StringSlice CLI should replace default values

[Mzack9999]

Description

StringSlice flags by default append values passed via CLI to default values instead of replacing them.

How to reproduce

Definition:

flagSet.StringSliceVarP(&test, "test", "t", []string{"a"}, "Test", goflags.CommaSeparatedStringSliceOptions),

CLI Command:

go run . -t b

Current Result

["a","b"]

Wanted Result

["b"]

[edoardottt]

I've tried to test this and what I get is different. Since in this loop ((flagSet *FlagSet) StringSliceVarP):

for _, defaultItem := range defaultValue {
		_ = field.Set(defaultItem)
		values, _ := ToStringSlice(defaultItem, options)
		for _, value := range values {
			_ = field.Set(value)
		}
	}

the field is set twice, the default value will be always duplicated.

Examples:

• Using examples/basic/main.go with

flagSet.StringSliceVarP(&testOptions.Email, "email", "e", []string{"A"}, "email of the user", goflags.CommaSeparatedStringSliceOptions),

and printing the result (fmt.Println(testOptions.Email)) I get:

go run examples/basic/main.go -e c
> ["A", "A", "c"]

• Same if the default value is []string{"A,A,A"}, I get

go run examples/basic/main.go -e c
> ["A", "A", "A", "A", "A", "A", "c"]

[edoardottt]

Moreover, I suspect that the problem is not only in StringSlice, but all the functions setting the default value, since also PortVarP is affected.

[Mzack9999]

@edoardottt nice catch! I'm keeping the issue open as the command line passed value should also override any default pre-existing value:

func TestSetDefaultValue(t *testing.T) {
	var data StringSlice
	flagSet := NewFlagSet()
	flagSet.StringSliceVar(&data, "test", []string{"A,A,A"}, "Default value for a test flag example", CommaSeparatedStringSliceOptions)
	flagSet.CommandLine.Parse([]string{"-test", "item1"})
	log.Fatal(data)
        // actual: ["A", "A", "A", "item1"] => wanted: ["item1"]
}