Clippy can run the wrong rustc, leading to "incompatible version of rustc" errors

[jorendorff]

Summary

I had several versions of Rust installed (via rustup) and was surprised that Clippy would sometimes give errors like this:

error[E0514]: found crate `paste` compiled by an incompatible version of rustc
...
  = help: please recompile that crate using this compiler (rustc 1.64.0 ...)
  = note: the following crate versions were found:
          crate `paste` compiled by rustc 1.63.0: ...

1.64.0 was in fact the version I wanted to be using.

The surprise came when I did rustup toolchain remove 1.63.0, then cargo clean && cargo clippy, and still got the same error!

It turns out I had yet another copy of Rust 1.63.0 installed, via Homebrew, as /usr/local/bin/rustc.
I think I must have done brew install rust-analyzer at some point and that brought in the rust package.

Obviously that was bad and I just removed it. But this means cargo clippy sometimes results in two different rustc executables being used. I think that must be a bug.

Reproducer

Possible steps to reproduce, using code in https://github.com/jorendorff/incompavers:

1. Have Homebrew and rustup installed

2. Run these commands:

   brew install rust
   git clone https://github.com/jorendorff/incompavers.git
   cd incompavers
   cargo clean && cargo clippy --verbose
   

Expected behavior: Clippy should lint the crate.

Actual behavior: Clippy produced the errors below.

❯ cargo clean && cargo clippy --verbose
    Checking base64 v0.13.0
   Compiling paste v1.0.9
     Running `rustc --crate-name base64 --edition=2018 /Users/jorendorff/.cargo/registry/src/github.com-1ecc6299db9ec823/base64-0.13.0/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 --cfg 'feature="default"' --cfg 'feature="std"' -C metadata=bd37c0a895c55f89 -C extra-filename=-bd37c0a895c55f89 --out-dir /Users/jorendorff/src/incompavers/target/debug/deps -L dependency=/Users/jorendorff/src/incompavers/target/debug/deps --cap-lints allow`
     Running `rustc --crate-name paste --edition=2018 /Users/jorendorff/.cargo/registry/src/github.com-1ecc6299db9ec823/paste-1.0.9/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type proc-macro --emit=dep-info,link -C prefer-dynamic -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C metadata=1cc8d85ad06b00de -C extra-filename=-1cc8d85ad06b00de --out-dir /Users/jorendorff/src/incompavers/target/debug/deps -L dependency=/Users/jorendorff/src/incompavers/target/debug/deps --extern proc_macro --cap-lints allow`
    Checking incompavers v0.1.0 (/Users/jorendorff/src/incompavers)
     Running `/Users/jorendorff/.rustup/toolchains/stable-x86_64-apple-darwin/bin/clippy-driver rustc --crate-name incompavers --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C metadata=8f4097126ae0e3f7 -C extra-filename=-8f4097126ae0e3f7 --out-dir /Users/jorendorff/src/incompavers/target/debug/deps -C incremental=/Users/jorendorff/src/incompavers/target/debug/incremental -L dependency=/Users/jorendorff/src/incompavers/target/debug/deps --extern base64=/Users/jorendorff/src/incompavers/target/debug/deps/libbase64-bd37c0a895c55f89.rmeta --extern paste=/Users/jorendorff/src/incompavers/target/debug/deps/libpaste-1cc8d85ad06b00de.dylib`
error[E0514]: found crate `paste` compiled by an incompatible version of rustc
 --> src/lib.rs:1:9
  |
1 | pub use paste::paste;
  |         ^^^^^
  |
  = help: please recompile that crate using this compiler (rustc 1.64.0 (a55dd71d5 2022-09-19)) (consider running `cargo clean` first)
  = note: the following crate versions were found:
          crate `paste` compiled by rustc 1.63.0: /Users/jorendorff/src/incompavers/target/debug/deps/libpaste-1cc8d85ad06b00de.dylib

error[E0514]: found crate `base64` compiled by an incompatible version of rustc
  --> src/lib.rs:22:26
   |
22 |     println!("hello {}", base64::encode(b"world"));
   |                          ^^^^^^
   |
   = help: please recompile that crate using this compiler (rustc 1.64.0 (a55dd71d5 2022-09-19)) (consider running `cargo clean` first)
   = note: the following crate versions were found:
           crate `base64` compiled by rustc 1.63.0: /Users/jorendorff/src/incompavers/target/debug/deps/libbase64-bd37c0a895c55f89.rmeta

error: could not compile `incompavers` due to 2 previous errors

Caused by:
  process didn't exit successfully: `/Users/jorendorff/.rustup/toolchains/stable-x86_64-apple-darwin/bin/clippy-driver rustc --crate-name incompavers --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C metadata=8f4097126ae0e3f7 -C extra-filename=-8f4097126ae0e3f7 --out-dir /Users/jorendorff/src/incompavers/target/debug/deps -C incremental=/Users/jorendorff/src/incompavers/target/debug/incremental -L dependency=/Users/jorendorff/src/incompavers/target/debug/deps --extern base64=/Users/jorendorff/src/incompavers/target/debug/deps/libbase64-bd37c0a895c55f89.rmeta --extern paste=/Users/jorendorff/src/incompavers/target/debug/deps/libpaste-1cc8d85ad06b00de.dylib` (exit status: 1)

