Is the "cant duplicate this flag" error (v3) makes sense? #1926

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1. tarampampam

   added

   kind/questionsomeone asking a questionsomeone asking a question

   status/triagemaintainers still need to look into thismaintainers still need to look into this

   area/v3relates to / is being considered for v3relates to / is being considered for v3

   on Jun 21, 2024
2. tarampampam

   assigned

   dearchap

   on Jun 21, 2024
3. tarampampam commented on Jun 21, 2024

   

   tarampampam

   on Jun 21, 2024

   Last edited by tarampampam

   ContributorAuthor

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   Ouch, I could provide a bit more context on how exactly I encountered this error.

   Usually, if the app I develop has more than one sub-command that requires the same flags, I prefer to define every flag that I could reuse in a separate package named shared:

   package shared
   
   import (
   	// ...
   	"github.com/urfave/cli/v3"
   )
   
   var ListenPortFlag = &cli.UintFlag{
   	Name:     "port",
   	Aliases:  []string{"p"},
   	Usage:    "TCP port number",
   	Value:    8080, // default port number
   	Sources:  cli.EnvVars("LISTEN_PORT"),
   	OnlyOnce: true,
   	Required: true,
   	Validator: func(port uint64) error {
   		if port == 0 || port > 65535 {
   			return fmt.Errorf("invalid TCP port number [%d]", port)
   		}
   		return nil
   	},
   }
   
   // ...

   And use it in my commands in this manner:

   import (
   	// ...
   	"github.com/urfave/cli/v3"
   )
   
   func NewCommand() *cli.Command {
   	return &cli.Command{
   		Name:    "some_command",
   		Aliases: []string{"some", "command"},
   		Action: func(ctx context.Context, c *cli.Command) error {
   			runtime.Gosched() // <-- important, can be replaced with something else
   
   			return nil // some code goes here
   		},
   		Flags: []cli.Flag{
   			shared.ListenPortFlag, // <-- important
   		},
   	}
   }

   Everything works fine until I write a unit test to test the command execution:

   func TestCommand_RunSuccess(t *testing.T) {
   	t.Parallel()
   
   	var cmd = healthcheck.NewCommand()
   
   	require.NoError(t, cmd.Run(context.Background(), []string{"", "--port", "1234"}))
   }
   
   func TestCommand_RunFail(t *testing.T) {
   	t.Parallel()
   
   	cmd := healthcheck.NewCommand()
   
   	require.NoError(t, cmd.Run(context.Background(), []string{"", "--port", "4321"}))
   }

   If you run each test one by one (not together - that's important), each of them will pass. But, if you run them in parallel (go test ./...), the test will fail with the error:

   === RUN   TestCommand_RunFail
   === PAUSE TestCommand_RunFail
   === CONT  TestCommand_RunFail
       command_test.go:47: 
           	Error Trace:	/path/to/command_test.go:666
           	Error:      	Received unexpected error:
           	            	invalid value "4321" for flag -port: cant duplicate this flag
           	Test:       	TestCommand_RunFail
   --- FAIL: TestCommand_RunFail (0.00s)
   

   To fix this, all I need to do is replace

   // file: shared/flags.go
   
   var ListenPortFlag = &cli.UintFlag{
   //                   ^

   with

   // file: shared/flags.go
   
   var ListenPortFlag = cli.UintFlag{
   
   // file: command.go
   
   func NewCommand() *cli.Command {
   	var portFlag = shared.ListenPortFlag // make a copy
   //      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   
   	return &cli.Command{
   		Name:    "some_command",
   		Aliases: []string{"some", "command"},
   		Action: func(ctx context.Context, c *cli.Command) error {
   			return nil // some code goes here
   		},
   		Flags: []cli.Flag{
   			&portFlag, // use the copy
   //                      ^^^^^^^^^
   		},
   	}
   }

   This was so strange that I decided to create this issue to highlight this workaround.

   Note

   TL;DR - flags have their own state, so don't reuse them using pointers.
4. dearchap commented on Jun 27, 2024

   

   dearchap

   on Jun 27, 2024

   Contributor

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   @tarampampam The OnlyOnce field is used to tell the cli library to expect this flag on the cmd line only once. So if it is specified twice , for example

   --port 1234 --port 4566
   

   then you will get that error. This is to protect users from themselves. Without this option in above example port would be set to 4566

   👍React with 👍1Reacted by Pаramtamtām
5. tarampampam

   closed this as not plannedon Jun 27, 2024