QgsReadWriteContext: add a category stack to know where the error message comes from

also change the QPair in favor of a struct for a better API

python/core/qgsproject.sip.in

@@ -912,7 +912,7 @@ Emitted when a layer from a projects was read.
 
     void loadingLayer( const QString &layerName );
 
-    void loadingLayerMessages( const QString &layerName, const QList<QPair<Qgis::MessageLevel, QString>> &messages );
+    void loadingLayerMessages( const QString &layerName, const QList<QgsReadWriteContext::ReadWriteMessage> &messages );
 %Docstring
  Emitted when loading layers has produced some messages
 @param layerName the layer name

python/core/qgsreadwritecontext.sip.in

@@ -22,11 +22,37 @@ The class is used as a container of context for various read/write operations on
 %End
   public:
 
+    struct ReadWriteMessage
+    {
+        ReadWriteMessage( const QString &message, Qgis::MessageLevel level = Qgis::Warning,  QStringList categories = QStringList() );
+%Docstring
+Construct a container for QgsReadWriteContext error or warning messages
+%End
+
+        QString message() const;
+%Docstring
+Return the message string
+%End
+
+        Qgis::MessageLevel level() const;
+%Docstring
+Return the message level
+%End
+
+        QStringList categories() const;
+%Docstring
+Return the stack of categories of the message
+%End
+
+    };
+
     QgsReadWriteContext();
 %Docstring
 Constructor for QgsReadWriteContext.
 %End
 
+    ~QgsReadWriteContext();
+
     const QgsPathResolver &pathResolver() const;
 %Docstring
 Returns path resolver for conversion between relative and absolute paths
@@ -37,14 +63,32 @@ Returns path resolver for conversion between relative and absolute paths
 Sets up path resolver for conversion between relative and absolute paths
 %End
 
-    void pushMessage( Qgis::MessageLevel level, const QString &message );
+    void pushMessage( const QString &message, Qgis::MessageLevel level );
 %Docstring
 append a message to the context
+
+.. versionadded:: 3.2
 %End
 
-    QList<QPair<Qgis::MessageLevel, QString>> takeMessages();
+    void enterCategory( const QString &category, const QString &details = QString() );
+%Docstring
+Push a category to the stack
+
+.. versionadded:: 3.2
+%End
+
+    void leaveCategory();
+%Docstring
+Pop the last category
+
+.. versionadded:: 3.2
+%End
+
+    QList<QgsReadWriteContext::ReadWriteMessage> takeMessages();
 %Docstring
 return the stored messages and remove them
+
+.. versionadded:: 3.2
 %End
 
 };

src/app/qgisapp.cpp

@@ -11240,11 +11240,11 @@ void QgisApp::showStatusMessage( const QString &message )
   mStatusBar->showMessage( message );
 }
 
-void QgisApp::loadingLayerMessages( const QString &layerName, const QList<QPair<Qgis::MessageLevel, QString> > &messages )
+void QgisApp::loadingLayerMessages( const QString &layerName, const QList<QgsReadWriteContext::ReadWriteMessage> &messages )
 {
   for ( const auto message : messages )
   {
-    messageBar()->pushMessage( layerName, message.second, message.first );
+    messageBar()->pushMessage( layerName, message.message(), message.level() );
   }
 }
 

src/app/qgisapp.h

@@ -926,7 +926,7 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
     void showProgress( int progress, int totalSteps );
     void showStatusMessage( const QString &message );
 
-    void loadingLayerMessages( const QString &layerName, const QList<QPair<Qgis::MessageLevel, QString>> &messages );
+    void loadingLayerMessages( const QString &layerName, const QList<QgsReadWriteContext::ReadWriteMessage> &messages );
 
     //! set the active layer
     bool setActiveLayer( QgsMapLayer * );

src/core/qgseditformconfig.cpp

@@ -260,6 +260,7 @@ void QgsEditFormConfig::setSuppress( QgsEditFormConfig::FeatureFormSuppress s )
 
 void QgsEditFormConfig::readXml( const QDomNode &node, QgsReadWriteContext &context )
 {
+  context.enterCategory( QString( "Edit form config" ) );
   d.detach();
 
   QDomNode editFormNode = node.namedItem( QStringLiteral( "editform" ) );
@@ -387,6 +388,8 @@ void QgsEditFormConfig::readXml( const QDomNode &node, QgsReadWriteContext &cont
       onRelationsLoaded();
     }
   }
+
+  context.leaveCategory();
 }
 
 void QgsEditFormConfig::writeXml( QDomNode &node, const QgsReadWriteContext &context ) const

src/core/qgsmaplayer.cpp

@@ -430,6 +430,8 @@ bool QgsMapLayer::readLayerXml( const QDomElement &layerElement,  QgsReadWriteCo
   // the subclass can also read custom properties
   readCustomProperties( layerElement );
 
+  context.enterCategory( tr( "Layer" ), mne.text() );
+
   // now let the children grab what they need from the Dom node.
   layerError = !readXml( layerElement, context );
 
@@ -555,6 +557,8 @@ bool QgsMapLayer::readLayerXml( const QDomElement &layerElement,  QgsReadWriteCo
   QDomElement metadataElem = layerElement.firstChildElement( QStringLiteral( "resourceMetadata" ) );
   mMetadata.readMetadataXml( metadataElem );
 
