Auto merge of #26699 - eddyb:unstable-prelude_import, r=huonw

Closes #26690.

src/test/compile-fail/feature-gate-prelude_import.rs

@@ -0,0 +1,14 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[prelude_import] //~ ERROR `#[prelude_import]` is for use by rustc only
+use std::prelude::v1::*;
+
+fn main() {}

src/test/pretty/issue-4264.pp

@@ -1,4 +1,4 @@
-#![feature(no_std)]
+#![feature(no_std, prelude_import)]
 #![no_std]
 #[prelude_import]
 use std::prelude::v1::*;