Subject: Re: Enhancing --show-function and --function-context in default configurations

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Mon, 02 Aug 2021 10:45:25 +0200

On Sun, Aug 01 2021, heapcrash heapcrash wrote:

> Hello all!
>
> Thanks to all of the Git community for making such amazing tools.
>
> Some of my favorite features of Git are the --show-function and
> --function-context features of git {grep,log,diff}.
>
> However, the default configuration leaves a bit to be desired --
> setting some simple flags in ~/.gitattributes for e.g.
>
>     *.cpp diff=cpp
>     *.py diff=python
>
> Makes these features MUCH more accurate and usable.  However, one has
> to know about gitattributes, diff filters, xfuncname, etc. in order to
> turn these settings on.
>
> I'd like to contribute changes to Git that makes the "obvious"
> correlations be the default setting.  Before I start, I wanted to
> gauge whether these changes would be accepted or not.  As far as I can
> tell, these would not change the default behavior of plain git
> {grep,log,diff} unless the --show-function or --function-context flags
> are specified -- and if they are, the results would be improved.
>
> Should I work on a patch that does this?

As Junio hinted at in his reply this doesn't just change diff behavior
with the -W or --function-context flag, but changes the work we do (even
if the output is the same) on all unified diff output.

I.e. to generate the "@@" context line we by default use a C function in
xdiff/, this is replaced with a regex-in-a-loop invoking the
userdiff.[ch] code.

I would like to see us have a setting to turn these on by default, but
think it would be better to make that a diff.* config setting to put
into ~/.gitconfig, i.e. we'd extend git itself to know about a list of
extensions for the given userdiff drivers, and use them when rendering
diffs.

It makes emitting the diffs take more CPU, but the same is true of other
options like colorMoved etc, so that in itself is not a dealbreaker.