+  context.leaveCategory();
+
   return true;
 } // bool QgsMapLayer::readLayerXML
 

src/core/qgsproject.h

@@ -42,6 +42,7 @@
 #include "qgsmaplayer.h"
 #include "qgsmaplayerstore.h"
 #include "qgsarchive.h"
+#include "qgsreadwritecontext.h"
 
 class QFileInfo;
 class QDomDocument;
@@ -894,7 +895,7 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      * @param layerName the layer name
      * @param messages a list of pairs of Qgis::MessageLevel and messages
      */
-    void loadingLayerMessages( const QString &layerName, const QList<QPair<Qgis::MessageLevel, QString>> &messages );
+    void loadingLayerMessages( const QString &layerName, const QList<QgsReadWriteContext::ReadWriteMessage> &messages );
 
     //! Emitted when the list of layer which are excluded from map identification changes
     void nonIdentifiableLayersChanged( QStringList nonIdentifiableLayers );

src/core/qgsreadwritecontext.cpp

@@ -13,3 +13,45 @@
  *                                                                         *
  ***************************************************************************/
 #include "qgsreadwritecontext.h"
+
+QgsReadWriteContext::~QgsReadWriteContext()
+{
+  // be sure that categories have been emptied
+  Q_ASSERT( mCategories.isEmpty() );
+}
+
+const QgsPathResolver &QgsReadWriteContext::pathResolver() const
+{
+  return mPathResolver;
+}
+
+void QgsReadWriteContext::setPathResolver( const QgsPathResolver &resolver )
+{
+  mPathResolver = resolver;
+}
+
+void QgsReadWriteContext::pushMessage( const QString &message, Qgis::MessageLevel level )
+{
+  mMessages.append( ReadWriteMessage( message, level, mCategories ) );
+}
+
+void QgsReadWriteContext::enterCategory( const QString &category, const QString &details )
+{
+  QString message = category;
+  if ( !details.isEmpty() )
+    message.append( QString( " :: %1" ).arg( details ) );
+  mCategories.push_front( message );
+}
+
+void QgsReadWriteContext::leaveCategory()
+{
+  if ( !mCategories.isEmpty() )
+    mCategories.pop_front();
+}
+
+QList<QgsReadWriteContext::ReadWriteMessage > QgsReadWriteContext::takeMessages()
+{
+  QList<QgsReadWriteContext::ReadWriteMessage > messages = mMessages;
+  mMessages.clear();
+  return messages;
+}

src/core/qgsreadwritecontext.h

@@ -31,26 +31,75 @@ class CORE_EXPORT QgsReadWriteContext
 {
   public:
 
+    /**
+     * Struct for QgsReadWriteContext error or warning messages
+     * \since QGIS 3.2
+     */
+    struct ReadWriteMessage
+    {
+        //! Construct a container for QgsReadWriteContext error or warning messages
+        ReadWriteMessage( const QString &message, Qgis::MessageLevel level = Qgis::Warning,  QStringList categories = QStringList() )
+          : mMessage( message )
+          , mLevel( level )
+          , mCategories( categories )
+        {}
+
+        //! Return the message string
+        QString message() const {return mMessage;}
+
+        //! Return the message level
+        Qgis::MessageLevel level() const {return mLevel;}
+
+        //! Return the stack of categories of the message
+        QStringList categories() const {return mCategories;}
+
+      private:
+        QString mMessage = QString();
+        Qgis::MessageLevel mLevel = Qgis::Warning;
+        QStringList mCategories = QStringList();
+    };
+
     /**
      * Constructor for QgsReadWriteContext.
      */
     QgsReadWriteContext() = default;
 
+    ~QgsReadWriteContext();
+
     //! Returns path resolver for conversion between relative and absolute paths
-    const QgsPathResolver &pathResolver() const { return mPathResolver; }
+    const QgsPathResolver &pathResolver() const;
 
     //! Sets up path resolver for conversion between relative and absolute paths
-    void setPathResolver( const QgsPathResolver &resolver ) { mPathResolver = resolver; }
+    void setPathResolver( const QgsPathResolver &resolver );
 
-    //! append a message to the context
-    void pushMessage( Qgis::MessageLevel level, const QString &message ) {mMessages.append( qMakePair( level, message ) );}
+    /**
+     * append a message to the context
+     * \since QGIS 3.2
+     */
+    void pushMessage( const QString &message, Qgis::MessageLevel level );
 
-    //! return the stored messages and remove them
-    QList<QPair<Qgis::MessageLevel, QString>> takeMessages() {return mMessages; mMessages.clear();}
+    /**
+     * Push a category to the stack
+     * \since QGIS 3.2
+     */
+    void enterCategory( const QString &category, const QString &details = QString() );
+
+    /**
+     * Pop the last category
+     * \since QGIS 3.2
+     */
+    void leaveCategory();
+
+    /**
+     * return the stored messages and remove them
+     * \since QGIS 3.2
+     */
+    QList<QgsReadWriteContext::ReadWriteMessage> takeMessages();
 
   private:
     QgsPathResolver mPathResolver;
-    QList<QPair<Qgis::MessageLevel, QString>> mMessages;
+    QList<ReadWriteMessage> mMessages;
+    QStringList mCategories = QStringList();
 };
 
 #endif // QGSREADWRITECONTEXT_H

src/core/qgsvectorlayer.cpp

@@ -1688,6 +1688,8 @@ void QgsVectorLayer::resolveReferences( QgsProject *project )
 
 bool QgsVectorLayer::readSymbology( const QDomNode &layerNode, QString &errorMessage, QgsReadWriteContext &context )
 {
+  context.enterCategory( tr( "Symbology" ) );
+
   if ( !mExpressionFieldBuffer )
     mExpressionFieldBuffer = new QgsExpressionFieldBuffer();
   mExpressionFieldBuffer->readXml( layerNode );
@@ -1873,6 +1875,8 @@ bool QgsVectorLayer::readSymbology( const QDomNode &layerNode, QString &errorMes
 
   updateFields();
 
+  context.leaveCategory();
+
   return true;
 }