Logging: mark qt_assert()/qt_assert_x()/qFatal() as nothrow

These functions are not supposed to return, not even by exception.
qt_message() _can_ throw, but we're fine with the compiler calling
std::terminate() then, since the backtrace will still include the
assertion location.

This behaviour is ensured by a new macro, QT_TERMINATE_ON_EXCEPTION,
which expands to something like
   try { expr; } catch(...) { std::terminate(); }
if the compiler doesn't support Q_DECL_NOEXCEPT (but maybe
Q_DECL_NOTHROW), and to something like just
   expr;
otherwise (including in the QT_NO_EXCEPTION case).

The real macro preserves scopes in all cases, and aims
to work even if <exception> isn't included in the TU it's used in,
so is a little bit more complex than that.

Change-Id: Ie6a2b7776e6aa77e57bd9aea6e184e5fa1cec81c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qglobal.cpp

@@ -1913,10 +1913,19 @@ void qBadAlloc()
     QT_THROW(std::bad_alloc());
 }
 
+/* \internal
+   Allows you to call std::terminate() without including <exception>.
+   Called internally from QT_TERMINATE_ON_EXCEPTION
+*/
+Q_NORETURN void qTerminate() Q_DECL_NOTHROW
+{
+    std::terminate();
+}
+
 /*
   The Q_ASSERT macro calls this function when the test fails.
 */
-void qt_assert(const char *assertion, const char *file, int line)
+void qt_assert(const char *assertion, const char *file, int line) Q_DECL_NOTHROW
 {
     qFatal("ASSERT: \"%s\" in file %s, line %d", assertion, file, line);
 }
@@ -1924,7 +1933,7 @@ void qt_assert(const char *assertion, const char *file, int line)
 /*
   The Q_ASSERT_X macro calls this function when the test fails.
 */
-void qt_assert_x(const char *where, const char *what, const char *file, int line)
+void qt_assert_x(const char *where, const char *what, const char *file, int line) Q_DECL_NOTHROW
 {
     qFatal("ASSERT failure in %s: \"%s\", file %s, line %d", where, what, file, line);
 }
@@ -3033,6 +3042,38 @@ bool QInternal::activateCallbacks(Callback cb, void **parameters)
     \sa Q_DECL_NOEXCEPT, Q_DECL_NOEXCEPT_EXPR
 */
 
+/*!
+    \macro QT_TERMINATE_ON_EXCEPTION(expr)
+    \relates <QtGlobal>
+    \internal
+
+    In general, use of the Q_DECL_NOEXCEPT macro is preferred over
+    Q_DECL_NOTHROW, because it exhibits well-defined behavior and
+    supports the more powerful Q_DECL_NOEXCEPT_EXPR variant. However,
+    use of Q_DECL_NOTHROW has the advantage that Windows builds
+    benefit on a wide range or compiler versions that do not yet
+    support the C++11 noexcept feature.
+
+    It may therefore be beneficial to use Q_DECL_NOTHROW and emulate
+    the C++11 behavior manually with an embedded try/catch.
+
+    Qt provides the QT_TERMINATE_ON_EXCEPTION(expr) macro for this
+    purpose. It either expands to \c expr (if Qt is compiled without
+    exception support or the compiler supports C++11 noexcept
+    semantics) or to
+    \code
+    try { expr; } catch(...) { qTerminate(); }
+    \endocde
+    otherwise.
+
+    Since this macro expands to just \c expr if the compiler supports
+    C++11 noexcept, expecting the compiler to take over responsibility
+    of calling std::terminate() in that case, it should not be used
+    outside Q_DECL_NOTHROW functions.
+
+    \sa Q_DECL_NOEXCEPT, Q_DECL_NOTHROW, qTerminate()
+*/
+
 /*!
     \macro Q_DECL_NOEXCEPT
     \relates <QtGlobal>

src/corelib/global/qglobal.h

@@ -546,11 +546,18 @@ inline void qt_noop(void) {}
 #  define QT_CATCH(A) else
 #  define QT_THROW(A) qt_noop()
 #  define QT_RETHROW qt_noop()
+#  define QT_TERMINATE_ON_EXCEPTION(expr) do { expr; } while (0)
 #else
 #  define QT_TRY try
 #  define QT_CATCH(A) catch (A)
 #  define QT_THROW(A) throw A
 #  define QT_RETHROW throw
+Q_NORETURN Q_CORE_EXPORT void qTerminate() Q_DECL_NOTHROW;
+#  ifdef Q_COMPILER_NOEXCEPT
+#    define QT_TERMINATE_ON_EXCEPTION(expr) do { expr; } while (0)
+#  else
+#    define QT_TERMINATE_ON_EXCEPTION(expr) do { try { expr; } catch (...) { qTerminate(); } } while (0)
+#  endif
 #endif
 
 Q_CORE_EXPORT const char *qVersion();
@@ -593,7 +600,7 @@ Q_CORE_EXPORT QString qt_error_string(int errorCode = -1);
 #ifndef Q_CC_MSVC
 Q_NORETURN
 #endif
-Q_CORE_EXPORT void qt_assert(const char *assertion, const char *file, int line);
+Q_CORE_EXPORT void qt_assert(const char *assertion, const char *file, int line) Q_DECL_NOTHROW;
 
 #if !defined(Q_ASSERT)
 #  if defined(QT_NO_DEBUG) && !defined(QT_FORCE_ASSERTS)
@@ -610,7 +617,7 @@ Q_CORE_EXPORT void qt_assert(const char *assertion, const char *file, int line);
 #ifndef Q_CC_MSVC
 Q_NORETURN
 #endif
-Q_CORE_EXPORT void qt_assert_x(const char *where, const char *what, const char *file, int line);
+Q_CORE_EXPORT void qt_assert_x(const char *where, const char *what, const char *file, int line) Q_DECL_NOTHROW;
 
 #if !defined(Q_ASSERT_X)
 #  if defined(QT_NO_DEBUG) && !defined(QT_FORCE_ASSERTS)

src/corelib/global/qlogging.cpp

@@ -240,11 +240,11 @@ QDebug QMessageLogger::critical()
 #endif
 
 #undef qFatal
-void QMessageLogger::fatal(const char *msg, ...)
+void QMessageLogger::fatal(const char *msg, ...) Q_DECL_NOTHROW
 {
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtFatalMsg, context, msg, ap);
+    QT_TERMINATE_ON_EXCEPTION(qt_message(QtFatalMsg, context, msg, ap));
 #ifndef Q_CC_MSVC
     Q_UNREACHABLE();
 #endif

src/corelib/global/qlogging.h

@@ -117,7 +117,7 @@ public:
 #ifndef Q_CC_MSVC
     Q_NORETURN
 #endif
-    void fatal(const char *msg, ...)
+    void fatal(const char *msg, ...) Q_DECL_NOTHROW
 #if defined(Q_CC_GNU) && !defined(__INSURE__)
     __attribute__ ((format (printf, 2, 3)))
 #endif