From ea844112b6df192b442c2ca2b35b410c85b9e312 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 05:13:55 +0300
Subject: [PATCH] checker: fix empty interface array push with fixed array c
 error (fixes #23011)

---
 vlib/v/checker/containers.v                                 | 4 ++++
 vlib/v/checker/infix.v                                      | 6 +++++-
 .../append_fixed_array_to_empty_interface_array_err.out     | 6 ++++++
 .../append_fixed_array_to_empty_interface_array_err.vv      | 6 ++++++
 4 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.out
 create mode 100644 vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.vv

diff --git a/vlib/v/checker/containers.v b/vlib/v/checker/containers.v
index 9655b8dc4..f87567f5a 100644
--- a/vlib/v/checker/containers.v
+++ b/vlib/v/checker/containers.v
@@ -948,6 +948,10 @@ fn (mut c Checker) check_append(mut node ast.InfixExpr, left_type ast.Type, righ
 		}
 	}
 	if left_value_sym.kind == .interface {
+		if right is ast.ArrayInit && right.is_fixed {
+			c.error('cannot append `${right_sym.name}` to `${left_sym.name}`', right_pos)
+			return ast.void_type
+		}
 		right_is_interface_value := c.table.does_type_implement_interface(c.unwrap_generic(right_type),
 			left_value_type)
 		if right_is_interface_value {
diff --git a/vlib/v/checker/infix.v b/vlib/v/checker/infix.v
index a0576e07f..c9e8804be 100644
--- a/vlib/v/checker/infix.v
+++ b/vlib/v/checker/infix.v
@@ -181,7 +181,11 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 				}
 			}
 		} else if mut node.right is ast.ArrayInit {
-			if node.right.exprs.len == 0 && node.right.elem_type == ast.void_type {
+			left_value_type := c.table.value_type(c.unwrap_generic(left_type))
+			if node.right.is_fixed
+				&& c.table.final_sym(c.unwrap_generic(left_value_type)).kind == .interface {
+				c.expected_type = ast.void_type
+			} else if node.right.exprs.len == 0 && node.right.elem_type == ast.void_type {
 				// handle arr << [] where [] is empty
 				info := c.table.sym(left_type).array_info()
 				node.right.elem_type = info.elem_type
diff --git a/vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.out b/vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.out
new file mode 100644
index 000000000..10b8ced2e
--- /dev/null
+++ b/vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.vv:5:12: error: cannot append `[2]int` to `[]Any`
+    3 | fn main() {
+    4 |     mut values := []Any{}
+    5 |     values << [7, 8]!
+      |               ~~~~~~~
+    6 | }
diff --git a/vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.vv b/vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.vv
new file mode 100644
index 000000000..9a88594bf
--- /dev/null
+++ b/vlib/v/checker/tests/append_fixed_array_to_empty_interface_array_err.vv
@@ -0,0 +1,6 @@
+interface Any {}
+
+fn main() {
+	mut values := []Any{}
+	values << [7, 8]!
+}
-- 
2.39.5