Warn if user calls `.to_string()` multiple times on variable.

What it does

Warn that .to_string() is only required once. Even with pedantic clippy this doesn't give any warning.

Advantage

It can happen to anyone if you process a lot of code that you accidently call .to_string() more then once on a variable. It takes up useless characters in your file and looks sloppy. This looks like something clippy could fix automatically with the --fix argument.

Drawbacks

I can't think of any since I don't know any situation where it would make sense to call .to_string() twice in a variable.

Example

 let uri = req.uri().path().to_string().to_string();

Could be written as:

 let uri = req.uri().path().to_string();

The issue names no files, tests, or entry points. Start by locating existing Clippy lints for redundant method calls and their UI tests; done means repeated .to_string() calls are warned about and the suggested fix leaves one call, including the shown example.