Do not consider ‘import a.b as b’ an explicit reexport

The point of the ‘import a as a’ and ‘from a import b as b’ syntax for
explicit reexport is that it indicates an intention to do something
different from the ordinary ‘import a’ and ‘from a import b’.

That is not the case with ‘import a.b as b’.  Even mypy’s own code
includes ‘import mypy.types as types’, which was not intended to be a
reexport; if it were, it would be written ‘from mypy import types as
types’.

Pyright agrees that ‘import a.b as b’ should not reexport.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

Author: andersk

mypy/semanal.py

@@ -2230,7 +2230,7 @@ def visit_import(self, i: Import) -> None:
             if as_id is not None:
                 base_id = id
                 imported_id = as_id
-                module_public = use_implicit_reexport or id.split(".")[-1] == as_id
+                module_public = use_implicit_reexport or id == as_id
             else:
                 base_id = id.split(".")[0]
                 imported_id = base_id

test-data/unit/check-modules.test

@@ -1809,6 +1809,7 @@ m = n  # E: Cannot assign multiple modules to name "m" without explicit "types.M
 from stub import Iterable  # E: Module "stub" does not explicitly export attribute "Iterable"
 from stub import D  # E: Module "stub" does not explicitly export attribute "D"
 from stub import C
+from stub import path  # E: Module "stub" does not explicitly export attribute "path"
 
 c = C()
 reveal_type(c.x)  # N: Revealed type is "builtins.int"
@@ -1819,6 +1820,7 @@ reveal_type(it)  # N: Revealed type is "typing.Iterable[builtins.int]"
 from typing import Iterable
 from substub import C as C
 from substub import C as D
+import os.path as path
 
 def fun(x: Iterable[str]) -> Iterable[int]: pass