[bugfix] Fix JSON report generation for deferred expressions

reframe/core/deferrable.py

@@ -77,6 +77,9 @@ def __iter__(self):
         '''Evaluate the deferred expression and iterate over the result.'''
         return iter(self.evaluate())
 
+    def __rfm_json_encode__(self):
+        return self.evaluate()
+
     # Overload Python operators to be able to defer any expression
     #
     # NOTE: In the following we are not using `self` for denoting the first

reframe/frontend/cli.py

@@ -21,6 +21,7 @@
 import reframe.frontend.check_filters as filters
 import reframe.frontend.dependency as dependency
 import reframe.utility.os_ext as os_ext
+import reframe.utility.json as jsonext
 from reframe.core.exceptions import (
     EnvironError, ConfigError, ReframeError,
     ReframeDeprecationWarning, ReframeFatalError,
@@ -810,7 +811,7 @@ def print_infoline(param, value):
                 report_file = generate_report_filename(report_file)
                 try:
                     with open(report_file, 'w') as fp:
-                        json.dump(json_report, fp, indent=2)
+                        jsonext.dump(json_report, fp, indent=2)
                 except OSError as e:
                     printer.warning(
                         f'failed to generate report in {report_file!r}: {e}'

reframe/utility/json.py

@@ -0,0 +1,24 @@
+# Copyright 2016-2020 Swiss National Supercomputing Centre (CSCS/ETH Zurich)
+# ReFrame Project Developers. See the top-level LICENSE file for details.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+import json
+
+
+class _ReframeJsonEncoder(json.JSONEncoder):
+    def default(self, obj):
+        if hasattr(obj, '__rfm_json_encode__'):
+            return obj.__rfm_json_encode__()
+
+        return json.JSONEncoder.default(self, obj)
+
+
+def dump(obj, fp, **kwargs):
+    kwargs['cls'] = _ReframeJsonEncoder
+    return json.dump(obj, fp, **kwargs)
+
+
+def dumps(obj, **kwargs):
+    kwargs['cls'] = _ReframeJsonEncoder
+    return json.dumps(obj, **kwargs)

unittests/test_utility.py

@@ -12,7 +12,9 @@
 import reframe
 import reframe.core.fields as fields
 import reframe.utility as util
+import reframe.utility.json as jsonext
 import reframe.utility.os_ext as os_ext
+import reframe.utility.sanity as sn
 from reframe.core.exceptions import (SpawnedProcessError,
                                      SpawnedProcessTimeout)
 
@@ -1293,3 +1295,25 @@ def test_cray_cle_info_missing_parts(tmp_path):
     assert cle_info.date is None
     assert cle_info.network is None
     assert cle_info.patchset == '09'
+
+
+def test_jsonext_dump(tmp_path):
+    json_dump = tmp_path / 'test.json'
+    with open(json_dump, 'w') as fp:
+        jsonext.dump({'foo': sn.defer(['bar'])}, fp)
+
+    with open(json_dump, 'r') as fp:
+        assert '{"foo": ["bar"]}' == fp.read()
+
+    with open(json_dump, 'w') as fp:
+        jsonext.dump({'foo': sn.defer(['bar'])}, fp, separators=(',', ':'))
+
+    with open(json_dump, 'r') as fp:
+        assert '{"foo":["bar"]}' == fp.read()
+
+
+def test_jsonext_dumps():
+    assert '"foo"' == jsonext.dumps('foo')
+    assert '{"foo": ["bar"]}' == jsonext.dumps({'foo': sn.defer(['bar'])})
+    assert '{"foo":["bar"]}' == jsonext.dumps({'foo': sn.defer(['bar'])},
+                                              separators=(',', ':'))