git-rebase-patch

#!/usr/bin/env bash
# Based on https://github.com/tj/git-extras/blob/master/bin/git-rebase-patch

set -eEu -o pipefail
IFS=$'\n\t'
PS4='+\t '

[[ "${TRACE:-0}" == "1" ]] && set -x


# Warn on a dirty work tree.
git rev-parse --verify HEAD >/dev/null || exit 1
git update-index -q --ignore-submodules --refresh
if ! git diff-files --quiet --ignore-submodules; then
    echo "WARNING (dirty work tree): The patch will only be checked against actual commits."
fi

# Warn on a dirty index.
if ! git diff-index --cached --quiet --ignore-submodules HEAD --; then
    echo "WARNING (dirty index): The patch will only be checked against actual commits."
fi

# Use a temporary index.
index=$(git_extra_mktemp)
cleanup() {
    rm "$index"
    exit 2
}
trap cleanup 2

# Go back in history while parent commits are available.
echo "Trying to find a commit the patch applies to..."
rev=$(git rev-parse HEAD)
while [[ $? = 0 ]]; do
    GIT_INDEX_FILE=$index git read-tree "$rev"

    # Try to apply the patch.
    GIT_INDEX_FILE=$index git apply --cached "$1" >/dev/null 2>&1
    patch_failed=$?

    # Do it again, but show the error, if the problem is the patch itself.
    if [[ $patch_failed = 128 ]]; then
        GIT_INDEX_FILE=$index git apply --index --check "$1"
        exit $patch_failed
    fi

    # The patch applied. Commit and rebase.
    if [[ $patch_failed = 0 ]]; then
        # Manufacture a commit.
        tree=$(GIT_INDEX_FILE=$index git write-tree)
        commit=$(git commit-tree "$tree" -p "$rev" -m "$1")
        rm "$index"

        echo "Patch applied to $(git rev-parse --short "$rev") as $(git rev-parse --short "$commit")"

        git cherry-pick "$commit"
        exit $?
    fi

    rev=$(git rev-parse --verify -q "$rev^")
done

# No compatible commit found. Restore.
echo "Failed to find a commit the patch applies to."
rm "$index"
exit 1