Unify behavior for long path or UNC prefix removal

Split the code out of QDir::fromNativeSeparator into a separate
reusable function to remove the above-mentioned prefixes. Fixes
and unifies behavior if the prefix was given with slashes instead
of backslashes. Add a couple more test cases.

Fixes: QTBUG-93868
Pick-to: 5.15 6.0 6.1
Change-Id: Ibd94ae283e2fb113f9c2db97475fbc7d89522bbf
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

1 files changed, 3 insertions, 28 deletions

diff --git a/src/corelib/io/qdir.cpp b/src/corelib/io/qdir.cpp
index c4dbd27aa1..e92d2f9ca7 100644
--- a/src/corelib/io/qdir.cpp
+++ b/src/corelib/io/qdir.cpp
@@ -953,35 +953,10 @@ QString QDir::toNativeSeparators(const QString &pathName)
 QString QDir::fromNativeSeparators(const QString &pathName)
 {
 #if defined(Q_OS_WIN)
-    const QChar nativeSeparator = u'\\';
-    int i = pathName.indexOf(nativeSeparator);
-    if (i != -1) {
-        QString n(pathName);
-        const QStringView uncPrefix(uR"(\\?\UNC\)");
-        const QStringView extendedLengthPathPrefix(uR"(\\?\)");
-        if (n.startsWith(uncPrefix)) {
-            // Keep the initial double-slash, chop out the rest of the prefix.
-            n = n.remove(2, uncPrefix.size() - 2);
-            if ((i = n.indexOf(nativeSeparator)) == -1)
-                return n;
-        } else if (n.startsWith(extendedLengthPathPrefix)) {
-            n = n.sliced(extendedLengthPathPrefix.size());
-            if ((i = n.indexOf(nativeSeparator)) == -1)
-                return n;
-        }
-
-        QChar * const data = n.data();
-        data[i++] = u'/';
-
-        for (; i < n.length(); ++i) {
-            if (data[i] == nativeSeparator)
-                data[i] = u'/';
-        }
-
-        return n;
-    }
-#endif
+    return QFileSystemEntry::removeUncOrLongPathPrefix(pathName).replace(u'\\', u'/');
+#else
     return pathName;
+#endif
 }
 
 static QString qt_cleanPath(const QString &path, bool *ok = nullptr);