Creating a trait function with a macro using block designator: error: expected ; or {, found { ... }

[birktj]

Given a simple macro:

macro_rules! def_fn{
    ($body:block) => {
        fn test() $body
    };
}

I can use it without problems to define a function:

def_fn!({println!("test"); });

I can also use it to define a struct method without problems:

struct Test {}

impl Test {
    def_fn!({println!("test"); });
}

However when I try to use it to define a default method for a trait it doesn't work:

trait Test {
    def_fn!({println!("test"); });
}

It gives an error message:

error: expected `;` or `{`, found `{ println!("test"); }`
  --> src/main.rs:9:19
   |
9  |         fn test() $body
   |                   ^^^^^ expected `;` or `{`
...
16 |     def_fn!({println!("test"); });
   |     ------------------------------ in this macro invocation
error: aborting due to previous error

If I change the macro to include braces around $body it works:

macro_rules! def_fn{
    ($body:block) => {
        fn test() {$body}
    };
}

I have no idea why this happens but I guess it is some sort of bug in how default trait methods are parsed.

[matthew-russo]

If no one is working on this, I'll take it.