`dylint_testing` does not work when `RUSTC_WRAPPER` is set

[smoelius]

Thanks for the headsup, @dcastro. I can reproduce. This appears to be the crucial bit:

called Result::unwrap() on an Err value: Found no rustc invocations for ui

@smoelius just so you're aware, I ran into a similar issue trying to run a test with ui_test_example/ui_test_examples while having RUSTC_WRAPPER=sccache set.

Tests using ui_test work fine though.

I can reproduce this on dylint's own tests, namely examples/restriction/try_io_result:

$ RUSTFLAGS='' cargo test
...
---- ui stdout ----

thread 'ui' panicked at /home/dc/dev/other/dylint/utils/testing/src/ui.rs:106:90:
called `Result::unwrap()` on an `Err` value: Found no `rustc` invocations for `ui`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
...

Setting RUSTC_WRAPPER='' works though.

Originally posted by @dcastro in #1691

[J4CKVVH173]

Hi @smoelius , I faced the same problem while setting up the sccache + gitlab-ci combination.
dylint is really cool, and I was wondering - do you plan to address this?

This is the error:

Error: Could not build metadata entries
Caused by:
    Could not find git dependency root: [
        "Err(fetching packages failed\nstdout: \"\"\nstderr: \"  /\\n\"\n\nCaused by:\n    0: `read_dir` failed for \"/usr/local/cargo/git/checkouts/common-lints-99801120106e95f6\"\n    1: No such file or directory (os error 2))",
        "Err(fetching packages failed\nstdout: \"\"\nstderr: \"  /\\n\"\n\nCaused by:\n    0: `read_dir` failed for \"/usr/local/cargo/git/checkouts/common-lints-99801120106e95f6\"\n    1: No such file or directory (os error 2))",
    ]

I could share the gitlab and Dockerfile if you need them

[smoelius]

@J4CKVVH173 Your error looks different than the original. What command caused it?

[J4CKVVH173]

@smoelius
For context: I was setting up a gitlab-ci job that combines sccache and dylint.
I have a set of custom linters installed directly from a repository (defined under [workspace.metadata.dylint] in Cargo.toml).

Here’s what the job looks like:

dylint:
  image: ${BASE_IMAGE}:${BASE_TAG}-builder
  variables:
    SCCACHE_BUCKET: ${S3_CACHE_BUCKET}
    SCCACHE_ENDPOINT: ${S3_CACHE_ADDRESS}
    RUSTC_WRAPPER: /usr/local/cargo/bin/sccache
    SCCACHE_REGION: eu-central-2
    SCCACHE_S3_USE_SSL: false
    AWS_ACCESS_KEY_ID: ${S3_CACHE_ACCESS_KEY}
    AWS_SECRET_ACCESS_KEY: ${S3_CACHE_SECRET_KEY}
    SCCACHE_S3_KEY_PREFIX: ${CI_COMMIT_REF_NAME}
  before_script:
    - sccache --start-server
  after_script:
    - sccache --stop-server
  script:
    - RUSTFLAGS="-D warnings" cargo dylint --all

The issue only shows up once sccache is in the mix - without it, everything works fine, I've checked it from the scratch.

[smoelius]

Sorry, I know little about GitLab and sccache, and I am having trouble figuring out what a fix should look like.

When I try this:

RUSTC_WRAPPER="sccache" "cargo" "test"

I get the errors below. Do you know what I could be doing wrong?

Errors

error[E0432]: unresolved imports `rustc_hir::ImplItemImplKind`, `rustc_hir::TraitImplHeader`
  --> /Users/samuel.moelius/.cargo/git/checkouts/rust-clippy-780b684d4f709d82/20ce69b/clippy_utils/src/check_proc_macro.rs:25:15
   |
25 |     ImplItem, ImplItemImplKind, ImplItemKind, IsAuto, Item, ItemKind, Lit, LoopSource, MatchSource, MutTy, Node, Path,
   |               ^^^^^^^^^^^^^^^^
   |               |
   |               no `ImplItemImplKind` in the root
   |               help: a similar name exists in the module: `ImplItemKind`
26 |     QPath, Safety, TraitImplHeader, TraitItem, TraitItemKind, Ty, TyKind, UnOp, UnsafeSource, Variant, VariantData,
   |                    ^^^^^^^^^^^^^^^ no `TraitImplHeader` in the root

