scripts: add cherry-pick-commit.sh for metadata-preserving cherry-picks

scripts/cherry-pick-commit.sh

@@ -0,0 +1,107 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+UPSTREAM="${UPSTREAM_CLONE:?set UPSTREAM_CLONE to the path of the upstream repo clone}"
+
+usage() {
+    echo "Usage: $(basename "$0") <hash> [-- path1 path2 ...]" >&2
+    exit 1
+}
+
+[[ $# -lt 1 ]] && usage
+
+hash="$1"
+shift
+
+paths=()
+if [[ $# -gt 0 && "$1" == "--" ]]; then
+    shift
+    paths=("$@")
+fi
+
+if ! git -C "$UPSTREAM" cat-file -e "${hash}^{commit}" 2>/dev/null; then
+    echo "error: commit $hash not found in $UPSTREAM" >&2
+    exit 1
+fi
+
+author_name=$(git -C "$UPSTREAM" log -1 --format="%an" "$hash")
+author_email=$(git -C "$UPSTREAM" log -1 --format="%ae" "$hash")
+author_date=$(git -C "$UPSTREAM" log -1 --format="%aD" "$hash")
+author_ts=$(git -C "$UPSTREAM" log -1 --format="%at" "$hash")
+committer_name=$(git -C "$UPSTREAM" log -1 --format="%cn" "$hash")
+committer_email=$(git -C "$UPSTREAM" log -1 --format="%ce" "$hash")
+committer_date=$(git -C "$UPSTREAM" log -1 --format="%cD" "$hash")
+message=$(git -C "$UPSTREAM" log -1 --format="%B" "$hash")
+
+apply_upstream() {
+    if [[ ${#paths[@]} -gt 0 ]]; then
+        git -C "$UPSTREAM" diff "${hash}^".."${hash}" -- "${paths[@]}" | git apply --index
+    else
+        git -C "$UPSTREAM" diff "${hash}^".."${hash}" | git apply --index
+    fi
+}
+
+commit_with_meta() {
+    local _author_name="$1" _author_email="$2" _author_date="$3"
+    local _committer_name="$4" _committer_email="$5" _committer_date="$6"
+    local _message="$7"
+    GIT_AUTHOR_NAME="$_author_name" GIT_AUTHOR_EMAIL="$_author_email" GIT_AUTHOR_DATE="$_author_date" \
+    GIT_COMMITTER_NAME="$_committer_name" GIT_COMMITTER_EMAIL="$_committer_email" GIT_COMMITTER_DATE="$_committer_date" \
+        git commit -m "$_message"
+}
+
+apply_upstream
+commit_with_meta \
+    "$author_name" "$author_email" "$author_date" \
+    "$committer_name" "$committer_email" "$committer_date" \
+    "$message"
+
+# Find the insertion point: last branch commit whose author timestamp <= new commit's
+insertion_point=""
+while IFS=" " read -r h t; do
+    [[ "$t" -le "$author_ts" ]] && insertion_point="$h"
+done < <(git log --reverse --format="%H %at" master..HEAD^)
+
+# Collect branch commits that must come after the new one
+to_replay=()
+recording=false
+[[ -z "$insertion_point" ]] && recording=true
+while IFS= read -r h; do
+    "$recording" && to_replay+=("$h")
+    [[ "$h" == "$insertion_point" ]] && recording=true
+done < <(git log --reverse --format="%H" master..HEAD^)
+
+[[ ${#to_replay[@]} -eq 0 ]] && exit 0
+
+echo "Reordering: moving before ${#to_replay[@]} later commit(s)..."
+
+tmp=$(mktemp -d)
+trap "rm -rf $tmp" EXIT
+
+for h in "${to_replay[@]}"; do
+    git log -1 --format="%an|%ae|%aD|%cn|%ce|%cD" "$h" > "$tmp/$h.meta"
+    git log -1 --format="%B" "$h" > "$tmp/$h.msg"
+    git diff "$h^" "$h" > "$tmp/$h.patch"
+done
+
+if [[ -z "$insertion_point" ]]; then
+    git reset --hard "$(git merge-base master HEAD)"
+else
+    git reset --hard "$insertion_point"
+fi
+
+apply_upstream
+commit_with_meta \
+    "$author_name" "$author_email" "$author_date" \
+    "$committer_name" "$committer_email" "$committer_date" \
+    "$message"
+
+for h in "${to_replay[@]}"; do
+    IFS="|" read -r r_author_name r_author_email r_author_date r_committer_name r_committer_email r_committer_date \
+        < "$tmp/$h.meta"
+    git apply --index < "$tmp/$h.patch"
+    commit_with_meta \
+        "$r_author_name" "$r_author_email" "$r_author_date" \
+        "$r_committer_name" "$r_committer_email" "$r_committer_date" \
+        "$(cat "$tmp/$h.msg")"
+done