Change the representation of meta-object string data

Up to and including meta-object revision 6, string data have been
stored as 0-terminated C-style strings, that were made directly
accessible as const char pointers through the public API
(QMetaMethod and friends).

This commit changes moc to generate an array of QByteArrayData
instead, and adapts the QObject kernel accordingly.

Generating an array of QByteArrayData (byte array literals)
means that the strings can now be returned from public (or private)
API as QByteArrays, rather than const char *, with zero allocation or
copying. Also, the string length is now computed at compile time
(it's part of the QByteArrayData).

This commit only changes the internal representation, and does
not affect existing public API. The actual (C) string data that the
byte array literals reference still consists of zero-terminated
strings. The benefit of having the QByteArrayData array will only
become apparent in the upcoming meta-object data format change, which
changes the format of property and method descriptors.

Support for the old meta-object string data format was kept; the
codepaths for old revisions (6 and below) will be removed in a
separate commit, once all the other meta-object changes are done and
affected code has been adapted accordingly.

Task-number: QTBUG-24154
Change-Id: I4ec3b363bbc31b8192e5d8915ef091c442c2efad
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>

4 files changed, 85 insertions, 46 deletions

diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp
index d53ba707f7..ce30e34f73 100644
--- a/src/corelib/kernel/qmetaobject.cpp
+++ b/src/corelib/kernel/qmetaobject.cpp
@@ -146,6 +146,43 @@ QT_BEGIN_NAMESPACE
 static inline const QMetaObjectPrivate *priv(const uint* data)
 { return reinterpret_cast<const QMetaObjectPrivate*>(data); }
 
+static inline const QByteArrayData &stringData(const QMetaObject *mo, int index)
+{
+    Q_ASSERT(priv(mo->d.data)->revision >= 7);
+    const QByteArrayData &data = mo->d.stringdata[index];
+    Q_ASSERT(data.ref.isStatic());
+    Q_ASSERT(data.alloc == 0);
+    Q_ASSERT(data.capacityReserved == 0);
+    Q_ASSERT(data.size >= 0);
+    return data;
+}
+
+static inline const char *legacyString(const QMetaObject *mo, int index)
+{
+    Q_ASSERT(priv(mo->d.data)->revision <= 6);
+    return reinterpret_cast<const char *>(mo->d.stringdata) + index;
+}
+
+static inline const char *rawStringData(const QMetaObject *mo, int index)
+{
+    if (priv(mo->d.data)->revision >= 7)
+        return stringData(mo, index).data();
+    else
+        return legacyString(mo, index);
+}
+
+const char *QMetaObjectPrivate::rawStringData(const QMetaObject *mo, int index)
+{
+    return QT_PREPEND_NAMESPACE(rawStringData)(mo, index);
+}
+
+static inline int stringSize(const QMetaObject *mo, int index)
+{
+    if (priv(mo->d.data)->revision >= 7)
+        return stringData(mo, index).size;
+    else
+        return qstrlen(legacyString(mo, index));
+}
 
 /*!
     \since 4.5
@@ -249,12 +286,14 @@ int QMetaObject::metacall(QObject *object, Call cl, int idx, void **argv)
 }
 
 /*!
-    \fn const char *QMetaObject::className() const
-
     Returns the class name.
 
     \sa superClass()
 */
+const char *QMetaObject::className() const
+{
+    return rawStringData(this, 0);
+}
 
 /*!
     \fn QMetaObject *QMetaObject::superClass() const
@@ -307,7 +346,7 @@ const QObject *QMetaObject::cast(const QObject *obj) const
 */
 QString QMetaObject::tr(const char *s, const char *c, int n) const
 {
-    return QCoreApplication::translate(d.stringdata, s, c, QCoreApplication::CodecForTr, n);
+    return QCoreApplication::translate(rawStringData(this, 0), s, c, QCoreApplication::CodecForTr, n);
 }
 
 /*!
@@ -315,7 +354,7 @@ QString QMetaObject::tr(const char *s, const char *c, int n) const
 */
 QString QMetaObject::trUtf8(const char *s, const char *c, int n) const
 {
-    return QCoreApplication::translate(d.stringdata, s, c, QCoreApplication::UnicodeUTF8, n);
+    return QCoreApplication::translate(rawStringData(this, 0), s, c, QCoreApplication::UnicodeUTF8, n);
 }
 #endif // QT_NO_TRANSLATION
 
