[qtcontacts-sqlite] Provide hook to debug SQL expansion of filters

Define QTCONTACTS_SQLITE_DEBUG_FILTERS to a non-empty value to report
the SQL expansion of contact filters.

src/engine/contactreader.cpp

@@ -1224,6 +1224,28 @@ static QString buildOrderBy(const QList<QContactSortOrder> &order, QString *join
     return fragments.join(QLatin1String(", "));
 }
 
+static void debugFilterExpansion(const QString &description, const QString &queryString, const QVariantList &bindings)
+{
+    static const bool debugFilters = !qgetenv("QTCONTACTS_SQLITE_DEBUG_FILTERS").isEmpty();
+    static const QChar marker = QChar::fromLatin1('?');
+
+    if (debugFilters) {
+        QString query(queryString);
+
+        int index = 0;
+        for (int i = 0; i < bindings.count(); ++i) {
+            QString value = bindings.at(i).toString();
+            index = query.indexOf(marker, index);
+            if (index == -1)
+                break;
+
+            query.replace(index, 1, value);
+            index += value.length();
+        }
+        qDebug() << description << query;
+    }
+}
+
 ContactReader::ContactReader(const QSqlDatabase &database)
     : m_database(database)
 {
@@ -1310,6 +1332,8 @@ static QContactManager::Error createTemporaryContactIdsTable(
             qWarning() << insertQuery.lastError();
             qWarning() << insertStatement;
             return QContactManager::UnspecifiedError;
+        } else {
+            debugFilterExpansion("Contacts selection:", insertStatement, boundValues);
         }
     } else {
         // specified by id list
@@ -1781,6 +1805,8 @@ QContactManager::Error ContactReader::readContactIds(
         qWarning() << query.lastError();
         qWarning() << queryString;
         return QContactManager::UnspecifiedError;
+    } else {
+        debugFilterExpansion("Contact IDs selection:", queryString, bindings);
     }
 
     do {