make doxygen to required

doc/doxygen/meson.build

@@ -8,19 +8,21 @@ doc_layout_files = files([
   'footer.html'
 ])
 
-doxygen = find_program('doxygen', required : false)
 
 #Build a Doxyfile based on Doxyfile.in
 cdata_doc = configuration_data()
 cdata_doc.set('VERSION', meson.project_version())
-cdata_doc.set('SRCDIR', meson.project_source_root())
-cdata_doc.set('BUILDDIR', meson.project_build_root())
+cdata_doc.set('SRCDIR', meson.source_root())
+cdata_doc.set('BUILDDIR', meson.build_root())
 if find_program('dot', required : false).found()
   cdata_doc.set('HAVE_DOT', 'YES')
 else
   cdata_doc.set('HAVE_DOT', 'NO')
 endif
 
+doxygen = find_program('doxygen', required : false)
+
+if doxygen.found()
   doxy_file = configure_file(
     input : 'Doxyfile.in',
     output : 'Doxyfile',
@@ -36,3 +38,4 @@ custom_target('doc',
     build_by_default : false,
     console : true,
   )
+endif