cgen: fix eq for anon C structs (#25152)

vlib/v/gen/c/auto_eq_methods.v

@@ -235,7 +235,14 @@ fn (mut g Gen) gen_struct_equality_fn(left_type ast.Type) string {
 				fn_builder.write_string('${eq_fn}_sumtype_eq(${left_arg}, ${right_arg})')
 			} else if field_type.sym.kind == .struct && !field.typ.is_ptr() {
 				eq_fn := g.gen_struct_equality_fn(field.typ)
-				fn_builder.write_string('${eq_fn}_struct_eq(${left_arg}, ${right_arg})')
+				if field_type.sym.struct_info().is_anon && !field.typ.has_flag(.option)
+					&& !field.typ.has_flag(.shared_f) {
+					styp := g.styp(field.typ)
+					fn_name_ := styp.replace('struct ', '')
+					fn_builder.write_string('${eq_fn}_struct_eq(*(${fn_name_}*)&(${left_arg}), *(${fn_name_}*)&(${right_arg}))')
+				} else {
+					fn_builder.write_string('${eq_fn}_struct_eq(${left_arg}, ${right_arg})')
+				}
 			} else if field_type.sym.kind == .array && !field.typ.is_ptr() {
 				eq_fn := g.gen_array_equality_fn(field.typ)
 				fn_builder.write_string('${eq_fn}_arr_eq(${left_arg}, ${right_arg})')

vlib/v/gen/c/auto_str_methods.v

@@ -1194,6 +1194,13 @@ fn struct_auto_str_func(sym &ast.TypeSymbol, lang ast.Language, _field_type ast.
 			}
 			return '${fn_name}(${obj})', true
 		}
+		if sym.kind == .struct {
+			if sym.info is ast.Struct && sym.info.is_anon && !_field_type.has_flag(.option)
+				&& !_field_type.has_flag(.shared_f) {
+				typed_obj := '*(${sym.cname}*)&(${obj})'
+				return '${fn_name}(${typed_obj})', true
+			}
+		}
 		return 'indent_${fn_name}(${obj}, indent_count + 1)', true
 	} else if sym.kind in [.array, .array_fixed, .map, .sum_type] {
 		obj := '${prefix}it${op}${final_field_name}${sufix}'

vlib/v/tests/c_structs/cstruct_anon_eq_test.c.v

@@ -0,0 +1,14 @@
+#insert "@VMODROOT/anon.h"
+
+@[typedef]
+struct C.outer {
+	inner struct {
+		x int
+	}
+}
+
+fn test_main() {
+	a := C.outer{}
+	b := C.outer{}
+	assert a == b
+}