Move the Bytecode.def parser, field type info, and layout computation
out of Rust/build.rs into a standalone BytecodeDef crate. This allows
both the Rust bytecode codegen (build.rs) and the upcoming AsmIntGen
tool to share a single source of truth for instruction field offsets
and sizes.
The AsmIntGen directory is excluded from the workspace since it has
its own Cargo.toml and is built separately by CMake.
Add the rust-stable SDK extension, pre-download Corrosion and all crate
dependencies, and set up cargo vendoring so the Flatpak build can
compile Rust code without network access during the build phase.
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.
