fix(46824): remove duplicate private identifier errors

Author: Andrewnt219

src/compiler/checker.ts

@@ -28224,12 +28224,18 @@ namespace ts {
             if (!getContainingClass(privId)) {
                 return grammarErrorOnNode(privId, Diagnostics.Private_identifiers_are_not_allowed_outside_class_bodies);
             }
-            if (!isExpressionNode(privId)) {
-                return grammarErrorOnNode(privId, Diagnostics.Private_identifiers_are_only_allowed_in_class_bodies_and_may_only_be_used_as_part_of_a_class_member_declaration_property_access_or_on_the_left_hand_side_of_an_in_expression);
-            }
-            if (!getSymbolForPrivateIdentifierExpression(privId)) {
-                return grammarErrorOnNode(privId, Diagnostics.Cannot_find_name_0, idText(privId));
+
+            if (!isForInStatement(privId.parent)) {
+                if (!isExpressionNode(privId)) {
+                    return grammarErrorOnNode(privId, Diagnostics.Private_identifiers_are_only_allowed_in_class_bodies_and_may_only_be_used_as_part_of_a_class_member_declaration_property_access_or_on_the_left_hand_side_of_an_in_expression);
+                }
+
+                const isInOperation = isBinaryExpression(privId.parent) && privId.parent.operatorToken.kind === SyntaxKind.InKeyword;
+                if (!getSymbolForPrivateIdentifierExpression(privId) && !isInOperation) {
+                    return grammarErrorOnNode(privId, Diagnostics.Cannot_find_name_0, idText(privId));
+                }
             }
+
             return false;
         }