Implement cfg_os_version_min

[madsmtm]

Implement the cfg_os_version_min feature that is being RFC'd in rust-lang/rfcs#3750, tracking issue #136866. This implementation only handles Apple targets, but it should be fairly easy to add support for other targets after this.

The RFC is not finalized, and as such things may change (especially the syntax). Regardless, I think it makes sense to start experimenting with it; even if the feature is ultimately rejected, it is necessary for the standard library (an example is that it would allow us to ship #122408 without a dangerous fallback).

Implementation-wise, the first two commits are refactoring required to move some Apple deployment target support code out of rustc_codegen_ssa and into a place where it could be accessed by rustc_attr_parsing. The third commit implements the feature.

Using this in the standard library is done in a draft PR.

CC @ChrisDenton @BlackHoleFox
@rustbot label O-apple
r? rust-lang/compiler

[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

These commits modify compiler targets.
(See the Target Tier Policy.)

[madsmtm]

since it looks like some of the design questions haven't quite settled yet

Hmm, I was hoping to resolve those in future PRs, since I believe this feature is useful to the standard library today (or rather yesterday), regardless of future semantics and syntax.

Would it help if I renamed it to rustc_os_version_min in the meantime?

[Urgau]

You should ask T-lang to approve this PR as an "T-lang experiment", that way it could implemented in the compiler even without an FCP on the RFC.

[madsmtm]

T-lang experiment

Right, that's what it's called, couldn't remember, thanks! (filed #136871 so that I'll be able to find it in the future)

[rust-log-analyzer]

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#21 exporting to docker image format
#21 sending tarball 28.2s done
#21 DONE 37.2s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-18]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-18', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-18/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
  Downloaded boml v0.3.1
   Compiling boml v0.3.1
   Compiling y v0.1.0 (/checkout/compiler/rustc_codegen_gcc/build_system)
    Finished `release` profile [optimized] target(s) in 3.97s
     Running `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-codegen/x86_64-unknown-linux-gnu/release/y test --use-system-gcc --use-backend gcc --out-dir /checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/cg_gcc --release --mini-tests --std-tests`
Using system GCC
warning: target feature `x87` must be enabled to ensure that the ABI of the current target can be implemented correctly
  |
  = note: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
---
##[group]Testing stage2 book unstable-book (x86_64-unknown-linux-gnu)
STDOUT:

running 1 test
test /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md - The_tracking_issue_for_this_feature_is__::Examples (line 41) ... FAILED
failures:


---- /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md - The_tracking_issue_for_this_feature_is__::Examples (line 41) stdout ----
error: expected one of `!`, `(`, `...`, `..=`, `..`, `::`, `:`, `{`, or `|`, found `,`
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:55:30
   |
16 |         fn preadv(libc::c_int, *const libc::iovec, libc::c_int, libc::off64_t) -> libc::ssize_t;
   |
   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
help: explicitly ignore the parameter name
   |
   |
16 |         fn preadv(_: libc::c_int, *const libc::iovec, libc::c_int, libc::off64_t) -> libc::ssize_t;

error: expected parameter name, found `*`
error: expected parameter name, found `*`
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:55:32
   |
16 |         fn preadv(libc::c_int, *const libc::iovec, libc::c_int, libc::off64_t) -> libc::ssize_t;


error: expected one of `!`, `(`, `...`, `..=`, `..`, `::`, `:`, `{`, or `|`, found `,`
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:55:63
   |
16 |         fn preadv(libc::c_int, *const libc::iovec, libc::c_int, libc::off64_t) -> libc::ssize_t;
   |
   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
help: explicitly ignore the parameter name
   |
   |
16 |         fn preadv(libc::c_int, *const libc::iovec, _: libc::c_int, libc::off64_t) -> libc::ssize_t;


error: expected one of `!`, `(`, `...`, `..=`, `..`, `::`, `:`, `{`, or `|`, found `)`
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:55:78
   |
16 |         fn preadv(libc::c_int, *const libc::iovec, libc::c_int, libc::off64_t) -> libc::ssize_t;
   |
   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
help: explicitly ignore the parameter name
   |
   |
16 |         fn preadv(libc::c_int, *const libc::iovec, libc::c_int, _: libc::off64_t) -> libc::ssize_t;

