[feat] Allow setting nested mapping types using the -S option

docs/manpage.rst

@@ -650,6 +650,9 @@ Options controlling ReFrame execution
    - Sequence types: ``-S seqvar=1,2,3,4``
    - Mapping types: ``-S mapvar=a:1,b:2,c:3``
 
+   Nested mapping types can also be converted using JSON syntax.
+   For example, the :attr:`~reframe.core.pipeline.RegressionTest.extra_resources` complex dictionary could be set with ``-S extra_resources='{"gpu": {"num_gpus_per_node":8}}'``.
+
    Conversions to arbitrary objects are also supported.
    See :class:`~reframe.utility.typecheck.ConvertibleType` for more details.
 
@@ -705,6 +708,9 @@ Options controlling ReFrame execution
 
       Allow setting variables in fixtures.
 
+   .. versionchanged:: 4.4
+
+      Allow setting nested mapping types using JSON syntax.
 
 .. option:: --skip-performance-check
 

reframe/utility/typecheck.py

@@ -95,6 +95,7 @@
 
 import abc
 import datetime
+import json
 import re
 
 
@@ -322,19 +323,23 @@ 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)
+
+        try:
+            items = json.loads(s)
+        except json.JSONDecodeError:
+            items = []
+            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
+
+                items.append((key_type(k), value_type(v)))
+
+        return mappping_type(items)
 
 
 class _StrType(_SequenceType):

unittests/test_typecheck.py

@@ -208,6 +208,14 @@ def test_mapping_type():
     # Test conversions
     assert typ.Dict[str, int]('a:1,b:2') == {'a': 1, 'b': 2}
 
+    # Conversion with JSON syntax, for nested dictionaries
+    s = '{"gpu":{"num_gpus_per_node": 8}, "mpi": {"num_slots": 64}}'
+    expected = {
+        'gpu': {'num_gpus_per_node': 8},
+        'mpi': {'num_slots': 64},
+    }
+    assert typ.Dict[str, typ.Dict[str, object]](s) == expected
+
     with pytest.raises(TypeError):
         typ.Dict[str, int]('a:1,b')