def expand_type_alias(target: Type, alias_tvars: List[str], args: List[Type],
fail: Callable[[str, Context], None], no_args: bool,
ctx: Context) -> Type:
"""Expand a (generic) type alias target following the rules outlined in TypeAlias docstring.
Here:
target: original target type (contains unbound type variables)
alias_tvars: type variable names
args: types to be substituted in place of type variables
fail: error reporter callback
no_args: whether original definition used a bare generic `A = List`
ctx: context where expansion happens
"""
exp_len = len(alias_tvars)
act_len = len(args)
if exp_len > 0 and act_len == 0:
# Interpret bare Alias same as normal generic, i.e., Alias[Any, Any, ...]
assert alias_tvars is not None
return set_any_tvars(target, alias_tvars, ctx.line, ctx.column)
if exp_len == 0 and act_len == 0:
if no_args:
assert isinstance(target, Instance)
return Instance(target.type, [], line=ctx.line, column=ctx.column)
return target
if exp_len == 0 and act_len > 0 and isinstance(target,
Instance) and no_args:
tp = Instance(target.type, args)
tp.line = ctx.line
tp.column = ctx.column
return tp
if act_len != exp_len:
fail(
'Bad number of arguments for type alias, expected: %s, given: %s' %
(exp_len, act_len), ctx)
return set_any_tvars(target,
alias_tvars or [],
ctx.line,
ctx.column,
implicit=False)
typ = replace_alias_tvars(target, alias_tvars, args, ctx.line, ctx.column)
# HACK: Implement FlexibleAlias[T, typ] by expanding it to typ here.
if (isinstance(typ, Instance)
and typ.type.fullname() == 'mypy_extensions.FlexibleAlias'):
typ = typ.args[-1]
return typ
