[yxshee]

What type of PR is this?

• bug

What this PR does / why we need it:

A -- ends flag parsing, and everything after it should be an argument of the command. That works for flags, but the first argument after -- is still looked up as a subcommand name:

cmd := &cli.Command{
	Name:     "app",
	Action:   func(_ context.Context, c *cli.Command) error { fmt.Println("args:", c.Args().Slice()); return nil },
	Commands: []*cli.Command{{Name: "sub", Action: func(context.Context, *cli.Command) error { fmt.Println("sub ran"); return nil }}},
}

On main, app -- sub prints sub ran, and app -- sub --x fails with flag provided but not defined: -x, because sub then parses --x as a flag. Expected: the root action runs with args: [sub] and args: [sub --x]. Shell completion already follows this rule: since #2412 it suggests nothing after a --, "only positional arguments are accepted after it", so app -- su<TAB> offers nothing but app -- sub runs the subcommand.

• command_parse.go: parseFlags records when the parsed args start right after a -- (nothing positional came before it).
• command_run.go: in that case the first arg is not looked up as a subcommand (or passed to SuggestCommandFunc). DefaultCommand still applies, so app -- foo behaves like app foo did before.
• command.go: the unexported field that holds this state.
• command_test.go: TestCommand_CommandNameAfterTerminatorIsAnArgument.

A -- that comes after a positional argument (app foo -- sub) already worked, since foo was taken as the first argument.

Which issue(s) this PR fixes:

None, found while checking -- handling with subcommands.

Testing

• TestCommand_CommandNameAfterTerminatorIsAnArgument fails on main with flag provided but not defined: -notAFlag and the subcommand must not run when its name follows "--", and passes with this change.
• make vet, make test, make test GFLAGS='--tags urfave_cli_no_template', make lint, make check-binary-size, make generate, make diffcheck and make v3diff pass, and golangci-lint run reports 0 issues.

Release Notes

A command name given after "--" is now passed to the command as an argument instead of running that subcommand.