checker, cgen: fix array of interfaces index() (#18232)

vlib/v/checker/check_types.v

@@ -4,6 +4,7 @@
 module checker
 
 import v.ast
+import v.token
 
 // TODO: promote(), check_types(), symmetric_check() and check() overlap - should be rearranged
 fn (mut c Checker) check_types(got ast.Type, expected ast.Type) bool {
@@ -274,6 +275,9 @@ fn (mut c Checker) check_expected_call_arg(got ast.Type, expected_ ast.Type, lan
 	} else {
 		got_typ_sym := c.table.sym(c.unwrap_generic(got))
 		expected_typ_sym := c.table.sym(c.unwrap_generic(expected_))
+		if expected_typ_sym.kind == .interface_ && c.type_implements(got, expected_, token.Pos{}) {
+			return
+		}
 
 		// Check on Generics types, there are some case where we have the following case
 		// `&Type[int] == &Type[]`. This is a common case we are implementing a function

vlib/v/checker/fn.v

@@ -2519,6 +2519,9 @@ fn (mut c Checker) array_builtin_method_call(mut node ast.CallExpr, left_type as
 				c.error('${err.msg()} in argument 1 to `.index()`', node.args[0].pos)
 			}
 		}
+		for i, arg in node.args {
+			node.args[i].typ = c.expr(arg.expr)
+		}
 		node.return_type = ast.int_type
 	} else if method_name in ['first', 'last', 'pop'] {
 		if node.args.len != 0 {

vlib/v/gen/c/array.v

@@ -986,7 +986,12 @@ fn (mut g Gen) gen_array_index(node ast.CallExpr) {
 	if node.args[0].expr.is_auto_deref_var() {
 		g.write('*')
 	}
-	g.expr(node.args[0].expr)
+	elem_typ := g.table.sym(node.left_type).array_info().elem_type
+	if g.table.sym(elem_typ).kind in [.interface_, .sum_type] {
+		g.expr_with_cast(node.args[0].expr, node.args[0].typ, elem_typ)
+	} else {
+		g.expr(node.args[0].expr)
+	}
 	g.write(')')
 }
 

vlib/v/tests/array_of_interfaces_index_test.v

@@ -0,0 +1,31 @@
+struct Entity {
+	id u64
+mut:
+	components []IComponent
+}
+
+interface IComponent {
+	hollow bool
+}
+
+struct IsControlledByPlayerTag {
+	hollow bool
+}
+
+fn get_component[T](entity Entity) !&T {
+	for component in entity.components {
+		if component is T {
+			return component
+		}
+	}
+
+	return error('Entity does not have component')
+}
+
+fn test_array_of_interfaces_index() {
+	entity := Entity{1, [IsControlledByPlayerTag{}]}
+	id := entity.components.index(*get_component[IsControlledByPlayerTag](entity)!)
+
+	println('id = ${id}')
+	assert id == 0
+}