qmake: fix file id mapping lifetime management, take 2

turns out that ref-counting the vfs class is insufficient, as now the
ProFile cache (which expires after a timeout) could outlive all VFS
instances and thus refer to ids which were discarded and later re-used.

to avoid this, we let the cache instance hold a reference to the vfs
class.

amends d03fb3506.

Task-number: QTCREATORBUG-20524
Change-Id: Idd4478ffc1c2405b3b83df32fba45b1f687f6a18
Reviewed-by: Robert Loehning <robert.loehning@qt.io>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/shared/proparser/qmakeparser.cpp

@@ -42,11 +42,17 @@ QT_BEGIN_NAMESPACE
 //
 ///////////////////////////////////////////////////////////////////////
 
+ProFileCache::ProFileCache()
+{
+    QMakeVfs::ref();
+}
+
 ProFileCache::~ProFileCache()
 {
     foreach (const Entry &ent, parsed_files)
         if (ent.pro)
             ent.pro->deref();
+    QMakeVfs::deref();
 }
 
 void ProFileCache::discardFile(const QString &fileName, QMakeVfs *vfs)

src/shared/proparser/qmakeparser.h

@@ -197,7 +197,7 @@ Q_DECLARE_OPERATORS_FOR_FLAGS(QMakeParser::ParseFlags)
 class QMAKE_EXPORT ProFileCache
 {
 public:
-    ProFileCache() {}
+    ProFileCache();
     ~ProFileCache();
 
     void discardFile(int id);

src/shared/proparser/qmakevfs.cpp

@@ -49,13 +49,23 @@ QMakeVfs::QMakeVfs()
 #ifndef QT_NO_TEXTCODEC
     m_textCodec = 0;
 #endif
+    ref();
+}
+
+QMakeVfs::~QMakeVfs()
+{
+    deref();
+}
+
+void QMakeVfs::ref()
+{
 #ifdef PROEVALUATOR_THREAD_SAFE
     QMutexLocker locker(&s_mutex);
 #endif
     ++s_refCount;
 }
 
-QMakeVfs::~QMakeVfs()
+void QMakeVfs::deref()
 {
 #ifdef PROEVALUATOR_THREAD_SAFE
     QMutexLocker locker(&s_mutex);
@@ -67,7 +77,6 @@ QMakeVfs::~QMakeVfs()
     }
 }
 
-
 #ifdef PROPARSER_THREAD_SAFE
 QMutex QMakeVfs::s_mutex;
 #endif

src/shared/proparser/qmakevfs.h

@@ -74,6 +74,9 @@ public:
     QMakeVfs();
     ~QMakeVfs();
 
+    static void ref();
+    static void deref();
+
     int idForFileName(const QString &fn, VfsFlags flags);
     QString fileNameForId(int id);
     bool writeFile(int id, QIODevice::OpenMode mode, VfsFlags flags, const QString &contents, QString *errStr);