Strange case with deepcopy() and Literal[True]

[jolaf]

The following code:

from copy import deepcopy
from typing import Literal, Union

def f(a: str, b: bool) -> Union[Literal[True], str]:
    return b or deepcopy(a)

print(f("abc", False))
print(f("abc", True))

produces the following output:

$ python3 test.py
abc
True

$ mypy test.py
test.py: note: In function "f":
test.py:5:12: error: Incompatible return value type (got "bool", expected "Union[Literal[True], str]")  [return-value]
        return b or deepcopy(a)
               ^
test.py:5:26: error: Argument 1 to "deepcopy" has incompatible type "str"; expected "bool"  [arg-type]
        return b or deepcopy(a)
                             ^
Found 2 errors in 1 file (checked 1 source file)

$ python3 --version
Python 3.8.10

$ mypy --version
mypy 0.931

$ cat /etc/issue
Ubuntu 20.04.3 LTS \n \l

$ uname -a
Linux ubuntu 5.4.0-94-generic #106-Ubuntu SMP Thu Jan 6 23:58:14 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

If deepcopy() call is removed, warnings go away.

In some similar cases only the second warning appears, which looks even weirder.

[brianschubert]

Related / duplicate of #10696, just using or instead of and. Both issues have to do with bidirectional inference going awry when analyzing the right operand using the type of the left operand as the type context.