From 1b2bed92424f45248aa4b2f547d05e8140825637 Mon Sep 17 00:00:00 2001
From: Shantanav Mukherjee <shantanav7@gmail.com>
Date: Fri, 16 Oct 2026 08:03:42 +0530
Subject: [PATCH] fs: ignore disappearing files in DiskUsage

A file or directory can disappear after filepath.Walk reads its parent but before the entry is inspected. Treat ENOENT for descendants as a transient condition because the removed entry no longer contributes to disk usage.

Keep returning errors for a missing root and for all other walk failures. Apply the behavior on Unix and Windows and cover the error handling with regression tests.

Assisted-by: OpenAI Codex
Signed-off-by: Shantanav Mukherjee <shantanav7@gmail.com>
---
 fs/du.go         | 12 +++++++++++-
 fs/du_test.go    | 20 ++++++++++++++++++++
 fs/du_unix.go    |  2 +-
 fs/du_windows.go |  2 +-
 4 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/fs/du.go b/fs/du.go
index fccc985d..e63ce10c 100644
--- a/fs/du.go
+++ b/fs/du.go
@@ -16,7 +16,17 @@
 
 package fs
 
-import "context"
+import (
+	"context"
+	"os"
+)
+
+func handleWalkError(root, path string, err error) error {
+	if err != nil && path != root && os.IsNotExist(err) {
+		return nil
+	}
+	return err
+}
 
 // Usage of disk information
 type Usage struct {
diff --git a/fs/du_test.go b/fs/du_test.go
index eb84b66c..29e0f61e 100644
--- a/fs/du_test.go
+++ b/fs/du_test.go
@@ -142,6 +142,26 @@ func TestUsage(t *testing.T) {
 	}
 }
 
+func TestHandleWalkError(t *testing.T) {
+	t.Parallel()
+
+	root := filepath.Join("root")
+	missing := filepath.Join(root, "removed")
+	notExistErr := &os.PathError{Op: "lstat", Path: missing, Err: os.ErrNotExist}
+
+	if err := handleWalkError(root, missing, notExistErr); err != nil {
+		t.Fatalf("expected missing child to be ignored, got %v", err)
+	}
+	if err := handleWalkError(root, root, notExistErr); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("expected missing root error, got %v", err)
+	}
+
+	permissionErr := &os.PathError{Op: "open", Path: missing, Err: os.ErrPermission}
+	if err := handleWalkError(root, missing, permissionErr); !errors.Is(err, os.ErrPermission) {
+		t.Fatalf("expected permission error, got %v", err)
+	}
+}
+
 // createSparseFile creates a sparse file filled with random
 // bytes for data parts
 // The parse alternate data length, hole length, data length, ....
diff --git a/fs/du_unix.go b/fs/du_unix.go
index d960b236..a77206ee 100644
--- a/fs/du_unix.go
+++ b/fs/du_unix.go
@@ -67,7 +67,7 @@ func diskUsage(ctx context.Context, roots ...string) (Usage, error) {
 	for _, root := range roots {
 		if err := filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
 			if err != nil {
-				return err
+				return handleWalkError(root, path, err)
 			}
 
 			select {
diff --git a/fs/du_windows.go b/fs/du_windows.go
index 48494e2c..3fb52bfe 100644
--- a/fs/du_windows.go
+++ b/fs/du_windows.go
@@ -32,7 +32,7 @@ func diskUsage(ctx context.Context, roots ...string) (Usage, error) {
 	for _, root := range roots {
 		if err := filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
 			if err != nil {
-				return err
+				return handleWalkError(root, path, err)
 			}
 
 			select {