False positive for PEP 604 `None | t` when used as value

[NiklasRosenstein]

Bug Report

Using None | t instead of t | None prompts an error when used as a value (not a type hint).

https://peps.python.org/pep-0604/#proposal

To Reproduce

a: None | int
b = None | int  # error: Unsupported left operand type for | ("None")  [operator]

Expected Behavior

Mypy does not complain about the second line.

Your Environment

• Mypy version used: 90.940
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):

  pretty = true
  namespace_packages = true
  warn_redundant_casts = true
  warn_no_return = true
  warn_unreachable = true
  show_error_context = true
  show_error_codes = true
  check_untyped_defs = true

• Python version used: 3.10.2
• Operating system and version: Ubuntu 20.04 WSL

[jhance]

I assume this means that isinstance(5, None | int) fails, which seems like a major bug.

[NiklasRosenstein]

@jhance Your assumption is correct.

[KotlinIsland]

This looks similar to other raised issues 🤔

#12005
#11673, #12363
#11582 (kind of the opposite of this issue)
#11426

a: None | int
b = None | int # error: Unsupported left operand type for | ("None")
isinstance(5, None | int) # error: Unsupported left operand type for | ("None")

playground

#12369 is probably related as well.