[tests] Adjusting SR-12425 diagnostics tests

Author: LucianoPAlmeida

lib/Sema/CSDiagnostics.h

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

lib/Sema/CSSimplify.cpp

@@ -3577,11 +3577,12 @@ bool ConstraintSystem::repairFailures(
     break;
   }
 
-  case ConstraintLocator::KeyPathRoot:
+  case ConstraintLocator::KeyPathRoot: {
     conversionsOrFixes.push_back(AllowKeyPathRootTypeMismatch::create(
         *this, lhs, rhs, getConstraintLocator(locator)));
 
     break;
+  }
 
   case ConstraintLocator::FunctionArgument: {
     auto *argLoc = getConstraintLocator(

test/attr/attr_dynamic_member_lookup.swift

@@ -811,9 +811,16 @@ internal var rightStructInstance: SR12425_R = SR12425_R()
 
 public extension SR12425_R {
   subscript<T>(dynamicMember member: WritableKeyPath<SR12425_S, T>) -> T {
-      // TODO(Diagnostics): bad diagnostic for member assign.
-      // A better diagnostic would be: key path of type WritableKeyPath<SR12425_S, T> cannot be applied to a base of type SR12425_R
-      get { rightStructInstance[keyPath: member] } // expected-error {{cannot convert return expression of type 'Any?' to return type 'T'}}
-      set { rightStructInstance[keyPath: member] = newValue } // expected-error {{type of expression is ambiguous without more context}}
+      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'}}
+  }
+}
+
+@dynamicMemberLookup
+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'}}
   }
 }