QFileSystemWatcher: lock autotest code away into a cold section

The code contained a sizeable chunk of string parsing along with
qDebug()s in the normal path of execution. That code, however, was
only used for Qt's own autotests.

The idea of this patch is, then, to not only move the autotest case
into the cold text section (using Q_UNLIKELY), but also to completely
exclude it, when QT_BUILD_INTERNAL is not set.

Unfortunately, the structure of the function did not really lend
itself to #ifdefing that part of the code out (production code was in
the middle of non-production code), so I transformed the engine
selection code into a lambda, replacing assignment with returns, and
swapping the branches of the central if around to yield a single block
of code that can be excluded from compilation with just one #ifdef.

As a consequence, the runtime code is almost unaffected, and the
function is much easier to read now.

Since the test-specific code is only compiled into Qt now in developer
builds, guard the tests that rely on this behavior with the same macro.

Change-Id: I9fd1c57020a13cef4cd1b1674ed2d3ab9424d7cd
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
 

1 files changed, 22 insertions, 21 deletions

diff --git a/src/corelib/io/qfilesystemwatcher.cpp b/src/corelib/io/qfilesystemwatcher.cpp
index f40e166d9f..9b47b27f5c 100644
--- a/src/corelib/io/qfilesystemwatcher.cpp
+++ b/src/corelib/io/qfilesystemwatcher.cpp
@@ -352,33 +352,34 @@ QStringList QFileSystemWatcher::addPaths(const QStringList &paths)
         return QStringList();
     }
 
-    QFileSystemWatcherEngine *engine = 0;
-
-    const QString on = objectName();
-
-    if (!on.startsWith(QLatin1String("_qt_autotest_force_engine_"))) {
+    const auto selectEngine = [this, d]() -> QFileSystemWatcherEngine* {
+#ifdef QT_BUILD_INTERNAL
+        const QString on = objectName();
+
+        if (Q_UNLIKELY(on.startsWith(QLatin1String("_qt_autotest_force_engine_")))) {
+            // Autotest override case - use the explicitly selected engine only
+            const QStringRef forceName = on.midRef(26);
+            if (forceName == QLatin1String("poller")) {
+                qDebug("QFileSystemWatcher: skipping native engine, using only polling engine");
+                d_func()->initPollerEngine();
+                return d->poller;
+            } else if (forceName == QLatin1String("native")) {
+                qDebug("QFileSystemWatcher: skipping polling engine, using only native engine");
+                return d->native;
+            }
+            return nullptr;
+        }
+#endif
         // Normal runtime case - search intelligently for best engine
         if(d->native) {
-            engine = d->native;
+            return d->native;
         } else {
             d_func()->initPollerEngine();
-            engine = d->poller;
+            return d->poller;
         }
+    };
 
-    } else {
-        // Autotest override case - use the explicitly selected engine only
-        const QStringRef forceName = on.midRef(26);
-        if(forceName == QLatin1String("poller")) {
-            qDebug("QFileSystemWatcher: skipping native engine, using only polling engine");
-            d_func()->initPollerEngine();
-            engine = d->poller;
-        } else if(forceName == QLatin1String("native")) {
-            qDebug("QFileSystemWatcher: skipping polling engine, using only native engine");
-            engine = d->native;
-        }
-    }
-
-    if(engine)
+    if (auto engine = selectEngine())
         p = engine->addPaths(p, &d->files, &d->directories);
 
     return p;