Fix some layout expression context handling, restore some tests

python/core/layout/qgslayoutitem.sip

@@ -979,6 +979,9 @@ Rotates the item by a specified ``angle`` in degrees clockwise around a specifie
 .. seealso:: :py:func:`itemRotation()`
 %End
 
+    virtual QgsExpressionContext createExpressionContext() const;
+
+
   signals:
 
     void frameChanged();

python/core/layout/qgslayoutpagecollection.sip

@@ -59,6 +59,7 @@ A None is returned if an invalid page number is specified.
 .. seealso:: :py:func:`pages()`
 %End
 
+
     int pageNumber( QgsLayoutItemPage *page ) const;
 %Docstring
 Returns the page number for the specified ``page``, or -1 if the page

python/core/qgsexpressioncontext.sip

@@ -1055,7 +1055,7 @@ For instance, current page name and number.
 
     static QgsExpressionContextScope *atlasScope( const QgsLayoutAtlas *atlas ) /Factory/;
 %Docstring
-Creates a new scope which contains variables and functions relating to a QgsLayoutAtlas.
+Creates a new scope which contains variables and functions relating to a :py:class:`QgsLayoutAtlas`.
 For instance, current page name and number.
 
 :param atlas: source atlas. If null, a set of default atlas variables will be added to the scope.
@@ -1067,6 +1067,14 @@ Creates a new scope which contains variables and functions relating to a :py:cla
 For instance, item size and position.
 
 :param composerItem: source composer item
+%End
+
+    static QgsExpressionContextScope *layoutItemScope( const QgsLayoutItem *item ) /Factory/;
+%Docstring
+Creates a new scope which contains variables and functions relating to a :py:class:`QgsLayoutItem`.
+For instance, item size and position.
+
+.. versionadded:: 3.0
 %End
 
     static void setComposerItemVariable( QgsComposerItem *composerItem, const QString &name, const QVariant &value );

src/core/layout/qgslayoutitem.cpp

@@ -1091,6 +1091,13 @@ void QgsLayoutItem::rotateItem( const double angle, const QPointF &transformOrig
   refreshItemRotation( &itemTransformOrigin );
 }
 
+QgsExpressionContext QgsLayoutItem::createExpressionContext() const
+{
+  QgsExpressionContext context = QgsLayoutObject::createExpressionContext();
+  context.appendScope( QgsExpressionContextUtils::layoutItemScope( this ) );
+  return context;
+}
+
 
 void QgsLayoutItem::refresh()
 {

src/core/layout/qgslayoutitem.h

@@ -886,6 +886,8 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
     */
     virtual void rotateItem( const double angle, const QPointF &transformOrigin );
 
+    QgsExpressionContext createExpressionContext() const override;
+
   signals:
 
     /**

src/core/layout/qgslayoutpagecollection.cpp

@@ -444,6 +444,11 @@ QgsLayoutItemPage *QgsLayoutPageCollection::page( int pageNumber )
   return mPages.value( pageNumber );
 }
 
+const QgsLayoutItemPage *QgsLayoutPageCollection::page( int pageNumber ) const
+{
+  return mPages.value( pageNumber );
+}
+
 int QgsLayoutPageCollection::pageNumber( QgsLayoutItemPage *page ) const
 {
   return mPages.indexOf( page );

src/core/layout/qgslayoutpagecollection.h

@@ -76,6 +76,16 @@ class CORE_EXPORT QgsLayoutPageCollection : public QObject, public QgsLayoutSeri
      */
     QgsLayoutItemPage *page( int pageNumber );
 
+    /**
+     * Returns a specific page (by \a pageNumber) from the collection.
+     * Internal page numbering starts at 0 - so a \a pageNumber of 0
+     * corresponds to the first page in the collection.
+     * A nullptr is returned if an invalid page number is specified.
+     * \see pages()
+     * \note Not available in Python bindings.
+     */
+    const QgsLayoutItemPage *page( int pageNumber ) const SIP_SKIP;
+
     /**
      * Returns the page number for the specified \a page, or -1 if the page
      * is not contained in the collection.

src/core/qgsexpressioncontext.cpp

@@ -33,6 +33,7 @@
 #include "qgsprocessingalgorithm.h"
 #include "qgslayoutatlas.h"
 #include "qgslayout.h"
+#include "qgslayoutpagecollection.h"
 
