From d00808660f18daee71d7ba3efded7a95cd4a937c Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@vlang.io>
Date: Thu, 16 Sep 2021 07:02:43 +0300
Subject: [PATCH] json: omitempty

---
 vlib/json/json_test.v | 14 ++++++++++++++
 vlib/v/gen/c/json.v   |  8 ++++++++
 2 files changed, 22 insertions(+)

diff --git a/vlib/json/json_test.v b/vlib/json/json_test.v
index ca6b2ac3e7..1c9f5b4496 100644
--- a/vlib/json/json_test.v
+++ b/vlib/json/json_test.v
@@ -366,3 +366,17 @@ fn test_pretty() {
 	"name":	"Bob"
 }'
 }
+
+struct Foo3 {
+	name string
+	age  int    [omitempty]
+}
+
+fn test_omit_empty() {
+	foo := Foo3{'Bob', 0}
+	assert json.encode_pretty(foo) == '{
+	"name":	"Bob"
+}'
+	// println('omitempty:')
+	// println(json.encode_pretty(foo))
+}
diff --git a/vlib/v/gen/c/json.v b/vlib/v/gen/c/json.v
index cfc480dea5..5a45420517 100644
--- a/vlib/v/gen/c/json.v
+++ b/vlib/v/gen/c/json.v
@@ -117,6 +117,8 @@ fn (mut g Gen) gen_struct_enc_dec(type_info ast.TypeInfo, styp string, mut enc s
 		mut is_raw := false
 		mut is_skip := false
 		mut is_required := false
+		mut is_omit_empty := false
+
 		for attr in field.attrs {
 			match attr.name {
 				'json' {
@@ -131,6 +133,9 @@ fn (mut g Gen) gen_struct_enc_dec(type_info ast.TypeInfo, styp string, mut enc s
 				'required' {
 					is_required = true
 				}
+				'omitempty' {
+					is_omit_empty = true
+				}
 				else {}
 			}
 		}
@@ -184,6 +189,9 @@ fn (mut g Gen) gen_struct_enc_dec(type_info ast.TypeInfo, styp string, mut enc s
 		}
 		// Encoding
 		mut enc_name := js_enc_name(field_type)
+		if is_omit_empty {
+			enc.writeln('\t if (val.${c_name(field.name)} != ${g.type_default(field.typ)}) \n')
+		}
 		if !is_js_prim(field_type) {
 			if field_sym.kind == .alias {
 				ainfo := field_sym.info as ast.Alias