Duplicate subcommands are silently ignored by ArgumentParser #976

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1. true-false-maybe commented on Sep 24, 2026

   

   true-false-maybe

   on Sep 24, 2026

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   As a small work around it's possible to do something like this, though i think it makes more sense if Argument-Parser would do something like this on it's own:

   /// A `ParsableCommand` which can validate *all* descendants. Therefore it on the root command.
   /// If there are duplicate commands the command will early exit before doing anything.
   ///
   /// IMPORTANT: if you overwrite `validate` you should call `validateCommandSubtree(command: Self.self)`,
   /// otherwise this protocol is useless
   public protocol ValidatedRootCommand: ParsableCommand {}
   
   public extension ValidatedRootCommand {
       func validate() throws {
           validateCommandSubtree(command: Self.self)
       }
   
       func validateCommandSubtree(command: any ParsableCommand.Type, commandPath: [String?] = []) {
           let commandPath = commandPath + [command.configuration.commandName]
   
           let failingCommands: [String?: [any ParsableCommand.Type]] = command.configuration.subcommands
               .grouped { $0.configuration.commandName }
               .filter { $0.value.count > 1 }
   
           guard failingCommands.isEmpty else {
               let errorTable = failingCommands.map {
                   return "- '\($0.key, default: "<nil>")':\n    - \(String($0.value.map { String(describing: $0) }.joined(separator: ", ")))"
               }.joined(separator: "\n\n")
   
               // NOTE: throwing is not enough, we need to exit
               Self.exit(withError: ValidationError("At command '\(String(commandPath.compacted().joined(separator: " ")))' there are multiple possible subcommand-types:\n\(errorTable)"))
           }
   
           for subcommand in command.configuration.subcommands {
               validateCommandSubtree(command: subcommand, commandPath: commandPath)
           }
       }
   }