@@ -513,7 +552,7 @@ static inline int indexOfMethodRelative(const QMetaObject **baseObject,
                         ? (priv(m->d.data)->signalCount) : 0;
         if (!normalizeStringData) {
             for (; i >= end; --i) {
-                const char *stringdata = m->d.stringdata + m->d.data[priv(m->d.data)->methodData + 5*i];
+                const char *stringdata = rawStringData(m, m->d.data[priv(m->d.data)->methodData + 5*i]);
                 if (method[0] == stringdata[0] && strcmp(method + 1, stringdata + 1) == 0) {
                     *baseObject = m;
                     return i;
@@ -521,7 +560,7 @@ static inline int indexOfMethodRelative(const QMetaObject **baseObject,
             }
         } else if (priv(m->d.data)->revision < 5) {
             for (; i >= end; --i) {
-                const char *stringdata = (m->d.stringdata + m->d.data[priv(m->d.data)->methodData + 5 * i]);
+                const char *stringdata = legacyString(m, m->d.data[priv(m->d.data)->methodData + 5 * i]);
                 const QByteArray normalizedSignature = QMetaObject::normalizedSignature(stringdata);
                 if (normalizedSignature == method) {
                     *baseObject = m;
@@ -549,7 +588,7 @@ int QMetaObject::indexOfConstructor(const char *constructor) const
     if (priv(d.data)->revision < 2)
         return -1;
     for (int i = priv(d.data)->constructorCount-1; i >= 0; --i) {
-        const char *data = d.stringdata + d.data[priv(d.data)->constructorData + 5*i];
+        const char *data = rawStringData(this, d.data[priv(d.data)->constructorData + 5*i]);
         if (data[0] == constructor[0] && strcmp(constructor + 1, data + 1) == 0) {
             return i;
         }
@@ -618,7 +657,7 @@ int QMetaObjectPrivate::indexOfSignalRelative(const QMetaObject **baseObject,
         int conflict = m->d.superdata->indexOfMethod(signal);
         if (conflict >= 0)
             qWarning("QMetaObject::indexOfSignal: signal %s from %s redefined in %s",
-                     signal, m->d.superdata->d.stringdata, m->d.stringdata);
+                     signal, rawStringData(m->d.superdata, 0), rawStringData(m, 0));
     }
 #endif
     return i;
@@ -654,7 +693,7 @@ int QMetaObjectPrivate::indexOfSlotRelative(const QMetaObject **m,
 static const QMetaObject *QMetaObject_findMetaObject(const QMetaObject *self, const char *name)
 {
     while (self) {
-        if (strcmp(self->d.stringdata, name) == 0)
+        if (strcmp(rawStringData(self, 0), name) == 0)
             return self;
         if (self->d.extradata) {
             const QMetaObject **e;
@@ -690,7 +729,7 @@ int QMetaObject::indexOfEnumerator(const char *name) const
     while (m) {
         const QMetaObjectPrivate *d = priv(m->d.data);
         for (int i = d->enumeratorCount - 1; i >= 0; --i) {
-            const char *prop = m->d.stringdata + m->d.data[d->enumeratorData + 4*i];
+            const char *prop = rawStringData(m, m->d.data[d->enumeratorData + 4*i]);
             if (name[0] == prop[0] && strcmp(name + 1, prop + 1) == 0) {
                 i += m->enumeratorOffset();
                 return i;
@@ -713,7 +752,7 @@ int QMetaObject::indexOfProperty(const char *name) const
     while (m) {
         const QMetaObjectPrivate *d = priv(m->d.data);
         for (int i = d->propertyCount-1; i >= 0; --i) {
-            const char *prop = m->d.stringdata + m->d.data[d->propertyData + 3*i];
+            const char *prop = rawStringData(m, m->d.data[d->propertyData + 3*i]);
             if (name[0] == prop[0] && strcmp(name + 1, prop + 1) == 0) {
                 i += m->propertyOffset();
                 return i;
@@ -744,8 +783,7 @@ int QMetaObject::indexOfClassInfo(const char *name) const
     const QMetaObject *m = this;
     while (m && i < 0) {
         for (i = priv(m->d.data)->classInfoCount-1; i >= 0; --i)
-            if (strcmp(name, m->d.stringdata
-                       + m->d.data[priv(m->d.data)->classInfoData + 2*i]) == 0) {
+            if (strcmp(name, rawStringData(m, m->d.data[priv(m->d.data)->classInfoData + 2*i])) == 0) {
                 i += m->classInfoOffset();
                 break;
             }
@@ -829,7 +867,7 @@ QMetaProperty QMetaObject::property(int index) const
     if (i >= 0 && i < priv(d.data)->propertyCount) {
         int handle = priv(d.data)->propertyData + 3*i;
         int flags = d.data[handle + 2];
-        const char *type = d.stringdata + d.data[handle + 1];
+        const char *type = rawStringData(this, d.data[handle + 1]);
         result.mobj = this;
         result.handle = handle;
         result.idx = i;
@@ -838,7 +876,7 @@ QMetaProperty QMetaObject::property(int index) const
             result.menum = enumerator(indexOfEnumerator(type));
             if (!result.menum.isValid()) {
                 const char *enum_name = type;
-                const char *scope_name = d.stringdata;
+                const char *scope_name = rawStringData(this, 0);
                 char *scope_buffer = 0;
 
