Matching on boolean expressions does not narrow based on the content of the boolean expression

Bug Report

When doing pattern matching with types, the match statement might be more readable than multiple if statements

match (a is None, b is None):
    case (True, True):
        ...
    case (True, False):
        ...
    case (False, True):
        ...
    case (False, False):
        ...

instead of

if a is None and b is None:
    ...
if a is None and b is not None:
    ...
if a is not None and b is None:
    ...
if a is not None and b is not None:
    ...

However, mypy is not able to infer types from the match statements like it is from if statements.

To Reproduce

Infer types using a match statement:

def example_with_match(a: str | None, b: str | None) -> str:
    match (a is None, b is None):
        case (True, True):
            return ""
        case (True, False):
            return b
        case (False, True):
            return a
        case (False, False):
            return a + b

    raise RuntimeError  # unreachable

Gist

Expected Behavior

Like in the equivalent using if statements (there are no mypy errors)

def example_with_if(a: str | None, b: str | None) -> str:
    if a is None and b is None:
        return ""
    if a is None and b is not None:
        return b
    if a is not None and b is None:
        return a
    if a is not None and b is not None:
        return a + b

    raise RuntimeError  # unreachable

Gist

Actual Behavior

whatever.py:6: error: Incompatible return value type (got "str | None", expected "str")  [return-value]
whatever.py:8: error: Incompatible return value type (got "str | None", expected "str")  [return-value]
whatever.py:10: error: Unsupported operand types for + ("str" and "None")  [operator]
whatever.py:10: error: Unsupported left operand type for + ("None")  [operator]

Your Environment

• Mypy version used: 1.15.0
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files):

[tool.mypy]
check_untyped_defs = true
no_implicit_optional = true
show_error_codes = true
warn_redundant_casts = true
warn_unreachable = true
python_version = "3.12"
ignore_missing_imports = true

• Python version used: 3.12.8

Inizia eseguendo mypy sul riproduttore Python fornito per un’istruzione match e confrontalo con l’esempio equivalente che usa un’istruzione if. L’issue non indica alcun file sorgente né alcun percorso dei test, quindi individua il punto di ingresso del restringimento dei tipi per il pattern matching e i test pertinenti. Il lavoro è completato quando tutti e quattro i rami restringono a e b a str dove appropriato, senza errori.