Utils: collect host root dir once

This improves the startup performance ~30% on certain machines

Change-Id: Ic7b74d42b0e13ec1dd695d4f322de021b996c051
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/utils/filepath.cpp

@@ -225,7 +225,7 @@ bool FilePath::isRootPath() const
         return true;
     }
 
-    return *this == FilePath::fromString(QDir::rootPath());
+    return *this == HostOsInfo::root();
 }
 
 QString FilePath::encodedHost() const
@@ -986,7 +986,7 @@ const QString &FilePath::specialRootName()
 
 const QString &FilePath::specialRootPath()
 {
-    static const QString rootPath = QDir::rootPath() + u"__qtc_devices__";
+    static const QString rootPath = HostOsInfo::root().path() + u"__qtc_devices__";
     return rootPath;
 }
 
@@ -998,7 +998,7 @@ const QString &FilePath::specialDeviceRootName()
 
 const QString &FilePath::specialDeviceRootPath()
 {
-    static const QString deviceRootPath =  QDir::rootPath() + u"__qtc_devices__/device";
+    static const QString deviceRootPath = HostOsInfo::root().path() + u"__qtc_devices__/device";
     return deviceRootPath;
 }
 

src/libs/utils/filesystemmodel.cpp

@@ -1053,10 +1053,8 @@ FileSystemNode *FileSystemModelPrivate::node(const QString &path, bool fetch) co
             elementPath = host;
             elementPath.append(separator);
         } else {
-            if (!pathElements.at(0).contains(QLatin1Char(':'))) {
-                QString rootPath = QDir(longPath).rootPath();
-                pathElements.prepend(rootPath);
-            }
+            if (!pathElements.at(0).contains(QLatin1Char(':')))
+                pathElements.prepend(HostOsInfo::root().path());
             if (pathElements.at(0).endsWith(QLatin1Char('/')))
                 pathElements[0].chop(1);
         }

src/libs/utils/fsengine/fileiteratordevicesappender.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include "../filepath.h"
+#include "../hostosinfo.h"
 
 #include <QtCore/private/qabstractfileengine_p.h>
 
@@ -97,7 +98,7 @@ private:
             // We only need QDir::cleanPath here, as the path is always
             // a fs engine path and will not contain scheme:// etc.
             const QString p = QDir::cleanPath(path());
-            if (p.compare(QDir::rootPath(), Qt::CaseInsensitive) == 0)
+            if (p.compare(HostOsInfo::root().path(), Qt::CaseInsensitive) == 0)
                 m_status = State::IteratingRoot;
 
             ((*m_baseIterator).*get(QAFEITag()))(p);

src/libs/utils/fsengine/fsenginehandler.cpp

@@ -71,7 +71,7 @@ QAbstractFileEngine *FSEngineHandler::create(const QString &fileName) const
             return new FSEngineImpl(removeDoubleSlash(fileName));
     }
 
-    if (fixedFileName.compare(QDir::rootPath(), Qt::CaseInsensitive) == 0)
+    if (fixedFileName.compare(HostOsInfo::root().path(), Qt::CaseInsensitive) == 0)
         return new RootInjectFSEngine(fileName);
 
     return nullptr;

src/libs/utils/hostosinfo.cpp

@@ -3,8 +3,11 @@
 
 #include "hostosinfo.h"
 
+#include "filepath.h"
 #include "utilstr.h"
 
+#include <QDir>
+
 #if !defined(QT_NO_OPENGL) && defined(QT_GUI_LIB)
 #include <QOpenGLContext>
 #endif
@@ -21,7 +24,7 @@
 #include <sys/sysctl.h>
 #endif
 
-using namespace Utils;
+namespace Utils {
 
 Qt::CaseSensitivity HostOsInfo::m_overrideFileNameCaseSensitivity = Qt::CaseSensitive;
 bool HostOsInfo::m_useOverrideFileNameCaseSensitivity = false;
@@ -116,3 +119,11 @@ std::optional<quint64> HostOsInfo::totalMemoryInstalledInBytes()
 #endif
     return {};
 }
+
+const FilePath &HostOsInfo::root()
+{
+    static const FilePath rootDir = FilePath::fromUserInput(QDir::rootPath());
+    return rootDir;
+}
+
+} // namespace Utils

src/libs/utils/hostosinfo.h

@@ -21,6 +21,8 @@ QT_END_NAMESPACE
 
 namespace Utils {
 
+class FilePath;
+
 class QTCREATOR_UTILS_EXPORT HostOsInfo
 {
 public:
@@ -86,6 +88,8 @@ public:
 
     static std::optional<quint64> totalMemoryInstalledInBytes();
 
+    static const FilePath &root();
+
 private:
     static Qt::CaseSensitivity m_overrideFileNameCaseSensitivity;
     static bool m_useOverrideFileNameCaseSensitivity;

src/plugins/projectexplorer/devicesupport/desktopdevice.cpp

@@ -125,7 +125,7 @@ Environment DesktopDevice::systemEnvironment() const
 FilePath DesktopDevice::rootPath() const
 {
     if (id() == DESKTOP_DEVICE_ID)
-        return FilePath::fromParts({}, {}, QDir::rootPath());
+        return HostOsInfo::root();
     return IDevice::rootPath();
 }