[CSSimplify] Add AnyHashable check to simplifyTransitivelyConformsTo

Just like `Optional` and `UnsafePointer` argument could be implicitly
converted to `AnyHashable`.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -6222,6 +6222,8 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
 ConstraintSystem::SolutionKind ConstraintSystem::simplifyTransitivelyConformsTo(
     Type type, Type protocolTy, ConstraintLocatorBuilder locator,
     TypeMatchOptions flags) {
+  auto &ctx = getASTContext();
+
   // Since this is a performance optimization, let's ignore it
   // in diagnostic mode.
   if (shouldAttemptFixes())
@@ -6270,10 +6272,11 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyTransitivelyConformsTo(
   typesToCheck.push_back(
       OptionalType::get(resolvedTy->getWithoutSpecifierType()));
 
-  // Unsafe{Mutable}Pointer<T>
-  {
-    auto &ctx = getASTContext();
+  // AnyHashable
+  typesToCheck.push_back(ctx.getAnyHashableDecl()->getDeclaredInterfaceType());
 
+  // Rest of the implicit conversions depend on the resolved type.
+  {
     auto *ptrDecl = ctx.getUnsafePointerDecl();
 
     // String -> UnsafePointer<Void>

test/Constraints/protocols.swift

@@ -441,11 +441,16 @@ extension UnsafePointer : Trivial {
   typealias T = Int
 }
 
+extension AnyHashable : Trivial {
+  typealias T = Int
+}
+
 func test_inference_through_implicit_conversion() {
-  class C {}
+  struct C : Hashable {}
 
   func test<T: Trivial>(_: T) -> T {}
 
   let _: C? = test(C()) // Ok -> argument is implicitly promoted into an optional
   let _: UnsafePointer<C> = test([C()]) // Ok - argument is implicitly converted to a pointer
+  let _: AnyHashable = test(C()) // Ok - argument is implicitly converted to `AnyHashable` because it's Hashable
 }