commit/from command in git-fast-import

commit/from command in git-fast-import

[Mike Hommey]

Hi,

I'm trying to make sense of the git fast-import manual page. This is
what it reads, as of git 1.7.8.3, from Debian unstable:

  Omitting the from command in the first commit of a new branch will
  cause fast-import to create that commit with no ancestor. This
  tends to be desired only for the initial commit of a project. If
  the frontend creates all files from scratch when making a new
  branch, a merge command may be used instead of from to start the
  commit with an empty tree. Omitting the from command on existing
  branches is usually desired, as the current commit on that branch
  is automatically assumed to be the first ancestor of the new
  commit.

When I do create a commit on a given branch with a stream like:
  commit refs/heads/branch
  author ...
  committer ...
  data <<EOF
  Commit message
  EOF
  deleteall

All I get is this warning:
  warning: Not updating refs/heads/branch (new tip new_sha1
does not contain old_sha1)

And the branch only has one commit, which is the one I just created.
On the other hand, if I add a "from" instruction in the above stream,
I have the expected branch history.

Arguably, this may be related to my use of deleteall, but nothing in the
deleteall description suggests this would happen.

Is it an expected behaviour and a lack of proper documentation, or is it
a bug in git fast-import ?

Mike

Re: commit/from command in git-fast-import

[David Barr]

On Fri, Jan 27, 2012 at 11:48 PM, Mike Hommey <mh@glandium.org> wrote:
> When I do create a commit on a given branch with a stream like:
>  commit refs/heads/branch
>  author ...
>  committer ...
>  data <<EOF
>  Commit message
>  EOF
>  deleteall
>
> All I get is this warning:
>  warning: Not updating refs/heads/branch (new tip new_sha1
> does not contain old_sha1)
>
> And the branch only has one commit, which is the one I just created.
> On the other hand, if I add a "from" instruction in the above stream,
> I have the expected branch history.

This is precisely the expected behavior.
If 'from' is omitted, the resulting commit has no preceding history.
On the other hand, what you want is to specify the parent so that
there is a continuation of history.

I hope this helps.
--
David Barr

Re: commit/from command in git-fast-import

[Mike Hommey]

On Sat, Jan 28, 2012 at 01:00:17AM +1100, David Barr wrote:
> On Fri, Jan 27, 2012 at 11:48 PM, Mike Hommey <mh@glandium.org> wrote:
> > When I do create a commit on a given branch with a stream like:
> >  commit refs/heads/branch
> >  author ...
> >  committer ...
> >  data <<EOF
> >  Commit message
> >  EOF
> >  deleteall
> >
> > All I get is this warning:
> >  warning: Not updating refs/heads/branch (new tip new_sha1
> > does not contain old_sha1)
> >
> > And the branch only has one commit, which is the one I just created.
> > On the other hand, if I add a "from" instruction in the above stream,
> > I have the expected branch history.
> 
> This is precisely the expected behavior.
> If 'from' is omitted, the resulting commit has no preceding history.
> On the other hand, what you want is to specify the parent so that
> there is a continuation of history.

This is however not what the manpage suggests in what I quoted in my
message:
  Omitting the from command on existing branches is usually desired, as
  the current commit on that branch is automatically assumed to be the
  first ancestor of the new commit.

Mike

Re: commit/from command in git-fast-import

[David Barr]

On Sat, Jan 28, 2012 at 1:47 AM, Mike Hommey <mh@glandium.org> wrote:
> On Sat, Jan 28, 2012 at 01:15:34AM +1100, David Barr wrote:
>> On Sat, Jan 28, 2012 at 1:08 AM, Mike Hommey <mh@glandium.org> wrote:
>> > On Sat, Jan 28, 2012 at 01:00:17AM +1100, David Barr wrote:
>> >> On Fri, Jan 27, 2012 at 11:48 PM, Mike Hommey <mh@glandium.org> wrote:
>> >> > When I do create a commit on a given branch with a stream like:
>> >> >  commit refs/heads/branch
>> >> >  author ...
>> >> >  committer ...
>> >> >  data <<EOF
>> >> >  Commit message
>> >> >  EOF
>> >> >  deleteall
>> >> >
>> >> > All I get is this warning:
>> >> >  warning: Not updating refs/heads/branch (new tip new_sha1
>> >> > does not contain old_sha1)
>> >> >
>> >> > And the branch only has one commit, which is the one I just created.
>> >> > On the other hand, if I add a "from" instruction in the above stream,
>> >> > I have the expected branch history.
>> >>
>> >> This is precisely the expected behavior.
>> >> If 'from' is omitted, the resulting commit has no preceding history.
>> >> On the other hand, what you want is to specify the parent so that
>> >> there is a continuation of history.
>> >
>> > This is however not what the manpage suggests in what I quoted in my
>> > message:
>> >  Omitting the from command on existing branches is usually desired, as
>> >  the current commit on that branch is automatically assumed to be the
>> >  first ancestor of the new commit.
>> >
>> > Mike
>>
>> Oh, right. I guess I wasn't paying enough attention, sorry.
>> That does sound like a bug then. Is it reproducible in a new repo?
>> eg:
>>   git init foo && cd foo && touch bar && git add -A && git commit -m "baz"
>>   git fast-import < ../fast-import-regression.txt
>
> It is.

