Fix check if example location is writable on Windows

The normal permission check done by QFileInfo is not sufficient in many
cases.

Task-number: QTCREATORBUG-18184
Change-Id: Icab92c592e6d3c8610304e0b987eded6142f4ab3
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/utils/fileutils.h

@@ -49,6 +49,11 @@ class QWidget;
 
 QTCREATOR_UTILS_EXPORT QDebug operator<<(QDebug dbg, const Utils::FileName &c);
 
+// for withNTFSPermissions
+#ifdef Q_OS_WIN
+extern Q_CORE_EXPORT int qt_ntfs_permission_lookup;
+#endif
+
 QT_END_NAMESPACE
 
 namespace Utils {
@@ -121,6 +126,28 @@ public:
     static QString resolvePath(const QString &baseDir, const QString &fileName);
 };
 
+// for actually finding out if e.g. directories are writable on Windows
+#ifdef Q_OS_WIN
+
+template <typename T>
+static T withNTFSPermissions(const std::function<T()> &task)
+{
+    qt_ntfs_permission_lookup++;
+    T result = task();
+    qt_ntfs_permission_lookup--;
+    return result;
+}
+
+#else // Q_OS_WIN
+
+template <typename T>
+static T withNTFSPermissions(const std::function<T()> &task)
+{
+    return task();
+}
+
+#endif // Q_OS_WIN
+
 class QTCREATOR_UTILS_EXPORT FileReader
 {
     Q_DECLARE_TR_FUNCTIONS(Utils::FileUtils) // sic!

src/plugins/qtsupport/gettingstartedwelcomepage.cpp

@@ -28,6 +28,7 @@
 #include "exampleslistmodel.h"
 #include "screenshotcropper.h"
 
+#include <utils/fileutils.h>
 #include <utils/pathchooser.h>
 #include <utils/winutils.h>
 
@@ -199,13 +200,16 @@ void ExamplesWelcomePage::openProject(const ExampleItem &item)
     if (!proFileInfo.exists())
         return;
 
-    QFileInfo pathInfo(proFileInfo.path());
     // If the Qt is a distro Qt on Linux, it will not be writable, hence compilation will fail
-    if (!proFileInfo.isWritable()
+    // Same if it is installed in non-writable location for other reasons
-            || !pathInfo.isWritable() /* path of .pro file */
+    const bool needsCopy = withNTFSPermissions<bool>([proFileInfo] {
-            || !QFileInfo(pathInfo.path()).isWritable() /* shadow build directory */) {
+        QFileInfo pathInfo(proFileInfo.path());
+        return !proFileInfo.isWritable()
+                || !pathInfo.isWritable() /* path of .pro file */
+                || !QFileInfo(pathInfo.path()).isWritable() /* shadow build directory */;
+    });
+    if (needsCopy)
         proFile = copyToAlternativeLocation(proFileInfo, filesToOpen, item.dependencies);
-    }
 
     // don't try to load help and files if loading the help request is being cancelled
     if (proFile.isEmpty())