Suggest box_string

[lengyijun]

What it does

Check for usage for Box<String> in struct definition and function parameter.

Categories (optional)

Perf, Warn

What is the advantage of the recommended code over the original code

String already allocates on heap, Box<String> allocates a pointer on heap.
Similar lints: rc_buffer, box_vec, redundant_allocation,

Drawbacks

None.

Example

struct foo(Box<String>)
fn bar(a: Box<String>){}

Could be written as:

struct foo(String)
fn bar(a: String){}

[F3real]

@rustbot claim

[camsteffen]

I think we should enhance and rename box_vec to box_collection. We can include all collection types like HashMap. String fits if you think about it as a Vec<u8>, which it actually is.