QTest: Extract Method qCaught() from THROWS_(NO_)EXCEPTION

We've already done a lot in 59600a514ba99ed62b46237d8f160dea84474190,
but we can do more:

Thanks to std::exception_ptr, we can drag the handling of unexpected
exceptions completely to out-of-line code, leaving only the catch(...)
as inline.

As a nice side-effect, we no longer need the nested try blocks in
QVERIFY_THROWS_EXCEPTION to work around GCC -Wexceptions or MSVC C2312
complaining about two handlers for the same exception type (which can
happen when exceptiontype is std::exception itself).

This may not handle __cxxabi::__forced_unwind correctly, but it
doesn't need to: Tests should not need to call THROWS_EXECPTION on
code that could emit a pthread cancellation; tests are controlled
environments.

Keep the old qCaught() function for BC. We don't promise BC in
QtTestLib, but it doesn't cost much.

Change-Id: I1e1627c6341b09197a8a79669fde061c47e6ba47
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
(cherry picked from commit f0dcbb66e8c54d497d5d118a13a7a0b4fc1b3d94)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/testlib/qtestcase.cpp

@@ -2614,6 +2614,39 @@ void QTest::qCaught(const char *expected, const char *what, const char *file, in
     qFail(message().toUtf8().constData(), file, line);
 }
 
+/*!
+    \internal
+
+    Contains the implementation of the catch(...) block of
+    QVERIFY_THROWS_EXCEPTION.
+
+    The function inspects std::current_exception() by rethrowing it using
+    std::rethrow_exception().
+
+    The function must be called from a catch handler.
+
+    If the exception inherits std::exception, its what() message is logged and
+    this function returns normally. The caller of this function must then
+    execute a \c{return} to exit from the test function.
+
+    Otherwise, a message saying an unknown exception was caught is logged and
+    this function rethrows the exception, skipping the \c{return} that follows
+    this function call in the caller.
+*/
+void QTest::qCaught(const char *expected, const char *file, int line)
+{
+    try {
+        // let's see what the cat brought us:
+        std::rethrow_exception(std::current_exception());
+    } catch (const std::exception &e) {
+        qCaught(expected, e.what(), file, line);
+    } catch (...) {
+        qCaught(expected, nullptr, file, line);
+        throw;
+    }
+    // caller shall invoke `return` if control reached here
+}
+
 
 #if QT_DEPRECATED_SINCE(6, 3)
 /*!

src/testlib/qtestcase.h

@@ -89,12 +89,9 @@ do { \
         QT_TRY { \
             __VA_ARGS__; \
             /* success */ \
-        } QT_CATCH (const std::exception &e) { \
-            QTest::qCaught(nullptr, e.what(), __FILE__, __LINE__); \
-            return; \
         } QT_CATCH (...) { \
-            QTest::qCaught(nullptr, nullptr, __FILE__, __LINE__); \
-            QT_RETHROW; \
+            QTest::qCaught(nullptr, __FILE__, __LINE__); \
+            return; \
         } \
     } while (false) \
     /* end */
@@ -112,20 +109,15 @@ inline void useVerifyThrowsException() {}
 #  define QVERIFY_THROWS_EXCEPTION(exceptiontype, ...) \
     do {\
         QT_TRY {\
-            QT_TRY {\
-                __VA_ARGS__;\
-                QTest::qFail("Expected exception of type " #exceptiontype " to be thrown" \
-                             " but no exception caught", __FILE__, __LINE__);\
-                return;\
-            } QT_CATCH (const exceptiontype &) {\
-                /* success */\
-            }\
-        } QT_CATCH (const std::exception &e) {\
-            QTest::qCaught(#exceptiontype, e.what(), __FILE__, __LINE__);\
-            return;\
+            __VA_ARGS__; \
+            QTest::qFail("Expected exception of type " #exceptiontype " to be thrown" \
+                         " but no exception caught", __FILE__, __LINE__); \
+            return; \
+        } QT_CATCH (const exceptiontype &) { \
+            /* success */ \
         } QT_CATCH (...) {\
-            QTest::qCaught(#exceptiontype, nullptr, __FILE__, __LINE__);\
-            QT_RETHROW;\
+            QTest::qCaught(#exceptiontype, __FILE__, __LINE__); \
+            return; \
         }\
     } while (false)
 
@@ -392,6 +384,8 @@ namespace QTest
                            const char *file, int line);
     Q_DECL_COLD_FUNCTION
     Q_TESTLIB_EXPORT void qCaught(const char *expected, const char *what, const char *file, int line);
+    Q_DECL_COLD_FUNCTION
+    Q_TESTLIB_EXPORT void qCaught(const char *expected, const char *file, int line);
 #if QT_DEPRECATED_SINCE(6, 3)
     QT_DEPRECATED_VERSION_X_6_3("Use qWarning() instead")
     Q_TESTLIB_EXPORT void qWarn(const char *message, const char *file = nullptr, int line = 0);