Fix: emit extern "C" fn for functions declared in extern "C" blocks

[Copilot]

Functions declared inside extern "C" { } blocks in C++ headers were being entirely ignored — not collected at all — because process_tu in crates/libs/rdl/src/clang/mod.rs did not handle CXCursor_LinkageSpec nodes. Additionally, when such functions are collected, they must be emitted with extern "C" fn (cdecl) rather than extern fn (system/stdcall ABI) to correctly represent their calling convention.

All changes are scoped to crates/libs/rdl.

Changes

• crates/libs/rdl/src/clang/cx.rs

  • Add Cursor::language() wrapping clang_getCursorLanguage from clang-sys

• crates/libs/rdl/src/clang/fn.rs

  • Add extern_c: bool to Fn to track C-linkage origin
  • Update parse() to accept the extern_c flag
  • Update write() to emit extern "C" fn (via conditional quote!) when extern_c is set

• crates/libs/rdl/src/clang/mod.rs

  • Pass extern_c = false for top-level CXCursor_FunctionDecl items
  • Add CXCursor_LinkageSpec arm that recurses into the block's children and collects any contained FunctionDecl with extern_c = (language == CXLanguage_C)

• New test: crates/tests/libs/clang/roundtrip/fn_extern_c.h / .rdl — round-trip coverage for extern "C" { } blocks

Example

Input header (C++ mode):

extern "C" {
    unsigned int GetTickCount();
    void SetLastErrorEx(unsigned a, signed b);
}

Before:

// (empty — functions were ignored entirely)

After:

extern "C" fn GetTickCount() -> u32;
extern "C" fn SetLastErrorEx(a: u32, b: i32);

[riverar]

Do not change the header2rdl crate. Focus on crates/libs/rdl instead. Start over.

[Copilot]

Do not change the header2rdl crate. Focus on crates/libs/rdl instead. Start over.

Done. Rewrote the fix in crates/libs/rdl/src/clang/ (commit 8cb2462):

• cx.rs: Added Cursor::language() wrapping clang_getCursorLanguage
• fn.rs: Added extern_c: bool to Fn; write() now emits extern "C" fn when set
• mod.rs: Added CXCursor_LinkageSpec handling that recurses into the block's children, passing extern_c = (language == CXLanguage_C) for each contained FunctionDecl

Reverted all header2rdl crate changes.

[riverar]

@copilot Address the build failure here.

[Copilot]

@copilot Address the build failure here.

Fixed in commit 23c710a — ran cargo fmt on fn.rs and mod.rs to reformat the long function signatures.