threads / discuss / 40284

[PATCHv1 0/2] git-p4: work on a detached head

Subject: [PATCHv1 0/2] git-p4: work on a detached head

## tl;dr

12 messages between Sep 5, 2015 and Oct 28, 2015.

replies: 11people: 4as markdown or json

Luke Diamand· Sep 5, 2015, 14:02 UTC · lore

git-p4 won't submit from a detached head. If you do, it gives a cryptic error message, and instead you have to create an endless series of throw-away branches, which can get very trying.

The first patch in this series demonstrates the problem, and the second patch fixes it. I've been using it for the last few days.

Luke Diamand (2):
  git-p4: add failing test for submit from detached head
  git-p4: work with a detached head
 git-p4.py               | 18 ++++++++++++------
 t/t9800-git-p4-basic.sh | 16 ++++++++++++++++
 2 files changed, 28 insertions(+), 6 deletions(-)
-- 
2.6.0.rc0.133.ga438a11.dirty
Luke Diamand· Sep 5, 2015, 14:02 UTC · re: Luke Diamand · lore

[PATCHv1 1/2] git-p4: add failing test for submit from detached head

git-p4 can't submit from a detached head. This test case demonstrates the problem.

Signed-off-by: Luke Diamand <luke@diamand.org>
---
 t/t9800-git-p4-basic.sh | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
diff --git a/t/t9800-git-p4-basic.sh b/t/t9800-git-p4-basic.sh
index 90d41ed..114b19f 100755
--- a/t/t9800-git-p4-basic.sh
+++ b/t/t9800-git-p4-basic.sh
@@ -241,6 +241,22 @@ test_expect_success 'unresolvable host in P4PORT should display error' '
 	)
 '
 
+test_expect_failure 'submit from detached head' '
+	test_when_finished cleanup_git &&
+	git p4 clone --dest="$git" //depot &&
+	(
+		cd "$git" &&
+		git checkout p4/master &&
+		>detached_head_test &&
+		git add detached_head_test &&
+		git commit -m "add detached_head" &&
+		git config git-p4.skipSubmitEdit true &&
+		git p4 submit &&
+		git p4 rebase &&
+		git log p4/master | grep detached_head
+	)
+'
+
 test_expect_success 'kill p4d' '
 	kill_p4d
 '

-- 
2.6.0.rc0.133.ga438a11.dirty
Luke Diamand· Sep 5, 2015, 14:02 UTC · re: Luke Diamand · lore

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

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 <luke@diamand.org>
---
 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
Junio C Hamano· Sep 9, 2015, 21:52 UTC · re: Luke Diamand · lore

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

Luke Diamand <luke@diamand.org> writes:
Show 7 quoted lines
>      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?

Luke Diamand· Sep 10, 2015, 07:29 UTC · re: Junio C Hamano · lore

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

On 9 September 2015 at 22:52, Junio C Hamano <gitster@pobox.com> wrote:
Show 23 quoted lines
> Luke Diamand <luke@diamand.org> 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

Junio C Hamano· Sep 10, 2015, 16:20 UTC · re: Luke Diamand · lore

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

Luke Diamand <luke@diamand.org> writes:
Show 26 quoted lines
> On 9 September 2015 at 22:52, Junio C Hamano <gitster@pobox.com> wrote:
>> Luke Diamand <luke@diamand.org> 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.
Junio C Hamano· Oct 28, 2015, 17:44 UTC · re: Luke Diamand · lore

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

Luke Diamand <luke@diamand.org> writes:
Show 15 quoted lines
> On 9 September 2015 at 22:52, Junio C Hamano <gitster@pobox.com> wrote:
>> Luke Diamand <luke@diamand.org> 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*].

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.
Luke Diamand· Oct 28, 2015, 19:03 UTC · re: Junio C Hamano · lore

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

On 28/10/15 17:44, Junio C Hamano wrote:
Show 23 quoted lines
> Luke Diamand <luke@diamand.org> writes:
>
>> On 9 September 2015 at 22:52, Junio C Hamano <gitster@pobox.com> wrote:
>>> Luke Diamand <luke@diamand.org> 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 "xyyyy". I'll see if I can sort something out in the next few days.

Luke
Show 9 quoted lines
>
> 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.
>
Lars Schneider· Sep 9, 2015, 12:03 UTC · re: Luke Diamand · lore

Re: [PATCHv1 0/2] git-p4: work on a detached head

I wanted to play with the patch and apply it to my source but the process is really complicated for me. I wonder if you can give me a few recommendations how to work efficiently with email patches. I don’t want to start a flame-war about what email client is “right", I am just curious how you work and what clients, scripts, or tricks you use :-)
Usually I use Apple Mail. I experimented with mutt but it was not dramatically more convenient.

