`no-redef` when `import`-importing a module to satisfy a protocol

[asottile]

Bug Report

modules-as-protocols triggers "no-redef" when using import-imports, but is fine with from-imports

(I'm testing out this unreleased feature on the primary branch)

# main.py
import os
from typing import Protocol

class P(Protocol):
    def f(self) -> str: ...

t: P
if os.environ.get('ENV') == 'prod':
    import t as t  # Name "t" already defined on line 7  [no-redef]
else:
    import u as t  # Name "t" already defined on line 7  [no-redef]

# t.py and u.py
def f() -> str:
    return ''

the errors triggered are inline above

oddly enough, a from import seems to work fine (so there's an easy workaround if the module isn't top-level):

mkdir y
touch y/__init__.py
mv {t,u}.py y

import os
from typing import Protocol

class P(Protocol):
    def f(self) -> str: ...

t: P
if os.environ.get('ENV') == 'prod':
    from y import t as t  # no errors!
else:
    from y import u as t  # no errors!

Your Environment

• Mypy version used: mypy 0.990+dev.dc5c299aa190949f2300b163ccc10257a779006d (compiled: no)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10.6

[hauntsaninja]

Thanks for the report!

Note mainly for self: looks like the difference is between add_symbol_table_node

mypy/mypy/semanal.py

Line 5457 in ddd9177

if (

and process_imported_symbol

mypy/mypy/semanal.py

Line 2309 in ddd9177

existing_symbol = self.globals.get(imported_id)

. It's not obvious to me why process_import_over_existing_name isn't called for normal imports, but just changing that should probably fix

[hauntsaninja]

Thanks for reporting! This should now be fixed on master, but isn't part of the 0.990 release.