Since PLplot is developed by so many people, the task of checking for backwards compatibility of the library is very hard. As for the 5.3.1 release, we do not have any rigorous regression test for check whether the library is really backwards compatible.
However, here are some rules to be followed by the Release Manager prior to releasing a new version of PLplot:
Check if there are any changes in
plplot.h. If no prototype is changed,
then the chances are high that no backwards incompatibilities
have been introduced. If new functions has been added, then
the library soname will be kept, although the soversion
strings in cmake/module/plplot_version.cmake
must be changed following the instructions in that file.
A necessary, but not sufficient test consists of the following:
first, install the previous released version of PLplot in the
system and compile all the examples
examples/c/x??c.. After that, install the
to-be-released version of PLplot and try to run the previously
compiled examples. If they either link or run incorrectly,
then backwards incompatibilities have been introduced and the
soversion string must be upgraded from x:y:z
to (x+1):0:0.