fix: ensure struct value by reflect type check

config/loader.go

@@ -50,18 +50,12 @@ type Fallback func() (string, error)
 //
 // Note: If the configuration is a pointer to a struct, the experimental feature behind viper.ExperimentalBindStruct() will not be used.
 func Load[T Settings](path string, fallbacks ...Fallback) (cfg T, err error) {
-	k := reflect.TypeOf(cfg).Kind()
-	if k != reflect.Struct && k != reflect.Pointer {
-		return cfg, errors.New("configuration must be a struct or a pointer to a struct")
-	}
-
-	var opts []viper.Option
-	// The feature behind this option only works on direct struct values (not pointers)
-	if k != reflect.Pointer {
-		opts = append(opts, viper.ExperimentalBindStruct())
+	cfg, err = ensureStruct(cfg)
+	if err != nil {
+		return cfg, fmt.Errorf("given type is not a struct: %w", err)
 	}
 
-	v := viper.NewWithOptions(opts...)
+	v := viper.NewWithOptions(viper.ExperimentalBindStruct())
 	v.SetFs(fsys)
 	if path == "" {
 		if len(fallbacks) == 0 {
@@ -121,3 +115,23 @@ func defaultFallback() (string, error) {
 	}
 	return filepath.Join(home, bin, "config.yaml"), nil
 }
+
+// ensureStruct ensures that the provided value is a struct or a pointer to a struct.
+func ensureStruct[T any](value T) (T, error) {
+	var empty T
+	t := reflect.TypeOf(value)
+
+	for t.Kind() == reflect.Pointer {
+		t = t.Elem()
+	}
+
+	if t.Kind() != reflect.Struct {
+		return empty, errors.New("value must be a struct or a pointer to a struct")
+	}
+
+	if reflect.TypeOf(value).Kind() == reflect.Pointer && reflect.ValueOf(value).IsNil() {
+		return reflect.New(t).Interface().(T), nil
+	}
+
+	return value, nil
+}

config/loader_test.go

@@ -16,7 +16,7 @@ type config struct {
 }
 
 func (c config) IsEmpty() bool {
-	return c == (config{})
+	return reflect.DeepEqual(c, config{})
 }
 
 func TestLoad(t *testing.T) {
@@ -108,6 +108,50 @@ func TestLoad_InvalidType(t *testing.T) {
 	}
 }
 
+func TestLoad_Pointer(t *testing.T) {
+	tests := []struct {
+		name    string
+		path    string
+		want    Settings
+		wantErr bool
+	}{
+		{
+			name: "pointer",
+			path: "testdata/config.yaml",
+			want: &config{
+				Host: "localhost",
+				Port: 8080,
+			},
+			wantErr: false,
+		},
+		{
+			name:    "nil pointer",
+			path:    "testdata/config.yaml",
+			want:    (*config)(nil),
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			setup(t, tt.path, tt.want)
+			if reflect.ValueOf(tt.want).IsNil() {
+				tt.want = &config{}
+			}
+
+			got, err := Load[*config](tt.path)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Load() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			if err == nil && !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("Load() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func setup(t *testing.T, path string, cfg Settings, fallbacks ...Fallback) {
 	t.Helper()
 	if path == "" {