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>

5 files changed, 231 insertions, 30 deletions

diff --git a/tools/qmlpreview/qmlpreview.pro b/tools/qmlpreview/qmlpreview.pro
index 7d443b5f6c..d42f2cbe07 100644
--- a/tools/qmlpreview/qmlpreview.pro
+++ b/tools/qmlpreview/qmlpreview.pro
@@ -3,10 +3,12 @@ CONFIG += no_import_scan
 
 SOURCES += \
     main.cpp \
-    qmlpreviewapplication.cpp
+    qmlpreviewapplication.cpp \
+    qmlpreviewfilesystemwatcher.cpp
 
 HEADERS += \
-    qmlpreviewapplication.h
+    qmlpreviewapplication.h \
+    qmlpreviewfilesystemwatcher.h
 
 QMAKE_TARGET_DESCRIPTION = QML Preview
 
diff --git a/tools/qmlpreview/qmlpreviewapplication.cpp b/tools/qmlpreview/qmlpreviewapplication.cpp
index 031381a948..02f10831ec 100644
--- a/tools/qmlpreview/qmlpreviewapplication.cpp
+++ b/tools/qmlpreview/qmlpreviewapplication.cpp
@@ -63,9 +63,9 @@ QmlPreviewApplication::QmlPreviewApplication(int &argc, char **argv) :
     connect(m_qmlPreviewClient.data(), &QQmlPreviewClient::request,
             this, &QmlPreviewApplication::serveRequest);
 
-    connect(&m_watcher, &QFileSystemWatcher::fileChanged,
+    connect(&m_watcher, &QmlPreviewFileSystemWatcher::fileChanged,
             this, &QmlPreviewApplication::sendFile);
-    connect(&m_watcher, &QFileSystemWatcher::directoryChanged,
+    connect(&m_watcher, &QmlPreviewFileSystemWatcher::directoryChanged,
             this, &QmlPreviewApplication::sendDirectory);
 }
 
@@ -212,17 +212,12 @@ void QmlPreviewApplication::serveRequest(const QString &path)
 
     if (info.isDir()) {
         m_qmlPreviewClient->sendDirectory(path, QDir(path).entryList());
-        m_watcher.addPath(path);
+        m_watcher.addDirectory(path);
     } else {
         QFile file(path);
         if (file.open(QIODevice::ReadOnly)) {
             m_qmlPreviewClient->sendFile(path, file.readAll());
-            m_watcher.addPath(path);
-
-            // Also watch the directory, because editors will rather replace a file than change it.
-            // Therefore when the file changes, we can't read it, but when the file is re-added we can
-            // see that from the directory changing.
-            m_watcher.addPath(info.absolutePath());
+            m_watcher.addFile(path);
         } else {
             logStatus(QString("Could not open file %1 for reading: %2").arg(path)
                       .arg(file.errorString()));
@@ -236,13 +231,10 @@ bool QmlPreviewApplication::sendFile(const QString &path)
     QFile file(path);
     if (file.open(QIODevice::ReadOnly)) {
         m_qmlPreviewClient->sendFile(path, file.readAll());
-        m_pendingFiles.removeAll(path);
         // Defer the Load, because files tend to change multiple times in a row.
         m_loadTimer.start();
         return true;
     }
-    if (!m_pendingFiles.contains(path))
-        m_pendingFiles.append(path);
     logStatus(QString("Could not open file %1 for reading: %2").arg(path).arg(file.errorString()));
     return false;
 }
@@ -250,17 +242,5 @@ bool QmlPreviewApplication::sendFile(const QString &path)
 void QmlPreviewApplication::sendDirectory(const QString &path)
 {
     m_qmlPreviewClient->sendDirectory(path, QDir(path).entryList());
-    for (auto it = m_pendingFiles.begin(); it != m_pendingFiles.end();) {
-        const QString filePath = *it;
-        QFile file(filePath);
-        if (file.open(QIODevice::ReadOnly)) {
-            logStatus(QString("Sending replaced file %1.").arg(filePath));
-            m_qmlPreviewClient->sendFile(filePath, file.readAll());
-            m_watcher.addPath(filePath);
-            it = m_pendingFiles.erase(it);
-        } else {
-            ++it;
-        }
-    }
     m_loadTimer.start();
 }
diff --git a/tools/qmlpreview/qmlpreviewapplication.h b/tools/qmlpreview/qmlpreviewapplication.h
index eb363b0eb6..7da4a9ab5c 100644
--- a/tools/qmlpreview/qmlpreviewapplication.h
+++ b/tools/qmlpreview/qmlpreviewapplication.h
@@ -29,13 +29,14 @@
 #ifndef QMLPREVIEWAPPLICATION_H
 #define QMLPREVIEWAPPLICATION_H
 
+#include "qmlpreviewfilesystemwatcher.h"
+
 #include <private/qqmlpreviewclient_p.h>
 #include <private/qqmldebugconnection_p.h>
 
 #include <QtCore/qcoreapplication.h>
 #include <QtCore/qprocess.h>
 #include <QtCore/qtimer.h>
-#include <QtCore/qfilesystemwatcher.h>
 
 #include <QtNetwork/qabstractsocket.h>
 
@@ -71,13 +72,11 @@ private:
 
     QScopedPointer<QQmlDebugConnection> m_connection;
     QScopedPointer<QQmlPreviewClient> m_qmlPreviewClient;
-    QFileSystemWatcher m_watcher;
+    QmlPreviewFileSystemWatcher m_watcher;
 
     QTimer m_loadTimer;
     QTimer m_connectTimer;
     uint m_connectionAttempts;
-
-    QStringList m_pendingFiles;
 };
 
 #endif // QMLPREVIEWAPPLICATION_H
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);
+    }
+}
diff --git a/tools/qmlpreview/qmlpreviewfilesystemwatcher.h b/tools/qmlpreview/qmlpreviewfilesystemwatcher.h
new file mode 100644
index 0000000000..a7ead641d8
--- /dev/null
+++ b/tools/qmlpreview/qmlpreviewfilesystemwatcher.h
@@ -0,0 +1,70 @@
+/****************************************************************************
+**
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QMLPREVIEWFILESYSTEMWATCHER_H
+#define QMLPREVIEWFILESYSTEMWATCHER_H
+
+#include <QtCore/qfilesystemwatcher.h>
+#include <QtCore/qobject.h>
+#include <QtCore/qset.h>
+
+class QmlPreviewFileSystemWatcher : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit QmlPreviewFileSystemWatcher(QObject *parent = nullptr);
+
+    void addFile(const QString &file);
+    void removeFile(const QString &file);
+    bool watchesFile(const QString &file) const;
+
+    void addDirectory(const QString &file);
+    void removeDirectory(const QString &file);
+    bool watchesDirectory(const QString &file) const;
+
+signals:
+    void fileChanged(const QString &path);
+    void directoryChanged(const QString &path);
+
+private:
+    using WatchEntrySet = QSet<QString>;
+    using WatchEntrySetIterator = WatchEntrySet::iterator;
+
+    void onDirectoryChanged(const QString &path);
+
+    WatchEntrySet m_files;
+    WatchEntrySet m_directories;
+
+    // Directories watched either explicitly or implicitly through files contained in them.
+    QHash<QString, int> m_directoryCount;
+
+    QFileSystemWatcher *m_watcher = nullptr;
+};
+
+#endif // QMLPREVIEWFILESYSTEMWATCHER_H