[ASTPrinter] Print the desugared constraint type following the 'any'

keyword.

Author: hborla

lib/AST/ASTPrinter.cpp

@@ -6211,7 +6211,12 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
     if (Options.PrintExplicitAny)
       Printer << "any ";
 
-    visit(T->getConstraintType());
+    // FIXME: The desugared type is used here only to support
+    // existential types with protocol typealiases in Swift
+    // interfaces. Verifying that the underlying type of a
+    // protocol typealias is a constriant type is fundamentally
+    // circular, so the desugared type should be written in source.
+    visit(T->getConstraintType()->getDesugaredType());
   }
 
   void visitLValueType(LValueType *T) {

test/ModuleInterface/existential-any.swift

@@ -38,3 +38,11 @@ public struct S {
   // CHECK: public var q: any main.Q
   public var q: any Q
 }
+
+
+public protocol ProtocolTypealias {
+  typealias A = P
+}
+
+// CHECK: public func dependentExistential<T>(value: (T) -> any main.P) where T : main.ProtocolTypealias
+public func dependentExistential<T: ProtocolTypealias>(value: (T) -> T.A) {}