git_merge_test.sh

#!/bin/zsh

# Script that tests if a TEST_BRANCH can be merged successfully into
# a TARGET_BRANCH.
#
# Usage: git_merge_test.sh [-i] [TARGET_BRANCH] [TEST_BRANCH]
#
# Example: git_merge_test.sh dev feature-new-stuff
#
# Inspect conflicts: the script will clean up automatically unless you
# pass -i. Then it will stop at the merge so you can see what conflicts (or not).
#
# Notes:
# - force creates a branch with the name: testmerge-TARGET-TEST ... so if that exists
#   running this script will break things for you

testMerge() {
    # make a branch from the origin's version of the target branch
    # (forced in case it exists)
    git checkout -B testmerge-$1-$2 origin/$1

    # make the merge happen, but don't follow or commit cause we just
    # want to trash this
    git merge --no-ff --no-commit $2

    # determine success/failure
    if [[ "$?" -ne 0 ]]; then
        echo '❌  Merge FAILED. Attempting to cleanup and go back to' $current_branch
    else
        echo '✅  Merge SUCCESS. Cleaning up and going back to' $current_branch
    fi
}

main() {
    # get the branch name we're currently on
    current_branch=$(git rev-parse --abbrev-ref HEAD)

    # make sure we have all changes
    git fetch

    testMerge $1 $2

    # I want out of here
    git merge --abort

    # switch back to the branch we started from
    git switch $current_branch

    # cleanup our testmerge branch
    git branch --delete --force testmerge-$1-$2
}

review() {
    # get the branch name we're currently on
    current_branch=$(git rev-parse --abbrev-ref HEAD)

    # make sure we have all changes
    git fetch

    testMerge $1 $2

    echo "To cleanup:"
    echo "    git merge --abort && git switch $current_branch && git branch --delete --force testmerge-$1-$2"
}

if [[ "$#" -lt 2 ]]; then
    echo 'Usage:' $0 'TARGET_BRANCH TEST_BRANCH'
    exit 1
fi

target_branch="unknown"
test_branch="unknown"
review=0

# figure out if any of the arguments are -i
for var in "$@"
do
    if [[ $var == "-i" ]]; then
        review=1
    elif [[ $target_branch == "unknown" ]]; then
        target_branch=$var
    elif [[ $test_branch == "unknown" ]]; then
        test_branch=$var
    fi
done

if [[ $review == 0 ]]; then
    main $target_branch $test_branch
else
    review $target_branch $test_branch
fi