def _is_reachable(
schema: s_schema.Schema,
cast_kwargs: Mapping[str, bool],
source: s_types.Type,
target: s_types.Type,
distance: int,
) -> int:
if source == target:
return distance
casts = schema.get_casts_to_type(target, **cast_kwargs)
if not casts:
return _NOT_REACHABLE
sources = {c.get_from_type(schema) for c in casts}
distance += 1
if source in sources:
return distance
else:
return min(
_is_reachable(schema, cast_kwargs, source, s, distance)
for s in sources
)
def is_assignment_castable(
schema: s_schema.Schema,
source: s_types.Type,
target: s_types.Type,
) -> bool:
# Implicitly castable implies assignment castable.
if is_implicitly_castable(schema, source, target):
return True
# Assignment casts are valid only as one-hop casts.
casts = schema.get_casts_to_type(target, assignment=True)
if not casts:
return False
for c in casts:
if c.get_from_type(schema) == source:
return True
return False
def is_castable(
schema: s_schema.Schema,
source: s_types.Type,
target: s_types.Type,
) -> bool:
# Implicitly castable
if is_implicitly_castable(schema, source, target):
return True
elif is_assignment_castable(schema, source, target):
return True
else:
casts = schema.get_casts_to_type(target)
if not casts:
return False
else:
for c in casts:
if c.get_from_type(schema) == source:
return True
else:
return False
