From af87a302faf517d41176e84ce8d7adc2817c3ac2 Mon Sep 17 00:00:00 2001
From: xieke <1023052645@qq.com>
Date: Mon, 8 Sep 2025 22:32:46 +0800
Subject: [PATCH] cgen: fix gen_struct_equality_fn null pointer crash (fix
 #25237) (#25231)

---
 .../tests/json_decode_option_alias_test.v     |  2 +-
 vlib/v/gen/c/auto_eq_methods.v                | 23 ++++++++--------
 vlib/v/gen/c/json.v                           | 13 ++++++++++
 .../struct_option_field_comparison_test.v     | 26 +++++++++++++++++++
 4 files changed, 52 insertions(+), 12 deletions(-)
 create mode 100644 vlib/v/tests/structs/struct_option_field_comparison_test.v

diff --git a/vlib/json/tests/json_decode_option_alias_test.v b/vlib/json/tests/json_decode_option_alias_test.v
index f4c7c51b96..26a499503e 100644
--- a/vlib/json/tests/json_decode_option_alias_test.v
+++ b/vlib/json/tests/json_decode_option_alias_test.v
@@ -15,6 +15,6 @@ fn test_main() {
 	assert data.str() == 'Alias(SomeStruct{
     random_field_a: Option(none)
     random_field_b: Option(none)
-    empty_field: Option(none)
+    empty_field: Option(Empty{})
 })'
 }
diff --git a/vlib/v/gen/c/auto_eq_methods.v b/vlib/v/gen/c/auto_eq_methods.v
index 7f58ad8e2e..497b507a55 100644
--- a/vlib/v/gen/c/auto_eq_methods.v
+++ b/vlib/v/gen/c/auto_eq_methods.v
@@ -214,21 +214,22 @@ fn (mut g Gen) gen_struct_equality_fn(left_type ast.Type) string {
 			field_type := g.unwrap(field.typ)
 			field_name := c_name(field.name)
 
-			left_arg := g.read_field(left_type, field_name, 'a')
-			right_arg := g.read_field(left_type, field_name, 'b')
+			mut left_arg := g.read_field(left_type, field_name, 'a')
+			mut right_arg := g.read_field(left_type, field_name, 'b')
 
 			if field.typ.has_flag(.option) {
-				fn_builder.write_string('((${left_arg}.state == ${right_arg}.state && ${right_arg}.state == 2) || ')
+				fn_builder.write_string('((${left_arg}.state == ${right_arg}.state && ${right_arg}.state == 2) || (${left_arg}.state != 2 && ${right_arg}.state != 2 && (')
 			}
 			if field_type.sym.kind == .string {
 				if field.typ.has_flag(.option) {
-					left_arg_opt := g.read_opt_field(left_type, field_name, 'a', field.typ)
-					right_arg_opt := g.read_opt_field(left_type, field_name, 'b', field.typ)
-					fn_builder.write_string('(((${left_arg_opt}).len == (${right_arg_opt}).len && (${left_arg_opt}).len == 0) || fast_string_eq(${left_arg_opt}, ${right_arg_opt}))')
-				} else if field.typ.is_ptr() {
-					fn_builder.write_string('((${left_arg}->len == ${right_arg}->len && ${left_arg}->len == 0) || fast_string_eq(*(${left_arg}), *(${right_arg})))')
+					left_arg = g.read_opt_field(left_type, field_name, 'a', field.typ)
+					right_arg = g.read_opt_field(left_type, field_name, 'b', field.typ)
+				}
+
+				if field.typ.is_ptr() {
+					fn_builder.write_string('(${left_arg} == ${right_arg} || (${left_arg} != 0 &&  ${right_arg} != 0 && ((${left_arg})->len == (${right_arg})->len && (${left_arg})->len == 0) || fast_string_eq(*(${left_arg}), *(${right_arg}))))')
 				} else {
-					fn_builder.write_string('((${left_arg}.len == ${right_arg}.len && ${left_arg}.len == 0) || fast_string_eq(${left_arg}, ${right_arg}))')
+					fn_builder.write_string('(((${left_arg}).len == (${right_arg}).len && (${left_arg}).len == 0) || fast_string_eq(${left_arg}, ${right_arg}))')
 				}
 			} else if field_type.sym.kind == .sum_type && !field.typ.is_ptr() {
 				eq_fn := g.gen_sumtype_equality_fn(field.typ)
@@ -260,7 +261,7 @@ fn (mut g Gen) gen_struct_equality_fn(left_type ast.Type) string {
 					fn_builder.write_string('${eq_fn}_alias_eq(${left_arg}, ${right_arg})')
 				}
 			} else if field_type.sym.kind == .function && !field.typ.has_flag(.option) {
-				fn_builder.write_string('*((voidptr*)(${left_arg})) == *((voidptr*)(${right_arg}))')
+				fn_builder.write_string('((voidptr*)(${left_arg})) == ((voidptr*)(${right_arg}))')
 			} else if field_type.sym.kind == .interface
 				&& (!field.typ.has_flag(.option) || !field.typ.is_ptr()) {
 				ptr := if field.typ.is_ptr() { '*'.repeat(field.typ.nr_muls()) } else { '' }
@@ -278,7 +279,7 @@ fn (mut g Gen) gen_struct_equality_fn(left_type ast.Type) string {
 				fn_builder.write_string('${left_arg} == ${right_arg}')
 			}
 			if field.typ.has_flag(.option) {
-				fn_builder.write_string(')')
+				fn_builder.write_string(')))')
 			}
 		}
 	} else {
diff --git a/vlib/v/gen/c/json.v b/vlib/v/gen/c/json.v
index 7b102074aa..df60727444 100644
--- a/vlib/v/gen/c/json.v
+++ b/vlib/v/gen/c/json.v
@@ -119,6 +119,19 @@ ${dec_fn_dec} {
 		}
 	}
 ')
+
+		if utyp.has_flag(.option) {
+			dec.writeln('\tif (cJSON_IsNull(root)) {')
+			dec.writeln('\t${result_name}_${ret_styp} ret;')
+			dec.writeln('\t_result_ok(&res, (${result_name}*)&ret, sizeof(res));')
+			dec.writeln('\treturn ret;')
+			dec.writeln('\t}')
+
+			base_type := utyp.clear_flag(.option)
+			base_type_str := g.styp(base_type)
+			dec.writeln('\t_option_ok(&(${base_type_str}[]){ ${g.type_default(base_type)} }, (${styp}*)&res, sizeof(${base_type_str}));\n')
+		}
+
 		extern_str := if g.pref.parallel_cc { 'extern ' } else { '' }
 		g.json_forward_decls.writeln('${extern_str}${dec_fn_dec};')
 		// Codegen encoder
diff --git a/vlib/v/tests/structs/struct_option_field_comparison_test.v b/vlib/v/tests/structs/struct_option_field_comparison_test.v
new file mode 100644
index 0000000000..7f88ae5e39
--- /dev/null
+++ b/vlib/v/tests/structs/struct_option_field_comparison_test.v
@@ -0,0 +1,26 @@
+pub struct SomeStruct {
+pub mut:
+	test ?string
+}
+
+pub struct MyStruct {
+pub mut:
+	id     string
+	result ?SomeStruct
+}
+
+fn test_struct_with_option_fields_inequality() {
+	a := MyStruct{
+		id:     'some id'
+		result: none
+	}
+	b := MyStruct{
+		id:     'some id'
+		result: SomeStruct{}
+	}
+	dump(a)
+	dump(b)
+	dump(a == b)
+	dump(a != b)
+	assert a != b
+}