Add check for single quoted values

confection/__init__.py

@@ -16,6 +16,7 @@
 import io
 import copy
 import re
+import warnings
 
 from .util import Decorator
 
@@ -43,8 +44,12 @@ def before_read(self, parser, section, option, value):
             json_value = srsly.json_loads(value)
             if isinstance(json_value, str) and json_value not in JSON_EXCEPTIONS:
                 value = json_value
-        except Exception:
-            pass
+        except ValueError:
+            if value and value[0] == value[-1] == "'":
+                warnings.warn(
+                    f"The value [{value}] seems to be single-quoted, but values "
+                    "use JSON formatting, which requires double quotes."
+                )
         return super().before_read(parser, section, option, value)
 
     def before_get(self, parser, section, option, value, defaults):

confection/tests/test_config.py

@@ -1379,3 +1379,20 @@ def test_config_overrides(greeting, value, expected):
     assert "${vars.a}" in str_cfg
     cfg = Config().from_str(str_cfg, overrides=overrides)
     assert expected in str(cfg)
+
+
+def test_warn_single_quotes():
+    str_cfg = f"""
+    [project]
+    commands = 'do stuff'
+    """
+
+    with pytest.warns(UserWarning, match="single-quoted"):
+        cfg = Config().from_str(str_cfg)
+
+    # should not warn if single quotes are in the middle
+    str_cfg = f"""
+    [project]
+    commands = some'thing
+    """
+    cfg = Config().from_str(str_cfg)