From 442544633d0f6a2ab3f6bafcec126fb09b683f51 Mon Sep 17 00:00:00 2001
From: kbkpbot <kbkpbot@sina.com>
Date: Mon, 29 Dec 2025 05:18:56 +0800
Subject: [PATCH] cgen: fix print interface when arg0 is function call (fix
 #26184) (#26188)

---
 vlib/v/gen/c/fn.v                             |  4 ++-
 .../interfaces/interface_err_msg_print_test.v | 27 +++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/interfaces/interface_err_msg_print_test.v

diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 4f9eb5cda..4f0de07e8 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -2143,7 +2143,9 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 		}
 	}
 	if !print_auto_str {
-		if is_print {
+		if is_print && node.args[0].expr !is ast.CallExpr {
+			// only need for `println(err)`
+			// not need for `println(err.msg())`
 			g.inside_interface_deref = true
 			defer(fn) {
 				g.inside_interface_deref = false
diff --git a/vlib/v/tests/interfaces/interface_err_msg_print_test.v b/vlib/v/tests/interfaces/interface_err_msg_print_test.v
new file mode 100644
index 000000000..da43306f6
--- /dev/null
+++ b/vlib/v/tests/interfaces/interface_err_msg_print_test.v
@@ -0,0 +1,27 @@
+struct MyError {
+	code  int
+	state string
+}
+
+pub fn (e MyError) msg() string {
+	return 'something went wrong'
+}
+
+pub fn (e MyError) code() int {
+	return e.code
+}
+
+fn foo() ! {
+	return MyError{}
+}
+
+fn test_interface_err_msg_print() {
+	foo() or {
+		if err is MyError {
+			eprintln(err.msg())
+			exit(err.code())
+		} else {
+			panic(err)
+		}
+	}
+}
-- 
2.39.5