[NoncopyableGenerics] handle ~Copyable in where, some, and compositions.
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We really should be checking for the presence of the ownership annotation from the top of the parameter's TypeRepr hierarchy, instead of the bottom. This fixes some missed edge cases that are now relevant, like `some ~Copyable`. parameters
This type will become the corresponding type that is resolved for an `InverseTypeRepr`. This kind of type is not expected to appear past type checking (currently, not even past requirement lowering!).
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Previously, inverses were only accounted-for in inheritance clauses. This batch of changes handles inverses appearing in other places, like: - Protocol compositions - `some ~Copyable` - where clauses with proper attribution of default requirements in their absence.
We're not yet going to allow noncopyable types into packs, so this change prevents the use of `~Copyable` on an `each T` generic parameter. It also fixes how we query for whether a `repeat X` parameter is copyable.
Since there is no propagation of inverse constraints in the requirement
machine, we need to fully desugar these requirements at the point of
defining a generic parameter. That desugaring involves determining which
default conformance requirements need to be applied to a generic
parameter, accounting for inverses.
But, nested generic contexts in scope of those expanded generic
parameters can still write constraints on that outer parameter. For
example, this method's where clause can have its own constraints on `T`:
```
struct S<T> {
func f() where T: ~Copyable {}
}
```
But, the generic signature of `S` already has a `T: Copyable` that was
expanded. The method `f` will always see a `T` that conforms to
`Copyable`, so it's impossible for `f` to claim that it applies for
`T`'s that lack Copyable.
Put another way, it's not valid for this method `f`, whose generic
signature is based on its parent's `S`, to weaken or remove requirements
from parent's signature. Only positive requirements can be
added to them.
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We already don't diagnose all redundant requirements. Because inverses can be written in both inheritance and where clauses, but they're not treated uniformly in the implementation, it's a bit annoying to try and account for the redundancies in both places; `checkInheritanceClause` will go over the same "requirements" that we'll also check again in `swift::rewriting::expandDefaultRequirements`.
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This is a pile of fixes and improvement for
NoncopyableGenerics:someparameters that are noncopyable.Copyableconformances.sometypes.~Copyablein protocol compositions.~Copyableconstraints inwhereclauses wherever they may appear.