Use alias names in error messages

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#2,968 4 comments 11 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start by reproducing the supplied tmp.py example with mypy and inspect how its diagnostic renders the expected type. Trace the relevant type-alias and error-reporting entry points, then verify that diagnostics use the alias name while also showing its expansion, without changing unrelated messages.

Written by the indexing model from the issue text.

Description

feature priority-1-normal topic-type-alias topic-usability

Given:

from typing import Tuple
from math import hypot

Point = Tuple[float, ...]
Centroid = Point

def dist(p: Centroid, q: Point) -> float:
    px, py = p
    qx, qy = q
    return hypot(px - qx, py - qy)

print( dist('xyz', (3.5, 7.2)) )

mypy detect the incorrect first argument:

$ mypy tmp.py
tmp.py:12: error: Argument 1 to "dist" has incompatible type "str"; expected Tuple[float, ...]

However, it would be much nicer is the error reporting could have used the alias name:

tmp.py:12: error: Argument 1 to "dist" has incompatible type "str"; expected "Centroid", which expands to Tuple[float, ...]

I realize it may be easy to do, but it would improve the usability of aliases.

Dominant language
Python
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