Fix comments.

Some are too long, some aren't complete sentences, some are complete
sentences but don't bother with an upper case letter at the start. All
annoying and hurt readability.

rustfmt.toml

@@ -3,24 +3,24 @@ version = "Two"
 use_small_heuristics = "Max"
 merge_derives = false
 
-# tidy only checks files which are not ignored, each entry follows gitignore style
+# Files to ignore. Each entry uses gitignore syntax.
 ignore = [
     "/build/",
     "/*-build/",
     "/build-*/",
     "/vendor/",
 
-    # tests for now are not formatted, as they are sometimes pretty-printing constrained
+    # Tests for now are not formatted, as they are sometimes pretty-printing constrained
-    # (and generally rustfmt can move around comments in UI-testing incompatible ways)
+    # (and generally rustfmt can move around comments in UI-testing incompatible ways).
     "/tests/*",
 
-    # but we still want to format rmake.rs files in tests/run-make/ so we need to do this
+    # But we still want to format rmake.rs files in tests/run-make/ so we need to do this
-    # dance to avoid the parent directory from being excluded
+    # dance to avoid the parent directory from being excluded.
     "!/tests/run-make/",
     "/tests/run-make/*/*.rs",
     "!/tests/run-make/*/rmake.rs",
 
-    # do not format submodules
+    # Do not format submodules.
     # FIXME: sync submodule list with tidy/bootstrap/etc
     # tidy/src/walk.rs:filter_dirs
     "library/backtrace",
@@ -42,7 +42,7 @@ ignore = [
     "src/tools/rustc-perf",
     "src/tools/rustfmt",
 
-    # these are ignored by a standard cargo fmt run
+    # These are ignored by a standard cargo fmt run.
     "compiler/rustc_codegen_cranelift/scripts",
     "compiler/rustc_codegen_cranelift/example/gen_block_iterate.rs", # uses edition 2024
 ]

src/bootstrap/src/core/build_steps/format.rs

@@ -12,8 +12,8 @@
 
 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,
+    // Avoid the submodule config paths from coming into play. We only allow a single global config
-    // we only allow a single global config for the workspace for now
+    // for the workspace for now.
     cmd.arg("--config-path").arg(&src.canonicalize().unwrap());
     cmd.arg("--edition").arg("2021");
     cmd.arg("--unstable-features");
@@ -24,7 +24,7 @@ fn rustfmt(src: &Path, rustfmt: &Path, paths: &[PathBuf], check: bool) -> impl F
     cmd.args(paths);
     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
+    // Poor man's async: return a closure that'll wait for rustfmt's completion.
     move |block: bool| -> bool {
         if !block {
             match cmd.try_wait() {
@@ -72,7 +72,7 @@ fn verify_rustfmt_version(build: &Builder<'_>) -> bool {
     !program_out_of_date(&stamp_file, &version)
 }
 
-/// Updates the last rustfmt version used
+/// Updates the last rustfmt version used.
 fn update_rustfmt_version(build: &Builder<'_>) {
     let Some((version, stamp_file)) = get_rustfmt_version(build) else {
         return;
@@ -168,9 +168,10 @@ pub fn format(build: &Builder<'_>, check: bool, paths: &[PathBuf]) {
                 untracked_count += 1;
                 fmt_override.add(&format!("!/{untracked_path}")).expect(untracked_path);
             }
-            // Only check modified files locally to speed up runtime.
+            // Only check modified files locally to speed up runtime. We still check all files in
-            // We still check all files in CI to avoid bugs in `get_modified_rs_files` letting regressions slip through;
+            // CI to avoid bugs in `get_modified_rs_files` letting regressions slip through; we
-            // we also care about CI time less since this is still very fast compared to building the compiler.
+            // also care about CI time less since this is still very fast compared to building the
+            // compiler.
             if !CiEnv::is_ci() && paths.is_empty() {
                 match get_modified_rs_files(build) {
                     Ok(Some(files)) => {
@@ -275,21 +276,23 @@ pub fn format(build: &Builder<'_>, check: bool, paths: &[PathBuf]) {
     .overrides(fmt_override)
     .build_parallel();
 
-    // there is a lot of blocking involved in spawning a child process and reading files to format.
+    // There is a lot of blocking involved in spawning a child process and reading files to format.
-    // spawn more processes than available concurrency to keep the CPU busy
+    // Spawn more processes than available concurrency to keep the CPU busy.
     let max_processes = build.jobs() as usize * 2;
 
-    // spawn child processes on a separate thread so we can batch entries we have received from ignore
+    // Spawn child processes on a separate thread so we can batch entries we have received from
+    // ignore.
     let thread = std::thread::spawn(move || {
         let mut children = VecDeque::new();
         while let Ok(path) = rx.recv() {
-            // try getting more paths from the channel to amortize the overhead of spawning processes
+            // Try getting more paths from the channel to amortize the overhead of spawning
+            // processes.
             let paths: Vec<_> = rx.try_iter().take(63).chain(std::iter::once(path)).collect();
 
             let child = rustfmt(&src, &rustfmt_path, paths.as_slice(), check);
             children.push_back(child);
 
-            // poll completion before waiting
+            // Poll completion before waiting.
             for i in (0..children.len()).rev() {
                 if children[i](false) {
                     children.swap_remove_back(i);
@@ -298,12 +301,12 @@ pub fn format(build: &Builder<'_>, check: bool, paths: &[PathBuf]) {
             }
 
             if children.len() >= max_processes {
-                // await oldest child
+                // Await oldest child.
                 children.pop_front().unwrap()(true);
             }
         }
 
-        // await remaining children
+        // Await remaining children.
         for mut child in children {
             child(true);
         }