quantity_input decorator is un-typed

[dstansby]

Description

I'm trying to add typing to some code I use with Quantity input.ouput. Using the u.quantity_input decorator errors with mypy though, complaining that the decorator is untyped.

Expected behavior

No complaint from mypy

Actual behavior

mypy errors with

test.py:3: error: Untyped decorator makes function "speed" untyped
Found 1 error in 1 file (checked 1 source file)

Steps to Reproduce

1. Save the following code to file
2. run mypy --strict test.py

import astropy.units as u

@u.quantity_input
def speed(distance: u.m, time: u.s) -> u.Quantity:
    return distance / time

System Details

macOS-12.6.1-arm64-arm-64bit
Python 3.10.8 | packaged by conda-forge | (main, Nov 22 2022, 08:25:29) [Clang 14.0.6 ]
Numpy 1.23.4
pyerfa 2.0.0.1
astropy 5.1.1
Scipy 1.9.3
Matplotlib 3.6.2
mypy 0.982 (compiled: yes)

[eerovaher]

See #14134 (comment)

[mhvk]

For quantity_input, @nstarman had a nice PR but it became a bit messy; see #10655 and hence that was closed. So far, what has been implemented is the part that one can do Quantity[unit] (#10662)

[nstarman]

Yeah. Typing quantity_input wouldn't actually be all that hard. I would welcome a PR. The underlying issues are that we are hesitant to add a lot of typing before an APE.

[Cadair]

I will just reiterate from #14134 that quantity_inputs existing use of function annotations as not-type-hints is perfectly legitimate and should remain supported even if it learns how to read valid type hints in addition.