[tldistro] poppler, pplib, and TeX Live

[Karl Berry]

Hello TeX distro folk. So you're not surprised at the next update, I
wanted to let you know that I've removed poppler from the upstream TL
sources (r55138). It was previously used by XeTeX to read PDF images,
but we've now changed its TL development sources to use the
semi-homegrown pplib (now in libs/pplib) instead. No other poppler
features were ever used.

We may switch pdftex to also using pplib in the future, but we may
not. Definitely not for TL'21, at least. LuaTeX started using pplib with
TL'19.

In TL, poppler was never used in pdftex, but I know many distros did
so. If you want to continue to do so, you'll need to figure out how to
keep the support up to date on your own hook. It doesn't make sense for
us to keep spending development time on something that isn't used.

The native TL pdftex has always used the (also) semi-homegrown library
libs/xpdf to read PDF images. It, like poppler, is derived from xpdf
source code, and we do keep it up to date. Because xpdf is not
aggressively developed as poppler has been, it doesn't have the new
compiler/language requirements, so it's not much trouble. My personal
wish would be for distros to adopt using libxpdf as well, so that pdftex
behavior could be clearly identical between native TL and distro TL.

BTW, the various engines which generate PDF output have never used
poppler (or any other third party library).

Good luck to us all,
Karl