[1.20 regression] "Unsupported operand types for |" with recursive type definition

[latentvoid]

Bug Report

When merging dicts with a value type that is union containing a recursive type (e.g. A = dict[str, A | int]), mypy incorrectly detects an "Unsupported operand types" error. This worked in version 1.19.1.

To Reproduce

type A = dict[str, A | int]		# can use arbitrary types instead of `str` and `int`

d1: A
d2: A
d3: A = {**d1, **d2}		# works
d4: A = d1 | d2		# equivalent to line above but fails
d5 = d1 | d2
d6: A = d5		# works (similar behavior to what was reported in https://github.com/python/mypy/issues/18236)

type B = dict[str, B]

d7: B
d8: B
d9: B = d7 | d8		# no union in type def works

type C = dict[str, float | int]

d10: C
d11: C
d12: C = d10 | d11		# no recursive type def works

Playground URL: https://mypy-play.net/?mypy=master&python=3.12&gist=1c39fc367614e2a0af2bd4d604c25aeb

The mypy playground seems to be bugged currently. Selecting version "mypy 1.20.0" results in HTTP 500 and "mypy latest (1.20.0)" does not reproduce the bug even though it should. "mypy master branch" does reproduce the bug.

Expected Behavior

None of the examples above should produce an error.

Actual Behavior

Mypy produces error: Unsupported operand types for | ("dict[str, A | int]" and "dict[str, A | int]") [operator]

Your Environment

• Mypy version used: 1.20.0
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.12.12, 3.12.13, 3.14.3

[hauntsaninja]

Thanks, this bisects to a change in typeshed #21021

[ilevkivskyi]

I have a wild guess this may be caused by a change in typeshed python/typeshed#14284. I will check later and if yes, I propose to revert that.

[hauntsaninja]

Probably python/typeshed#14284

[hauntsaninja]

Oh I'm too slow :-)