Support for cargo-hakari with cargo-udeps

[tzilist]

Right now, cargo-hakari generates an immense amount of failures since none of the dependencies are used within the actual crate. It would be nice if there was an ability to automatically generate an ignored section like so:

### BEGIN HAKARI SECTION
[dependencies]
a = { version = "1.0" }
b = { version = "1.0" }

[package.metadata.cargo-udeps.ignore]
normal = ["a", "b"]
### END HAKARI SECTION

Or something along these lines.

Thank you!

[sunshowers]

Thanks for the report! Could you point me to the format expected by cargo-udeps?

[tzilist]

@sunshowers I believe this is what you are lookin' for

https://github.com/est31/cargo-udeps#ignoring-some-of-the-dependencies

Let me know if you need anything else, and thanks again!

[sunshowers]

Thanks for the link! I'm going to try and get this done some time next week.

Notes:

This should be gated behind an optional config to maintain BC. I think it should look like:

[extras]
cargo-udeps-ignore = "1"

The "1" means format version 1. If the format changes in the future, the output can change as well.

[sunshowers]

@tzilist I had a look at this and it looks like it's a bit more complicated than I thought. There are two things that need to be done:

1. Add the workspace-hack to every crate's ignores.
2. Add dependencies to workspace-hack's ignores.

In more detail:

1. Add a config option around adding udeps output.
2. Add information about this to https://github.com/facebookincubator/cargo-guppy/blob/2873d1708d0a1fc2c54770265b396df85b4631e7/tools/hakari/src/cli_ops/workspace_ops.rs#L62-L70 and https://github.com/facebookincubator/cargo-guppy/blob/2873d1708d0a1fc2c54770265b396df85b4631e7/tools/hakari/src/cli_ops/workspace_ops.rs#L255-L259 -- I think we'd have to make the add_to_cargo_toml and remove_from_cargo_toml methods more complicated, because it'll be:

• add dependency line + udeps line
• add dependency line without udeps line
• add udeps line, dependency line already exists
• remove udeps line, dependency line already exists
• remove entirely

This is unfortunately quite a bit more complex than I thought it would be, so I'm disinclined to do it myself. However, I'd be happy to accept a PR--would you like to do it? Happy to mentor you through the process if required.

[tzilist]

I would love to take a stab at this! Work is pretty busy at the moment but I intend to try and do this in the next week or two 😊