I accidentally took this thread off-list.
Looks like we have a real fast-import bug, in Debian Unstable at least.
--
David Barr

Re: commit/from command in git-fast-import

[Jonathan Nieder]

David Barr wrote:
>>> On Sat, Jan 28, 2012 at 1:08 AM, Mike Hommey <mh@glandium.org> wrote:

>>>> This is however not what the manpage suggests in what I quoted in my
>>>> message:
>>>>  Omitting the from command on existing branches is usually desired, as
>>>>  the current commit on that branch is automatically assumed to be the
>>>>  first ancestor of the new commit.
[...]
> Looks like we have a real fast-import bug, in Debian Unstable at least.

Yep, this is a real fast-import documentation bug.  The manual says:

	Omitting the from command in the first commit of a new branch
	will cause fast-import to create that commit with no ancestor.
	This tends to be desired only for the initial commit of a
	project.
[...]
	The special case of restarting an incremental import from the
	current branch value should be written as:

		from refs/heads/branch^0

The unfortunate term here is "existing branches", which seems to have
been intended to refer to refs that have already been populated in
this fast-import stream by a "commit" or "reset" command, rather than
any old ref that already exists in the repository.

In other words, instead of "existing branch", the manual should say
something along the lines of "branch already in fast-import's internal
branch table".

Here's a sketch.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 Documentation/git-fast-import.txt |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-fast-import.txt b/Documentation/git-fast-import.txt
index ec6ef311..28a317ff 100644
--- a/Documentation/git-fast-import.txt
+++ b/Documentation/git-fast-import.txt
@@ -306,9 +306,9 @@ and control the current import process.  More detailed discussion
 (with examples) of each command follows later.
 
 `commit`::
-	Creates a new branch or updates an existing branch by
-	creating a new commit and updating the branch to point at
-	the newly created commit.
+	Creates a new branch or updates a branch by creating a new
+	commit and updating the branch to point at the newly created
+	commit.
 
 `tag`::
 	Creates an annotated tag object from an existing commit or
@@ -317,7 +317,7 @@ and control the current import process.  More detailed discussion
 	in time.
 
 `reset`::
-	Reset an existing branch (or a new branch) to a specific
+	Reset an existing branch or a new branch to a specific
 	revision.  This command must be used to change a branch to
 	a specific revision without making a commit on it.
 
@@ -439,13 +439,15 @@ The `from` command is used to specify the commit to initialize
 this branch from.  This revision will be the first ancestor of the
 new commit.
 
-Omitting the `from` command in the first commit of a new branch
+Omitting the `from` command in the first commit of a branch that
+has not been created previously with a `commit` or `reset` command
 will cause fast-import to create that commit with no ancestor. This
 tends to be desired only for the initial commit of a project.
 If the frontend creates all files from scratch when making a new
 branch, a `merge` command may be used instead of `from` to start
 the commit with an empty tree.
-Omitting the `from` command on existing branches is usually desired,
+Omitting the `from` command on branches that have already been
+initialized in the same stream is usually desired,
 as the current commit on that branch is automatically assumed to
 be the first ancestor of the new commit.
 
-- 
1.7.9.rc2

Re: commit/from command in git-fast-import

[Sverre Rabbelier]

On Fri, Jan 27, 2012 at 15:09, Jonathan Nieder <jrnieder@gmail.com> wrote:
> The unfortunate term here is "existing branches", which seems to have
> been intended to refer to refs that have already been populated in
> this fast-import stream by a "commit" or "reset" command, rather than
> any old ref that already exists in the repository.
>
> In other words, instead of "existing branch", the manual should say
> something along the lines of "branch already in fast-import's internal
> branch table".

Looks sane.

-- 
Cheers,

Sverre Rabbelier