`type: ignore` only works when deleting mypy cache

[l0b0]

Bug Report

mypy reliably fails to take into account a type: ignore comment on the second run after deleting the cache.

To Reproduce

1. rm -r .mypy_cache
2. mypy .
3. mypy .

Expected Behavior

The second run of mypy should behave exactly the same as the first run.

Actual Behavior

$ rm -r .mypy_cache
$ mypy .
Success: no issues found in 23 source files
$ mypy .
infra/app.py:9: error: Skipping analyzing 'aws_cdk': found module but no type hints or library stubs
infra/datalake/datalake_stack.py:4: error: Skipping analyzing 'aws_cdk': found module but no type hints or library stubs
infra/datalake/datalake_stack.py:4: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
Found 2 errors in 2 files (checked 23 source files)

Some subsequent runs will succeed, but I've not looked into the pattern. I was able to run while pre-commit run --all-files mypy; do rm -r .mypy_cache; done a bunch of rounds without failure.

Your Environment

• Mypy version used: 0.790
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.8.6
• Operating system and version: Arch Linux

Relevant commit

Workaround

Add --no-incremental to the mypy arguments.

[hauntsaninja]

Fixed by #10937