What is squash in the context of software development?

Squash in the context of software development — often when working with Git — is the process of combining multiple consecutive commits into a single new commit.

The main goals of using squash:

• Simplifying history: Makes the commit log cleaner and more understandable, hiding intermediate commits that do not carry independent value (e.g., typo fixes, minor improvements).
• Logical grouping of changes: Combines a series of commits related to implementing a single feature or fixing a single bug into a single atomic change.
• Reducing "noise" when viewing change history.
• Preparing history before merging, especially for branches containing many small iterations.

The squash process is usually performed using Git's interactive rebase:

git rebase -i <parent_commit_or_hash>

After executing this command, an editor opens with a list of commits. For commits that need to be combined with the previous one, replace pick with squash or s.

pick abcde12 My first commit
pick fghij34 Added function X
squash klmno56 Fixed typo in function X  // This commit will be combined with the previous
squash pqrst78 Added tests for function X // This commit will also be combined

# Rebase 1234567..uvwxyz9 onto 1234567 (4 commands)
#
# Commands:
# p, pick = use commit
# r, reword = use commit, but edit the commit message
# e, edit = use commit, but stop for amending
# s, squash = use commit, but meld into previous commit
# f, fixup = like "squash", but discard this commit's log message
# x, exec = run command (the rest of the line) using shell
# d, drop = remove commit
# ... (other instructions)

After saving and closing the editor, Git will combine the marked commits and prompt to edit the message of the combined commit.

It is important to remember that squash rewrites Git history. This means that the hashes of the combined commits will change. Therefore, squashing commits that have already been pushed to a shared remote repository and are being worked on by others is not recommended, as it can cause conflicts during subsequent pull and push operations. Squash is usually applied to local branches before merging or pushing to a remote repository.