librustc: Disallow trait bounds in types, enumerations, and structure definitions #4660
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…ules. "Dual impls" are impls that are both type implementations and trait implementations. They can lead to ambiguity and so this patch removes them from the language. This also enforces coherence rules. Without this patch, records can implement traits not defined in the current crate. This patch fixes this, and updates all of rustc to adhere to the new enforcement. Most of this patch is fixing rustc to obey the coherence rules, which involves converting a bunch of records to structs.
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Doesn't have to be in the same pull request, but we need to document why you're not allowed to have trait bounds in these locations, and what to do instead. (In fact, I don't completely get the gist of it: I assume the issue is that writing |
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r+ -- making it a parse error instead of a type error would be nice, but isn't necessary. |
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r? @catamorphism
I had to take an alarmingly large hatchet to most of the trait bounds in pipes. There is some bug in the interactions between the pipes compiler, the code generated by the pipes compiler, and the kind checker. However, I believe the code to still be safe; it should still not be possible to send a garbage-collected value over a channel.