Auto merge of #38689 - pnkfelix:dont-check-stability-on-private-items, r=nikomatsakis

Dont check stability for items that are not pub to universe.

Dont check stability for items that are not pub to universe.

In other words, skip it for private and even `pub(restricted)` items, because stability checks are only relevant to things visible in other crates.

Fix #38412.

src/test/compile-fail/issue-38412.rs

@@ -0,0 +1,20 @@
+// Copyright 2016 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.
+
+fn main() {
+    let Box(a) = loop { };
+    //~^ ERROR field `0` of struct `std::boxed::Box` is private
+
+    // (The below is a trick to allow compiler to infer a type for
+    // variable `a` without attempting to ascribe a type to the
+    // pattern or otherwise attempting to name the Box type, which
+    // would run afoul of issue #22207)
+    let _b: *mut i32 = *a;
+}