sl push: more helpful message

[stepancheg]

sl push   # no args

abort: nothing to push - current commit is already at origin/master

instead of

abort: use '--to' to specify destination bookmark

[meta-codesync]

@facebook-github-bot has imported this pull request. If you are a Meta employee, you can view this in D100203517. (Because this pull request was imported automatically, there will not be any future comments.)

[quark-zju]

Review automatically exported from Phabricator review in Meta.

[quark-zju]

(seems comment isn't synced so I pasted it here)

The code seems fragile - it currently depends on the subtle behavior that _guesspushtobookmark returns None for "nothing to push" case, but _guesspushtobookmark could also return None for other reasons. It also prints all remotenames of the current commit, instead of the intended implicit "to".

How do you think about?

1. Change _guesspushtobookmark report the "origin/foo" even if it is the current commit.
2. (Optionally) Names to print (at_bookmarks) use the explicit or implicit "to", not listing what names the current commit has.
3. (Optionally) If nothing pushed (note the local remotenames can be outdated, so attempt to push is still needed), exit 1 instead of 255.