glom branch exception tracing

branches.py

def _glom(spec, target, scope):
  scope[CHILD_ERRORS] = []
  try:
    ...
  except Exception as e:
    scope.parent[CHILD_ERRORS].append((scope, e))
    raise
  else:
    del scope[CHILD_ERRORS]

# scope[CHILD_ERRORS][-1] is always the last branch
# scope[CHILD_ERRORS][:-1] are the side branches

assert glom(1, Or('a', 'b', 'c')) ==
"""
 Target-Spec trace (most recent last):
 - Target: 1
 - Spec: Or('a', 'b', 'c')
 Failed Branch:
  - Spec: 'a'
  glom.core.MatchError: 1 != 'a'
 Failed Branch:
  - Spec: 'b'
  glom.core.MatchError: 1 != 'b'
 - Spec: 'c'
glom.core.MatchError: 1 != 'c'
"""


# this may be worth reworking into debug helpers, depending on the amount of bugs in this area
def debug():
      try:
        glom([None], Match(Switch(
        [(1, 1), ('a', 'a'), ([None], T.a)])))
    except Exception as e:
        import pprint
        from glom.core import LAST_CHILD_SCOPE, CHILD_ERRORS, Spec, UP
        print("")
        def sub(s, key, sofar):
            if key not in s:
                return None
            return scope_fmt(s[key].maps[0], sofar)
        def multi_sub(s, key, sofar):
            if key not in s:
                return None
            return [scope_fmt(sub_s.maps[0], sofar) for sub_s in s[key]]
        sofar = set()
        def scope_fmt(s, sofar):
            if id(s) in sofar:
                return "ref - " + str(id(s) % 1000)
            sofar.add(id(s))
            return {
                "spec": s.get(Spec, "MISSING"),
                "id": id(s) % 1000,
                "CHILD_ERRORS": multi_sub(s, CHILD_ERRORS, sofar),
                "LAST_CHILD_SCOPE": sub(s, LAST_CHILD_SCOPE, sofar),
                "UP": sub(s, UP, sofar),
            }
        pprint.pprint([scope_fmt(s, sofar) for s in e._scope.maps[:-2]])