Support *url.URL in flags as well as arguments (#201)

Author: FollowTheProcess

README.md

@@ -234,6 +234,7 @@ The types you can use for flags currently are:
 - `time.Time`
 - `time.Duration`
 - `net.IP`
+- `*url.URL`
 - `[]int`
 - `[]int8`
 - `[]int16`

flag/flag.go

@@ -3,6 +3,7 @@ package flag
 
 import (
 	"net"
+	"net/url"
 	"time"
 )
 
@@ -46,6 +47,7 @@ type Flaggable interface {
 		time.Time |
 		time.Duration |
 		net.IP |
+		*url.URL |
 		[]int |
 		[]int8 |
 		[]int16 |

internal/arg/arg.go

@@ -120,7 +120,7 @@ func (a Arg[T]) Default() string {
 //nolint:cyclop // No other way of doing this realistically
 func (a Arg[T]) String() string {
 	if a.value == nil {
-		return "<nil>"
+		return format.Nil
 	}
 
 	switch typ := any(*a.value).(type) {
@@ -174,7 +174,7 @@ func (a Arg[T]) String() string {
 //nolint:cyclop // No other way of doing this realistically
 func (a Arg[T]) Type() string {
 	if a.value == nil {
-		return "<nil>"
+		return format.Nil
 	}
 
 	switch typ := any(*a.value).(type) {

internal/flag/flag.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"net/url"
 	"strconv"
 	"strings"
 	"time"
@@ -136,7 +137,7 @@ func (f Flag[T]) NoArgValue() string {
 //nolint:cyclop // No other way of doing this realistically
 func (f Flag[T]) String() string {
 	if f.value == nil {
-		return "<nil>"
+		return format.Nil
 	}
 
 	switch typ := any(*f.value).(type) {
@@ -179,6 +180,12 @@ func (f Flag[T]) String() string {
 	case time.Duration:
 		return typ.String()
 	case net.IP:
+		return typ.String()
+	case *url.URL:
+		if typ == nil {
+			return format.Nil
+		}
+
 		return typ.String()
 	case []int:
 		return format.Slice(typ)
@@ -212,7 +219,7 @@ func (f Flag[T]) String() string {
 // Type returns a string representation of the type of the Flag.
 func (f Flag[T]) Type() string { //nolint:cyclop // No other way of doing this realistically
 	if f.value == nil {
-		return "<nil>"
+		return format.Nil
 	}
 
 	switch typ := any(*f.value).(type) {
@@ -256,6 +263,8 @@ func (f Flag[T]) Type() string { //nolint:cyclop // No other way of doing this r
 		return format.TypeDuration
 	case net.IP:
 		return format.TypeIP
+	case *url.URL:
+		return format.TypeURL
 	case []int:
 		return format.TypeIntSlice
 	case []int8:
@@ -480,6 +489,15 @@ func (f Flag[T]) Set(str string) error {
 
 		*f.value = *parse.Cast[T](&val)
 
+		return nil
+	case *url.URL:
+		val, err := url.ParseRequestURI(str)
+		if err != nil {
+			return parse.Error(parse.KindFlag, f.name, str, typ, err)
+		}
+
+		*f.value = *parse.Cast[T](&val)
+
 		return nil
 	case []int:
 		// Like Count, a slice flag is a read/write op
@@ -759,6 +777,8 @@ func isZeroIsh[T flag.Flaggable](value T) bool { //nolint:cyclop // Not much els
 		return len(typ) == 0
 	case net.IP:
 		return len(typ) == 0
+	case *url.URL:
+		return typ == nil
 	case []int:
 		return len(typ) == 0
 	case []int8:

internal/flag/flag_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"errors"
 	"net"
+	"net/url"
 	"slices"
 	"testing"
 	"time"
@@ -914,6 +915,32 @@ func TestFlaggableTypes(t *testing.T) {
 		test.Equal(t, sliceFlag.Type(), "[]string")
 		test.Equal(t, sliceFlag.String(), `["a string", "another string"]`)
 	})
+
+	t.Run("url valid", func(t *testing.T) {
+		var u *url.URL
+
+		urlFlag, err := flag.New(&u, "url", 'u', "Set a URL", flag.Config[*url.URL]{})
+		test.Ok(t, err)
+
+		err = urlFlag.Set("https://example.com/path")
+		test.Ok(t, err)
+		test.Equal(t, u.Scheme, "https")
+		test.Equal(t, u.Host, "example.com")
+		test.Equal(t, u.Path, "/path")
+		test.Equal(t, urlFlag.Type(), "url")
+		test.Equal(t, urlFlag.String(), "https://example.com/path")
+	})
+
+	t.Run("url invalid", func(t *testing.T) {
+		var u *url.URL
+
+		urlFlag, err := flag.New(&u, "url", 'u', "Set a URL", flag.Config[*url.URL]{})
+		test.Ok(t, err)
+
+		err = urlFlag.Set("not a url")
+		test.Err(t, err)
+		test.True(t, errors.Is(err, parse.Err))
+	})
 }
 
 func TestFlagValidation(t *testing.T) {
@@ -1045,8 +1072,8 @@ func TestFlagNilSafety(t *testing.T) {
 	t.Run("composite literal", func(t *testing.T) {
 		// Users doing naughty things, should still be nil safe
 		flag := flag.Flag[bool]{}
-		test.Equal(t, flag.String(), "<nil>")
-		test.Equal(t, flag.Type(), "<nil>")
+		test.Equal(t, flag.String(), format.Nil)
+		test.Equal(t, flag.Type(), format.Nil)
 
 		err := flag.Set(format.True)
 		test.Err(t, err)

internal/format/format.go

@@ -68,6 +68,9 @@ const (
 // default values and when flags have a NoArgValue.
 const True = "true"
 
+// Nil is the string representation of a Go nil value.
+const Nil = "<nil>"
+
 // Int returns a string representation of an integer.
 func Int[T constraints.Signed](n T) string {
 	return strconv.FormatInt(int64(n), base10)