Add option on layer to read extent from xml in case of data source without metadata

python/core/qgsvectordataprovider.sip

@@ -524,6 +524,15 @@ Returns a list of available encodings
  :rtype: str
 %End
 
+    virtual bool hasMetadata() const;
+%Docstring
+ Returns true if the data source has metadata, false otherwise.
+
+ :return: true if data source has metadata, false otherwise.
+
+.. versionadded:: 3.0
+ :rtype: bool
+%End
   signals:
 
     void raiseError( const QString &msg ) const;

python/core/qgsvectorlayer.sip

@@ -315,7 +315,8 @@ class QgsVectorLayer : QgsMapLayer, QgsExpressionContextGenerator, QgsFeatureSin
     };
 
     QgsVectorLayer( const QString &path = QString(), const QString &baseName = QString(),
-                    const QString &providerLib = "ogr", bool loadDefaultStyleFlag = true );
+                    const QString &providerLib = "ogr", bool loadDefaultStyleFlag = true,
+                    bool readExtent = false );
 %Docstring
  Constructor - creates a vector layer
 
@@ -328,6 +329,7 @@ class QgsVectorLayer : QgsMapLayer, QgsExpressionContextGenerator, QgsFeatureSin
  \param  baseName The name used to represent the layer in the legend
  \param  providerLib  The name of the data provider, e.g., "memory", "postgres"
  \param  loadDefaultStyleFlag whether to load the default style
+ \param  readExtent Read extent from XML if true or let provider determine it if false
 %End
 
 
@@ -1727,6 +1729,25 @@ Returns the current blending mode for features
 .. versionadded:: 3.0
 %End
 
+    void setReadExtent( bool readExtent );
+%Docstring
+ Flag allowing to indicate if the extent has be read from the XML
+ document when data source has no metadata or if the data provider has
+ to determine it.
+
+.. versionadded:: 3.0
+%End
+
+    bool readExtent() const;
+%Docstring
+ Returns true if the extent is read from the XML document when data
+ source has no metadata, false if it's the data provider which determines
+ it.
+
+.. versionadded:: 3.0
+ :rtype: bool
+%End
+
   public slots:
 
     void select( QgsFeatureId featureId );

src/core/qgsproject.cpp

@@ -717,6 +717,16 @@ bool QgsProject::addLayer( const QDomElement &layerElem, QList<QDomNode> &broken
   if ( type == QLatin1String( "vector" ) )
   {
     mapLayer = new QgsVectorLayer;
+
+    // apply specific settings to vector layer
+    QgsSettings s;
+    if ( QgsVectorLayer *vl = qobject_cast<QgsVectorLayer *>( mapLayer ) )
+    {
+      if ( s.value( QStringLiteral( "/qgis/trustProject" ), false ).toBool() )
+      {
+        vl->setReadExtent( true );
+      }
+    }
   }
   else if ( type == QLatin1String( "raster" ) )
   {

src/core/qgsvectordataprovider.h

@@ -516,6 +516,14 @@ class CORE_EXPORT QgsVectorDataProvider : public QgsDataProvider, public QgsFeat
      */
     virtual QString translateMetadataValue( const QString &mdKey, const QVariant &value ) const { Q_UNUSED( mdKey ); return value.toString(); }
 
+    /** Returns true if the data source has metadata, false otherwise.
+     *
+     * \returns true if data source has metadata, false otherwise.
+     *
+     * \since QGIS 3.0
+     */
+    virtual bool hasMetadata() const { return true; };
+
   signals:
 
     /**

src/core/qgsvectorlayer.cpp

@@ -133,7 +133,8 @@ typedef bool deleteStyleById_t(
 QgsVectorLayer::QgsVectorLayer( const QString &vectorLayerPath,
                                 const QString &baseName,
                                 const QString &providerKey,
-                                bool loadDefaultStyleFlag )
+                                bool loadDefaultStyleFlag,
+                                bool readExtent )
   : QgsMapLayer( VectorLayer, baseName, vectorLayerPath )
   , mDataProvider( nullptr )
   , mProviderKey( providerKey )
@@ -153,6 +154,7 @@ QgsVectorLayer::QgsVectorLayer( const QString &vectorLayerPath,
   , mLazyExtent( true )
   , mSymbolFeatureCounted( false )
   , mEditCommandActive( false )
+  , mReadExtent( readExtent )
 
 {
   mActions = new QgsActionManager( this );
@@ -222,6 +224,7 @@ QgsVectorLayer *QgsVectorLayer::clone() const
   layer->setAttributeTableConfig( attributeTableConfig() );
   layer->setFeatureBlendMode( featureBlendMode() );
   layer->setOpacity( opacity() );
+  layer->setReadExtent( readExtent() );
 
