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c-api: install headers from build.rs without requiring cmake - #14144
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Isekai923 wants to merge 1 commit into
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c-api: install headers from build.rs without requiring cmake#14144Isekai923 wants to merge 1 commit into
Isekai923 wants to merge 1 commit into
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The build script previously shelled out to `cmake -P cmake/install-headers.cmake` to produce the C API headers in OUT_DIR. cmake was only being used as a scripting engine there: it substitutes the #cmakedefine lines in conf.h.in and copies the .h/.hh files. This made cmake a build requirement for every crate that transitively depends on wasmtime-c-api-impl (e.g. anything using tree-sitter's `wasm` feature), even though nothing is compiled with it. Reimplement the header install directly in build.rs with std only: - conf.h is generated from conf.h.in by turning each `#cmakedefine WASMTIME_FEATURE_X` line into `#define ...` or `/* #undef ... */` based on the corresponding CARGO_FEATURE_* env var, with CRLF newlines to match cmake's NEWLINE_STYLE CRLF. The feature list is read from the template itself, so build.rs no longer needs its own copy of WASMTIME_FEATURE_LIST. - headers are copied recursively, matching file(INSTALL ... FILES_MATCHING REGEX "\.hh?$"). The cmake scripts are untouched and still used by the standalone CMake build; build.rs simply no longer invokes cmake. Verified that the OUT_DIR include tree is byte-for-byte identical to the cmake-generated one (all-features-off and a cranelift/gc-drc/wasi/ wat set), and that `cargo check -p wasmtime-c-api-impl` succeeds with cmake removed from PATH.
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Currently
wasmtime-c-api-impl's build script shells out tocmake -P cmake/install-headers.cmaketo produce the C API headers inOUT_DIR. cmake is only used as a scripting engine there — it substitutes the#cmakedefinelines inconf.h.inand copies the.h/.hhfiles — but this makes cmake a build requirement for every crate that transitively depends onwasmtime-c-api-impl, most notably anything using tree-sitter'swasmfeature, even though nothing is actually compiled with cmake.This regularly surprises downstream users because the failure only appears when the build-script fingerprint is invalidated ("it built yesterday"), and the error (
failed to spawn 'cmake') doesn't look related to their code. See e.g. zed-industries/zed#18084; we hit the same thing in our project when a dev machine lost its cmake install.What this PR does
Reimplements the header install directly in
build.rsusing std only (~60 lines):wasmtime/conf.his generated fromconf.h.inby turning each#cmakedefine WASMTIME_FEATURE_Xline into#define ...//* #undef ... */based on the correspondingCARGO_FEATURE_*env var, with CRLF newlines matching cmake'sNEWLINE_STYLE CRLF. The feature list is read from the template itself, sobuild.rsno longer needs its own copy of theWASMTIME_FEATURE_LIST.file(INSTALL ... FILES_MATCHING REGEX "\.hh?$").The cmake scripts themselves are untouched and still used by the standalone CMake build of the C API;
build.rssimply no longer invokes cmake.Verification
OUT_DIR/includetree is byte-for-byte identical (diff -r) to the cmake-generated one, tested in both directions: all features off, and withgc-drc/cranelift/wasi/watenabled (covering#defineand/* #undef */paths, CRLF endings, and the recursive copy).cargo check -p wasmtime-c-api-implsucceeds with cmake removed fromPATH.