[feat] Parse convertible mapping objects with json module

The advantage is that we can automatically convert nested mappings, like for
example the `extra_resources` attribute, which can thus be set from the command
line.

reframe/utility/typecheck.py

@@ -95,6 +95,7 @@
 
 import abc
 import datetime
+import json
 import re
 
 
@@ -322,19 +323,15 @@ def __rfm_cast_str__(cls, s):
         mappping_type = cls._type
         key_type = cls._key_type
         value_type = cls._value_type
-        seq = []
-        for key_datum in s.split(','):
-            try:
-                k, v = key_datum.split(':')
-            except ValueError:
-                # Re-raise as TypeError
-                raise TypeError(
-                    f'cannot convert string {s!r} to {cls.__name__!r}'
-                ) from None
-
-            seq.append((key_type(k), value_type(v)))
-
-        return mappping_type(seq)
+        # Convert string to JSON format: wrap it with braces and add double
+        # quotes where necessary.
+        s = f'{{{s}}}'
+        s = re.sub('([:,{] *)([^":,{}]+)', r'\1"\2"', s)
+        # Parse the JSON string.
+        d = json.loads(s)
+        # Enforce the desired output types.
+        d = {key_type(key): value_type(value) for key, value in d.items()}
+        return mappping_type(d)
 
 
 class _StrType(_SequenceType):

unittests/test_typecheck.py

@@ -6,7 +6,7 @@
 import pytest
 
 import reframe.utility.typecheck as typ
-
+import json
 
 def assert_type_hierarchy(builtin_type, ctype):
     assert isinstance(ctype, type)
@@ -208,7 +208,7 @@ def test_mapping_type():
     # Test conversions
     assert typ.Dict[str, int]('a:1,b:2') == {'a': 1, 'b': 2}
 
-    with pytest.raises(TypeError):
+    with pytest.raises(json.decoder.JSONDecodeError):
         typ.Dict[str, int]('a:1,b')