vfs: fix duplicates on rename - fixes #5469

Before this change, if there was an existing file being uploaded when
a file was renamed on top of it, then both would be uploaded. This
causes a duplicate in Google Drive as both files get uploaded at the
same time. This was triggered reliably by LibreOffice saving doc
files.

This fix removes any duplicates in the upload queue on rename.

vfs/vfscache/writeback/writeback_test.go

@@ -585,6 +585,53 @@ func TestWriteBackRename(t *testing.T) {
 	assert.Equal(t, wbItem.name, "three")
 }
 
+// TestWriteBackRenameDuplicates checks that if we rename an entry and
+// make a duplicate, we remove the duplicate.
+func TestWriteBackRenameDuplicates(t *testing.T) {
+	wb, cancel := newTestWriteBack(t)
+	defer cancel()
+
+	// add item "one"
+	pi1 := newPutItem(t)
+	id1 := wb.Add(0, "one", true, pi1.put)
+	wbItem1 := wb.lookup[id1]
+	checkOnHeap(t, wb, wbItem1)
+	checkInLookup(t, wb, wbItem1)
+	assert.Equal(t, wbItem1.name, "one")
+
+	<-pi1.started
+	checkNotOnHeap(t, wb, wbItem1)
+	checkInLookup(t, wb, wbItem1)
+
+	// add item "two"
+	pi2 := newPutItem(t)
+	id2 := wb.Add(0, "two", true, pi2.put)
+	wbItem2 := wb.lookup[id2]
+	checkOnHeap(t, wb, wbItem2)
+	checkInLookup(t, wb, wbItem2)
+	assert.Equal(t, wbItem2.name, "two")
+
+	<-pi2.started
+	checkNotOnHeap(t, wb, wbItem2)
+	checkInLookup(t, wb, wbItem2)
+
+	// rename "two" to "one"
+	wb.Rename(id2, "one")
+
+	// check "one" is cancelled and removed from heap and lookup
+	checkNotOnHeap(t, wb, wbItem1)
+	checkNotInLookup(t, wb, wbItem1)
+	assert.True(t, pi1.cancelled)
+	assert.Equal(t, wbItem1.name, "one")
+
+	// check "two" (now called "one"!) has been cancelled and will
+	// be retried
+	checkOnHeap(t, wb, wbItem2)
+	checkInLookup(t, wb, wbItem2)
+	assert.True(t, pi2.cancelled)
+	assert.Equal(t, wbItem2.name, "one")
+}
+
 func TestWriteBackCancelUpload(t *testing.T) {
 	wb, cancel := newTestWriteBack(t)
 	defer cancel()