From db181f8fd660be86857489f6de94babbf06032ce Mon Sep 17 00:00:00 2001
From: Nathan Baulch <nathan.baulch@gmail.com>
Date: Fri, 22 Aug 2025 11:30:47 +1000
Subject: [PATCH] Add `omitzero` tag support

---
 marshaler.go      | 20 ++++++++++++++
 marshaler_test.go | 67 ++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/marshaler.go b/marshaler.go
index 334c828c..13193ed5 100644
--- a/marshaler.go
+++ b/marshaler.go
@@ -161,6 +161,8 @@ func (enc *Encoder) SetMarshalJsonNumbers(indent bool) *Encoder {
 //
 // The "omitempty" option prevents empty values or groups from being emitted.
 //
+// The "omitzero" option prevents zero values or groups from being emitted.
+//
 // The "commented" option prefixes the value and all its children with a comment
 // symbol.
 //
@@ -196,6 +198,7 @@ func (enc *Encoder) Encode(v interface{}) error {
 type valueOptions struct {
 	multiline bool
 	omitempty bool
+	omitzero  bool
 	commented bool
 	comment   string
 }
@@ -384,6 +387,10 @@ func shouldOmitEmpty(options valueOptions, v reflect.Value) bool {
 	return options.omitempty && isEmptyValue(v)
 }
 
+func shouldOmitZero(options valueOptions, v reflect.Value) bool {
+	return options.omitzero && v.IsZero()
+}
+
 func (enc *Encoder) encodeKv(b []byte, ctx encoderCtx, options valueOptions, v reflect.Value) ([]byte, error) {
 	var err error
 
@@ -774,6 +781,7 @@ func walkStruct(ctx encoderCtx, t *table, v reflect.Value) {
 		options := valueOptions{
 			multiline: opts.multiline,
 			omitempty: opts.omitempty,
+			omitzero:  opts.omitzero,
 			commented: opts.commented,
 			comment:   fieldType.Tag.Get("comment"),
 		}
@@ -834,6 +842,7 @@ type tagOptions struct {
 	multiline bool
 	inline    bool
 	omitempty bool
+	omitzero  bool
 	commented bool
 }
 
@@ -862,6 +871,8 @@ func parseTag(tag string) (string, tagOptions) {
 			opts.inline = true
 		case "omitempty":
 			opts.omitempty = true
+		case "omitzero":
+			opts.omitzero = true
 		case "commented":
 			opts.commented = true
 		}
@@ -896,6 +907,9 @@ func (enc *Encoder) encodeTable(b []byte, ctx encoderCtx, t table) ([]byte, erro
 		if shouldOmitEmpty(kv.Options, kv.Value) {
 			continue
 		}
+		if shouldOmitZero(kv.Options, kv.Value) {
+			continue
+		}
 		hasNonEmptyKV = true
 
 		ctx.setKey(kv.Key)
@@ -915,6 +929,9 @@ func (enc *Encoder) encodeTable(b []byte, ctx encoderCtx, t table) ([]byte, erro
 		if shouldOmitEmpty(table.Options, table.Value) {
 			continue
 		}
+		if shouldOmitZero(table.Options, table.Value) {
+			continue
+		}
 		if first {
 			first = false
 			if hasNonEmptyKV {
@@ -949,6 +966,9 @@ func (enc *Encoder) encodeTableInline(b []byte, ctx encoderCtx, t table) ([]byte
 		if shouldOmitEmpty(kv.Options, kv.Value) {
 			continue
 		}
+		if shouldOmitZero(kv.Options, kv.Value) {
+			continue
+		}
 
 		if first {
 			first = false
diff --git a/marshaler_test.go b/marshaler_test.go
index 675e6d9d..267c70e2 100644
--- a/marshaler_test.go
+++ b/marshaler_test.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"math"
 	"math/big"
+	"net/netip"
 	"reflect"
 	"strings"
 	"testing"
@@ -1117,6 +1118,9 @@ func TestEncoderOmitempty(t *testing.T) {
 		Ptr     *string           `toml:",omitempty,multiline"`
 		Iface   interface{}       `toml:",omitempty,multiline"`
 		Struct  struct{}          `toml:",omitempty,multiline"`
+		Inline  struct {
+			String string `toml:",omitempty,multiline"`
+		} `toml:",inline"`
 	}
 
 	d := doc{}
@@ -1124,7 +1128,68 @@ func TestEncoderOmitempty(t *testing.T) {
 	b, err := toml.Marshal(d)
 	assert.NoError(t, err)
 
-	expected := ``
+	expected := `Inline = {}
+`
+
+	assert.Equal(t, expected, string(b))
+}
+
+func TestEncoderOmitzero(t *testing.T) {
+	type doc struct {
+		String  string            `toml:",omitzero,multiline"`
+		Bool    bool              `toml:",omitzero,multiline"`
+		Int     int               `toml:",omitzero,multiline"`
+		Int8    int8              `toml:",omitzero,multiline"`
+		Int16   int16             `toml:",omitzero,multiline"`
+		Int32   int32             `toml:",omitzero,multiline"`
+		Int64   int64             `toml:",omitzero,multiline"`
+		Uint    uint              `toml:",omitzero,multiline"`
+		Uint8   uint8             `toml:",omitzero,multiline"`
+		Uint16  uint16            `toml:",omitzero,multiline"`
+		Uint32  uint32            `toml:",omitzero,multiline"`
+		Uint64  uint64            `toml:",omitzero,multiline"`
+		Float32 float32           `toml:",omitzero,multiline"`
+		Float64 float64           `toml:",omitzero,multiline"`
+		MapNil  map[string]string `toml:",omitzero,multiline"`
+		Slice   []string          `toml:",omitzero,multiline"`
+		Ptr     *string           `toml:",omitzero,multiline"`
+		Iface   interface{}       `toml:",omitzero,multiline"`
+		Struct  struct{}          `toml:",omitzero,multiline"`
+		Time    time.Time         `toml:",omitzero,multiline"`
+		IP      netip.Addr        `toml:",omitzero,multiline"`
+		Inline  struct {
+			String string `toml:",omitzero,multiline"`
+		} `toml:",inline"`
+	}
+
+	d := doc{}
+
+	b, err := toml.Marshal(d)
+	assert.NoError(t, err)
+
+	expected := `Inline = {}
+`
+
+	assert.Equal(t, expected, string(b))
+}
+
+func TestEncoderOmitzeroOpaqueStruct(t *testing.T) {
+	type doc struct {
+		Time time.Time  `toml:",omitzero"`
+		IP   netip.Addr `toml:",omitzero"`
+	}
+
+	d := doc{
+		Time: time.Date(2001, 2, 3, 4, 5, 6, 7, time.UTC),
+		IP:   netip.MustParseAddr("192.168.178.35"),
+	}
+
+	b, err := toml.Marshal(d)
+	assert.NoError(t, err)
+
+	expected := `Time = 2001-02-03T04:05:06.000000007Z
+IP = '192.168.178.35'
+`
 
 	assert.Equal(t, expected, string(b))
 }