filer: allow renaming into a sibling that shares the name prefix (#12337)

CanRename rejected a move whenever the new parent directory's path started
with the source path as a plain string, so moving /dir/a into /dir/a.d
(or anything under /dir/ab) failed with "can not move directory to a
subdirectory of itself". Check the path boundary instead: reject only
when the new parent is the source itself or lies under it.


Claude-Session: https://claude.ai/code/session_01VncHKTehVroSAzRMUHykEX

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/filer/filer_rename.go

@@ -10,7 +10,7 @@ import (
 
 func (f *Filer) CanRename(ctx context.Context, source, target util.FullPath, oldName string) error {
 	sourcePath := source.Child(oldName)
-	if strings.HasPrefix(string(target), string(sourcePath)) {
+	if movesIntoItself(sourcePath, target) {
 		return fmt.Errorf("mv: can not move directory to a subdirectory of itself")
 	}
 
@@ -33,6 +33,13 @@ func (f *Filer) CanRename(ctx context.Context, source, target util.FullPath, old
 	return nil
 }
 
+// movesIntoItself reports whether target, the new parent directory, is
+// sourcePath or lies under it. A sibling that only shares a name prefix,
+// such as /a.d for /a, does not.
+func movesIntoItself(sourcePath, target util.FullPath) bool {
+	return target == sourcePath || target.IsUnder(sourcePath)
+}
+
 func (f *Filer) DetectBucket(source util.FullPath) (bucket string) {
 	if strings.HasPrefix(string(source), f.DirBucketsPath+"/") {
 		bucketAndObjectKey := string(source)[len(f.DirBucketsPath)+1:]

weed/filer/filer_rename_test.go

@@ -29,3 +29,27 @@ func TestDetectBucket(t *testing.T) {
 		})
 	}
 }
+
+func TestMovesIntoItself(t *testing.T) {
+	tests := []struct {
+		name       string
+		sourcePath string
+		target     string
+		want       bool
+	}{
+		{"into itself", "/dir/a", "/dir/a", true},
+		{"into a child", "/dir/a", "/dir/a/b", true},
+		{"into a deeper descendant", "/dir/a", "/dir/a/b/c", true},
+		{"into a sibling sharing the name prefix", "/dir/a", "/dir/a.d", false},
+		{"into a descendant of that sibling", "/dir/a", "/dir/ab/c", false},
+		{"into the parent", "/dir/a", "/dir", false},
+		{"into an unrelated directory", "/dir/a", "/other", false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := movesIntoItself(util.FullPath(tt.sourcePath), util.FullPath(tt.target)); got != tt.want {
+				t.Errorf("movesIntoItself(%q, %q) = %v, want %v", tt.sourcePath, tt.target, got, tt.want)
+			}
+		})
+	}
+}