Re: [PATCHv1 2/2] git-p4: work with a detached head

[Luke Diamand]

On 28/10/15 17:44, Junio C Hamano wrote:

Luke Diamand  writes:


On 9 September 2015 at 22:52, Junio C Hamano  wrote:

Luke Diamand  writes:
...
 def currentGitBranch():
 return read_pipe("git name-rev HEAD").split(" ")[1].strip()

Yuck.  I know it is not entirely the fault of this patch, but
shouldn't it be reading from

 $ git symbolic-ref HEAD

and catch the error "fatal: ref HEAD is not a symbolic ref" and use
it as a signal to tell that the HEAD is detached?


That sounds much nicer. I'll redo the patch accordingly.


No need to rush, but should I expect a reroll of this sometime, or
have things around this topic changed to make this topic no longer
necessary?  I am only asking so that I can decide to either keep or
drop ld/p4-detached-head topic that is listed in the [Stalled]
section for quite some time [*1*].


I was waiting for the other git-p4 changes to go through before starting 
this up again.


It definitely needs fixing - it was annoying me a lot today, as I kept 
on having to invent temporary branch names to needlessly keep git-p4 happy.


After getting to "for-p4-9", I'm now onto "x". I'll see if I can 
sort something out in the next few days.


Luke




Thanks.


[Footnote]

*1* Not that my dropping a topic from 'pu' means very much; a
 dropped topic can still be submitted and requeued after all.



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Re: [PATCHv1 2/2] git-p4: work with a detached head

[Luke Diamand]

On 9 September 2015 at 22:52, Junio C Hamano  wrote:
> Luke Diamand  writes:
>
>>  def run(self, args):
>>  if len(args) == 0:
>>  self.master = currentGitBranch()
>> -if len(self.master) == 0 or not gitBranchExists("refs/heads/%s" 
>> % self.master):
>> -die("Detecting current git branch failed!")
>> +if self.master == "undefined":
>> +self.master = None
>
> The comparison with textual "undefined" smelled fishy and I ended up
> looking at the implementation of currentGitBranch().
>
> def currentGitBranch():
> return read_pipe("git name-rev HEAD").split(" ")[1].strip()
>
> Yuck.  I know it is not entirely the fault of this patch, but
> shouldn't it be reading from
>
> $ git symbolic-ref HEAD
>
> and catch the error "fatal: ref HEAD is not a symbolic ref" and use
> it as a signal to tell that the HEAD is detached?

That sounds much nicer. I'll redo the patch accordingly.

Thanks,
Luke
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Re: [PATCHv1 2/2] git-p4: work with a detached head

[Junio C Hamano]

Luke Diamand  writes:

> On 9 September 2015 at 22:52, Junio C Hamano  wrote:
>> Luke Diamand  writes:
>>
>>>  def run(self, args):
>>>  if len(args) == 0:
>>>  self.master = currentGitBranch()
>>> -if len(self.master) == 0 or not 
>>> gitBranchExists("refs/heads/%s" % self.master):
>>> -die("Detecting current git branch failed!")
>>> +if self.master == "undefined":
>>> +self.master = None
>>
>> The comparison with textual "undefined" smelled fishy and I ended up
>> looking at the implementation of currentGitBranch().
>>
>> def currentGitBranch():
>> return read_pipe("git name-rev HEAD").split(" ")[1].strip()
>>
>> Yuck.  I know it is not entirely the fault of this patch, but
>> shouldn't it be reading from
>>
>> $ git symbolic-ref HEAD
>>
>> and catch the error "fatal: ref HEAD is not a symbolic ref" and use
>> it as a signal to tell that the HEAD is detached?
>
> That sounds much nicer. I'll redo the patch accordingly.

While "symbolic-ref" _is_ the right way to learn what the currently
checked out branch is, I think you'd need to be a bit careful while
analysing the ramifications of that fix.

Notice:

$ git checkout ld/p4-detached-head
$ git symbolic-ref -q HEAD; echo $?
refs/heads/ld/p4-detached-head
0
$ git checkout HEAD^0
$ git symbolic-ref -q HEAD; echo $?
1
$ git name-rev HEAD
HEAD ld/p4-detached-head

A few implications of the above observation:

 * The fact that the code used to use 'name-rev HEAD' means that it
   behaved as if you are on some branch when you are in a detached
   HEAD state, if your current commit happened to be at the tip of
   some branch.  Users could be relying on this behaviour, i.e. 
   you can detach (perhaps because you do not want to accidentally
   advance the history of the real branch) at the tip of a branch,
   and have "git p4" still apply the configuration based on the name
   of the original branch.

 * If there were multiple branches that point at your current
   commit, then what is returned by currentGitBranch based on
   name-rev is unpredictable.  So in that sense, the workflow that
   relies on the existing "use the configuration based on the branch
   name returned by name-rev" behaviour is already broken, but not
   many people have two or more branches pointing at the same commit
   very often, so they may perceive existing breakage of their
   workflow a non-issue.  To them, fixing the implementation of
   currentGitBranch may appear to be a regression.

