The Rust bytecode pipeline stores SharedFunctionInstanceData pointers
as raw void pointers invisible to the GC. If garbage collection runs
during compilation (triggered by heap allocation of a new SFD), it
can collect previously created SFDs, leaving stale pointers that
crash during the next GC marking phase.
Every other Rust compilation entry point (compile_script, compile_eval,
compile_shadow_realm_eval, compile_dynamic_function, compile_function)
already uses GC::DeferGC to prevent this. Add the missing DeferGC to
compile_module and compile_builtin_file.
Implement a complete Rust reimplementation of the LibJS frontend:
lexer, parser, AST, scope collector, and bytecode code generator.
The Rust pipeline is built via Corrosion (CMake-Cargo bridge) and
linked into LibJS as a static library. It is gated behind a build
flag (ENABLE_RUST, on by default except on Windows) and two runtime
environment variables:
- LIBJS_CPP: Use the C++ pipeline instead of Rust
- LIBJS_COMPARE_PIPELINES=1: Run both pipelines in lockstep,
aborting on any difference in AST or bytecode generated.
The C++ side communicates with Rust through a C FFI layer
(RustIntegration.cpp/h) that passes source text to Rust and receives
a populated Executable back via a BytecodeFactory interface.
