`dict(...)` hides incompatible assignment when source has `Any` key type

Bug Report

Using dict(...) around an otherwise incompatible mapping structure leads mypy to omit errors about the type incompatibility. My original code called dict on a collections.defaultdict, though that doesn't seem to be required to reproduce this.

To Reproduce

from typing import Any, Dict

foo: Dict[str, str]
bar: Dict[Any, int] = {}
foo = bar  # Incompatible types in assignment (expected, correct)
foo = dict(bar)  # no error (unexpected, IMO incorrect)

This seems to be related to the fact that the key type is Any. Changing the key to int causes an error on both assignment lines (even if the value type is Any).

Your Environment

• Mypy version used: 0.812
• Mypy command-line flags: none needed, though notable that --strict doesn't affect this
• Python version used: 3.7.10
• Operating system and version: Ubuntu 20.04

Nel report non sono indicati né un file sorgente né un test. Inizia eseguendo la riproduzione fornita con mypy 0.812, quindi traccia il modo in cui dict(...) inferisce i mapping quando il tipo della chiave sorgente è Any. Aggiungi un test di regressione che copra l'assegnazione segnalata e verifica che l'assegnazione incompatibile venga diagnosticata.