Mypy hangs indefinitely trying to analyse a file with huge nested dicts

[AlexWaygood]

Bug Report

Mypy hangs indefinitely when trying to analyse a file with huge nested dicts.

To Reproduce

1. Copy and paste the contents of this file into a .py file: repro.txt
2. Run mypy on the file
3. Wait

Comments

This is similar to #14636. However, the dicts aren't nearly as deeply nested as in #14636, they're just very, very big.

The dicts are so huge because this is a partially generated file, the result of a codemod by stubdefaulter. Mypy is far from the only tool to have difficulty with this file: it also made black and flake8 hang, and crashed IDLE. Pyright did manage to analyse the file, but also took a lot longer than usual.

Your Environment

• Mypy version used: 1.1.1; also master branch @ 2e75cbaa8e5c0fb8aa3548d5c7c8ccfd00131057
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.11.2

[dgellow]

We are facing this exact issue for a ~10k lines dictionary we codegen. Pyright and other tools don't have issues.

[njgrisafi]

+1 seeing most performance hits come from deeply nested dictionaries.

[ilevkivskyi]

Mypy compiled on current master type-checks the original 15MB file in under 10 sec. I don't think we need to keep this open.

[AlexWaygood]

Nice!