New stack macro implementation triggers clippy::toplevel_ref_arg warning

[dsemi]

This line triggers the clippy::toplevel_ref_arg warning for users of stack!.

Example warning:

warning: `ref` on an entire `let` pattern is discouraged, take a reference with `&` instead
  --> src/main.rs:35:15
   |
35 |       let rhs = stack![ bp.cross(&bv) - ap.cross(&av);
   |  _______________^
36 | |                       cp.cross(&cv) - ap.cross(&av) ];
   | |_____________________________________________________^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#toplevel_ref_arg
   = note: `#[warn(clippy::toplevel_ref_arg)]` on by default
   = note: this warning originates in the macro `stack` (in Nightly builds, run with -Z macro-backtrace for more info)

[Andlon]

Uhm, does clippy normally give warnings from code generated by macros in external crates? That seems... excessive? Did you enable any particular options?

[dsemi]

It seems so: rust-lang/rust-clippy#702. I don't understand why that decision was made.

[Andlon]

This comment suggests that it's due to our use of spans in the stack! macro to improve error messages. We should fix this by just plastering #[allow(clippy::all)] in the macro-generated code.

I'm not sure off the top of my head if we can put these attributes on code blocks though (not a function/impl block).