[feat] Add JSON support to the configuration conversion tool

docs/migration_2_to_3.rst

@@ -24,18 +24,24 @@ As soon as it detects an old-style configuration file, it will convert it to the
    ./bin/reframe: the syntax of the configuration file 'unittests/resources/settings_old_syntax.py' is deprecated
    ./bin/reframe: configuration file has been converted to the new syntax here: '/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/tmph5n8u3kf.py'
 
-Alternatively, you can convert any old configuration file using the conversion tool ``tools/convert_config.py``:
+Alternatively, you can convert any old configuration file using the conversion tool |convert_config|_:
+
+.. |convert_config| replace:: :obj:`convert-config`
+.. _convert_config: https://github.com/eth-cscs/reframe/blob/master/tools/convert-config
 
 .. code-block:: none
 
-   $ ./tools/convert-config unittests/resources/settings_old_syntax.py
-   Conversion successful! The converted file can be found at '/var/folders/h7/k7cgrdl13r996m4dmsvjq7v80000gp/T/tmpz4f6yer4.py'.
+   $ ./tools/convert-config unittests/resources/settings_old_syntax.py new_config.py
+   Conversion successful! The converted file can be found at 'new_config.py'.
 
 
 Another important change is that default locations for looking up a configuration file has changed (see `Configuring ReFrame for Your Site <configure.html>`__ for more details).
 That practically means that if you were relying on ReFrame loading your ``reframe/settings.py`` by default, this is no longer true.
 You have to move it to any of the default settings locations or set the corresponding command line option or environment variable.
 
+.. note::
+   The conversion tool will create a JSON configuration file if the extension of the target file is ``.json``.
+
 
 Automatic conversion limitations
 ================================

reframe/core/config.py

@@ -530,7 +530,11 @@ def handler_list(handler_config):
 
     if newfilename:
         with open(newfilename, 'w') as fp:
-            fp.write(contents)
+            if newfilename.endswith('.json'):
+                json.dump(converted, fp, indent=4)
+            else:
+                fp.write(contents)
+
     else:
         with tempfile.NamedTemporaryFile(mode='w', suffix='.py',
                                          delete=False) as fp:

tools/convert_config.py

@@ -20,6 +20,9 @@
         print(f'{sys.argv[0]}: too few arguments', file=sys.stderr)
         print(f'Usage: {sys.argv[0]} OLD_CONFIG_FILE [NEW_CONFIG_FILE]',
               file=sys.stderr)
+        print('       Use the extension of NEW_CONFIG_FILE to specify\n'
+              '       python (.py) or json (.json) format.',
+              file=sys.stderr)
         sys.exit(1)
 
     try: