question concerning branches

question concerning branches

[Ingo Brueckl]

I'm a git novice and have a comprehension question concerning branches.

Within a git repository, I do:

  git branch test
  git checkout test
  # edit foo.bar
  git checkout master

I'd expect that master is in the exactly same unchanged state it was at
branching time, but what a surprise, foo.bar is modified here, too!

If I continue now working in the master branch (applying patches and such) I
will use a changed foo.bar with testing branch content. I can't even apply
patches to foo.bar without conflict.

Of what use are branches if the files aren't totally separated from each
other?

What must I do to get a test branch I can't work without affecting master?

Ingo

Re: question concerning branches

[Bruce Stephens]

ib@wupperonline.de (Ingo Brueckl) writes:

> I'm a git novice and have a comprehension question concerning branches.
>
> Within a git repository, I do:
>
>   git branch test
>   git checkout test
>   # edit foo.bar
>   git checkout master
>
> I'd expect that master is in the exactly same unchanged state it was at
> branching time, but what a surprise, foo.bar is modified here, too!

You didn't commit your change to foo.bar.

[...]

> What must I do to get a test branch I can't work without affecting master?

commit changes.

Re: question concerning branches

[Avery Pennarun]

On Wed, Aug 19, 2009 at 5:33 PM, Ingo Brueckl<ib@wupperonline.de> wrote:
> Within a git repository, I do:
>
>  git branch test
>  git checkout test
>  # edit foo.bar
>  git checkout master
>
> I'd expect that master is in the exactly same unchanged state it was at
> branching time, but what a surprise, foo.bar is modified here, too!

You seem to have forgotten the "git commit" step before switching back
to master.  You have a modified file in your repository; what did you
*want* to happen when you switched branches?  (Many people find the
current behaviour very convenient.)

You might also want to look at the "git stash" command.

Avery

question concerning branches

[Ingo Brueckl]

Avery Pennarun <apenwarr@gmail.com> writes:

> You seem to have forgotten the "git commit" step before switching back
> to master.

No, I passed over the commit in my example. I know that after the commit the
things are as they ought to be, but what if I can't do a commit because I am
in the middle of coding and have to have a break?

> You have a modified file in your repository; what did you *want* to happen
> when you switched branches?

I want an unchanged file in master if I switch there (because I worked in a
different branch) and a changed version in the test branch.

Why is the *master* different depending on whether my work in test in still
going on or committed?!

Actually, I cannot image how branches are practicable if I always have to
have in mind possibly still uncommitted work. Shouldn't it be git's work
to ensure that master will remain it was when branching?

Without git I'd make a copy for testing new features. With git, it seems that
I have to do the same (a clone). This is what I don't understand.

> (Many people find the current behaviour very convenient.)

I find it highly confusing. I understood a branch as something I can do in
whatever I want without affecting master. But now a learn that everything I
do in the branch will happen in master, too, until I commit. Strange. Very
strange.

> You might also want to look at the "git stash" command.

Yes, but isn't it annoying to leave the test branch always either with stash
or commit in order to have an unchanged master?!

Ingo

Re: question concerning branches

[Jakub Narebski]

ib@wupperonline.de (Ingo Brueckl) writes:

> Avery Pennarun <apenwarr@gmail.com> writes:
> 
> > You seem to have forgotten the "git commit" step before switching back
> > to master.
> 
> No, I passed over the commit in my example. I know that after the commit the
> things are as they ought to be, but what if I can't do a commit because I am
> in the middle of coding and have to have a break?

Then you use git-stash.  It was invented for that.
 
> > You have a modified file in your repository; what did you *want* to happen
> > when you switched branches?
> 
> I want an unchanged file in master if I switch there (because I worked in a
> different branch) and a changed version in the test branch.
> 
> Why is the *master* different depending on whether my work in test in still
> going on or committed?!

Branches are about commits.  State of a working directory doesn't
belong to a branch (in Git).  Learning concepts behind Git would help
you in understanding it (Git is very consistent), which in turn would
help in using it.

