feat(cli): Add support for completing --config values in Bash

[nspin]

What does this PR try to resolve?

Currently, cargo.bashcomp.sh doesn't support completing the --config flag, let alone its value. This PR adds support for completing both the --config flag and a _filedir value for it. This support includes both cases where it appears before the cargo subcommand, and cases where it appears after. In the process of implementing the former, I also added support for completing values for --color before the cargo subcommand. Currently, completing values for --color is only supported after the cargo subcommand.

How to test and review this PR?

In a Bash shell, run:

source src/etc/cargo.bashcomp.sh

Then, observe that the following completions behave as expected:

cargo --co<tab>
cargo --config <tab>
cargo --color <tab>
cargo build --co<tab>
cargo build --config <tab>

[rustbot]

r? @epage

rustbot has assigned @epage.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[epage]

The first commit, I would be fine merging immediately. The second commit, I don't quite feel qualified to review. If you want to split this PR, then we can get that first commit merged.

Note: overall our focused has shifted towards stabilizing https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#native-completions

[nspin]

The first commit, I would be fine merging immediately. The second commit, I don't quite feel qualified to review. If you want to split this PR, then we can get that first commit merged.

I've removed the second commit from this PR, leaving only the first.

The second commit depends on the first, so I'll open that PR after this is merged.

Note: overall our focused has shifted towards stabilizing https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#native-completions

Thanks for the heads up, I'll look into adding this feature over there too.

[weihanglo]

Thanks!

View changes since this review

[nspin]

I've opened #16249, which adds this feature for native-completions.