GLProfile fails to select default core profiles when no compat profiles are available. This is what is left from Bug 1382: Compat profiles being disabled via GLRendererQuirks.GLNonCompliant and GLProfile fails to use the highest core profile available as default.
Fixed as described in the git logs. First patches clean-up the affected code-path w/o semantic change, where the subsequent patches clean up semantics and fix the issue. GLRendererQuirks.GLNonCompliant -> GLRendererQuirks.GL3CompatNonCompliant Notable is Bug 1385, i.e. GL3CompatNonCompliant is now more required for Mesa >= 18.2.0 ;-) However, this cleanup & fix was worth its time.
commit 21f82eb8b74a60cc8a869e073e124d44c75f217e Tighten version/profile qualification: fail if: requested compat profile && has core profile On Mesa, if requesting a 3.1 compat profile, we receive a 4.5 core profile. This is natural due to constraints within glXCreateContextAttribsARB, i.e. GLX_CONTEXT_PROFILE_MASK_ARB is only a available for versions >= 3.2 and these are not available on Mesa. Tested with Mesa 18.3.6 of Debian 10 Buster, which also confirms Bug 1385 fix of limitating GL3CompatNonCompliant to Mesa < 18.2.0
(In reply to Sven Gothel from comment #1) > Notable is Bug 1385, i.e. GL3CompatNonCompliant is now more required > for Mesa >= 18.2.0 ;-) > You meant "no more" of course.