checker: fix error for cast to alias of reference struct (#13278)

vlib/szip/szip.v

@@ -88,7 +88,7 @@ pub fn open(name string, level CompressionLevel, mode OpenMode) ?&Zip {
 	if name.len == 0 {
 		return error('szip: name of file empty')
 	}
-	p_zip := &Zip(C.zip_open(&char(name.str), int(level), char(mode.to_byte())))
+	p_zip := unsafe { &Zip(C.zip_open(&char(name.str), int(level), char(mode.to_byte()))) }
 	if isnil(p_zip) {
 		return error('szip: cannot open/create/append new zip archive')
 	}

vlib/v/checker/checker.v

@@ -2661,7 +2661,7 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		if !c.table.sumtype_has_variant(to_type, from_type, false) && !to_type.has_flag(.optional) {
 			c.error('cannot cast `$from_sym.name` to `$to_sym.name`', node.pos)
 		}
-	} else if mut to_sym.info is ast.Alias {
+	} else if mut to_sym.info is ast.Alias && !(final_to_sym.kind == .struct_ && to_type.is_ptr()) {
 		if !c.check_types(from_type, to_sym.info.parent_type) && !(final_to_sym.is_int()
 			&& final_from_sym.kind in [.enum_, .bool, .i8, .char]) {
 			c.error('cannot convert type `$from_sym.name` to `$to_sym.name` (alias to `$final_to_sym.name`)',

vlib/v/tests/cast_to_alias_test.v

@@ -34,3 +34,20 @@ fn test_cast_to_alias() {
 	println(ret_str)
 	assert ret_str == '1'
 }
+
+struct Foo {
+	x int
+	y string
+}
+
+type Alias = Foo
+
+fn test_cast_to_alias_of_ref_struct() {
+	foo := &Foo(0)
+	println(typeof(foo).name)
+	assert typeof(foo).name == '&Foo'
+
+	bar := &Alias(0)
+	println(typeof(bar).name)
+	assert typeof(bar).name == '&Alias'
+}