rustfmt and rust-analyzer support for impl_self / impl_scope / impl_anon

[dhardy]

impl_scope! { ... } and impl_anon! { ... } should be formatted internally just like a module. rustfmt does not currently support this: see rust-lang/rustfmt#5538.

#53 introduced #[impl_self] mod { ... } as a replacement for impl_scope! { ... }. The usage of a fake module appears to have completely solved rustfmt compatibility, but comes with a new problem: rust-analyzer sometimes inserts use ...; statements inside this fake module, leading to macro parse errors.

Possible solutions:

• Wait for rustfmt to support formatting braced-wrapped macros as a module?
• Try getting rust-analyzer to ignore the fake module? This seems an unlikely approach; it would require r-a to either have an exception for this macro or expand macros before adding use statements (which may also have issues).
• Propose an RFC with similar functionality to the above? There have been some related proposals in the past (example).