checker: fix interface checking of array arguments; closes #2377

vlib/v/checker/checker.v

@@ -1575,12 +1575,6 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 			c.type_implements(typ, arg.typ, call_arg.expr.position())
 			continue
 		}
-		// Handle expected interface array
-		/*
-		if exp_type_sym.kind == .array && t.get_type_symbol(t.value_type(exp_idx)).kind == .interface_ {
-			return true
-		}
-		*/
 		c.check_expected(typ, arg.typ) or {
 			// str method, allow type with str method if fn arg is string
 			// Passing an int or a string array produces a c error here
@@ -1631,6 +1625,9 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 }
 
 fn (mut c Checker) type_implements(typ table.Type, inter_typ table.Type, pos token.Position) bool {
+	$if debug_interface_type_implements ? {
+		eprintln('> type_implements typ: $typ.debug() | inter_typ: $inter_typ.debug()')
+	}
 	typ_sym := c.table.get_type_symbol(typ)
 	mut inter_sym := c.table.get_type_symbol(inter_typ)
 	styp := c.table.type_to_str(typ)
@@ -2388,6 +2385,7 @@ pub fn (mut c Checker) array_init(mut array_init ast.ArrayInit) table.Type {
 				if i == 0 {
 					elem_type = expected_value_type
 					c.expected_type = elem_type
+					c.type_implements(typ, elem_type, expr.position())
 				}
 				continue
 			}

vlib/v/gen/cgen.v

@@ -5638,6 +5638,10 @@ fn (mut g Gen) interface_table() string {
 			// cctype is the Cleaned Concrete Type name, *without ptr*,
 			// i.e. cctype is always just Cat, not Cat_ptr:
 			cctype := g.cc_type(st)
+			$if debug_interface_table ? {
+				eprintln('>> interface name: $ityp.name | concrete type: $st.debug() | st symname: ' +
+					g.table.get_type_symbol(st).name)
+			}
 			// Speaker_Cat_index = 0
 			interface_index_name := '_${interface_name}_${cctype}_index'
 			if already_generated_mwrappers[interface_index_name] > 0 {

vlib/v/gen/fn.v

@@ -324,6 +324,9 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 	mut receiver_type_name := util.no_dots(g.cc_type2(g.unwrap_generic(node.receiver_type)))
 	if typ_sym.kind == .interface_ {
 		// Speaker_name_table[s._interface_idx].speak(s._object)
+		$if debug_interface_method_call ? {
+			eprintln('>>> interface typ_sym.name: $typ_sym.name | receiver_type_name: $receiver_type_name')
+		}
 		g.write('${c_name(receiver_type_name)}_name_table[')
 		g.expr(node.left)
 		dot := if node.left_type.is_ptr() { '->' } else { '.' }

vlib/v/tests/interface_edge_cases/array_of_interfaces_test.v

@@ -0,0 +1,28 @@
+struct Dog {
+	breed string
+}
+
+fn (d Dog) name() string {
+	return 'Dog'
+}
+
+// Utility helper function, to force interface _name_table generation
+fn get_name(s Speaker) {
+}
+
+//
+fn test_an_array_of_interfaces_works() {
+	dog := Dog{}
+	// get_name(dog) // uncommenting this line fixes the example
+	get_names([dog, dog])
+}
+
+fn get_names(speakers []Speaker) {
+	for s in speakers {
+		println(s.name())
+	}
+}
+
+interface Speaker {
+	name() string
+}

vlib/v/tests/interface_edge_cases/array_of_interfaces_with_utility_fn_test.v

@@ -0,0 +1,28 @@
+struct Dog {
+	breed string
+}
+
+fn (d Dog) name() string {
+	return 'Dog'
+}
+
+// Utility helper function, to force interface _name_table generation
+fn get_name(s Speaker) {
+}
+
+//
+fn test_an_array_of_interfaces_works() {
+	dog := Dog{}
+	get_name(dog) // NB: this line does nothing, but forces interface _name_table generation
+	get_names([dog, dog])
+}
+
+fn get_names(speakers []Speaker) {
+	for s in speakers {
+		println(s.name())
+	}
+}
+
+interface Speaker {
+	name() string
+}