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

Beginnen Sie damit, mypy auf dem bereitgestellten Python-Reproduktionsbeispiel für eine match-Anweisung auszuführen und es mit dem entsprechenden Beispiel für eine if-Anweisung zu vergleichen. Das Issue nennt weder eine Quelldatei noch einen Testpfad. Lokalisieren Sie daher den Einstiegspunkt für die Typverengung beim Pattern Matching und die relevanten Tests. Als erledigt gilt die Aufgabe, wenn alle vier Zweige a und b, wo zutreffend, auf str verengen, ohne Fehler.