Add cargo_cfg_target_family_multivalued FCW #147545
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madsmtm added A-lints 
rustbot added the S-waiting-on-review 
madsmtm commented Oct 10, 2025
| /// | ||
| /// [CARGO_CFG_TARGET_FAMILY]: https://doc.rust-lang.org/cargo/reference/environment-variables.html#:~:text=CARGO_CFG_TARGET_FAMILY | ||
| /// [cfg-target_family]: https://doc.rust-lang.org/reference/conditional-compilation.html#target_family | ||
| CARGO_CFG_TARGET_FAMILY_MULTIVALUED, |
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What do you think about the name? cargo_cfg_target_family_multivalued is kinda long, but I felt that shortening it risked loosing meaning. _multivalued isn't the best descriptor though, perhaps _direct_comparison would be better?
| struct ReplaceWithSplitAny { | ||
| #[suggestion_part(code = "!")] | ||
| negate: Option<Span>, | ||
| #[suggestion_part(code = ".split(',').any(|x| x == ")] |
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We could suggest .contains("unix") instead, that'd work as well. I felt .split(',').any(|x| x == "unix") was more principled, but I'd be fine with either.
| Warn, | ||
| "comparing `CARGO_CFG_TARGET_FAMILY` env var with a single value", | ||
| @future_incompatible = FutureIncompatibleInfo { | ||
| reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange, |
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Unsure if this is the intended use of a FCW? I would like it to trigger in dependents some day, but there wasn't precedent for using FutureReleaseSemanticsChange anywhere.
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petrochenkov added S-waiting-on-t-lang 
traviscross added the P-lang-drag-2 
| Just to summarize, I think the main questions for lang is:
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madsmtm changed the title cargo_cfg_target_family_multivalued lintcargo_cfg_target_family_multivalued FCW Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
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Add
cargo_cfg_target_family_multivaluedlint which detects simple comparisons like==ormatchon theCARGO_CFG_TARGET_FAMILYenvironment variable. These are wrong, sinceCARGO_CFG_TARGET_FAMILYis multi-valued (currently only onwasm32-unknown-emscriptenandwasm32-wali-linux-musl, so admittedly pretty rare).This lint is inherently incomplete, because we can't track a value like this through arbitrary control flow. Regardless, I've found that it works pretty well in practice, from the various repos I took a look at that used
CARGO_CFG_TARGET_FAMILY, I'd guess at least 80% of them would hit this lint.This should unblock at some point adding
#[cfg(target_family = "darwin")]as a replacement for#[cfg(target_vendor = "apple")], which in turns unblocks #100343.There exist other multi-valued cfgs such as
CARGO_CFG_TARGET_HAS_ATOMICorCARGO_CFG_TARGET_FEATURE, but these were very clearly multi-valued from the beginning, and thus doesn't make sense to lint for.This is my first time adding a lint, so beware that I'm a bit unsure if I did things right. Especially unsure if I should feature-gate the lint to start with, or if we should insta-stabilize it? I'm pretty sure it needs a lang FCP though.
r? compiler
CC @thomcc @workingjubilee