@eht16 and @kugel- while I don't disagree, and as @kugel- said the author knows better what makes sensible commits (for me that means things that can be independent, the project needs to build and test with any commit or git bisect won't work). Just saying "squash" without any guidance is useless, I tend to squash everything into one since I have no idea what is independent and do not have the time to review and test to find out, especially with a big PR. So a merger might as well just hit the green button, thats what its there for.
But to inject a note of pragmatism, "When is the end?". How many times are last minute fixups added, all the time, so I would suggest squash and merge by author happen only _when the reviewer(s) agree_. Whilst @b4n's workflow is the ideal he noted its for git experts and we don't have many of those contributing to Geany.
Basically, making the process harder for either of authors or mergers is not a good idea for a project with so little effort available as Geany.