bug#36644: Git log search

[Dmitry Gutov <dgutov@yandex.ru>]

On 19.07.2019 1:32, Juri Linkov wrote:
>> We can't really use this approach. VC is a high level abstraction,
>> so we try to define the semantics well.
> 
> I tend to agree with Robert.  A string have to be passed to the backend as is.
> It seems such situations when these strings should be compatible between
> different backends (such as running the same command on one backend,
> and then repeating the same search on another backend by retrieving
> a previous argument from the history via M-p) are very rare.

I might agree with you from the practical standpoint, but vc-log-search 
needs a docstring that actually describes what the function is going to 
do. Including info on how PATTERN is going to be interpreted.

E.g. whether "foo.txt" will only match literally, or whether "." can be 
substituted by any character.

And if PATTERN is a regexp, what kind of regexp it's going to be 
interepreted as: basic RE, extended RE, Emacs RE, or Perl RE (probably 
not the last one anyway).

I suppose we can choose one of these and say e.g. that pattern is 
interpreted as an extended regular expression, except for some backends 
that don't support that. I wonder how we're going to convey the latter 
to the user.