Report missing source maps in profile comments

[szegedi]

(This builds on #292.)

Rationale

In the backend, we want to better identify profiles that might require server-side unminification because their source maps were not present locally in the application. We will depend on customers emitting generated/minified sources with the sourceMappingURL annotation present, but I think that's fair; most modern tools will add it by default and users must go out of their way to set a flag for the annotation to not be emitted. If we don't support server-side unminification for those, I think that's fine. We'll have to document it like that once when we roll out the feature.

I expect rolling this out will massively reduce the number of profile candidates for server-side unminification.

Summary

• Tracks JS files that declare a sourceMappingURL annotation but for which no map file is found after both phases of source map discovery
• SourceMapper.mappingInfo() returns missingMapFile: true on the SourceLocation for such files
• serialize() in the profile serializer emits a single dd:has-missing-map-files token into profile.comment when at least one such file is encountered during serialization

Details

Only files that declare a sourceMappingURL are flagged — files with no annotation that simply have no map are not reported. A file resolved via the .map-file fallback (Phase 2) is not flagged even if its annotation pointed to a missing path.

The token approach (single well-known string in comment) keeps profile size impact minimal: the string is only added to the string table when needed, and no per-path data is emitted.

Test plan

• SourceMapper unit tests: missingMapFile=true set when annotation declares missing map, not set for plain files or files resolved via fallback
• serialize() tests: token emitted for both serializeTimeProfile and serializeHeapProfile, not emitted when no source mapper is used or when all maps are resolved

🤖 Generated with Claude Code

Jira: PROF-13985

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-03-13 10:24:53

Comparing candidate commit 69692ee in PR branch szegedi/report-unmapped with baseline commit 6ab3e39 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 87 metrics, 33 unstable metrics.

[github-actions]

Overall package size

Self size: 2.05 MB
Deduped: 2.41 MB
No deduping: 2.41 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | source-map | 0.7.6 | 185.63 kB | 185.63 kB | | pprof-format | 2.2.1 | 163.06 kB | 163.06 kB | | node-gyp-build | 3.9.0 | 8.81 kB | 8.81 kB |

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}