lint String::as_str()

[llogiq]

Using my_string.as_str() is noisy and adds no value in comparison to &my_string. This lint should not apply to using it in a .map(_) or some other higher-order stuff, just calling the function directly.

[mseri]

I am giving a shot to this but I am lost at making sure the lint is not applied to higher-order functions. Is there a standard way to check if we are inside a closure in some higher order function or I need to make up one?

[llogiq]

If the function is directly called (match on MethodCall with ident + 0th argument type), you can be quite sure it was called. Perhaps add a macro check for good measure.

[theemathas]

What's the status of this?

[Manishearth]

Feel free to work on it if you want to. (If someone has claimed an issue and not shown activity for months just feel free to claim it yourself)

[mseri]

I was stuck on it and then had no time to try again. Feel free to work on it. It is outdated now, but this is what I had https://github.com/mseri/rust-clippy/commits/string_as_str (I was not able to distinguish being inside a higher order function or not, I did not push the few attempts I made)

[theemathas]

I think it should be possible to just check if the method is immediately called instead of checking if it's inside a higher-order function. I'll implement it.

[theemathas]

I think this lint should still trigger on something like slice.iter().any(|v| v.as_str() == "1"). When @llogiq said that "This lint should not apply to using it in a .map(_) or some other higher-order stuff", I think he meant something like slice.iter().any(String::as_str)

[theemathas]

I just realized that |s: String| s.as_str() has different semantics from |s: String| &s. The former returns &str, while the latter returns &String. To make it return &str without using .as_str(), it has to be |s: String| &*s.

How do I deal with this case?

[camsteffen]

I'd generalize this as coercible_deref_method - using a method that derefs the value where the deref could be coerced implicitly. This would also apply to Vec::as_slice for example.