Merge pull request #2067 from simoncozens/fealib-debug-subclassable

Only stash lookup location if buildLookups_ has cooperated

Lib/fontTools/feaLib/builder.py

@@ -30,6 +30,7 @@ from fontTools.otlLib.error import OpenTypeLibError
 from collections import defaultdict
 import itertools
 import logging
+import warnings
 
 
 log = logging.getLogger(__name__)
@@ -707,9 +708,13 @@ class Builder(object):
                 continue
 
             for ix in lookup_indices:
-                self.lookup_locations[tag][str(ix)] = self.lookup_locations[tag][
-                    str(ix)
-                ]._replace(feature=key)
+                try:
+                    self.lookup_locations[tag][str(ix)] = self.lookup_locations[tag][
+                        str(ix)
+                    ]._replace(feature=key)
+                except KeyError:
+                    warnings.warn("feaLib.Builder subclass needs upgrading to "
+                        "stash debug information. See fonttools#2065.")
 
             feature_key = (feature_tag, lookup_indices)
             feature_index = feature_indices.get(feature_key)