Tracking Issue for `-Zrustdoc-depinfo`

[weihanglo]

Summary

Original issue: #12266
Implementation: #15359 #15605
Documentation: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#rustdoc-depinfo

The -Z rustdoc-depinfo flag leverages rustdoc’s dep-info files to determine whether documentations are required to re-generate. This can be combined with -Z checksum-freshness to detect checksum changes rather than file mtime.

Testing instructions: #15370 (comment)

Unresolved Issues

Blockers:

• To generate the correct styled docs, Cargo needs to pass --emit=toolchain-shared-resources,invocation-specific,dep-info=<PATH> to rustdoc. We need to stabilize the required rustdoc emit types all at once.
  • Multiple uses of --emit=dep-info do different things in rustc and rustdoc rust#141664
  • feat(rustdoc): stabilize --emit flag rust#146220
• Rustdoc should track extra theme/ CSS files as part of the rebuild detection
  • Ensure external paths passed via flags end up in rustdoc depinfo rust#144600

Open design questions:

• Where should rustdoc dep-info be emitted to?
  • The current implementation is under the fingerprint directory, e.g., target/debug/.fingerprint/serde-12d29d32b3b8b38f/doc-lib-serde.d. This might not be a blocker because fingerprint is not a stable interface Cargo guarantees.

Future Extensions

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