exclude should imply a per-module follow import skip for matching modules

Bug Report

I recently converted this project (linked to at the most recent commit) from a plain script to a Python package. This included adding an un-annotated _version.py file generated by versioneer to the package. mypy (when run as mypy src) now reports errors due to _version.py lacking any type annotations, and I cannot get it to ignore that file.

What I've tried:

• Adding exclude = _version.py to the [mypy] section in setup.cfg
• Adding exclude = src/tinuous/_version.py to the [mypy] section
• Adding exclude = src/tinuous/_(version|_init__).py to the [mypy] section
• Running just mypy src/tinuous/__main__.py
• Running mypy --exclude _version.py src

In all of these cases, mypy spits out errors relating to _version.py even though I thought I told it to ignore that file.

Your Environment

• Mypy version used: 0.812
• Mypy command-line flags: --exclude or nothing
• Mypy configuration options from mypy.ini (and other config files):

[mypy]
ignore_missing_imports = True
disallow_untyped_defs = True
disallow_incomplete_defs = True
no_implicit_optional = True
warn_redundant_casts = True
warn_return_any = True
warn_unreachable = True
local_partial_types = True
no_implicit_reexport = True
strict_equality = True
show_error_codes = True
show_traceback = True
pretty = True
plugins = pydantic.mypy
# Various "exclude" options (see above)

• Python version used: 3.9.4
• Operating system and version: macOS 11.2.1

Reproduce the report with mypy 0.812 using mypy src and the exclude settings shown in setup.cfg or mypy.ini, focusing on src/tinuous/_version.py. Trace how --exclude and imported modules are handled, then verify that matching modules are skipped without errors while other modules in src are still checked.