From cf88b9aaecc84fdfc1398963c9e7ab8442a51933 Mon Sep 17 00:00:00 2001
From: Seth Hillbrand <seth@kipro-pcb.com>
Date: Thu, 17 Feb 2022 15:22:18 -0800
Subject: [PATCH] Maintain connectivity while cleaning tracks/vias

When merging segments that loop back on each other, we need to merge
them in such a way to to keep the resulting endpoints connected to the
original adjoining endpoints

Fixes https://gitlab.com/kicad/code/kicad/issues/10780

(cherry picked from commit 8e9d44942f54e2771c364f823b8bbb104ecb328e)
---
 pcbnew/tracks_cleaner.cpp | 57 +++++++++++++++++++++++++++++++--------
 1 file changed, 46 insertions(+), 11 deletions(-)

diff --git a/pcbnew/tracks_cleaner.cpp b/pcbnew/tracks_cleaner.cpp
index 7ced9cc5ff..a17e8377cb 100644
--- a/pcbnew/tracks_cleaner.cpp
+++ b/pcbnew/tracks_cleaner.cpp
@@ -464,7 +464,40 @@ bool TRACKS_CLEANER::mergeCollinearSegments( PCB_TRACK* aSeg1, PCB_TRACK* aSeg2
     if( aSeg1->IsLocked() || aSeg2->IsLocked() )
         return false;
 
-    auto connectivity = m_brd->GetConnectivity();
+    std::shared_ptr<CONNECTIVITY_DATA> connectivity = m_brd->GetConnectivity();
+
+    std::vector<PCB_TRACK*> tracks = connectivity->GetConnectedTracks( aSeg1 );
+    std::vector<PCB_TRACK*> tracks2 = connectivity->GetConnectedTracks( aSeg2 );
+
+    std::move( tracks2.begin(), tracks2.end(), std::back_inserter( tracks ) );
+
+    tracks.erase(
+            std::remove_if( tracks.begin(), tracks.end(), [ aSeg1, aSeg2 ]( PCB_TRACK* aTest )
+            {
+                return ( aTest == aSeg1 ) || ( aTest == aSeg2 );
+            } ), tracks.end() );
+
+    std::set<VECTOR2I> pts;
+
+    // Collect the unique points where the two tracks are connected to others
+    for( PCB_TRACK* track : tracks )
+    {
+        if( track->IsPointOnEnds( aSeg1->GetStart() ) )
+            pts.emplace( aSeg1->GetStart() );
+
+        if( track->IsPointOnEnds( aSeg1->GetEnd() ) )
+            pts.emplace( aSeg1->GetEnd() );
+
+        if( track->IsPointOnEnds( aSeg2->GetStart() ) )
+            pts.emplace( aSeg2->GetStart() );
+
+        if( track->IsPointOnEnds( aSeg2->GetEnd() ) )
+            pts.emplace( aSeg2->GetEnd() );
+    }
+
+    // This means there is a node in the center
+    if( pts.size() > 2 )
+        return false;
 
     // Verify the removed point after merging is not a node.
     // If it is a node (i.e. if more than one other item is connected, the segments cannot be merged
@@ -492,17 +525,19 @@ bool TRACKS_CLEANER::mergeCollinearSegments( PCB_TRACK* aSeg1, PCB_TRACK* aSeg2
         dummy_seg.SetEnd( VECTOR2I( max_x, min_y ) );
     }
 
-    // Now find the removed end(s) and stop merging if it is a node:
-    if( aSeg1->GetStart() != dummy_seg.GetStart() && aSeg1->GetStart() != dummy_seg.GetEnd() )
+    // If the existing connected points are not the same as the points generated by our
+    // min/max alg, then assign the missing points to the end closest.  This ensures that
+    // our replacment track is still connected
+    for( auto pt : pts )
     {
-        if( testTrackEndpointIsNode( aSeg1, true ) )
-            return false;
-    }
-
-    if( aSeg1->GetEnd() != dummy_seg.GetStart() && aSeg1->GetEnd() != dummy_seg.GetEnd() )
-    {
-        if( testTrackEndpointIsNode( aSeg1, false ) )
-            return false;
+        if( !dummy_seg.IsPointOnEnds( wxPoint( pt.x, pt.y ) ) )
+        {
+            if( ( VECTOR2I( dummy_seg.GetStart() ) - pt ).SquaredEuclideanNorm() <
+                    ( VECTOR2I( dummy_seg.GetEnd() ) - pt ).SquaredEuclideanNorm() )
+                dummy_seg.SetStart( wxPoint( pt.x, pt.y ) );
+            else
+                dummy_seg.SetEnd( wxPoint( pt.x, pt.y ) );
+        }
     }
 
     std::shared_ptr<CLEANUP_ITEM> item = std::make_shared<CLEANUP_ITEM>( CLEANUP_MERGE_TRACKS );