QFileSystemWatcher/Windows: Recreate handle for files

QWindowsFileSystemWatcherEngine uses one change notification
per directory to watch directories or files within that
directory. Adding files and their directories in a sequence
caused the value in QWindowsFileSystemWatcherEngineThread::HandleForDirHash
to be overwritten.
Relax the check for the flags (watcher attributes) to use >= and recreate
the change notification of a directory should its flags be insufficient.
This triggers when a file is added after its directory since files
require more attributes.

Task-number: QTBUG-61792
Change-Id: I371a72f1934fa82c53aaf84beb907825031f1c81
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qfilesystemwatcher_win.cpp

@@ -71,6 +71,19 @@ QT_BEGIN_NAMESPACE
 #  define DEBUG if (false) qDebug
 #endif
 
+static Qt::HANDLE createChangeNotification(const QString &path, uint flags)
+{
+    // Volume and folder paths need a trailing slash for proper notification
+    // (e.g. "c:" -> "c:/").
+    QString nativePath = QDir::toNativeSeparators(path);
+    if ((flags & FILE_NOTIFY_CHANGE_ATTRIBUTES) == 0 && !nativePath.endsWith(QLatin1Char('\\')))
+        nativePath.append(QLatin1Char('\\'));
+    const HANDLE result = FindFirstChangeNotification(reinterpret_cast<const wchar_t *>(nativePath.utf16()),
+                                                      FALSE, flags);
+    DEBUG() << __FUNCTION__ << nativePath << hex <<showbase << flags << "returns" << result;
+    return result;
+}
+
 #ifndef Q_OS_WINRT
 ///////////
 // QWindowsRemovableDriveListener
@@ -404,8 +417,29 @@ QStringList QWindowsFileSystemWatcherEngine::addPaths(const QStringList &paths,
             thread = *jt;
             QMutexLocker locker(&(thread->mutex));
 
-            handle = thread->handleForDir.value(QFileSystemWatcherPathKey(absolutePath));
-            if (handle.handle != INVALID_HANDLE_VALUE && handle.flags == flags) {
+            const auto hit = thread->handleForDir.find(QFileSystemWatcherPathKey(absolutePath));
+            if (hit != thread->handleForDir.end() && hit.value().flags < flags) {
+                // Requesting to add a file whose directory has been added previously.
+                // Recreate the notification handle to add the missing notification attributes
+                // for files (FILE_NOTIFY_CHANGE_ATTRIBUTES...)
+                DEBUG() << "recreating" << absolutePath << hex << showbase << hit.value().flags
+                    << "->" << flags;
+                const Qt::HANDLE fileHandle = createChangeNotification(absolutePath, flags);
+                if (fileHandle != INVALID_HANDLE_VALUE) {
+                    const int index = thread->handles.indexOf(hit.value().handle);
+                    const auto pit = thread->pathInfoForHandle.find(hit.value().handle);
+                    Q_ASSERT(index != -1);
+                    Q_ASSERT(pit != thread->pathInfoForHandle.end());
+                    FindCloseChangeNotification(hit.value().handle);
+                    thread->handles[index] = hit.value().handle = fileHandle;
+                    hit.value().flags = flags;
+                    thread->pathInfoForHandle.insert(fileHandle, pit.value());
+                    thread->pathInfoForHandle.erase(pit);
+                }
+            }
+            // In addition, check on flags for sufficient notification attributes
+            if (hit != thread->handleForDir.end() && hit.value().flags >= flags) {
+                handle = hit.value();
                 // found a thread now insert...
                 DEBUG() << "Found a thread" << thread;
 
@@ -426,14 +460,9 @@ QStringList QWindowsFileSystemWatcherEngine::addPaths(const QStringList &paths,
         }
 
         // no thread found, first create a handle
-        if (handle.handle == INVALID_HANDLE_VALUE || handle.flags != flags) {
+        if (handle.handle == INVALID_HANDLE_VALUE) {
             DEBUG() << "No thread found";
-            // Volume and folder paths need a trailing slash for proper notification
-            // (e.g. "c:" -> "c:/").
-            const QString effectiveAbsolutePath =
-                    isDir ? (absolutePath + QLatin1Char('/')) : absolutePath;
-
-            handle.handle = FindFirstChangeNotification((wchar_t*) QDir::toNativeSeparators(effectiveAbsolutePath).utf16(), false, flags);
+            handle.handle = createChangeNotification(absolutePath, flags);
             handle.flags = flags;
             if (handle.handle == INVALID_HANDLE_VALUE)
                 continue;

tests/auto/corelib/io/qfilesystemwatcher/tst_qfilesystemwatcher.cpp

@@ -568,6 +568,10 @@ void tst_QFileSystemWatcher::watchFileAndItsDirectory()
     QCOMPARE(fileChangedSpy.count(), 0);
     QCOMPARE(dirChangedSpy.count(), 1);
 
+    // QTBUG-61792, removal should succeed (bug on Windows which uses one change
+    // notification per directory).
+    QVERIFY(watcher.removePath(testDir.absolutePath()));
+
     QVERIFY(temporaryDir.rmdir(testDirName));
 }