add StringLongVar and StringShortVar helpers

Add helper functions to avoid repeating the `0` and/or `""`
in the case of `Var` flagset method calls.

command_test.go

@@ -64,14 +64,16 @@ func TestCommandReset(t *testing.T) {
 	})
 
 	t.Run("second run after reset", func(t *testing.T) {
-		args := []string{"--config-file=my.conf", "foo", "bar", "-a3", "hello world"}
+		args := []string{"--config-file=my.conf", "foo", "bar", "-a3", "--dseta=baz", "-tqux", "hello world"}
 		if err := rootcmd.ParseAndRun(ctx, args); err != nil {
 			t.Fatalf("second run: %v", err)
 		}
 
 		want := defaults // copy
 		want.ConfigFile = "my.conf"
 		want.Alpha = 3
+		want.Dseta = "baz"
+		want.Eta = "qux"
 
 		compareTestCommandVars(t, want, *testvars)
 	})
@@ -107,6 +109,8 @@ func makeTestCommand(t *testing.T) (*ff.Command, *testCommandVars) {
 	barFlags := ff.NewFlagSet("bar").SetParent(fooFlags)
 	barFlags.DurationVar(&vars.Delta, 'd', "delta", 3*time.Second, "delta `δ` duration")
 	barFlags.Float64Var(&vars.Epsilon, 'e', "epsilon", 3.21, "epsilon float")
+	rootFlags.StringLongVar(&vars.Dseta, "dseta", "dseta", "dseta string")
+	rootFlags.StringShortVar(&vars.Eta, 't', "eta", "eta string")
 	barCommand := &ff.Command{
 		Name:      "bar",
 		Usage:     "bar [FLAGS] ...",
@@ -126,6 +130,8 @@ type testCommandVars struct {
 	Beta       bool
 	Delta      time.Duration
 	Epsilon    float64
+	Dseta      string
+	Eta        string
 }
 
 var loremIpsum = strings.TrimSpace(`

flag_set.go

@@ -839,6 +839,16 @@ func (fs *FlagSet) StringVar(pointer *string, short rune, long string, def strin
 	return fs.Value(short, long, ffval.NewValueDefault(pointer, def), usage)
 }
 
+// StringShortVar defines a new flag in the flag set, and panics on any error.
+func (fs *FlagSet) StringShortVar(pointer *string, short rune, def string, usage string) Flag {
+	return fs.Value(short, "", ffval.NewValueDefault(pointer, def), usage)
+}
+
+// StringLongVar defines a new flag in the flag set, and panics on any error.
+func (fs *FlagSet) StringLongVar(pointer *string, long string, def string, usage string) Flag {
+	return fs.Value(0, long, ffval.NewValueDefault(pointer, def), usage)
+}
+
 // String defines a new flag in the flag set, and panics on any error.
 func (fs *FlagSet) String(short rune, long string, def string, usage string) *string {
 	var value string