Atlas scope variables are all static

These won't be changed in the lifetime of the scope, which will
only ever be used for a single atlas feature only

Marking them as static means that the expression preparation
of atlas related expressions can replace any use of @atlas* vars
with static precalculated nodes, resulting in a nice performance
boost when working with complex atlas setups.

src/core/expression/qgsexpressioncontextutils.cpp

@@ -650,18 +650,18 @@ QgsExpressionContextScope *QgsExpressionContextUtils::atlasScope( const QgsLayou
   {
     //add some dummy atlas variables. This is done so that as in certain contexts we want to show
     //users that these variables are available even if they have no current value
-    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_pagename" ), QString(), true ) );
-    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_feature" ), QVariant::fromValue( QgsFeature() ), true ) );
-    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_featureid" ), QVariant(), true ) );
-    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_geometry" ), QVariant::fromValue( QgsGeometry() ), true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_pagename" ), QString(), true, true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_feature" ), QVariant::fromValue( QgsFeature() ), true, true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_featureid" ), QVariant(), true, true ) );
+    scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_geometry" ), QVariant::fromValue( QgsGeometry() ), true, true ) );
     return scope;
   }
 
   //add known atlas variables
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_totalfeatures" ), atlas->count(), true ) );
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_featurenumber" ), atlas->currentFeatureNumber() + 1, true ) );
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_filename" ), atlas->currentFilename(), true ) );
-  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_pagename" ), atlas->nameForPage( atlas->currentFeatureNumber() ), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_totalfeatures" ), atlas->count(), true, true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_featurenumber" ), atlas->currentFeatureNumber() + 1, true, true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_filename" ), atlas->currentFilename(), true, true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "atlas_pagename" ), atlas->nameForPage( atlas->currentFeatureNumber() ), true, true ) );
 
   if ( atlas->enabled() && atlas->coverageLayer() )
   {