Tracking Issue for `-Zembed-metadata`

[Kobzol]

Summary

Implementation:

• Add support for -Zembed-metadata #15378
• Rename -Zno-embed-metadata to -Zembed-metadata=no #17149
• Allow setting -Zembed-metadata value from the config #17266
• Enable -Zembed-metadata=no by default on nightly Cargo #17267

Documentation: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#embed-metadata

The -Zembed-metadata=no flag tells Cargo to pass -Zembed-metadata=no to rustc, which saves disk space in the target directory, by avoiding generating duplicated metadata.

Unresolved Issues

• Is this a breaking change? Since rlibs/dylibs will not contain metadata after this change, it could break some users who depended on this. rmeta file is not uplifted when -Zembed-metadata=no is used #17359

Future Extensions

No response

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

[epage]

For the Unresolved Issue

Is this a breaking change? Since rlibs/dylibs will not contain metadata after this change, it could break some users who depended on this.

See the conversation starting at #15378 (comment), particularly #15378 (comment) which includes

I'm ok with experimenting with this behind a -Z flag, but if this is ever going to be on a path to stabilization, in the future it may need to have some opt-in mechanism (like a cargo config option).

[jplatte]

Is it intentional that the .cargo/config.toml way to use this is unstable.embed-metadata = "DoNotEmbed", rather than unstable.embed-metadata = "no"?

[weihanglo]

Is it intentional that the .cargo/config.toml way to use this is unstable.embed-metadata = "DoNotEmbed", rather than unstable.embed-metadata = "no"?

No. That is a bug.

[Kobzol]

Hmm, I noticed that some other unstable flags are also parsed via their enum values in the config, e.g. FixEdition. I can send a PR to fix setting of EmbedMetadata, but it doesn't seem that at least the unstable flags have stable value formats in the config.

[weihanglo]

Or we just make it Option<bool>, which yes|no is already handled here?

[Kobzol]

I think I wanted the third variant for something, but I can't remember what now. Anyway, I opened #17266, let me know what you think.