QgsProviderSublayerTask: make it possible to restrict it to a particular provider

Avoids the 'ERROR: Status 2: File  pagingEnabled='false'
preferCoordinatesForWfsT11='false' restrictToRequestBBOX='1'
srsname='EPSG:25832' typename='dvg:nw_dvg1_bld'
url='https://www.wfs.nrw.de/geobasis/wfs_nw_dvg' version='auto' could
not be found' type of message in the scenario described by
https://github.com/qgis/QGIS/pull/51144#issuecomment-1345507627

python/core/auto_generated/providers/qgsprovidermetadata.sip.in

@@ -398,7 +398,7 @@ The optional ``feedback`` argument can be used to provide cancellation support f
 
     virtual QString suggestGroupNameForUri( const QString &uri ) const;
 %Docstring
-Returns a name that can be used as a group name for sublayers got from
+Returns a name that can be used as a group name for sublayers retrieved from
 the specified ``uri``.
 
 The default implementation returns an empty string.

python/core/auto_generated/providers/qgsprovidersublayertask.sip.in

@@ -39,6 +39,14 @@ possible, regardless of how expensive this may be.
 %Docstring
 Constructor for QgsProviderSublayerTask, which retrieves sublayer details for the
 specified ``uri``.
+%End
+
+    QgsProviderSublayerTask( const QString &uri, const QString &providerKey, bool includeSystemTables = false );
+%Docstring
+Constructor for QgsProviderSublayerTask, which retrieves sublayer details for the
+specified ``uri``, restricted to a particular provider.
+
+.. versionadded:: 3.30
 %End
 
     ~QgsProviderSublayerTask();

src/app/layers/qgsapplayerhandling.cpp

@@ -324,7 +324,7 @@ QList< QgsMapLayer * > QgsAppLayerHandling::addOgrVectorLayers( const QStringLis
           case SublayerHandling::AskUser:
           {
             // prompt user for sublayers
-            QgsProviderSublayersDialog dlg( uri, path, sublayers, {QgsMapLayerType::VectorLayer}, QgisApp::instance() );
+            QgsProviderSublayersDialog dlg( uri, QString(), path, sublayers, {QgsMapLayerType::VectorLayer}, QgisApp::instance() );
 
             if ( dlg.exec() )
               sublayers = dlg.selectedLayers();
@@ -534,7 +534,7 @@ bool QgsAppLayerHandling::askUserForZipItemLayers( const QString &path, const QL
       case SublayerHandling::AskUser:
       {
         // prompt user for sublayers
-        QgsProviderSublayersDialog dlg( path, path, sublayers, acceptableTypes, QgisApp::instance() );
+        QgsProviderSublayersDialog dlg( path, QString(), path, sublayers, acceptableTypes, QgisApp::instance() );
 
         if ( dlg.exec() )
           sublayers = dlg.selectedLayers();
@@ -936,7 +936,7 @@ QList< QgsMapLayer * > QgsAppLayerHandling::openLayer( const QString &fileName,
         case SublayerHandling::AskUser:
         {
           // prompt user for sublayers
-          QgsProviderSublayersDialog dlg( fileName, fileName, sublayers, {}, QgisApp::instance() );
+          QgsProviderSublayersDialog dlg( fileName, QString(), fileName, sublayers, {}, QgisApp::instance() );
           dlg.setNonLayerItems( nonLayerItems );
 
           if ( dlg.exec() )
@@ -1373,7 +1373,7 @@ T *QgsAppLayerHandling::addLayerPrivate( QgsMapLayerType type, const QString &ur
       {
         case SublayerHandling::AskUser:
         {
-          QgsProviderSublayersDialog dlg( updatedUri, path, sublayers, {type}, QgisApp::instance() );
+          QgsProviderSublayersDialog dlg( updatedUri, providerKey, path, sublayers, {type}, QgisApp::instance() );
           QString groupName = providerMetadata->suggestGroupNameForUri( uri );
           if ( !groupName.isEmpty() )
             dlg.setGroupName( groupName );

src/core/providers/qgsprovidermetadata.h

@@ -458,7 +458,7 @@ class CORE_EXPORT QgsProviderMetadata : public QObject
     virtual QList< QgsProviderSublayerDetails > querySublayers( const QString &uri, Qgis::SublayerQueryFlags flags = Qgis::SublayerQueryFlags(), QgsFeedback *feedback = nullptr ) const;
 
     /**
-     * Returns a name that can be used as a group name for sublayers got from
+     * Returns a name that can be used as a group name for sublayers retrieved from
      * the specified \a uri.
      *
      * The default implementation returns an empty string.

src/core/providers/qgsprovidersublayertask.cpp

@@ -17,6 +17,7 @@
 
 #include "qgsprovidersublayertask.h"
 #include "qgsfeedback.h"
+#include "qgsprovidermetadata.h"
 #include "qgsproviderregistry.h"
 #include "qgsprovidersublayerdetails.h"
 #include "qgsreadwritelocker.h"
@@ -28,6 +29,14 @@ QgsProviderSublayerTask::QgsProviderSublayerTask( const QString &uri, bool inclu
 {
 }
 
