Rollup merge of rust-lang#48880 - petrochenkov:badstderr, r=kennytm

tidy: Add a check for stray `.stderr` and `.stdout` files in UI test directories

Author: Mark-Simulacrum

Diff for: src/test/ui/lifetime-errors/ex3-both-anon-regions-4.stderr

@@ -51,6 +51,7 @@ pub mod features;
 pub mod cargo;
 pub mod pal;
 pub mod deps;
+pub mod ui_tests;
 pub mod unstable_book;
 
 fn filter_dirs(path: &Path) -> bool {

Diff for: src/test/ui/nll/closure-requirements/propagate-approximated-to-empty.stderr

@@ -45,6 +45,7 @@ fn main() {
         deps::check(&path, &mut bad);
     }
     deps::check_whitelist(&path, &cargo, &mut bad);
+    ui_tests::check(&path, &mut bad);
 
     if bad {
         eprintln!("some tidy checks failed");

Diff for: src/test/ui/resolve-error.stderr

@@ -0,0 +1,26 @@
+// Copyright 2018 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.
+
+//! Tidy check to ensure that there are no stray `.stderr` files in UI test directories.
+
+use std::path::Path;
+
+pub fn check(path: &Path, bad: &mut bool) {
+    super::walk_many(&[&path.join("test/ui"), &path.join("test/ui-fulldeps")],
+                     &mut |_| false,
+                     &mut |file_path| {
+        if let Some(ext) = file_path.extension() {
+            if (ext == "stderr" || ext == "stdout") && !file_path.with_extension("rs").exists() {
+                println!("Stray file with UI testing output: {:?}", file_path);
+                *bad = true;
+            }
+        }
+    });
+}