From ef7454b5e28b87b1efe7be46c468960bd759c136 Mon Sep 17 00:00:00 2001
From: spaceface <spaceface7777@gmail.com>
Date: Sat, 8 May 2021 21:26:13 +0200
Subject: [PATCH] checker: fix calling functions with variadic interface
 parameters (#10052)

---
 vlib/v/checker/checker.v               | 13 +++++++++++--
 vlib/v/tests/interface_variadic_test.v | 17 +++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 6024f27eb59f69..c54c5a7d2730ce 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1854,7 +1854,12 @@ pub fn (mut c Checker) method_call(mut call_expr ast.CallExpr) ast.Type {
 				c.error('when forwarding a variadic variable, it must be the final argument',
 					arg.pos)
 			}
-			if exp_arg_sym.kind == .interface_ {
+			mut final_arg_sym := exp_arg_sym
+			if method.is_variadic && exp_arg_sym.info is ast.Array {
+				final_arg_sym = c.table.get_type_symbol(exp_arg_sym.array_info().elem_type)
+			}
+			// Handle expected interface
+			if final_arg_sym.kind == .interface_ {
 				c.type_implements(got_arg_typ, exp_arg_typ, arg.expr.position())
 				continue
 			}
@@ -2436,8 +2441,12 @@ pub fn (mut c Checker) fn_call(mut call_expr ast.CallExpr) ast.Type {
 				c.fail_if_unreadable(call_arg.expr, typ, 'argument')
 			}
 		}
+		mut final_arg_sym := arg_typ_sym
+		if func.is_variadic && arg_typ_sym.info is ast.Array {
+			final_arg_sym = c.table.get_type_symbol(arg_typ_sym.array_info().elem_type)
+		}
 		// Handle expected interface
-		if arg_typ_sym.kind == .interface_ {
+		if final_arg_sym.kind == .interface_ {
 			c.type_implements(typ, param.typ, call_arg.expr.position())
 			continue
 		}
diff --git a/vlib/v/tests/interface_variadic_test.v b/vlib/v/tests/interface_variadic_test.v
index e49b6ba5cf4105..020af540e1df54 100644
--- a/vlib/v/tests/interface_variadic_test.v
+++ b/vlib/v/tests/interface_variadic_test.v
@@ -23,3 +23,20 @@ fn test_variadic_multiple_args() {
 
 	assert a[0].method(0.0, 1.0) == '[0, 1]'
 }
+
+interface Animal {}
+
+struct Cat {}
+
+struct Dog {}
+
+fn test_variadic_interface_fn_arg() {
+	c := Cat{}
+	d := Dog{}
+	check_animals(c, d)
+}
+
+fn check_animals(animals ...Animal) {
+	assert animals[0] is Cat
+	assert animals[1] is Dog
+}