Tarpaulin fails to build binaries with --engine llvm on Nightly, when clap_builder crate is used in a project.

[Sewer56]

Summary

Originally reported as:

• proc-macro crate in workspace unexpectently exits #1642 (comment)

Nightly builds of Rust (since around 2025, January, 12) fail to build the clap_builder crate when used in a project.
(Either directly or transitively)

As caught on my daily cron job that tests a GitHub Composite Action

To Reproduce

dummy_criterion.zip

Here's a dummy library project, with an attached dummy benchmark which uses criterion (most popular benchmarking library).
This is a 'realistic' setup, as benchmarking library projects is a fairly common use case. For a simpler setup

To reproduce the issue, build with cargo tarpaulin --engine llvm.

Sample stdout (from my machine):

➜  dummy_criterion git:(master) ✗ cargo tarpaulin --engine llvm
2025-01-16T19:40:23.675874Z  INFO cargo_tarpaulin::config: Creating config
2025-01-16T19:40:23.729267Z  INFO cargo_tarpaulin: Running Tarpaulin
2025-01-16T19:40:23.729275Z  INFO cargo_tarpaulin: Building project
2025-01-16T19:40:23.729278Z  INFO cargo_tarpaulin::cargo: Cleaning project
   Compiling proc-macro2 v1.0.93
   Compiling unicode-ident v1.0.14
   Compiling crossbeam-utils v0.8.21
   Compiling serde v1.0.217
   Compiling autocfg v1.4.0
   Compiling either v1.13.0
   Compiling serde_json v1.0.135
   Compiling libc v0.2.169
   Compiling rayon-core v1.12.1
   Compiling cfg-if v1.0.0
   Compiling clap_lex v0.7.4
   Compiling itoa v1.0.14
   Compiling plotters-backend v0.3.7
   Compiling memchr v2.7.4
   Compiling ryu v1.0.18
   Compiling ciborium-io v0.2.2
   Compiling regex-syntax v0.8.5
   Compiling anstyle v1.0.10
   Compiling cast v0.3.0
   Compiling same-file v1.0.6
   Compiling once_cell v1.20.2
   Compiling anes v0.1.6
   Compiling oorandom v11.1.4
   Compiling half v2.4.1
   Compiling num-traits v0.2.19
   Compiling walkdir v2.5.0
   Compiling itertools v0.10.5
   Compiling plotters-svg v0.3.7
   Compiling clap_builder v4.5.26
   Compiling ciborium-ll v0.2.2
   Compiling regex-automata v0.4.9
   Compiling criterion-plot v0.5.0
   Compiling crossbeam-epoch v0.9.18
   Compiling crossbeam-deque v0.8.6
   Compiling quote v1.0.38
   Compiling plotters v0.3.7
   Compiling syn v2.0.96
   Compiling is-terminal v0.4.13
   Compiling regex v1.11.1
   Compiling rayon v1.10.0
   Compiling serde_derive v1.0.217
error: could not compile `clap_builder` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
2025-01-16T19:40:25.390163Z ERROR cargo_tarpaulin: Failed to compile tests!
error: symbol `_RNCNCNvMs2_NtNtCs87SbzEJgdEg_12clap_builder7builder7commandNtB9_7Command29get_global_arg_conflicts_with00Bd_` is already defined
    --> /home/sewer/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/clap_builder-4.5.26/src/builder/command.rs:3992:39
     |
3992 | ...                   .flat_map(|x| x.args.args()),
     |                                 ^^^


Error: "Failed to compile tests!\nerror: symbol `_RNCNCNvMs2_NtNtCs87SbzEJgdEg_12clap_builder7builder7commandNtB9_7Command29get_global_arg_conflicts_with00Bd_` is already defined\n    --> /home/sewer/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/clap_builder-4.5.26/src/builder/command.rs:3992:39\n     |\n3992 | ...                   .flat_map(|x| x.args.args()),\n     |                                 ^^^\n\n"

Edit:

If you wish to test with an even simpler setup, simply try building any crate with a (direct or transitive) dependency on clap_builder, i.e.

[dev-dependencies]
clap_builder = { version = "4.5.26" }

That should reproduce the error.

Affected Platforms/Targets

To my awareness, all targets when using --engine llvm.

Which means on some platforms on nightly, it's not possible to do coverage at all as llvm is the only/default implementation.

I've tested on:

• i686-unknown-linux-gnu
• x86_64-unknown-linux-gnu
• i686-pc-windows-msvc
• x86_64-pc-windows-msvc

I don't have any hardware to text more exotic configurations, but in CI I've also seen failures for:

• x86_64-apple-darwin
• aarch64-apple-darwin

The default engine on Linux (ptrace) is not affected.

[Sewer56]

It's a very curious case; in any case. I don't know the exact details of the project internals here, how it all interacts with LLVM, etc.
Will wait for thoughts/feedback.

After some more poking around, I also noticed that simply depending on clap_builder in any capacity at all causes the build error; so I amended the original post to reflect this.

Notably tarpaulin itself also has a transitive dependency on clap_builder.

[XiNiHa]

For me, this also happens on stable if --doc is passed. (aarch64-apple-darwin)

[xd009642]

@XiNiHa doc test coverage needs nightly as it relies on unstable rust features so tarpaulin adds a +nightly for you