Fixes catastrophic backtracking for long strings of spaces

[caliskanmehmet]

Solves #473

With a very long input of spaces and the current CODE_BLOCK_R regex, the number of possible combinations becomes huge, causing the regex engine to take an extremely long time to test the input. This small change to the regex reduces the backtracking and prevents catastrophic backtracking when faced with a long string of spaces.

Tester for catastrophic backtracing: https://regex101.com/r/85LH2r/1
Reproduction: https://stackblitz.com/edit/markdown-to-jsx-reproduction-473?file=src%2FApp.tsx

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[quantizor]

Thank you! Could you add a changeset please?

[caliskanmehmet]

Hey @quantizor, thanks for the review!

Unfortunately, I've discovered that the new regex doesn't conform to the CommonMark specs and fails the test case below.

it('should not interrupt paragraphs', () => {
  render(compiler('foo\n    bar'))

  expect(root.innerHTML).toMatchInlineSnapshot(`
    <p>
      foo
        bar
    </p>
  `)
})

- Snapshot  -  4
+ Received  + 10

- <p>
+ <div>
+   <p>
-   foo
+     foo
-     bar
- </p>
+   </p>
+   <pre>
+     <code>
+       bar
+     </code>
+   </pre>
+ </div>

I think changing the regex won't be the final solution here, and the block parsing algorithm should be improved to handle indented code blocks.

It looks like we have two options:

1. Merge the PR and allow indented code blocks to interrupt paragraphs until the block parsing algorithm is fixed.
2. Don’t merge the PR, and risk catastrophic backtracking.

[quantizor]

I'm pretty sure there is already code to handle indentation

[caliskanmehmet]

Sorry for the confusion. I meant using block parsing to identify indented code blocks, instead of using regex.