What about untracked files?  Do you want to lose them when you switch
branches?

> 
> Actually, I cannot image how branches are practicable if I always have to
> have in mind possibly still uncommitted work. Shouldn't it be git's work
> to ensure that master will remain it was when branching?
> 
> Without git I'd make a copy for testing new features. With git, it seems that
> I have to do the same (a clone). This is what I don't understand.

You finish old work (or stash it away), _then_ you begin new work.

> 
> > (Many people find the current behaviour very convenient.)

Take the following example.  You started coding some feature on
'master' branch, then you realized that this feature is more
complicated than you thought at first, so it should be developed in
separate topic branch.  You do "git checkout -b featureA", and voila
you are now coding on feature branch 'featureA'.

> > You might also want to look at the "git stash" command.
> 
> Yes, but isn't it annoying to leave the test branch always either with stash
> or commit in order to have an unchanged master?!

No, it isn't.

-- 
Jakub Narebski

Git User's Survey 2009: http://tinyurl.com/GitSurvey2009

question concerning branches

[Ingo Brueckl]

Jakub Narebski <jnareb@gmail.com> writes:

> You finish old work (or stash it away), _then_ you begin new work.

Ok, this helps me a little bit to understand.

The branches aren't designed to split my work, but rather something to
collect the different parts of my work.

But as software development often is something where you are coding on
several issues at the same time which can't be committed immediately, it
sounds that 'stash' is the developer's best friend.

Ingo

Re: question concerning branches

[Avery Pennarun]

On Wed, Aug 19, 2009 at 7:45 PM, Ingo Brueckl<ib@wupperonline.de> wrote:
> Jakub Narebski <jnareb@gmail.com> writes:
>
>> You finish old work (or stash it away), _then_ you begin new work.
>
> Ok, this helps me a little bit to understand.
>
> The branches aren't designed to split my work, but rather something to
> collect the different parts of my work.
>
> But as software development often is something where you are coding on
> several issues at the same time which can't be committed immediately, it
> sounds that 'stash' is the developer's best friend.

Or you could just 'commit' more frequently, but don't 'push' so you're
not disturbing anyone else until you're done.

This is a big difference from how centralized VCSs work: there, a
commit is a major operation that you're afraid to do in case you make
someone else mad.  In git, commits are cheap, you just need to be
careful about pushing.

(You can also clean up your series of commits before pushing by using
'git rebase')

Have fun,

Avery

Re: question concerning branches

[Matthieu Moy]

Avery Pennarun <apenwarr@gmail.com> writes:

> This is a big difference from how centralized VCSs work: there, a
> commit is a major operation that you're afraid to do in case you make
> someone else mad.  In git, commits are cheap, you just need to be
> careful about pushing.

I second this. "commit" is indeed a bad name in decentralized VCSs.
There's no commitment from the developer, you don't commit to swear
the code is good, but you commit just to record a set of changes, and
attach a descriptive message to it.

In Git, a commit takes usually a fraction of a second, and can be
modified later easily until it's pushed.

'git commit --amend' will allow you to change either the changes or
the message associated to a commit.

'git reset HEAD^' will just undo the commit, turning your commited
changes into uncommited ones.

'git rebase --interactive' will allow you another bunch of cool
things.

So, keeping your changes uncommited has very few advantage, and indeed
has one big drawback: uncommited changes have no descriptive message
associated, so if you leave a branch for some time, it makes it more
difficult for you to remember what you were doing on it when you
switch back to it:

git checkout -b topic-branch
# edit foo.bar
git checkout master
# hack
git commit
# go on holiday
# come back
git checkout topic-branch
git status
# err, what is this all about?

OTOH:

git checkout -b topic-branch
# edit foo.bar
git commit -m "started feature foo, but bar is still to be done"
git checkout master
# hack
git commit
# go on holiday
# come back
git checkout topic-branch
git show
# Ah, I remember!

