fix: ensure pointers can be detected as bools

This required adding a BoolMapperExt interface.

mapper.go

@@ -123,9 +123,16 @@ type VarsContributor interface {
 //
 // This is used solely for formatting help.
 type BoolMapper interface {
+	Mapper
 	IsBool() bool
 }
 
+// BoolMapperExt allows a Mapper to dynamically determine if a value is a boolean.
+type BoolMapperExt interface {
+	Mapper
+	IsBoolFromValue(v reflect.Value) bool
+}
+
 // A MapperFunc is a single function that complies with the Mapper interface.
 type MapperFunc func(ctx *DecodeContext, target reflect.Value) error
 
@@ -186,6 +193,7 @@ func (r *Registry) ForType(typ reflect.Type) Mapper {
 	// Check if the type implements MapperValue.
 	for _, impl := range []reflect.Type{typ, reflect.PtrTo(typ)} {
 		if impl.Implements(mapperValueType) {
+			// FIXME: This should pass in the bool mapper.
 			return &mapperValueAdapter{impl.Implements(boolMapperType)}
 		}
 	}
@@ -223,8 +231,8 @@ func (r *Registry) RegisterKind(kind reflect.Kind, mapper Mapper) *Registry {
 //
 // eg.
 //
-// 		Mapper string `kong:"type='colour'`
-//   	registry.RegisterName("colour", ...)
+//			Mapper string `kong:"type='colour'`
+//	  	registry.RegisterName("colour", ...)
 func (r *Registry) RegisterName(name string, mapper Mapper) *Registry {
 	r.names[name] = mapper
 	return r
@@ -275,7 +283,7 @@ func (r *Registry) RegisterDefaults() *Registry {
 		RegisterName("existingfile", existingFileMapper(r)).
 		RegisterName("existingdir", existingDirMapper(r)).
 		RegisterName("counter", counterMapper()).
-		RegisterKind(reflect.Ptr, ptrMapper(r))
+		RegisterKind(reflect.Ptr, ptrMapper{r})
 }
 
 type boolMapper struct{}
@@ -676,20 +684,40 @@ func existingDirMapper(r *Registry) MapperFunc {
 	}
 }
 
-func ptrMapper(r *Registry) MapperFunc {
-	return func(ctx *DecodeContext, target reflect.Value) error {
-		elem := reflect.New(target.Type().Elem()).Elem()
-		nestedMapper := r.ForValue(elem)
-		if nestedMapper == nil {
-			return fmt.Errorf("cannot find mapper for %v", target.Type().Elem().String())
-		}
-		err := nestedMapper.Decode(ctx, elem)
-		if err != nil {
-			return err
-		}
-		target.Set(elem.Addr())
-		return nil
+type ptrMapper struct {
+	r *Registry
+}
+
+var _ BoolMapperExt = (*ptrMapper)(nil)
+
+// IsBoolFromValue implements BoolMapperExt
+func (p ptrMapper) IsBoolFromValue(target reflect.Value) bool {
+	elem := reflect.New(target.Type().Elem()).Elem()
+	nestedMapper := p.r.ForValue(elem)
+	if nestedMapper == nil {
+		return false
 	}
+	if bm, ok := nestedMapper.(BoolMapper); ok && bm.IsBool() {
+		return true
+	}
+	if bm, ok := nestedMapper.(BoolMapperExt); ok && bm.IsBoolFromValue(target) {
+		return true
+	}
+	return target.Kind() == reflect.Ptr && target.Type().Elem().Kind() == reflect.Bool
+}
+
+func (p ptrMapper) Decode(ctx *DecodeContext, target reflect.Value) error {
+	elem := reflect.New(target.Type().Elem()).Elem()
+	nestedMapper := p.r.ForValue(elem)
+	if nestedMapper == nil {
+		return fmt.Errorf("cannot find mapper for %v", target.Type().Elem().String())
+	}
+	err := nestedMapper.Decode(ctx, elem)
+	if err != nil {
+		return err
+	}
+	target.Set(elem.Addr())
+	return nil
 }
 
 func counterMapper() MapperFunc {
@@ -753,7 +781,7 @@ func urlMapper() MapperFunc {
 //
 // It differs from strings.Split() in that the separator can exist in a field by escaping it with a \. eg.
 //
-//     SplitEscaped(`hello\,there,bob`, ',') == []string{"hello,there", "bob"}
+//	SplitEscaped(`hello\,there,bob`, ',') == []string{"hello,there", "bob"}
 func SplitEscaped(s string, sep rune) (out []string) {
 	if sep == -1 {
 		return []string{s}
@@ -786,7 +814,7 @@ func SplitEscaped(s string, sep rune) (out []string) {
 
 // JoinEscaped joins a slice of strings on sep, but also escapes any instances of sep in the fields with \. eg.
 //
-//     JoinEscaped([]string{"hello,there", "bob"}, ',') == `hello\,there,bob`
+//	JoinEscaped([]string{"hello,there", "bob"}, ',') == `hello\,there,bob`
 func JoinEscaped(s []string, sep rune) string {
 	escaped := []string{}
 	for _, e := range s {

model.go

@@ -318,6 +318,9 @@ func (v *Value) IsMap() bool {
 
 // IsBool returns true if the underlying value is a boolean.
 func (v *Value) IsBool() bool {
+	if m, ok := v.Mapper.(BoolMapperExt); ok && m.IsBoolFromValue(v.Target) {
+		return true
+	}
 	if m, ok := v.Mapper.(BoolMapper); ok && m.IsBool() {
 		return true
 	}