Expose Substitution's archetype, replacement, and conformances only through getters so we can actually assert invariants about them. To start, require replacement types to be materializable in order to catch cases where the type-checker tries to bind type variables to lvalue or inout types, and require the conformance array to match the number of protocol conformances required by the archetype. This exposes some latent bugs in the test suite I've marked as failures for now:
- test/Constraints/overload.swift was quietly suffering from <rdar://problem/17507421>, but we didn't notice because we never tried to codegen it.
- test/SIL/Parser/array_roundtrip.swift doesn't correctly roundtrip substitutions, which I filed as <rdar://problem/17781140>.
Swift SVN r20418
Pass in the context generic parameters that correspond to the substitution vector in Substitution::subst. When we build the type substitution map, also collect the conformances from the substitutions into a map we can use to fill in those conformances in substituted substitutions where necessary, without relying on the '.Archetype' field.
Swift SVN r14964
Substitute a...um...substitution by remapping its Replacement mapping and recursively remapping any ProtocolConformances it has. Modify the Specializer to use Substitution::subst when specializing the substitutions of ArchetypeMethod and Apply instructions.
Swift SVN r12900
Previously, we only tracked the mapping from associated types to their
type witnesses. Now, also track the protocol conformances for each of
the requirements placed on the associated types.
Swift SVN r6655
