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suggest `where T: Foo` for the first bound on a trait, then suggest `, T: Foo` when the suggested bound would add to an existing set of `where` clauses. `where T: Foo` may be the first bound if `T` has a default, because we'd rather suggest ``` trait A<T=()> where T: Copy ``` than ``` trait A<T: Copy=()> ``` for legibility reasons.
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