From ec53f3d879df0d3e447aea19231da45201bb49c7 Mon Sep 17 00:00:00 2001
From: Jiri Drbalek <jiri.drbalek@firma.seznam.cz>
Date: Wed, 17 Jan 2018 09:53:45 +0000
Subject: [PATCH] Fix crash in case of empty ring

---
 .../geometry/polygon_vertex_processor.hpp     |  6 +-
 .../geometry/polygon_vertex_processor.cpp     | 62 +++++++++++++++++++
 2 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100644 test/unit/geometry/polygon_vertex_processor.cpp

diff --git a/include/mapnik/geometry/polygon_vertex_processor.hpp b/include/mapnik/geometry/polygon_vertex_processor.hpp
index 5c95aed14..b632c800f 100644
--- a/include/mapnik/geometry/polygon_vertex_processor.hpp
+++ b/include/mapnik/geometry/polygon_vertex_processor.hpp
@@ -24,6 +24,7 @@
 #define MAPNIK_GEOMETRY_POLYGON_VERTEX_PROCESSOR_HPP
 
 // geometry
+#include <mapnik/geometry/point.hpp>
 #include <mapnik/geometry/polygon.hpp>
 
 namespace mapnik { namespace geometry {
@@ -46,7 +47,10 @@ struct polygon_vertex_processor
                     ring.emplace_back(p);
                     break;
                 case SEG_CLOSE:
-                    ring.emplace_back(ring.front());
+                    if (!ring.empty())
+                    {
+                        ring.emplace_back(ring.front());
+                    }
                     polygon_.emplace_back(std::move(ring));
                     ring = linear_ring<T>();
                     break;
diff --git a/test/unit/geometry/polygon_vertex_processor.cpp b/test/unit/geometry/polygon_vertex_processor.cpp
new file mode 100644
index 000000000..c40c26900
--- /dev/null
+++ b/test/unit/geometry/polygon_vertex_processor.cpp
@@ -0,0 +1,62 @@
+#include "catch.hpp"
+#include "unit/vertex_adapter/fake_path.hpp"
+
+#include <mapnik/geometry/polygon_vertex_processor.hpp>
+
+TEST_CASE("polygon_vertex_processor") {
+
+SECTION("empty polygon") {
+
+    fake_path path = {};
+    mapnik::geometry::polygon_vertex_processor<double> proc;
+    proc.add_path(path);
+    CHECK(proc.polygon_.size() == 0);
+}
+
+SECTION("empty outer ring") {
+
+    fake_path path = {};
+    path.vertices_.emplace_back(0, 0, mapnik::SEG_CLOSE);
+    path.rewind(0);
+
+    mapnik::geometry::polygon_vertex_processor<double> proc;
+    proc.add_path(path);
+    REQUIRE(proc.polygon_.size() == 1);
+    REQUIRE(proc.polygon_.front().size() == 0);
+}
+
+SECTION("empty inner ring") {
+
+    fake_path path = {};
+    path.vertices_.emplace_back(-1, -1, mapnik::SEG_MOVETO);
+    path.vertices_.emplace_back( 1, -1, mapnik::SEG_LINETO);
+    path.vertices_.emplace_back( 1,  1, mapnik::SEG_LINETO);
+    path.vertices_.emplace_back(-1,  1, mapnik::SEG_LINETO);
+    path.vertices_.emplace_back( 0,  0, mapnik::SEG_CLOSE);
+    path.vertices_.emplace_back( 0,  0, mapnik::SEG_CLOSE);
+    path.rewind(0);
+
+    mapnik::geometry::polygon_vertex_processor<double> proc;
+    proc.add_path(path);
+
+    REQUIRE(proc.polygon_.size() == 2);
+    auto outer_ring = proc.polygon_.front();
+    REQUIRE(outer_ring.size() == 5);
+
+    CHECK(outer_ring[0].x == Approx(-1));
+    CHECK(outer_ring[0].y == Approx(-1));
+
+    CHECK(outer_ring[1].x == Approx( 1));
+    CHECK(outer_ring[1].y == Approx(-1));
+
+    CHECK(outer_ring[2].x == Approx( 1));
+    CHECK(outer_ring[2].y == Approx( 1));
+
+    CHECK(outer_ring[3].x == Approx(-1));
+    CHECK(outer_ring[3].y == Approx( 1));
+
+    CHECK(outer_ring[4].x == Approx(-1));
+    CHECK(outer_ring[4].y == Approx(-1));
+}
+
+}