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

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merged 3 commits into from
Mar 2, 2022
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Provide C FFI types via core::ffi, not just in std #94503

merged 3 commits into from
Mar 2, 2022

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@joshtriplett joshtriplett commented Mar 1, 2022 •
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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.

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r? @kennytm

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

@rust-highfive rust-highfive assigned Amanieu and unassigned kennytm Mar 1, 2022
@joshtriplett joshtriplett added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Mar 1, 2022
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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.

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joshtriplett commented Mar 1, 2022 •
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@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.

@joshtriplett joshtriplett force-pushed the core-ffi-c branch 2 times, most recently from 0974b39 to 06db9fa Compare March 2, 2022 00:09
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Add a copy of cfg_if to core's internal_macros.rs
0f505c6 
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.
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Amanieu commented Mar 2, 2022

r=me once CI passes

@joshtriplett joshtriplett force-pushed the core-ffi-c branch 2 times, most recently from 459f3f3 to 34ada45 Compare March 2, 2022 00:45
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Provide C FFI types via core::ffi, not just in std
335c960 
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.
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Temporarily make CStr not a link in the c_char docs
75c3e9c 
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).
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@bors r=@Amanieu

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bors commented Mar 2, 2022

📌 Commit 75c3e9c has been approved by Amanieu

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 2, 2022
@matthiaskrgr matthiaskrgr mentioned this pull request Mar 2, 2022
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bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 2, 2022
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Auto merge of rust-lang#94514 - matthiaskrgr:rollup-pdzn82h, r=matthi…
2a280de 
…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
@bors bors merged commit 3ea9eeb into rust-lang:master Mar 2, 2022
@rustbot rustbot added this to the 1.61.0 milestone Mar 2, 2022
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@joshtriplett joshtriplett deleted the core-ffi-c branch March 2, 2022 11:03
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