After discussions on IRC with ender/Jernej and frogonia:
* exchndl.dll (drmingw) requires dbgcore.dll and dbghelp.dll which seem to ship
with win10+, but not win7 (we don't know for Win8). So for Win7, Jernej had to
manually add it back (otherwise, building then running on Win10, it looks
fine, but GIMP fails to start on Win7).
* MSYS2 dropped Win7 support anyway and supports now Win 8.1+.
See: https://www.msys2.org/docs/windows_support/
So even though it looks like GIMP works fine on Win7 (after special-casing the
2 DLLs above by adding them manually in the installed files), there might be
unforeseen issues in the long run.
* Win7 official support by Microsoft now ended. And Win8 support is soon to be
(it actually already has, "except for Server 2012 [based on Win8], which's
supported for another 2 months"). Win8 never had much adoption anyway.
* frogonia confirms they didn't see many Win 7 reports, if at all, in the last
year.
So based on all these, and in order not to make our life over-complicated, we
drop Win 7/8 support for the next 2.99 versions and for the upcoming stable 3.0
series.
Though we keep support to these versions in the 2.10 series, in order not to
disrupt current usage too much.
While Debian testing is the sensible choice for dependency requirements while we
are in full-dev mode, now we are getting closer to 3.0 release, and Debian 12
"bookworm" barely got out.
If we continue to develop at current pace, GIMP 3.0 should be released before
the next stable Debian, so we should not use dependencies unavailable on the
latest stable (otherwise GIMP 3.0 won't be distributable soon enough on Debian,
nor on Debian derivatives such as Ubuntu, Mint, etc.).
This is why we are now basing GIMP dependency requirement on Debian bookworm.
We'll likely get back to the next "testing" after GIMP 3.0 release.
I create this file so that we can refer to it to know whether we can use
a OS-specific API, or if we want to know if we can safely bump a
dependency, etc.
Lukas Oberhuber