Please provide special case for name=name in format

[joshtriplett]

I'd like to avoid reformats like this:

-                v.push(new.paint(format!("{:nwidth$}: {:idwidth$}", i2 + offset, c2_short_id, nwidth=nwidth, idwidth=idwidth).as_bytes().to_owned()));
+                v.push(new.paint(format!("{:nwidth$}: {:idwidth$}", i2 + offset, c2_short_id, nwidth = nwidth, idwidth = idwidth).as_bytes().to_owned()));

Could we special-case samename=samename in the arguments of format!-like macros, and avoid adding spaces around the =?

[topecongiro]

This seems a bit too narrow to special-case in rustfmt.

[joshtriplett]

It ends up producing a lot of noise when you have a long list of x=x, y=y, z=z in a format-like call, and rustfmt already has special-case logic for format-like calls.

[joshtriplett]

Nevermind, I think rust-lang/rfcs#2795 would fully address the cases where I find myself wanting this.