                 const char *colon = strrchr(enum_name, ':');
@@ -1285,7 +1323,7 @@ const char *QMetaMethod::signature() const
 {
     if (!mobj)
         return 0;
-    return mobj->d.stringdata + mobj->d.data[handle];
+    return rawStringData(mobj, mobj->d.data[handle]);
 }
 
 /*!
@@ -1298,7 +1336,7 @@ QList<QByteArray> QMetaMethod::parameterTypes() const
     if (!mobj)
         return QList<QByteArray>();
     return QMetaObjectPrivate::parameterTypeNamesFromSignature(
-            mobj->d.stringdata + mobj->d.data[handle]);
+            rawStringData(mobj, mobj->d.data[handle]));
 }
 
 /*!
@@ -1311,10 +1349,10 @@ QList<QByteArray> QMetaMethod::parameterNames() const
     QList<QByteArray> list;
     if (!mobj)
         return list;
-    const char *names =  mobj->d.stringdata + mobj->d.data[handle + 1];
+    const char *names =  rawStringData(mobj, mobj->d.data[handle + 1]);
     if (*names == 0) {
         // do we have one or zero arguments?
-        const char *signature = mobj->d.stringdata + mobj->d.data[handle];
+        const char *signature = rawStringData(mobj, mobj->d.data[handle]);
         while (*signature && *signature != '(')
             ++signature;
         if (*++signature != ')')
@@ -1340,7 +1378,7 @@ const char *QMetaMethod::typeName() const
 {
     if (!mobj)
         return 0;
-    return mobj->d.stringdata + mobj->d.data[handle + 2];
+    return rawStringData(mobj, mobj->d.data[handle + 2]);
 }
 
 /*!
@@ -1377,7 +1415,7 @@ const char *QMetaMethod::tag() const
 {
     if (!mobj)
         return 0;
-    return mobj->d.stringdata + mobj->d.data[handle + 3];
+    return rawStringData(mobj, mobj->d.data[handle + 3]);
 }
 
 
@@ -1580,10 +1618,10 @@ bool QMetaMethod::invoke(QObject *object,
     int metaMethodArgumentCount = 0;
     {
         // based on QMetaObject::parameterNames()
-        const char *names = mobj->d.stringdata + mobj->d.data[handle + 1];
+        const char *names = rawStringData(mobj, mobj->d.data[handle + 1]);
         if (*names == 0) {
             // do we have one or zero arguments?
-            const char *signature = mobj->d.stringdata + mobj->d.data[handle];
+            const char *signature = rawStringData(mobj, mobj->d.data[handle]);
             while (*signature && *signature != '(')
                 ++signature;
             if (*++signature != ')')
@@ -1803,7 +1841,7 @@ const char *QMetaEnum::name() const
 {
     if (!mobj)
         return 0;
-    return mobj->d.stringdata + mobj->d.data[handle];
+    return rawStringData(mobj, mobj->d.data[handle]);
 }
 
 /*!
@@ -1831,7 +1869,7 @@ const char *QMetaEnum::key(int index) const
     int count = mobj->d.data[handle + 2];
     int data = mobj->d.data[handle + 3];
     if (index >= 0  && index < count)
-        return mobj->d.stringdata + mobj->d.data[data + 2*index];
+        return rawStringData(mobj, mobj->d.data[data + 2*index]);
     return 0;
 }
 