Version

rustc 1.64.0 (a55dd71d5 2022-09-19)
binary: rustc
commit-hash: a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52
commit-date: 2022-09-19
host: x86_64-apple-darwin
release: 1.64.0
LLVM version: 14.0.6

Additional Labels

No response

[fritzrehde]

I have encountered this problem as well.

[drueck]

I'm running into this as well. I have another thing installed via homebrew that has rust as a dependency, and so I can't uninstall the system rust without first uninstalling the other thing (which I don't want to uninstall). Is there a workaround for this? Like a way to just configure clippy to use a specific rustc?

[ewoolsey]

I'm running into this as well. I have another thing installed via homebrew that has rust as a dependency, and so I can't uninstall the system rust without first uninstalling the other thing (which I don't want to uninstall). Is there a workaround for this? Like a way to just configure clippy to use a specific rustc?

Same here. Would love an update to this problem.

[your-diary]

Any workaround? cargo check and cargo build work. Only cargo clippy doesn't work.

[jorendorff]

If your system is like mine, the workaround is brew uninstall rust.

[homologay]

I had this issue, it finally worked when I deleted rustc directly (by sudo rm /usr/bin/rustc) (or wherever your rustc lies). Then cargo clean and cargo clippy in my project directory.

rustc version 1.66.1
clippy version 0.1.66
cargo version 1.64.0
rustup 1.25.1
void linux x86_64 kernel 6.1.6_1

[milesj]

Thank you for this thread. Clippy hasn't worked for weeks and it turns out that rust was somehow installed via homebrew. Uninstalling it fixed my problem.

[simonhammes]

I've also run into this and tried to debug the problem.
In my case, building something from source via Homebrew is also the most likely culprit.

I believe that this actually stems from a different cargo binary being used, as Clippy invokes cargo here:

rust-clippy/src/main.rs

Line 129 in a7335cb

let mut cmd = Command::new("cargo");

Running the following command on my local machine probably explains why this is happening:

find $(echo $PATH | tr ':' '\n') -type f,l -name "cargo"

Output:

/home/linuxbrew/.linuxbrew/bin/cargo
/home/$USER/.cargo/bin/cargo

---

=> cargo from brew comes first, which means that any command running cargo will use this binary

This issue probably references the same problem: Homebrew/brew#13281:
By default, /home/linuxbrew/.linuxbrew/bin/brew shellenv (which is in ~/.profile) prepends the brew bin directories to $PATH instead of appending them, causing the brew binaries to have a higher priority.

As Homebrew/brew#13281 (comment) suggests, setting $PATH yourself might be the correct solution, although I haven't tried that yet.

---

As I do not own a Mac, I can't verify whether this is the reason for the error in the OP.
But I would be glad if someone else would dig a little deeper and verify this ;)

[jorendorff]

Nice debugging, @simonhammes.

It looks like this repo uses Command::new("cargo") in a few places. I wonder if using the CARGO environment variable instead would fix this bug.

[dvdsk]

This issue is about to come up a lot more frequent I fear.

As rust is now used in the kernel 🥳 rustc has become part of the linux-headers package on Ubuntu and its derivatives. When I run clippy the system installed rustc is used.

Use dpkg-query -S rustc to see the packages that installed rustc.

Now the question is whether this goes wrong in clippy or cargo...

[hoijui]

Under Debian (probably also Ubuntu & co.):

# Removes the rustc installed though apt, leaving only the one installed though rustup (hopefully)
sudo apt-get remove rustc
# Removes all compile artifacts, including the ones compiled with the apt-installed rustc
cargo clean
# This should now work
cargo clippy

[Coconop]

I had this issue on Windows too because I initially installed the standalone version before using the rustup-init.exe.
Note that both cargo clippy and cargo check were raising erros.

Inspired by @simonhammes and this question on Rust users forum I looked up for conflicting installs from powershell:

rustup which rustc

Ouput: C:\Users\Coconop\.rustup\toolchains\stable-x86_64-pc-windows-msvc\bin\rustc.exe

On the other hand:

Get-Command rustc.exe

Output: C:\Program Files\Rust stable MSVC 1.77

I wasn't sure how to uninstall standalone version so I just updated the PATH environment variable to point to the rustup toolchain and now both cargo check and cargo clippy are happy :)