[Refactoring] Use known alternative in async refactoring if one exists

include/swift/AST/Decl.h

@@ -6220,7 +6220,7 @@ class AbstractFunctionDecl : public GenericContext, public ValueDecl {
   /// handler if \p asyncAlternative is not set (with the same conditions on
   /// its type as above).
   Optional<unsigned> findPotentialCompletionHandlerParam(
-      AbstractFunctionDecl *asyncAlternative = nullptr) const;
+      const AbstractFunctionDecl *asyncAlternative = nullptr) const;
 
   /// Determine whether this function is implicitly known to have its
   /// parameters of function type be @_unsafeSendable.
@@ -6599,6 +6599,10 @@ class AccessorDecl final : public FuncDecl {
     Bits.AccessorDecl.IsTransparentComputed = 1;
   }
 
+  /// A representation of the name to be displayed to users. \c getNameStr
+  /// for anything other than a getter or setter.
+  void printUserFacingName(llvm::raw_ostream &out) const;
+
   static bool classof(const Decl *D) {
     return D->getKind() == DeclKind::Accessor;
   }

include/swift/AST/DiagnosticsSema.def

@@ -30,6 +30,8 @@ NOTE(decl_declared_here,none,
      "%0 declared here", (DeclName))
 NOTE(kind_declared_here,none,
      "%0 declared here", (DescriptiveDeclKind))
+NOTE(descriptive_decl_declared_here,none,
+     "'%0' declared here", (StringRef))
 NOTE(implicit_member_declared_here,none,
      "%1 '%0' is implicitly declared", (StringRef, StringRef))
 NOTE(extended_type_declared_here,none,

lib/AST/Attr.cpp

@@ -886,17 +886,10 @@ bool DeclAttribute::printImpl(ASTPrinter &Printer, const PrintOptions &Options,
     } else if (Attr->RenameDecl) {
       Printer << ", renamed: \"";
       if (auto *Accessor = dyn_cast<AccessorDecl>(Attr->RenameDecl)) {
-        switch (Accessor->getAccessorKind()) {
-        case AccessorKind::Get:
-          Printer << "getter:";
-          break;
-        case AccessorKind::Set:
-          Printer << "setter:";
-          break;
-        default:
-          break;
-        }
-        Printer << Accessor->getStorage()->getName() << "()";
+        SmallString<32> Name;
+        llvm::raw_svector_ostream OS(Name);
+        Accessor->printUserFacingName(OS);
+        Printer << Name.str();
       } else {
         Printer << Attr->RenameDecl->getName();
       }

lib/AST/Decl.cpp

@@ -7120,7 +7120,7 @@ static bool isPotentialCompletionHandler(const ParamDecl *param) {
 }
 
 Optional<unsigned> AbstractFunctionDecl::findPotentialCompletionHandlerParam(
-    AbstractFunctionDecl *asyncAlternative) const {
+    const AbstractFunctionDecl *asyncAlternative) const {
   const ParameterList *params = getParameters();
   if (params->size() == 0)
     return None;
@@ -7203,7 +7203,7 @@ Optional<unsigned> AbstractFunctionDecl::findPotentialCompletionHandlerParam(
 
     // The next original param should match the current async, so don't
     // increment the async index
-    potentialParam = asyncParamIndex;
+    potentialParam = paramIndex;
     paramIndex++;
   }
   return potentialParam;
@@ -7910,6 +7910,28 @@ bool AccessorDecl::isSimpleDidSet() const {
                            SimpleDidSetRequest{mutableThis}, false);
 }
 
+void AccessorDecl::printUserFacingName(raw_ostream &out) const {
+  switch (getAccessorKind()) {
+  case AccessorKind::Get:
+    out << "getter:";
+    break;
+  case AccessorKind::Set:
+    out << "setter:";
+    break;
+  default:
+    out << getName();
+    return;
+  }
+
+  out << getStorage()->getName() << "(";
+  if (this->isSetter()) {
+    for (const auto *param : *getParameters()) {
+      out << param->getName() << ":";
+    }
+  }
+  out << ")";
+}
+
 StaticSpellingKind FuncDecl::getCorrectStaticSpelling() const {
   assert(getDeclContext()->isTypeContext());
   if (!isStatic())