fix: slice handling (#16)

load.go

@@ -69,6 +69,8 @@ func loadConfig(cfg Config, flags flagRefs, configurations ...any) error {
 		// unmarshal fully populated viper object onto config
 		err := v.Unmarshal(configuration, func(dc *mapstructure.DecoderConfig) {
 			dc.TagName = cfg.TagName
+			// ZeroFields will use what is present in the config file instead of modifying existing defaults
+			dc.ZeroFields = true
 		})
 		if err != nil {
 			return err
@@ -284,6 +286,10 @@ func isStruct(typ reflect.Type) bool {
 	return typ.Kind() == reflect.Struct
 }
 
+func isSlice(typ reflect.Type) bool {
+	return typ.Kind() == reflect.Slice
+}
+
 func isNotFoundErr(err error) bool {
 	var notFound *viper.ConfigFileNotFoundError
 	return err != nil && errors.As(err, &notFound)

load_test.go

@@ -252,6 +252,35 @@ func Test_flagBoolPtrValues(t *testing.T) {
 	require.Equal(t, true, *a.Bool)
 }
 
+func Test_zeroFields(t *testing.T) {
+	type s struct {
+		List []string `mapstructure:"list"`
+	}
+	a := &s{
+		List: []string{
+			"default1",
+			"default2",
+			"default3",
+		},
+	}
+
+	cmd := &cobra.Command{}
+
+	cfg := NewConfig("app")
+	err := Load(cfg, cmd, a)
+	require.NoError(t, err)
+
+	require.Equal(t, []string{"default1", "default2", "default3"}, a.List)
+
+	t.Setenv("APP_LIST", "set1,set2")
+
+	cfg = NewConfig("app")
+	err = Load(cfg, cmd, a)
+	require.NoError(t, err)
+
+	require.Equal(t, []string{"set1", "set2"}, a.List)
+}
+
 func Test_AllFieldTypes(t *testing.T) {
 	appName := "app"
 	envName := func(name string) string {

summarize.go

@@ -17,7 +17,7 @@ func Summarize(cfg Config, descriptions DescriptionProvider, values ...any) stri
 		v := reflect.ValueOf(value)
 		summarize(cfg, descriptions, root, v, nil)
 	}
-	return root.stringify()
+	return root.stringify(cfg)
 }
 
 func SummarizeCommand(cfg Config, cmd *cobra.Command, values ...any) string {
@@ -98,9 +98,71 @@ func summarize(cfg Config, descriptions DescriptionProvider, s *section, value r
 	}
 }
 
-func printVal(value reflect.Value) string {
-	v, _ := base(value)
-	if v.CanInterface() {
+// printVal prints a value in YAML format
+func printVal(cfg Config, value reflect.Value, indent string) string {
+	buf := bytes.Buffer{}
+
+	v, t := base(value)
+	switch {
+	case isSlice(t):
+		if v.Len() == 0 {
+			return "[]"
+		}
+
+		for i := 0; i < v.Len(); i++ {
+			v := v.Index(i)
+			buf.WriteString("\n")
+			buf.WriteString(indent)
+			buf.WriteString("- ")
+
+			val := printVal(cfg, v, indent+"  ")
+			val = strings.TrimSpace(val)
+			buf.WriteString(val)
+
+			// separate struct entries by an empty line
+			_, t := base(v)
+			if isStruct(t) {
+				buf.WriteString("\n")
+			}
+		}
+
+	case isStruct(t):
+		for i := 0; i < t.NumField(); i++ {
+			f := t.Field(i)
+			if !f.IsExported() {
+				continue
+			}
+
+			name := f.Name
+
+			if tag, ok := f.Tag.Lookup(cfg.TagName); ok {
+				parts := strings.Split(tag, ",")
+				tag = parts[0]
+				if tag == "-" {
+					continue
+				}
+				switch {
+				case contains(parts, "squash"):
+					name = ""
+				case tag == "":
+				default:
+					name = tag
+				}
+			}
+
+			v := v.Field(i)
+
+			buf.WriteString("\n")
+			buf.WriteString(indent)
+
+			val := printVal(cfg, v, indent+"  ")
+
+			val = fmt.Sprintf("%s: %s", name, val)
+
+			buf.WriteString(val)
+		}
+
+	case v.CanInterface():
 		v := v.Interface()
 		switch v.(type) {
 		case string:
@@ -109,7 +171,11 @@ func printVal(value reflect.Value) string {
 			return fmt.Sprintf("%v", v)
 		}
 	}
-	return ""
+
+	val := buf.String()
+	// for slices, there will be an extra newline, which we want to remove
+	val = strings.TrimSuffix(val, "\n")
+	return val
 }
 
