Sema: Add TypeResolverContext::ExistentialConstraint

Previously we would resolve the constraint type of an `any`
using TypeResolverContext::GenericRequirement, but this does
not allow us to distinguish between parametrized protocol
types in generic requirements (which are supported) from
parametrized protocol types inside an `any`, like
`any Sequence<Int>`, which is not supported for now.

Author: slavapestov

lib/Sema/TypeCheckType.cpp

@@ -3666,6 +3666,7 @@ NeverNullType TypeResolver::resolveImplicitlyUnwrappedOptionalType(
   case TypeResolverContext::TypeAliasDecl:
   case TypeResolverContext::GenericTypeAliasDecl:
   case TypeResolverContext::GenericRequirement:
+  case TypeResolverContext::ExistentialConstraint:
   case TypeResolverContext::SameTypeRequirement:
   case TypeResolverContext::ProtocolMetatypeBase:
   case TypeResolverContext::MetatypeBase:
@@ -3881,7 +3882,7 @@ NeverNullType
 TypeResolver::resolveExistentialType(ExistentialTypeRepr *repr,
                                      TypeResolutionOptions options) {
   auto constraintType = resolveType(repr->getConstraint(),
-      options.withContext(TypeResolverContext::GenericRequirement));
+      options.withContext(TypeResolverContext::ExistentialConstraint));
   if (constraintType->is<ExistentialMetatypeType>())
     return constraintType;
 

lib/Sema/TypeCheckType.h

@@ -122,7 +122,10 @@ enum class TypeResolverContext : uint8_t {
   /// Whether we are checking the underlying type of a generic typealias.
   GenericTypeAliasDecl,
 
-  /// Whether we are in a requirement of a generic declaration
+  /// Whether we are in the constraint type of an existential type.
+  ExistentialConstraint,
+
+  /// Whether we are in a requirement of a generic declaration.
   GenericRequirement,
 
   /// Whether we are in a same-type requirement of a generic
@@ -225,6 +228,7 @@ class TypeResolutionOptions {
     case Context::TypeAliasDecl:
     case Context::GenericTypeAliasDecl:
     case Context::GenericRequirement:
+    case Context::ExistentialConstraint:
     case Context::SameTypeRequirement:
     case Context::ProtocolMetatypeBase:
     case Context::MetatypeBase: