Fix tidy issues

Author: petrochenkov

src/libsyntax/feature_gate.rs

@@ -245,7 +245,7 @@ declare_features! (
     (active, allocator_internals, "1.20.0", None, None),
 
     // Allows using the `format_args_nl` macro.
-    (active, format_args_nl, "1.29.0", None, None),
+    (active, format_args_nl, "1.29.0", Some(0), None),
 
     // no-tracking-issue-end
 

src/tools/tidy/src/libcoretest.rs

@@ -13,7 +13,8 @@ pub fn check(path: &Path, bad: &mut bool) {
         &mut |entry, contents| {
             let subpath = entry.path();
             if let Some("rs") = subpath.extension().and_then(|e| e.to_str()) {
-                if contents.contains("#[test]") {
+                let contents = contents.trim();
+                if !contents.starts_with("//") && contents.contains("#[test]") {
                     tidy_error!(
                         bad,
                         "{} contains #[test]; libcore tests must be placed inside \