Type is not narrowed in walrus conditional

[layday]

Describe the bug
This is another issue that was raised on the mypy tracker that also affects Pyright. Conditionals of assignment expressions are not narrowed for type, producing errors like this one:

{
	"resource": "test.py",
	"owner": "_generated_diagnostic_collection_name_#0",
	"severity": 8,
	"message": "'foo' is not a known member of 'None'",
	"source": "pyright (reportOptionalMemberAccess)",
	"startLineNumber": 16,
	"startColumn": 11,
	"endLineNumber": 16,
	"endColumn": 14
}

To Reproduce
Type check the snippet below.

Expected behavior
That a would not be None under the bad conditional.

Screenshots or Code

# pyright: strict

from typing import Optional

class C:
    def foo(self):
        pass

def good(b: Optional[C]) -> None:
    a = b
    if a:
        a.foo()

def bad(b: Optional[C]) -> None:
    if a := b:
        a.foo()

VS Code extension or command-line
extension, 1.1.17

Additional context
See python/mypy#7316.

[erictraut]

Thanks for the bug report. This will be addressed in the next version of Pyright.

[erictraut]

This support is now included in 1.1.19, which I just published.

[alexkoay]

There might be a regression with this.

import re
def foo(s: str) -> str:
	if m := re.fullmatch('(test).+', s):
		return m.group(1)
	return 'oops'

group reports a reportOptionalMemberAccess error under Pyright 1.1.38.