Rustfmt: Could rustfmt format Cargo.toml ?

[Stargateur]

I actually use a very very small tool toml-fmt, I currently use it like:

toml-fmt < Cargo.toml > Cargo.toml.new && mv Cargo.toml.new Cargo.toml

That not very practical and I must remember to use it. Could rustfmt handle it too ? I think Cargo.toml is also a part of rust file so maybe it's ok to add it.

[calebcartwright]

That's an interesting idea @Stargateur

Formatting toml files is outside rustfmt's scope (at least currently), though I can see how having the optional/opt-in ability to format toml files would be beneficial. prettier also supports formatting json and yaml files in addition to JavaScript and TypeScript, so it's not completely unheard of.

How would you envision the behavior when running cargo fmt in a multi-crate workspace? Would the expectation be that cargo fmt would support formatting all the detected Cargo.toml files in the workspace?

[Stargateur]

How would you envision the behavior when running cargo fmt in a multi-crate workspace? Would the expectation be that cargo fmt would support formatting all the detected Cargo.toml files in the workspace?

I guess the same that the actual behaviour, if the actual behaviour is to format all detected rust file in a workspace than yes, if no than no.

[calebcartwright]

It looks like the Style Guide actually already includes a spec for Cargo.toml, so IMO formatting Cargo.toml files accordingly is something that rustfmt should indeed support.

There's a few things to think through (default behavior, cli args/opts, configurable via rustfmt.toml, etc.) but it should be a fun project if anyone is interested in working on it!

[gilescope]

You could start small and gradually crank it up. Alphabetical ordering of blocks of dependencies (with newlines demarcating different blocks of dependencies) would be good.
Adding spaces around dependencies. I.e. foo = "1.2" rather than foo="1.2".

Those two would probably be 80% of the file sorted out nicely - the dependencies are going to have the most change so they are the areas that benefit the most from consistency.

[Nikhil0487]

@calebcartwright
Can I try this one following yours and @gilescope directions?

[calebcartwright]

@Nikhil0487 - absolutely! I suspect this may end up being a sizeable effort, but can likely be developed iteratively. I still don't have a feel for what the end state would look like from an experience/usability perspective, nor have I really had the bandwidth to think on it.

As such I'd advise starting with the formatting logic (something that takes in an unformatted string and returns a formatted one) and we'll figure out the rest later on. Feel free to put this in a new mod under src/formatting

[thomaseizinger]

For people watching this issue, I've developed a dprint plugin that does some formatting of Cargo.toml files: https://github.com/thomaseizinger/dprint-plugin-cargo-toml

dprint also has a rustfmt plugin which means you can have a single tool for all your formatting needs :)