The Single Responsibility Principle.

Every source control commit should serve only one purpose. If you have to put the word "and" or "also" in your summary, you need to split it up.

You can do this with git using git add -p or with Mercurial using chunk selection and Mercurial Queues in TortoiseHg.

The Single Responsibility Principle.

Every source control commit should serve only one purpose. If you have to put the word "and" or "also" in your summary, you need to split it up.

It's very common to end up with lots of separate unrelated or semi-related changes in your working copy. This is called the "tangled working copy problem," and it's actually very hard to avoid even for disciplined developers. However, Git and Mercurial both give you tools to resolve it -- git add -p or chunk selection and Mercurial Queues in TortoiseHg respectively.