Allow speciyfing the priority for filters

Higher priority (i.e. more important) filter results get shown
first. This means filters like project layers & composers will
show above 'cruder' filters like the actions/processing filters.

python/gui/locator/qgslocatorfilter.sip

@@ -66,6 +66,15 @@ class QgsLocatorFilter : QObject
 %End
   public:
 
+    enum Priority
+    {
+      Highest,
+      High,
+      Medium,
+      Low,
+      Lowest
+    };
+
     QgsLocatorFilter( QObject *parent = 0 );
 %Docstring
  Constructor for QgsLocatorFilter.
@@ -85,6 +94,13 @@ class QgsLocatorFilter : QObject
  :rtype: str
 %End
 
+    virtual Priority priority() const;
+%Docstring
+ Returns the priority for the filter, which controls how results are
+ ordered in the locator.
+ :rtype: Priority
+%End
+
     virtual void fetchResults( const QString &string, const QgsLocatorContext &context, QgsFeedback *feedback ) = 0;
 %Docstring
  Retrieves the filter results for a specified search ``string``. The ``context``

python/plugins/processing/gui/AlgorithmLocatorFilter.py

@@ -45,6 +45,9 @@ class AlgorithmLocatorFilter(QgsLocatorFilter):
     def displayName(self):
         return self.tr('Processing Algorithms')
 
+    def priority(self):
+        return QgsLocatorFilter.Low
+
     def fetchResults(self,string,context,feedback):
         for a in QgsApplication.processingRegistry().algorithms():
             if feedback.isCanceled():

src/app/locator/qgsinbuiltlocatorfilters.h

@@ -30,6 +30,7 @@ class QgsLayerTreeLocatorFilter : public QgsLocatorFilter
     QgsLayerTreeLocatorFilter( QObject *parent = nullptr );
     virtual QString name() const override { return QStringLiteral( "layertree" ); }
     virtual QString displayName() const override { return tr( "Project layers" ); }
+    virtual Priority priority() const override { return Highest; }
 
     void fetchResults( const QString &string, const QgsLocatorContext &context, QgsFeedback *feedback ) override;
     void triggerResult( const QgsLocatorResult &result ) override;
@@ -45,6 +46,7 @@ class QgsLayoutLocatorFilter : public QgsLocatorFilter
     QgsLayoutLocatorFilter( QObject *parent = nullptr );
     virtual QString name() const override { return QStringLiteral( "layouts" ); }
     virtual QString displayName() const override { return tr( "Project layouts" ); }
+    virtual Priority priority() const override { return Highest; }
 
     void fetchResults( const QString &string, const QgsLocatorContext &context, QgsFeedback *feedback ) override;
     void triggerResult( const QgsLocatorResult &result ) override;
@@ -60,6 +62,7 @@ class QgsActionLocatorFilter : public QgsLocatorFilter
     QgsActionLocatorFilter( const QList<QWidget *> &parentObjectsForActions, QObject *parent = nullptr );
     virtual QString name() const override { return QStringLiteral( "actions" ); }
     virtual QString displayName() const override { return tr( "Actions" ); }
+    virtual Priority priority() const override { return Lowest; }
 
     void fetchResults( const QString &string, const QgsLocatorContext &context, QgsFeedback *feedback ) override;
     void triggerResult( const QgsLocatorResult &result ) override;

src/gui/locator/qgslocatorfilter.h

@@ -86,6 +86,16 @@ class GUI_EXPORT QgsLocatorFilter : public QObject
 
   public:
 
+    //! Filter priority. Controls the order of results in the locator.
+    enum Priority
+    {
+      Highest, //!< Highest priority
+      High, //!< High priority
+      Medium, //!< Medium priority
+      Low, //!< Low priority
+      Lowest //!< Lowest priority
+    };
+
     /**
      * Constructor for QgsLocatorFilter.
      */
@@ -103,6 +113,12 @@ class GUI_EXPORT QgsLocatorFilter : public QObject
      */
     virtual QString displayName() const = 0;
 
+    /**
+     * Returns the priority for the filter, which controls how results are
+     * ordered in the locator.
+     */
+    virtual Priority priority() const { return Medium; }
+
     /**
      * Retrieves the filter results for a specified search \a string. The \a context
      * argument encapsulates the context relating to the search (such as a map

src/gui/locator/qgslocatorwidget.cpp

@@ -42,7 +42,7 @@ QgsLocatorWidget::QgsLocatorWidget( QWidget *parent )
   setSizePolicy( sizePolicy );
   setMinimumSize( QSize( 200, 0 ) );
 
