rustdoc: Tracking issue for mergeable cross-crate info

This is a tracking issue for the RFC "Mergeable rustdoc cross-crate info" (rust-lang/rfcs#3662).

[!NOTE]

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Steps

• Implement the RFC (#129337)
  • Implement the RFC in Cargo
    • https://github.com/rust-lang/rust/pull/148234
    • https://github.com/rust-lang/cargo/pull/16167
    • https://github.com/rust-lang/cargo/pull/16309
• Add documentation (to Rustdoc Book) -- cc @EtomicBomb
  • https://github.com/rust-lang/rust/pull/148234
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

• Consider removing --merge=shared and only allow it by not providing a --merge flag. This would allow removing the implementation of shared CCI later, once Cargo uses mergeable CCI. https://github.com/rust-lang/rfcs/pull/3662#discussion_r1735147546
  • resolved: We removed --merge altogether, and it's inferred from the presence of the flags for which dirs to read/write from.
• What happens if two rustdoc invocations have the same --write-doc-meta-dir directory? https://github.com/rust-lang/rust/pull/159473#issuecomment-5147472710

Implementation history

• #129337
• #128252
• #128161
• https://github.com/rust-lang/rust/pull/148186

Start by reading RFC 3662 and the stabilization instructions linked in the issue, then review the implementation PRs listed under the completed checklist. The remaining work is a stabilization PR and consideration of concurrent use of the same --write-doc-meta-dir directory; done means the feature is stabilized and that unresolved behavior is addressed.