From 9a2df0df0e0bdfa74c4f3036583c6a6ae939eb24 Mon Sep 17 00:00:00 2001
From: yuyi <yuyi98@163.com>
Date: Mon, 28 Feb 2022 19:31:04 +0800
Subject: [PATCH] cgen: fix fn mut argument of interface type (#13616)

---
 vlib/v/gen/c/fn.v                           |  5 ++++
 vlib/v/tests/fn_mut_arg_of_interface_test.v | 27 +++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 vlib/v/tests/fn_mut_arg_of_interface_test.v

diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 868ad196e4..3d7e06364d 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -1709,6 +1709,11 @@ fn (mut g Gen) ref_or_deref_arg(arg ast.CallArg, expected_type ast.Type, lang as
 				g.write('&/*sum*/')
 				g.expr(arg.expr)
 				return
+			} else if arg_sym.kind == .interface_ && exp_sym.kind == .interface_
+				&& (arg.expr is ast.Ident || arg.expr is ast.SelectorExpr) {
+				g.write('&/*iface*/')
+				g.expr(arg.expr)
+				return
 			}
 		}
 		if !g.is_json_fn {
diff --git a/vlib/v/tests/fn_mut_arg_of_interface_test.v b/vlib/v/tests/fn_mut_arg_of_interface_test.v
new file mode 100644
index 0000000000..7d96706455
--- /dev/null
+++ b/vlib/v/tests/fn_mut_arg_of_interface_test.v
@@ -0,0 +1,27 @@
+interface TheInterface {
+mut:
+	an_interface() ?
+}
+
+struct Implementation {
+}
+
+fn (mut i Implementation) an_interface() ? {
+	return
+}
+
+fn maker() ?TheInterface {
+	inner := Implementation{}
+	return inner
+}
+
+fn do(mut inter TheInterface) string {
+	return 'ok'
+}
+
+fn test_fn_mut_arg_of_interface() ? {
+	mut inner := maker() ?
+	ret := do(mut inner)
+	println(ret)
+	assert ret == 'ok'
+}