[Diagnostics] Added new diagnostic error string for composed property wrapper mismatch in DiagnosticsSema.def and made changes to show the new composed property wrapper mismatch type diagnostic in both CSDiagnostics.cpp and CSDiagnostics.h.

Author: Strieker

include/swift/AST/DiagnosticsSema.def

@@ -5678,8 +5678,8 @@ ERROR(wrapped_value_mismatch, none,
       "property type %0 does not match 'wrappedValue' type %1",
       (Type, Type))
 ERROR(composed_property_wrapper_mismatch, none,
-      "composed wrapper type %0 does not match former 'wrappedValue' type %1",
-      (Type, Type))
+      "composed wrapper type %0 does not match the type of %1.wrappedValue, which is %2",
+      (Type, Type, Type))
 
 ERROR(property_wrapper_type_access,none,
       "%select{%select{variable|constant}0|property}1 "

lib/Sema/CSDiagnostics.cpp

@@ -348,6 +348,15 @@ bool RequirementFailure::isStaticOrInstanceMember(const ValueDecl *decl) {
   return decl->isStatic();
 }
 
+bool WrappedValueMismatch::diagnoseAsError() {
+  auto *locator = getLocator();
+  auto elt = locator->getLastElementAs<LocatorPathElt::WrappedValue>();
+
+  emitDiagnostic(diag::composed_property_wrapper_mismatch, resolveType(getFromType()), elt->getType(), getToType());
+
+  return true;
+}
+
 bool RequirementFailure::diagnoseAsError() {
   const auto *reqDC = getRequirementDC();
   auto *genericCtx = getGenericContext();
@@ -639,11 +648,10 @@ Optional<Diag<Type, Type>> GenericArgumentsMismatchFailure::getDiagnosticFor(
     return diag::cannot_convert_condition_value;
   case CTP_WrappedProperty:
     return diag::wrapped_value_mismatch;
-  case CTP_ComposedPropertyWrapper:
-    return diag::composed_property_wrapper_mismatch;
 
   case CTP_ThrowStmt:
   case CTP_ForEachStmt:
+  case CTP_ComposedPropertyWrapper:
   case CTP_Unused:
   case CTP_CannotFail:
   case CTP_YieldByReference:
@@ -3132,11 +3140,10 @@ ContextualFailure::getDiagnosticFor(ContextualTypePurpose context,
 
   case CTP_WrappedProperty:
     return diag::wrapped_value_mismatch;
-  case CTP_ComposedPropertyWrapper:
-    return diag::composed_property_wrapper_mismatch;
 
   case CTP_ThrowStmt:
   case CTP_ForEachStmt:
+  case CTP_ComposedPropertyWrapper:
   case CTP_Unused:
   case CTP_CannotFail:
   case CTP_YieldByReference:

lib/Sema/CSDiagnostics.h

@@ -769,6 +769,16 @@ class MissingOptionalUnwrapFailure final : public ContextualFailure {
   void offerForceUnwrapFixIt(const Expr *expr) const;
 };
 
+class WrappedValueMismatch final : public ContextualFailure {
+public:
+  WrappedValueMismatch(const Solution &solution, Type fromType,
+                       Type toType, ConstraintLocator *locator)
+      : ContextualFailure(solution, fromType, toType, locator) {
+  }
+
+  bool diagnoseAsError() override;
+};
+
 /// Diagnostics for mismatched generic arguments e.g
 /// ```swift
 /// struct F<G> {}