 #include <QSettings>
 #include <QDir>
@@ -700,6 +701,41 @@ class GetComposerItemVariables : public QgsScopedExpressionFunction
 
 };
 
+class GetLayoutItemVariables : public QgsScopedExpressionFunction
+{
+  public:
+    GetLayoutItemVariables( const QgsLayout *c )
+      : QgsScopedExpressionFunction( QStringLiteral( "item_variables" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "id" ) ), QStringLiteral( "Layout" ) )
+      , mLayout( c )
+    {}
+
+    QVariant func( const QVariantList &values, const QgsExpressionContext *, QgsExpression *, const QgsExpressionNodeFunction * ) override
+    {
+      if ( !mLayout )
+        return QVariant();
+
+      QString id = values.at( 0 ).toString().toLower();
+
+      const QgsLayoutItem *item = mLayout->itemByUuid( id );
+      if ( !item )
+        return QVariant();
+
+      QgsExpressionContext c = item->createExpressionContext();
+
+      return c.variablesToMap();
+    }
+
+    QgsScopedExpressionFunction *clone() const override
+    {
+      return new GetLayoutItemVariables( mLayout );
+    }
+
+  private:
+
+    const QgsLayout *mLayout = nullptr;
+
+};
+
 class GetLayerVisibility : public QgsScopedExpressionFunction
 {
   public:
@@ -1079,16 +1115,34 @@ QgsExpressionContextScope *QgsExpressionContextUtils::layoutScope( const QgsLayo
 
   //add known layout context variables
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_name" ), layout->name(), true ) );
-#if 0 //TODO
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_numpages" ), composition->numPages(), true ) );
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pageheight" ), composition->paperHeight(), true ) );
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pagewidth" ), composition->paperWidth(), true ) );
+
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_numpages" ), layout->pageCollection()->pageCount(), true ) );
+  if ( layout->pageCollection()->pageCount() > 0 )
+  {
+    // just take first page size
+    QSizeF s = layout->pageCollection()->page( 0 )->sizeWithUnits().toQSizeF();
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pageheight" ), s.height(), true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pagewidth" ), s.width(), true ) );
+  }
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_dpi" ), layout->context().dpi(), true ) );
-#endif
 
-#if 0 //TODO
-  scope->addFunction( QStringLiteral( "item_variables" ), new GetComposerItemVariables( composition ) );
-#endif
+  scope->addFunction( QStringLiteral( "item_variables" ), new GetLayoutItemVariables( layout ) );
+
+  if ( layout->context().layer() )
+  {
+    scope->setFields( layout->context().layer()->fields() );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_layerid" ), layout->context().layer()->id(), true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_layername" ), layout->context().layer()->name(), true ) );
+  }
+
+  if ( layout->context().feature().isValid() )
+  {
+    QgsFeature atlasFeature = layout->context().feature();
+    scope->setFeature( atlasFeature );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_feature" ), QVariant::fromValue( atlasFeature ), true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_featureid" ), atlasFeature.id(), true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_geometry" ), QVariant::fromValue( atlasFeature.geometry() ), true ) );
+  }
 
   return scope.release();
 }
@@ -1233,6 +1287,52 @@ QgsExpressionContextScope *QgsExpressionContextUtils::composerItemScope( const Q
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "item_id" ), composerItem->id(), true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "item_uuid" ), composerItem->uuid(), true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_page" ), composerItem->page(), true ) );
+  return scope;
+}
+
+QgsExpressionContextScope *QgsExpressionContextUtils::layoutItemScope( const QgsLayoutItem *item )
+{
+  QgsExpressionContextScope *scope = new QgsExpressionContextScope( QObject::tr( "Layout Item" ) );
+  if ( !item )
+    return scope;
+
+  //add variables defined in composer item properties
+  const QStringList variableNames = item->customProperty( QStringLiteral( "variableNames" ) ).toStringList();
+  const QStringList variableValues = item->customProperty( QStringLiteral( "variableValues" ) ).toStringList();
+
+  int varIndex = 0;
+  for ( const QString &variableName : variableNames )
+  {
+    if ( varIndex >= variableValues.length() )
+    {
+      break;
+    }
+
+    QVariant varValue = variableValues.at( varIndex );
+    varIndex++;
+    scope->setVariable( variableName, varValue );
+  }
+
+  //add known composer item context variables
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "item_id" ), item->id(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "item_uuid" ), item->uuid(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_page" ), item->page() + 1, true ) );
+
+  if ( item->layout() )
+  {
+    const QgsLayoutItemPage *page = item->layout()->pageCollection()->page( item->page() );
+    if ( page )
+    {
+      const QSizeF s = page->sizeWithUnits().toQSizeF();
+      scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pageheight" ), s.height(), true ) );
+      scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pagewidth" ), s.width(), true ) );
+    }
+    else
+    {
+      scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pageheight" ), QVariant(), true ) );
+      scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "layout_pagewidth" ), QVariant(), true ) );
+    }
+  }
 
