Warn for passing `Box<&dyn Any>` to function taking `&dyn std::any::Any`

What it does

Issue a warning if a function takes any of

• &dyn std::any::Any
• &mut dyn std::any::Any

The recommendation is to either use an existing trait type or create a "marker trait" to specify what the method can actually process in order to avoid passing (by accident) object references of unexpected types.

EDIT: Only warn when Box<&dyn Any> is passed as-is. Recommend box.as_ref()

Advantage

Beside the obvious advantages of a more concrete type, there's major pitfalls with &dyn Any: Since &Box<Any> itself implements Any, it can easily happen that one accidentally passes the box directly instead of the desired box.as_ref(). This can be the cause of quite hard to debug issues.

Drawbacks

While it's more often than not a shortcut for not defining a trait type, there are likely legitimate usecases for passing &dyn Any (examples?)

Example

Updated suggestion:

fn func(value: &dyn std::any::Any) { ... }

func(box);

Could be written as:

fn func(value: &dyn std::any::Any) { ... }

func(box.as_ref());

Previous suggestion:

fn func(value: &dyn std::any::Any) { ... }

Could be written as:

fn func(value: &dyn MyTrait) { ... }

No source file, test, or entry point is named in the issue. Start by locating existing Clippy lints that inspect function arguments and calls involving std::any::Any. Done means warning only when Box<&dyn Any> is passed directly to a function accepting &dyn Any or &mut dyn Any, with a recommendation to use box.as_ref().