From 742895e2290c6c20c135b0b1e571a2920f6d661f Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 04:48:39 +0300
Subject: [PATCH] cgen: fix circular printing not showing item count in array
 (fixes #21689)

---
 vlib/builtin/autostr.v                        | 21 +++++++++++++++++++
 vlib/v/gen/c/auto_str_methods.v               |  8 +++++--
 .../string_interpolation_struct_test.v        | 13 ++++++++++++
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/vlib/builtin/autostr.v b/vlib/builtin/autostr.v
index 089c90dd7..d6ba55c5f 100644
--- a/vlib/builtin/autostr.v
+++ b/vlib/builtin/autostr.v
@@ -1,5 +1,7 @@
 module builtin
 
+import strings
+
 const autostr_type_stack_max_depth = 64
 
 __global g_autostr_type_stack = [autostr_type_stack_max_depth]int{}
@@ -64,3 +66,22 @@ fn autostr_addr_pop() {
 		g_autostr_addr_stack_len--
 	}
 }
+
+@[markused]
+fn autostr_array_circular(len int) string {
+	if len <= 0 {
+		return '[]'
+	}
+	mut sb := strings.new_builder(2 + len * 12)
+	sb.write_string('[')
+	for i in 0 .. len {
+		if i > 0 {
+			sb.write_string(', ')
+		}
+		sb.write_string('<circular>')
+	}
+	sb.write_string(']')
+	res := sb.str()
+	unsafe { sb.free() }
+	return res
+}
diff --git a/vlib/v/gen/c/auto_str_methods.v b/vlib/v/gen/c/auto_str_methods.v
index b53e32d03..17bdc3760 100644
--- a/vlib/v/gen/c/auto_str_methods.v
+++ b/vlib/v/gen/c/auto_str_methods.v
@@ -1167,12 +1167,16 @@ fn (mut g Gen) gen_str_for_struct(info ast.Struct, lang ast.Language, styp strin
 		// handle circular ref type of struct to the struct itself
 		if styp == field_styp && !allow_circular {
 			if is_field_array {
+				tmpvar := g.new_tmp_var()
 				if is_opt_field {
 					arr_styp := g.base_type(field.typ)
-					fn_body.write_string('${it_field_name}.state != 2 && (*(${arr_styp}*)${it_field_name}.data).len > 0 ? ${funcprefix}_S("[<circular>]") : ${funcprefix}_S("[]")')
+					fn_body_surrounder.add('\tstring ${tmpvar} = ${funcprefix}builtin__autostr_array_circular(${it_field_name}.state != 2 ? (*(${arr_styp}*)${it_field_name}.data).len : 0);',
+						'\tbuiltin__string_free(&${tmpvar});')
 				} else {
-					fn_body.write_string('${it_field_name}.len > 0 ? ${funcprefix}_S("[<circular>]") : ${funcprefix}_S("[]")')
+					fn_body_surrounder.add('\tstring ${tmpvar} = ${funcprefix}builtin__autostr_array_circular(${it_field_name}.len);',
+						'\tbuiltin__string_free(&${tmpvar});')
 				}
+				fn_body.write_string(tmpvar)
 			} else {
 				fn_body.write_string('${funcprefix}_S("<circular>")')
 			}
diff --git a/vlib/v/tests/builtin_strings_and_interpolation/string_interpolation_struct_test.v b/vlib/v/tests/builtin_strings_and_interpolation/string_interpolation_struct_test.v
index 78f8d69c8..f20265393 100644
--- a/vlib/v/tests/builtin_strings_and_interpolation/string_interpolation_struct_test.v
+++ b/vlib/v/tests/builtin_strings_and_interpolation/string_interpolation_struct_test.v
@@ -91,3 +91,16 @@ fn test_cross_reference_field_auto_str() {
 	s := '${window}'.replace('\n', '|')
 	assert s == '&CrossRefWindow{|    widgets: [CrossRefWidget{|        parent: &CrossRefWindow{|            widgets: [CrossRefWidget{|                parent: &<circular>|            }]|        }|    }]|}'
 }
+
+struct CircularArray {
+mut:
+	children []CircularArray
+}
+
+fn test_circular_array_field_auto_str_keeps_item_count() {
+	mut value := CircularArray{}
+	value.children << CircularArray{}
+	value.children << CircularArray{}
+	s := '${value}'.replace('\n', '|')
+	assert s == 'CircularArray{|    children: [<circular>, <circular>]|}'
+}
-- 
2.39.5