According to http://www.debian.org/doc/debian-policy/ch-source.html , section "4.14 Source package handling: debian/README.source":
If running dpkg-source -x on a source package doesn't produce the source of > the package, ready for editing, and allow one to make changes and run > dpkg-buildpackage to produce a modified package without taking any > additional steps, creating a debian/README.source documentation file is > recommended. So since you need to run the Smarty_3_x_x/development/Makefile after modifying the .y file, the current package is lacking (there is no debian/README.source file either). IMO, the debian/rules "build" rule should run the Smarty_3_x_x/development/Makefile to compile the .y and .plex files , even though smarty SVN comes with a compiled version. That way you are also sure that the installed compiled version of these files actually corresponds to the source version. Regards, Thue