compile-extension: Rust (cc-rs) C code misses -fwasm-exceptions/SUPPORT_LONGJMP and ZVAL_LONG64 flags, so the .so fails to load (bad export type for '__THREW__') #4377

@php-wasm/compile-extension builds Rust (ext-php-rs) extensions that fail to load in the JSPI runtimes with bad export type for '__THREW__', and with a 32-bit zend_long.

In packages/php-wasm/compile-extension/scripts/build-in-docker.sh (trunk e1634b3), the flags the script applies to the extension's C code —

BASE_CFLAGS="-DZEND_ENABLE_ZVAL_LONG64 -D__x86_64__ -fPIC -O${OPTIMIZE}"   # line 31
ASYNC_FLAGS="-sSUPPORT_LONGJMP=wasm -fwasm-exceptions -sJSPI"             # line 39

— don't reach the C that cargo compiles through cc-rs (ext-php-rs's wrapper.c), which gets only:

export CFLAGS_wasm32_unknown_emscripten="-fPIC ${CFLAGS_wasm32_unknown_emscripten:-}"   # line 54

So wrapper.c is compiled with JS-based setjmp/longjmp (hence __THREW__ at load) and with a 32-bit zend_long, while PHP itself has a 64-bit one. Adding the same four flags there (and to CXXFLAGS_wasm32_unknown_emscripten) fixes it:

export CFLAGS_wasm32_unknown_emscripten="-fPIC -DZEND_ENABLE_ZVAL_LONG64 -D__x86_64__ -sSUPPORT_LONGJMP=wasm -fwasm-exceptions ${CFLAGS_wasm32_unknown_emscripten:-}"

With that, an ext-php-rs extension built on stable Rust 1.99 loads into the stock @php-wasm/node / @php-wasm/web 3.1.56 runtimes (PHP 8.5, JSPI) and runs under node and in headless Chromium.

Two README notes for the same tool: it says Rust extensions need nightly and -Zbuild-std, but stable Rust's prebuilt wasm32-unknown-emscripten std links and loads fine; and it reads as if the Rust build runs inside the image, which has no rustc or libclang (bindgen needs both).

Happy to send a PR if useful.