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.
Replace 20 separate Put instructions (5 PutKinds x 4 forms) with
4 unified instructions (PutById, PutByIdWithThis, PutByValue,
PutByValueWithThis), each carrying a PutKind field at runtime instead
of being a separate opcode.
This reduces the number of handler entry points in the dispatch loop
and eliminates template instantiations of put_by_property_key and
put_by_value that were being duplicated 5x each when inlined by LTO.
Small changes but many of them:
- all codegen now directly writes into the target file instead of
creating intermediate Strings via the Write trait
- all unwraps are now a combination of Results and ?
- field_type_info now returns a structure instead of a tuple.
- rebuilding now no longer appends the same code again, but truncates
before codegen
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.
