Need a safe way to import dispatch and Block headers on Linux

[lhoward]

Description

I often use GCD on Linux to wrap existing callback-based APIs so they may be better imported by Swift. The GCD headers are present in $prefix/usr/lib/swift/dispatch and .../Block but are not in the include path.

Alternatives considered

• rewrite wrappers in Swift; this is a fine long-term solution
• use unsafe C flags to amend include path; because unsafe flags break tagged imports, this is not a long-term workable solution
• copy and paste necessary headers; this is workable for _Block_copy() and _Block_release() but gets hairy for libdispatch
• wrap the headers in new modules; this ultimately creates a module import conflict

Proposed solution

Currently I'm copy pasting declarations in (third alternative solution above), but ideally those headers would be in the include path for C modules built by Swift.

Swift Package Manager version/commit hash

Swift Package Manager - Swift 6.0.2-dev

Swift & OS version (output of swift --version && uname -a)

Swift version 6.0.2 (swift-6.0.2-RELEASE)
Target: aarch64-unknown-linux-gnu
Linux liebling 6.8.0-41-generic #41-Ubuntu SMP PREEMPT_DYNAMIC Fri Aug  2 23:26:06 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux