Only add extensions in module file if there are extensions

This fixes easybuilders#4330.

easybuild/framework/easyblock.py

@@ -1727,16 +1727,24 @@ def _make_extension_list(self):
         # Each extension in exts_list is either a string or a list/tuple with name, version as first entries
         return [(ext, ) if isinstance(ext, string_type) else ext[:2] for ext in self.cfg.get_ref('exts_list')]
 
-    def make_extension_string(self, name_version_sep='-', ext_sep=', ', sort=True):
+    def make_extension_list(self, name_version_sep='-', sort=True):
         """
-        Generate a string with a list of extensions.
+        Generate a list of extensions.
 
-        The name and version are separated by name_version_sep and each extension is separated by ext_sep
+        The name and version are separated by name_version_sep
         """
         exts_list = (name_version_sep.join(ext) for ext in self._make_extension_list())
         if sort:
             exts_list = sorted(exts_list, key=str.lower)
-        return ext_sep.join(exts_list)
+        return exts_list
+
+    def make_extension_string(self, name_version_sep='-', ext_sep=', ', sort=True):
+        """
+        Generate a string with a list of extensions.
+
+        The name and version are separated by name_version_sep and each extension is separated by ext_sep
+        """
+        return ext_sep.join(self.make_extension_list(name_version_sep=name_version_sep, sort=sort))
 
     def prepare_for_extensions(self):
         """

easybuild/tools/module_generator.py

@@ -622,7 +622,7 @@ def _generate_extensions_list(self):
         """
         Generate a list of all extensions in name/version format
         """
-        return self.app.make_extension_string(name_version_sep='/', ext_sep=',').split(',')
+        return self.app.make_extension_list(name_version_sep='/')
 
     def _generate_help_text(self):
         """

test/framework/module_generator.py

@@ -756,6 +756,16 @@ def test_module_extensions(self):
             regex = re.compile(pattern, re.M)
             self.assertTrue(regex.search(desc), "Pattern '%s' found in: %s" % (regex.pattern, desc))
 
+        # check if the extensions is missing if there are no extensions
+        test_ec = os.path.join(test_dir, 'easyconfigs', 'test_ecs', 't', 'toy', 'toy-0.0-test.eb')
+
+        ec = EasyConfig(test_ec)
+        eb = EasyBlock(ec)
+        modgen = self.MODULE_GENERATOR_CLASS(eb)
+        desc = modgen.get_description()
+
+        self.assertFalse(re.search("\s*extensions\(", desc), "No extensions found in: %s" % desc)
+
     def test_prepend_paths(self):
         """Test generating prepend-paths statements."""
         # test prepend_paths