migrate_rename_commit.sh

#!/bin/bash
# Migrate the patch set across a commit of the target repository that
# RENAMES (or moves) files targeted by the patch set.
#
# "git apply" cannot follow renames: when commit T renames a patched file,
# applying the patch fails at T even though there is no semantic conflict.
# This script uses git's rename detection instead:
#   1. Apply the patch set at T^ (the parent) on a temporary branch and
#      commit the patched state.
#   2. Merge that temporary branch INTO T - git's rename detection carries
#      the patched changes over to the new file paths.
# Any real conflicts are left in the tree for manual resolution (same
# workflow as a failed 3way apply, see README).
#
# Afterwards (once the tree looks right / conflicts are resolved):
#   cd <target_dp> && git add -A && git reset --mixed <rename_commit>
#   create_patches.sh ...   # regenerate the patch set at the new paths
# Remember to delete patch files whose target path no longer exists.
#
# Exit codes:
#   0  merged cleanly
#   1  merge left conflicts (manual resolution required)
#   2  invalid arguments / paths
#   3  patch set does not apply at the parent commit

script_dp="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"

usage() {
    echo "Usage: $0
        --patch_dp <patch_dp>
        --target_dp <target_dp>
        --commit <rename_commit>
        [--branch <working_branch>(default: vissat)]"
    echo "--patch_dp:"
    echo "  Path to the directory containing the patch files."
    echo "--target_dp:"
    echo "  Path to the directory containing the target repository."
    echo "--commit:"
    echo "  The commit of the target repository that renames patched files."
    echo "--branch:"
    echo "  Working branch left checked out with the merge result."
    exit 2
}

patch_dp=""
target_repository_dp=""
commit=""
working_branch="vissat"
tmp_branch="repositorypatcher_tmp_premigrate"

while [[ $# -gt 0 ]]; do
    case "$1" in
        -p|--patch_dp)
            shift; patch_dp="$1"; shift ;;
        -r|--target_repository_dp|--target_dp)
            shift; target_repository_dp="$1"; shift ;;
        -c|--commit)
            shift; commit="$1"; shift ;;
        -b|--branch)
            shift; working_branch="$1"; shift ;;
        *)
            echo "Error: Unknown option $1"
            usage ;;
    esac
done

if [[ -z "$patch_dp" || -z "$target_repository_dp" || -z "$commit" ]]; then
    echo "Error: All mandatory parameters must be provided."
    usage
fi

# Resolve and validate the paths (no implicit defaults - operating on the
# wrong repository must fail loudly, not silently).
patch_dp="$(realpath "$patch_dp" 2>/dev/null)"
if [[ -z "$patch_dp" || ! -d "$patch_dp" ]]; then
    echo "Error: --patch_dp does not exist."
    exit 2
fi
target_repository_dp="$(realpath "$target_repository_dp" 2>/dev/null)"
if [[ -z "$target_repository_dp" || ! -d "$target_repository_dp" ]]; then
    echo "Error: --target_dp does not exist."
    exit 2
fi
if ! git -C "$target_repository_dp" rev-parse --git-dir >/dev/null 2>&1; then
    echo "Error: --target_dp is not a git repository: $target_repository_dp"
    exit 2
fi
num_patch_files=$(find "$patch_dp" -type f -name "*.patch" | wc -l)
if [ "$num_patch_files" -eq 0 ]; then
    echo "Error: No *.patch files found in --patch_dp: $patch_dp"
    exit 2
fi

cd "$target_repository_dp"

if ! git rev-parse --verify --quiet "${commit}^{commit}" >/dev/null; then
    echo "Error: --commit is not a commit of the target repository: $commit"
    exit 2
fi
parent="$(git rev-parse "${commit}^")"

echo "Patch DP: $patch_dp ($num_patch_files patch files)"
echo "Target DP: $target_repository_dp"
echo "Rename commit: $commit"
echo "Parent commit: $parent"

# 1. Patched state at the parent commit on a temporary branch.
if [ -n "$(git branch --list $tmp_branch)" ]; then
    git branch --force --delete $tmp_branch >/dev/null
fi
git switch --force --create $tmp_branch "$parent" >/dev/null 2>&1

apply_failed=0
for patch_fp in "$patch_dp"/*.patch; do
    if ! git apply "$patch_fp" 2>/dev/null; then
        # Context drift since the last checkpoint - try 3way. A remaining
        # conflict is a real failure: the patch set must first be made
        # compatible with the parent commit (regular apply_patches.sh walk).
        if git apply --3way "$patch_fp" 2>/dev/null; then
            echo "3way-merged at parent: $(basename "$patch_fp")"
        else
            echo "APPLY FAIL at parent: $(basename "$patch_fp")"
            apply_failed=1
        fi
    fi
done
if [ $apply_failed -ne 0 ]; then
    echo "Error: The patch set does not apply at the parent commit $parent."
    echo "Bring the patch set up to the parent first (apply_patches.sh)."
    git switch --force "$working_branch" >/dev/null 2>&1
    git branch --force --delete $tmp_branch >/dev/null
    exit 3
fi
git add -A
git commit --quiet -m "RepositoryPatcher: temporary patched state at $parent"

# 2. Merge the patched parent state into the rename commit - git's rename
#    detection carries the patched changes to the new paths.
if [ -n "$(git branch --list $working_branch)" ]; then
    git branch --force --delete $working_branch >/dev/null
fi
git switch --force --create $working_branch "$commit" >/dev/null 2>&1

if git merge $tmp_branch >/dev/null 2>&1; then
    echo "MERGE CLEAN - the patched changes were carried to the new paths."
    merge_result=0
else
    echo "MERGE CONFLICTS - resolve manually in the following files:"
    git diff --name-only --diff-filter=U
    merge_result=1
fi
git branch --force --delete $tmp_branch >/dev/null

echo ""
echo "Next steps:"
if [ $merge_result -ne 0 ]; then
    echo "  1. Resolve the conflicts (e.g. VSCode merge editor), then: git add -A"
    echo "  2. git reset --mixed $commit"
    echo "  3. Regenerate the patch set with create_patches.sh (and delete"
    echo "     patch files whose target path no longer exists)."
else
    echo "  1. git reset --mixed $commit"
    echo "  2. Regenerate the patch set with create_patches.sh (and delete"
    echo "     patch files whose target path no longer exists)."
fi
exit $merge_result