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Allow configuring arbitrary codegen backends #15562

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Merged
merged 1 commit into from
May 19, 2025
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Allow configuring arbitrary codegen backends #15562

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29 changes: 5 additions & 24 deletions src/cargo/util/toml/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2465,25 +2465,15 @@ pub fn validate_profile(
features: &Features,
warnings: &mut Vec<String>,
) -> CargoResult<()> {
validate_profile_layer(root, name, cli_unstable, features)?;
validate_profile_layer(root, cli_unstable, features)?;
if let Some(ref profile) = root.build_override {
validate_profile_override(profile, "build-override")?;
validate_profile_layer(
profile,
&format!("{name}.build-override"),
cli_unstable,
features,
)?;
validate_profile_layer(profile, cli_unstable, features)?;
}
if let Some(ref packages) = root.package {
for (override_name, profile) in packages {
for profile in packages.values() {
validate_profile_override(profile, "package")?;
validate_profile_layer(
profile,
&format!("{name}.package.{override_name}"),
cli_unstable,
features,
)?;
validate_profile_layer(profile, cli_unstable, features)?;
}
}

Expand Down Expand Up @@ -2548,26 +2538,17 @@ pub fn validate_profile(
/// This is a shallow check, which is reused for the profile itself and any overrides.
fn validate_profile_layer(
profile: &manifest::TomlProfile,
name: &str,
cli_unstable: &CliUnstable,
features: &Features,
) -> CargoResult<()> {
if let Some(codegen_backend) = &profile.codegen_backend {
if profile.codegen_backend.is_some() {
match (
features.require(Feature::codegen_backend()),
cli_unstable.codegen_backend,
) {
(Err(e), false) => return Err(e),
_ => {}
}

if codegen_backend.contains(|c: char| !c.is_ascii_alphanumeric() && c != '_') {
bail!(
"`profile.{}.codegen-backend` setting of `{}` is not a valid backend name.",
name,
codegen_backend,
);
}
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If preferred I can also keep this check on the cargo side when nightly features are disabled.

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How arbitrary you'd like to have for codegen-backend name? What is the real use case here?

The change seems fine to me though, as a nightly feature.

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Basically -Zcodegen-backend allows either of the following:

  • The name of a builtin codegen backend. This will eventually be stabilized once one of the non-LLVM backends gets stabilized.
  • The full path to a dylib implementing a codegen backend. This will never be stable. It exists to allow codegen backends not shipped as part of rustc to be used. For example cg_clif uses it when you locally build it or when using the version from its CI rather than the rustup distributed version (the CI version is newer). Same for cg_gcc when you locally build it.

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Thanks for the info! It makes sense to relax it a bit for now.

When stabilization, Cargo should only allow a set of known backends. We should track it somewhere, though we dont really have a Cargo tracking issue for codegen-backend right now.

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rust-lang/rust#77933 (comment)

}
if profile.rustflags.is_some() {
match (
Expand Down