qC{Debug,Info,Warning,Critical}: Simplify #ifndef QT_NO_xxx_OUTPUT

Further simplifies the definition of the macros.

The class is placed in an unnamed namespace so two translation units can
still have different settings.

A difference is that the expanded no-output code is now using QDebug,
not QNoDebug, but it should get dead-code-eliminated either way.

Change-Id: I3eb1bd30e0124f89a052fffd16a7564f4450ec8a
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

1 files changed, 32 insertions, 24 deletions

diff --git a/src/corelib/io/qloggingcategory.h b/src/corelib/io/qloggingcategory.h
index 2314c388b0..5a66bb2e68 100644
--- a/src/corelib/io/qloggingcategory.h
+++ b/src/corelib/io/qloggingcategory.h
@@ -106,13 +106,25 @@ private:
     Q_DECL_UNUSED_MEMBER bool placeholder[4]; // reserved for future use
 };
 
+namespace { // allow different TUs to have different QT_NO_xxx_OUTPUT
 template <QtMsgType Which> struct QLoggingCategoryMacroHolder
 {
-    const QLoggingCategory &category;
-    bool control;
+    static const bool IsOutputEnabled;
+    const QLoggingCategory *category = nullptr;
+    bool control = false;
     QLoggingCategoryMacroHolder(const QLoggingCategory &cat)
-        : category(cat)
     {
+        if (IsOutputEnabled)
+            init(cat);
+    }
+    QLoggingCategoryMacroHolder(QMessageLogger::CategoryFunction catfunc)
+    {
+        if (IsOutputEnabled)
+            init(catfunc());
+    }
+    void init(const QLoggingCategory &cat) noexcept
+    {
+        category = &cat;
         // same as:
         //  control = cat.isEnabled(Which);
         // but without an out-of-line call
@@ -126,10 +138,22 @@ template <QtMsgType Which> struct QLoggingCategoryMacroHolder
             control = cat.isCriticalEnabled();
         }
     }
-    operator const char *() const { return category.categoryName(); }
+    operator const char *() const { return category->categoryName(); }
     operator bool() const { return Q_UNLIKELY(control); }
 };
 
+template <QtMsgType Which> const bool QLoggingCategoryMacroHolder<Which>::IsOutputEnabled = true;
+#if defined(QT_NO_DEBUG_OUTPUT)
+template <> const bool QLoggingCategoryMacroHolder<QtDebugMsg>::IsOutputEnabled = false;
+#endif
+#if defined(QT_NO_INFO_OUTPUT)
+template <> const bool QLoggingCategoryMacroHolder<QtInfoMsg>::IsOutputEnabled = false;
+#endif
+#if defined(QT_NO_WARNING_OUTPUT)
+template <> const bool QLoggingCategoryMacroHolder<QtWarningMsg>::IsOutputEnabled = false;
+#endif
+} // unnamed namespace
+
 #define Q_DECLARE_LOGGING_CATEGORY(name) \
     extern const QLoggingCategory &name();
 
@@ -140,29 +164,13 @@ template <QtMsgType Which> struct QLoggingCategoryMacroHolder
         return category; \
     }
 
-
 #define QT_MESSAGE_LOGGER_COMMON(category, level) \
-    for (QLoggingCategoryMacroHolder<level> qt_category(category()); qt_category; qt_category.control = false) \
+    for (QLoggingCategoryMacroHolder<level> qt_category(category); qt_category; qt_category.control = false) \
         QMessageLogger(QT_MESSAGELOG_FILE, QT_MESSAGELOG_LINE, QT_MESSAGELOG_FUNC, qt_category)
 
-#if !defined(QT_NO_DEBUG_OUTPUT)
-#  define qCDebug(category, ...) QT_MESSAGE_LOGGER_COMMON(category, QtDebugMsg).debug(__VA_ARGS__)
-#else
-#  define qCDebug(category, ...) QT_NO_QDEBUG_MACRO()
-#endif
-
-#if !defined(QT_NO_INFO_OUTPUT)
-#  define qCInfo(category, ...) QT_MESSAGE_LOGGER_COMMON(category, QtInfoMsg).info(__VA_ARGS__)
-#else
-#  define qCInfo(category, ...) QT_NO_QDEBUG_MACRO()
-#endif
-
-#if !defined(QT_NO_WARNING_OUTPUT)
-#  define qCWarning(category, ...) QT_MESSAGE_LOGGER_COMMON(category, QtWarningMsg).warning(__VA_ARGS__)
-#else
-#  define qCWarning(category, ...) QT_NO_QDEBUG_MACRO()
-#endif
-
+#define qCDebug(category, ...) QT_MESSAGE_LOGGER_COMMON(category, QtDebugMsg).debug(__VA_ARGS__)
+#define qCInfo(category, ...) QT_MESSAGE_LOGGER_COMMON(category, QtInfoMsg).info(__VA_ARGS__)
+#define qCWarning(category, ...) QT_MESSAGE_LOGGER_COMMON(category, QtWarningMsg).warning(__VA_ARGS__)
 #define qCCritical(category, ...) QT_MESSAGE_LOGGER_COMMON(category, QtCriticalMsg).critical(__VA_ARGS__)
 
 QT_END_NAMESPACE