[0.4.0] Windows Cross-Compilation Fails with pthread Type Size Assertions

[AllenDang]

Building for Windows target (x86_64-pc-windows-msvc) using cargo-xwin fails with compile-time overflow errors in generated gdextension_interface.rs due to POSIX-specific pthread types. The project builds successfully on macOS for native target.

• Host OS: macOS (Darwin 25.0.0)
• Target: x86_64-pc-windows-msvc (cross-compilation)
• Rust Version: 1.90.0 (1159e78c4 2025-09-14)
• Cargo Version: 1.90.0 (840b83a10 2025-07-30)
• cargo-xwin Version: 0.19.2
• gdext Commit: 4a582106 (master branch)
• gdextension-api Version: 0.3.0 (from godot4-prebuilt, branch release-v0.3)

Build command is cargo-xwin build --target x86_64-pc-windows-msvc, and below is the error log

Compiling godot-ffi v0.4.0 (/Users/allen/Documents/RustProjects/gdext/godot-ffi)
error[E0080]: attempt to compute `60_usize - 64_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:164:40
    |
164 |     ["Size of _opaque_pthread_attr_t"][::std::mem::size_of::<_opaque_pthread_attr_t>() - 64usize];
    |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error[E0080]: attempt to compute `44_usize - 48_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:180:40
    |
180 |     ["Size of _opaque_pthread_cond_t"][::std::mem::size_of::<_opaque_pthread_cond_t>() - 48usize];
    |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error[E0080]: attempt to compute `12_usize - 16_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:197:10
    |
197 |         [::std::mem::size_of::<_opaque_pthread_condattr_t>() - 16usize];
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error[E0080]: attempt to compute `60_usize - 64_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:213:41
    |
213 |     ["Size of _opaque_pthread_mutex_t"][::std::mem::size_of::<_opaque_pthread_mutex_t>() - 64usize];
    |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error[E0080]: attempt to compute `12_usize - 16_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:230:10
    |
230 |         [::std::mem::size_of::<_opaque_pthread_mutexattr_t>() - 16usize];
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error[E0080]: attempt to compute `12_usize - 16_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:246:40
    |
246 |     ["Size of _opaque_pthread_once_t"][::std::mem::size_of::<_opaque_pthread_once_t>() - 16usize];
    |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error[E0080]: attempt to compute `196_usize - 200_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:263:10
    |
263 |         [::std::mem::size_of::<_opaque_pthread_rwlock_t>() - 200usize];
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error[E0080]: attempt to compute `20_usize - 24_usize`, which would overflow
   --> /Users/allen/Documents/RustProjects/gdext/target/x86_64-pc-windows-msvc/debug/build/godot-ffi-e7d67e72d2f75b7b/out/gdextension_interface.rs:280:10
    |
280 |         [::std::mem::size_of::<_opaque_pthread_rwlockattr_t>() - 24usize];
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `gen::gdextension_interface::_` failed here

error: could not compile `godot-ffi` (lib) due to 8 previous errors

Seems the issue was introduced in commit e86f723e9b89357be7b3ca84d80de9a3658cc465 ("Enable support for Godot 4.5") from September 27, 2025, which updated the gdextension-api dependency.

1. The godot-ffi/build.rs generates Rust bindings from the prebuilt C header file provided by gdextension-api

2. The prebuilt header (v0.3.0) contains POSIX-specific pthread type definitions:

   • _opaque_pthread_attr_t
   • _opaque_pthread_cond_t
   • _opaque_pthread_condattr_t
   • _opaque_pthread_mutex_t
   • _opaque_pthread_mutexattr_t
   • _opaque_pthread_once_t
   • _opaque_pthread_rwlock_t
   • _opaque_pthread_rwlockattr_t

3. When bindgen processes these types for the Windows target, it generates struct definitions with different sizes than expected (smaller than the hardcoded size assertions)

4. The generated code contains compile-time assertions that fail during compilation for Windows targets