feat: add OffsetDateTime, nesting limits and uniform Marshaler dispatch

Assisted-by: DeepSeek V4.1 Flash

decode_test.go

@@ -951,3 +951,130 @@ func TestQuotedStringNeverBecomesDateTime(t *testing.T) {
 		t.Fatal("expected a quoted string to be rejected for LocalDate")
 	}
 }
+
+func TestDecoderMaxDepth(t *testing.T) {
+	deep := func(n int) []byte {
+		return []byte("v = " + strings.Repeat("[", n) + strings.Repeat("]", n) + "\n")
+	}
+	var cfg struct {
+		V any `toml:"v"`
+	}
+	if err := NewDecoder().MaxDepth(4).Decode(deep(4), &cfg); err != nil {
+		t.Fatalf("at the limit: %v", err)
+	}
+	err := NewDecoder().MaxDepth(4).Decode(deep(5), &cfg)
+	if err == nil {
+		t.Fatal("expected a nesting error")
+	}
+	if !strings.Contains(err.Error(), "limit of 4") {
+		t.Errorf("err = %v, want it to name the limit", err)
+	}
+}
+
+func TestDecoderMaxInputSize(t *testing.T) {
+	doc := []byte("v = \"ab\"\n")
+	var cfg struct {
+		V string `toml:"v"`
+	}
+	if err := NewDecoder().MaxInputSize(len(doc)).Decode(doc, &cfg); err != nil {
+		t.Fatalf("at the limit: %v", err)
+	}
+	err := NewDecoder().MaxInputSize(len(doc)-1).Decode(doc, &cfg)
+	if err == nil {
+		t.Fatal("expected a size error")
+	}
+	if !strings.Contains(err.Error(), "over the limit of 8") {
+		t.Errorf("err = %v, want it to name the limit", err)
+	}
+	// Parse carries the nesting default and no size limit.
+	if _, err := Parse(doc); err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+}
+
+// --- OffsetDateTime --------------------------------------------------------
+
+func TestOffsetDateTimeIsTheParsedType(t *testing.T) {
+	// A document's offset date-time arrives as the wrapper, and a plain
+	// time.Time destination still takes it, so a timestamp field needs no
+	// change to keep working.
+	in := []byte("stamp = 2026-06-26T10:00:00-07:00\n")
+	want := time.Date(2026, 6, 26, 10, 0, 0, 0, time.FixedZone("", -7*3600))
+
+	var plain struct {
+		Stamp time.Time `toml:"stamp"`
+	}
+	if err := Unmarshal(in, &plain); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if !plain.Stamp.Equal(want) {
+		t.Errorf("time.Time destination = %v, want %v", plain.Stamp, want)
+	}
+
+	var wrapped struct {
+		Stamp OffsetDateTime `toml:"stamp"`
+	}
+	if err := Unmarshal(in, &wrapped); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if !wrapped.Stamp.Time.Equal(want) {
+		t.Errorf("OffsetDateTime destination = %v, want %v", wrapped.Stamp.Time, want)
+	}
+	if got := wrapped.Stamp.String(); got != "2026-06-26T10:00-07:00" {
+		t.Errorf("String() = %q, want 2026-06-26T10:00-07:00", got)
+	}
+}
+
+func TestOffsetDateTimeFromHandBuiltTree(t *testing.T) {
+	// A tree built by hand may carry a plain time.Time, which is the other
+	// source of the offset kind; both date-time destinations take it.
+	tree := map[string]any{"stamp": time.Date(2026, 6, 26, 10, 0, 0, 0, time.UTC)}
+	want := time.Date(2026, 6, 26, 10, 0, 0, 0, time.UTC)
+
+	var plain struct {
+		Stamp time.Time `toml:"stamp"`
+	}
+	if err := newDecoder().decode(tree, &plain); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if !plain.Stamp.Equal(want) {
+		t.Errorf("time.Time destination = %v, want %v", plain.Stamp, want)
+	}
+
+	var wrapped struct {
+		Stamp OffsetDateTime `toml:"stamp"`
+	}
+	if err := newDecoder().decode(tree, &wrapped); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if !wrapped.Stamp.Time.Equal(want) {
+		t.Errorf("OffsetDateTime destination = %v, want %v", wrapped.Stamp.Time, want)
+	}
+}
+
+// dateKindReceiver records the Go type UnmarshalTOML was handed.
+type dateKindReceiver struct{ Kind string }
+
+func (r *dateKindReceiver) UnmarshalTOML(data any) error {
+	r.Kind = fmt.Sprintf("%T", data)
+	return nil
+}
+
+func TestUnmarshalerReceivesOffsetDateTime(t *testing.T) {
+	// The interface sees the wrapper, which names the date-time kind on its
+	// own; the local kinds keep their own wrappers.
+	var cfg struct {
+		O dateKindReceiver `toml:"o"`
+		L dateKindReceiver `toml:"l"`
+	}
+	in := []byte("o = 2026-06-26T10:00:00Z\nl = 2026-06-26T10:00:00\n")
+	if err := Unmarshal(in, &cfg); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if cfg.O.Kind != "interpres.OffsetDateTime" {
+		t.Errorf("offset kind = %q, want interpres.OffsetDateTime", cfg.O.Kind)
+	}
+	if cfg.L.Kind != "interpres.LocalDateTime" {
+		t.Errorf("local kind = %q, want interpres.LocalDateTime", cfg.L.Kind)
+	}
+}