move logic to QgsProcessingUtils and create a convenient method resolveDefaultEncoding()

python/core/auto_generated/processing/qgsprocessingutils.sip.in

@@ -615,6 +615,16 @@ Pre-processes a set of ``parameter`` values for the qgis_process command.
 In particular, this function upgrades encoded data defined values to :py:class:`QgsProperty` objects.
 
 .. versionadded:: 3.30
+%End
+
+    static QString resolveDefaultEncoding();
+%Docstring
+Returns the default encoding.
+
+The default encoding could be the one from "/Processing/encoding" or when it's not an allowed encoding name
+like "System", the default encoding system (mostly UTF-8 on Unix-like, windows-1252 on Windows).
+
+.. versionadded:: 3.32
 %End
 
 };

python/plugins/processing/tools/dataobjects.py

@@ -29,12 +29,13 @@ from qgis.core import (QgsDataProvider,
                        QgsProject,
                        QgsSettings,
                        QgsProcessingContext,
+                       QgsProcessingUtils,
                        QgsFeatureRequest,
                        QgsExpressionContext,
                        QgsExpressionContextUtils,
                        QgsExpressionContextScope)
 from qgis.gui import QgsSublayersDialog
-from qgis.PyQt.QtCore import QCoreApplication, QTextCodec
+from qgis.PyQt.QtCore import QCoreApplication
 from qgis.utils import iface
 
 from processing.core.ProcessingConfig import ProcessingConfig
@@ -70,11 +71,7 @@ def createContext(feedback=None):
     context.setInvalidGeometryCheck(invalid_features_method)
 
     settings = QgsSettings()
-    default_codec = "System"
+    context.setDefaultEncoding(settings.value("/Processing/encoding", QgsProcessingUtils.resolveDefaultEncoding()))
-    system_codec = QTextCodec.codecForLocale()
-    if (system_codec):
-        default_codec = system_codec.name().data().decode()
-    context.setDefaultEncoding(settings.value("/Processing/encoding", default_codec))
 
     context.setExpressionContext(createExpressionContext())
 

src/core/processing/qgsprocessingutils.cpp

@@ -38,6 +38,7 @@
 #include "qgsannotationlayer.h"
 #include "qgstiledmeshlayer.h"
 #include <QRegularExpression>
+#include <QTextCodec>
 #include <QUuid>
 
 QList<QgsRasterLayer *> QgsProcessingUtils::compatibleRasterLayers( QgsProject *project, bool sort )
@@ -1573,6 +1574,20 @@ QVariantMap QgsProcessingUtils::preprocessQgisProcessParameters( const QVariantM
   return output;
 }
 
+QString QgsProcessingUtils::resolveDefaultEncoding( const QString &defaultEncoding )
+{
+  if ( ! QTextCodec::availableCodecs().contains( defaultEncoding.toLatin1() ) )
+  {
+    const QString systemCodec = QTextCodec::codecForLocale()->name();
+    if ( ! systemCodec.isEmpty() )
+    {
+      return systemCodec;
+    }
+  }
+
+  return defaultEncoding;
+}
+
 //
 // QgsProcessingFeatureSource
 //

src/core/processing/qgsprocessingutils.h

@@ -589,6 +589,16 @@ class CORE_EXPORT QgsProcessingUtils
      */
     static QVariantMap preprocessQgisProcessParameters( const QVariantMap &parameters, bool &ok, QString &error );
 
+    /**
+     * Returns the default encoding.
+     *
+     * The default encoding could be the one from "/Processing/encoding" or when it's not an allowed encoding name
+     * like "System", the default encoding system (mostly UTF-8 on Unix-like, windows-1252 on Windows).
+     *
+     * \since QGIS 3.32
+     */
+    static QString resolveDefaultEncoding(const QString &defaultEncoding = "System");
+
   private:
     static bool canUseLayer( const QgsRasterLayer *layer );
     static bool canUseLayer( const QgsMeshLayer *layer );

src/gui/processing/qgsprocessingoutputdestinationwidget.cpp

@@ -53,17 +53,8 @@ QgsProcessingLayerOutputDestinationWidget::QgsProcessingLayerOutputDestinationWi
   mSelectButton->setPopupMode( QToolButton::InstantPopup );
 
   QgsSettings settings;
-  mEncoding = settings.value( QStringLiteral( "/Processing/encoding" ), QStringLiteral( "System" ) ).toString();
+  mEncoding = QgsProcessingUtils::resolveDefaultEncoding( settings.value( QStringLiteral( "/Processing/encoding" ), QStringLiteral( "System" ) ).toString() );
-
-  if ( ( mEncoding == "System" ) || ( ! QTextCodec::availableCodecs().contains( mEncoding.toLatin1() ) ) )
-  {
-    const QString systemCodec = QTextCodec::codecForLocale()->name();
-    if ( ! systemCodec.isEmpty() )
-    {
-      mEncoding = systemCodec;
   settings.setValue( QStringLiteral( "/Processing/encoding" ), mEncoding );
-    }
-  }
 
   if ( !mParameter->defaultValueForGui().isValid() )
   {
@@ -614,18 +605,11 @@ void QgsProcessingLayerOutputDestinationWidget::selectEncoding()
   QgsEncodingSelectionDialog dialog( this, tr( "File encoding" ), mEncoding );
   if ( dialog.exec() )
   {
-    mEncoding = dialog.encoding();
+    mEncoding = QgsProcessingUtils::resolveDefaultEncoding( dialog.encoding() );
-    if ( ( mEncoding == "System" ) || ( ! QTextCodec::availableCodecs().contains( mEncoding.toLatin1() ) ) )
-    {
-      const QString systemCodec = QTextCodec::codecForLocale()->name();
-      if ( ! systemCodec.isEmpty() )
-      {
-        mEncoding = systemCodec;
-      }
-    }
 
     QgsSettings settings;
     settings.setValue( QStringLiteral( "/Processing/encoding" ), mEncoding );
+
     emit destinationChanged();
   }
 }