Meta feature tracking: Language server support for `Cargo.toml` file

[tgross35]

This issue is an attempt to put all information regarding potential Cargo.toml support in one place.

Blockers

There is no TOML support in RA, and needs a format-preserving parser. toml-edit is maintained along with toml and probably the best choice.

Potential features

• Autocomplete or schema help (reference: https://doc.rust-lang.org/cargo/reference/manifest.html)
  • Autocomplete keys
  • Suggest valid values for fixed keys like edition, rust-version, license
  • Suggest in-workspace files for license-file, readme, build
  • Autocomplete dependencies (also handled by the crates extension)
  • Autocomplete dependency features
• Schema validation and warnings/errors, based on the above
• Quick actions & refactoring
  • "Move feature to dev-dependencies/dependencies/build-dependencies"
  • "Update crate to latest compatible version"
  • "Update crate to latest incompatible version"
  • Toggle no-default-features
  • Refactor simple dependencies to objects and back, like RustRover does Meta feature tracking: Language server support for Cargo.toml file #15741 (comment)
    
• Add crates to Cargo.toml from a use statement feature: from use statement, add crate to cargo.toml #10904
• Lower priority features that are already well-handled with other ecosystem extensions:
  • Link to crates like the crates extension: Feature Request: Link to crates.io on hover in Cargo.lock and Cargo.toml #13532
  • Add syntax highlighting to TOML files Add syntax highlighting for TOML files. #3565. I think the syntax highlighting is not much of a concern since Even better TOML does it well, but there are some good general suggestions in the issue

See also the label S-needs-toml issue requiring toml support

[obsgolem]

My issue #10117 needs the needs-toml label.

[tgross35]

My issue #10117 needs the needs-toml label.

Thanks for the link, I added it to the list

[alibektas]

I want to point out that I am indirectly working on this issue. I am trying to implement a .rust-analyzer.toml (#13529) file support. I hope to end up with an integrated TOML parser in ra although it is not my primary concern ( RATOML's first prototype won't be needing a TOML parser, ser-de should be enough for now). I would be happy if contributors to this issue could reach out to me so that we can talk about its implementation.

At the very least I will be making some changes to the core DBs of ra to distinguish .rs files from .tomls ( strictly speaking, from .rust-analyzer.toml files and cargo.toml files, each of which needing special care here and there).

[tgross35]

@alibektas that sounds very cool!

I think that toml-edit is more or less a drop in for toml and works with the same structs with Serde. The difference is that the untyped representation (toml_edit::Document, a strict superset of toml::Value) has support for format preservation. Maybe it makes sense to prototype with toml-edit instead of the usual toml just so its use can be expanded in the future?

Not that I expect RA would be editing .rust-analyzer.toml ever, but it could make sense for any framework that will eventually be shared with Cargo.toml

[alibektas]

👋

There are couple of things that I first need to look into before giving you an answer.

1. Will RA maintainers be OK with toml-edit being included in RA? The impression that I got thus far is that we are very conservative when it comes to using external crates. ( This I will be asking Veykril next week )

2. How well will toml-edit be compatible with RA's incremental computation principles? ( This is a concern that goes beyond the prototyping phase. )

For the prototype your proposition seems to be the way to go, but this is just me speaking without having really looked at toml-edit in depth. I will get back to you with a more detailed answer possibly next week, but let me at least say that I agree toml-edit being better in this regard than toml.

[Veykril]

Fwiw, we most likely want to end up with a toml parser thats built on top of rowan, which kind of exist https://docs.rs/taplo/latest/taplo/ so we probably want to strip that down / adjust to our needs.

[alibektas]

@tgross35 👋 I think Veykril's reply answers the greater part of your question, but I think it comes down to determining how long it will take us to integrate the said taplo crate to RA.

[wyatt-herkamp]

This is a feature I would really like to see. I was debating building a separate plugin to some of the features listed.

 Is this a feature that RA will accept into its code base? 

if So I would be interesting in starting to add it to RA?

[Veykril]

Definitely something we want to have, its just a lot of work and requires some other things to be done first, like creating / integrating a rowan based syntax library for toml -> #15908