-  QHBoxLayout *layout = new QHBoxLayout( this );
+  QHBoxLayout *layout = new QHBoxLayout();
   layout->setMargin( 0 );
   layout->setContentsMargins( 0, 0, 0, 0 );
   layout->addWidget( mLineEdit );
@@ -293,32 +293,38 @@ QVariant QgsLocatorModel::data( const QModelIndex &index, int role ) const
     case Qt::DisplayRole:
     case Qt::EditRole:
     {
-      if ( mResults.at( index.row() ).filterTitle.isEmpty() )
+      if ( !mResults.at( index.row() ).filter )
         return mResults.at( index.row() ).result.displayString;
       else
         return mResults.at( index.row() ).filterTitle;
     }
 
     case Qt::DecorationRole:
-      if ( mResults.at( index.row() ).filterTitle.isEmpty() )
+      if ( !mResults.at( index.row() ).filter )
         return mResults.at( index.row() ).result.icon;
       else
         return QVariant();
 
     case ResultDataRole:
-      if ( mResults.at( index.row() ).filterTitle.isEmpty() )
+      if ( !mResults.at( index.row() ).filter )
         return QVariant::fromValue( mResults.at( index.row() ).result );
       else
         return QVariant();
 
     case ResultTypeRole:
-      if ( mResults.at( index.row() ).filterTitle.isEmpty() )
-        return 1;
-      else
+      if ( mResults.at( index.row() ).filter )
         return 0;
+      else
+        return 1;
+
+    case ResultFilterPriorityRole:
+      if ( !mResults.at( index.row() ).filter )
+        return mResults.at( index.row() ).result.filter->priority();
+      else
+        return mResults.at( index.row() ).filter->priority();
 
     case ResultFilterNameRole:
-      if ( mResults.at( index.row() ).filterTitle.isEmpty() )
+      if ( !mResults.at( index.row() ).filter )
         return mResults.at( index.row() ).result.filter->displayName();
       else
         return mResults.at( index.row() ).filterTitle;
@@ -354,6 +360,7 @@ void QgsLocatorModel::addResult( const QgsLocatorResult &result )
   {
     Entry entry;
     entry.filterTitle = result.filter->displayName();
+    entry.filter = result.filter;
     mResults << entry;
   }
   Entry entry;
@@ -418,16 +425,25 @@ QgsLocatorProxyModel::QgsLocatorProxyModel( QObject *parent )
 
 bool QgsLocatorProxyModel::lessThan( const QModelIndex &left, const QModelIndex &right ) const
 {
+  // first go by filter priority
+  int leftFilterPriority = sourceModel()->data( left, QgsLocatorModel::ResultFilterPriorityRole ).toInt();
+  int rightFilterPriority  = sourceModel()->data( right, QgsLocatorModel::ResultFilterPriorityRole ).toInt();
+  if ( leftFilterPriority != rightFilterPriority )
+    return leftFilterPriority < rightFilterPriority;
+
+  // then filter name
   QString leftFilter = sourceModel()->data( left, QgsLocatorModel::ResultFilterNameRole ).toString();
   QString rightFilter = sourceModel()->data( right, QgsLocatorModel::ResultFilterNameRole ).toString();
   if ( leftFilter != rightFilter )
     return QString::localeAwareCompare( leftFilter, rightFilter ) < 0;
 
+  // then make sure filter title appears before filter's results
   int leftTypeRole = sourceModel()->data( left, QgsLocatorModel::ResultTypeRole ).toInt();
   int rightTypeRole = sourceModel()->data( right, QgsLocatorModel::ResultTypeRole ).toInt();
   if ( leftTypeRole != rightTypeRole )
     return leftTypeRole < rightTypeRole;
 
+  // lastly sort filter's results by string
   leftFilter = sourceModel()->data( left, Qt::DisplayRole ).toString();
   rightFilter = sourceModel()->data( right, Qt::DisplayRole ).toString();
   return QString::localeAwareCompare( leftFilter, rightFilter ) < 0;

src/gui/locator/qgslocatorwidget.h

@@ -127,6 +127,7 @@ class QgsLocatorModel : public QAbstractListModel
     {
       ResultDataRole = Qt::UserRole + 1, //!< QgsLocatorResult data
       ResultTypeRole,
+      ResultFilterPriorityRole,
       ResultFilterNameRole,
     };
 
@@ -158,6 +159,7 @@ class QgsLocatorModel : public QAbstractListModel
     {
       QgsLocatorResult result;
       QString filterTitle;
+      QgsLocatorFilter *filter = nullptr;
     };
 
     QList<Entry> mResults;