Suggest to remove unneeded trailing comma

[nyurik]

What it does

In most cases, a trailing comma before parentheses is not needed, especially in a macro invocation. Yet, I suspect this cannot be fully automated by rustfmt because there are some edge cases which do require that comma to be present. I think there should be a lint offering to remove it.

Advantage

• Cleaner, easier to read code

Drawbacks

extremely rare edge cases might be tricky to detect

Example

debug!("Foo={}", 1,);

Could be written as:

debug!("Foo={}", 1);

[sivchari]

@rustbot claim

[sivchari]

The syntax of calling function is formatted by rustfmt. Presumably, it's good to check only macro calling.

[nyurik]

I agree - this probably should only apply to the macros. In the help text, you may also want to add a comment that a macro declaration should have $(,)? at the end to allow optional trailing comma - which would also educate users how to write macro_rules

[samueltardieu]

If implemented, I think it should be a restriction lint (which is "allow by default"), because some people prefer having a trailing comma when macro calls (e.g., vec![], or other initializers) span multiple lines.

[nyurik]

I think this lint should only apply to a single line macros