Click 8.2.2 breaks auto-reloader-active on flask --debug

[liffiton]

On upgrading click to version 8.2.2, flask --debug run no longer automatically enables the reloader. If I downgrade click to 8.2.1, it works again.

$ uv pip install flask
Using Python 3.13.2 environment at: venv
Resolved 7 packages in 2ms
Installed 7 packages in 3ms
 + blinker==1.9.0
 + click==8.2.2
 + flask==3.1.1
 + itsdangerous==2.2.0
 + jinja2==3.1.6
 + markupsafe==3.0.2
 + werkzeug==3.1.3

$ cat app.py 
from flask import Flask

app = Flask(__name__)

if __name__ == '__main__':
    app.run()

$ flask run --debug
 * Debug mode: on
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on http://127.0.0.1:5000
Press CTRL+C to quit
^C

$ uv pip install click==8.2.1
Using Python 3.13.2 environment at: venv
Resolved 1 package in 1ms
Uninstalled 1 package in 0.65ms
Installed 1 package in 1ms
 - click==8.2.2
 + click==8.2.1

$ flask run --debug
 * Debug mode: on
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on http://127.0.0.1:5000
Press CTRL+C to quit
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 575-957-529

[From my trace, it looks like the issue affects the debugger as well, but I haven't been using or testing that.]

This appears to be connected to #2952, but I'm not sure if the issue is now in click or in how flask is using click.

The issue occurs because the --reload/--no-reload option is now defaulting to False when it is not specified on the command line, meaning the if reload is None: condition is not triggered to activate the reloader based on the debug flag.

Environment:

• Python version: 3.13.3
• Flask version: 3.1.1

[davidism]

@kdeldycke @Rowlando13 we'll need to fix this and add a test for it. I'm assuming the fix started setting False instead of None when not present at all.

[davidism]

Moved this to Click as I'm fairly sure it's Click that needs to change, not Flask, but if you discover otherwise I can move it back.

[davidism]

default=None needs to continue to work with --reload/--no-reload boolean flags, to indicate that the flag wasn't given. Essentially, there's three states to the flag, not two, if default=None.

[edgarrmondragon]

Maybe related, but let me know if you'd prefer I create a separate issue:

The flag value example in the docs is broken:

import click
import sys

@click.command()
@click.option('--upper', 'transformation', flag_value='upper', default=True)
@click.option('--lower', 'transformation', flag_value='lower')
def info(transformation):
    click.echo(f"{transformation=} ({type(transformation)=})")
    click.echo(getattr(sys.platform, transformation)())


if __name__ == "__main__":
    info()

with 8.2.1, it outputs

transformation='upper' (type(transformation)=<class 'str'>)
DARWIN

but with 8.2.2

transformation='True' (type(transformation)=<class 'str'>)
Traceback (most recent call last):
  File "/Users/me/Arch/meltano/repro.py", line 17, in <module>
    info()
    ~~~~^^
  File "/Users/me/.cache/uv/environments-v2/repro-5f3657bf1e3afc32/lib/python3.13/site-packages/click/core.py", line 1442, in __call__
    return self.main(*args, **kwargs)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/me/.cache/uv/environments-v2/repro-5f3657bf1e3afc32/lib/python3.13/site-packages/click/core.py", line 1363, in main
    rv = self.invoke(ctx)
  File "/Users/me/.cache/uv/environments-v2/repro-5f3657bf1e3afc32/lib/python3.13/site-packages/click/core.py", line 1226, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/me/.cache/uv/environments-v2/repro-5f3657bf1e3afc32/lib/python3.13/site-packages/click/core.py", line 794, in invoke
    return callback(*args, **kwargs)
  File "/Users/me/Arch/meltano/repro.py", line 13, in info
    click.echo(getattr(sys.platform, transformation)())
               ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'str' object has no attribute 'True'

[sridharam]

Seeing similar issue for semgrep --version command

semgrep --version
python3.13/site-packages/opentelemetry/instrumentation/dependencies.py:4: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
  from pkg_resources import (
Usage: semgrep --version [OPTIONS] [TARGETS]...

Error: Invalid value for '--pro': False

Steps to reproduce.

1. pip3 install semgrep==1.99.0
2. semgrep --version

Could it be because of the fix #2956
cc: @kdeldycke

[jwodder]

Here's another, related breaking case to consider:

from enum import Enum
import click

Mode = Enum("Mode", "FOO BAR")


@click.command()
@click.option("--foo", "mode", flag_value=Mode.FOO, type=click.UNPROCESSED)
@click.option("--bar", "mode", flag_value=Mode.BAR, type=click.UNPROCESSED)
def main(mode: Mode | None) -> None:
    print(repr(mode))


if __name__ == "__main__":
    main()

Prior to click 8.2.2, running this with no options prints None, but using click 8.2.2 causes False to be output instead.

[jwodder]

Another case:

from typing import Any
import click

#: A sentinel object used to disable reading from a configuration file
NO_CONFIG = object()


class ConfigParamType(click.ParamType):
    """
    Like ``click.Path(exists=True, dir_okay=False)``, except that `NO_CONFIG`
    is also allowed as a value
    """

    name = "config"

    def convert(
        self,
        value: Any,
        param: click.Parameter | None,
        ctx: click.Context | None,
    ) -> Any:
        if value is NO_CONFIG:
            return value
        else:
            return click.Path(exists=True, dir_okay=False).convert(value, param, ctx)


@click.command()
@click.option(
    "-c",
    "--config",
    type=ConfigParamType(),
    help="Use the specified configuration file",
)
@click.option(
    "--no-config",
    "config",
    flag_value=NO_CONFIG,
    type=ConfigParamType(),
    help="Do not read from a configuration file",
)
def main(config: Any) -> None:
    if config is NO_CONFIG:
        print("NO_CONFIG")
    else:
        print(repr(config))


if __name__ == "__main__":
    main()

Prior to click 8.2.2, running this with no options prints None, but under click 8.2.2, the script fails with:

/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/types.py:983: RuntimeWarning: bool is used as a file descriptor
  st = os.stat(rv)
Traceback (most recent call last):
  File "/Users/jwodder/work/sand/python/libraries/click/no-config.py", line 50, in <module>
    main()
    ~~~~^^
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 1442, in __call__
    return self.main(*args, **kwargs)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 1362, in main
    with self.make_context(prog_name, args, **extra) as ctx:
         ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 1186, in make_context
    self.parse_args(ctx, args)
    ~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 1197, in parse_args
    value, args = param.handle_parse_result(ctx, opts, args)
                  ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 2416, in handle_parse_result
    value = self.process_value(ctx, value)
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 2349, in process_value
    value = self.type_cast_value(ctx, value)
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 2337, in type_cast_value
    return convert(value)
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/core.py", line 2309, in convert
    return self.type(value, param=self, ctx=ctx)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/types.py", line 90, in __call__
    return self.convert(value, param, ctx)
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/Users/jwodder/work/sand/python/libraries/click/no-config.py", line 25, in convert
    return click.Path(exists=True, dir_okay=False).convert(value, param, ctx)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/var/folders/l7/wrkq93d133d8zpn36fmqrq0r0000gn/T/pip-run-nyrvu7if/click/types.py", line 1012, in convert
    if self.readable and not os.access(rv, os.R_OK):
                             ~~~~~~~~~^^^^^^^^^^^^^
TypeError: access: path should be string, bytes or os.PathLike, not bool