Thanks, Lars

On 05 Sep 2015, at 16:02, Luke Diamand <luke@diamand.org> wrote:
Show 22 quoted lines
> git-p4 won't submit from a detached head. If you do, it gives a
> cryptic error message, and instead you have to create an endless
> series of throw-away branches, which can get very trying.
> 
> The first patch in this series demonstrates the problem, and the
> second patch fixes it. I've been using it for the last few days.
> 
> Luke Diamand (2):
>  git-p4: add failing test for submit from detached head
>  git-p4: work with a detached head
> 
> git-p4.py               | 18 ++++++++++++------
> t/t9800-git-p4-basic.sh | 16 ++++++++++++++++
> 2 files changed, 28 insertions(+), 6 deletions(-)
> 
> -- 
> 2.6.0.rc0.133.ga438a11.dirty
> 
> --
> To unsubscribe from this list: send the line "unsubscribe git" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
Jacob Keller· Sep 10, 2015, 01:57 UTC · re: Lars Schneider · lore

Re: [PATCHv1 0/2] git-p4: work on a detached head

On Wed, Sep 9, 2015 at 5:03 AM, Lars Schneider <larsxschneider@gmail.com> wrote:
Show 6 quoted lines
> I wanted to play with the patch and apply it to my source but the process is really complicated for me. I wonder if you can give me a few recommendations how to work efficiently with email patches. I don’t want to start a flame-war about what email client is “right", I am just curious how you work and what clients, scripts, or tricks you use :-)
>
> Usually I use Apple Mail. I experimented with mutt but it was not dramatically more convenient.
>
> Thanks,
> Lars

Generally, any client which lets you save patches as mbox format. Then you can feed the file via git-am

I don't know what clients make this easy. I normally use Evolution, which has as "save as mbox" option. It's possible Apple Mail does too.

Regards, Jake

Jacob Keller· Sep 10, 2015, 01:59 UTC · re: Jacob Keller · lore

Re: [PATCHv1 0/2] git-p4: work on a detached head

On Wed, Sep 9, 2015 at 6:57 PM, Jacob Keller <jacob.keller@gmail.com> wrote:
Show 16 quoted lines
> On Wed, Sep 9, 2015 at 5:03 AM, Lars Schneider <larsxschneider@gmail.com> wrote:
>> I wanted to play with the patch and apply it to my source but the process is really complicated for me. I wonder if you can give me a few recommendations how to work efficiently with email patches. I don’t want to start a flame-war about what email client is “right", I am just curious how you work and what clients, scripts, or tricks you use :-)
>>
>> Usually I use Apple Mail. I experimented with mutt but it was not dramatically more convenient.
>>
>> Thanks,
>> Lars
>
> Generally, any client which lets you save patches as mbox format. Then
> you can feed the file via git-am
>
> I don't know what clients make this easy. I normally use Evolution,
> which has as "save as mbox" option. It's possible Apple Mail does too.
>
> Regards,
> Jake

For the record, you can use "show original" from GMail, and save that file as well, I believe. I don't know about Apple Mail specifically, however.

Regards, Jake

Luke Diamand· Sep 10, 2015, 12:23 UTC · re: Jacob Keller · lore

Re: [PATCHv1 0/2] git-p4: work on a detached head

On 10 September 2015 at 02:59, Jacob Keller <jacob.keller@gmail.com> wrote:
Show 21 quoted lines
> On Wed, Sep 9, 2015 at 6:57 PM, Jacob Keller <jacob.keller@gmail.com> wrote:
>> On Wed, Sep 9, 2015 at 5:03 AM, Lars Schneider <larsxschneider@gmail.com> wrote:
>>> I wanted to play with the patch and apply it to my source but the process is really complicated for me. I wonder if you can give me a few recommendations how to work efficiently with email patches. I don’t want to start a flame-war about what email client is “right", I am just curious how you work and what clients, scripts, or tricks you use :-)
>>>
>>> Usually I use Apple Mail. I experimented with mutt but it was not dramatically more convenient.
>>>
>>> Thanks,
>>> Lars
>>
>> Generally, any client which lets you save patches as mbox format. Then
>> you can feed the file via git-am
>>
>> I don't know what clients make this easy. I normally use Evolution,
>> which has as "save as mbox" option. It's possible Apple Mail does too.
>>
>> Regards,
>> Jake
>
> For the record, you can use "show original" from GMail, and save that
> file as well, I believe. I don't know about Apple Mail specifically,
> however.

I also don't use Apple Mail, but it must surely have a way to get the original email text. Save that and then do:

$ git am /path/to/saved-file
At least, that's what I do.
Luke

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