[CSDiagnostics] Adjusting KeyPathRootTypeMismatchFailure implementation and message

Author: LucianoPAlmeida

include/swift/AST/DiagnosticsSema.def

@@ -580,6 +580,9 @@ ERROR(expr_keypath_subscript_index_not_hashable, none,
 ERROR(expr_smart_keypath_application_type_mismatch,none,
       "key path of type %0 cannot be applied to a base of type %1",
       (Type, Type))
+ERROR(expr_keypath_root_type_mismatch, none,
+      "key path with root type %0 cannot be applied to a base of type %1",
+      (Type, Type))
 ERROR(expr_swift_keypath_anyobject_root,none,
       "the root type of a Swift key path cannot be 'AnyObject'", ())
 WARNING(expr_deprecated_writable_keypath,none,

lib/Sema/CSDiagnostics.cpp

@@ -6226,21 +6226,13 @@ bool CoercionAsForceCastFailure::diagnoseAsError() {
 }
 
 bool KeyPathRootTypeMismatchFailure::diagnoseAsError() {
-  auto &cs = getConstraintSystem();
   auto locator = getLocator();
-  auto anchor = locator->getAnchor();
-
   assert(locator->isKeyPathRoot() && "Expect a key path root");
+  
+  auto baseType = getFromType();
+  auto rootType = getToType();
 
-  if (auto *subscriptExpr = dyn_cast_or_null<SubscriptExpr>(anchor)) {
-    auto *tupleExpr = cast<TupleExpr>(subscriptExpr->getIndex());
-    auto keyPathType = cs.getType(tupleExpr->getElement(0));
-    auto baseType = cs.getType(subscriptExpr->getBase());
-
-    emitDiagnosticAt(anchor->getLoc(),
-                     diag::expr_smart_keypath_application_type_mismatch,
-                     keyPathType, baseType->getRValueType());
-    return true;
-  }
-  return false;
+  emitDiagnostic(diag::expr_keypath_root_type_mismatch,
+                 rootType, baseType);
+  return true;
 }

lib/Sema/CSDiagnostics.h

@@ -2023,7 +2023,7 @@ class CoercionAsForceCastFailure final : public ContextualFailure {
   bool diagnoseAsError() override;
 };
 
-/// Diagnose n key path root type that cannot be applied to an instance
+/// Diagnose a key path root type that cannot be applied to an instance
 /// base that has another type.
 ///
 /// \code

test/attr/attr_dynamic_member_lookup.swift

@@ -811,8 +811,8 @@ internal var rightStructInstance: SR12425_R = SR12425_R()
 
 public extension SR12425_R {
   subscript<T>(dynamicMember member: WritableKeyPath<SR12425_S, T>) -> T {
-      get { rightStructInstance[keyPath: member] } // expected-error {{key path of type 'WritableKeyPath<SR12425_S, T>' cannot be applied to a base of type 'SR12425_R'}}
-      set { rightStructInstance[keyPath: member] = newValue } // expected-error {{key path of type 'WritableKeyPath<SR12425_S, T>' cannot be applied to a base of type 'SR12425_R'}}
+      get { rightStructInstance[keyPath: member] } // expected-error {{key path with root type 'SR12425_S' cannot be applied to a base of type 'SR12425_R'}}
+      set { rightStructInstance[keyPath: member] = newValue } // expected-error {{key path with root type 'SR12425_S' cannot be applied to a base of type 'SR12425_R'}}
   }
 }
 
@@ -821,6 +821,6 @@ public struct SR12425_R1 {}
 
 public extension SR12425_R1 {
   subscript<T>(dynamicMember member: KeyPath<SR12425_R1, T>) -> T {
-    get { rightStructInstance[keyPath: member] } // expected-error {{key path of type 'KeyPath<SR12425_R1, T>' cannot be applied to a base of type 'SR12425_R'}}
+    get { rightStructInstance[keyPath: member] } // expected-error {{key path with root type 'SR12425_R1' cannot be applied to a base of type 'SR12425_R'}}
   }
 }