possible 'git cp'/how does git detect copies

possible 'git cp'/how does git detect copies

[Mircea Bardac]

I was looking today at duplicating a file but, I soon realized that 
there is no 'git cp' command (this was the "deductive approach to git 
commands", starting from git mv/rm/...). How does "git diff -C" detect 
copies (-C is used for this, according to the documentation)?

On a very simple test, I couldn't see this working. I just copied one 
file, added it, committed the change, ran "git diff -C HEAD^!". There is 
no place saying that it's contents is copied from some other file (both 
files are in the repository now).

"git blame -C new_copied_file" also doesn't show the commits for the 
original file.

This is all with 1.5.6.1.

I am probably missing something here... but I can't produce an example 
of copied contents that actually works. Any hint would be appreciated.

I found this older thread [1] on "git cp" but the discussion appears to 
have stalled at some point. If there is indeed no use of a "git cp" 
command, I would like at least some info on how content copies are being 
detected, since I haven't seen this working.

[1] http://kerneltrap.org/mailarchive/git/2008/2/3/705424


Many thanks,
Mircea

--
http://mircea.bardac.net

Re: possible 'git cp'/how does git detect copies

[Santi Béjar]

On Fri, Jun 27, 2008 at 14:40, Mircea Bardac <dev@mircea.bardac.net> wrote:
> I was looking today at duplicating a file but, I soon realized that there is
> no 'git cp' command (this was the "deductive approach to git commands",
> starting from git mv/rm/...). How does "git diff -C" detect copies (-C is
> used for this, according to the documentation)?

Did you followed the "See also −−find−copies−harder."?

>From the man page

--find-copies-harder::
        For performance reasons, by default, `-C` option finds copies only
        if the original file of the copy was modified in the same
        changeset.  This flag makes the command
        inspect unmodified files as candidates for the source of
        copy.  This is a very expensive operation for large
        projects, so use it with caution.  Giving more than one
        `-C` option has the same effect.


>
> On a very simple test, I couldn't see this working. I just copied one file,
> added it, committed the change, ran "git diff -C HEAD^!". There is no place
> saying that it's contents is copied from some other file (both files are in
> the repository now).
>
> "git blame -C new_copied_file" also doesn't show the commits for the
> original file.

git blame -C -C new_copied_file

Re: possible 'git cp'/how does git detect copies

[Mircea Bardac]

Hi,

Santi Béjar wrote:
> On Fri, Jun 27, 2008 at 14:40, Mircea Bardac <dev@mircea.bardac.net> wrote:
>> I was looking today at duplicating a file but, I soon realized that there is
>> no 'git cp' command (this was the "deductive approach to git commands",
>> starting from git mv/rm/...). How does "git diff -C" detect copies (-C is
>> used for this, according to the documentation)?
> 
> Did you followed the "See also −−find−copies−harder."?

I knew this from before but for some reason I forgot about it when I 
tried it now. The documentation for "git diff -C" is a bit misleading. I 
have originally tested on git 1.5.2.something and the documentation for 
-C didn't point to --find-copies-harder. I've quickly installed 1.5.6.1 
to test the behavior but not the man pages.

Looking over the online docs for 1.5.6.1, it appears that there is now a 
reference to --find-copies-harder.

Even so, saying just that "Detect copies as well as renames." is not 
enough, as it assumes that there is no restriction on the detection process.

 From --find-copies-harder
"For performance reasons, by default, -C option finds copies only if the 
original file of the copy was modified in the same changeset." should be 
moved to -C.

>> On a very simple test, I couldn't see this working. I just copied one file,
>> added it, committed the change, ran "git diff -C HEAD^!". There is no place
>> saying that it's contents is copied from some other file (both files are in
>> the repository now).
>>
>> "git blame -C new_copied_file" also doesn't show the commits for the
>> original file.
> 
> git blame -C -C new_copied_file

Ah, duplicating the parameter. Looking better over these options I have 
noticed that --find-copies-harder for "git diff" can also be replaced 
with an extra -C. A little bit of consistency would help: either
"-C -C", either "--find-copies-harder" in both git blame/diff. Removing 
from the documentation the deprecated version but keeping the 
implementation for backwards compatibility might be a solution.


Many thanks,
Mircea

P.S. I know that patches are encouraged and technically it's pretty 
simple to create a documentation patch, but I have not yet formed myself 
a workflow for sending patches via Git to a maillist (this is a pending 
task for me)

--
http://mircea.bardac.net

Re: possible 'git cp'/how does git detect copies

[Pierre Habouzit]

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On Fri, Jun 27, 2008 at 12:40:22PM +0000, Mircea Bardac wrote:
> I was looking today at duplicating a file but, I soon realized that there 
> is no 'git cp' command (this was the "deductive approach to git 
> commands", starting from git mv/rm/...). How does "git diff -C" detect 
> copies (-C is used for this, according to the documentation)?

  By comparing if files (blobs) are alike. It has some heuristics to
guess which files have good changes to be copies or renames of each
others. But it recomputes the information each time.

> On a very simple test, I couldn't see this working. I just copied one 
> file, added it, committed the change, ran "git diff -C HEAD^!". There is 
> no place saying that it's contents is copied from some other file (both 
> files are in the repository now).
> 
> "git blame -C new_copied_file" also doesn't show the commits for the 
> original file.

  You probably want to use -C -C -M actually.

> I found this older thread [1] on "git cp" but the discussion appears to 
> have stalled at some point. If there is indeed no use of a "git cp" 
> command, I would like at least some info on how content copies are being 
> detected, since I haven't seen this working.

  If you really need it, you can and an alias alias.cp=!cp and be done
with it ;P

-- 
·O·  Pierre Habouzit
··O                                                madcoder@debian.org
OOO                                                http://www.madism.org

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Re: possible 'git cp'/how does git detect copies

[Miklos Vajna]

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On Fri, Jun 27, 2008 at 03:00:06PM +0200, Pierre Habouzit <madcoder@debian.org> wrote:
>   If you really need it, you can and an alias alias.cp=!cp and be done
> with it ;P

Actually that's not that easy. git-mv moves untracked files and adds
tracked files to the index as well. So such a git-cp would have to copy
tracked and untracked files, and add tracked files to the index.

I did it in the past:

http://thread.gmane.org/gmane.comp.version-control.git/72388/focus=73347

but then we agreed about it's better not encouraging copy-and-paste.

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Re: possible 'git cp'/how does git detect copies

[Johannes Sixt]

Mircea Bardac schrieb:
> I was looking today at duplicating a file but, I soon realized that
> there is no 'git cp' command (this was the "deductive approach to git
> commands", starting from git mv/rm/...). How does "git diff -C" detect
> copies (-C is used for this, according to the documentation)?
> 
> On a very simple test, I couldn't see this working. I just copied one
> file, added it, committed the change, ran "git diff -C HEAD^!". There is
> no place saying that it's contents is copied from some other file (both
> files are in the repository now).
> 
> "git blame -C new_copied_file" also doesn't show the commits for the
> original file.
> 
> This is all with 1.5.6.1.
> 
> I am probably missing something here... but I can't produce an example
> of copied contents that actually works. Any hint would be appreciated.

If you modify the original file in the same commit, then you should see
the copy. Otherwise, you can try git diff -C -C aka --find-copies-harder.

-- Hannes