nixpkgs/pkgs/build-support/rust/hooks/cargo-setup-hook.sh

cargoSetupPostUnpackHook() {
    echo "Executing cargoSetupPostUnpackHook"

    # Some cargo builds include build hooks that modify their own vendor
    # dependencies. This copies the vendor directory into the build tree and makes
    # it writable. If we're using a tarball, the unpackFile hook already handles
    # this for us automatically.
    if [ -z $cargoVendorDir ]; then
        unpackFile "$cargoDeps"
        export cargoDepsCopy=$(stripHash $cargoDeps)
    else
      cargoDepsCopy="$sourceRoot/${cargoRoot:+$cargoRoot/}${cargoVendorDir}"
    fi

    if [ ! -d .cargo ]; then
        mkdir .cargo
    fi

    config="$(pwd)/$cargoDepsCopy/.cargo/config";
    if [[ ! -e $config ]]; then
      config=@defaultConfig@
    fi;

    tmp_config=$(mktemp)
    substitute $config $tmp_config \
      --subst-var-by vendor "$(pwd)/$cargoDepsCopy"
    cat ${tmp_config} >> .cargo/config

    cat >> .cargo/config <<'EOF'
    @rustTarget@
EOF

    echo "Finished cargoSetupPostUnpackHook"
}

# After unpacking and applying patches, check that the Cargo.lock matches our
# src package. Note that we do this after the patchPhase, because the
# patchPhase may create the Cargo.lock if upstream has not shipped one.
cargoSetupPostPatchHook() {
    echo "Executing cargoSetupPostPatchHook"

    cargoDepsLockfile="$NIX_BUILD_TOP/$cargoDepsCopy/Cargo.lock"
    srcLockfile="$NIX_BUILD_TOP/$sourceRoot/${cargoRoot:+$cargoRoot/}/Cargo.lock"

    echo "Validating consistency between $srcLockfile and $cargoDepsLockfile"
    if ! @diff@ $srcLockfile $cargoDepsLockfile; then

      # If the diff failed, first double-check that the file exists, so we can
      # give a friendlier error msg.
      if ! [ -e $srcLockfile ]; then
        echo "ERROR: Missing Cargo.lock from src. Expected to find it at: $srcLockfile"
        echo "Hint: You can use the cargoPatches attribute to add a Cargo.lock manually to the build."
        exit 1
      fi

      if ! [ -e $cargoDepsLockfile ]; then
        echo "ERROR: Missing lockfile from cargo vendor. Expected to find it at: $cargoDepsLockfile"
        exit 1
      fi

      echo
      echo "ERROR: cargoSha256 is out of date"
      echo
      echo "Cargo.lock is not the same in $cargoDepsCopy"
      echo
      echo "To fix the issue:"
      echo '1. Use "0000000000000000000000000000000000000000000000000000" as the cargoSha256 value'
      echo "2. Build the derivation and wait for it to fail with a hash mismatch"
      echo "3. Copy the 'got: sha256:' value back into the cargoSha256 field"
      echo

      exit 1
    fi

    unset cargoDepsCopy

    echo "Finished cargoSetupPostPatchHook"
}

if [ -z "${dontCargoSetupPostUnpack-}" ]; then
  postUnpackHooks+=(cargoSetupPostUnpackHook)
fi

if [ -z ${cargoVendorDir-} ]; then
  postPatchHooks+=(cargoSetupPostPatchHook)
fi