`cargo-gpu` in build scripts breaks clippy and miri

[tuguzT]

Recently I stumbled upon a minor issue when trying to use cargo-gpu inside of a workspace.
Workspace of my project contains crates with unsafe code which I want to test with Miri to catch soundness issues.

Recently added library API of cargo-gpu works great inside of build scripts, but when I try to call Miri at a workspace root, build scripts which compiles my shader crates fails.

I've created minimal reproducible example of such workspace at https://github.com/tuguzT/cargo-gpu-miri; I am sure that workspace of my project is too complicated to demonstrate such issue.

Here is what actually happens there:

1. Using recently added cargo-gpu library API fails with this error:

error: failed to run custom build command for `simple_shader_builder_api v0.0.0 (C:\Users\tuguzT\Projects\cargo-gpu-miri\simple_shader_builder_api)`

Caused by:
  process didn't exit successfully: `C:\Users\tuguzT\Projects\cargo-gpu-miri\target\miri\debug\build\simple_shader_builder_api-de35662e45b75b83\build-script-build` (exit code: 1)
  --- stderr
  error: process didn't exit successfully: `C:\Users\tuguzT\.rustup\toolchains\nightly-x86_64-pc-windows-msvc\bin\cargo-miri.exe C:\Users\tuguzT\.rustup\toolchains\nightly-2024-11-22-x86_64-pc-windows-msvc\bin\rustc.exe -vV` (exit code: 1)
  --- stderr
  fatal error: `cargo-miri` called without RUSTC set; please only invoke this binary through `cargo miri`

  Error: BuildFailed

2. Before using cargo-gpu library API, I used to create std::process::Command and call it with locally installed cargo-gpu executable; it was silently failing with the similar error with such stderr dump which I took from target/miri/x86_64-pc-windows-msvc/debug/build/simple_shader_builder_command-c861efd69eece953/stderr file:

failed to build shaders:
error: process didn't exit successfully: `C:\Users\tuguzT\.rustup\toolchains\nightly-x86_64-pc-windows-msvc\bin\cargo-miri.exe C:\Users\tuguzT\.rustup\toolchains\nightly-2024-11-22-x86_64-pc-windows-msvc\bin\rustc.exe -vV` (exit code: 1)
--- stderr
fatal error: `cargo-miri` called without RUSTC set; please only invoke this binary through `cargo miri`

[2025-07-03T16:30:24Z ERROR cargo_gpu] build failed
Error: build failed

It failed silently because contents of std::process::Command were not checked inside of build script and because examples and benchmarks which compiled such shaders were not executed, and so absence of shader compiled into SPIR-V were not checked.

3. After looking at Miri source code, I found this line which, I think, causes these errors described earlier:
   https://github.com/rust-lang/miri/blob/8481c42358eeed1a233b8ead7717683529ffde94/cargo-miri/src/main.rs#L102

---

And so, the question: how cargo-gpu should behave in such case?
Should it really somehow bypass Miri and compile shaders normally or is this an intended behaviour?

• On the one hand, it's not too hard to manually call Miri only on crates which code should be tested on UB, or to filter packages via --package option.
• On the other hand, running build scripts successfully could be slightly more convenient.

[tuguzT]

I wanted to close this issue (due to Miri not supporting Command API, see rust-lang/miri#3374)
But upon testing my hypothesis I made some changes to the linked repository to call unsafe code inside of build scripts themselves, and I noticed that Miri does not check UB inside of build scripts at all

So it should be totally possible to resolve such issue (maybe even by myself)
I've actually started to read Miri source code to find a way to solve an issue

[tuguzT]

I've noticed via "debugging" of simple_shader_builder_api build script (by the way, I've just initialized logging inside of it) that "install" phase of build script (cargo_gpu::Install::run()) works regardless of Miri usage.

But "build" phase (spirv_builder::SpirvBuilder::build()) fails (if our build script is being called by Miri) with familiar message:

error: process didn't exit successfully: `C:\Users\tuguzT\.rustup\toolchains\nightly-x86_64-pc-windows-msvc\bin\cargo-miri.exe C:\Users\tuguzT\.rustup\toolchains\nightly-2024-11-22-x86_64-pc-windows-msvc\bin\rustc.exe -vV` (exit code: 1)
--- stderr
fatal error: `cargo-miri` called without RUSTC set; please only invoke this binary through `cargo miri`

The only reference of -vV argument in rust-gpu project which I found is located here:
https://github.com/Rust-GPU/rust-gpu/blob/de24a8911b724a95f5df3c304c99995b07335a9c/crates/rustc_codegen_spirv/build.rs#L32

But Command API inherits all the environment variables of the parent process (as stated in docs) which, I guess, removed it here:
https://github.com/Rust-GPU/rust-gpu/blob/de24a8911b724a95f5df3c304c99995b07335a9c/crates/spirv-builder/src/lib.rs#L1033

But I'm not sure this is the very line of code that causes this issue, because I haven't tried to debug spirv_builder inside of build script yet.

