`cargo metadata` should return default workspace members

[sunshowers]

Describe the problem you are trying to solve

For a workspace, it is possible to specify default members through the workspace.default-members key. It would be great to expose this information through cargo metadata.

Describe the solution you'd like
The same format as workspace_members in cargo metadata -- a list of package IDs.

[sunshowers]

cc @metajack

[charles-r-earp]

I implemented this here https://github.com/charles-r-earp/cargo. I fixed one test "cargo_metadata_simple".

[sunshowers]

@charles-r-earp that looks great! you can probably submit that as a PR to this repo.

[weihanglo]

Hello all. Thanks for the proposal and the pull request. I'd like to know more about why default members in cargo metadata output is useful. Could you share some details?

Will do a simple FCP collecting options from the team then if it is reasonable.

(And sorry for the way too late reply 😅)

[sunshowers]

A simple use case is writing a linter that triggers only on default workspace members. Without support for this, one has to manually scrape the root Cargo.toml.

[charles-r-earp]

Cargo extensions and dev tools will want to emulate cargo, like having options like --manifest-path, --workspace, --package, etc. There are tools to do this like clap_cargo + cargo_metadata which makes use of cargo metadata. This allows cargo-foo bar to operate on all workspace default members just like cargo check / build / test / etc.

[weihanglo]

Thank you all for sharing!

I propose adding workspace default member information to the output of cargo metadata, to make external plugins easier to align to Cargo's behavior.

One concern is that the size of the output grows overtime.

@rfcbot fcp merge

We don't need to wait for 10 days after the poll btw.

[rfcbot]

Team member @weihanglo has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Eh2406
• @Muscraft
• @arlosi
• @ehuss
• @epage
• @joshtriplett
• @weihanglo

No concerns currently listed.

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