[Refactoring] Promote call to refactored completion handlers to return

When a function’s completion handler is being passed to another function and the function that the completion handler is being declared in is converted to async, replace the call to the completion handler by a `return` statement.

For example:
```swift
func foo(completion: (String) -> Void) {
  bar(completion)
}
```

becomes
```swift
func foo() async -> String {
  return await bar()
}
```

Previously, we were calling the completion handler, which no longer exists in the newly created `async` function.

Author: ahoppen

lib/IDE/Refactoring.cpp

@@ -4367,6 +4367,11 @@ struct AsyncHandlerParamDesc : public AsyncHandlerDesc {
     return AsyncHandlerParamDesc(AsyncHandlerDesc::get(Param, ignoreName),
                                  Index);
   }
+
+  bool operator==(const AsyncHandlerParamDesc &Other) const {
+    return Handler == Other.Handler && Type == Other.Type &&
+           HasError == Other.HasError && Index == Other.Index;
+  }
 };
 
 enum class ConditionType { INVALID, NIL, NOT_NIL };
@@ -4944,6 +4949,7 @@ class AsyncConverter : private SourceEntityWalker {
       OS << "await ";
       addCallToAsyncMethod(FD, TopHandler);
     });
+    OS << "\n";
     OS << tok::r_brace << "\n"; // end 'async'
     OS << tok::r_brace << "\n"; // end function body
     return true;
@@ -5292,6 +5298,22 @@ class AsyncConverter : private SourceEntityWalker {
       return;
     }
     if (auto CallbackDecl = getReferencedDecl(CallbackArg)) {
+      if (CallbackDecl == TopHandler.getHandler()) {
+        // We are refactoring the function that declared the completion handler
+        // that would be called here. We can't call the completion handler
+        // anymore because it will be removed. But since the function that
+        // declared it is being refactored to async, we can just return the
+        // values.
+        if (!HandlerDesc.willAsyncReturnVoid()) {
+          OS << tok::kw_return << " ";
+        }
+        addAwaitCall(CE, ArgList.ref(), ClassifiedBlock(), {}, HandlerDesc,
+                     /*AddDeclarations=*/false);
+        return;
+      }
+      // We are not removing the completion handler, so we can call it once the
+      // async function returns.
+
       // The completion handler that is called as part of the \p CE call.
       // This will be called once the async function returns.
       auto CompletionHandler = AsyncHandlerDesc::get(CallbackDecl,
@@ -5448,7 +5470,7 @@ class AsyncConverter : private SourceEntityWalker {
       OS << "\n";
       OS << tok::r_brace << " " << tok::kw_catch << " " << tok::l_brace << "\n";
       addCallToCompletionHandler(/*HasResult=*/false, HandlerDesc, HandlerName);
-      OS << "\n" << tok::r_brace << "\n"; // end catch
+      OS << "\n" << tok::r_brace; // end catch
     } else {
       if (!HandlerDesc.willAsyncReturnVoid()) {
         OS << tok::kw_let << " result";
@@ -5458,7 +5480,6 @@ class AsyncConverter : private SourceEntityWalker {
       AddAwaitCall();
       OS << "\n";
       addCallToCompletionHandler(/*HasResult=*/true, HandlerDesc, HandlerName);
-      OS << "\n";
     }
   }