Cannot set rustcSource to rustc-dev rustup package

[RalfJung]

In an attempt to get rust-analyzer to work better for working on Miri (which imports rustc-private crates), I tried setting rust-analyzer.rustcSource to /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/, where the rustc-dev rustup package puts the sources. However, that does not work -- I am getting an error saying "the manifest path must be a path to a Cargo.toml file".

Is there any way to make rust-analyzer use the sources included in the rustc-dev package?

[bjorn3]

I think you need to point to /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/Cargo.toml.

[RalfJung]

But in that directory there's only the lib source, not the compiler source.

[RalfJung]

There's no such file:

$ ls /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/
Cargo.lock  compiler

[bjorn3]

Maybe try the Cargo.toml of rustc_driver?

[flodiebold]

I would assume you need an actual checkout of rustc.

[RalfJung]

I would assume you need an actual checkout of rustc.

That would be rather unpractical -- the crates it is linking against are installed via rustup, so to make sure the source matches, that should also be taken from rustup.

The rustc-dev package can probably be extended with some more files if that helps.

[RalfJung]

Maybe try the Cargo.toml of rustc_driver?

No that does not work either:

rust-analyzer failed to load workspace: Failed to read Cargo metadata for Rust sources: Failed to run `cargo metadata --manifest-path /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc_driver/Cargo.toml` in `/home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc_driver`: `cargo metadata` exited with an error:     Updating crates.io index
error: failed to get `build_helper` as a dependency of package `rustc_llvm v0.0.0 (/home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc_llvm)`
    ... which is depended on by `rustc_codegen_llvm v0.0.0 (/home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc_codegen_llvm)`
    ... which is depended on by `rustc_interface v0.0.0 (/home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc_interface)`
    ... which is depended on by `rustc_driver v0.0.0 (/home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc_driver)`

Caused by:
  failed to load source for dependency `build_helper`

Caused by:
  Unable to update /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/src/build_helper

Caused by:
  failed to read `/home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/src/build_helper/Cargo.toml`

Caused by:
  No such file or directory (os error 2)

[bnjbvr]

I've found what the root cause of this particular issue is: the src/build_helper directory is missing from the distributed sources. If you manualloy copy it from the Rustc src to ~/.rustup/toolchains/{toolchain}/lib/rustlib/rustc-src/rust/src/build_helper, it works just fine! I'll open a PR for adding this directory when distributing rustc.

[lnicola]

@bnjbvr can this be closed now?

[RalfJung]

With the latest rustc, pointing to /home/r/.rustup/toolchains/miri/lib/rustlib/rustc-src/rust/compiler/rustc_driver/Cargo.toml seems to do something -- I now get more auto-completion than before.

However, it seems rather strange that I would have to pick one of the many compiler crates. Why rustc_driver? At the very least, the docstring for rustcSource should explicitly say "set this to the Cargo.toml of rustc_driver", or so.

[Veykril]

Pointing it to <sysroot>/lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.toml should work nowadays (that's what we try to lookup by default), so I believe this can be closed? (I'll close it, re-open if you think otherwise)

[RalfJung]

We are setting "rust-analyzer.rustc.source": "discover" and that's working just fine for years now, so yeah this can be closed.