error[E0433]: failed to resolve: could not find `AssocContainer` in `rustc_ty`
    --> /Users/samuel.moelius/.cargo/git/checkouts/rust-clippy-780b684d4f709d82/20ce69b/clippy_utils/src/lib.rs:3248:19
     |
3248 |         rustc_ty::AssocContainer::Trait => get_path_to_callee(tcx, from, def_id),
     |                   ^^^^^^^^^^^^^^
     |                   |
     |                   could not find `AssocContainer` in `rustc_ty`
     |                   help: an enum with a similar name exists: `AssocItemContainer`

error[E0433]: failed to resolve: could not find `AssocContainer` in `rustc_ty`
    --> /Users/samuel.moelius/.cargo/git/checkouts/rust-clippy-780b684d4f709d82/20ce69b/clippy_utils/src/lib.rs:3249:19
     |
3249 |         rustc_ty::AssocContainer::InherentImpl | rustc_ty::AssocContainer::TraitImpl(_) => {
     |                   ^^^^^^^^^^^^^^
     |                   |
     |                   could not find `AssocContainer` in `rustc_ty`
     |                   help: an enum with a similar name exists: `AssocItemContainer`

error[E0433]: failed to resolve: could not find `AssocContainer` in `rustc_ty`
    --> /Users/samuel.moelius/.cargo/git/checkouts/rust-clippy-780b684d4f709d82/20ce69b/clippy_utils/src/lib.rs:3249:60
     |
3249 |         rustc_ty::AssocContainer::InherentImpl | rustc_ty::AssocContainer::TraitImpl(_) => {
     |                                                            ^^^^^^^^^^^^^^
     |                                                            |
     |                                                            could not find `AssocContainer` in `rustc_ty`
     |                                                            help: an enum with a similar name exists: `AssocItemContainer`

error[E0531]: cannot find unit struct, unit variant or constant `panic_display` in module `sym`
    --> /Users/samuel.moelius/.cargo/git/checkouts/rust-clippy-780b684d4f709d82/20ce69b/clippy_utils/src/macros.rs:259:18
     |
 259 |               sym::panic_display => {
     |                    ^^^^^^^^^^^^^ help: a constant with a similar name exists: `new_display`
     |
    ::: /Users/samuel.moelius/.rustup/toolchains/stable-aarch64-apple-darwin/lib/rustlib/rustc-src/rust/compiler/rustc_span/src/symbol.rs:22:1
     |
  22 | / symbols! {
...    |
2396 | | }
     | |_- similarly named constant `new_display` defined here

EDIT: sccache 0.10.0 installed with Cargo

[J4CKVVH173]

Are you trying this locally or inside a runner?

sccache works as a daemon process, so you need to start its backend first (sccache --start-server) and also configure cache storage via environment variables.

Here’s a minimal script I tested in my setup that runs sccache together with the tests:

sccache --start-server
RUSTC_WRAPPER="sccache" cargo test --lib
sccache --stop-server

UPD:

I tried this inside my own custom linters for dylint. The tests did compile and run, but I noticed something odd:

• without sccache all tests pass
• with sccache enabled, one of the tests fails (this might still be an issue on my side though).

ccache 0.10.0
cc v1.2.39
channel = "nightly-2025-09-18"

UPD2:

Did you try cargo clean?

[smoelius]

I suspect the errors you are getting have a different underlying cause, so I'm going to open a new issue. Please add any additional context you can there.

But to answer your question:

Are you trying this locally or inside a runner?

Locally with the Dylint repo itself.

To be more explicit, I added a test like this to utils/testing/src/lib.rs from f8a9afb:

#[cfg(test)]
mod test {
    use dylint_internal::{CommandExt, packaging::new_template};
    use tempfile::tempdir;

    #[test]
    fn rustc_wrapper() {
        let tempdir = tempdir().unwrap();

        new_template(tempdir.path()).unwrap();

        dylint_internal::cargo::test("dylint-template with `RUSTC_WRAPPER` set")
            .build()
            .current_dir(&tempdir)
            .env("RUSTC_WRAPPER", "sccache")
            .success()
            .unwrap();
    }
}

The original issue was about dylint_testing not finding the rustc invocations in cargo build output:

dylint/utils/testing/src/lib.rs

Line 345 in 478fb16

if args.first().is_some_and(is_rustc)

That makes sense to me because the invocations would be of sccache, not rustc.

But I'm confused as to why I am I getting the errors I'm getting. They seem to suggest sccache is finding the wrong toolchain.

[J4CKVVH173]

fair enough