ADDED: Optional check for four way junctions

Defaults to off because this is likely contentious

Fixes https://gitlab.com/kicad/code/kicad/-/issues/17870

eeschema/erc/erc.cpp

@@ -607,6 +607,60 @@ int ERC_TESTER::TestMissingNetclasses()
 }
 
 
+int ERC_TESTER::TestFourWayJunction()
+{
+    int err_count = 0;
+
+    for( const SCH_SHEET_PATH& sheet : m_schematic->GetSheets() )
+    {
+        std::map<VECTOR2I, std::vector<SCH_ITEM*>> connMap;
+        SCH_SCREEN* screen = sheet.LastScreen();
+
+        for( SCH_ITEM* item : screen->Items().OfType( SCH_SYMBOL_T ) )
+        {
+            SCH_SYMBOL* symbol = static_cast<SCH_SYMBOL*>( item );
+
+            for( SCH_PIN* pin : symbol->GetPins( &sheet ) )
+                connMap[pin->GetPosition()].emplace_back( pin );
+        }
+
+        for( SCH_ITEM* item : screen->Items().OfType( SCH_LINE_T ) )
+        {
+            SCH_LINE* line = static_cast<SCH_LINE*>( item );
+
+            if( line->IsGraphicLine() )
+                continue;
+
+            for( const VECTOR2I& pt : line->GetConnectionPoints() )
+                connMap[pt].emplace_back( line );
+        }
+
+        for( const std::pair<const VECTOR2I, std::vector<SCH_ITEM*>>& pair : connMap )
+        {
+            if( pair.second.size() >= 4 )
+            {
+                err_count++;
+
+                std::shared_ptr<ERC_ITEM> ercItem = ERC_ITEM::Create( ERCE_FOUR_WAY_JUNCTION );
+
+                ercItem->SetItems( pair.second[0], pair.second[1], pair.second[2], pair.second[3] );
+
+                wxString msg = wxString::Format( _( "Four items connected at %d, %d" ),
+                                                 pair.first.x, pair.first.y );
+                ercItem->SetErrorMessage( msg );
+
+                ercItem->SetSheetSpecificPath( sheet );
+
+                SCH_MARKER* marker = new SCH_MARKER( ercItem, pair.first );
+                sheet.LastScreen()->Append( marker );
+            }
+        }
+    }
+
+    return err_count;
+}
+
+
 int ERC_TESTER::TestNoConnectPins()
 {
     int err_count = 0;
@@ -1436,6 +1490,14 @@ void ERC_TESTER::RunTests( DS_PROXY_VIEW_ITEM* aDrawingSheet, SCH_EDIT_FRAME* aE
         TestOffGridEndpoints();
     }
 
+    if( settings.IsTestEnabled( ERCE_FOUR_WAY_JUNCTION ) )
+    {
+        if( aProgressReporter )
+            aProgressReporter->AdvancePhase( _( "Checking for four way junctions..." ) );
+
+        TestFourWayJunction();
+    }
+
     if( settings.IsTestEnabled( ERCE_UNDEFINED_NETCLASS ) )
     {
         if( aProgressReporter )

eeschema/erc/erc.h

@@ -111,6 +111,11 @@ public:
      */
     int TestSimilarLabels();
 
+    /**
+     * Test to see if there are potentially confusing 4-way junctions in the schematic.
+    */
+    int TestFourWayJunction();
+
     /**
      * Test symbols for changed library symbols and broken symbol library links.
      * @return the number of issues found

eeschema/erc/erc_item.cpp

@@ -75,6 +75,10 @@ ERC_ITEM ERC_ITEM::hierLabelMismatch( ERCE_HIERACHICAL_LABEL,
         _( "Mismatch between hierarchical labels and sheet pins" ),
         wxT( "hier_label_mismatch" ) );
 
+ERC_ITEM ERC_ITEM::fourWayJunction( ERCE_FOUR_WAY_JUNCTION,
+        _( "Four connection points are joined together" ),
+        wxT( "four_way_junction" ) );
+
 ERC_ITEM ERC_ITEM::noConnectConnected( ERCE_NOCONNECT_CONNECTED,
         _( "A pin with a \"no connection\" flag is connected" ),
         wxT( "no_connect_connected" ) );
@@ -212,6 +216,7 @@ std::vector<std::reference_wrapper<RC_ITEM>> ERC_ITEM::allItemTypes( {
                  ERC_ITEM::wireDangling,
                  ERC_ITEM::busEntryNeeded,
                  ERC_ITEM::endpointOffGrid,
+                 ERC_ITEM::fourWayJunction,
 