 * Of course, if the user happens to have a branch whose name is
   "undefined", you may have detached the HEAD at a totally
   unrelated commit, and the existing code in run() would first set
   self.master to "undefined", notices "refs/heads/undefined"
   exists, and without even noticing that these two are not related
   to each other at all, happily goes ahead and uses "undefined"
   branch.  I don't know what happens in that case---perhaps it is
   the same as the second case where configuration for an unrelated
   branch is applied and no other damage is done.  Perhaps the code
   gets confused and sometimes updates HEAD and sometimes updates
   the tip of self.master branch.  In either case, the existing
   behaviour cannot be something the users have sensibly relied on.

A good write-up of the bug in the externally visible behaviour that
is corrected by fixing currentGitBranch implementation in the
Release Notes (when this fix hits a release) should be sufficient, I
think.

Thanks.

   
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Re: [PATCHv1 2/2] git-p4: work with a detached head

[Junio C Hamano]

Luke Diamand  writes:

>  def run(self, args):
>  if len(args) == 0:
>  self.master = currentGitBranch()
> -if len(self.master) == 0 or not gitBranchExists("refs/heads/%s" 
> % self.master):
> -die("Detecting current git branch failed!")
> +if self.master == "undefined":
> +self.master = None

The comparison with textual "undefined" smelled fishy and I ended up
looking at the implementation of currentGitBranch().

def currentGitBranch():
return read_pipe("git name-rev HEAD").split(" ")[1].strip()

Yuck.  I know it is not entirely the fault of this patch, but
shouldn't it be reading from

$ git symbolic-ref HEAD

and catch the error "fatal: ref HEAD is not a symbolic ref" and use
it as a signal to tell that the HEAD is detached?
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[PATCHv1 2/2] git-p4: work with a detached head

[Luke Diamand]

When submitting, git-p4 finds the current branch in
order to know if it is allowed to submit (configuration
"git-p4.allowSubmit").

On a detached head, detecting the branch would fail, and
git-p4 would report a cryptic error.

This change teaches git-p4 to recognise a detached head and
submit successfully.

Signed-off-by: Luke Diamand 
---
 git-p4.py   | 18 --
 t/t9800-git-p4-basic.sh |  2 +-
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/git-p4.py b/git-p4.py
index 2677c89..a22ae01 100755
--- a/git-p4.py
+++ b/git-p4.py
@@ -1651,8 +1651,8 @@ class P4Submit(Command, P4UserMap):
 def run(self, args):
 if len(args) == 0:
 self.master = currentGitBranch()
-if len(self.master) == 0 or not gitBranchExists("refs/heads/%s" % 
self.master):
-die("Detecting current git branch failed!")
+if self.master == "undefined":
+self.master = None
 elif len(args) == 1:
 self.master = args[0]
 if not branchExists(self.master):
@@ -1660,9 +1660,10 @@ class P4Submit(Command, P4UserMap):
 else:
 return False
 
-allowSubmit = gitConfig("git-p4.allowSubmit")
-if len(allowSubmit) > 0 and not self.master in allowSubmit.split(","):
-die("%s is not in git-p4.allowSubmit" % self.master)
+if self.master:
+allowSubmit = gitConfig("git-p4.allowSubmit")
+if len(allowSubmit) > 0 and not self.master in 
allowSubmit.split(","):
+die("%s is not in git-p4.allowSubmit" % self.master)
 
 [upstream, settings] = findUpstreamBranchPoint()
 self.depotPath = settings['depot-paths'][0]
@@ -1730,7 +1731,12 @@ class P4Submit(Command, P4UserMap):
 self.check()
 
 commits = []
-for line in read_pipe_lines(["git", "rev-list", "--no-merges", 
"%s..%s" % (self.origin, self.master)]):
+if self.master:
+commitish = self.master
+else:
+commitish = 'HEAD'
+
+for line in read_pipe_lines(["git", "rev-list", "--no-merges", 
"%s..%s" % (self.origin, commitish)]):
 commits.append(line.strip())
 commits.reverse()
 
diff --git a/t/t9800-git-p4-basic.sh b/t/t9800-git-p4-basic.sh
index 114b19f..0730f18 100755
--- a/t/t9800-git-p4-basic.sh
+++ b/t/t9800-git-p4-basic.sh
@@ -241,7 +241,7 @@ test_expect_success 'unresolvable host in P4PORT should 
display error' '
)
 '
 
-test_expect_failure 'submit from detached head' '
+test_expect_success 'submit from detached head' '
test_when_finished cleanup_git &&
git p4 clone --dest="$git" //depot &&
(
-- 
2.6.0.rc0.133.ga438a11.dirty

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