[Diagnostics] Improve the error message for when a type fails to satisfy

`AnyObject` layout requirement.

Author: hborla

include/swift/AST/DiagnosticsSema.def

@@ -1716,12 +1716,18 @@ ERROR(type_does_not_conform_owner,none,
 ERROR(type_does_not_conform_in_decl_ref,none,
       "referencing %0 %1 on %2 requires that %3 conform to %4",
       (DescriptiveDeclKind, DeclName, Type, Type, Type))
+ERROR(type_does_not_conform_anyobject_in_decl_ref,none,
+      "referencing %0 %1 on %2 requires that %3 be a class type",
+      (DescriptiveDeclKind, DeclName, Type, Type, Type))
 ERROR(type_does_not_conform_decl_owner,none,
       "%0 %1 requires that %2 conform to %3",
       (DescriptiveDeclKind, DeclName, Type, Type))
-ERROR(type_does_not_conform_in_opaque_return,none,
-      "return type of %0 %1 requires that %2 conform to %3",
+ERROR(type_does_not_conform_anyobject_decl_owner,none,
+      "%0 %1 requires that %2 be a class type",
       (DescriptiveDeclKind, DeclName, Type, Type))
+ERROR(type_does_not_conform_in_opaque_return,none,
+      "return type of %0 %1 requires that %2 %select{conform to %3|be a class type}4",
+      (DescriptiveDeclKind, DeclName, Type, Type, bool))
 ERROR(types_not_equal_decl,none,
       "%0 %1 requires the types %2 and %3 be equivalent",
       (DescriptiveDeclKind, DeclName, Type, Type))
@@ -1741,7 +1747,7 @@ NOTE(where_requirement_failure_both_subst,none,
 NOTE(requirement_implied_by_conditional_conformance,none,
      "requirement from conditional conformance of %0 to %1", (Type, Type))
 NOTE(wrapped_type_satisfies_requirement,none,
-     "wrapped type %0 satisfies this requirement", (Type))
+     "wrapped type %0 satisfies this requirement; did you mean to unwrap?", (Type))
 NOTE(candidate_types_conformance_requirement,none,
      "candidate requires that %0 conform to %1 "
      "(requirement specified as %2 == %3%4)",

lib/Sema/CSDiagnostics.cpp

@@ -478,7 +478,8 @@ bool RequirementFailure::diagnoseAsError() {
     auto *namingDecl = OTD->getNamingDecl();
     emitDiagnostic(
         anchor->getLoc(), diag::type_does_not_conform_in_opaque_return,
-        namingDecl->getDescriptiveKind(), namingDecl->getFullName(), lhs, rhs);
+        namingDecl->getDescriptiveKind(), namingDecl->getFullName(), lhs, rhs,
+        rhs->isAnyObject());
 
     if (auto *repr = namingDecl->getOpaqueResultTypeRepr()) {
       emitDiagnostic(repr->getLoc(), diag::opaque_return_type_declared_here)

lib/Sema/CSDiagnostics.h

@@ -434,11 +434,15 @@ class MissingConformanceFailure final : public RequirementFailure {
   bool diagnoseAsAmbiguousOperatorRef();
 
   DiagOnDecl getDiagnosticOnDecl() const override {
-    return diag::type_does_not_conform_decl_owner;
+    return (getRequirement().getKind() == RequirementKind::Layout ?
+            diag::type_does_not_conform_anyobject_decl_owner :
+            diag::type_does_not_conform_decl_owner);
   }
 
   DiagInReference getDiagnosticInRereference() const override {
-    return diag::type_does_not_conform_in_decl_ref;
+    return (getRequirement().getKind() == RequirementKind::Layout ?
+            diag::type_does_not_conform_anyobject_in_decl_ref :
+            diag::type_does_not_conform_in_decl_ref);
   }
 
   DiagAsNote getDiagnosticAsNote() const override {

test/APINotes/versioned-objc.swift

@@ -16,7 +16,7 @@ class ProtoWithVersionedUnavailableMemberImpl: ProtoWithVersionedUnavailableMemb
 func testNonGeneric() {
   // CHECK-DIAGS-4:[[@LINE+1]]:{{[0-9]+}}: error: cannot convert value of type 'Any' to specified type 'Int'
   let _: Int = NewlyGenericSub.defaultElement()
-  // CHECK-DIAGS-5:[[@LINE-1]]:{{[0-9]+}}: error: generic class 'NewlyGenericSub' requires that 'Int' conform to 'AnyObject'
+  // CHECK-DIAGS-5:[[@LINE-1]]:{{[0-9]+}}: error: generic class 'NewlyGenericSub' requires that 'Int' be a class type
 
   // CHECK-DIAGS-4:[[@LINE+1]]:{{[0-9]+}}: error: cannot specialize non-generic type 'NewlyGenericSub'
   let _: Int = NewlyGenericSub<Base>.defaultElement()

test/Constraints/closures.swift

@@ -281,7 +281,7 @@ struct S<T> {
 
   func subscribe<Object: AnyObject>(object: Object?, method: (Object, T) -> ()) where Object: Hashable {
     let wrappedMethod = { (object: AnyObject, value: T) in }
-    // expected-error @+2 {{instance method 'append(value:forKey:)' requires that 'Object?' conform to 'AnyObject'}}
+    // expected-error @+2 {{instance method 'append(value:forKey:)' requires that 'Object?' be a class type}}
     // expected-note @+1 {{wrapped type 'Object' satisfies this requirement}}
     cs.forEach { $0.w.append(value: wrappedMethod, forKey: object) }
   }
@@ -295,7 +295,7 @@ func simplified1069() {
     // expected-note@-1 {{where 'T' = 'Optional<C>'}}
 
     func f(_ a: C?, _ b: C?, _ c: C) {
-      genericallyNonOptional(a, b, c) // expected-error {{instance method 'genericallyNonOptional' requires that 'Optional<C>' conform to 'AnyObject'}}
+      genericallyNonOptional(a, b, c) // expected-error {{instance method 'genericallyNonOptional' requires that 'Optional<C>' be a class type}}
       // expected-note @-1 {{wrapped type 'C' satisfies this requirement}}
     }
   }

test/decl/var/property_wrappers.swift

@@ -1587,7 +1587,7 @@ extension SR_11288_P4 where Self: AnyObject { // expected-note 2 {{where 'Self'
 
 struct SR_11288_S4: SR_11288_P4 {
   // FIXME: We shouldn't diagnose the arg-to-param mismatch (rdar://problem/56345248)
-  @SR_11288_Wrapper4 var answer = 42 // expected-error 2 {{referencing type alias 'SR_11288_Wrapper4' on 'SR_11288_P4' requires that 'SR_11288_S4' conform to 'AnyObject'}}
+  @SR_11288_Wrapper4 var answer = 42 // expected-error 2 {{referencing type alias 'SR_11288_Wrapper4' on 'SR_11288_P4' requires that 'SR_11288_S4' be a class type}}
   // expected-error @-1 {{cannot convert value of type '<<error type>>' to expected argument type 'Int'}}
 }