Further, what does `git checkout a/b` do?

* Checkout a file called a/b

* Checkout branch b from remote a

* Checkout a local branch called a/b

I've seen people end up with local branches with names like 'upstream/mybranch', then get super-confused about how these branches aren't "upstream". git should really ban local branches with a / in their name.

It's a bug that "git checkout" does not complain in this case. I'll try to fix or report it.

That bug will never be fixed. https://redfin.engineering/two-commits-that-wrecked-the-user...

Though I agree with you, a warning could be issued.

Sounds like an edge case. This isn’t really a problem with Git per se.

A single command doing two completely different things arbitrarily depending on file matches isn't an "edge case".

But this very common for many tools:

  touch -- -l
  ls *

However, if you run both commands consistently, nothing untoward occurs:

  touch -- -l
  ls -- *

The fact that you have to use a double-hyphen flag to create a file with a name starting with a hyphen is a strong indication that this situation is an edge case.

And git handles the edge case the same way. That was my point.

  rm master
  git checkout -- master
  git checkout a1b1
  git checkout master -- master

all works as expected

Not quite. I believe the point is that it's not an edge case, since "master" isn't a particularly unusual name, not in the Unix tradition, nor, AFAIK, on any other OS.

You'll note that, for example, your "rm" didn't require a double-hyphen.

The OC's point (and maybe the GP's point [1]), ultimately, is about git command syntax ambiguity. With traditional Unix commands, there's not much ambiguity. At worst, there's merely no obvious way to pass an argument that's a filename starting with a hyphen. The question "what does 'ls -l' do?" would not plausibly have an answer of "output '-l' if a directory entry with that name exists" in addition to "output a long listing of all directory entries".

[1] Does git actually behave differently based on the existence of a directory entry named "master" or does it merely require extra effort to work with such an entry, which would actually be directly analagous to filenames beginning with a hyphen?

That's bad too.