RFE: add option to specify path to Cargo.lock

[igor-raits]

In Fedora we package all crate sources (including tests) in /usr/share/cargo/registry which is not user-writable. However, we would like to run tests for them after installation. There is already option for target-dir and it would be very nice to get option to put Cargo.lock in some other directory so that we could run cargo test from there.

[igor-raits]

@alexcrichton any idea how the option could be named? I'm thinking about making a patch.

[alexcrichton]

Perhaps --lockfile-path to mirror --manifest-path?

[epage]

We talked about this in the Cargo team meeting and are open to people experimenting with this

• CLI flag only, no config, no manifest support
• Name: --lockfile-path <path>
• Behind -Zunstable-options and docs
  • The flag's docs / --help should have (unstable) in them
• Looks like it belongs on all commands that take --manifest-path except cargo locate-project
• cargo install should make --lockfile-path imply --locked
• Must require the file_name be Cargo.lock (like we do for --manifest-path). We can always re-evaluate this in the future
• Main question is how this should work if the lockfile or a parent directory is not present
  • I would lean towards "create them" rather than "error"

[ifropc]

@rustbot claim