Parse macros named "default" correctly.

[qnighy]

Fixes #42292.

[rust-highfive]

r? @nikomatsakis

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[petrochenkov]

Could you do something like this instead, to keep default in the expected token set

fn eat_defaultness(&self) -> bool {
    let is_defaultness = self.is_defaultness();
    if is_defaultness {
        self.bump();
    } else {
        self.expected_tokens.push(/*default keyword token*/);
    }
    is_defaultness
}

All this logic can probably be just inlined into parse_defaultness as well.

[qnighy]

Done!

[petrochenkov]

Thanks!
@bors r+

[bors]

📌 Commit b670930 has been approved by petrochenkov

[Mark-Simulacrum]

@bors rollup