Fix: support absolute filename in preprocessor

[JounQin]

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What changes did you make? (Give an overview)

fix #11989 (comment)

Is there anything you'd like reviewers to focus on?

[eslint-github-bot]

Hi @JounQin!, thanks for the Pull Request

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[mdjermanovic]

We intentionally don't allow absolute paths, because the processor can then return any path, while it must be a child file of the original file, as specified in the Specifying Processor user documentation:

ESLint handles such a named code block as a child file of the original file. You can specify additional configurations for named code blocks in the overrides section of the config.

The returned path also shouldn't contain any path separators (e.g., ../filename.js or \dir\filename.js).

[JounQin]

This limitation breaks rules which require file exist like typescript-eslint/typescript-eslint#3174

I was thinking to create a temporary file for typescript-eslint.

I don't understand why it should be limited, what's the benif?

[mdjermanovic]

I don't understand why it should be limited, what's the benif?

• Expected behavior, so that users can configure overrides accordingly, knowing that the exported code blocks are child paths.
• Performance. If the path can be anything, our config system would have to determine the configuration for a path that might be unrelated to the original path, and that may include config files lookup.

[JounQin]

OK, fair enough to me. Let's continue to discuss it on the original issue for getting real path.