Rollup merge of #105829 - the8472:tidy-style, r=jyn514

Speed up tidy

This can be reviewed commit by commit since they contain separate optimizations.

```
# master
$ taskset -c 0-5 hyperfine './x test tidy'
Benchmark #1: ./x test tidy
  Time (mean ± σ):      4.857 s ±  0.064 s    [User: 12.967 s, System: 2.014 s]
  Range (min … max):    4.779 s …  4.997 s    10 runs

# PR
$ taskset -c 0-5 hyperfine './x test tidy'
Benchmark #1: ./x test tidy
  Time (mean ± σ):      3.672 s ±  0.035 s    [User: 10.524 s, System: 2.029 s]
  Range (min … max):    3.610 s …  3.725 s    10 runs
```

3 files changed, 70 insertions, 34 deletions

diff --git a/src/bootstrap/format.rs b/src/bootstrap/format.rs
index 5e7264fe765..b2f6afead79 100644
--- a/src/bootstrap/format.rs
+++ b/src/bootstrap/format.rs
@@ -8,7 +8,7 @@ use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
 use std::sync::mpsc::SyncSender;
 
-fn rustfmt(src: &Path, rustfmt: &Path, paths: &[PathBuf], check: bool) -> impl FnMut() {
+fn rustfmt(src: &Path, rustfmt: &Path, paths: &[PathBuf], check: bool) -> impl FnMut(bool) -> bool {
     let mut cmd = Command::new(&rustfmt);
     // avoid the submodule config paths from coming into play,
     // we only allow a single global config for the workspace for now
@@ -23,7 +23,13 @@ fn rustfmt(src: &Path, rustfmt: &Path, paths: &[PathBuf], check: bool) -> impl F
     let cmd_debug = format!("{:?}", cmd);
     let mut cmd = cmd.spawn().expect("running rustfmt");
     // poor man's async: return a closure that'll wait for rustfmt's completion
-    move || {
+    move |block: bool| -> bool {
+        if !block {
+            match cmd.try_wait() {
+                Ok(Some(_)) => {}
+                _ => return false,
+            }
+        }
         let status = cmd.wait().unwrap();
         if !status.success() {
             eprintln!(
@@ -34,6 +40,7 @@ fn rustfmt(src: &Path, rustfmt: &Path, paths: &[PathBuf], check: bool) -> impl F
             );
             crate::detail_exit(1);
         }
+        true
     }
 }
 
@@ -146,15 +153,23 @@ pub fn format(build: &Builder<'_>, check: bool, paths: &[PathBuf]) {
             let child = rustfmt(&src, &rustfmt_path, paths.as_slice(), check);
             children.push_back(child);
 
+            // poll completion before waiting
+            for i in (0..children.len()).rev() {
+                if children[i](false) {
+                    children.swap_remove_back(i);
+                    break;
+                }
+            }
+
             if children.len() >= max_processes {
                 // await oldest child
-                children.pop_front().unwrap()();
+                children.pop_front().unwrap()(true);
             }
         }
 
         // await remaining children
         for mut child in children {
-            child();
+            child(true);
         }
     });
 
diff --git a/src/tools/tidy/src/main.rs b/src/tools/tidy/src/main.rs
index b0b11cafca5..6714c63ee62 100644
--- a/src/tools/tidy/src/main.rs
+++ b/src/tools/tidy/src/main.rs
@@ -35,15 +35,26 @@ fn main() {
 
     let bad = std::sync::Arc::new(AtomicBool::new(false));
 
+    let drain_handles = |handles: &mut VecDeque<ScopedJoinHandle<'_, ()>>| {
+        // poll all threads for completion before awaiting the oldest one
+        for i in (0..handles.len()).rev() {
+            if handles[i].is_finished() {
+                handles.swap_remove_back(i).unwrap().join().unwrap();
+            }
+        }
+
+        while handles.len() >= concurrency.get() {
+            handles.pop_front().unwrap().join().unwrap();
+        }
+    };
+
     scope(|s| {
         let mut handles: VecDeque<ScopedJoinHandle<'_, ()>> =
             VecDeque::with_capacity(concurrency.get());
 
         macro_rules! check {
             ($p:ident $(, $args:expr)* ) => {
-                while handles.len() >= concurrency.get() {
-                    handles.pop_front().unwrap().join().unwrap();
-                }
+                drain_handles(&mut handles);
 
                 let handle = s.spawn(|| {
                     let mut flag = false;
@@ -97,9 +108,8 @@ fn main() {
         check!(alphabetical, &library_path);
 
         let collected = {
-            while handles.len() >= concurrency.get() {
-                handles.pop_front().unwrap().join().unwrap();
-            }
+            drain_handles(&mut handles);
+
             let mut flag = false;
             let r = features::check(&src_path, &compiler_path, &library_path, &mut flag, verbose);
             if flag {
diff --git a/src/tools/tidy/src/style.rs b/src/tools/tidy/src/style.rs
index e3a094caf91..f91e38262f6 100644
--- a/src/tools/tidy/src/style.rs
+++ b/src/tools/tidy/src/style.rs
@@ -17,7 +17,7 @@
 //! `// ignore-tidy-CHECK-NAME`.
 
