lint: Show dynamic description for WarnOnFunction config

Fix #1075

rpmlint/lint.py

@@ -304,8 +304,15 @@ def print_explanation(self, messages, config):
         """
         for message in messages:
             explanation = self.output.get_description(message, config)
+            if not explanation:
+                # check if it's a WarnOnFunction warning configuration
+                forbidden_functions = config.configuration['WarnOnFunction']
+                if message in forbidden_functions:
+                    explanation = forbidden_functions[message].get('description')
+
             if not explanation:
                 explanation = 'Unknown message, please report a bug if the description should be present.\n\n'
+
             print(f'{message}:\n{explanation}')
 
     def load_checks(self):

test/test_lint.py

@@ -125,6 +125,27 @@ def test_explain_known(capsys):
     assert not err
 
 
+@pytest.mark.parametrize('configs', [
+    # Message defined in configs/Fedora/warn-on-functions.toml
+    (Path('configs/Fedora/warn-on-functions.toml'), False),
+    (Path('configs/Fedora/scoring.toml'), True),
+])
+def test_explain_known_warn_on_function(capsys, configs):
+    extraconfig, unknown = configs
+    message = ['crypto-policy-non-compliance-openssl']
+    additional_options = {
+        'explain': message,
+        'config': [extraconfig],
+    }
+    options = {**options_preset, **additional_options}
+    linter = Lint(options)
+    linter.run()
+    out, err = capsys.readouterr()
+
+    assert ('Unknown message' in out) == unknown
+    assert not err
+
+
 def test_explain_with_unknown(capsys):
     message = ['infopage-not-compressed', 'blablablabla']
     additional_options = {