Fix compilation with QT_NAMESPACE and tracing on Linux

The tracegen tool was not taking into account that Qt could be build
with a custom namespace. As a result, the combination of namespace
build and tracing enabled was not working, because tracegen generated
classes without the namespace.

This patch fixes it.
We cannot add QT_BEGIN_NAMESPACE/QT_END_NAMESPACE because of the
tricky logic that recursively includes the generated header file
multiple times, also including the code like

static const struct lttng_event_desc *_TP_COMBINE_TOKENS(__event_desc___, TRACEPOINT_PROVIDER)[] = {
(hash)include TRACEPOINT_INCLUDE
    NULL, /* Dummy, C99 forbids 0-len array. */
};

where TRACEPOINT_INCLUDE is the path to the generated header.

This patch is using QT_USE_NAMESPACE, wrapped into some #ifdefs.
This should be safe, considering that the generated trace headers
are only used as private API.

The windows tracing support seems to be broken even in a
non-namespace build, so it's not handled in this patch.

Task-number: QTBUG-97246
Pick-to: 6.2
Change-Id: I12db76e199a3aa3abde641fbf99a6e1a3d7de203
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Ievgenii Meshcheriakov <ievgenii.meshcheriakov@qt.io>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/tools/tracegen/lttng.cpp b/src/tools/tracegen/lttng.cpp
index e628fbd680..9a8dfc9f4a 100644
--- a/src/tools/tracegen/lttng.cpp
+++ b/src/tools/tracegen/lttng.cpp
@@ -130,6 +130,12 @@ static void writePrologue(QTextStream &stream, const QString &fileName, const Pr
            << "#define TRACEPOINT_INCLUDE \"" << fileName << "\"\n\n";
 
     stream << "#include <lttng/tracepoint.h>\n\n";
+
+    const QString namespaceGuard = guard + QStringLiteral("_USE_NAMESPACE");
+    stream << "#if !defined(" << namespaceGuard << ")\n"
+           << "#define " << namespaceGuard << "\n"
+           << "QT_USE_NAMESPACE\n"
+           << "#endif // " << namespaceGuard << "\n\n";
 }
 
 static void writeEpilogue(QTextStream &stream, const QString &fileName)
@@ -154,6 +160,7 @@ static void writeWrapper(QTextStream &stream,
     stream << "\n"
            << "#ifndef " << includeGuard << "\n"
            << "#define " << includeGuard << "\n"
+           << "QT_BEGIN_NAMESPACE\n"
            << "namespace QtPrivate {\n";
 
     stream << "inline void trace_" << name << "(" << argList << ")\n"
@@ -172,6 +179,7 @@ static void writeWrapper(QTextStream &stream,
            << "}\n";
 
     stream << "} // namespace QtPrivate\n"
+           << "QT_END_NAMESPACE\n"
            << "#endif // " << includeGuard << "\n\n";
 }