Conversion errors from &str to String should suggest .to_owned() instead

[mqudsi]

Currently, attempting to compile code that expects a String while providing an &'static str causes the following to be shown:

error[E0308]: mismatched types
  --> src/incoming.rs:70:90
   |
70 |             timestamp: headers.get_raw("x-timestamp").unwrap_or(ErrorKind::MissingHeader("x-timestamp"))?,
   |                                                                                          ^^^^^^^^^^^^^ expected struct `std::string::String`, found reference
   |
   = note: expected type `std::string::String`
              found type `&'static str`
   = help: here are some functions which might fulfill your needs:
           - .escape_debug()
           - .escape_default()
           - .escape_unicode()
           - .to_lowercase()
           - .to_uppercase()

I'm guessing that these suggestions are automatically generated/derived by the compiler, but none of them are good "generic" suggestions.

The compiler should probably suggest either .to_owned() or .into() in this case instead.

[zackmdavis]

(See also #42929 for related discussion.)

[steveklabnik]

to_string is the idiomatic choice here.

[mqudsi]

@steveklabnik thanks... man, do I wish rust wasn't 1.0 yet so all these naming issues could be cleaned up.

[estebank]

Current output:

error[E0308]: mismatched types
 --> src/main.rs:2:21
  |
2 |     let x: String = "";
  |                     ^^
  |                     |
  |                     expected struct `std::string::String`, found reference
  |                     help: try using a conversion method: `"".to_string()`
  |
  = note: expected type `std::string::String`
             found type `&'static str`