single_char_pattern doesn't recognize scape sequences

Example (playground):

string.find("\"");

errors with

  |
3 |     string.find("\"");
  |                ^^^^ help: try using a char instead: `'\"'`
  |
  = note: #[warn(single_char_pattern)] on by default
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#single_char_pattern

However, the appropriate char to use is '"' without the escape: \.

Start by reproducing the single_char_pattern warning with the Rust example in the linked playground, then locate the lint's handling of escaped string literals. The issue does not name a source file or test; done means the suggested char literal is '"' without the unnecessary escape and the warning remains correct for other cases.