Breaking: Add cli.FlagOption for configuring flags

Author: FollowTheProcess

README.md

@@ -77,7 +77,7 @@ func run() error {
         cli.Stdout(os.Stdout),
         cli.Example("Do a thing", "quickstart something"),
         cli.Example("Count the things", "quickstart something --count 3"),
-        cli.Flag(&count, "count", 'c', 0, "Count the things"),
+        cli.Flag(&count, "count", 'c', "Count the things"),
         cli.Run(func(ctx context.Context, cmd *cli.Command) error {
             fmt.Fprintf(cmd.Stdout(), "Hello from quickstart!, my args were: %v, count was %d\n", cmd.Args(), count)
             return nil
@@ -168,10 +168,10 @@ func buildCmd() (*cli.Command, error) {
     return cli.New(
         // ...
         // Signature is cli.Flag(*T, name, shorthand, default, description)
-        cli.Flag(&options.name, "name", 'n', "", "The name of something"),
-        cli.Flag(&options.force, "force", cli.NoShortHand, false, "Force delete without confirmation"),
-        cli.Flag(&options.size, "size", 's', 0, "Size of something"),
-        cli.Flag(&options.items, "items", 'i', nil, "Items to include"),
+        cli.Flag(&options.name, "name", 'n', "The name of something"),
+        cli.Flag(&options.force, "force", cli.NoShortHand, "Force delete without confirmation"),
+        cli.Flag(&options.size, "size", 's', "Size of something"),
+        cli.Flag(&options.items, "items", 'i', "Items to include"),
         // ...
     )
 }
@@ -374,7 +374,7 @@ Consider the following example of a bad shorthand value:
 var delete bool
 
 // Note: "de" is a bad shorthand, it's two letters
-cli.New("demo", cli.Flag(&delete, "delete", "de", false, "Delete something"))
+cli.New("demo", cli.Flag(&delete, "delete", "de", "Delete something"))
 ```
 
 In `cli` this is impossible as we use `rune` as the type for a flag shorthand, so the above example would not compile. Instead you must specify a valid rune:
@@ -383,14 +383,14 @@ In `cli` this is impossible as we use `rune` as the type for a flag shorthand, s
 var delete bool
 
 // Ahhh, that's better
-cli.New("demo", cli.Flag(&delete, "delete", 'd', false, "Delete something"))
+cli.New("demo", cli.Flag(&delete, "delete", 'd', "Delete something"))
 ```
 
 And if you don't want a shorthand? i.e. just `--delete` with no `-d` option:
 
 ```go
 var delete bool
-cli.New("demo", cli.Flag(&delete, "delete", cli.NoShortHand, false, "Delete something"))
+cli.New("demo", cli.Flag(&delete, "delete", cli.NoShortHand, "Delete something"))
 ```
 
 ## In the Wild

command.go

@@ -65,10 +65,10 @@ func New(name string, options ...Option) (*Command, error) {
 	}
 
 	// Ensure we always have at least help and version flags
-	err := Flag(&cfg.helpCalled, "help", 'h', false, "Show help for "+name).apply(&cfg)
+	err := Flag(&cfg.helpCalled, "help", 'h', "Show help for "+name).apply(&cfg)
 	errs = errors.Join(errs, err) // nil errors are discarded in join
 
-	err = Flag(&cfg.versionCalled, "version", 'V', false, "Show version info for "+name).apply(&cfg)
+	err = Flag(&cfg.versionCalled, "version", 'V', "Show version info for "+name).apply(&cfg)
 
 	errs = errors.Join(errs, err)
 	if errs != nil {

command_test.go

@@ -105,7 +105,7 @@ func TestExecute(t *testing.T) {
 
 					return nil
 				}),
-				cli.Flag(&force, "force", 'f', false, "Force something"),
+				cli.Flag(&force, "force", 'f', "Force something"),
 			}
 
 			cmd, err := cli.New("test", slices.Concat(options, tt.options)...)
@@ -270,8 +270,8 @@ func TestSubCommandExecute(t *testing.T) {
 
 			sub1 := func() (*cli.Command, error) {
 				defaultOpts := []cli.Option{
-					cli.Flag(&force, "force", 'f', false, "Force for sub1"),
-					cli.Flag(&something, "something", 's', "", "Something for sub1"),
+					cli.Flag(&force, "force", 'f', "Force for sub1"),
+					cli.Flag(&something, "something", 's', "Something for sub1"),
 					cli.Run(func(ctx context.Context, cmd *cli.Command) error {
 						if something == "" {
 							something = "<empty>"
@@ -315,8 +315,8 @@ func TestSubCommandExecute(t *testing.T) {
 
 						return nil
 					}),
-					cli.Flag(&deleteMe, "delete", 'd', false, "Delete for sub2"),
-					cli.Flag(&number, "number", 'n', -1, "Number for sub2"),
+					cli.Flag(&deleteMe, "delete", 'd', "Delete for sub2"),
+					cli.Flag(&number, "number", 'n', "Number for sub2", cli.FlagDefault(-1)),
 				}
 
