mdbook build hangs forever if \$ is in a formula

[llllvvuu]

Reproduce:

We randomly assign: $r \xleftarrow{\$} G $.
We randomly assign: $r \xleftarrow{\\$} G $.

Expected:
We randomly assign: $r \xleftarrow{\$} G $

Actual:
Neither expression works. The \\$ produces a new line followed by ending the expression. The \$ causes the preprocessor to hang forever.

I believe the issue stems from https://github.com/lzanini/mdbook-katex/blob/master/src/lib.rs#L456 :

self.index += self.string[self.index..].find(&delim.right).ok_or(())?;

I'll try to fix...

[SichangHe]

The first case should work after I fix it.
The second case is already working as intended. The \\ indicates that the following $ should not be escaped and should be seen as the right delimiter for this inline math block.
Let me know if you have different opinions.

[SichangHe]

Thank you, @llllvvuu, for catching what I messed up! 🎉