Actually, all the VCSs I know about (Mercurial, Bazaar, Subversion,
and IIRC GNU Arch) deal with this the way Git does. Hey! there must be
a reason ;-).

-- 
Matthieu

Re: question concerning branches

[Jacob Helwig]

On Wed, Aug 19, 2009 at 12:45, Ingo Brueckl<ib@wupperonline.de> wrote:
>
> But as software development often is something where you are coding on
> several issues at the same time which can't be committed immediately, it
> sounds that 'stash' is the developer's best friend.
>
> Ingo
>

There is no problem with having temporary commits on local branches,
however.

Quite frequently, I'll "git commit -a -m 'Temp commit'; git checkout
other-branch".  As long as you don't make these temporary commits
public, it's very easy to munge them (See: "git rebase --interactive
<commitish>", and "git reset --soft <commitish>").

-Jacob

Re: question concerning branches

[Jakub Narebski]

On Wed, 19 Aug 2009, Ingo Brueckl wrote:
> Jakub Narebski <jnareb@gmail.com> writes:
> 
> > You finish old work (or stash it away), _then_ you begin new work.
> 
> Ok, this helps me a little bit to understand.
> 
> The branches aren't designed to split my work, but rather something to
> collect the different parts of my work.

Well, git is flexible enough that it can support also the workflow you 
tried to use.  

Namely you can have many working directories tied to single repository 
(each of those checkouts should be of different branch).  You can use 
git-new-workdir script from contrib/worktree for that.  Then to switch 
branches you would just cd to appropriate directory (and keep unsaved 
changes and untracked files).  That said it is [much] less used 
workflow.
 
> But as software development often is something where you are coding on
> several issues at the same time which can't be committed immediately,
> it sounds that 'stash' is the developer's best friend.

Well, you can also commit and then clean up history with interactive 
rebase (or patch management interface such as StGit or Guilt).  In 
distributed version control systems like Git the act of publishing 
changes is separate from the act of committing them (you should not 
rewrite published history, though).

-- 
Jakub Narebski
Poland

Re: question concerning branches

[Theodore Tso]

On Wed, Aug 19, 2009 at 09:45:00PM +0200, Ingo Brueckl wrote:
> Jakub Narebski <jnareb@gmail.com> writes:
> 
> > You finish old work (or stash it away), _then_ you begin new work.
> 
> Ok, this helps me a little bit to understand.
> 
> The branches aren't designed to split my work, but rather something to
> collect the different parts of my work.
> 
> But as software development often is something where you are coding on
> several issues at the same time which can't be committed immediately, it
> sounds that 'stash' is the developer's best friend.

Context switching has overhead; so it's usually better to try to
complete one task before switching to another.  Granted, sometimes it
can't be done, but it's something you should really try to do.

Also, commits are easier to review if they are kept small; if you
localize changes into separate commits, it's often easier to detet
problems when doing "git bisect", for example.  So if you are often
needing to switch while leaving something that isn't ready to be
committed, you might want to ask yourself if you are putting too many
changes into a single ocmmit.

Personally, in the cases where I can't finish a commit before I need
to switch away to another branch, my preference is to not use "git
stash", but instead to create a topic branch, and then check in a
partially completed change on the topic branch, which I can later
ammend using "git commit --amend" (or if I have multiple commits on
the topic branch, "git rebase --interactive").  This is because I can
use the commit description to leave myself some notes about what still
needs to be done before the commit can be finalized.

						- Ted

Re: question concerning branches

[Jakub Narebski]

Theodore Tso wrote:

> Personally, in the cases where I can't finish a commit before I need
> to switch away to another branch, my preference is to not use "git
> stash", but instead to create a topic branch, and then check in a
> partially completed change on the topic branch, which I can later
> ammend using "git commit --amend" (or if I have multiple commits on
> the topic branch, "git rebase --interactive").  This is because I can
> use the commit description to leave myself some notes about what still
> needs to be done before the commit can be finalized.

Errr... you are aware that you can use "git stash save <message>" (i.e. 
specify commit message for stash; well, the subject), don't you?

