rust/docs/rustc_testing.md

Building and testing with changes in rustc code

This is useful when changing code in rustc_codegen_cranelift as part of changing main Rust repository. This can happen, for example, when you are implementing a new compiler intrinsic.

Instruction below uses $RustCheckoutDir as substitute for any folder where you cloned Rust repository.

You need to do this steps to successfully compile and use the cranelift backend with your changes in rustc code:

1. cd $RustCheckoutDir
2. Run python x.py setup and choose option for compiler (b).
3. Build compiler and necessary tools: python x.py build --stage=2 compiler library/std src/tools/rustdoc src/tools/rustfmt
   • (Optional) You can also build cargo by adding src/tools/cargo to previous command.
4. Copy cargo from a nightly toolchain: cp $(rustup +nightly which cargo) ./build/host/stage2/bin/cargo. Note that you would need to do this every time you rebuilt rust repository.
5. Link your new rustc to toolchain: rustup toolchain link stage2 ./build/host/stage2/.
6. (Windows only) compile the build system: rustc +stage2 -O build_system/main.rs -o y.exe.
7. You need to prefix every ./y.sh (or y if you built build_system/main.rs as y) command by rustup run stage2 to make cg_clif use your local changes in rustc.

• rustup run stage2 ./y.sh prepare
• rustup run stage2 ./y.sh build
• (Optional) run tests: rustup run stage2 ./y.sh test

8. Now you can use your cg_clif build to compile other Rust programs, e.g. you can open any Rust crate and run commands like $RustCheckoutDir/compiler/rustc_codegen_cranelift/dist/cargo-clif build --release.

You can also set rust-analyzer.rustc.source to your rust workspace to get rust-analyzer to understand your changes.