[Nix-dev] How to downgrade or patch freetype-2.7 ?

[Volth]

Hi

Freetype changed defaults in 2.7, the truetype interpreter became v40
instead of v35.
The new defaults are incomatible in a weird way with some old fonts
(notably PragmataPro).

There is upstream-recommended way to "globally" set old interpreted
version via environment variable FREETYPE_PROPERTIES, which is not a
solution obviously: many processes do not inherit parent environment
(sudo, browser renderers run in sandbox, ...) .

So fretype is to be patched and recompiled. This is simple on say
Ubuntu, make a new .deb, install it.

But on NixOS this - flipping one bit in libfreetype.so - means either
to recompile all NixOS (too many packages depends on freetype, not
only GUI apps, also devtools) or to live with corrupt nixstore.

Is there a more elegant solution?