feat: honour the omitzero and omitempty tag options on encode

Assisted-by: GLM 5.3 Flash

encode_test.go

@@ -748,6 +748,85 @@ func TestMarshalEmbeddedStructAsTable(t *testing.T) {
 	}
 }
 
+func TestMarshalTagOptionOmitZero(t *testing.T) {
+	type Server struct {
+		Host string `toml:"host"`
+	}
+	type Cfg struct {
+		Name   string    `toml:"name,omitzero"`
+		Count  int       `toml:"count,omitzero"`
+		Ratio  float64   `toml:"ratio,omitzero"`
+		When   time.Time `toml:"when,omitzero"`
+		Server Server    `toml:"server,omitzero"`
+		Always string    `toml:"always"`
+	}
+	out, err := Marshal(Cfg{Always: "kept"})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	// Every omitzero field sits at its zero value, so only always is emitted.
+	want := "always = \"kept\"\n"
+	if string(out) != want {
+		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+
+	when := time.Date(2026, 9, 17, 12, 0, 0, 0, time.UTC)
+	out, err = Marshal(Cfg{Name: "x", Count: 1, Ratio: 0.5, When: when, Server: Server{Host: "h"}, Always: "kept"})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want = "name = \"x\"\ncount = 1\nratio = 0.5\nwhen = 2026-09-17T12:00:00Z\nalways = \"kept\"\n\n[server]\nhost = \"h\"\n"
+	if string(out) != want {
+		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
+func TestMarshalTagOptionOmitEmpty(t *testing.T) {
+	type Cfg struct {
+		Tags   []string       `toml:"tags,omitempty"`
+		Ports  []int          `toml:"ports,omitempty"`
+		Matrix [][]int        `toml:"matrix,omitempty"`
+		Extra  map[string]any `toml:"extra,omitempty"`
+		Name   string         `toml:"name,omitempty"`
+		Keep   []string       `toml:"keep"`
+	}
+	out, err := Marshal(Cfg{
+		Ports:  []int{},
+		Matrix: [][]int{{1}},
+		Extra:  map[string]any{},
+		Name:   "set",
+		Keep:   []string{},
+	})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	// tags is nil (omitted anyway), ports and extra are empty collections
+	// dropped by omitempty, matrix is populated, name is a string the option
+	// does not cover, keep is empty but carries no option so it emits [].
+	want := "matrix = [[1]]\nname = \"set\"\nkeep = []\n"
+	if string(out) != want {
+		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
+func TestMarshalTagOptionOnTaggedEmbeddedStruct(t *testing.T) {
+	type Inner struct {
+		N int `toml:"n"`
+	}
+	type Cfg struct {
+		Inner Inner  `toml:"inner,omitzero"`
+		Name  string `toml:"name"`
+	}
+	out, err := Marshal(Cfg{Name: "x"})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "name = \"x\"\n"
+	if string(out) != want {
+		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
 func TestMarshalMapKeysSorted(t *testing.T) {
 	m := map[string]any{
 		"zeta":  1,