Swig code generation - git src vs tarball src

[Geert Janssens]

Our build system behaves differently when a build is started from a git 
cloned repository or from a release tarball: swig interface files are 
only converted into c files when building from git. The tarball assumes 
these should be present.

What is the original reason it was implemented this way ? Or put 
differently is there (still) a good reason to avoid on the fly swig code 
generation for a (release) tarball build ?

It seems to me these diverging code paths are needlessly complicating 
the code.

Background: I ran into this while trying to set up a nightly build 
system for fedora/rhel rpms. Based on the guidelines I found for 
Fedora's copr and tito tools I'm trying to build from a tarball that is 
created from the git repository (not via make dist).

The build system detects it's not running from git and will fail because 
the swig generated files are missing.

Pretending I'm building from git using BUILDING_FROM_SCM=yes will cause 
the build to fail as well when trying to extract version information 
from git...

I'm not sure my experiment is achievable. But it got me thinking about 
this diverging code path in our source anyway. So to summarize again:

What is the original reason it was implemented this way ? Or put 
differently is there (still) a good reason to avoid on the fly swig code 
generation for a (release) tarball build ?

Regards,

Geert