Unrecognized escape sequence

[ThomasdenH]

Clippy version: clippy 0.0.212 (265318d 2019-05-17)

I get the following error when linting code, and I have a feeling it might be a bug. If it is not, it maybe clippy can give a correct suggestion?

error: regex syntax error: unrecognized escape sequence
   --> src/compiler/utilities.rs:187:52
    |
187 |         static ref RE: Regex = Regex::new("^..?($|[\\/])").unwrap();
    |                                                    ^^
    |
    = note: #[deny(clippy::invalid_regex)] on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#invalid_regex

[flip1995]

This indeed looks like valid regex. But Clippy uses the parser of rust-lang/regex to detect invalid regex. This means the regex parser fails to parse what seems to be valid regex. You should probably open an issue in rust-lang/regex.

Building a suggestion for this lint is hard or even impossible, since Clippy can't really guess what the correct regex would be.

[ThomasdenH]

I opened an issue there, thanks.

[ThomasdenH]

I found the solution here. The reason it fails is because it should be escaped once for the string literal, and once for the regex. If possible, a better description of the problem would be nice.

[flip1995]

Yeah, I was just about to write this, after testing this.

You could also use a raw string:

-static ref RE: Regex = Regex::new("^..?($|[\\/])").unwrap();
+static ref RE: Regex = Regex::new(r"^..?($|[\\/])").unwrap();

[flip1995]

Ok in this case, a (multipart) suggestion would be possible:

"Try escaping the \ twice: \\\\"

"Or use a raw string: r"regex""

[mr-cheffy]

Hm... I recently had this problem. My solution was to just remove the \\ since apparently, it can handle / in a raw string