+QgsProviderSublayerTask::QgsProviderSublayerTask( const QString &uri, const QString &providerKey, bool includeSystemTables )
+  : QgsTask( tr( "Retrieving layers" ), QgsTask::CanCancel | QgsTask::CancelWithoutPrompt | QgsTask::Silent )
+  , mUri( uri )
+  , mProviderKey( providerKey )
+  , mIncludeSystemTables( includeSystemTables )
+{
+}
+
 QList<QgsProviderSublayerDetails> QgsProviderSublayerTask::results() const
 {
   const QgsReadWriteLocker locker( mLock, QgsReadWriteLocker::Read );
@@ -44,7 +53,15 @@ bool QgsProviderSublayerTask::run()
   if ( mIncludeSystemTables )
     flags |= Qgis::SublayerQueryFlag::IncludeSystemTables;
 
-  const QList<QgsProviderSublayerDetails> res = QgsProviderRegistry::instance()->querySublayers( mUri, flags, mFeedback.get() );
+  QList<QgsProviderSublayerDetails> res;
+  if ( mProviderKey.isEmpty() )
+    res = QgsProviderRegistry::instance()->querySublayers( mUri, flags, mFeedback.get() );
+  else
+  {
+    QgsProviderMetadata *provider = QgsProviderRegistry::instance()->providerMetadata( mProviderKey );
+    if ( provider )
+      res = provider->querySublayers( mUri, flags, mFeedback.get() );
+  }
 
   const QgsReadWriteLocker locker( mLock, QgsReadWriteLocker::Write );
   mResults = res;

src/core/providers/qgsprovidersublayertask.h

@@ -55,6 +55,14 @@ class CORE_EXPORT QgsProviderSublayerTask : public QgsTask
      */
     QgsProviderSublayerTask( const QString &uri, bool includeSystemTables = false );
 
+    /**
+     * Constructor for QgsProviderSublayerTask, which retrieves sublayer details for the
+     * specified \a uri, restricted to a particular provider.
+     *
+     * \since QGIS 3.30
+     */
+    QgsProviderSublayerTask( const QString &uri, const QString &providerKey, bool includeSystemTables = false );
+
     ~QgsProviderSublayerTask() override;
 
     /**
@@ -72,6 +80,8 @@ class CORE_EXPORT QgsProviderSublayerTask : public QgsTask
 
     QString mUri;
 
+    QString mProviderKey;
+
     bool mIncludeSystemTables = false;
 
     std::unique_ptr< QgsFeedback > mFeedback;

src/gui/qgsprovidersublayersdialog.cpp

@@ -111,7 +111,7 @@ void QgsProviderSublayerDialogModel::setGeometryTypesResolved( bool resolved )
   emit dataChanged( index( 0, 0 ), index( rowCount( QModelIndex() ), columnCount() ) );
 }
 
-QgsProviderSublayersDialog::QgsProviderSublayersDialog( const QString &uri, const QString &filePathIn, const QList<QgsProviderSublayerDetails> initialDetails, const QList<QgsMapLayerType> &acceptableTypes, QWidget *parent, Qt::WindowFlags fl )
+QgsProviderSublayersDialog::QgsProviderSublayersDialog( const QString &uri, const QString &providerKey, const QString &filePathIn, const QList<QgsProviderSublayerDetails> initialDetails, const QList<QgsMapLayerType> &acceptableTypes, QWidget *parent, Qt::WindowFlags fl )
   : QDialog( parent, fl )
 {
   setupUi( this );
@@ -177,7 +177,7 @@ QgsProviderSublayersDialog::QgsProviderSublayersDialog( const QString &uri, cons
   if ( QgsProviderUtils::sublayerDetailsAreIncomplete( initialDetails ) )
   {
     // initial details are incomplete, so fire up a task in the background to fully populate the model...
-    mTask = new QgsProviderSublayerTask( uri, true );
+    mTask = new QgsProviderSublayerTask( uri, providerKey, true );
     connect( mTask.data(), &QgsProviderSublayerTask::taskCompleted, this, [ = ]
     {
       QList< QgsProviderSublayerDetails > res = mTask->results();

src/gui/qgsprovidersublayersdialog.h

@@ -78,6 +78,7 @@ class GUI_EXPORT QgsProviderSublayersDialog : public QDialog, private Ui::QgsPro
      * Constructor.
      */
     QgsProviderSublayersDialog( const QString &uri,
+                                const QString &providerKey,
                                 const QString &filePath,
                                 const QList< QgsProviderSublayerDetails> initialDetails = QList< QgsProviderSublayerDetails>(),
                                 const QList< QgsMapLayerType > &acceptableTypes = QList< QgsMapLayerType >(),