From de67f29b3fe3693739c8d431ce4156dce73a7d6d Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Wed, 6 May 2026 17:01:07 +0100
Subject: [PATCH] sync: fix --fix-case rename failing on backends that can't
 update modtime

When --fix-case was used (e.g. by bisync) on backends that can't set
modification times in place - such as Dropbox - files whose content
matched but whose modtimes differed would fail to rename with a
"from_lookup/not_found" error and abort the operation.

This happened because operations.NeedTransfer was called before the
fix-case rename. NeedTransfer's equality check would delete the
destination as a precursor to re-uploading it (the standard way to
update a modtime on these backends), so by the time the rename ran the
file no longer existed on the remote.

Fix by running the fix-case rename first, so that any subsequent
delete/re-upload happens at the correctly-cased destination path.

See: #8881
---
 fs/sync/sync.go | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/fs/sync/sync.go b/fs/sync/sync.go
index 6ec0c074f..b3eca0a86 100644
--- a/fs/sync/sync.go
+++ b/fs/sync/sync.go
@@ -380,6 +380,20 @@ func (s *syncCopyMove) pairChecker(in *pipe, out *pipe, fraction int, wg *sync.W
 		tr := accounting.Stats(s.ctx).NewCheckingTransfer(src, "checking")
 		// Check to see if can store this
 		if src.Storable() {
+			// Fix case for case insensitive filesystems before checking
+			// whether a transfer is needed, since NeedTransfer may delete
+			// the destination (when content matches but modtime can't be
+			// set without re-upload), which would cause the rename below
+			// to fail with a "not found" error.
+			if s.ci.FixCase && !s.ci.Immutable && src.Remote() != pair.Dst.Remote() {
+				if newDst, err := operations.Move(s.ctx, s.fdst, nil, src.Remote(), pair.Dst); err != nil {
+					fs.Errorf(pair.Dst, "Error while attempting to rename to %s: %v", src.Remote(), err)
+					s.processError(err)
+				} else {
+					fs.Infof(pair.Dst, "Fixed case by renaming to: %s", src.Remote())
+					pair.Dst = newDst
+				}
+			}
 			needTransfer := operations.NeedTransfer(s.ctx, pair.Dst, pair.Src)
 			if needTransfer {
 				NoNeedTransfer, err := operations.CompareOrCopyDest(s.ctx, s.fdst, pair.Dst, pair.Src, s.compareCopyDest, s.backupDir)
@@ -391,16 +405,6 @@ func (s *syncCopyMove) pairChecker(in *pipe, out *pipe, fraction int, wg *sync.W
 					needTransfer = false
 				}
 			}
-			// Fix case for case insensitive filesystems
-			if s.ci.FixCase && !s.ci.Immutable && src.Remote() != pair.Dst.Remote() {
-				if newDst, err := operations.Move(s.ctx, s.fdst, nil, src.Remote(), pair.Dst); err != nil {
-					fs.Errorf(pair.Dst, "Error while attempting to rename to %s: %v", src.Remote(), err)
-					s.processError(err)
-				} else {
-					fs.Infof(pair.Dst, "Fixed case by renaming to: %s", src.Remote())
-					pair.Dst = newDst
-				}
-			}
 			if needTransfer {
 				// If files are treated as immutable, fail if destination exists and does not match
 				if s.ci.Immutable && pair.Dst != nil {