Vendors rust-skia 0.97.0 (from crates.io tarballs) into
vendor/skia-safe-op/{skia-bindings,skia-safe} and adds a single new
platform module — build_support/platform/wasm_unknown.rs — that
recompiles Skia C++ directly into the wasm32-unknown-unknown ABI:
- reuses emsdk's libc / libcxx headers via -isystem
- drops C++ exceptions + RTTI (-fno-exceptions -fno-rtti) so the
resulting .o files do not import emscripten's exception runtime
- forces clang's target via --target=wasm32-unknown-unknown
- sets CC_/CXX_/AR_wasm32_unknown_unknown so the cc-crate FFI shim
also picks up emsdk's bundled clang (host clang lacks wasm32)
- on every gn_args invocation overwrites skia/bin/activate-emsdk
with a no-op python stub so Skia's GN does not try to bootstrap
a parallel emsdk install (we use emsdk's clang directly)
Why a fork: wasm-bindgen --target=web on wasm32-unknown-emscripten
emits emscripten library glue, not a browser-loadable ES module,
which is incompatible with our distribution model. Compiling Skia
to wasm32-unknown-unknown unblocks the browser ES module path; the
remaining libc/libcxx/libm gap is filled by crates/wasm-libc-shim
in a follow-up commit.
The Skia C++ source tree under skia-bindings/skia/ (~770 MB, 30k+
files) is gitignored — it is fetched at build time by
binary_cache::download. Only the Rust source from the upstream
0.97.0 crate tarballs and the new wasm_unknown platform module are
committed here.
Step 1b §3.2 P0.5B Run path, sub-phase C-hard.1.
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