Suggest better repeated macro param declaration pattern

What it does

Try to catch bad macro param patterns, and suggest better ones:

• Replace <anything>, $($e:expr),* with <anything> $(, $e:expr)* $(,)?
  • this must also replace all usages of <anything>, $($e,)* with <anything> $(, $e)*
• Add missing trailing comma - can be fixed by adding $(,)?. See also #1848
• ? some other bad patterns ?

Lint Name

bad_macro_param_pattern

Category

suspicious

Advantage

• keeps macro declarations more consistent
• catches common errors like using format-like macro: my_macro!("{}", foo) not being replaceable by my_macro!("{foo}") (i.e. it is no longer requires a single comma to always be present)

Drawbacks

possible formatting issues on auto-fix

Example

macro_rules! my_macro {
    ($fmt:literal, $($e:expr),*) => {
        println!($fmt, $($e,)*)
    }
}

Could be written as:

macro_rules! my_macro {
    ($fmt:literal $(, $e:expr)* $(,)?) => {
        println!($fmt $(, $e)*)
    }
}

Start with the bad_macro_param_pattern proposal and its macro_rules! examples, including the repeated expression pattern and optional trailing comma. Define the supported bad patterns and expected suggestions before implementing the lint; done means the named patterns are detected with suitable fixes and formatting concerns are covered.