From e7cc93a1209c74f1940f3b8be86926236237fc76 Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Wed, 16 Jun 2021 09:20:01 +0300
Subject: [PATCH] v.checker: allow for a `f(unsafe{voidptr(0)})` call of `fn
 f(x &Interface){}`

---
 vlib/v/checker/checker.v                      |  7 +++++--
 ...pass_voidptr_as_interface_reference_test.v | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 vlib/v/tests/interface_edge_cases/pass_voidptr_as_interface_reference_test.v

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 83edab195e..cf88401336 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2698,8 +2698,11 @@ fn (mut c Checker) type_implements(typ ast.Type, interface_type ast.Type, pos to
 			}
 			continue
 		}
-		c.error("`$styp` doesn't implement method `$imethod.name` of interface `$inter_sym.name`",
-			pos)
+		// voidptr is an escape hatch, it should be allowed to be passed
+		if utyp != ast.voidptr_type {
+			c.error("`$styp` doesn't implement method `$imethod.name` of interface `$inter_sym.name`",
+				pos)
+		}
 	}
 	// Verify fields
 	if mut inter_sym.info is ast.Interface {
diff --git a/vlib/v/tests/interface_edge_cases/pass_voidptr_as_interface_reference_test.v b/vlib/v/tests/interface_edge_cases/pass_voidptr_as_interface_reference_test.v
new file mode 100644
index 0000000000..0e332e2c74
--- /dev/null
+++ b/vlib/v/tests/interface_edge_cases/pass_voidptr_as_interface_reference_test.v
@@ -0,0 +1,19 @@
+interface IAbc {
+	xyz()
+}
+
+struct Abc {}
+
+fn (a Abc) xyz() {}
+
+fn f(i &IAbc) string {
+	return '$i'
+}
+
+fn test_passing_voidptr_as_an_interface_reference() {
+	i := IAbc(Abc{})
+	assert f(&i) == '&IAbc(Abc{})'
+	// a voidptr() cast is an escape hatch, that should be allowed
+	// but perhaps it should be forced by the compiler to be in unsafe{}
+	assert f(unsafe { voidptr(0) }) == '&IAbc(0)'
+}