From fc1ded802eefb6ba99156c33ddad15498442d256 Mon Sep 17 00:00:00 2001
From: Damiano Lombardi <damiano@opengis.ch>
Date: Thu, 10 Jun 2021 14:43:19 +0200
Subject: [PATCH] Fix #43539 Bad edit button states in relation editor widget
 for n:m relations (#43579)

* Fix #43539

Use QgsVectorLayer::supportsEditing() instead of QgsVectorLayer::Capability::ChangeAttributeValues

Additional fix link and save edit buttons enabled/disabled correctly
when only the final or the middle table are editable

* Layers should not read only

* Toggle button enabled if at least one involved layer supports editing
---
 src/gui/qgsrelationeditorwidget.cpp | 34 ++++++++---------------------
 1 file changed, 9 insertions(+), 25 deletions(-)

diff --git a/src/gui/qgsrelationeditorwidget.cpp b/src/gui/qgsrelationeditorwidget.cpp
index 24e0a0a0a6e3..9b7b9d56d9fe 100644
--- a/src/gui/qgsrelationeditorwidget.cpp
+++ b/src/gui/qgsrelationeditorwidget.cpp
@@ -273,6 +273,7 @@ void QgsRelationEditorWidget::setViewMode( QgsDualView::ViewMode mode )
 
 void QgsRelationEditorWidget::updateButtons()
 {
+  bool toggleEditingButtonEnabled = false;
   bool editable = false;
   bool linkable = false;
   bool spatial = false;
@@ -280,6 +281,7 @@ void QgsRelationEditorWidget::updateButtons()
 
   if ( mRelation.isValid() )
   {
+    toggleEditingButtonEnabled = mRelation.referencingLayer()->supportsEditing();
     editable = mRelation.referencingLayer()->isEditable();
     linkable = mRelation.referencingLayer()->isEditable();
     spatial = mRelation.referencingLayer()->isSpatial();
@@ -287,10 +289,12 @@ void QgsRelationEditorWidget::updateButtons()
 
   if ( mNmRelation.isValid() )
   {
+    toggleEditingButtonEnabled |= mNmRelation.referencedLayer()->supportsEditing();
     editable = mNmRelation.referencedLayer()->isEditable();
     spatial = mNmRelation.referencedLayer()->isSpatial();
   }
 
+  mToggleEditingButton->setEnabled( toggleEditingButtonEnabled );
   mAddFeatureButton->setEnabled( editable );
   mAddFeatureGeometryButton->setEnabled( editable );
   mDuplicateFeatureButton->setEnabled( editable && selectionNotEmpty );
@@ -299,7 +303,7 @@ void QgsRelationEditorWidget::updateButtons()
   mUnlinkFeatureButton->setEnabled( linkable && selectionNotEmpty );
   mZoomToFeatureButton->setEnabled( selectionNotEmpty );
   mToggleEditingButton->setChecked( editable );
-  mSaveEditsButton->setEnabled( editable );
+  mSaveEditsButton->setEnabled( editable || linkable );
 
   mToggleEditingButton->setVisible( !mLayerInSameTransactionGroup );
 
@@ -503,25 +507,16 @@ void QgsRelationEditorWidget::beforeSetRelationFeature( const QgsRelation &newRe
 
 void QgsRelationEditorWidget::afterSetRelationFeature()
 {
-  mToggleEditingButton->setEnabled( false );
-
   if ( ! mRelation.isValid() )
+  {
+    updateButtons();
     return;
+  }
 
   connect( mRelation.referencingLayer(), &QgsVectorLayer::editingStarted, this, &QgsRelationEditorWidget::updateButtons );
   connect( mRelation.referencingLayer(), &QgsVectorLayer::editingStopped, this, &QgsRelationEditorWidget::updateButtons );
 
-  QgsVectorLayer *vl = mRelation.referencingLayer();
-  bool canChangeAttributes = vl->dataProvider()->capabilities() & QgsVectorDataProvider::ChangeAttributeValues;
-  if ( canChangeAttributes && !vl->readOnly() )
-  {
-    mToggleEditingButton->setEnabled( true );
-    updateButtons();
-  }
-  else
-  {
-    mToggleEditingButton->setEnabled( false );
-  }
+  updateButtons();
 
   QgsFeatureRequest myRequest = mRelation.getRelatedFeaturesRequest( mFeature );
   initDualView( mRelation.referencingLayer(), myRequest );
@@ -559,17 +554,6 @@ void QgsRelationEditorWidget::afterSetRelations()
     connect( mNmRelation.referencedLayer(), &QgsVectorLayer::editingStopped, this, &QgsRelationEditorWidget::updateButtons );
   }
 
-  QgsVectorLayer *vl = mRelation.referencingLayer();
-  bool canChangeAttributes = vl->dataProvider()->capabilities() & QgsVectorDataProvider::ChangeAttributeValues;
-  if ( canChangeAttributes && !vl->readOnly() )
-  {
-    mToggleEditingButton->setEnabled( true );
-  }
-  else
-  {
-    mToggleEditingButton->setEnabled( false );
-  }
-
   updateButtons();
 }