`--verifytypes` sometimes reports imported symbol as partially unknown, despite `--ignoreexternal`

[MarcoGorelli]

Describe the bug

If I write an annotation using sqlalchemy and then using --verifytypes with --ignoreexternal, the sqlalchemy symbol may still end up being reported as unknown, depending on how the annotation was written

Code or Screenshots

My file foo/__init__.py:

class NDFrame:
    def to_sql_1(
        self,
        con,
    ) -> None:
        return None

    def to_sql_2(
        self,
        con,
    ) -> None:
        return None

My file foo/__init__.pyi:

from sqlalchemy.engine import Connectable
import sqlalchemy.engine


class NDFrame:
    def to_sql_1(
        self,
        con: str | Connectable,
    ) -> None: ...

    def to_sql_2(
        self,
        con: str | sqlalchemy.engine.Connectable,
    ) -> None: ...

The annotations should in theory be identical, as far as I understand.

However, if I run pyright --verifytypes foo --ignoreexternal, I get:

Module name: "foo"
Package directory: "/home/marcogorelli/tmp-repo/foo"
Module directory: "/home/marcogorelli/tmp-repo/foo"
Path of py.typed file: "/home/marcogorelli/tmp-repo/foo/py.typed"

Public modules: 1
   foo

Symbols used in public interface:
foo.NDFrame.to_sql_2
  /home/marcogorelli/tmp-repo/foo/__init__.pyi:11:9 - error: Type of parameter "con" is partially unknown
    Parameter type is "str | Unknown"

Symbols exported by "foo": 3
  With known type: 1
  With ambiguous type: 0
  With unknown type: 2
    (Ignoring unknown types imported from other packages)

Other symbols referenced but not exported by "foo": 0
  With known type: 0
  With ambiguous type: 0
  With unknown type: 0

Symbols without documentation:
  Functions without docstring: 2
  Functions without default param: 0
  Classes without docstring: 1

Type completeness score: 33.3%

Completed in -0.202sec

Note how:

• con is treated fine (ignored by --ignoreexternal) in to_sql_1
• but not in to_sql_2 where it shows Type of parameter "con" is partially unknown

VS Code extension or command-line

$ pyright --version
pyright 1.1.407