QmlDesigner: Fix assets library warning case

Fixed a warning that appears if the search moves from the
"no match found" case to a match case. Also added a small optimization
to searching.

Change-Id: I9e4759fe00959bcbe1a7018c1bdc6cc43069fca7
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

share/qtcreator/qmldesigner/itemLibraryQmlSources/Assets.qml

@@ -445,7 +445,7 @@ Item {
                         hideHeader: dirDepth === 0
                         showLeftBorder: dirDepth > 0
                         expanded: dirExpanded
-                        visible: !assetsModel.isEmpty && dirVisible
+                        visible: dirVisible
                         expandOnClick: false
                         useDefaulContextMenu: false
 

src/plugins/qmldesigner/components/assetslibrary/assetslibrarymodel.cpp

@@ -341,8 +341,14 @@ void AssetsLibraryModel::setRootPath(const QString &path)
 
     beginResetModel();
     m_assetsDir = new AssetsLibraryDir(path, 0, true, this);
-    bool noAssets = parseDirRecursive(m_assetsDir, 1);
+    bool isEmpty = parseDirRecursive(m_assetsDir, 1);
-    setIsEmpty(noAssets);
+    setIsEmpty(isEmpty);
+
+    bool noAssets = m_searchText.isEmpty() && isEmpty;
+    // noAssets: the model has no asset files (project has no assets added)
+    // isEmpty: the model has no asset files (assets could exist but are filtered out)
+
+    m_assetsDir->setDirVisible(!noAssets); // if there are no assets, hide all empty asset folders
     endResetModel();
 }
 

src/plugins/qmldesigner/components/assetslibrary/assetslibrarymodel.h

@@ -59,6 +59,8 @@ public:
     void setRootPath(const QString &path);
     void setSearchText(const QString &searchText);
 
+    bool isEmpty() const;
+
     static const QStringList &supportedImageSuffixes();
     static const QStringList &supportedFragmentShaderSuffixes();
     static const QStringList &supportedShaderSuffixes();
@@ -93,7 +95,6 @@ signals:
 private:
     const QSet<QString> &supportedSuffixes() const;
 
-    bool isEmpty() const;
     void setIsEmpty(bool empty);
 
     SynchronousImageCache &m_fontImageCache;

src/plugins/qmldesigner/components/assetslibrary/assetslibrarywidget.cpp

@@ -201,10 +201,11 @@ QList<QToolButton *> AssetsLibraryWidget::createToolBarWidgets()
 
 void AssetsLibraryWidget::handleSearchfilterChanged(const QString &filterText)
 {
-    if (filterText != m_filterText) {
+    if (filterText == m_filterText || (m_assetsModel->isEmpty() && filterText.contains(m_filterText)))
+            return;
+
     m_filterText = filterText;
     updateSearch();
-    }
 }
 
 void AssetsLibraryWidget::handleAddAsset()