Tone-down the case of default=True for flags in documentation (pallets#3049)

Author: Rowlando13

CHANGES.rst

@@ -5,14 +5,16 @@ Version 8.3.x
 
 Unreleased
 
--   Rework relationship between ``flag_value`` and ``default``: the value given to
-    ``default`` is now left untouched, and keep the value it receive. So
-    ``default=<desired_value>`` is respected and ``<desired_value>`` is passed on as-is
-    to the CLI function. With the exception of flag options, where setting
-    ``default=True`` maintain the legacy behavior of defaulting to the ``flag_value``.
-    This allow ``default`` to be of any type, including ``bool`` or ``None``, fixing
-    inconsistencies reported in: :issue:`1992` :issue:`2012` :issue:`2514`
-    :issue:`2610` :issue:`3024` :pr:`3030`
+-   **Improved flag option handling**: Reworked the relationship between ``flag_value``
+    and ``default`` parameters for better consistency:
+
+    * The ``default`` parameter value is now preserved as-is and passed directly
+      to CLI functions (no more unexpected transformations)
+    * Exception: flag options with ``default=True`` maintain backward compatibility
+      by defaulting to their ``flag_value``
+    * The ``default`` parameter can now be any type (``bool``, ``None``, etc.)
+    * Fixes inconsistencies reported in: :issue:`1992` :issue:`2514` :issue:`2610`
+      :issue:`3024` :pr:`3030`
 -   Allow ``default`` to be set on ``Argument`` for ``nargs = -1``. :issue:`2164`
     :pr:`3030`
 -   Show correct auto complete value for ``nargs`` option in combination with flag

docs/options.md

@@ -335,14 +335,12 @@ To have an flag pass a value to the underlying function set `flag_value`. This a
     invoke(info)
 ```
 
-````{caution}
-The `default` argument of options always give to the underlying function its value *as-is*.
+````{note}
+The `default` value is given to the underlying function as-is. So if you set `default=None`, the value passed to the function is the `None` Python value. Same for any other type.
 
-But for flags, the interaction between `flag_value` and `default` is a bit special.
+But there is a special case for flags. If a flag has a `flag_value`, then setting `default=True` is interpreted as *the flag should be activated by default*. So instead of the underlying function receiving the `True` Python value, it will receive the `flag_value`.
 
-If a flag has a `flag_value`, setting `default` to `True` means that the flag is activated by default. Not that the value passed to the underlying function is the `True` Python value. Instead, the default value will be aligned to the `flag_value` behind the scenes.
-
-Which means, the in example above, this option:
+Which means, in example above, this option:
 
 ```python
 @click.option('--upper', 'transformation', flag_value='upper', default=True)
@@ -354,9 +352,7 @@ is equivalent to:
 @click.option('--upper', 'transformation', flag_value='upper', default='upper')
 ```
 
-This was implemented to support legacy behavior, that will be removed in Click 9.0 to allow for default to take any value, including `True`.
-
-In the mean time, to avoid confusion, it is recommended to always set `default` to the actual default value you want to pass to the underlying function, and not use `True`, `False` or `None`. Unless that's the precise value you want to explicitly force as default.
+Because the two are equivalent, it is recommended to always use the second form, and set `default` to the actual value you want to pass. And not use the special `True` case. This makes the code more explicit and predictable.
 ````
 
 ## Values from Environment Variables

src/click/core.py

@@ -2606,15 +2606,6 @@ class Option(Parameter):
     :param hidden: hide this option from help outputs.
     :param attrs: Other command arguments described in :class:`Parameter`.
 