@@ -1878,7 +1916,7 @@ bool QMetaEnum::isFlag() const
 */
 const char *QMetaEnum::scope() const
 {
-    return mobj?mobj->d.stringdata : 0;
+    return mobj?rawStringData(mobj, 0) : 0;
 }
 
 /*!
@@ -1910,8 +1948,8 @@ int QMetaEnum::keyToValue(const char *key, bool *ok) const
     int count = mobj->d.data[handle + 2];
     int data = mobj->d.data[handle + 3];
     for (int i = 0; i < count; ++i) {
-        if ((!scope || (qstrlen(mobj->d.stringdata) == scope && strncmp(qualified_key, mobj->d.stringdata, scope) == 0))
-             && strcmp(key, mobj->d.stringdata + mobj->d.data[data + 2*i]) == 0) {
+        if ((!scope || (stringSize(mobj, 0) == int(scope) && strncmp(qualified_key, rawStringData(mobj, 0), scope) == 0))
+             && strcmp(key, rawStringData(mobj, mobj->d.data[data + 2*i])) == 0) {
             if (ok != 0)
                 *ok = true;
             return mobj->d.data[data + 2*i + 1];
@@ -1936,7 +1974,7 @@ const char* QMetaEnum::valueToKey(int value) const
     int data = mobj->d.data[handle + 3];
     for (int i = 0; i < count; ++i)
         if (value == (int)mobj->d.data[data + 2*i + 1])
-            return mobj->d.stringdata + mobj->d.data[data + 2*i];
+            return rawStringData(mobj, mobj->d.data[data + 2*i]);
     return 0;
 }
 
@@ -1979,8 +2017,8 @@ int QMetaEnum::keysToValue(const char *keys, bool *ok) const
         }
         int i;
         for (i = count-1; i >= 0; --i)
-            if ((!scope || (qstrlen(mobj->d.stringdata) == scope && strncmp(qualified_key.constData(), mobj->d.stringdata, scope) == 0))
-                 && strcmp(key, mobj->d.stringdata + mobj->d.data[data + 2*i]) == 0) {
+            if ((!scope || (stringSize(mobj, 0) == int(scope) && strncmp(qualified_key.constData(), rawStringData(mobj, 0), scope) == 0))
+                 && strcmp(key, rawStringData(mobj, mobj->d.data[data + 2*i])) == 0) {
                 value |= mobj->d.data[data + 2*i + 1];
                 break;
             }
@@ -2013,7 +2051,7 @@ QByteArray QMetaEnum::valueToKeys(int value) const
             v = v & ~k;
             if (!keys.isEmpty())
                 keys += '|';
-            keys += mobj->d.stringdata + mobj->d.data[data + 2*i];
+            keys += rawStringData(mobj, mobj->d.data[data + 2*i]);
         }
     }
     return keys;
@@ -2092,7 +2130,7 @@ const char *QMetaProperty::name() const
     if (!mobj)
         return 0;
     int handle = priv(mobj->d.data)->propertyData + 3*idx;
-    return mobj->d.stringdata + mobj->d.data[handle];
+    return rawStringData(mobj, mobj->d.data[handle]);
 }
 
 /*!
@@ -2105,7 +2143,7 @@ const char *QMetaProperty::typeName() const
     if (!mobj)
         return 0;
     int handle = priv(mobj->d.data)->propertyData + 3*idx;
-    return mobj->d.stringdata + mobj->d.data[handle + 1];
+    return rawStringData(mobj, mobj->d.data[handle + 1]);
 }
 
 /*!
@@ -2254,7 +2292,7 @@ QVariant QMetaProperty::read(const QObject *object) const
     } else {
         int handle = priv(mobj->d.data)->propertyData + 3*idx;
         uint flags = mobj->d.data[handle + 2];
-        const char *typeName = mobj->d.stringdata + mobj->d.data[handle + 1];
+        const char *typeName = rawStringData(mobj, mobj->d.data[handle + 1]);
         t = (flags >> 24);
         if (t == QVariant::Invalid)
             t = QMetaType::type(typeName);
@@ -2325,7 +2363,7 @@ bool QMetaProperty::write(QObject *object, const QVariant &value) const
         uint flags = mobj->d.data[handle + 2];
         t = flags >> 24;
         if (t == QVariant::Invalid) {
-            const char *typeName = mobj->d.stringdata + mobj->d.data[handle + 1];
+            const char *typeName = rawStringData(mobj, mobj->d.data[handle + 1]);
             const char *vtypeName = value.typeName();
             if (vtypeName && strcmp(typeName, vtypeName) == 0)
                 t = value.userType();
@@ -2691,7 +2729,7 @@ const char *QMetaClassInfo::name() const
 {
     if (!mobj)
         return 0;
-    return mobj->d.stringdata + mobj->d.data[handle];
+    return rawStringData(mobj, mobj->d.data[handle]);
 }
 
