···
[crane](https://github.com/ipetkov/crane),
[naersk](https://github.com/nix-community/naersk),
and cross compilation in its [Examples](https://github.com/nix-community/fenix#examples) section.
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## Using `git bisect` on the Rust compiler {#using-git-bisect-on-the-rust-compiler}
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Sometimes an upgrade of the Rust compiler (`rustc`) will break a
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downstream package. In these situations, being able to `git bisect`
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the `rustc` version history to find the offending commit is quite
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useful. Nixpkgs makes it easy to do this.
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First, roll back your nixpkgs to a commit in which its `rustc` used
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*the most recent one which doesn't have the problem.* You'll need
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to do this because of `rustc`'s extremely aggressive
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Next, add the following overlay, updating the Rust version to the
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one in your rolled-back nixpkgs, and replacing `/git/scratch/rust`
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with the path into which you have `git clone`d the `rustc` git
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(final: prev: /*lib.optionalAttrs prev.stdenv.targetPlatform.isAarch64*/ {
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lib.updateManyAttrsByPath [{
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path = [ "packages" "stable" ];
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update = old: old.overrideScope(final: prev: {
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rustc = prev.rustc.overrideAttrs (_: {
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src = lib.cleanSource /git/scratch/rust;
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# do *not* put passthru.isReleaseTarball=true here
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If the problem you're troubleshooting only manifests when
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cross-compiling you can uncomment the `lib.optionalAttrs` in the
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example above, and replace `isAarch64` with the target that is
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having problems. This will speed up your bisect quite a bit, since
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the host compiler won't need to be rebuilt.
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Now, you can start a `git bisect` in the directory where you checked
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out the `rustc` source code. It is recommended to select the
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endpoint commits by searching backwards from `origin/master` for the
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*commits which added the release notes for the versions in
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question.* If you set the endpoints to commits on the release
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branches (i.e. the release tags), git-bisect will often get confused
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by the complex merge-commit structures it will need to traverse.
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+
The command loop you'll want to use for bisecting looks like this:
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git bisect {good,bad} # depending on result of last build
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git submodule update --init
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CARGO_NET_OFFLINE=false cargo vendor \
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--sync ./src/tools/cargo/Cargo.toml \
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--sync ./src/tools/rust-analyzer/Cargo.toml \
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--sync ./compiler/rustc_codegen_cranelift/Cargo.toml \
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--sync ./src/bootstrap/Cargo.toml
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nix-build $NIXPKGS -A package-broken-by-rust-changes
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The `git submodule update --init` and `cargo vendor` commands above
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require network access, so they can't be performed from within the
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`rustc` derivation, unfortunately.
pyrox.dev