From 4f742ad1b2f0b4a049c26d2683a516b90496464a Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Thu, 15 Feb 2024 01:41:10 -0300
Subject: [PATCH] json: fix decode struct ptr (#20828)

---
 vlib/json/json_decode_struct_ptr_test.v | 22 ++++++++++++++++++++++
 vlib/v/gen/c/json.v                     |  9 ++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 vlib/json/json_decode_struct_ptr_test.v

diff --git a/vlib/json/json_decode_struct_ptr_test.v b/vlib/json/json_decode_struct_ptr_test.v
new file mode 100644
index 00000000000000..954d025c2717e8
--- /dev/null
+++ b/vlib/json/json_decode_struct_ptr_test.v
@@ -0,0 +1,22 @@
+import json
+
+struct Message {
+mut:
+	id       int
+	text     string
+	reply_to &Message
+}
+
+fn test_main() {
+	mut json_data := '{"id": 1, "text": "Hello", "reply_to": {"id": 2, "text": "Hi"}}'
+	mut message := json.decode(Message, json_data)!
+	assert message.reply_to.id == 2
+
+	json_data = '{"id": 1, "text": "Hello", "reply_to": {"id": 2, "text": "Hi", "reply_to": {}}}'
+	message = json.decode(Message, json_data)!
+	assert message.reply_to.reply_to.reply_to == unsafe { nil }
+
+	json_data = '{"id": 1, "text": "Hello", "reply_to": {"id": 2, "text": "Hi", "reply_to": {"id": 5}}}'
+	message = json.decode(Message, json_data)!
+	assert message.reply_to.reply_to.id == 5
+}
diff --git a/vlib/v/gen/c/json.v b/vlib/v/gen/c/json.v
index 13d647c0704958..9c0b94a89ca76d 100644
--- a/vlib/v/gen/c/json.v
+++ b/vlib/v/gen/c/json.v
@@ -75,10 +75,17 @@ fn (mut g Gen) gen_jsons() {
 				g.set_current_pos_as_last_stmt_pos()
 				pos := g.out.len
 				g.write(init_styp)
+				if utyp.is_ptr() {
+					ptr_styp := g.typ(utyp.set_nr_muls(utyp.nr_muls() - 1))
+					g.write('HEAP(${ptr_styp}, ')
+				}
 				g.expr(ast.Expr(ast.StructInit{
-					typ: utyp
+					typ: utyp.set_nr_muls(0)
 					typ_str: styp
 				}))
+				if utyp.is_ptr() {
+					g.write(')')
+				}
 				init_styp = g.out.cut_to(pos).trim_space()
 			}
 		}