-    .. caution::
-        Flags specifying a ``flag_value`` and whose ``default=True`` will have
-        their ``default`` aligned to the ``flag_value``.
-
-        This means there is no way to setup a flag whose default ``True`` and
-        whose ``flag_value`` is something else than ``True``.
-
-        This is to support legacy behavior that will be removed in Click 9.0.
-
     .. versionchanged:: 8.2
         ``envvar`` used with ``flag_value`` will always use the ``flag_value``,
         previously it would use the value of the environment variable.
@@ -2742,23 +2733,13 @@ def __init__(
             if self.default is UNSET and not self.required:
                 self.default = False
 
-        # XXX Support the legacy case of aligning the default value with the flag_value
-        # for flags whose default is explicitly set to True. As long as we have this
-        # condition, there is no way a flag can have a default set to True, unless its
-        # flag_value itself is set to True. Refs:
+        # Support the special case of aligning the default value with the flag_value
+        # for flags whose default is explicitly set to True. Note that as long as we
+        # have this condition, there is no way a flag can have a default set to True,
+        # and a flag_value set to something else. Refs:
         # https://github.com/pallets/click/issues/3024#issuecomment-3146199461
-        # https://github.com/pallets/click/pull/3030/files#r2288936493
+        # https://github.com/pallets/click/pull/3030/commits/06847da
         if self.default is True and self.flag_value is not UNSET:
-            # This message is a convoluted way to explain that if you want things
-            # to be equal, make them equal.
-            # warnings.warn(
-            #     "A flag's `default` value will no longer be aligned with its "
-            #     "`flag_value` if `default=True` in Click 9.0. If you want the flag "
-            #     "to get the same `default` as its `flag_value`, update the option "
-            #     "to make its `default` parameter equal to its `flag_value`.",
-            #     DeprecationWarning,
-            #     stacklevel=2,
-            # )
             self.default = self.flag_value
 
         # Set the default flag_value if it is not set.
@@ -3070,11 +3051,14 @@ def prompt_for_value(self, ctx: Context) -> t.Any:
             # one.
             if default in (UNSET, None):
                 default = None
-            # Nothing prevent you to declare an option that is auto-detected as a
-            # boolean flag, is allow to prompt but still declare a non-boolean default.
-            # So with this casting, we aligns the default value to the prompt behavior.
-            # The prompt is going to default to [Y/n]), and so not entering a value for
-            # input is expected to make the option takes True as the default.
+            # Nothing prevent you to declare an option that is simultaneously:
+            # 1) auto-detected as a boolean flag,
+            # 2) allowed to prompt, and
+            # 3) still declare a non-boolean default.
+            # This forced casting into a boolean is necessary to align any non-boolean
+            # default to the prompt, which is going to be a [y/n]-style confirmation
+            # because the option is still a boolean flag. That way, instead of [y/n],
+            # we get [Y/n] or [y/N] depending on the truthy value of the default.
             # Refs: https://github.com/pallets/click/pull/3030#discussion_r2289180249
             else:
                 default = bool(default)

tests/test_basic.py

@@ -302,8 +302,8 @@ def cli(flag):
         (None, [], None),
         # Default is normalized to None if it is UNSET.
         (UNSET, [], None),
-        # Legacy case: if default=True and flag_value is set, The value returned is the
-        # flag_value, not default itself.
+        # Special case: if default=True and flag_value is set, the value returned is the
+        # flag_value, not the True Python value itself.
         (True, [], "upper"),
         # Non-string defaults are process as strings by the default Parameter's type.
         (False, [], "False"),

tests/test_options.py

@@ -1478,11 +1478,11 @@ def cmd(foo):
         ("xMl", [], "xMl"),
         (" ᕕ( ᐛ )ᕗ ", [], " ᕕ( ᐛ )ᕗ "),
         (None, [], None),
-        # Legacy case: UNSET is not exposed directly to the callback, but converted to
+        # Special case: UNSET is not provided as-is to the callback, but normalized to
         # None.
         (UNSET, [], None),
-        # Legacy case: if default=True and flag_value is set, The value returned is the
-        # flag_value, not default itself.
+        # Special case: if default=True and flag_value is set, the value returned is the
+        # flag_value, not the True Python value itself.
         (True, [], "js"),
         # Non-string defaults are process as strings by the default Parameter's type.
         (False, [], "False"),