From d9cf939ba1f2cfa40feb77c4923694e2a8556204 Mon Sep 17 00:00:00 2001
From: Roberto Fernandez Bautista <roberto.fer.bau@gmail.com>
Date: Thu, 12 Aug 2021 16:32:06 +0100
Subject: [PATCH] SHAPE_LINE_CHAIN::Replace Don't call front() or back() if
 empty Fixes https://gitlab.com/kicad/code/kicad/-/issues/8949

---
 libs/kimath/src/geometry/shape_line_chain.cpp | 17 ++++++++++-
 .../kimath/geometry/test_shape_line_chain.cpp | 29 +++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/libs/kimath/src/geometry/shape_line_chain.cpp b/libs/kimath/src/geometry/shape_line_chain.cpp
index 7f73a86aae..d21697ee8c 100644
--- a/libs/kimath/src/geometry/shape_line_chain.cpp
+++ b/libs/kimath/src/geometry/shape_line_chain.cpp
@@ -478,11 +478,25 @@ void SHAPE_LINE_CHAIN::Replace( int aStartIndex, int aEndIndex, const SHAPE_LINE
 
     SHAPE_LINE_CHAIN newLine = aLine;
 
+    // Zero points to add?
+    if( newLine.PointCount() == 0 )
+    {
+        Remove( aStartIndex, aEndIndex );
+        return;
+    }
+
     // Remove coincident points in the new line
     if( newLine.m_points.front() == m_points[aStartIndex] )
     {
         aStartIndex++;
         newLine.Remove( 0 );
+
+        // Zero points to add?
+        if( newLine.PointCount() == 0 )
+        {
+            Remove( aStartIndex, aEndIndex );
+            return;
+        }
     }
 
     if( newLine.m_points.back() == m_points[aEndIndex] && aEndIndex > 0 )
@@ -493,7 +507,8 @@ void SHAPE_LINE_CHAIN::Replace( int aStartIndex, int aEndIndex, const SHAPE_LINE
 
     Remove( aStartIndex, aEndIndex );
 
-    if( !newLine.PointCount() )
+    // Zero points to add?
+    if( newLine.PointCount() == 0 )
         return;
 
     // The total new arcs index is added to the new arc indices
diff --git a/qa/libs/kimath/geometry/test_shape_line_chain.cpp b/qa/libs/kimath/geometry/test_shape_line_chain.cpp
index 7c3acdc873..bab11efb52 100644
--- a/qa/libs/kimath/geometry/test_shape_line_chain.cpp
+++ b/qa/libs/kimath/geometry/test_shape_line_chain.cpp
@@ -290,5 +290,34 @@ BOOST_AUTO_TEST_CASE( NearestPointPt )
 }
 
 
+// Test SHAPE_LINE_CHAIN::Replace( SHAPE_LINE_CHAIN )
+BOOST_AUTO_TEST_CASE( ReplaceChain )
+{
+    BOOST_TEST_INFO( "8949 crash" );
+
+    std::vector<VECTOR2I> linePts = {
+        { 206000000, 140110000 }, { 192325020, 140110000 }, { 192325020, 113348216 },
+        { 192251784, 113274980 }, { 175548216, 113274980 }, { 175474980, 113348216 },
+        { 175474980, 136694980 }, { 160774511, 121994511 }, { 160774511, 121693501 },
+        { 160086499, 121005489 }, { 159785489, 121005489 }, { 159594511, 120814511 },
+        { 160086499, 120814511 }, { 160774511, 120126499 }, { 160774511, 119153501 },
+        { 160086499, 118465489 }, { 159113501, 118465489 }, { 158425489, 119153501 },
+        { 158425489, 119645489 }, { 157325020, 118545020 }, { 157325020, 101925020 },
+        { 208674980, 101925020 }, { 208674980, 145474980 }, { 192325020, 145474980 },
+        { 192325020, 140110000 }
+    };
+
+    SHAPE_LINE_CHAIN baseChain( linePts, false );
+    baseChain.SetWidth( 250000 );
+    BOOST_CHECK_EQUAL( baseChain.PointCount(), linePts.size() );
+
+    SHAPE_LINE_CHAIN replaceChain( { VECTOR2I( 192325020, 140110000 ) }, false );
+    BOOST_CHECK_EQUAL( replaceChain.PointCount(), 1 );
+
+    baseChain.Replace( 1, 23, replaceChain );
+
+    BOOST_CHECK_EQUAL( baseChain.PointCount(), linePts.size() - ( 23 - 1 ) );
+}
+
 
 BOOST_AUTO_TEST_SUITE_END()