error: unexpected token: `...`
error: unexpected token: `...`
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:72:12
   |
33 |     preadv(...) // Use preadv, it's available
   |
help: use `..` for an exclusive range
   |
   |
33 -     preadv(...) // Use preadv, it's available
33 +     preadv(..) // Use preadv, it's available
help: or `..=` for an inclusive range
   |
   |
33 -     preadv(...) // Use preadv, it's available
33 +     preadv(..=) // Use preadv, it's available

error[E0586]: inclusive range with no end
error[E0586]: inclusive range with no end
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:72:12
   |
33 |     preadv(...) // Use preadv, it's available
   |
   |
   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
   |
   |
33 -     preadv(...) // Use preadv, it's available
33 +     preadv(..) // Use preadv, it's available

warning: version is set unnecessarily low, the minimum supported by Rust on this platform is 1.0
warning: version is set unnecessarily low, the minimum supported by Rust on this platform is 1.0
##[warning]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:51:32
   |
12 |     os_version_min("visionos", "1.0")
   |     ---------------------------^^^^^- help: use `target_os` instead: `target_os = "visionos"`
warning: version is set unnecessarily low, the minimum supported by Rust on this platform is 1.0
warning: version is set unnecessarily low, the minimum supported by Rust on this platform is 1.0
##[warning]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:67:32
   |
28 |     os_version_min("visionos", "1.0")
   |     ---------------------------^^^^^- help: use `target_os` instead: `target_os = "visionos"`
error[E0432]: unresolved import `libc`
error[E0432]: unresolved import `libc`
##[error] --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:43:5
4 | use libc;
  |     ^^^^ no `libc` in the root

error: cannot find macro `weak` in this scope
error: cannot find macro `weak` in this scope
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:69:1
   |
30 | weak!(fn preadv(libc::c_int, *const libc::iovec, libc::c_int, libc::off64_t) -> libc::ssize_t);


error[E0425]: cannot find value `preadv` in this scope
##[error]  --> /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md:71:23
   |
32 | if let Some(preadv) = preadv {

error: aborting due to 9 previous errors; 2 warnings emitted

Some errors have detailed explanations: E0425, E0432, E0586.
Some errors have detailed explanations: E0425, E0432, E0586.
For more information about an error, try `rustc --explain E0425`.
Couldn't compile the test.

failures:
    /checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md - The_tracking_issue_for_this_feature_is__::Examples (line 41)
test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.06s




Command CFG_RELEASE_CHANNEL="nightly" RUSTC_BOOTSTRAP="1" RUSTC_STAGE="2" RUSTC_SYSROOT="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" RUSTDOC_LIBDIR="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" RUSTDOC_REAL="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustdoc" RUST_TEST_THREADS="16" "/checkout/obj/build/bootstrap/debug/rustdoc" "-Wrustdoc::invalid_codeblock_attributes" "-Dwarnings" "-Znormalize-docs" "-Z" "unstable-options" "--test" "/checkout/src/doc/unstable-book/src/language-features/cfg-os-version-min.md" "--test-args" "" (failure_mode=DelayFail) has failed. Rerun with -v to see more details.
  local time: Tue Feb 11 15:15:55 UTC 2025
  network time: Tue, 11 Feb 2025 15:15:56 GMT
##[error]Process completed with exit code 1.
Post job cleanup.

[jieyouxu]

Hmm, I was hoping to resolve those in future PRs, since I believe this feature is useful to the standard library today (or rather yesterday), regardless of future semantics and syntax.

Would it help if I renamed it to rustc_os_version_min in the meantime?

Probably worth trying this as a T-lang experiment yeah

[SparrowLii]

Thanks for your work! But I know little about this feature so r? compiler

[bors]

☔ The latest upstream changes (presumably #137046) made this pull request unmergeable. Please resolve the merge conflicts.