   return scope;
 }

src/core/qgsexpressioncontext.h

@@ -41,6 +41,7 @@ class QgsSymbol;
 class QgsProcessingAlgorithm;
 class QgsProcessingContext;
 class QgsLayoutAtlas;
+class QgsLayoutItem;
 
 /**
  * \ingroup core
@@ -943,6 +944,13 @@ class CORE_EXPORT QgsExpressionContextUtils
      */
     static QgsExpressionContextScope *composerItemScope( const QgsComposerItem *composerItem ) SIP_FACTORY;
 
+    /**
+     * Creates a new scope which contains variables and functions relating to a QgsLayoutItem.
+     * For instance, item size and position.
+     * \since QGIS 3.0
+     */
+    static QgsExpressionContextScope *layoutItemScope( const QgsLayoutItem *item ) SIP_FACTORY;
+
     /**
      * Sets a composer item context variable. This variable will be contained within scopes retrieved via
      * composerItemScope().

tests/src/core/testqgslayoutitem.cpp

@@ -168,6 +168,7 @@ class TestQgsLayoutItem: public QObject
     void excludeFromExports();
     void setSceneRect();
     void page();
+    void itemVariablesFunction();
 
   private:
 
@@ -1386,6 +1387,41 @@ void TestQgsLayoutItem::page()
   QCOMPARE( item->positionWithUnits(), QgsLayoutPoint( 5, 38, QgsUnitTypes::LayoutCentimeters ) );
 }
 
+void TestQgsLayoutItem::itemVariablesFunction()
+{
+  QgsRectangle extent( 2000, 2800, 2500, 2900 );
+  QgsLayout l( QgsProject::instance() );
+
+  QgsExpression e( QStringLiteral( "map_get( item_variables( 'map_id' ), 'map_scale' )" ) );
+  // no map
+  QgsExpressionContext c = l.createExpressionContext();
+  QVariant r = e.evaluate( &c );
+  QVERIFY( !r.isValid() );
+
+  QgsLayoutItemMap *map = new QgsLayoutItemMap( &l );
+  map->setExtent( extent );
+  map->attemptSetSceneRect( QRectF( 30, 60, 200, 100 ) );
+  map->setCrs( QgsCoordinateReferenceSystem( QStringLiteral( "EPSG:4326" ) ) );
+  l.addLayoutItem( map );
+  map->setId( QStringLiteral( "map_id" ) );
+
+  c = l.createExpressionContext();
+  r = e.evaluate( &c );
+  QGSCOMPARENEAR( r.toDouble(), 1.38916e+08, 100 );
+
+  QgsExpression e2( QStringLiteral( "map_get( item_variables( 'map_id' ), 'map_crs' )" ) );
+  r = e2.evaluate( &c );
+  QCOMPARE( r.toString(), QString( "EPSG:4326" ) );
+
+  QgsExpression e3( QStringLiteral( "map_get( item_variables( 'map_id' ), 'map_crs_definition' )" ) );
+  r = e3.evaluate( &c );
+  QCOMPARE( r.toString(), QString( "+proj=longlat +datum=WGS84 +no_defs" ) );
+
+  QgsExpression e4( QStringLiteral( "map_get( item_variables( 'map_id' ), 'map_units' )" ) );
+  r = e4.evaluate( &c );
+  QCOMPARE( r.toString(), QString( "degrees" ) );
+}
+
 void TestQgsLayoutItem::rotation()
 {
   QgsProject proj;