qmlpreview: Use a better file system watcher

We need to keep watching files even if they are removed and re-added as
editors frequently do when manipulating text files. QFileSystemWatcher
cannot do this by itself, and our simplistic timeout-based attempt
didn't work work properly either.

Fixes: QTBUG-71768
Change-Id: I21e914138179ad8adf07f0196fec8ddcda2cbfca
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

1 files changed, 150 insertions, 0 deletions

diff --git a/tools/qmlpreview/qmlpreviewfilesystemwatcher.cpp b/tools/qmlpreview/qmlpreviewfilesystemwatcher.cpp
new file mode 100644
index 0000000000..78a6ccead3
--- /dev/null
+++ b/tools/qmlpreview/qmlpreviewfilesystemwatcher.cpp
@@ -0,0 +1,150 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qmlpreviewfilesystemwatcher.h"
+
+#include <QtCore/qdebug.h>
+#include <QtCore/qdir.h>
+#include <QtCore/qfilesystemwatcher.h>
+
+QmlPreviewFileSystemWatcher::QmlPreviewFileSystemWatcher(QObject *parent) :
+    QObject(parent), m_watcher(new QFileSystemWatcher(this))
+{
+    connect(m_watcher, &QFileSystemWatcher::fileChanged,
+            this, &QmlPreviewFileSystemWatcher::fileChanged);
+    connect(m_watcher, &QFileSystemWatcher::directoryChanged,
+            this, &QmlPreviewFileSystemWatcher::onDirectoryChanged);
+}
+
+bool QmlPreviewFileSystemWatcher::watchesFile(const QString &file) const
+{
+    return m_files.contains(file);
+}
+
+void QmlPreviewFileSystemWatcher::addFile(const QString &file)
+{
+    if (watchesFile(file)) {
+        qWarning() << "FileSystemWatcher: File" << file << "is already being watched.";
+        return;
+    }
+
+    QStringList toAdd(file);
+    m_files.insert(file);
+
+    const QString directory = QFileInfo(file).path();
+    const int dirCount = ++m_directoryCount[directory];
+    Q_ASSERT(dirCount > 0);
+
+    if (dirCount == 1)
+        toAdd.append(directory);
+
+    m_watcher->addPaths(toAdd);
+}
+
+void QmlPreviewFileSystemWatcher::removeFile(const QString &file)
+{
+    WatchEntrySetIterator it = m_files.find(file);
+    if (it == m_files.end()) {
+        qWarning() << "FileSystemWatcher: File" << file <<  "is not watched.";
+        return;
+    }
+
+    QStringList toRemove(file);
+    m_files.erase(it);
+    m_watcher->removePath(file);
+
+    const QString directory = QFileInfo(file).path();
+    const int dirCount = --m_directoryCount[directory];
+    Q_ASSERT(dirCount >= 0);
+
+    if (!dirCount)
+        toRemove.append(directory);
+
+    m_watcher->removePaths(toRemove);
+}
+
+bool QmlPreviewFileSystemWatcher::watchesDirectory(const QString &directory) const
+{
+    return m_directories.contains(directory);
+}
+
+void QmlPreviewFileSystemWatcher::addDirectory(const QString &directory)
+{
+    if (watchesDirectory(directory)) {
+        qWarning() << "FileSystemWatcher: Directory" << directory << "is already being watched.";
+        return;
+    }
+
+    m_directories.insert(directory);
+    const int count = ++m_directoryCount[directory];
+    Q_ASSERT(count > 0);
+
+    if (count == 1)
+        m_watcher->addPath(directory);
+}
+
+void QmlPreviewFileSystemWatcher::removeDirectory(const QString &directory)
+{
+    WatchEntrySetIterator it = m_directories.find(directory);
+    if (it == m_directories.end()) {
+        qWarning() << "FileSystemWatcher: Directory"  << directory << "is not watched.";
+        return;
+    }
+
+    m_directories.erase(it);
+
+    const int count = --m_directoryCount[directory];
+    Q_ASSERT(count >= 0);
+
+    if (!count)
+        m_watcher->removePath(directory);
+}
+
+void QmlPreviewFileSystemWatcher::onDirectoryChanged(const QString &path)
+{
+    if (m_directories.contains(path))
+        emit directoryChanged(path);
+
+    QStringList toReadd;
+    const QDir dir(path);
+    for (const QFileInfo &entry : dir.entryInfoList(QDir::Files)) {
+        const QString file = entry.filePath();
+        if (m_files.contains(file))
+            toReadd.append(file);
+    }
+
+    if (!toReadd.isEmpty()) {
+        const QStringList remove = m_watcher->addPaths(toReadd);
+        for (const QString &rejected : remove)
+            toReadd.removeOne(rejected);
+
+        // If we've successfully added the file, that means it was deleted and replaced.
+        for (const QString &reAdded : qAsConst(toReadd))
+            emit fileChanged(reAdded);
+    }
+}