Avoid linting in macros, if MacroReport is set in declare_lint

[xFrednet]

A common pattern during linting is to check if the current code originates from a macro, and if so, abort early. This works well in most instances, but has some edge cases, where it doesn't. Mostly, proc macros, that manipulate spans for error reporting.

When I designed the initial Lint struct, I proposed (and by this mean, just added) a MacroReport enum, which allows the user to directly specify how macros should be handled by lint emissions. The idea was to automate a macro handling and make it as simple as possible.

So, this issue is about implementing the required functions for MacroReport. I'm guessing it should be enough to do so, in the adapter. It might also be possible to track the current status InsideMacro/UserCode/... in the AstContext to safe some performance for lookups.

There is no tried and true methods, this requires some prototyping :)

[xFrednet]

I just learned, that span::is_from_macro() isn't even working correctly right now 😅

Reproducible/Test code:

Lint code:

        if matches!(lint.report_in_macro, MacroReport::No | MacroReport::Local)
            && span.is_from_macro()
        {
            return;
        }

Test file:

macro_rules! ignore_macro_magic {
    () => {
        static FIND_ITEM: u32 = 4;
    }
}

mod find_real_item {
    static FIND_ITEM: u32 = 4;
}

mod ignore_macro_item {
    ignore_macro_magic!();
}

fn main() {}