Only try to set flag_value if is_flag is true (#2829)

Co-authored-by: Andreas Backx <[email protected]>

CHANGES.rst

@@ -91,6 +91,9 @@ Unreleased
 -   Add a ``catch_exceptions`` parameter to :class:`CliRunner`. If
     ``catch_exceptions`` is not passed to :meth:`CliRunner.invoke`,
     the value from :class:`CliRunner`. :issue:`2817` :pr:`2818`
+-   ``Option.flag_value`` will no longer have a default value set based on
+    ``Option.default`` if ``Option.is_flag`` is ``False``. This results in
+    ``Option.default`` not needing to implement `__bool__`. :pr:`2829`
 
 Version 8.1.8
 -------------

src/click/core.py

@@ -2597,11 +2597,10 @@ def __init__(
             else:
                 self.default = False
 
-        if flag_value is None:
-            flag_value = not self.default
-
         self.type: types.ParamType
         if is_flag and type is None:
+            if flag_value is None:
+                flag_value = not self.default
             # Re-guess the type from the flag value instead of the
             # default.
             self.type = types.convert_type(None, flag_value)

tests/test_info_dict.py

@@ -58,7 +58,7 @@
         "help": None,
         "prompt": None,
         "is_flag": False,
-        "flag_value": False,
+        "flag_value": None,
         "count": False,
         "hidden": False,
     },