Stop guessing whether Paths are polygons on new MPL.

The main things that suffered from this are font glyphs, fixed in 2.0.1,
and contours, which were fixed with Matplotlib's new contouring code.
Legacy contouring was remove in 2.2.0.

Also, our own geos_to_path, which was just fixed.

lib/cartopy/mpl/patch.py

@@ -29,6 +29,7 @@
 from __future__ import (absolute_import, division, print_function)
 
 import numpy as np
+import matplotlib
 from matplotlib.path import Path
 import shapely.geometry as sgeom
 
@@ -163,15 +164,16 @@ def path_to_geos(path, force_ccw=False):
         if len(path_verts) == 0:
             continue
 
-        # XXX A path can be given which does not end with close poly, in that
-        # situation, we have to guess?
         verts_same_as_first = np.all(path_verts[0, :] == path_verts[1:, :],
                                      axis=1)
         if all(verts_same_as_first):
             geom = sgeom.Point(path_verts[0, :])
         elif path_verts.shape[0] > 4 and path_codes[-1] == Path.CLOSEPOLY:
             geom = sgeom.Polygon(path_verts[:-1, :])
-        elif path_verts.shape[0] > 3 and verts_same_as_first[-1]:
+        elif (matplotlib.__version__ < '2.2.0' and
+                # XXX A path can be given which does not end with close poly,
+                # in that situation, we have to guess?
+                path_verts.shape[0] > 3 and verts_same_as_first[-1]):
             geom = sgeom.Polygon(path_verts)
         else:
             geom = sgeom.LineString(path_verts)

lib/cartopy/tests/mpl/test_patch.py

@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2015 - 2017, Met Office
+# (C) British Crown Copyright 2015 - 2018, Met Office
 #
 # This file is part of cartopy.
 #
@@ -17,7 +17,9 @@
 
 from __future__ import (absolute_import, division, print_function)
 
+import matplotlib
 from matplotlib.path import Path
+import pytest
 import shapely.geometry as sgeom
 
 import cartopy.mpl.patch as cpatch
@@ -33,12 +35,21 @@ def test_empty_polyon(self):
         assert [type(geom) for geom in geoms] == [sgeom.Point, sgeom.Point]
         assert len(geoms) == 2
 
+    @pytest.mark.skipif(matplotlib.__version__ < '2.2.0',
+                        reason='Paths may not be closed with old Matplotlib.')
+    def test_non_polygon_loop(self):
+        p = Path([[0, 10], [170, 20], [-170, 30], [0, 10]],
+                 codes=[1, 2, 2, 2])
+        geoms = cpatch.path_to_geos(p)
+        assert [type(geom) for geom in geoms] == [sgeom.MultiLineString]
+        assert len(geoms) == 1
+
     def test_polygon_with_interior_and_singularity(self):
         # A geometry with two interiors, one a single point.
         p = Path([[0, -90], [200, -40], [200, 40], [0, 40], [0, -90],
                   [126, 26], [126, 26], [126, 26], [126, 26], [126, 26],
                   [114, 5], [103, 8], [126, 12], [126, 0], [114, 5]],
-                 codes=[1, 2, 2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 2])
+                 codes=[1, 2, 2, 2, 79, 1, 2, 2, 2, 79, 1, 2, 2, 2, 79])
         geoms = cpatch.path_to_geos(p)
         assert [type(geom) for geom in geoms] == [sgeom.Polygon, sgeom.Point]
         assert len(geoms[0].interiors) == 1