warn during system check it shapely speedups are not available

src/c3nav/mapdata/utils/geometry.py

@@ -1,6 +1,7 @@
 from itertools import chain
 
 import matplotlib.pyplot as plt
+from django.core import checks
 from matplotlib.patches import PathPatch
 from matplotlib.path import Path
 from shapely import speedups
@@ -10,6 +11,20 @@ if speedups.available:
     speedups.enable()
 
 
+@checks.register()
+def check_svg_renderer(app_configs, **kwargs):
+    errors = []
+    if not speedups.available:
+        errors.append(
+            checks.Warning(
+                'Your shapely version does not have speedups enabled. This will significantly slow down c3nav!',
+                obj='rtree.index.Index',
+                id='c3nav.mapdata.W001',
+            )
+        )
+    return errors
+
+
 def clean_geometry(geometry):
     """
     if the given geometry is a Polygon and invalid, try to make it valid if it results in a Polygon (not MultiPolygon)

src/c3nav/mapdata/utils/index.py

@@ -62,9 +62,9 @@ def check_svg_renderer(app_configs, **kwargs):
     if not rtree_index:
         errors.append(
             checks.Warning(
-                'The libspatialindex_c library is missing. This will drastically slow down c3nav rendering.',
+                'The libspatialindex_c library is missing. This will slow down c3nav in future versions.',
                 obj='rtree.index.Index',
-                id='c3nav.mapdata.W001',
+                id='c3nav.mapdata.W002',
             )
         )
     return errors