Dmypy crashes when adding import and rechecking

Crash Report

Daemon crashes after adding an import flask statement and re-checking.

Traceback

Daemon crashed!
Traceback (most recent call last):
  File "mypy/dmypy_server.py", line 221, in serve
  File "mypy/dmypy_server.py", line 264, in run_command
  File "mypy/dmypy_server.py", line 323, in cmd_run
  File "mypy/dmypy_server.py", line 385, in check
  File "mypy/dmypy_server.py", line 564, in fine_grained_increment_follow_imports
  File "mypy/dmypy_server.py", line 679, in find_reachable_changed_modules
KeyError: 'jinja2'

To Reproduce

mkdir test && cd test
touch hi.py
dmypy run -- . # works
echo "import flask" > hi.py
dmypy run -- . # crashes
dmypy run -- . # works

Note that flask is not installed.

Your Environment

• Mypy version used: 0.800
• Mypy command-line flags: dmypy run -- .
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.9.1
• Operating system and version: macOS 10.15.7

Empieza por mypy/dmypy_server.py y sigue cmd_run, check, fine_grained_increment_follow_imports y find_reachable_changed_modules usando la reproducción proporcionada. Investiga la búsqueda ausente de 'jinja2' después de añadir una importación de flask no disponible; se considera terminado cuando la ejecución repetida de dmypy ya no se bloquea.