Fix timestamp value when --timestamp is passed no arguments

Author: Vasileios Karakasis

reframe/frontend/argparse.py

@@ -184,8 +184,7 @@ def add_argument(self, *flags, **kwargs):
         kwargs['dest'] = opt_name
 
         # Convert 'store_true' and 'store_false' actions to their
-        # 'store_const' equivalents, because they otherwise imply imply a
-        # default
+        # 'store_const' equivalents, because they otherwise imply a default
         action = kwargs.get('action', None)
         if action == 'store_true' or action == 'store_false':
             kwargs['action'] = 'store_const'

reframe/frontend/cli.py

@@ -217,7 +217,8 @@ def main():
         envvar='RFM_SAVE_LOG_FILES', configvar='general/save_log_files'
     )
     output_options.add_argument(
-        '--timestamp', action='store', nargs='?', const='', metavar='TIMEFMT',
+        '--timestamp', action='store', nargs='?', const='%FT%T',
+        metavar='TIMEFMT',
         help=('Append a timestamp to the output and stage directory prefixes '
               '(default: "%%FT%%T")'),
         envvar='RFM_TIMESTAMP_DIRS', configvar='general/timestamp_dirs'

unittests/test_argparser.py

@@ -104,7 +104,7 @@ def extended_parser():
         envvar='RFM_KEEP_STAGE_FILES', configvar='general/keep_stage_files'
     )
     foo_options.add_argument(
-        '--timestamp', action='store', nargs='?', const='',
+        '--timestamp', action='store',
         envvar='RFM_TIMESTAMP_DIRS', configvar='general/timestamp_dirs'
     )
     foo_options.add_argument(
@@ -180,10 +180,3 @@ def test_option_envvar_conversion_error(default_exec_ctx, extended_parser):
         options = extended_parser.parse_args(['--nocolor'])
         errors = options.update_config(site_config)
         assert len(errors) == 1
-
-
-def test_option_nargs(default_exec_ctx, extended_parser):
-    site_config = rt.runtime().site_config
-    options = extended_parser.parse_args(['--timestamp'])
-    assert options.timestamp == ''
-    assert site_config.get('general/0/timestamp_dirs') == '%FT%T'