 /*!
@@ -2703,7 +2741,7 @@ const char* QMetaClassInfo::value() const
 {
     if (!mobj)
         return 0;
-    return mobj->d.stringdata + mobj->d.data[handle + 1];
+    return rawStringData(mobj, mobj->d.data[handle + 1]);
 }
 
 /*!
diff --git a/src/corelib/kernel/qmetaobject_p.h b/src/corelib/kernel/qmetaobject_p.h
index 59a5c5f280..d789711bb4 100644
--- a/src/corelib/kernel/qmetaobject_p.h
+++ b/src/corelib/kernel/qmetaobject_p.h
@@ -109,7 +109,7 @@ class QMutex;
 
 struct QMetaObjectPrivate
 {
-    enum { OutputRevision = 6 }; // Used by moc and qmetaobjectbuilder
+    enum { OutputRevision = 7 }; // Used by moc, qmetaobjectbuilder and qdbus
 
     int revision;
     int className;
@@ -122,10 +122,13 @@ struct QMetaObjectPrivate
     int signalCount; //since revision 4
     // revision 5 introduces changes in normalized signatures, no new members
     // revision 6 added qt_static_metacall as a member of each Q_OBJECT and inside QMetaObject itself
+    // revision 7 is Qt 5
 
     static inline const QMetaObjectPrivate *get(const QMetaObject *metaobject)
     { return reinterpret_cast<const QMetaObjectPrivate*>(metaobject->d.data); }
 
+    static const char *rawStringData(const QMetaObject *mo, int index);
+
     static int indexOfSignalRelative(const QMetaObject **baseObject,
                                      const char* name,
                                      bool normalizeStringData);
diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index 8fa5dcdcff..d8c82ddc9f 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -4036,9 +4036,9 @@ QMetaObject::Connection QObject::connectImpl(const QObject *sender, void **signa
     locker.unlock();
 
     // reconstruct the signature to call connectNotify
-    const char *sig = senderMetaObject->d.stringdata + senderMetaObject->d.data[
+    const char *sig = QMetaObjectPrivate::rawStringData(senderMetaObject, senderMetaObject->d.data[
         reinterpret_cast<const QMetaObjectPrivate*>(senderMetaObject->d.data)->methodData
-            + 5 * (signal_index - signalOffset)];
+            + 5 * (signal_index - signalOffset)]);
     QVarLengthArray<char> signalSignature(qstrlen(sig) + 2);
     signalSignature.data()[0] = char(QSIGNAL_CODE + '0');
     strcpy(signalSignature.data() + 1 , sig);
diff --git a/src/corelib/kernel/qobjectdefs.h b/src/corelib/kernel/qobjectdefs.h
index ec51251531..6c40733877 100644
--- a/src/corelib/kernel/qobjectdefs.h
+++ b/src/corelib/kernel/qobjectdefs.h
@@ -50,11 +50,12 @@ QT_BEGIN_NAMESPACE
 
 
 class QByteArray;
+struct QByteArrayData;
 
 class QString;
 
 #ifndef Q_MOC_OUTPUT_REVISION
-#define Q_MOC_OUTPUT_REVISION 64
+#define Q_MOC_OUTPUT_REVISION 65
 #endif
 
 // The following macros are our "extensions" to C++
@@ -437,7 +438,7 @@ struct Q_CORE_EXPORT QMetaObject
 
     struct { // private data
         const QMetaObject *superdata;
-        const char *stringdata;
+        const QByteArrayData *stringdata;
         const uint *data;
         const void *extradata;
     } d;
@@ -478,9 +479,6 @@ struct QMetaObjectExtraData
     StaticMetacallFunction static_metacall;
 };
 
-inline const char *QMetaObject::className() const
-{ return d.stringdata; }
-
 inline const QMetaObject *QMetaObject::superClass() const
 { return d.superdata; }