 use crate::walk::{filter_dirs, walk};
-use regex::Regex;
+use regex::{Regex, RegexSet};
 use std::path::Path;
 
 /// Error code markdown is restricted to 80 columns because they can be
@@ -225,6 +225,7 @@ pub fn check(path: &Path, bad: &mut bool) {
         .chain(PROBLEMATIC_CONSTS.iter().map(|v| format!("{:x}", v)))
         .chain(PROBLEMATIC_CONSTS.iter().map(|v| format!("{:X}", v)))
         .collect();
+    let problematic_regex = RegexSet::new(problematic_consts_strings.as_slice()).unwrap();
     walk(path, &mut skip, &mut |entry, contents| {
         let file = entry.path();
         let filename = file.file_name().unwrap().to_string_lossy();
@@ -281,7 +282,27 @@ pub fn check(path: &Path, bad: &mut bool) {
         let mut trailing_new_lines = 0;
         let mut lines = 0;
         let mut last_safety_comment = false;
+        let is_test = file.components().any(|c| c.as_os_str() == "tests");
+        // scanning the whole file for multiple needles at once is more efficient than
+        // executing lines times needles separate searches.
+        let any_problematic_line = problematic_regex.is_match(contents);
         for (i, line) in contents.split('\n').enumerate() {
+            if line.is_empty() {
+                if i == 0 {
+                    leading_new_lines = true;
+                }
+                trailing_new_lines += 1;
+                continue;
+            } else {
+                trailing_new_lines = 0;
+            }
+
+            let trimmed = line.trim();
+
+            if !trimmed.starts_with("//") {
+                lines += 1;
+            }
+
             let mut err = |msg: &str| {
                 tidy_error!(bad, "{}:{}: {}", file.display(), i + 1, msg);
             };
@@ -308,28 +329,29 @@ pub fn check(path: &Path, bad: &mut bool) {
                 suppressible_tidy_err!(err, skip_cr, "CR character");
             }
             if filename != "style.rs" {
-                if line.contains("TODO") {
+                if trimmed.contains("TODO") {
                     err("TODO is deprecated; use FIXME")
                 }
-                if line.contains("//") && line.contains(" XXX") {
+                if trimmed.contains("//") && trimmed.contains(" XXX") {
                     err("XXX is deprecated; use FIXME")
                 }
-                for s in problematic_consts_strings.iter() {
-                    if line.contains(s) {
-                        err("Don't use magic numbers that spell things (consider 0x12345678)");
+                if any_problematic_line {
+                    for s in problematic_consts_strings.iter() {
+                        if trimmed.contains(s) {
+                            err("Don't use magic numbers that spell things (consider 0x12345678)");
+                        }
                     }
                 }
             }
-            let is_test = || file.components().any(|c| c.as_os_str() == "tests");
             // for now we just check libcore
-            if line.contains("unsafe {") && !line.trim().starts_with("//") && !last_safety_comment {
-                if file.components().any(|c| c.as_os_str() == "core") && !is_test() {
+            if trimmed.contains("unsafe {") && !trimmed.starts_with("//") && !last_safety_comment {
+                if file.components().any(|c| c.as_os_str() == "core") && !is_test {
                     suppressible_tidy_err!(err, skip_undocumented_unsafe, "undocumented unsafe");
                 }
             }
-            if line.contains("// SAFETY:") {
+            if trimmed.contains("// SAFETY:") {
                 last_safety_comment = true;
-            } else if line.trim().starts_with("//") || line.trim().is_empty() {
+            } else if trimmed.starts_with("//") || trimmed.is_empty() {
                 // keep previous value
             } else {
                 last_safety_comment = false;
@@ -337,7 +359,8 @@ pub fn check(path: &Path, bad: &mut bool) {
             if (line.starts_with("// Copyright")
                 || line.starts_with("# Copyright")
                 || line.starts_with("Copyright"))
-                && (line.contains("Rust Developers") || line.contains("Rust Project Developers"))
+                && (trimmed.contains("Rust Developers")
+                    || trimmed.contains("Rust Project Developers"))
             {
                 suppressible_tidy_err!(
                     err,
@@ -351,18 +374,6 @@ pub fn check(path: &Path, bad: &mut bool) {
             if filename.ends_with(".cpp") && line.contains("llvm_unreachable") {
                 err(LLVM_UNREACHABLE_INFO);
             }
-            if line.is_empty() {
-                if i == 0 {
-                    leading_new_lines = true;
-                }
-                trailing_new_lines += 1;
-            } else {
-                trailing_new_lines = 0;
-            }
-
-            if !line.trim().starts_with("//") {
-                lines += 1;
-            }
         }
         if leading_new_lines {
             let mut err = |_| {