From 84573729c81d254244508a325f34092ec2284cdd Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Sat, 13 Jun 2026 10:03:29 +0000
Subject: [PATCH] perf: replace entry.path().is_file() with
 entry.file_type().is_some_and(|ft| ft.is_file())

When using directory traversal crates like `ignore`, calling `entry.path().is_file()` performs an unnecessary `stat` syscall on the underlying path. By switching to `entry.file_type()`, the code can accurately use the file metadata already retrieved during the `readdir` operation, significantly speeding up directory traversals.

Co-authored-by: mudcube <101564+mudcube@users.noreply.github.com>
---
 .jules/bolt.md                                                | 4 ++++
 crates/mill-handlers/src/handlers/common/checksums.rs         | 4 +++-
 crates/mill-handlers/src/handlers/prune_ops.rs                | 4 +++-
 .../mill-handlers/src/handlers/rename_ops/directory_rename.rs | 4 +++-
 .../src/services/filesystem/file_service/rename.rs            | 4 +++-
 5 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/.jules/bolt.md b/.jules/bolt.md
index 541c0ab51..af606a123 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -17,3 +17,7 @@
 ## 2025-05-19 - File Discovery Allocations
 **Learning:** In `discover_importing_files`, `WalkBuilder` results were being converted to `PathBuf` via `.map(|e| e.into_path())` *before* filtering. This caused allocations for every single file in the workspace (including excluded files and directories).
 **Action:** Filter `ignore::DirEntry` directly using `entry.file_type()` and `entry.path()` before mapping to `PathBuf`. This avoids allocations for non-matching files.
+
+## 2025-10-24 - Directory Traversal is_file()
+**Learning:** When using directory traversal crates like `ignore` or `walkdir` in Rust, calling `entry.path().is_file()` on directory entries performs an unnecessary `stat` syscall. Using `entry.file_type().is_some_and(|ft| ft.is_file())` utilizes the metadata already retrieved during the `readdir` operation, significantly improving performance.
+**Action:** Avoid calling `entry.path().is_file()` on `DirEntry` values from traversal libraries. Use `entry.file_type().is_some_and(|ft| ft.is_file())` instead.
diff --git a/crates/mill-handlers/src/handlers/common/checksums.rs b/crates/mill-handlers/src/handlers/common/checksums.rs
index 79a48a327..3e61c434f 100644
--- a/crates/mill-handlers/src/handlers/common/checksums.rs
+++ b/crates/mill-handlers/src/handlers/common/checksums.rs
@@ -79,7 +79,9 @@ pub async fn calculate_checksums_for_directory_rename(
         .build();
 
     for entry in walker.flatten() {
-        if entry.path().is_file() {
+        // Avoid `entry.path().is_file()` to prevent unnecessary `stat` syscalls,
+        // relying on the cached metadata from the `readdir` operation.
+        if entry.file_type().is_some_and(|ft| ft.is_file()) {
             if let Ok(content) = context.app_state.file_service.read_file(entry.path()).await {
                 file_checksums.insert(
                     entry.path().to_string_lossy().to_string(),
diff --git a/crates/mill-handlers/src/handlers/prune_ops.rs b/crates/mill-handlers/src/handlers/prune_ops.rs
index 2f9ca3a91..f95d68732 100644
--- a/crates/mill-handlers/src/handlers/prune_ops.rs
+++ b/crates/mill-handlers/src/handlers/prune_ops.rs
@@ -665,7 +665,9 @@ impl PrunePlanner {
             let walker = ignore::WalkBuilder::new(&abs_dir).hidden(false).build();
             let files = walker
                 .flatten()
-                .filter(|entry| entry.path().is_file())
+                // Avoid `entry.path().is_file()` to prevent unnecessary `stat` syscalls,
+                // relying on the cached metadata from the `readdir` operation.
+                .filter(|entry| entry.file_type().is_some_and(|ft| ft.is_file()))
                 .map(|entry| entry.path().to_path_buf())
                 .collect();
             Ok((files, abs_dir))
diff --git a/crates/mill-handlers/src/handlers/rename_ops/directory_rename.rs b/crates/mill-handlers/src/handlers/rename_ops/directory_rename.rs
index 68aead607..43fb84d67 100644
--- a/crates/mill-handlers/src/handlers/rename_ops/directory_rename.rs
+++ b/crates/mill-handlers/src/handlers/rename_ops/directory_rename.rs
@@ -287,7 +287,9 @@ impl RenameService {
         let mut files_to_move = 0;
         let walker = ignore::WalkBuilder::new(&old_path).hidden(false).build();
         for entry in walker.flatten() {
-            if entry.path().is_file() {
+            // Avoid `entry.path().is_file()` to prevent unnecessary `stat` syscalls,
+            // relying on the cached metadata from the `readdir` operation.
+            if entry.file_type().is_some_and(|ft| ft.is_file()) {
                 files_to_move += 1;
             }
         }
diff --git a/crates/mill-services/src/services/filesystem/file_service/rename.rs b/crates/mill-services/src/services/filesystem/file_service/rename.rs
index b8b364ffa..c3c53f803 100644
--- a/crates/mill-services/src/services/filesystem/file_service/rename.rs
+++ b/crates/mill-services/src/services/filesystem/file_service/rename.rs
@@ -469,7 +469,9 @@ impl FileService {
         let mut files = Vec::new();
         let walker = ignore::WalkBuilder::new(dir).hidden(false).build();
         for entry in walker.flatten() {
-            if entry.path().is_file() {
+            // Avoid `entry.path().is_file()` to prevent unnecessary `stat` syscalls,
+            // relying on the cached metadata from the `readdir` operation.
+            if entry.file_type().is_some_and(|ft| ft.is_file()) {
                 files.push(entry.path().to_path_buf());
             }
         }