Major Changes

Portable Types

In #1266, we added support for transpiling portable integer types like size_t and uint64_t. Previously, these were translated in a platform-dependent way, as C defines these portable types as typedefs of the platform-dependent primitive types like int and long. Now we special case these portable integer types and make sure to translate them as the equivalent Rust portable types, so size_t becomes usize and uint64_t becomes u64, for example.

These still often go through multiple typedefs in C, which become multiple type aliases in Rust, so the definitions are not always textually identical in Rust, but the underlying types should always be portable now.

Const Macros

We previously had an unstable and often broken --translate-const-macros option, which translated const/object-like C macros as Rust consts. This has now been significantly improved and --translate-const-macros conservative is enabled by default. The option has been split into none, conservative, and experimental, so we still allow the previous more experimental translations under experimental, but conservative should generally work and thus is enabled by default. However, some const macros are not yet translatable, like macros referencing other variables, functions, etc., which conservative skips, while some const macros can never be properly translated as a Rust const, such as when it references a variable that is not yet defined. We're still working on improving these cases so that more const macros can be successfully translated, but the current version should capture most usages in the wild. For tmux, 98% of const macro definitions and expansions are successfully translated, for example.

One area in particular we're still working on is the combination of const macros and portable types. The features don't yet work together seamlessly, with const macro types using the old non-portable types and then casting to the portable type at use sites.

SrcLoc Sorting

On stable, sorting now panics when a non-total order is discovered, which was the case in fn compare_src_locs. We had previously tried to fix this, and fixed it in a bunch of cases, but it was still cropping up sometimes, like when transpiling libxml2.

We've now fixed the root cause of incorrect SrcLoc::fileids when we calculate #include paths. Besides fixing any panics, this should improve the sorting of items, which was sometimes buggy before, likely due to this.

cmake 4.0 Support

#1214 adds support for cmake 4.0 by increasing the minimum to cmake 3.5. This should fix any installation issues due to using a new cmake.

LLVM/Clang Support

• (#1243, #1244) LLVM 18
• (#1230) LLVM 19
• (#1248) LLVM 20
• (#1274) LLVM 21

Misc. Bug Fixes

• (#1265) Handle all cases of extra braces in string initializers.
• (#1340) Remove extraneous :: separators in paths with arguments (e.g. ::core::mem::size_of::<libc::c_int>::()).
• (#1359) Store alloca vector at function-level scope, matching C.
• (#1360) Avoid mutable transmutes (UB) for string literals (mem::transmute::<[u8; N], [c_char; N]>(*b"") instead of *mem::transmute::<&[u8; N], &mut [c_char; N]>(b"")).
• (#1361) Support anonymous struct/union/enums within structs and unions.
• (#1374) Inline asm fixes for ioq3.

Misc. Improvements

• (#1221, #1222, #1229, #1381) Prefer core:: over libc:: and std::, fixing --emit-no-std.
• (#1218) Prefer [x; N] over [x, ..., x].
• (#1344) Skip redundant expressions for ++ and -- (i += 1; i; vs. i += 1;).
• (#1373) use libc only when needed.

New Instrinsics Added

• (#814) C11 atomics
• (#1342) _Static_assert
• (#1235) __float128
• (#1259, #1260) __builtin_rotateright*
• (#1263, #1292) __builtin_ia32_pause
• (#1263, #1292) __builtin_arm_yield
• (#1129) __builtin_ia32_vperm2f128_pd256
• (#1129) _mm256_permute2f128_pd

Changelog

• docs/readme: Update bear arguments by @javierhonduco in https://github.com/immunant/c2rust/pull/1206
• GH Actions: bump tagged versions of actions/cache by @brk in https://github.com/immunant/c2rust/pull/1212
• build: support cmake 4.0 by @chenrui333 in https://github.com/immunant/c2rust/pull/1214
• CI updates (Ubuntu 22, LLVM 15, pinned once_cell) by @folkertdev in https://github.com/immunant/c2rust/pull/1219
• Remove some libc dependencies. by @nnethercote in https://github.com/immunant/c2rust/pull/1221
• Fixes to rust-toolchain.toml handling by @joshtriplett in https://github.com/immunant/c2rust/pull/1225
• Reduce libc usage in c2rust-transpile by @nnethercote in https://github.com/immunant/c2rust/pull/1222
• Remove more unnecessary libc usage by @nnethercote in https://github.com/immunant/c2rust/pull/1229
• Make test_translator.py tests pass on LLVM 19 by @nnethercote in https://github.com/immunant/c2rust/pull/1230
• Support __float128, which shows up in clang headers on some systems by @joshtriplett in https://github.com/immunant/c2rust/pull/1235
• Allow running multiple transpiles in parallel by @jameysharp in https://github.com/immunant/c2rust/pull/1241
• transpile: remove invalid Punct::new(' ') in fn convert_asm and update proc-macro2 by @kkysen in https://github.com/immunant/c2rust/pull/1244
• Move Linux CI from Azure Pipelines to GitHub Actions by @joshtriplett in https://github.com/immunant/c2rust/pull/1232
• Bump bindgen to be able to handle CXCursor_LinkageSpec in LLVM18+ by @spastorino in https://github.com/immunant/c2rust/pull/1243
• Fix getBitWidthValue compilation error on LLVM 20+ by @shirok1 in https://github.com/immunant/c2rust/pull/1248
• Introduce some snapshot tests of c2rust-transpile by @jameysharp in https://github.com/immunant/c2rust/pull/1246
• transpile: some snapshot test fixes by @kkysen in https://github.com/immunant/c2rust/pull/1258
• Support C11 atomics required by dav1d by @thedataking in https://github.com/immunant/c2rust/pull/814
• transpile: impl __builtin_ia32_pause and __builtin_arm_yield by @thedataking in https://github.com/immunant/c2rust/pull/1263
• Various small cleanups by @fw-immunant in https://github.com/immunant/c2rust/pull/1267
• More driveby cleanups by @fw-immunant in https://github.com/immunant/c2rust/pull/1268
• transpile: Add SIMD intrinsic by @Kriskras99 in https://github.com/immunant/c2rust/pull/1129

New Contributors

• @javierhonduco made their first contribution in https://github.com/immunant/c2rust/pull/1206
• @brk made their first contribution in https://github.com/immunant/c2rust/pull/1212
• @chenrui333 made their first contribution in https://github.com/immunant/c2rust/pull/1214
• @nnethercote made their first contribution in https://github.com/immunant/c2rust/pull/1221
• @joshtriplett made their first contribution in https://github.com/immunant/c2rust/pull/1225
• @spastorino made their first contribution in https://github.com/immunant/c2rust/pull/1243
• @shirok1 made their first contribution in https://github.com/immunant/c2rust/pull/1248
• @Chobbes made their first contribution in https://github.com/immunant/c2rust/pull/1269
• @Rua made their first contribution in https://github.com/immunant/c2rust/pull/1363

Also, many thanks to @Rua and @bungcip for helping us fix a ton of bugs!

Full Changelog: https://github.com/immunant/c2rust/compare/v0.20.0...v0.21.0