Unable to find a matching function overload

[schperplata]

Issue Type: Question
Is there anything obviously wrong with my type hints that VSC complains about: No overloads for "colorize(data, 'red')" match parameters?

@overload
def colorize(data: str, color: str) -> str: ...
@overload
def colorize(data: List[str], color: str) -> List[str]: ...

def colorize(data: Union[List[str], str], color: str) -> Union[List[str], str]:
    if isinstance(data, list):
        if len(data):
            data[0] = f"<div style=\"color: {color};\">{data[0]}"
            data[-1] = f"{data[-1]}</div>"
    else:
        data = f"<span style=\"color: {color};\">{data}</span>"

    return data


@overload
def inRedColor(data: str) -> str: ...
@overload
def inRedColor(data: List[str]) -> List[str]: ...


def inRedColor(data: Union[List[str], str]) -> Union[List[str], str]:
    return colorize(data, 'red')

Error:

Extension version: 2020.10.3
VS Code version: Code 1.50.1 (d2e414d9e4239a252d1ab117bd7067f125afd80a, 2020-10-13T15:06:15.712Z)
OS version: Windows_NT x64 10.0.18363

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz (8 x 2712)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on oop_rasterization: disabled_off opengl: enabled_on protected_video_decode: unavailable_off rasterization: enabled skia_renderer: disabled_off_ok video_decode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	15.92GB (5.83GB free)
Process Argv	W:\AsystLib\isys\python\VSCodeDevWorkspace_refactor.code-workspace --crash-reporter-id 919e0ed9-46f3-4ad4-9e28-f35755bf8266
Screen Reader	no
VM	0%

[erictraut]

This is related to this issue: microsoft/pyright#1119

It speaks to a subtle difference between the way pyright/pylance handle overloads versus mypy. We've talked about possibly switching to a behavior that is consistent with mypy, but it's a big code change and has potential significant performance impact.

[erictraut]

You can easily work around the issue by adding a third overload:

@overload
def colorize(data: Union[List[str], str], color: str) -> Union[List[str], str]: ...

[erictraut]

Reopening this issue. We've received a sufficient number of bug reports about the overload matching behavior that I decided to change the behavior to more closely match mypy's. This eliminates the need for workarounds like the one I posted above. This change will be in the next version of pylance.

[jakebailey]

This issue has been fixed in version 2021.4.3, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202143-29-april-2021