-- 
Jakub Narebski
Poland

Re: question concerning branches

[Theodore Tso]

On Wed, Aug 19, 2009 at 10:57:21PM +0200, Jakub Narebski wrote:
> Errr... you are aware that you can use "git stash save <message>" (i.e. 
> specify commit message for stash; well, the subject), don't you?

I wasn't aware, but usually I like leaving more notes to myself than
just a single lines' worth of state.  I should probably take another
look at "git stash" and see if it's a handy tool for me to use; but so
far I've been happy enough with "git checkout -b topic-name; git
commit".

						- Ted

Re: question concerning branches

[Linus Torvalds]

On Wed, 19 Aug 2009, Ingo Brueckl wrote:

> Jakub Narebski <jnareb@gmail.com> writes:
> 
> > You finish old work (or stash it away), _then_ you begin new work.
> 
> Ok, this helps me a little bit to understand.
> 
> The branches aren't designed to split my work, but rather something to
> collect the different parts of my work.

Hmm. Yes. That's one way of looking at it.

At the same time, thinking about it another way may explain the git 
choices in this area. There's two issues:

 - if we _don't_ carry the edits around across branch switches, then what 
   would we do?

   Basically, since you haven't committed things, it's kind of floating 
   around. You switch to another branch, what should we do? There are 
   really only two choices: either we'd need to 'stash' the state with the 
   branch we switch away from (which is apparently what you expected), or 
   we need to just move the changes to the new branch (which is what git 
   does, or complains if it cannot).

   Now, 'stashing' the changes is actually very much against the whole git 
   philosophy. Git was built up around the index and the database, and 
   branches have always been pointers to the top-of-commit, so there 
   literally isn't any way to stash things that makes sense. Sure, later 
   on we ended up having the 'stash' command, but that's totally separate 
   from branches, and is an independently useful thing.

 - One of the big reasons to act like git does is that the way at least 
   _I_ work is to actually create a new branch with the explicit intention 
   of committing work I have already done!

   IOW, your example was

	git branch test
	git checkout test
	# edit foo.bar
	git checkout master

   and you were surprised that the edit followed you back to the "master" 
   branch, but what is actualyl a much more natural way of working is

	# edit foo.bar
	# realize that this was actually the start of a new feature
	git branch new-feature
	git checkout new-feature
	# maybe continue to edit foo.bar until it's all good
	git commit -a

   ie the git behavior explicitly _encourages_ you to not have to decide 
   before-the-fact to create a branch - it may be that only after you've 
   done the changes do you realize that "oops, these changes were _way_ 
   more intrusive than I originally anticipated, and I don't want to 
   commit them on the master branch, I want to commit them on an 
   experimental topic branch instead"

So there are two different reasons why git works the way it does: a pure 
implementation reason ("working any other way would not fit the git 
model") and a practical workflow reason ("you are _expected_ to move dirty 
state around with your branches, because one common case is to create a 
branch _for_ that dirty state").

			Linus

Re: question concerning branches

[Randal L. Schwartz]

>>>>> "Linus" == Linus Torvalds <torvalds@linux-foundation.org> writes:

Linus> 	git branch new-feature
Linus> 	git checkout new-feature

Or my favorite: "git checkout -b new-feature".

-- 
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<merlyn@stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
Smalltalk/Perl/Unix consulting, Technical writing, Comedy, etc. etc.
See http://methodsandmessages.vox.com/ for Smalltalk and Seaside discussion

question concerning branches

[Ingo Brueckl]

Linus Torvalds <torvalds@linux-foundation.org> writes:

> branches have always been pointers to the top-of-commit

Obviously I expected them to be pointers on trees.

A kind of automatical starting commit in a newly created branch would at
least warn if one has begun changing files and wants to checkout back.
(Is this a feature worth of discussion?)

> the git behavior explicitly _encourages_ you to not have to decide
> before-the-fact to create a branch

Thanks for the explanation which help me to understand why git works like it
does.

