Ensure that Path.arc works for any full circle.

Depending on the inputs, the range may get squashed down to ~0 when
trying to remove extra 2pi revolutions.

Fixes matplotlib#8992.

Author: QuLogic

lib/matplotlib/path.py

@@ -868,6 +868,10 @@ def arc(cls, theta1, theta2, n=None, is_wedge=False):
 
         eta1 = theta1
         eta2 = theta2 - 360 * np.floor((theta2 - theta1) / 360)
+        # Ensure 2pi range is not flattened to 0 due to floating-point errors,
+        # but don't try to expand existing 0 range.
+        if theta2 != theta1 and eta2 <= eta1:
+            eta2 += 360
         eta1, eta2 = np.deg2rad([eta1, eta2])
 
         # number of curve segments to make

lib/matplotlib/tests/test_path.py

@@ -205,3 +205,15 @@ def test_path_deepcopy():
     path2 = Path(verts, codes)
     copy.deepcopy(path1)
     copy.deepcopy(path2)
+
+
+@pytest.mark.parametrize('offset', range(-720, 361, 45))
+def test_full_arc(offset):
+    low = offset
+    high = 360 + offset
+
+    path = Path.arc(low, high)
+    mins = np.min(path.vertices, axis=0)
+    maxs = np.max(path.vertices, axis=0)
+    np.testing.assert_allclose(mins, -1)
+    assert np.allclose(maxs, 1)