Suggest use of captured format args

[kornelski]

What it does

In edition 2021 format! and related macros have a new ability to use implicitly captured variables instead of positional arguments: format!("hello {name}");

Lint Name

format_uncaptured_variables

Category

pedantic

Advantage

A lint with an auto-fix could help migrate codebases to the new style. Opposite of #5404.

Drawbacks

format! with a mix of captured and positional args may be confusing:

format("{} {second}", x.first);

so the lint could be limited to cases where all args can be captured.

Example

format!("hello {:^5}", name);

Could be written as:

format!("hello {name:^5}");

[kraktus]

Already implemented on nightly as uninlined_format_args