Why "You cannot combine --squash with --no-ff" in git merge?

Hi All,

the message "You cannot combine --squash with --no-ff" appeared in 2008, in the commit 1c7b76be7d620bbaf2e6b8417f04012326bbb9df ("Build in merge"). I don't understand the logic of this restriction.

Imagine, I have the following branches, where A is a master and B is a feature branch:

	A---B1---B2---B3---B4---B

`git checkout A && git merge --squash --no-ff B` says:

	fatal: You cannot combine --squash with --no-ff.

`git merge --squash --ff` will happily move the A ref to the B commit.

But what I want, and expect, is:

	A---B'

where B' has the same tree as B.

This can of course be done with `git rebase --interactive` and marking all commits for squash or fixup. But `git merge --squash` works with not-fastforwarding feature branch, why should it refuse to work in a fastforwarding case?