Provide C FFI types via core::ffi, not just in std #94503

joshtriplett · 2022-03-01T22:55:08Z

Tracking issue: #94501

The ability to interoperate with C code via FFI is not limited to crates
using std; this allows using these types without std.

The existing types in std::os::raw become type aliases for the ones in
core::ffi. This uses type aliases rather than re-exports, to allow the
std types to remain stable while the core types are unstable.

This also moves the currently unstable NonZero_ variants and
c_size_t/c_ssize_t/c_ptrdiff_t types to core::ffi, while leaving
them unstable.

Historically, we didn't do this because these types are target-dependent.
However, core itself is also target-dependent. core should not call
any OS services, but it knows the target and the target's ABI.

rust-highfive · 2022-03-01T22:55:11Z

r? @kennytm

(rust-highfive has picked a reviewer for you, use r? to override)

joshtriplett · 2022-03-01T22:55:51Z

r? @Amanieu

Amanieu

I would like to see some additional C types here, specifically all the ones that are defined in stddef.h and stdint.h. These two headers are part of the freestanding subset of C which has no OS dependencies.

Specifically I would like to see the C99 fixed-width integer types and:

wchar_t
char8_t, char16_t, char32_t
max_align_t

The idea is that anyone interface with C code should be able to blindly use the equivalent c_* type without having to think too much about what the exact equivalent Rust type is.

library/core/src/ffi.rs

joshtriplett · 2022-03-01T23:21:27Z

@Amanieu I'd absolutely love to add more C FFI types, but I really don't want this PR to do anything more than move the types we already have. Similarly, the ssize_t and similar types are feature-gated for various reasons, and this PR leaves them feature-gated, so moving them shouldn't be conditional on deciding if they should be un-feature-gated.

I'm trying to make zero semantic changes here apart from the move, to make this easy to review and approve.

library/std/src/os/raw/mod.rs

core can't depend on external crates the way std can. Rather than revert usage of cfg_if, add a copy of it to core. This does not export our copy, even unstably; such a change could occur in a later commit.

Amanieu · 2022-03-02T00:39:46Z

r=me once CI passes

The ability to interoperate with C code via FFI is not limited to crates using std; this allows using these types without std. The existing types in `std::os::raw` become type aliases for the ones in `core::ffi`. This uses type aliases rather than re-exports, to allow the std types to remain stable while the core types are unstable. This also moves the currently unstable `NonZero_` variants and `c_size_t`/`c_ssize_t`/`c_ptrdiff_t` types to `core::ffi`, while leaving them unstable.

When CStr moves to core with an alias in std, this can link to `crate::ffi::CStr`. However, linking in the reverse direction (from core to std) requires a relative path, and that path can't work from both core::ffi and std::os::raw (different number of `../` traversals required).

joshtriplett · 2022-03-02T02:25:37Z

@bors r=@Amanieu

bors · 2022-03-02T02:25:39Z

📌 Commit 75c3e9c has been approved by Amanieu

…askrgr Rollup of 9 pull requests Successful merges: - rust-lang#94464 (Suggest adding a new lifetime parameter when two elided lifetimes should match up for traits and impls.) - rust-lang#94476 (7 - Make more use of `let_chains`) - rust-lang#94478 (Fix panic when handling intra doc links generated from macro) - rust-lang#94482 (compiler: fix some typos) - rust-lang#94490 (Update books) - rust-lang#94496 (tests: accept llvm intrinsic in align-checking test) - rust-lang#94498 (9 - Make more use of `let_chains`) - rust-lang#94503 (Provide C FFI types via core::ffi, not just in std) - rust-lang#94513 (update Miri) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

rust-highfive assigned kennytm Mar 1, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 1, 2022

joshtriplett mentioned this pull request Mar 1, 2022

Tracking Issue for core_ffi_c #94501

Closed

3 tasks

rust-highfive assigned Amanieu and unassigned kennytm Mar 1, 2022

joshtriplett added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Mar 1, 2022