Auto merge of #137535 - Kobzol:split-metadata, r=petrochenkov

Introduce `-Zembed-metadata` to allow omitting full metadata from rlibs and dylibs

This is a continuation of https://github.com/rust-lang/rust/pull/120855 (I was mentored by `@bjorn3` to move it forward). Most of the original code was written by bjorn3, I tried to clean it up a bit and add some documentation and tests.

This PR introduces a new unstable compiler flag called `-Zembed-metadata=[no|yes]`, with the default being `yes` (see https://github.com/rust-lang/rust/issues/57076 for context). When set to `no`, rustc will only store a small metadata stub inside rlibs/dylibs instead of the full metadata, to keep their size smaller. It should be used in combination with `--emit=metadata`, so that the users of such a compiled library can still read the metadata from the corresponding `.rmeta` file. [This comment](https://github.com/rust-lang/rust/pull/120855#issuecomment-1937018169) shows an example of binary/artifact size wins that can be achieved using this approach.

Contrary to https://github.com/rust-lang/rust/pull/120855, this PR only introduces the new flag, along with a couple of run-make tests and documentation, but does not yet use it in bootstrap to actually compile rustc. I plan to do that as a follow-up step (along with integration in Cargo, which should ideally just always pass this flag to reduce the size of target directories).

Fixes https://github.com/rust-lang/rust/issues/23366
Closes https://github.com/rust-lang/rust/issues/29511
Fixes https://github.com/rust-lang/rust/issues/57076

Another attempt of https://github.com/rust-lang/rust/pull/93945 and https://github.com/rust-lang/rust/pull/120855.

r? `@petrochenkov`
tree: 97cb9f615e176a09ebac384569fa660a2180944a
  1. .github/
  2. compiler/
  3. library/
  4. LICENSES/
  5. src/
  6. tests/
  7. .clang-format
  8. .editorconfig
  9. .git-blame-ignore-revs
  10. .gitattributes
  11. .gitignore
  12. .gitmodules
  13. .ignore
  14. .mailmap
  15. bootstrap.example.toml
  16. Cargo.lock
  17. Cargo.toml
  18. CODE_OF_CONDUCT.md
  19. configure
  20. CONTRIBUTING.md
  21. COPYRIGHT
  22. INSTALL.md
  23. LICENSE-APACHE
  24. license-metadata.json
  25. LICENSE-MIT
  26. README.md
  27. RELEASES.md
  28. REUSE.toml
  29. rust-bors.toml
  30. rustfmt.toml
  31. triagebot.toml
  32. x
  33. x.ps1
  34. x.py
README.md

Website | Getting started | Learn | Documentation | Contributing

This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.

Why Rust?

  • Performance: Fast and memory-efficient, suitable for critical services, embedded devices, and easily integrated with other languages.

  • Reliability: Our rich type system and ownership model ensure memory and thread safety, reducing bugs at compile-time.

  • Productivity: Comprehensive documentation, a compiler committed to providing great diagnostics, and advanced tooling including package manager and build tool (Cargo), auto-formatter (rustfmt), linter (Clippy) and editor support (rust-analyzer).

Quick Start

Read “Installation” from The Book.

Installing from Source

If you really want to install from source (though this is not recommended), see INSTALL.md.

Getting Help

See https://www.rust-lang.org/community for a list of chat platforms and forums.

Contributing

See CONTRIBUTING.md.

License

Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.

See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.

Trademark

The Rust Foundation owns and protects the Rust and Cargo trademarks and logos (the “Rust Trademarks”).

If you want to use these names or brands, please read the Rust language trademark policy.

Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.