I'm able to follow your examples, but what I had it mind when I started the
topic and my example was:

Assume a project is released (i.e. no more open bugs we know about) - I know
we're drifting towards fantasy now. ;-)

On the one hand, I want to add single new features (such as other developers
do) which will be written, tested and committed. I want to push/pull
frequently to be up to date all the time. (master branch)

On the other hand, I want to completely rewrite the core of the program.
(test or rewrite branch)

What is the git way to do this in a the right (and clever) manner?

In a branch, I learned, I have to commit or stash before I return to master
for push/pull to follow the project. If I forget, I'm screwed, because files
have changed due to the rewrite (in that branch), I won't get a warning until
my first commit (in that branch) and commits (in master) will conflict.

Ingo

Re: question concerning branches

[Johannes Sixt]

[Please don't cull the Cc list.]

Ingo Brueckl schrieb:
> On the one hand, I want to add single new features (such as other developers
> do) which will be written, tested and committed. I want to push/pull
> frequently to be up to date all the time. (master branch)

If you want to stay up-to-date while you are creating a new feature, then
your workflow is sub-optimal. This message by Linus is good to read:

http://www.mail-archive.com/dri-devel@lists.sourceforge.net/msg39091.html

The important rule is "Don't merge upstream code at random points".

Once you learnt this rule, then you also see that it is not important to
always stay up-to-date. It is important to complete (test, debug) your
feature on a stable base. During that time, you don't care about upstream;
you care about your feature.

> In a branch, I learned, I have to commit or stash before I return to master
> for push/pull to follow the project. If I forget, I'm screwed, because files
> have changed due to the rewrite (in that branch), I won't get a warning until
> my first commit (in that branch) and commits (in master) will conflict.

You are obviously of a CVS or SVN mindset, where making a commit is such
an important operation that you don't dare to make it until your work is
*completed*.

With a git mindset, it won't happen that you "forget" whether you have
anything uncommitted; you simply never have because committing half-baked
stuff is the rule, not the exception. That is, before you get a cup of
coffee, you commit; before you answer a phone call, you commit; before you
turn your attention away, you commit. (That may be exaggerated, perhaps it
even isn't, but you get the point.)

When you have completed your work, you go back to make your commit history
look nice, comprehensible, and bisectable.

And only then comes the heavy operation: You publish your work for
consumption by interested parties. This may be even only you yourself:
"Consumption" would be to merge the work into your release branch. This is
the right time to care about upstream again.

-- Hannes

Re: question concerning branches

[Jakub Narebski]

Johannes Sixt <j.sixt@viscovery.net> writes:

> Ingo Brueckl schrieb:

> > In a branch, I learned, I have to commit or stash before I return to master
> > for push/pull to follow the project. If I forget, I'm screwed, because files
> > have changed due to the rewrite (in that branch), I won't get a warning until
> > my first commit (in that branch) and commits (in master) will conflict.

Errr... if having unknown files in status info when comitting doesn't
clue you in that you have spurious uncomitted changes, 

  # On branch master
  # Changes to be committed:
  #   (use "git reset HEAD <file>..." to unstage)
  #
  #       modified:   somefile

and neither commit diff summary

   n files changed, kk insertions(+), ll deletions(-)

doesn't clue you in, then you have more serous problems!


Second, you can use git-aware prompt to tell you if you have
uncomitted changes, so you will know when switching branches that you
have some changes that don't belong to branch you switch from.

> 
> You are obviously of a CVS or SVN mindset, where making a commit is such
> an important operation that you don't dare to make it until your work is
> *completed*.
> 
> With a git mindset, it won't happen that you "forget" whether you have
> anything uncommitted; you simply never have because committing half-baked
> stuff is the rule, not the exception. That is, before you get a cup of
> coffee, you commit; before you answer a phone call, you commit; before you
> turn your attention away, you commit. (That may be exaggerated, perhaps it
> even isn't, but you get the point.)
> 
> When you have completed your work, you go back to make your commit history
> look nice, comprehensible, and bisectable.

