router: clean up shoved traces after aborting differential pair routing in shove mode

Note: the single-trace placer (LINE_PLACER) has moved to the FIXED_TAIL for tracking the interim placed routes (and reverting them if user pressed backspace). Unfortunately the DIFF_PAIR_PLACER didn't follow. The result was the dummy CommitPlacement() call at the end of aborted routing would commit the last shove state, even if FixRoute() was never called. For longer-term fix: fix ROUTER_TOOL logic to indicated aborted routing to the router/placer (AbortPlacement() is already there). Also implement FIXED_TAIL in diff pair placement mode.

pcbnew/router/pns_diff_pair_placer.cpp

@@ -642,6 +642,7 @@ bool DIFF_PAIR_PLACER::Start( const VECTOR2I& aP, ITEM* aStartItem )
     m_currentTraceOk = false;
     m_currentTrace = DIFF_PAIR();
     m_currentTrace.SetNets( m_netP, m_netN );
+    m_lastFixNode = nullptr;
 
     initPlacement();
 
@@ -842,9 +843,15 @@ bool DIFF_PAIR_PLACER::FixRoute( const VECTOR2I& aP, ITEM* aEndItem, bool aForce
     topo.SimplifyLine( &lineN );
 
     m_prevPair = m_currentTrace.EndingPrimitives();
+    m_lastFixNode = m_lastNode;
+
+    // avoid an use-after-free error (CommitPlacement calls NODE::Commit which will invalidate the shove heads state. Need to rethink the memory management).
+    if( Settings().Mode() == RM_Shove )
+        m_shove = std::make_unique<SHOVE>( m_world, Router() );
 
     CommitPlacement();
     m_placingVia = false;
+    m_lastFixNode = nullptr;
 
     if( m_snapOnTarget || aForceFinish )
     {
@@ -862,6 +869,7 @@ bool DIFF_PAIR_PLACER::FixRoute( const VECTOR2I& aP, ITEM* aEndItem, bool aForce
 bool DIFF_PAIR_PLACER::AbortPlacement()
 {
     m_world->KillChildren();
+    m_lastNode = nullptr;
     return true;
 }
 
@@ -874,9 +882,10 @@ bool DIFF_PAIR_PLACER::HasPlacedAnything() const
 
 bool DIFF_PAIR_PLACER::CommitPlacement()
 {
-    if( m_lastNode )
-        Router()->CommitRouting( m_lastNode );
+    if( m_lastFixNode )
+        Router()->CommitRouting( m_lastFixNode );
 
+    m_lastFixNode = nullptr;
     m_lastNode = nullptr;
     m_currentNode = nullptr;
     return true;

pcbnew/router/pns_diff_pair_placer.h

@@ -249,6 +249,7 @@ private:
 
     ///< Postprocessed world state (including marked collisions & removed loops)
     NODE* m_lastNode;
+    NODE* m_lastFixNode;
 
     SIZES_SETTINGS m_sizes;
 
@@ -277,6 +278,7 @@ private:
     ITEM* m_currentEndItem;
 
     bool m_idle;
+    bool m_hasFixedAnything;
 };
 
 }