QUrl: fromLocalFile(QString()) should lead to an empty URL.

This is much more useful than the URL "file:", it allows to use
"empty path" and "empty URL" for the same meaning (e.g. not set).

QFileDialog actually uses "file:" though, as the URL for the
"My Computer" item in the sidebar. This patch preserves that.

[ChangeLog][QtCore][QUrl] QUrl::fromLocalFile now returns an empty URL
if the input string is empty.

Change-Id: Ib5ce1a3cdf5f229368e5bcd83c62c1d1ac9f8a17
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qurl.cpp

@@ -3738,11 +3738,15 @@ bool QUrl::isDetached() const
     "//servername/path/to/file.txt". Note that only certain platforms can
     actually open this file using QFile::open().
 
+    An empty \a localFile leads to an empty URL (since Qt 5.4).
+
     \sa toLocalFile(), isLocalFile(), QDir::toNativeSeparators()
 */
 QUrl QUrl::fromLocalFile(const QString &localFile)
 {
     QUrl url;
+    if (localFile.isEmpty())
+        return url;
     url.setScheme(fileScheme());
     QString deslashified = QDir::fromNativeSeparators(localFile);
 

src/widgets/dialogs/qfiledialog.cpp

@@ -2736,7 +2736,7 @@ void QFileDialogPrivate::createWidgets()
     qFileDialogUi->setupUi(q);
 
     QList<QUrl> initialBookmarks;
-    initialBookmarks << QUrl::fromLocalFile(QLatin1String(""))
+    initialBookmarks << QUrl(QLatin1String("file:"))
                      << QUrl::fromLocalFile(QDir::homePath());
     qFileDialogUi->sidebar->setModelAndUrls(model, initialBookmarks);
     QFileDialog::connect(qFileDialogUi->sidebar, SIGNAL(goToUrl(QUrl)),
@@ -3713,7 +3713,7 @@ void QFileDialogComboBox::showPopup()
         idx = idx.parent();
     }
     // add "my computer"
-    list.append(QUrl::fromLocalFile(QLatin1String("")));
+    list.append(QUrl(QLatin1String("file:")));
     urlModel->addUrls(list, 0);
     idx = model()->index(model()->rowCount() - 1, 0);
 

src/widgets/dialogs/qsidebar.cpp

@@ -249,7 +249,8 @@ void QUrlModel::addUrls(const QList<QUrl> &list, int row, bool move)
             continue;
         //this makes sure the url is clean
         const QString cleanUrl = QDir::cleanPath(url.toLocalFile());
-        url = QUrl::fromLocalFile(cleanUrl);
+        if (!cleanUrl.isEmpty())
+            url = QUrl::fromLocalFile(cleanUrl);
 
         for (int j = 0; move && j < rowCount(); ++j) {
             QString local = index(j, 0).data(UrlRole).toUrl().toLocalFile();

tests/auto/corelib/io/qurl/tst_qurl.cpp

@@ -237,6 +237,11 @@ void tst_QUrl::constructing()
     QVERIFY(url == url);
     QVERIFY(!(url < url));
 
+    QUrl fromLocal = QUrl::fromLocalFile(QString());
+    QVERIFY(!fromLocal.isValid());
+    QVERIFY(fromLocal.isEmpty());
+    QCOMPARE(fromLocal.toString(), QString());
+
     QUrl justHost("qt-project.org");
     QVERIFY(!justHost.isEmpty());
     QVERIFY(justHost.host().isEmpty());