly from load().
• With relative sourceRoot, map paths are not rebased for Rollup’s collapse base (dirname(id)), so path segments effectively get re-applied and produce invalid/duplicated sources paths.

Related history I considered:

• [@rollup/plugin-typescript] unable to generate source map sources correctly #1861 (same symptom family: duplicated src/src-style sourcemap paths)
• fix(typescript): fix sourcemap sourcecontent referencing non-existent files #1571 (prior sourcemap-path fix in this same outputFile/index flow)
• fix(typescript): rebase sourcemap sources paths when outDir differs from source directory #1967 (open PR for Incorrect sourcemap sources paths when outDir differs from source directory #1966 outDir rebasing): useful context, but does not address this sourceRoot duplication case.

Recommended fix:

1. In packages/typescript/src/outputFile.ts, parse and rewrite emitted sourcemaps before returning them:
   • fold sourceRoot into each sources entry,
   • resolve/rebase to paths relative to dirname(id),
   • normalize to POSIX (/) with existing normalization utilities,
   • remove sourceRoot after folding to avoid downstream double-application,
   • skip rebasing for URL-like sourceRoot / sources entries.
2. Add a regression fixture + test for this exact case (sourceRoot: "./src" with nested imports) asserting no duplicated segments in final map.sources.
3. Keep companion regression coverage for the Incorrect sourcemap sources paths when outDir differs from source directory #1966/fix(typescript): rebase sourcemap sources paths when outDir differs from source directory #1967 outDir scenario to avoid regressions across both path-rebasing paths.

If helpful, I can follow up with a PR implementing this approach.