fix epoch parsing

Author: aignas

python/private/version.bzl

@@ -596,7 +596,10 @@ def _parse_epoch(value):
     if not value:
         return 0
 
-    return int(value)
+    if not value.endswith("!"):
+        fail("epoch string segment needs to end with '!', got: {}".format(value))
+
+    return int(value[:-1])
 
 def _parse_release(value):
     return tuple([int(d) for d in value.split(".")])

tests/pypi/pep508/evaluate_tests.bzl

@@ -338,6 +338,7 @@ def _test_ordering(env):
         "1.0.post456",
         "1.0.15",
         "1.1.dev1",
+        "1!0.1",
     ]
 
     for lower, higher in zip(want[:-1], want[1:]):