[postgis-devel] Can we put back GEOS 3.5 support in 3.0?

[Bas Couwenberg]

On 2019-01-24 10:10, Raúl Marín Rodríguez wrote:
>> the ABI never changes, there’s never a reason to not just dump the 
>> latest GEOS into place. What can we do to convince packagers we are 
>> sincere?
> 
> This isn't completely true:
> ```
> $ ldd /usr/lib/postgresql/postgis-3.so
> [...]
>        libgeos-3.8.0.so => /usr/lib/libgeos-3.8.0.so 
> (0x00007f8a80163000)
> [...]
> ```
> Since linking against the c API means algo linking against the C++
> library, updating geos means rebuilding postgis and any other package
> that depends on it (in my system gdal and qgis). If I understand
> correctly, the C++ ABI isn't stable so, because of how the dependency
> propagates, the C ABI isn't stable either. Please correct me if I'm
> missing something.

ldd output is misleading, use objdump instead:

  $ objdump -x /usr/lib/postgresql/11/lib/postgis-2.5.so | grep NEEDED
    NEEDED               liblwgeom-2.5.so.0
    NEEDED               libgeos_c.so.1
    NEEDED               libproj.so.13
    NEEDED               libjson-c.so.3
    NEEDED               libprotobuf-c.so.1
    NEEDED               libxml2.so.2
    NEEDED               libSFCGAL.so.1
    NEEDED               libc.so.6

In Debian the only package that requires the C++ API is OSSIM, 
everything else (including gdal & qgis) uses the C API and don't require 
rebuild for new GEOS releases.

Kind Regards,

Bas