AST: Add a couple of comments noting that UnboundGenericType is deprecated

Author: slavapestov

include/swift/AST/Decl.h

@@ -2986,6 +2986,11 @@ class TypeAliasDecl : public GenericTypeDecl {
   Type getCachedUnderlyingType() const { return UnderlyingTy.getType(); }
 
   /// For generic typealiases, return the unbound generic type.
+  ///
+  /// Since UnboundGenericType is on its way out, so is this method. Try to
+  /// avoid introducing new callers if possible. Instead of passing around
+  /// an UnboundGenericType, considering passing around the Decl itself
+  /// instead.
   UnboundGenericType *getUnboundGenericType() const;
 
   /// Retrieve a sugared interface type containing the structure of the interface
@@ -3372,6 +3377,11 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
 
   /// getDeclaredType - Retrieve the type declared by this entity, without
   /// any generic parameters bound if this is a generic type.
+  ///
+  /// Since UnboundGenericType is on its way out, so is this method. Try to
+  /// avoid introducing new callers if possible. Instead of passing around
+  /// an UnboundGenericType, considering passing around the Decl itself
+  /// instead.
   Type getDeclaredType() const;
 
   /// getDeclaredInterfaceType - Retrieve the type declared by this entity, with

include/swift/AST/Types.h

@@ -2179,6 +2179,8 @@ END_CAN_TYPE_WRAPPER(TupleType, Type)
 
 /// UnboundGenericType - Represents a generic type where the type arguments have
 /// not yet been resolved.
+///
+/// This type is on its way out. Try to avoid introducing new usages.
 class UnboundGenericType : public AnyGenericType,
     public llvm::FoldingSetNode {
 private: