rust-project.json sysroot crates question

[tobywf]

I've followed the instructions for non-Cargo based projects, and it largely works great, so thank you for implementing this. There's a small issue about picking up sysroot crates that I'm hitting, where std is being resolved fine, but proc_macro isn't.

I think I understand what's going on with SYSROOT_CRATES and STD_DEPS, but still have some questions around the best way to reference other sysroot crates (further down). For context, take this minimal working example, with just src/example/lib.rs:

use std;
use proc_macro;

And rust-project.json:

{
  "sysroot_src": "/Users/user/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/",
  "crates": [
    {
      "cfg": [],
      "deps": [],
      "edition": "2018",
      "env": {},
      "is_workspace_member": true,
      "root_module": "src/example/lib.rs"
    }
  ]
}

The status tells me:

file info:
crate: CrateId(10)
deps: core=CrateId(1), alloc=CrateId(0), std=CrateId(6)

Which corresponds to SYSROOT_CRATES, and because of STD_DEPS, by default crates don't get proc_macro. However, I can't simply add "deps": [{"crate": 4, "name": "proc_macro"}], since crate 4 does not exist in the rust-project.json. If I manually add a proc_macro crate, then it works:

{
  "sysroot_src": "/Users/user/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/",
  "crates": [
    {
      "cfg": [],
      "deps": [],
      "edition": "2018",
      "env": {},
      "is_workspace_member": false,
      "root_module": "/Users/user/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/lib.rs"
    },
    {
      "cfg": [],
      "deps": [
        {
          "crate": 0,
          "name": "proc_macro"
        }
      ],
      "edition": "2018",
      "env": {},
      "is_workspace_member": true,
      "root_module": "src/example/lib.rs"
    }
  ]
}

And I get:

file info:
crate: CrateId(11)
deps: core=CrateId(1), alloc=CrateId(0), std=CrateId(6), proc_macro=CrateId(10)

Although this indicates to me there are probably two proc_macro crates, one with CrateId(4) and one with CrateId(10).

TL;DR:

Is manually specifying proc_macro while still using sysroot_src the way to go? Or could having two proc_macro crates cause a problem? If so, would it be better to omit sysroot_src and populate all sysroot crates myself in rust-project.json? In this case, it seems like crates don't get STD_DEPS, which is fine.

I'm just looking for some guidance on which is the way to go for rust-project.json users. Either approach works fine, although begin able to continue to use sysroot_src would be less effort.

(Another consideration could be to allow specifying further standard dependencies from the sysroot crates i.e. when using sysroot_src? The crate field in deps could allow other values if this seems like a useful feature.)

Thanks for your time and work on Rust Analyzer! It's an invaluable tool.

[matklad]

Just to check that I understand correctly:

You are using rust-project.json, and one of your crates is a proc-macro. For this crate, you don't get a dep on libprocmacro?

I think this isn't supported at the moment: project.json projects can use proc macros, but can't define them.

Here's a place in code where we ignore proc macro dep:

https://github.com/rust-analyzer/rust-analyzer/blob/6aeaceaf45508383c4664bc253fb21e48034d1bc/crates/project_model/src/workspace.rs#L449

This shouldn't be hard to support though! One needs to add is_proc_macro: bool here, and than thread that data to the previous link:

https://github.com/rust-analyzer/rust-analyzer/blob/6aeaceaf45508383c4664bc253fb21e48034d1bc/crates/project_model/src/project_json.rs#L124-L139

Would you like to submit a PR? ^^

Note that we sadly don't have a super-great way to test this. We added an initial smoke test just a week ago:

https://github.com/rust-analyzer/rust-analyzer/blob/6aeaceaf45508383c4664bc253fb21e48034d1bc/crates/project_model/src/tests.rs#L1

You can try extending that, but that's going to be an adventure, and that's not required.

[tobywf]

Classic X/Y problem. I see now how this is done for Cargo-based projects:
https://github.com/rust-analyzer/rust-analyzer/blob/84302bdde8671fc69a40a0d3382e1406a1739e3a/crates/project_model/src/workspace.rs#L526-L528

I'd be happy to try and make a PR, seems like a useful addition.