Add support for the unstable check-cfg feature behind an environment variable
#3037
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r? @JohnTitor (rustbot has picked a reviewer for you, use r? to override) |
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Thanks for the detailed explanation, that sounds sensible! Could you fix Cirrus CI's failures? |
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I'll get to that in the new year (this is work-related and I'm on vacation). |
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Rebased on top of master. I have no clue why FreeBSD is failing though, my PR only changes how |
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Turns out the problem was enabling |
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Sorry for the delay, I'll review in a few days! |
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☔ The latest upstream changes (presumably #3127) made this pull request unmergeable. Please resolve the merge conflicts. |
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Could you resolve the merge conflict (I made it to remove the semver checks, sorry)? |
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Rebased, and added |
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Great, thank you! @bors r+ |
Add support for the unstable `check-cfg` feature behind an environment variable `check-cfg` ([Rust](https://doc.rust-lang.org/stable/unstable-book/compiler-flags/check-cfg.html), [Cargo](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#check-cfg)) is an unstable features that warns when you write an unknown `#[cfg]` (likely due to a typo). The feature works out of the box for default cfgs and features provided by Cargo, but requires providing the list of extra cfgs when custom ones are used. This PR adds the `LIBC_CHECK_CFG` environment variable. When enabled, the build script will use the `cargo:rustc-check-cfg` println to instruct the compiler of all the possible cfgs set by libc. The build script was also refactored to ensure all cfgs are accounted for, and a CI job using `-Z check-cfg` was added. This PR is best reviewed commit-by-commit. ## Why is this needed? The main motivation for this PR is that `rust-lang/rust` enforces `check-cfg` across the whole codebase. Normally this is not a problem for dependencies like `libc`, as Cargo caps the lints and thus doesn't show the generated warnings. When developing support for new targets though, it's helpful to use a custom libc fork to develop the libc port and the std port together. Unfortunately doing that today results in a bunch of compilation errors, since lints are not capped with `path` dependencies. My goal with this PR is to address that shortcoming, as we'd then be able to set the `LIBC_CHECK_CFG=1` environment variable in the Rust build system and remove the compilation errors. This PR might also be helpful for libc maintainers, as the CI check might spot typos in `#[cfg]`s.
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💔 Test failed - checks-actions |
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@bors delegate+ |
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✌️ @pietroalbini can now approve this pull request |
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@bors r=JohnTitor |
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☀️ Test successful - checks-actions, checks-cirrus-freebsd-12, checks-cirrus-freebsd-13, checks-cirrus-freebsd-14 |
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☀️ Test successful - checks-actions, checks-cirrus-freebsd-12, checks-cirrus-freebsd-13, checks-cirrus-freebsd-14 |
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👀 Test was successful, but fast-forwarding failed: 422 Changes must be made through a pull request. |
…k-Simulacrum Set `LIBC_CHECK_CFG=1` when building Rust code in bootstrap Downstream forks of the Rust compiler might want to use a custom `libc` to add support for targets that are not yet available upstream. Adding a patch to replace `libc` with a custom one would cause compilation errors though, because Cargo would interpret the custom `libc` as part of the workspace, and apply the check-cfg lints on it. Since rust-lang/libc#3037, the `libc` build script emits check-cfg flags only when the `LIBC_CHECK_CFG` environment variable is set, so this PR allows the use of custom `libc`s.
check-cfg(Rust, Cargo) is an unstable features that warns when you write an unknown#[cfg](likely due to a typo). The feature works out of the box for default cfgs and features provided by Cargo, but requires providing the list of extra cfgs when custom ones are used.This PR adds the
LIBC_CHECK_CFGenvironment variable. When enabled, the build script will use thecargo:rustc-check-cfgprintln to instruct the compiler of all the possible cfgs set by libc. The build script was also refactored to ensure all cfgs are accounted for, and a CI job using-Z check-cfgwas added.This PR is best reviewed commit-by-commit.
Why is this needed?
The main motivation for this PR is that
rust-lang/rustenforcescheck-cfgacross the whole codebase. Normally this is not a problem for dependencies likelibc, as Cargo caps the lints and thus doesn't show the generated warnings.When developing support for new targets though, it's helpful to use a custom libc fork to develop the libc port and the std port together. Unfortunately doing that today results in a bunch of compilation errors, since lints are not capped with
pathdependencies. My goal with this PR is to address that shortcoming, as we'd then be able to set theLIBC_CHECK_CFG=1environment variable in the Rust build system and remove the compilation errors.This PR might also be helpful for libc maintainers, as the CI check might spot typos in
#[cfg]s.