[tex-live] behaviour of kpsewhich on case-insensitive mac system

[Karl Berry]

    Date: Mon, 18 Sep 2017 13:52:40 -0300
    From: "George N. White III" <gnwiii at gmail.com>
    [...]
    kpsewhich --ignore-case eXample-ImaGe-A.pdf
    /usr/local/texlive/2017/texmf-dist/tex/latex/mwe/example-image-a.pdf

I didn't implement exactly that, but I did implement a subcase for 2018:
a case-insensitive fallback match in directories that are searched
explicitly (not texmf-dist or texmf-local).  What I've observed in
practice is that the mixed-case errors are nearly all with user-created
files (.tex files and images), not system directories.(*)

Thus, on a case-sensitive (not Windows, not current Mac) (file)system,
if we have a ./foo.tex,
kpsewhich --casefold-search Foo.tex  # or \input Foo
will return ./foo.tex, whereas before it would fail.

On the other hand, if we have both ./Foo.tex and ./foo.tex,
then \input Foo will still return Foo.tex, as it always has.

There are other shadowy cases where something different can be returned
now than before, but I hope they will not matter in practice. I wrote a
new section in the kpathsea manual full of details.

The feature is controlled by a variable in texmf.cnf, namely
texmf_casefold_search, which is on by default, and can be overridden in
all the usual ways.

The whole thing has zero effect on Windows; the code is not even
compiled.

We'll see how it goes when the pretest starts I guess ... --best, karl.

(*) I did not want to double my time and effort merely for the mwe
package, which was the occasion of the original report in this thread;
it seems to me that people using the mwe package should also be capable
of making the effort to get the case right.