utility script to facilitate cherry-picking (#1782)

Script which helps to determine the complete list
of commits so that a given commit can be
cherry-picked without problems.

UTILS/get_cherrypick_commit_list.sh

@@ -0,0 +1,134 @@
+#!/bin/bash
+
+# given a commit cp_commit on branch source_branch as well
+# as another branch target_branch, this script finds the list
+# of all commits that are needed to succesfully cherry-pick cp_commit
+# onto the target branch
+
+cp_commit=$1        # Commit you want to cherry-pick
+source_branch=$2    # Branch containing commit cp_commit (e.g., master)
+target_branch=$3    # Branch you want to cherry-pick onto (e.g., foo)
+
+# Check if all required arguments are provided
+if [ -z "$cp_commit" ] || [ -z "$source_branch" ] || [ -z "$target_branch" ]; then
+    echo "Usage: $0 <commit-hash-A> <source-branch> <target-branch>"
+    exit 1
+fi
+
+# Function to check if two git commits modify at least one common file
+modifies_common_files() {
+    if [ "$#" -ne 2 ]; then
+        echo "Usage: check_common_files <commit1> <commit2>"
+        return 1
+    fi
+
+    local commit1="$1"
+    local commit2="$2"
+
+    # Get the list of modified files for each commit
+    local files_commit1
+    files_commit1=$(git diff --name-only "${commit1}^" "${commit1}")
+
+    local files_commit2
+    files_commit2=$(git diff --name-only "${commit2}^" "${commit2}")
+
+    # Check for common files
+    local common_files
+    common_files=$(echo -e "${files_commit1}\n${files_commit2}" | sort | uniq -d)
+
+    # Output result
+    if [ -n "$common_files" ]; then
+	return 1
+    fi
+    return 0
+}
+
+# function to check if 2 commits can be swapped. This can determine if a commit needs
+# to come stricly before another commit.
+can_swap_commits() {
+    local commitA="$1"
+    shift
+    local commitB=("$@")   # this is the list of commits that should swap (as a whole) with commitA
+
+    reverseCommitList=()
+
+    # Loop through the original array in reverse order
+    for ((i=${#commitB[@]}-1; i>=0; i--)); do
+      reverseCommitList+=("${commitB[i]}")
+    done
+
+    # Create a temporary branch for testing
+    local temp_branch="temp_swap_test_branch"
+
+    # record current state
+    GIT_CUR=$(git branch --show-current)
+    # Create a new temporary branch from the current HEAD
+    git checkout ${commitA}^ -b "$temp_branch" &> /dev/null
+
+    RC=1
+    for commit in "${reverseCommitList[@]}"; do
+      # Cherry-pick commit B onto a branch without commitA
+      if git cherry-pick "$commit" &> /dev/null; then
+        # RC=1  # Commits can be swapped
+	RC_local=1
+      else
+        RC=0  # Cannot swap due to conflict when cherry-picking B
+        git cherry-pick --abort
+      fi
+    done
+
+    # Cleanup: Reset to the original branch and delete the temp branch
+    git checkout ${GIT_CUR} &> /dev/null
+    git branch -D "$temp_branch" &>/dev/null
+    return ${RC}
+}
+
+# Step 1: Identify branch-break off point
+BRANCHPOINT=$(git merge-base "$source_branch" "$target_branch")
+
+
+COMMITLIST=()
+# Collect the initial set of commits to consider using a while loop
+while IFS= read -r line; do
+    COMMITLIST+=("$line")
+done < <(git log ${cp_commit}^...${BRANCHPOINT} --pretty=format:"%H")
+
+# filter out commits not touching the same files
+FILTERED_COMMITS1=()
+for commit_hash in "${COMMITLIST[@]}"; do
+    modifies_common_files ${commit_hash} ${cp_commit}
+    RC=$?
+    if [ ${RC} -eq 1 ]; then
+	FILTERED_COMMITS1+=(${commit_hash})
+    fi
+done
+
+# Next, filter out commits which are irrelevant for ${cp_commit}
+CP_COMMIT_LIST=(${cp_commit}) # The list of CP=cherry_pick commits to keep/construct
+
+for commit_hash in "${FILTERED_COMMITS1[@]}"; do
+    if [ ! "${commit_hash}" == "${cp_commit}" ]; then
+      can_swap_commits "${commit_hash}" "${CP_COMMIT_LIST[@]}"
+      if [ $? -eq 0 ]; then
+        # echo "COMMIT ${commit_hash} is needed"
+	# in this case we need to record it to the list of relevant commits
+	# and also trace it's dependencies in turn
+	CP_COMMIT_LIST+=(${commit_hash})
+      fi
+    fi
+done
+
+# reverse the final list to have correct cherry-pick order
+
+CP_COMMITS_REVERSED=()
+for ((i=${#CP_COMMIT_LIST[@]}-1; i>=0; i--)); do
+  CP_COMMITS_REVERSED+=("${CP_COMMIT_LIST[i]}")
+done
+
+# List the commits
+echo "To cherry-pick ${cp_commit} onto branch ${target_branch}, we need to apply:"
+for ((i=0;i<${#CP_COMMITS_REVERSED[@]}; i++)); do
+  echo "${i}: ${CP_COMMITS_REVERSED[i]}"
+done
+
+exit 0