...with "git rebase --interactive" or patch management interface
(StGit, Guilt), or topic branch management interface (TopGit).

> 
> And only then comes the heavy operation: You publish your work for
> consumption by interested parties. This may be even only you yourself:
> "Consumption" would be to merge the work into your release branch. This is
> the right time to care about upstream again.

-- 
Jakub Narebski
Poland
ShadeHawk on #git

Re: question concerning branches

[Junio C Hamano]

ib@wupperonline.de (Ingo Brueckl) writes:

> I'm a git novice and have a comprehension question concerning branches.
>
> Within a git repository, I do:
>
>   git branch test
>   git checkout test
>   # edit foo.bar
>   git checkout master
>
> I'd expect that master is in the exactly same unchanged state it was at
> branching time, but what a surprise, foo.bar is modified here, too!

No.  Local modification that are not committed do not belong to any
branch.  Rather it belongs to your work tree and the index, and follow you
when you switch branches.

This is one of the most useful features.  For example, it is an essential
part of supporting the workflow described here:

    http://gitster.livejournal.com/25892.html

On the other hand, there are cases that you do not want to see your local
changes to foo.bar appear when you switch back to master, and the most
obvious case is "I started working on something, and I used a separate
branch 'test' because the change will be involved.  I am in the middle of
the work, the changes so far I made to foo.bar is far from ready, but I
have to handle emergency fix on the master branch".  For that kind of
situation, you can use "git stash", like:

    http://gitster.livejournal.com/29577.html

question concerning branches

[Ingo Brueckl]

Junio C Hamano <gitster@pobox.com> writes:

> This is one of the most useful features.

Wow. I'm sursprised to hear that, because I consider it at the moment as a
very strange one.

> For example, it is an essential
> part of supporting the workflow described here:
>     http://gitster.livejournal.com/25892.html

Here is what I'd expect to do with git (described with my own words, not in
git commands):

1. commit the quick fix to the release branch
2. push this single commit to origin and master

Now that all branches have the commit a later push and pull should notice
this and "skip" it.

This leads to a second question I have. Assuming I have three patches in my
repo (#1, #2 and #3), is it possible to push only #2 (because it is a
quick fix) and later, maybe after I committed #4, the rest, i.e. #1, #2 and
#4?

Ingo

Re: question concerning branches

[Andreas Ericsson]

Ingo Brueckl wrote:
> Junio C Hamano <gitster@pobox.com> writes:
> 
>> This is one of the most useful features.
> 
> Wow. I'm sursprised to hear that, because I consider it at the moment as a
> very strange one.
> 
>> For example, it is an essential
>> part of supporting the workflow described here:
>>     http://gitster.livejournal.com/25892.html
> 
> Here is what I'd expect to do with git (described with my own words, not in
> git commands):
> 
> 1. commit the quick fix to the release branch
> 2. push this single commit to origin and master
> 
> Now that all branches have the commit a later push and pull should notice
> this and "skip" it.
> 
> This leads to a second question I have. Assuming I have three patches in my
> repo (#1, #2 and #3), is it possible to push only #2 (because it is a
> quick fix) and later, maybe after I committed #4, the rest, i.e. #1, #2 and
> #4?
> 

If they're on different branches, yes. If they're on the same branch, no.
This is because a commit in git is named uniquely not only by its contents,
but also by its ancestry.

You can, however, run "git rebase --interactive" and re-order the commits
before you push them, so that #2 becomes #1 and vice versa. Then you can
push only #1 (the old #2) while leaving #2 (the old #1), #3 and #4 on
your machine only. This involves knowing the commit identifier of #1
though. Assuming it's "deadbeef", you can update the remote branch "foo"
to hold your new commit by running the following command:

  git push <remote> deadbeef:refs/heads/foo

HTH

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

Considering the successes of the wars on alcohol, poverty, drugs and
terror, I think we should give some serious thought to declaring war
on peace.