                  ERC_ITEM::heading_conflicts,
                  ERC_ITEM::duplicateReference,
@@ -263,6 +268,7 @@ std::shared_ptr<ERC_ITEM> ERC_ITEM::Create( int aErrorCode )
     case ERCE_HIERACHICAL_LABEL:       return std::make_shared<ERC_ITEM>( hierLabelMismatch );
     case ERCE_NOCONNECT_CONNECTED:     return std::make_shared<ERC_ITEM>( noConnectConnected );
     case ERCE_NOCONNECT_NOT_CONNECTED: return std::make_shared<ERC_ITEM>( noConnectDangling );
+    case ERCE_FOUR_WAY_JUNCTION:       return std::make_shared<ERC_ITEM>( fourWayJunction );
     case ERCE_LABEL_NOT_CONNECTED:     return std::make_shared<ERC_ITEM>( labelDangling );
     case ERCE_SIMILAR_LABELS:          return std::make_shared<ERC_ITEM>( similarLabels );
     case ERCE_SINGLE_GLOBAL_LABEL:     return std::make_shared<ERC_ITEM>( singleGlobalLabel );

eeschema/erc/erc_item.h

@@ -192,6 +192,7 @@ private:
     static ERC_ITEM pinTableError;
     static ERC_ITEM hierLabelMismatch;
     static ERC_ITEM noConnectConnected;
+    static ERC_ITEM fourWayJunction;
     static ERC_ITEM noConnectDangling;
     static ERC_ITEM labelDangling;
     static ERC_ITEM globalLabelDangling;

eeschema/erc/erc_settings.cpp

@@ -110,6 +110,7 @@ ERC_SETTINGS::ERC_SETTINGS( JSON_SETTINGS* aParent, const std::string& aPath ) :
     m_ERCSeverities[ERCE_MISSING_INPUT_PIN]       = RPT_SEVERITY_WARNING;
     m_ERCSeverities[ERCE_MISSING_BIDI_PIN]        = RPT_SEVERITY_WARNING;
     m_ERCSeverities[ERCE_SIMULATION_MODEL]        = RPT_SEVERITY_IGNORE;
+    m_ERCSeverities[ERCE_FOUR_WAY_JUNCTION]       = RPT_SEVERITY_IGNORE;
 
     m_params.emplace_back( new PARAM_LAMBDA<nlohmann::json>( "rule_severities",
             [&]() -> nlohmann::json

eeschema/erc/erc_settings.h

@@ -82,9 +82,10 @@ enum ERCE_T
     ERCE_DIFFERENT_UNIT_VALUE,    ///< Units of same symbol have different values.
     ERCE_DUPLICATE_REFERENCE,     ///< More than one symbol with the same reference.
     ERCE_BUS_ENTRY_NEEDED,        ///< Importer failed to auto-place a bus entry.
+    ERCE_FOUR_WAY_JUNCTION,       ///< A four-way junction was found.
 
 
-    ERCE_LAST = ERCE_BUS_ENTRY_NEEDED,
+    ERCE_LAST = ERCE_FOUR_WAY_JUNCTION,
 
     // Errors after this point will not automatically appear in the Severities Panel
 

qa/tests/eeschema/CMakeLists.txt

@@ -51,6 +51,7 @@ set( QA_EESCHEMA_SRCS
 
     sch_io/altium/test_altium_parser_sch.cpp
 
+    erc/test_erc_four_way.cpp
 	erc/test_erc_label_not_connected.cpp
 	erc/test_erc_stacking_pins.cpp
 	erc/test_erc_global_labels.cpp

qa/tests/eeschema/erc/test_erc_four_way.cpp

@@ -0,0 +1,75 @@
+/*
+ * This program source code file is part of KiCad, a free EDA CAD application.
+ *
+ * Copyright (C) 2022 KiCad Developers, see AUTHORS.TXT for contributors.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 3
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you may find one at
+ * http://www.gnu.org/licenses/
+ */
+
+#include <qa_utils/wx_utils/unit_test_utils.h>
+#include <schematic_utils/schematic_file_util.h>
+
+#include <connection_graph.h>
+#include <schematic.h>
+#include <erc/erc_settings.h>
+#include <erc/erc.h>
+#include <erc/erc_report.h>
+#include <settings/settings_manager.h>
+#include <locale_io.h>
+
+struct ERC_REGRESSION_TEST_FIXTURE
+{
+    ERC_REGRESSION_TEST_FIXTURE() :
+            m_settingsManager( true /* headless */ )
+    { }
+
+    SETTINGS_MANAGER           m_settingsManager;
+    std::unique_ptr<SCHEMATIC> m_schematic;
+};
+
+
+BOOST_FIXTURE_TEST_CASE( ERCFourWayJunctions, ERC_REGRESSION_TEST_FIXTURE )
+{
+    LOCALE_IO dummy;
+
+    // Check for Errors when using global labels
+    std::vector<std::pair<wxString, int>> tests =
+    {
+        { "issue17870",                   6  }
+    };
+
+    for( const std::pair<wxString, int>& test : tests )
+    {
+        KI_TEST::LoadSchematic( m_settingsManager, test.first, m_schematic );
+
+        ERC_SETTINGS& settings = m_schematic->ErcSettings();
+        SHEETLIST_ERC_ITEMS_PROVIDER errors( m_schematic.get() );
+
+        settings.m_ERCSeverities[ERCE_FOUR_WAY_JUNCTION] = RPT_SEVERITY_ERROR;
+
+        ERC_TESTER tester( m_schematic.get() );
+        tester.TestFourWayJunction();
+
+        errors.SetSeverities( RPT_SEVERITY_ERROR | RPT_SEVERITY_WARNING );
+
+        ERC_REPORT reportWriter( m_schematic.get(), EDA_UNITS::MILLIMETRES );
+
+        BOOST_CHECK_MESSAGE( errors.GetCount() == test.second,
+                             "Expected " << test.second << " errors in " << test.first.ToStdString()
+                                         << " but got " << errors.GetCount() << "\n"
+                                         << reportWriter.GetTextReport() );
+
+    }
+}