Re: [idea] File history tracking hints

> On Mon, Sep 11, 2017 at 12:11 AM, Pavel Kretov <firegurafiku@gmail.com> wrote:
>> Hi all,
>>
>> Excuse me if the topic I'm going to raise here has been already discussed
>> on the mailing list, forums, or IRC, but I couldn't find anything related.
>>
>>
>> The problem:
>>
>> Git, being "a stupid content tracker", doesn't try to keep an eye on
>> operations which happens to individual files; things like file renames
>> aren't recorded during commit, but heuristically detected later.
>>
>> Unfortunately, the heuristic can only deal with simple file renames with
>> no substantial content changes; it's helpless when you:
>>
>>  - rename file and change it's content significantly;
>>  - split single file into several files;
>>  - merge several files into another;
>>  - copy entire file from another commit, and do other things like these.
>>
>> However, if we're able to preserve this information, it's possible
>> not only to do more accurate 'git blame', but also merge revisions with
>> fewer conflicts.
>>
>>
>> The proposal:
>>
>> The idea is to let user give hints about what was changed during
>> the commit. For example, if user did a rename which wasn't automatically
>> detected, he would append something like the following to his commit
>> message:
>>
>>     Tracking-hints: rename dev-vcs/git/git-1.0.ebuild ->
>> dev-vcs/git/git-2.0.ebuild
>>
>> or (if full paths of affected files can be unambiguously omitted):
>>
>>     Tracking-hints: rename git-1.0.ebuild -> git-2.0.ebuild
>>
>> There may be other hint types:
>>
>>     Tracking-hint: recreate LICENSE.txt
>>     Tracking-hint: split main.c -> main.c cmdline.c
>>     Tracking-hint: merge linalg.py <- vector.py matrix.py
>>
>> or even something like this:
>>
>>     Tracking-hint: copy json.py <-
>> libs/json.py@4db88291251151d8c5c8e4f20430fa4def2cb2ed
>>
>> If file transformation cannot be described by a single tracking hint, it shall
>> be possible to specify a sequence of hints at once:
>>
>>     Tracking-hint:
>>         split Utils.java -> AppHelpers.java StringHelpers.java
>>         recreate Utils.java
>>
>> Note that in the above example the order of operations really matters, so
>> both lines have to reside in one 'Tracking-hint' block.
>>
>> * * *
>>
>> How do you think, is this idea worth implementing?
>> Any other thoughts on this?
>>
>> -- Pavel Kretov.
>
> This was discussed a couple of times on the mailing list
> (though not recently).
>
> I searched for "rename tracking files site:public-inbox.org/git"
> and came up with
> https://public-inbox.org/git/Pine.LNX.4.58.0504141102430.7211@ppc970.osdl.org/
> (the nearby emails seem to also be relevant to this discussion)
>
> tl:dr: When encoding these hints, you do it at commit time,
> but the heuristic can be improved upon later.
> So you can assume the heuristic is better for the
> common case, as someone will fix the heuristic for the
> common case. Also Gits model is to track objects.