deprecate YAML as diff values formatter

Author: mr-mixas

.github/workflows/tests.yml

@@ -38,7 +38,7 @@ jobs:
     - name: Run essential tests
       if: ${{ matrix.tests != 'extended' }}
       run: |
-        pip install --quiet -e '.[cli,test]'
+        pip install -e '.[cli,test]'
         pytest
 
     - name: Run extra linters and report coverage

nested_diff/diff_tool.py

@@ -17,6 +17,7 @@
 import argparse
 import os
 import sys
+import warnings
 
 import nested_diff
 import nested_diff.cli
@@ -152,7 +153,8 @@ def get_optional_args_parser(self):
             default='repr',
             help='values format; "none" means no values printed, "repr" is a '
             'python representation of the object, rest are themselves; default'
-            ' is "%(default)s"',
+            ' is "%(default)s". NOTE: yaml is deprecated here due to explicit'
+            ' ends for scalar values in yaml v1.2',
         )
 
         parser.add_argument(
@@ -333,6 +335,14 @@ def __init__(self, *args, **kwargs):
                 if values == 'json':
                     self.__val_encoder = nested_diff.cli.JsonDumper(indent=2)
                 elif values == 'yaml':
+                    warnings.warn(
+                        (
+                            'YAML as diff values formatter is deprecated and'
+                            ' will be removed soon'
+                        ),
+                        FutureWarning,
+                        stacklevel=3,
+                    )
                     self.__val_encoder = nested_diff.cli.YamlDumper(
                         explicit_start=False,
                     )

tests/cli/test_diff_tool.py

@@ -714,6 +714,10 @@ def test_values_json(capsys, expected, rpath):
     assert captured.out == expected
 
 
+@pytest.mark.skipif(
+    sys.implementation.name == 'pypy',
+    reason='--values yaml is deprecated (produce explicit ends on pypy 3.8)',
+)
 def test_values_yaml(capsys, expected, rpath):
     exit_code = nested_diff.diff_tool.App(
         args=(