Rollup merge of rust-lang#98717 - RalfJung:make-tidy-less-annoying, r…

…=jyn514

get rid of tidy 'unnecessarily ignored' warnings

I think these warnings are quite pointless: when I say `allow(foo)` in my code, that doesn't necessarily mean that I expect `foo` to happen -- it just means that I am okay with `foo` happening.

For example, having to add and remove `ignore-tidy-linelength` as the longest line in the file keeps growing and shrinking is just annoying and doesn't benefit anyone, IMO. This usually incurs *two* CI roundtrips: first CI tells you that line lengths in your test file are ignored unnecessarily, so you go and remove that attribute; then CI tells you that now your line numbers changed, so you re-bless your tests (often takes >5min if parts of rustc need rebuilding because `./x.py fmt` changed something somewhere). That's just a lot of wasted effort and time and patience.

src/tools/tidy/src/style.rs

@@ -395,9 +395,6 @@ pub fn check(path: &Path, bad: &mut bool) {
                 );
             };
             suppressible_tidy_err!(err, skip_file_length, "");
-        } else if lines > (LINES * 7) / 10 {
-            // Just set it to something that doesn't trigger the "unnecessarily ignored" warning.
-            skip_file_length = Directive::Ignore(true);
         }
 
         if let Directive::Ignore(false) = skip_cr {
@@ -406,12 +403,6 @@ pub fn check(path: &Path, bad: &mut bool) {
         if let Directive::Ignore(false) = skip_tab {
             tidy_error!(bad, "{}: ignoring tab characters unnecessarily", file.display());
         }
-        if let Directive::Ignore(false) = skip_line_length {
-            tidy_error!(bad, "{}: ignoring line length unnecessarily", file.display());
-        }
-        if let Directive::Ignore(false) = skip_file_length {
-            tidy_error!(bad, "{}: ignoring file length unnecessarily", file.display());
-        }
         if let Directive::Ignore(false) = skip_end_whitespace {
             tidy_error!(bad, "{}: ignoring trailing whitespace unnecessarily", file.display());
         }
@@ -424,5 +415,9 @@ pub fn check(path: &Path, bad: &mut bool) {
         if let Directive::Ignore(false) = skip_copyright {
             tidy_error!(bad, "{}: ignoring copyright unnecessarily", file.display());
         }
+        // We deliberately do not warn about these being unnecessary,
+        // that would just lead to annoying churn.
+        let _unused = skip_line_length;
+        let _unused = skip_file_length;
     })
 }