Lock RO

[powerboat9]

Fixes #10096 by adding a new command line flag ("--lock-ro") to unobtrusively disable Cargo.lock writing. It can be tested by running "cargo metadata --lock-ro" in a read only directory with no existing Cargo.lock file.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @ehuss (or someone else) soon.

Please see the contribution instructions for more information.

[powerboat9]

It looks like rustc isn't compiling when its vendored version of cargo is patched with these changes, as the util::config::Config::configure() method signature changes. I'm not sure if this means that my changes need to preserve the old method signature, or if I should attempt to patch rustc next.

[ehuss]

Thanks for the PR! Unfortunately we don't have the capacity to review new features at this time. As per the contributing guide, I'm closing this until the associated issue is agreed upon to the point that we can mark it as accepted:

Due to limited review capacity, the Cargo team is not accepting new features or major changes at this time. Please consult with the team before opening a new PR. Only issues that have been explicitly marked as accepted will be reviewed.

https://doc.crates.io/contrib/process/index.html

As a quick look at #10096, I'm not sure that is something that would warrant supporting or adding a new flag for, at least not without significant justification.