cp: small check around coordinates

Author: shs96c

private/lib/coordinates.bzl

@@ -26,7 +26,7 @@ def unpack_coordinates(coords):
 
     # If we're using BOMs, the version is optional. That means at this point
     # we could be dealing with g:a:p or g:a:v
-    is_gradle = pieces[2][0].isdigit()
+    is_gradle = len(pieces[2]) and pieces[2][0].isdigit()
 
     if len(pieces) == 3:
         if is_gradle:

tests/unit/coordinates_test.bzl

@@ -114,6 +114,18 @@ def _multiple_formats_impl(ctx):
 
 multiple_formats_test = unittest.make(_multiple_formats_impl)
 
+def _old_format_omitting_version_impl(ctx):
+    env = unittest.begin(ctx)
+
+    unpacked = unpack_coordinates("group:artifact:packaging:")
+
+    asserts.equals(env, "", unpacked.version)
+    asserts.equals(env, "packaging", unpacked.packaging)
+
+    return unittest.end(env)
+
+old_format_omitting_version_test = unittest.make(_old_format_omitting_version_impl)
+
 def coordinates_test_suite():
     unittest.suite(
         "coordinates_tests",
@@ -125,4 +137,5 @@ def coordinates_test_suite():
         gradle_format_with_type_and_classifier_test,
         gradle_format_with_type_but_no_classifier_test,
         multiple_formats_test,
+        old_format_omitting_version_test,
     )