[Firestar99]

I'm aware of it since #77 but haven't had the time to investigate why. clippy seems to cause the cargo +toolchain build call to turn into path/to/clippy cargo +toolchain build and fail due to nonsensical args. Let's make this the primary issue though.

[tuguzT]

Yeah, if I call cargo clippy --package simple_shader_builder_api, I get this error:

error: failed to run `rustc` to learn about target-specific information

  Caused by:
    process didn't exit successfully: `C:\Users\tuguzT\.rustup\toolchains\stable-x86_64-pc-windows-msvc\bin\clippy-driver.exe C:\Users\tuguzT\.rustup\toolchains\nightly-2024-11-22-x86_64-pc-windows-msvc\bin\rustc.exe - --crate-name ___ --print=file-names -Zcodegen-backend=C:\Users\tuguzT\AppData\Local\rust-gpu\codegen\https___github.com_Rust-GPU_rust-gpu+f5837407\rustc_codegen_spirv.dll -Zbinary-dep-depinfo -Csymbol-mangling-version=v0 -Zcrate-attr=feature(register_tool) -Zcrate-attr=register_tool(rust_gpu) -Coverflow-checks=off -Cdebug-assertions=off -Zinline-mir=off -Zmir-enable-passes=-GVN -Cllvm-args=--spirv-metadata=full --target \\?\C:\Users\tuguzT\AppData\Local\rust-gpu\codegen\https___github.com_Rust-GPU_rust-gpu+f5837407\target-specs\spirv-unknown-vulkan1.2.json --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg` (exit code: 1)
    --- stderr
    error: the option `Z` is only accepted on the nightly compiler

    help: consider switching to a nightly toolchain: `rustup default nightly`

    note: selecting a toolchain with `+toolchain` arguments require a rustup proxy; see <https://rust-lang.github.io/rustup/concepts/index.html>

    note: for more information about Rust's stability policy, see <https://doc.rust-lang.org/book/appendix-07-nightly-rust.html#unstable-features>

    error: 1 nightly option were parsed

  Error: BuildFailed

But if I call cargo +nightly clippy --package simple_shader_builder_api, I get this instead:

error: failed to run `rustc` to learn about target-specific information

  Caused by:
    process didn't exit successfully: `C:\Users\tuguzT\.rustup\toolchains\nightly-x86_64-pc-windows-msvc\bin\clippy-driver.exe C:\Users\tuguzT\.rustup\toolchains\nightly-2024-11-22-x86_64-pc-windows-msvc\bin\rustc.exe - --crate-name ___ --print=file-names -Zcodegen-backend=C:\Users\tuguzT\AppData\Local\rust-gpu\codegen\https___github.com_Rust-GPU_rust-gpu+f5837407\rustc_codegen_spirv.dll -Zbinary-dep-depinfo -Csymbol-mangling-version=v0 -Zcrate-attr=feature(register_tool) -Zcrate-attr=register_tool(rust_gpu) -Coverflow-checks=off -Cdebug-assertions=off -Zinline-mir=off -Zmir-enable-passes=-GVN -Cllvm-args=--spirv-metadata=full --target \\?\C:\Users\tuguzT\AppData\Local\rust-gpu\codegen\https___github.com_Rust-GPU_rust-gpu+f5837407\target-specs\spirv-unknown-vulkan1.2.json --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg` (exit code: 1)
    --- stderr
    error: error loading target specification: `unknown` os can only be used on particular targets; use `none` for bare-metal targets
      |
      = help: run `rustc --print target-list` for a list of built-in targets

  Error: BuildFailed

[tuguzT]

I've noticed via "debugging" of simple_shader_builder_api build script (by the way, I've just initialized logging inside of it) that "install" phase of build script (cargo_gpu::Install::run()) works regardless of Miri usage.

No, this is actually misleading: this phase passes only if it was successful before (i.e. build script called without Miri or Clippy).

But it fails with the same message if called for the first time (via Miri):

error: process didn't exit successfully: `C:\Users\tuguzT\.rustup\toolchains\nightly-x86_64-pc-windows-msvc\bin\cargo-miri.exe C:\Users\tuguzT\.rustup\toolchains\nightly-2025-06-23-x86_64-pc-windows-msvc\bin\rustc.exe -vV` (exit code: 1)
--- stderr
fatal error: `cargo-miri` called without RUSTC set; please only invoke this binary through `cargo miri`

P.S.: it seems to successfully install required toolchains, but fails on this step:

[cargo_gpu::install] building artifacts with `"cargo" "+toolchain" "build" "--release"`

cargo-gpu/crates/cargo-gpu/src/install.rs

Line 308 in 7fc4560

log::debug!("building artifacts with `{cargo:?}`");