replace_squash.sh

replace_squash.sh

#!/bin/bash

# Replaces current HEAD (last commit of active branch) with squashed content of a branch merge/<current_branch>.
# Leave the original commit message inteact (ignore all messages from the squashed commits)
# This script in intended for interaction with OSS projects which only accept single commit in a PR

set -euo pipefail

# Ensure we're in a git repo
if ! git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
    echo "Error: not inside a Git repository" >&2
    exit 1
fi

current_branch="$(git rev-parse --abbrev-ref HEAD)"
branch="merge/$current_branch"

# Ensure the branch exists
if ! git rev-parse --verify "$branch" >/dev/null 2>&1; then
    echo "Error: branch '$branch' does not exist" >&2
    exit 1
fi

# Save the original HEAD so we can revert on failure
original_head="$(git rev-parse HEAD)"

# Save the current commit message
commit_msg="$(git log -1 --format=%B)"

# Determine the upstream branch name
if git rev-parse --verify main >/dev/null 2>&1; then
    upstream=main
elif git rev-parse --verify master >/dev/null 2>&1; then
    upstream=master
else
    echo "Error: neither 'main' nor 'master' branch exists" >&2
    exit 1
fi

# Update upstream without relying on explicit remote name
git switch  "$upstream"
git pull

# Maintain the merge bracnh to avoid discrepancies after squash
git switch  "$branch"
git merge --no-edit "$upstream"


# Hard-reset HEAD to discard the last commit entirely
git switch "$current_branch"
git reset --hard "$upstream"

# Merge the branch's content into the index (squash, no commit)
git merge --squash "$branch"

# Commit everything with the original message
git commit --no-edit -m "$commit_msg"

# Verify the squashed commit tree matches the branch tree exactly
if [ "$(git rev-parse HEAD^{tree})" != "$(git rev-parse "$branch"^{tree})" ]; then
    echo "Error: tree content differs between squashed commit and $branch" >&2
    git reset --hard "$original_head"
    exit 1
fi

# Record a merge on the branch so it knows about the squashed commit
squashed_commit="$(git rev-parse HEAD)"
git checkout "$branch"
git merge --no-ff -m "Merge squashed commit from $current_branch" "$squashed_commit"
git checkout "$current_branch"