Re: [PATCH v3 1/2] difftool: add a skeleton for the upcoming builtin

> Jeff King <peff@peff.net> writes:
> 
> > On Sat, Nov 26, 2016 at 02:01:36PM +0100, Johannes Schindelin wrote:
> >
> >> > If you want to control it from outside the test script, you'd need
> >> > something like:
> >> > 
> >> >   if test "$GIT_TEST_DIFFTOOL" = "builtin"
> >> 
> >> That is a bit magic. I first used "GIT_USE_BUILTIN_DIFFTOOL" and it did
> >> not work. My name is arguably more correct (see also Jakub's note about
> >> "naming is hard"), but yours works because there is a "TEST" substring in
> >> it.
> >
> > Yes. You are free to add an exception to the env list in test-lib.sh,
> > but we usually use GIT_TEST_* to avoid having to do so.
> 
> Perhaps
> 
>  - The switch between "do I use builtin, or scripted?" mechanism in
>    1/2 can look at an environment (just like the old "am" rewrite
>    series did), instead of configuration.  This would make the code
>    a lot more simppler (you do not have to worry about the
>    interaction between "setup" and .git/config).
> 
>  - That environment variable can be named GIT_TEST_BUILTIN_DIFFTOOL;
>    after all, people are opting into helping to test the new shiny
>    to make/prove it ready sooner.
> 
>  - The bulk of the existing test for difftool can be moved to a
>    dot-included file (in a way similar to t/annotate-tests are
>    usable to test both annotate and blame-imitating-annotate).
>    Existing PERL prerequisites can all be lost.
> 
>  - Two tests can include that dot-included file; one would
>    explicitly unset that environment (and gives up without PERL
>    prerequisite), while the other explicitly sets it.