Count qwt axes when removing a plot axis

ApplicationLibCode/FeatureTests/Tests/CMakeLists_files.cmake

@@ -13,6 +13,7 @@ set(SOURCE_GROUP_SOURCE_FILES
     ${CMAKE_CURRENT_LIST_DIR}/RicCreatePolygonFeature-Test.cpp
     ${CMAKE_CURRENT_LIST_DIR}/RicNewCellIndexFilterFeature-Test.cpp
     ${CMAKE_CURRENT_LIST_DIR}/RicExportScheduleFeature-Test.cpp
+    ${CMAKE_CURRENT_LIST_DIR}/RiuQwtPlotWidget-Test.cpp
 )
 
 list(APPEND SOURCE_FEATURETEST_FILES ${SOURCE_GROUP_SOURCE_FILES})

ApplicationLibCode/FeatureTests/Tests/RiuQwtPlotWidget-Test.cpp

@@ -0,0 +1,40 @@
+/////////////////////////////////////////////////////////////////////////////////
+//
+//  Copyright (C) 2026     Equinor ASA
+//
+//  ResInsight is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  ResInsight is distributed in the hope that it will be useful, but WITHOUT ANY
+//  WARRANTY; without even the implied warranty of MERCHANTABILITY or
+//  FITNESS FOR A PARTICULAR PURPOSE.
+//
+//  See the GNU General Public License at <http://www.gnu.org/licenses/gpl.html>
+//  for more details.
+//
+/////////////////////////////////////////////////////////////////////////////////
+
+#include "gtest/gtest.h"
+
+#include "RiuPlotAxis.h"
+#include "RiuQwtPlotWidget.h"
+
+//--------------------------------------------------------------------------------------------------
+/// Pruning must keep the axis mapping in sync with the axes owned by qwt. A stale mapping makes
+/// QwtPlot::axisScaleDraw() return null, which crashed enableAxisNumberLabels().
+//--------------------------------------------------------------------------------------------------
+TEST( RiuQwtPlotWidget, PruneAxesKeepsAxisMappingValid )
+{
+    RiuQwtPlotWidget plotWidget( nullptr );
+
+    plotWidget.pruneAxes( {} );
+    plotWidget.ensureAxisIsCreated( RiuPlotAxis( RiaDefines::PlotAxis::PLOT_AXIS_LEFT, 1 ) );
+    plotWidget.pruneAxes( {} );
+
+    plotWidget.enableAxis( RiuPlotAxis::defaultLeft(), true );
+    EXPECT_TRUE( plotWidget.axisEnabled( RiuPlotAxis::defaultLeft() ) );
+
+    plotWidget.enableAxisNumberLabels( RiuPlotAxis::defaultLeft(), true );
+}

ApplicationLibCode/UserInterface/RiuQwtPlotWidget.cpp

@@ -1689,27 +1689,18 @@ void RiuQwtPlotWidget::onMouseMoveEvent( QMouseEvent* event )
 //--------------------------------------------------------------------------------------------------
 void RiuQwtPlotWidget::moveAxis( RiuPlotAxis oldAxis, RiuPlotAxis newAxis )
 {
-    auto countAxis = [this]( RiaDefines::PlotAxis axis )
-    {
-        int count = 0;
-        for ( auto [plotAxis, qwtMapping] : m_axisMapping )
-        {
-            if ( plotAxis.axis() == axis ) count++;
-        }
-        return count;
-    };
-
     auto isLastItem = [this]( RiuPlotAxis plotAxis, int count )
     {
         auto qwtAxis = toQwtPlotAxis( plotAxis );
         return qwtAxis.id == ( count - 1 );
     };
 
-    auto removeAxis = [this, countAxis, isLastItem]( RiuPlotAxis plotAxis )
+    auto removeAxis = [this, isLastItem]( RiuPlotAxis plotAxis )
     {
         auto qwtAxisPos = RiuQwtPlotTools::toQwtPlotAxisEnum( plotAxis.axis() );
 
-        int count = countAxis( plotAxis.axis() );
+        // Count from qwt, not the mapping. Qwt keeps at least one axis per side, also when unmapped
+        int count = m_plot->axesCount( qwtAxisPos );
 
         bool isLast = isLastItem( plotAxis, count );
         if ( isLast )