What is a squash?

Squashing in Git is the process of combining multiple commits into one. It helps to simplify the commit history, making it more tidy and readable.

Typically, squashing is performed during:

• Merging a feature branch into the main branch. A short branch with many small commits (fixes, cosmetic changes) can be collapsed into a single large commit representing all the functionality of the branch.
• Editing commit history (interactive rebase). It allows merging consecutive commits for a cleaner presentation of changes.

The squashing process usually involves:

1. Selecting commits: Determining the range of commits to be combined.
2. Editing (interactive rebase): Using the command git rebase -i <commit_before_range> or git rebase -i HEAD~<number_of_commits>.
3. Marking squash or s: In the editor that opens, mark commits to be combined with the previous one using the word squash or the abbreviation s. The first commit in the list remains with pick.
4. Editing the message: Git will open an editor to write a new message for the combined commit.
5. Applying changes: After saving the rebase history file and the new commit message file, Git will perform the merge.

Example of an interactive rebase to combine the last three commits:

git rebase -i HEAD~3
# An editor will open with lines like:
# pick 08f66c1 Commit 1
# pick d7e8a23 Commit 2
# pick 1b2c3d4 Commit 3
# Change to:
# pick 08f66c1 Commit 1
# squash d7e8a23 Commit 2
# squash 1b2c3d4 Commit 3
# Save and exit. Then edit the message of the new commit.

Advantages of squashing:

• Clean history: Reduces the number of insignificant commits, making change logs more understandable.
• Simplified search: Easier to find significant changes in history.
• Ease of rollback: One large commit is easier to revert than many small ones.

Disadvantages:

• Loss of detail: Combining commits results in losing information about each small step.
• Complexity in collaborative work: Squashing commits that have already been pushed to a shared repository can cause conflicts in subsequent pushes by other team members. When squashing published commits, git push --force must be used, which can be risky.

Using squashing should be considered carefully and depends on the team's policy and the project's specifics.