Don't allow pins with NC electrical type to join other nets

Fixes https://gitlab.com/kicad/code/kicad/-/issues/1826

eeschema/dialogs/dialog_erc.cpp

@@ -326,6 +326,9 @@ void DIALOG_ERC::TestErc( REPORTER& aReporter )
     if( settings.IsTestEnabled( ERCE_UNRESOLVED_VARIABLE ) )
         tester.TestTextVars( m_parent->GetCanvas()->GetView()->GetWorksheet() );
 
+    if( settings.IsTestEnabled( ERCE_NOCONNECT_CONNECTED ) )
+        tester.TestNoConnectPins();
+
     // Display diags:
     m_markerTreeModel->SetProvider( m_markerProvider );
 

eeschema/erc.cpp

@@ -525,6 +525,46 @@ void ERC_TESTER::TestOthersItems( NETLIST_OBJECT_LIST* aList, unsigned aNetItemR
     }
 }
 
+
+int ERC_TESTER::TestNoConnectPins()
+{
+    int err_count = 0;
+
+    for( const SCH_SHEET_PATH& sheet : m_schematic->GetSheets() )
+    {
+        std::map<wxPoint, std::vector<SCH_PIN*>> pinMap;
+
+        for( SCH_ITEM* item : sheet.LastScreen()->Items().OfType( SCH_COMPONENT_T ) )
+        {
+            SCH_COMPONENT* comp = static_cast<SCH_COMPONENT*>( item );
+
+            for( SCH_PIN* pin : comp->GetSchPins( &sheet ) )
+                pinMap[pin->GetPosition()].emplace_back( pin );
+        }
+
+        for( auto& pair : pinMap )
+        {
+            if( pair.second.size() > 1 )
+            {
+                err_count++;
+
+                ERC_ITEM* ercItem = ERC_ITEM::Create( ERCE_NOCONNECT_CONNECTED );
+
+                ercItem->SetItems( pair.second[0], pair.second[1],
+                                   pair.second.size() > 2 ? pair.second[2] : nullptr,
+                                   pair.second.size() > 3 ? pair.second[3] : nullptr );
+                ercItem->SetErrorMessage( _( "Pins with \"no connection\" type are connected" ) );
+
+                SCH_MARKER* marker = new SCH_MARKER( ercItem, pair.first );
+                sheet.LastScreen()->Append( marker );
+            }
+        }
+    }
+
+    return err_count;
+}
+
+
 // this code try to detect similar labels, i.e. labels which are identical
 // when they are compared using case insensitive coparisons.
 

eeschema/erc.h

@@ -99,6 +99,13 @@ public:
      */
     int TestMultiunitFootprints();
 
+    /**
+     * In KiCad 5 and earlier, you could connect stuff up to pins with NC electrical type.
+     * In KiCad 6, this no longer results in those pins joining the net, so we need to warn about it
+     * @return the error count
+     */
+    int TestNoConnectPins();
+
 private:
     /**
      * Performs ERC testing and creates an ERC marker to show the ERC problem for aNetItemRef

eeschema/sch_pin.cpp

@@ -141,4 +141,8 @@ bool SCH_PIN::HitTest( const wxPoint& aPosition, int aAccuracy ) const
 }
 
 
-
+bool SCH_PIN::ConnectionPropagatesTo( const EDA_ITEM* aItem ) const
+{
+    // Reciprocal checking is done in CONNECTION_GRAPH anyway
+    return !( m_libPin->GetType() == ELECTRICAL_PINTYPE::PT_NC );
+}

eeschema/sch_pin.h

@@ -107,6 +107,8 @@ public:
 
     bool IsPowerConnection() const { return m_libPin->IsPowerConnection(); }
 
+    bool ConnectionPropagatesTo( const EDA_ITEM* aItem ) const override;
+
 
 #if defined(DEBUG)
     void Show( int nestLevel, std::ostream& os ) const override {}