Re: [PATCH/RFC] builtin-checkout: suggest creating local branch when appropriate to do so

Johannes Schindelin [off-list ref] writes:

quoted

4. Are there any (scripted?) use-cases where git-checkout should fail
   because it was given an invalid branch name?

The following gives a hint, though they could of course be fixed and
the ^0 case doesn't really count:

  $ git grep 'git checkout .*||' -- "*.sh"
  git-bisect.sh:        git checkout "$start_head" -- || exit
  git-rebase--interactive.sh:  output git checkout $first_parent 2> /dev/null ||
  git-rebase--interactive.sh:  output git checkout "$1" ||
  git-rebase.sh:git checkout -q "$onto^0" || die "could not detach HEAD"
  t/t2007-checkout-symlink.sh:git checkout -f master || exit

Actually, in said cases (with exception of the test case, which should be 
fine, however, having no remote branches), I would expect the user to be 
grateful if the DWIMery would happen.

Did you check the context before making that assertion?

 - The one in git-bisect switches to (or detaches at) what was earlier
   written in BISECT_START, which is either a branch name or a commit
   object name, so the user definitely does not want DWIMery if it could
   check out something else --- I do not think DWIMery hurts as long as
   the user does not delete the original branch while bisecting, though.

 - The first one in "rebase -i" is always fed a commit object name;
   DWIMery is not needed (and it would not hurt).

 - The second one in "rebase -i" is about switching to the branch being
   rebased, and it has an explicit check to see if "$1" is a branch name;
   DWIMery is not needed (and it would not hurt because of the check
   before it).

 - The one in "rebase" proper, as Thomas pointed out, is an explicit
   request to detach, so DWIMery won't happen.

The first three cases that could trigger DWIMery fall into "DWIMery does
not hurt because it happens to be a no-op in the way it is used" category,
not "In this case, the users would actively appreciate DWIMery".  IOW,
this does not look particularly a good argument to support DWIMery to me.

About the second one in "rebase -i", and also the corresponding one in
"rebase", which is:

	test -z "$switch_to" || git checkout "$switch_to"

If the command did DWIM, you would fork a local branch from the remote and
immediately rebase it.  Any good git tutorial teaches not to rebase work
by others, and keeping the result of such a rebase on a local branch goes
directly against it [*1*]; the script needs to be updated to protect
itself from DWIMery if we were to change "checkout" in these cases.


[Footnote]

*1* It is quite useful to temporarily rebase others work, e.g. in order to
compare what got changed in the newer version of series, so I wouldn't
object if the user did

    git checkout origin/topic
    git rebase $(git merge-base origin/topic@{1} origin/topic)
    git show-branch origin/topic@{1} HEAD

but notice that it all happens on detached HEAD, not to be kept.