Motivation: `GenericSignatureImpl::getCanonicalSignature` crashes for
`GenericSignature` with underlying `nullptr`. This led to verbose workarounds
when computing `CanGenericSignature` from `GenericSignature`.
Solution: `GenericSignature::getCanonicalSignature` is a wrapper around
`GenericSignatureImpl::getCanonicalSignature` that returns the canonical
signature, or `nullptr` if the underlying pointer is `nullptr`.
Rewrite all verbose workarounds using `GenericSignature::getCanonicalSignature`.
box descriptors
We want to substitute opaque result types in addTypeRef but when we pass
SILFunctionTypes this would fail because AST type substitution does not
support lowered SIL types.
Instead add addLoweredTypeRef which substitutes based on SILTypes.
rdar://54529445
Doing so will cause linkage errors and is not neccessary since we call
the witness of the enclosing type as soon as its fields are not ABI
accessible.
rdar://40868358
They're not used inside the thunk so it's a waste passing them in, and
if they involve private types from a different translation unit we will
get a linking error from referencing the metadata accessor function.
Fixes the test case in <rdar://problem/39470607>, but the more general
problem remains.
Fixes a regression in the source compatibility suite which I had a
lot of trouble extracting into a separate test case.
Most of this patch is just moving the outlining code into a separate
file and organizing it into a helper class instead of copy/pasting
so much code. The main functional change is implicit in the difference
between collecting formal metadata and collecting it for layout, which
then is exploited in bindMetadataParameters.
As a secondary change, stop collecting metadata for class-bounded
archetypes; we don't actually need it to do value operations.
