Do not handle ignore-tidy directives in UI test mode

This is so the collection script can properly omit collecting tidy
directives.

Author: jieyouxu

src/tools/compiletest/src/header.rs

@@ -999,26 +999,41 @@ pub fn make_test_description<R: Read>(
             }
 
             macro_rules! decision {
-            ($e:expr) => {
-                match $e {
-                    IgnoreDecision::Ignore { reason } => {
-                        ignore = true;
-                        // The ignore reason must be a &'static str, so we have to leak memory to
-                        // create it. This is fine, as the header is parsed only at the start of
-                        // compiletest so it won't grow indefinitely.
-                        ignore_message = Some(&*Box::leak(Box::<str>::from(reason)));
+                ($e:expr) => {
+                    match $e {
+                        IgnoreDecision::Ignore { reason } => {
+                            ignore = true;
+                            // The ignore reason must be a &'static str, so we have to leak memory to
+                            // create it. This is fine, as the header is parsed only at the start of
+                            // compiletest so it won't grow indefinitely.
+                            ignore_message = Some(&*Box::leak(Box::<str>::from(reason)));
+                        }
+                        IgnoreDecision::Error { message } => {
+                            eprintln!("error: {}:{line_number}: {message}", path.display());
+                            *poisoned = true;
+                            return;
+                        }
+                        IgnoreDecision::Continue => {}
                     }
-                    IgnoreDecision::Error { message } => {
-                        eprintln!("error: {}:{line_number}: {message}", path.display());
-                        *poisoned = true;
-                        return;
-                    }
-                    IgnoreDecision::Continue => {}
+                };
+            }
+
+            // Do not handle `// ignore-tidy` or `// ignore-tidy-*` because they are tidy directives,
+            // not compiletest directives (which would begin with `//@` for UI tests).
+            if config.mode == Mode::Ui {
+                let split = og_ln.trim_start().split_once("//");
+                if !split
+                    .map(|(pre, post)| {
+                        pre.is_empty() && post.trim_start().starts_with("ignore-tidy")
+                    })
+                    .unwrap_or(false)
+                {
+                    decision!(cfg::handle_ignore(config, ln));
                 }
-            };
-        }
+            } else {
+                decision!(cfg::handle_ignore(config, ln));
+            }
 
-            decision!(cfg::handle_ignore(config, ln));
             decision!(cfg::handle_only(config, ln));
             decision!(needs::handle_needs(&cache.needs, config, ln));
             decision!(ignore_llvm(config, ln));