[Typechecker] Diagnose the original wrapped property instead of the nearest non-implicit decl context

Author: theblixguy

include/swift/AST/DiagnosticsSema.def

@@ -756,7 +756,8 @@ ERROR(invalid_redecl_init,none,
       "invalid redeclaration of synthesized %select{|memberwise }1%0",
       (DeclName, bool))
 ERROR(invalid_redecl_implicit,none,
-      "invalid redeclaration of synthesized %select{%0|witness for protocol requirement}1 %2",
+      "invalid redeclaration of synthesized "
+      "%select{%0|implementation for protocol requirement}1 %2",
       (DescriptiveDeclKind, bool, DeclName))
 WARNING(invalid_redecl_swift5_warning,none,
         "redeclaration of %0 is deprecated and will be an error in Swift 5",
@@ -765,7 +766,9 @@ WARNING(invalid_redecl_swift5_warning,none,
 NOTE(invalid_redecl_prev,none,
      "%0 previously declared here", (DeclName))
 NOTE(invalid_redecl_implicit_wrapper,none,
-     "%0 synthesized for property wrapper %select{projected value|backing storage}1", (DeclName, bool))
+     "%0 synthesized for property wrapper "
+     "%select{projected value|backing storage}1",
+     (DeclName, bool))
 
 ERROR(ambiguous_type_base,none,
       "%0 is ambiguous for type lookup in this context", (DeclNameRef))

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -722,10 +722,20 @@ CheckRedeclarationRequest::evaluate(Evaluator &eval, ValueDecl *current) const {
           // 'other' is implicit, we diagnose 'current'.
           const auto *declToDiagnose = currentDC->getAsDecl();
           if (current->isImplicit() && other->isImplicit()) {
-            // Get the nearest non-implicit decl context
-            while (declToDiagnose && declToDiagnose->isImplicit() &&
-                   declToDiagnose->getDeclContext()) {
-              declToDiagnose = declToDiagnose->getDeclContext()->getAsDecl();
+            // If 'current' is a property wrapper backing storage property
+            // or projected value property, then diagnose the wrapped
+            // property instead of the nearest non-implicit DC.
+            if (auto VD = dyn_cast<VarDecl>(current)) {
+              if (auto originalWrappedProperty =
+                      VD->getOriginalWrappedProperty()) {
+                declToDiagnose = originalWrappedProperty;
+              }
+            } else {
+              // Get the nearest non-implicit decl context
+              while (declToDiagnose && declToDiagnose->isImplicit() &&
+                     declToDiagnose->getDeclContext()) {
+                declToDiagnose = declToDiagnose->getDeclContext()->getAsDecl();
+              }
             }
           } else {
             declToDiagnose = current->isImplicit() ? other : current;
@@ -748,7 +758,7 @@ CheckRedeclarationRequest::evaluate(Evaluator &eval, ValueDecl *current) const {
           // Emit a specialized note if the one of the declarations is
           // the backing storage property ('_foo') or projected value
           // property ('$foo') for a wrapped property. The backing or
-          // storage var has the same source location as the wrapped
+          // projected var has the same source location as the wrapped
           // property we diagnosed above, so we don't need to extract
           // the original property.
           const VarDecl *varToDiagnose = nullptr;