 				opts := slices.Concat(defaultOpts, tt.sub2Options)
@@ -433,7 +433,7 @@ func TestHelp(t *testing.T) {
 				cli.OverrideArgs([]string{"--help"}),
 				cli.Arg(new(string), "src", "The file to copy"),                                           // This one is required
 				cli.Arg(new(string), "dest", "Destination to copy to", cli.ArgDefault("destination.txt")), // This one is optional
-				cli.Flag(new(flag.Count), "verbosity", 'v', 0, "Increase the verbosity level"),
+				cli.Flag(new(flag.Count), "verbosity", 'v', "Increase the verbosity level"),
 				cli.Run(func(ctx context.Context, cmd *cli.Command) error { return nil }),
 			},
 			wantErr: false,
@@ -493,10 +493,16 @@ func TestHelp(t *testing.T) {
 				cli.Short("A cool CLI to do things"),
 				cli.Long("A longer, probably multiline description"),
 				cli.SubCommands(sub1, sub2),
-				cli.Flag(new(bool), "delete", 'd', false, "Delete something"),
-				cli.Flag(new(int), "count", flag.NoShortHand, -1, "Count something"),
-				cli.Flag(new([]string), "things", flag.NoShortHand, nil, "Names of things"),
-				cli.Flag(new([]string), "more", flag.NoShortHand, []string{"one", "two"}, "Names of things with a default"),
+				cli.Flag(new(bool), "delete", 'd', "Delete something"),
+				cli.Flag(new(int), "count", flag.NoShortHand, "Count something", cli.FlagDefault(-1)),
+				cli.Flag(new([]string), "things", flag.NoShortHand, "Names of things"),
+				cli.Flag(
+					new([]string),
+					"more",
+					flag.NoShortHand,
+					"Names of things with a default",
+					cli.FlagDefault([]string{"one", "two"}),
+				),
 			},
 			wantErr: false,
 		},
@@ -735,16 +741,16 @@ func TestOptionValidation(t *testing.T) {
 		{
 			name: "flag already exists",
 			options: []cli.Option{
-				cli.Flag(new(int), "count", 'c', 0, "Count something"),
-				cli.Flag(new(int), "count", 'c', 0, "Count something (again)"),
+				cli.Flag(new(int), "count", 'c', "Count something"),
+				cli.Flag(new(int), "count", 'c', "Count something (again)"),
 			},
 			errMsg: `flag "count" already defined`,
 		},
 		{
 			name: "flag short already exists",
 			options: []cli.Option{
-				cli.Flag(new(int), "count", 'c', 0, "Count something"),
-				cli.Flag(new(string), "config", 'c', "", "Path to config file"),
+				cli.Flag(new(int), "count", 'c', "Count something"),
+				cli.Flag(new(string), "config", 'c', "Path to config file"),
 			},
 			errMsg: `could not add flag "config" to command "test": shorthand "c" already in use for flag "count"`,
 		},
@@ -884,8 +890,8 @@ func TestCommandOptionOrder(t *testing.T) {
 		cli.Arg(new(string), "third", "Third arg"),
 		cli.Version("v1.2.3"),
 		cli.SubCommands(sub),
-		cli.Flag(&f, "flag", 'f', false, "Set a bool flag"),
-		cli.Flag(&count, "count", 'c', 0, "Count a thing"),
+		cli.Flag(&f, "flag", 'f', "Set a bool flag"),
+		cli.Flag(&count, "count", 'c', "Count a thing"),
 	}
 
 	baseLineOptions := slices.Concat(
@@ -1001,9 +1007,9 @@ func BenchmarkNew(b *testing.B) {
 			cli.Version("dev"),
 			cli.Commit("dfdddaf"),
 			cli.Example("An example", "bench --help"),
-			cli.Flag(new(bool), "force", 'f', false, "Force something"),
-			cli.Flag(new(string), "name", 'n', "", "The name of something"),
-			cli.Flag(new(int), "count", 'c', 1, "Count something"),
+			cli.Flag(new(bool), "force", 'f', "Force something"),
+			cli.Flag(new(string), "name", 'n', "The name of something"),
+			cli.Flag(new(int), "count", 'c', "Count something", cli.FlagDefault(1)),
 			cli.Run(func(ctx context.Context, cmd *cli.Command) error { return nil }),
 		)
 		if err != nil {

examples/cover/main.go

@@ -20,7 +20,7 @@ func main() {
 		cli.Version("v1.2.3"),
 		cli.Stdout(os.Stdout),
 		cli.Example("Do a thing", "demo thing --count"),
-		cli.Flag(&count, "count", 'c', 0, "Count the thing"),
+		cli.Flag(&count, "count", 'c', "Count the thing"),
 		cli.Run(func(ctx context.Context, cmd *cli.Command) error {
 			fmt.Fprintln(cmd.Stdout(), "Hello from demo, my arguments were: ", cmd.Args())
 			return nil

