[flake8-type-checking] Skip quoting annotation if it becomes invalid syntax (TCH001)

[Glyphack]

Fix: #13934

Summary

Current implementation has a bug when the current annotation contains a string with single and double quotes.

TL;DR: I think these cases happen less than other use cases of Literal. So instead of fixing them we skip the fix in those cases.

One of the problematic cases:

from typing import Literal
from third_party import Type

def error(self, type1: Type[Literal["'"]]):
    pass

The outcome is:

- def error(self, type1: Type[Literal["'"]]):
+ def error(self, type1: "Type[Literal[''']]"):

While it should be:

"Type[Literal['\'']"

The solution in this case is that we check if there’s any quotes same as the quote style we want to use for this Literal parameter then escape that same quote used in the string.

Also this case is not uncommon to have: https://grep.app/search?current=2&q=Literal["'

But this can get more complicated for example in case of:

- def error(self, type1: Type[Literal["\'"]]):
+ def error(self, type1: "Type[Literal[''']]"):

Here we escaped the inner quote but in the generated annotation it gets removed. Then we flip the quote style of the Literal paramter and the formatting is wrong.

In this case the solution is more complicated.

1. When generating the string of the source code preserve the backslash.
2. After we have the annotation check if there isn’t any escaped quote of the same type we want to use for the Literal parameter. In this case check if we have any ’ without \ before them. This can get more complicated since there can be multiple backslashes so checking for only \’ won’t be enough.

Another problem is when the string contains \n. In case of Type[Literal["\n"]] we generate 'Type[Literal["\n"]]' and both pyright and mypy reject this annotation.
https://pyright-play.net/?code=GYJw9gtgBALgngBwJYDsDmUkQWEMoAySMApiAIYA2AUAMaXkDOjUAKoiQNqsC6AXFAB0w6tQAmJYLBKMYAfQCOAVzCk5tMChjlUjOQCNytANaMGjABYAKRiUrAANLA4BGAQHJ2CLkVIVKnABEADoogTw87gCUfNRQ8VAITIyiElKksooqahpaOih6hiZmTNa29k7w3m5sHJy%2BZFRBoeE8MXEJScxAA

Test Plan

I added test cases for the original code in the reported issue and two more cases for backslash and new line.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[Glyphack]

Hi @dhruvmanila I spent some time on finding the issue and the fix and wrote it down below. I'm not sure if it's okay to skip fixing these tricky cases
but would be happy to find a better one with your guidance.
Let me know what you think.

[dhruvmanila]

Hey, thanks for looking into this and opening this PR.

I think the solution for now would be to avoid providing a fix if the annotation contains the preferred quote (the one used in to surround the annotation in the fix) or if it contains any escape characters like a newline character. Although Pyright supports them, the initial implementation for string annotations in red knot will reject them (#14151). There's also this discussion about the different string kinds here.

I think that's what this PR is doing right now based on looking at the snapshot changes, right?

[Glyphack]

Yes @dhruvmanila this will skip the fix for those scenarios. sorry the point was not clear in the description.

[dhruvmanila]

Thanks for looking into this.

[dhruvmanila]

(I updated the PR to get it into the next release.)