 func base(v reflect.Value) (reflect.Value, reflect.Type) {
@@ -171,13 +237,13 @@ func (s *section) add(log logger.Logger, name string, value reflect.Value, descr
 	return add
 }
 
-func (s *section) stringify() string {
+func (s *section) stringify(cfg Config) string {
 	out := &bytes.Buffer{}
-	stringifySection(out, s, "")
+	stringifySection(cfg, out, s, "")
 	return out.String()
 }
 
-func stringifySection(out *bytes.Buffer, s *section, indent string) {
+func stringifySection(cfg Config, out *bytes.Buffer, s *section, indent string) {
 	nextIndent := indent
 
 	if s.name != "" {
@@ -215,14 +281,15 @@ func stringifySection(out *bytes.Buffer, s *section, indent string) {
 
 		if s.value.IsValid() {
 			out.WriteString(" ")
-			out.WriteString(printVal(s.value))
+			val := printVal(cfg, s.value, indent+"  ")
+			out.WriteString(val)
 		}
 
 		out.WriteString("\n")
 	}
 
 	for _, s := range s.subsections {
-		stringifySection(out, s, nextIndent)
+		stringifySection(cfg, out, s, nextIndent)
 		if len(s.subsections) == 0 {
 			out.WriteString(nextIndent)
 			out.WriteString("\n")

summarize_test.go

@@ -255,12 +255,18 @@ var _ FlagAdder = (*Summarize3)(nil)
 var _ FieldDescriber = (*Summarize3)(nil)
 
 func Test_SummarizeValuesWithPointers(t *testing.T) {
+	type Sub struct {
+		SubValue string
+		IntSlice []int
+	}
 	type T1 struct {
-		TopBool    bool
-		TopString  string
-		Summarize1 `mapstructure:",squash"`
-		Pointer    *Summarize2 `mapstructure:"ptr"`
-		NilPointer *Summarize3 `mapstructure:"nil"`
+		TopBool     bool
+		TopString   string
+		Summarize1  `mapstructure:",squash"`
+		Pointer     *Summarize2 `mapstructure:"ptr"`
+		NilPointer  *Summarize3 `mapstructure:"nil"`
+		StringSlice []string
+		SubSlice    []Sub
 	}
 
 	cfg := NewConfig("my-app")
@@ -269,6 +275,19 @@ func Test_SummarizeValuesWithPointers(t *testing.T) {
 			Name: "summarize2 name",
 			Val:  2,
 		},
+		StringSlice: []string{
+			"s1",
+			"s2",
+		},
+		SubSlice: []Sub{
+			{
+				SubValue: "sv1",
+			},
+			{
+				SubValue: "sv2",
+				IntSlice: []int{3, 2, 1},
+			},
+		},
 	}
 
 	cmd := &cobra.Command{}
@@ -306,6 +325,22 @@ nil:
   # val 2 description (env: MY_APP_NIL_VAL)
   Val: 0
   
+# (env: MY_APP_STRINGSLICE)
+StringSlice: 
+  - 's1'
+  - 's2'
+
+# (env: MY_APP_SUBSLICE)
+SubSlice: 
+  - SubValue: 'sv1'
+    IntSlice: []
+
+  - SubValue: 'sv2'
+    IntSlice: 
+      - 3
+      - 2
+      - 1
+
 `, s)
 }