PostGIS, CentOS 6 / RHEL 6, and Pg 12

Hi folks

I've been contacted by someone to ask about why PostGIS 2.5 or 3.0 rpms
aren't produced for RHEL 6 or CentOS 6. They were produced for PostgreSQL
11.

I've done some digging in the repo which suggests that PostGIS 2.5 can't be
built for EL-6 due to missing proj49, dependencies in the spec defined
against newer geos and proj that cannot be built on EL-6, and dependency on
an unavailable gdal version.

I don't see any announcement or detail on this.

Was de-supporting PostGIS on EL-6 an intentional step as part of the Pg12
migration?

I've made changes to build Pg12 / EL-6 / PostGIS 2.5 in my local tree.
They're not clean to push as a patch upstream as-is, but I can clean them
up if they will be accepted. The only change likely to be controversial is
that I need to bring back proj49 (for EL-6 only).

Thoughts?

I've attached the patch, which also contains some unrelated changes to make
local builds under Docker easier and provides a wrapper for building. The
patch is NOT TO BE MERGED, it's only to help others with this issue.

Details on Pg12/EL-6/PostGIS 2.5 compat:

* PostGIS 3.0 requires C++11 and cannot be built on EL-6 due to
compiler version

* The PostGIS 2.5 spec depends on libgeos 3.8 and proj62

* PostGIS 2.5 can be built successfully against the older proj49 and
libgeos 3.6
but the spec doesn't permit that as currently written and we don't build
those
dependencies for EL-6 anymore

* libgeos 3.7 and 3.8 require a C++ compiler and cannot be built on EL-6

* proj62 and proj52 require a C++11 compiler and cannot be built on EL-6

* proj49 can be built on EL-6 but has been removed from the repository
by commit caf2197d4 "Remove proj49 and proj52 from repos. No longer
needed"
on September 24

* libgeos 3.6 builds on EL-6 but is not built for pg12 - there's no
rpm/redhat/12/geos36/EL-6 symlink, though a
rpm/redhat/11/geos36/EL-6 exists

* postgis 2.5 appears to be enabled for pg11 since
rpm/redhat/11/postgis25/EL-6 exists - but it cannot be built given the
dependencies defined.

I repeat, patch is NOT FOR MERGE.

--
Craig Ringer http://www.2ndQuadrant.com/
2ndQuadrant - PostgreSQL Solutions for the Enterprise