Re: Git: new feature suggestion

> On Wed, Jan 18, 2017 at 2:40 AM, Joao Pinto <Joao.Pinto@synopsys.com> wrote:
>> Hello,
>>
>> My name is Joao Pinto, I work at Synopsys and I am a frequent Linux Kernel
>> contributor.
>>
>> Let me start by congratulate you for the fantastic work you have been doing with
>> Git which is an excellent tool.
>>
>> The Linux Kernel as all systems needs to be improved and re-organized to be
>> better prepared for future development and sometimes we need to change
>> folder/files names or even move things around.
>> I have seen a lot of Linux developers avoid this re-organization operations
>> because they would lose the renamed file history, because a new log is created
>> for the new file, even if it is a renamed version of itself.
> 
> Well there are a couple of things to help with digging in the logs.
> 
> git log:
>        --follow
>            Continue listing the history of a file beyond renames (works only
>            for a single file).
> 
>         -M[<n>], --find-renames[=<n>]
>            If generating diffs, detect and report renames for each commit. For
>            following files across renames while traversing history, see
>            --follow. If n is specified, it is a threshold on the similarity
>            index (i.e. amount of addition/deletions compared to the file’s
>            size). For example, -M90% means Git should consider a delete/add
>            pair to be a rename if more than 90% of the file hasn’t changed.
>            Without a % sign, the number is to be read as a fraction, with a
>            decimal point before it. I.e., -M5 becomes 0.5, and is thus the
>            same as -M50%. Similarly, -M05 is the same as -M5%. To limit
>            detection to exact renames, use -M100%. The default similarity
>            index is 50%.
> 
>        -C[<n>], --find-copies[=<n>]
>            Detect copies as well as renames. See also --find-copies-harder. If
>            n is specified, it has the same meaning as for -M<n>.
> 
> 
> 
>> I am sending you this e-mail to suggest the creation of a new feature in Git:
>> when renamed, a file or folder should inherit his parent’s log and a “rename: …”
>> would be automatically created or have some kind of pointer to its “old” form to
>> make history analysis easier.
> 
> How do you currently analyse history, which detailed feature is missing?
> 
> Mind that in the Git data model we deliberately do not record the rename
> at commit time, but rather want to identify the renames at log time.
> This is because
> in the meantime between commit and log viewing someone could have written
> a better rename detection, whereas at commit time we'd be stuck with ancient
> cruft forever. ;)
> 
>>
>> I volunteer to help in the new feature if you find it useful. I think it would
>> improve log history analysis and would enable developers to better organize old
>> code.
> 
> IMHO complete renames (i.e. git mv path/a/file.c path/b/thing.c) are already
> covered quite well. Partial rename (e.g. moving code from one file into two
> separate files or vice versa) is still a bit hard.
> 
> I started such a new feature, see
> https://urldefense.proofpoint.com/v2/url?u=https-3A__public-2Dinbox.org_git_20160903033120.20511-2D1-2Dsbeller-40google.com_&d=DwIFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=s2fO0hii0OGNOv9qQy_HRXy-xAJUD1NNoEcc3io_kx0&m=BseICq5hy9UHxmX2XP8oPYLbn-HoEUlEuVUzqPHkX58&s=PybtKK0ELH3Nld_CQSYZnLqCQOWvnU4Fjj5iV_7EKqE&e= 
> latest code is at https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_stefanbeller_git_commits_colored-5Fdiff12&d=DwIFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=s2fO0hii0OGNOv9qQy_HRXy-xAJUD1NNoEcc3io_kx0&m=BseICq5hy9UHxmX2XP8oPYLbn-HoEUlEuVUzqPHkX58&s=pkTehcEmeHVLHdcNbUiU03meyH10cgUbGqLgOqXcL6w&e= ,
> but the latest two commits are bogus and need rewriting.
> 
> I think this feature is not 100% what you are aiming at, but is very close.
> 
> Thanks,
> Stefan
>