QTest: expose API needed for Qt Quick Test to print crash backtraces

As discussed in QTQAINFRA-6146, there were two potential approaches to
enabling backtraces in Qt Quick tests:

- Either via a thorough refactoring of quicktest.cpp so that each
testcase is a Slot in a programmatically-created QObject-derived class,
which will be executed via QTest::qExec() similar to the documented
QTest way. This way the pre-existing code in QTest::qRun() will setup
the fatal signal handler.
- Or as a quick fix, modify quick_test_main_with_setup() to setup a
FatalSignalHandler class and invoke prepareStackTrace() like it's
already done in QTest::qRun(). This would require exporting these
symbols in the private header.

This patch enables the implementation of the latter, as it has a
fairly light footprint, is easily revertable (should we need to),
and allows us to immediately gain insight into crashes in CI.

Task-number: QTQAINFRA-6146
Change-Id: Iedffc968acb3e570214df34884ab0afcb6b30850
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/testlib/qtestcase.cpp

@@ -432,11 +432,14 @@ static int eventDelay = -1;
 #if QT_CONFIG(thread)
 static int timeout = -1;
 #endif
-static bool noCrashHandler = false;
 static int repetitions = 1;
 static bool repeatForever = false;
 static bool skipBlacklisted = false;
 
+namespace Internal {
+bool noCrashHandler = false;
+}
+
 static bool invokeTestMethodIfValid(QMetaMethod m, QObject *obj = QTest::currentTestObject)
 {
     if (!m.isValid())
@@ -843,7 +846,7 @@ Q_TESTLIB_EXPORT void qtest_qParseArgs(int argc, const char *const argv[], bool
                 repeatForever = repetitions < 0;
             }
         } else if (strcmp(argv[i], "-nocrashhandler") == 0) {
-            QTest::noCrashHandler = true;
+            QTest::Internal::noCrashHandler = true;
         } else if (strcmp(argv[i], "-skipblacklisted") == 0) {
             QTest::skipBlacklisted = true;
         } else if (strcmp(argv[i], "-throwonfail") == 0) {
@@ -1889,7 +1892,7 @@ int QTest::qRun()
     {
         std::optional<CrashHandler::FatalSignalHandler> handler;
         CrashHandler::prepareStackTrace();
-        if (!noCrashHandler)
+        if (!Internal::noCrashHandler)
             handler.emplace();
 
         bool seenBad = false;

src/testlib/qtestcase.h

@@ -377,6 +377,9 @@ namespace QTest
         return msg;
     }
 
+    // Exported so Qt Quick Test can also use it for generating backtraces upon crashes.
+    Q_TESTLIB_EXPORT extern bool noCrashHandler;
+
     } // namespace Internal
 
     template<typename T>

src/testlib/qtestcrashhandler_p.h

@@ -82,7 +82,7 @@ namespace CrashHandler {
 #endif
 
     void maybeDisableCoreDump();
-    void prepareStackTrace();
+    Q_TESTLIB_EXPORT void prepareStackTrace();
 
 #if defined(Q_OS_WIN)
     // Helper class for resolving symbol names by dynamically loading "dbghelp.dll".
@@ -135,7 +135,7 @@ namespace CrashHandler {
         SymFromAddrType m_symFromAddr;
     };
 
-    class WindowsFaultHandler
+    class Q_TESTLIB_EXPORT WindowsFaultHandler
     {
     public:
         WindowsFaultHandler();
@@ -145,7 +145,7 @@ namespace CrashHandler {
     };
     using FatalSignalHandler = WindowsFaultHandler;
 #elif defined(Q_OS_UNIX) && !defined(Q_OS_WASM)
-    class FatalSignalHandler
+    class Q_TESTLIB_EXPORT FatalSignalHandler
     {
     public:
     #  define OUR_SIGNALS(F)    \
@@ -241,7 +241,7 @@ namespace CrashHandler {
         static bool pauseOnCrash;
     };
 #else // Q_OS_WASM or weird systems
-class FatalSignalHandler {};
+class Q_TESTLIB_EXPORT FatalSignalHandler {};
 inline void blockUnixSignals() {}
 #endif // Q_OS_* choice
 } // namespace CrashHandler