Add ERC check that a pin appears in only one net

Fixes: lp:1680638
* https://bugs.launchpad.net/kicad/+bug/1680638

eeschema/dialogs/dialog_erc.cpp

@@ -47,6 +47,7 @@
 #include <sch_marker.h>
 #include <sch_sheet.h>
 #include <lib_pin.h>
+#include <sch_component.h>
 
 #include <dialog_erc.h>
 #include <erc.h>
@@ -491,6 +492,12 @@ void DIALOG_ERC::TestErc( REPORTER& aReporter )
     unsigned nextItemIdx = lastItemIdx = 0;
     int MinConn    = NOC;
 
+    /* Check that a pin appears in only one net.  This check is necessary
+     * because multi-unit components that have shared pins can be wired to
+     * different nets.
+     */
+    std::unordered_map<wxString, wxString> pin_to_net_map;
+
     /* The netlist generated by SCH_EDIT_FRAME::BuildNetListBase is sorted
      * by net number, which means we can group netlist items into ranges
      * that live in the same net. The range from nextItem to the current
@@ -555,11 +562,38 @@ void DIALOG_ERC::TestErc( REPORTER& aReporter )
             break;
 
         case NET_PIN:
+        {
+            // Check if this pin has appeared before on a different net
+            if( item->m_Link )
+            {
+                auto ref = item->GetComponentParent()->GetRef( &item->m_SheetPath );
+                wxString pin_name = ref + "_" + item->m_PinNum;
+
+                if( pin_to_net_map.count( pin_name ) == 0 )
+                {
+                    pin_to_net_map[pin_name] = item->GetNetName();
+                }
+                else if( pin_to_net_map[pin_name] != item->GetNetName() )
+                {
+                    SCH_MARKER* marker = new SCH_MARKER();
+
+                    marker->SetTimeStamp( GetNewTimeStamp() );
+                    marker->SetData( ERCE_DIFFERENT_UNIT_NET, item->m_Start,
+                        wxString::Format( _( "Pin %s on %s is connected to both %s and %s" ),
+                        item->m_PinNum, ref, pin_to_net_map[pin_name], item->GetNetName() ),
+                        item->m_Start );
+                    marker->SetMarkerType( MARKER_BASE::MARKER_ERC );
+                    marker->SetErrorLevel( MARKER_BASE::MARKER_SEVERITY_ERROR );
+
+                    item->m_SheetPath.LastScreen()->Append( marker );
+                }
+            }
 
             // Look for ERC problems between pins:
             TestOthersItems( objectsConnectedList.get(), itemIdx, nextItemIdx, &MinConn );
             break;
         }
+        }
 
         lastItemIdx = itemIdx;
     }

eeschema/drc_erc_item.cpp

@@ -60,6 +60,8 @@ wxString DRC_ITEM::GetErrorText() const
         return wxString( _("Global labels are similar (lower/upper case difference only)") );
     case ERCE_DIFFERENT_UNIT_FP:
         return wxString( _("Different footprint assigned in another unit of the same component") );
+    case ERCE_DIFFERENT_UNIT_NET:
+        return wxString( _("Different net assigned to a shared pin in another unit of the same component" ) );
 
     default:
         wxFAIL_MSG( "Missing ERC error description" );

eeschema/erc.h

@@ -62,6 +62,8 @@ extern const wxString CommentERC_V[];
 #define ERCE_SIMILAR_GLBL_LABELS  10   // 2 labels are equal fir case insensitive comparisons
 #define ERCE_DIFFERENT_UNIT_FP    11   // different units of the same component have different
                                        // footprints assigned
+#define ERCE_DIFFERENT_UNIT_NET   12   // a shared pin in a multi-unit component is connected
+                                       // to more than one net
 
 /* Minimal connection table */
 #define NPI    4  // Net with Pin isolated, this pin has type Not Connected and must be left N.C.