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Having multiple relaxed bounds like `?Sized + ?Iterator` is actually *fine*. We actually want to reject *duplicate* relaxed bounds like `?Sized + ?Sized` because these most certainly represent a user error. Note that this doesn't mean that we accept more code because a bound like `?Iterator` is still invalid as it's not relaxing a *default* trait and the only way to define / use more default bounds is under the experimental and internal feature `more_maybe_bounds` plus `lang_items` plus unstable flag `-Zexperimental-default-bounds` (historical context: for the longest time, bounds like `?Iterator` were actually allowed and lead to a hard warning). Ultimately, this simply *reframes* the diagnostic. The scope of `more_maybe_bounds` / `-Zexperimental-default-bounds` remains unchanged as well.
23 lines
952 B
Rust
23 lines
952 B
Rust
fn dupes<T: ?Sized + ?Sized + ?Iterator + ?Iterator>() {}
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//~^ ERROR duplicate relaxed `Sized` bounds
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//~| ERROR duplicate relaxed `Iterator` bounds
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//~| ERROR bound modifier `?` can only be applied to `Sized`
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//~| ERROR bound modifier `?` can only be applied to `Sized`
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trait Trait {
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// We used to say "type parameter has more than one relaxed default bound"
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// even on *associated types* like here. Test that we no longer do that.
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type Type: ?Sized + ?Sized;
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//~^ ERROR duplicate relaxed `Sized` bounds
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//~| ERROR duplicate relaxed `Sized` bounds
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}
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// We used to emit an additional error about "multiple relaxed default bounds".
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// However, multiple relaxed bounds are actually *fine* if they're distinct.
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// Ultimately, we still reject this because `Sized` is
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// the only (stable) default trait, so we're fine.
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fn not_dupes<T: ?Sized + ?Iterator>() {}
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//~^ ERROR bound modifier `?` can only be applied to `Sized`
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fn main() {}
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