From 0b65a616ba760437340386ad0c8fec39b4be5924 Mon Sep 17 00:00:00 2001
From: Simon Frei <freisim93@gmail.com>
Date: Mon, 8 Jun 2020 08:14:50 +0200
Subject: [PATCH] lib/scanner: Save one stat call per file (#6715)

---
 lib/scanner/walk.go | 30 ++++++++++++++----------------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/lib/scanner/walk.go b/lib/scanner/walk.go
index 35d910dda..39114ac4f 100644
--- a/lib/scanner/walk.go
+++ b/lib/scanner/walk.go
@@ -265,7 +265,7 @@ func (w *walker) walkAndHashFiles(ctx context.Context, toHashChan chan<- protoco
 
 		if ignoredParent == "" {
 			// parent isn't ignored, nothing special
-			return w.handleItem(ctx, path, toHashChan, finishedChan, skip)
+			return w.handleItem(ctx, path, info, toHashChan, finishedChan, skip)
 		}
 
 		// Part of current path below the ignored (potential) parent
@@ -274,17 +274,22 @@ func (w *walker) walkAndHashFiles(ctx context.Context, toHashChan chan<- protoco
 		// ignored path isn't actually a parent of the current path
 		if rel == path {
 			ignoredParent = ""
-			return w.handleItem(ctx, path, toHashChan, finishedChan, skip)
+			return w.handleItem(ctx, path, info, toHashChan, finishedChan, skip)
 		}
 
 		// The previously ignored parent directories of the current, not
 		// ignored path need to be handled as well.
-		if err = w.handleItem(ctx, ignoredParent, toHashChan, finishedChan, skip); err != nil {
-			return err
-		}
-		for _, name := range strings.Split(rel, string(fs.PathSeparator)) {
+		// Prepend an empty string to handle ignoredParent without anything
+		// appended in the first iteration.
+		for _, name := range append([]string{""}, strings.Split(rel, string(fs.PathSeparator))...) {
 			ignoredParent = filepath.Join(ignoredParent, name)
-			if err = w.handleItem(ctx, ignoredParent, toHashChan, finishedChan, skip); err != nil {
+			info, err = w.Filesystem.Lstat(ignoredParent)
+			// An error here would be weird as we've already gotten to this point, but act on it nonetheless
+			if err != nil {
+				w.handleError(ctx, "scan", ignoredParent, err, finishedChan)
+				return skip
+			}
+			if err = w.handleItem(ctx, ignoredParent, info, toHashChan, finishedChan, skip); err != nil {
 				return err
 			}
 		}
@@ -294,16 +299,9 @@ func (w *walker) walkAndHashFiles(ctx context.Context, toHashChan chan<- protoco
 	}
 }
 
-func (w *walker) handleItem(ctx context.Context, path string, toHashChan chan<- protocol.FileInfo, finishedChan chan<- ScanResult, skip error) error {
-	info, err := w.Filesystem.Lstat(path)
-	// An error here would be weird as we've already gotten to this point, but act on it nonetheless
-	if err != nil {
-		w.handleError(ctx, "scan", path, err, finishedChan)
-		return skip
-	}
-
+func (w *walker) handleItem(ctx context.Context, path string, info fs.FileInfo, toHashChan chan<- protocol.FileInfo, finishedChan chan<- ScanResult, skip error) error {
 	oldPath := path
-	path, err = w.normalizePath(path, info)
+	path, err := w.normalizePath(path, info)
 	if err != nil {
 		w.handleError(ctx, "normalizing path", oldPath, err, finishedChan)
 		return skip