   Q_FOREACH ( const QgsAction &action, actions()->actions() )
   {
@@ -800,8 +803,19 @@ QgsRectangle QgsVectorLayer::extent() const
 
   if ( !mValidExtent && mLazyExtent && mDataProvider )
   {
-    // get the extent
-    QgsRectangle mbr = mDataProvider->extent();
+    QgsRectangle mbr;
+
+    // get the extent from xml
+    if ( mReadExtent && !mXmlExtent.isNull() && !mDataProvider->hasMetadata() )
+    {
+      mbr = mXmlExtent;
+    }
+
+    // get the extent data provider if not yet defined
+    if ( mbr.isNull() )
+    {
+      mbr = mDataProvider->extent();
+    }
 
     // show the extent
     QgsDebugMsg( "Extent of layer: " + mbr.toString() );
@@ -1428,6 +1442,16 @@ bool QgsVectorLayer::readXml( const QDomNode &layer_node, const QgsReadWriteCont
 
   setLegend( QgsMapLayerLegend::defaultVectorLegend( this ) );
 
+  // read extent
+  if ( mReadExtent )
+  {
+    QDomNode extentNode = layer_node.namedItem( QStringLiteral( "extent" ) );
+    if ( !extentNode.isNull() )
+    {
+      mXmlExtent = QgsXmlUtils::readRectangle( extentNode.toElement() );
+    }
+  }
+
   return mValid;               // should be true if read successfully
 
 } // void QgsVectorLayer::readXml
@@ -4418,3 +4442,13 @@ QgsAbstractVectorLayerLabeling *QgsVectorLayer::readLabelingFromCustomProperties
 
   return labeling;
 }
+
+void QgsVectorLayer::setReadExtent( bool readExtent )
+{
+  mReadExtent = readExtent;
+}
+
+bool QgsVectorLayer::readExtent() const
+{
+  return mReadExtent;
+}

src/core/qgsvectorlayer.h

@@ -389,10 +389,12 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
      * \param  baseName The name used to represent the layer in the legend
      * \param  providerLib  The name of the data provider, e.g., "memory", "postgres"
      * \param  loadDefaultStyleFlag whether to load the default style
+     * \param  readExtent Read extent from XML if true or let provider determine it if false
      *
      */
     QgsVectorLayer( const QString &path = QString(), const QString &baseName = QString(),
-                    const QString &providerLib = "ogr", bool loadDefaultStyleFlag = true );
+                    const QString &providerLib = "ogr", bool loadDefaultStyleFlag = true,
+                    bool readExtent = false );
 
 
     virtual ~QgsVectorLayer();
@@ -1604,6 +1606,24 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
      */
     void setEditFormConfig( const QgsEditFormConfig &editFormConfig );
 
+    /**
+     * Flag allowing to indicate if the extent has be read from the XML
+     * document when data source has no metadata or if the data provider has
+     * to determine it.
+     *
+     * \since QGIS 3.0
+     */
+    void setReadExtent( bool readExtent );
+
+    /**
+     * Returns true if the extent is read from the XML document when data
+     * source has no metadata, false if it's the data provider which determines
+     * it.
+     *
+     * \since QGIS 3.0
+     */
+    bool readExtent() const;
+
   public slots:
 
     /**
@@ -2041,6 +2061,9 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
     //! True while an undo command is active
     bool mEditCommandActive;
 
+    bool mReadExtent;
+    QgsRectangle mXmlExtent;
+
     QgsFeatureIds mDeletedFids;
 
     QgsAttributeTableConfig mAttributeTableConfig;

src/providers/postgres/qgspostgresprovider.cpp

@@ -4291,6 +4291,19 @@ QgsPostgresProvider::Relkind QgsPostgresProvider::relkind() const
   return kind;
 }
 
+bool QgsPostgresProvider::hasMetadata() const
+{
+  bool hasMetadata = true;
+  QgsPostgresProvider::Relkind kind = relkind();
+
+  if ( kind == Relkind::View || kind == Relkind::MaterializedView )
+  {
+    hasMetadata = false;
+  }
+
+  return hasMetadata;
+}
+
 /**
  * Class factory to return a pointer to a newly created
  * QgsPostgresProvider object

src/providers/postgres/qgspostgresprovider.h

@@ -197,6 +197,17 @@ class QgsPostgresProvider : public QgsVectorDataProvider
     virtual QList<QgsRelation> discoverRelations( const QgsVectorLayer *self, const QList<QgsVectorLayer *> &layers ) const override;
     virtual QgsAttrPalIndexNameHash palAttributeIndexNames() const override;
 
+    /** Returns true if the data source has metadata, false otherwise. For
+     * example, if the kind of relation for the layer is a view or a
+     * materialized view, then no metadata are associated with the data
+     * source.
+     *
+     * \returns true if data source has metadata, false otherwise.
+     *
+     * \since QGIS 3.0
+     */
+    virtual bool hasMetadata() const override;
+
   signals:
 
     /**