cc_env tests fail on nightly-2026-07-31 toolchain

[xtqqczze]

cc_env tests appear to regress on nightly-2026-07-31.

The tests pass on nightly-2026-07-30 but all 10 tests fail on nightly-2026-07-31 with the same ENOENT error:

thread '<test>' (<thread-id>) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

Passing toolchain: nightly-2026-07-30

$ cargo +nightly-2026-07-30 test -q -p cc --test cc_env

running 10 tests
..........
test result: ok. 10 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.48s

Failing toolchain: nightly-2026-07-31

$ cargo +nightly-2026-07-31 test -q -p cc --test cc_env

running 10 tests
distcc --- FAILED
ccache_spaces --- FAILED
ccache --- FAILED
ccache_env_flags --- FAILED
extra_flags --- FAILED
clang_cl --- FAILED
leading_spaces --- FAILED
env_var_alternatives_override --- FAILED
more_spaces --- FAILED
path_to_ccache --- FAILED

failures:

---- distcc stdout ----

thread 'distcc' (6544163) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- ccache_spaces stdout ----

thread 'ccache_spaces' (6544161) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ccache stdout ----

thread 'ccache' (6544159) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- ccache_env_flags stdout ----

thread 'ccache_env_flags' (6544160) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- extra_flags stdout ----

thread 'extra_flags' (6544165) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- clang_cl stdout ----

thread 'clang_cl' (6544162) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- leading_spaces stdout ----

thread 'leading_spaces' (6544166) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- env_var_alternatives_override stdout ----

thread 'env_var_alternatives_override' (6544164) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- more_spaces stdout ----

thread 'more_spaces' (6544167) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

---- path_to_ccache stdout ----

thread 'path_to_ccache' (6544168) panicked at tests/support/mod.rs:114:60:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }


failures:
    ccache
    ccache_env_flags
    ccache_spaces
    clang_cl
    distcc
    env_var_alternatives_override
    extra_flags
    leading_spaces
    more_spaces
    path_to_ccache

test result: FAILED. 0 passed; 10 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

Since all cc_env tests fail immediately with the same ENOENT error and there was no change to the tests between these toolchains, this may be a Rust toolchain regression rather than an issue in cc-rs.

[NobodyXu]

Yeah it's strange...If it persists on the next nightly then it'd worth investigating into

[xtqqczze]

Passing toolchain: nightly-2026-07-30:

[tests/support/mod.rs:114:9] &self.gcc = "~/cc-rs/target/debug/cc-shim"

Failing toolchain: nightly-2026-07-31:

[tests/support/mod.rs:114:9] &self.gcc = "~/cc-rs/target/debug/build/cc/096bd8b294f01352/out/cc-shim"

[xtqqczze]

The cause appears to be the new build directory layout introduced by rust-lang/cargo#17258.

Disabling the new layout makes the tests pass again:

$ __CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT=1 cargo +nightly-2026-07-31 test -q -p cc --test cc_env

running 10 tests
..........
test result: ok. 10 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.46s

cc: @weihanglo

[NobodyXu]

The reason is that we are trying to access a compiled object in tests:

cc-rs/tests/support/mod.rs

Line 57 in 228195a

let mut gcc = env::current_exe().unwrap();

It's trying to access to the cc-shim

cc-rs/src/bin/cc-shim.rs

Line 13 in 228195a

fn main() -> ExitCode {

It assumed the target dir layout:

        let mut gcc = env::current_exe().unwrap();
        gcc.pop();
        if gcc.ends_with("deps") {
            gcc.pop();
        }

[NobodyXu]

It seems that we can just use:

env!("CARGO_BIN_EXE_<name>")

[weihanglo]

Or get it via runtime, which ever works. See some other similar issues:

• feat(test): Make CARGO_BIN_EXE_ available at runtime  cargo#16421
• cli_test_dir: Relies on internals of Cargo and will break with existing / upcoming features emk/subtitles-rs#65

[NobodyXu]

Thanks for the help @xtqqczze @weihanglo I've fixed it on main