feat: honour the omitzero and omitempty tag options on encode

Assisted-by: GLM 5.3 Flash

encode.go

@@ -189,6 +189,9 @@ func buildStructDoc(v reflect.Value, doc *tomlDoc, ctx string) error {
 		if name == "-" {
 			continue
 		}
+		if fieldOmitted(f, v.Field(i)) {
+			continue
+		}
 		if err := addField(doc, name, v.Field(i), ctx); err != nil {
 			return err
 		}
@@ -196,6 +199,49 @@ func buildStructDoc(v reflect.Value, doc *tomlDoc, ctx string) error {
 	return nil
 }
 
+// isZeroer mirrors encoding/json's omitzero: a type that knows its own zero
+// state decides through that method before reflection is consulted.
+type isZeroer interface{ IsZero() bool }
+
+// fieldOmitted reports whether the field's tag options drop it from the
+// output: omitzero skips the zero value of the field's type, omitempty skips
+// an empty collection (slice, array, or map). The decoder ignores both
+// options; they shape emission only.
+func fieldOmitted(f reflect.StructField, v reflect.Value) bool {
+	tag, ok := f.Tag.Lookup("toml")
+	if !ok {
+		return false
+	}
+	_, opts, _ := strings.Cut(tag, ",")
+	for opts != "" {
+		var opt string
+		opt, opts, _ = strings.Cut(opts, ",")
+		switch opt {
+		case "omitzero":
+			if isZeroValue(v) {
+				return true
+			}
+		case "omitempty":
+			switch v.Kind() {
+			case reflect.Slice, reflect.Array, reflect.Map:
+				if v.Len() == 0 {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+func isZeroValue(v reflect.Value) bool {
+	if v.CanInterface() {
+		if z, ok := v.Interface().(isZeroer); ok {
+			return z.IsZero()
+		}
+	}
+	return v.IsZero()
+}
+
 // fieldName returns the TOML key for a struct field, honouring the `toml`
 // tag (name or `-`) and falling back to a lower-cased field name.
 func fieldName(f reflect.StructField) string {