examples/quickstart/main.go

@@ -29,7 +29,7 @@ func run() error {
 		cli.Stdout(os.Stdout),
 		cli.Example("Do a thing", "quickstart something"),
 		cli.Example("Count the things", "quickstart something --count 3"),
-		cli.Flag(&count, "count", 'c', 0, "Count the things"),
+		cli.Flag(&count, "count", 'c', "Count the things"),
 		cli.Run(func(ctx context.Context, cmd *cli.Command) error {
 			fmt.Fprintf(cmd.Stdout(), "Hello from quickstart!, my args were: %v, count was %d\n", cmd.Args(), count)
 			return nil

examples/subcommands/cli.go

@@ -39,10 +39,10 @@ func buildSayCommand() (*cli.Command, error) {
 		cli.Short("Print a message"),
 		cli.Example("Say a well known phrase", "demo say hello world"),
 		cli.Example("Now louder", "demo say hello world --shout"),
-		cli.Flag(&options.shout, "shout", 's', false, "Say the message louder"),
-		cli.Flag(&options.count, "count", 'c', 0, "Count the things"),
-		cli.Flag(&options.thing, "thing", 't', "", "Name of the thing"),
-		cli.Flag(&options.items, "item", 'i', nil, "Items to add to a list"),
+		cli.Flag(&options.shout, "shout", 's', "Say the message louder"),
+		cli.Flag(&options.count, "count", 'c', "Count the things"),
+		cli.Flag(&options.thing, "thing", 't', "Name of the thing"),
+		cli.Flag(&options.items, "item", 'i', "Items to add to a list"),
 		cli.Run(func(ctx context.Context, cmd *cli.Command) error {
 			if options.shout {
 				for _, arg := range cmd.Args() {
@@ -88,10 +88,10 @@ func buildDoCommand() (*cli.Command, error) {
 		cli.Example("Do it for a specific duration", "demo do something --duration 1m30s"),
 		cli.Version("do version"),
 		cli.Arg(&thing, "thing", "Thing to do"),
-		cli.Flag(&options.count, "count", 'c', 1, "Number of times to do the thing"),
-		cli.Flag(&options.fast, "fast", 'f', false, "Do the thing quickly"),
-		cli.Flag(&options.verbosity, "verbosity", 'v', 0, "Increase the verbosity level"),
-		cli.Flag(&options.duration, "duration", 'd', 1*time.Second, "Do the thing for a specific duration"),
+		cli.Flag(&options.count, "count", 'c', "Number of times to do the thing", cli.FlagDefault(1)),
+		cli.Flag(&options.fast, "fast", 'f', "Do the thing quickly"),
+		cli.Flag(&options.verbosity, "verbosity", 'v', "Increase the verbosity level"),
+		cli.Flag(&options.duration, "duration", 'd', "Do the thing for a specific duration", cli.FlagDefault(1*time.Second)),
 		cli.Run(func(ctx context.Context, cmd *cli.Command) error {
 			if options.fast {
 				fmt.Fprintf(

internal/flag/config.go

@@ -0,0 +1,9 @@
+package flag
+
+import "go.followtheprocess.codes/cli/flag"
+
+// Config represents the internal configuration of a [Flag].
+type Config[T flag.Flaggable] struct {
+	// DefaultValue holds the intended default value of the flag.
+	DefaultValue T
+}

internal/flag/flag.go

@@ -33,12 +33,7 @@ type Flag[T flag.Flaggable] struct {
 //
 // The name should be as it appears on the command line, e.g. "force" for a --force flag. An optional
 // shorthand can be created by setting short to a single letter value, e.g. "f" to also create a -f version of "force".
-//
-// If you want the flag to be longhand only, pass "" for short.
-//
-//	var force bool
-//	flag.New(&force, "force", 'f', false, "Force deletion without confirmation")
-func New[T flag.Flaggable](p *T, name string, short rune, value T, usage string) (Flag[T], error) {
+func New[T flag.Flaggable](p *T, name string, short rune, usage string, config Config[T]) (Flag[T], error) {
 	if err := validateFlagName(name); err != nil {
 		return Flag[T]{}, fmt.Errorf("invalid flag name %q: %w", name, err)
 	}
@@ -51,14 +46,14 @@ func New[T flag.Flaggable](p *T, name string, short rune, value T, usage string)
 		p = new(T)
 	}
 
-	*p = value
+	*p = config.DefaultValue
 
 	// If the default value is not the zero value for the type, it is treated as
 	// significant and shown to the user
-	if !isZeroIsh(value) {
+	if !isZeroIsh(*p) {
 		// \t so that defaults get aligned by tabwriter when the command
 		// dumps the flags
-		usage += fmt.Sprintf("\t[default: %v]", value)
+		usage += fmt.Sprintf("\t[default: %v]", *p)
 	}
 
 	flag := Flag[T]{