Context different in `click.pass_context` and `shell_complete`

Discussed in https://github.com/pallets/click/discussions/2302

^{Originally posted by amal-thundiyil June 2, 2022}

Description

• The click.core.Context is different in click.pass_context and shell_complete.
• Related to click (issue) #942 and click (discussion) #2170

Steps to reproduce

1. Run pip install . in the folder with yourscript.py and setup.py in a virtual environment.
2. Setup shell completion by following the docs.
3. Run yourscript clone and notice output without errors.
4. Run youscript clone and press <TAB> for shell completion and see the error.

File name: yourscript.py

import os
import click


class Repo(object):
    def __init__(self, home=None, debug=False):
        self.home = os.path.abspath(home or ".")
        self.debug = debug


def tab_completer(ctx, param, incomplete):
    return [ctx.obj.home]


@click.group()
@click.pass_context
def cli(ctx):
    ctx.obj = Repo()


@cli.command()
@click.argument("option", shell_complete=tab_completer, required=False)
@click.pass_context
def clone(ctx, option):
    click.echo(ctx.obj.home)

File name: setup.py

from setuptools import setup

setup(
    name="yourscript",
    version="0.1",
    py_modules=["yourscript"],
    install_requires=[
        "Click",
    ],
    entry_points="""
        [console_scripts]
        yourscript=yourscript:cli
    """,
)

Stack trace:

  File "/home/amal/Documents/random/click-test/venv/bin/yourscript", line 11, in <module>
    load_entry_point('yourscript==0.1', 'console_scripts', 'yourscript')()
  File "/home/amal/Documents/random/click-test/venv/lib/python3.8/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/home/amal/Documents/random/click-test/venv/lib/python3.8/site-packages/click/core.py", line 1050, in main
    self._main_shell_completion(extra, prog_name, complete_var)
  File "/home/amal/Documents/random/click-test/venv/lib/python3.8/site-packages/click/core.py", line 1125, in _main_shell_completion
    rv = shell_complete(self, ctx_args, prog_name, complete_var, instruction)
  File "/home/amal/Documents/random/click-test/venv/lib/python3.8/site-packages/click/shell_completion.py", line 49, in shell_complete
    echo(comp.complete())
  File "/home/amal/Documents/random/click-test/venv/lib/python3.8/site-packages/click/shell_completion.py", line 291, in complete
    completions = self.get_completions(args, incomplete)
  File "/home/amal/Documents/random/click-test/venv/lib/python3.8/site-packages/click/shell_completion.py", line 273, in get_completions
    return obj.shell_complete(ctx, incomplete)
  File "/home/amal/Documents/random/click-test/venv/lib/python3.8/site-packages/click/core.py", line 2397, in shell_complete
    results = self._custom_shell_complete(ctx, self, incomplete)
  File "/home/amal/Documents/random/click-test/yourscript.py", line 12, in tab_completer
    return [ctx.obj.home]
AttributeError: 'NoneType' object has no attribute 'home'

Expected Result

Output should tab complete to print out the current directory to the console.

Versions

• Click version: 8.1.3
• Python version: 3.8

Trace shell completion from click/core.py through click/shell_completion.py, comparing the context passed to click.pass_context and the tab_completer callback. Reproduce the example with yourscript.py and shell completion, then inspect the related discussions and issues for intended context behavior. Done means the provided completion callback can access the expected context and the reproduction no longer raises AttributeError.