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https://github.com/Instagram/LibCST.git
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dbbe3d1927
Add metadata access and dependency logic in `CSTVisitor` and `Module.visit` to generate all metadata dependencies before performing a visit pass over a tree and validate access to metadata.
81 lines
2.4 KiB
Python
81 lines
2.4 KiB
Python
# Copyright (c) Facebook, Inc. and its affiliates.
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#
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# This source code is licensed under the MIT license found in the
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# LICENSE file in the root directory of this source tree.
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# pyre-strict
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from abc import ABC
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from typing import TYPE_CHECKING, ClassVar, Sequence, Type, TypeVar, Union
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from libcst._removal_sentinel import RemovalSentinel
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if TYPE_CHECKING:
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# Circular dependency for typing reasons only
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from libcst.nodes._base import CSTNode
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from libcst.metadata.base_provider import BaseMetadataProvider
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# RemovalSentinel is re-exported
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__all__ = ["CSTVisitor", "RemovalSentinel"]
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CSTNodeT = TypeVar("CSTNodeT", bound="CSTNode")
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_T = TypeVar("_T")
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_UNDEFINED_DEFAULT = object()
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class CSTVisitor(ABC):
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"""
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The low-level base visitor class.
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This shouldn't be used directly, instead we should provide a more user-friendly
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subclass.
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"""
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METADATA_DEPENDENCIES: ClassVar[Sequence[Type["BaseMetadataProvider[object]"]]] = ()
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def on_visit(self, node: "CSTNode") -> bool:
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"""
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Called every time a node is visited, before we've visited its children.
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Returns `True` if children should be visited, and returns `False` otherwise.
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"""
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return True
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def on_leave(
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self, original_node: CSTNodeT, updated_node: CSTNodeT
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) -> Union[CSTNodeT, RemovalSentinel]:
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"""
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Called every time we leave a node, after we've visited its children.
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A RemovalSentinel indicates that the node should be removed from its parent.
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This is not always possible, and may raise an exception.
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"""
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return updated_node
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@classmethod
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def get_metadata(
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cls,
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key: Type["BaseMetadataProvider[_T]"],
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node: CSTNodeT,
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default: _T = _UNDEFINED_DEFAULT,
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) -> _T:
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"""
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Gets metadata provided by the [key] provider if it is accessible from
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this vistor. Metadata is accessible if [key] is the same as [cls] or
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if [key] is in METADATA_DEPENDENCIES.
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"""
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if key not in cls.METADATA_DEPENDENCIES and key is not cls:
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raise KeyError(
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f"{key.__name__} is not declared as a dependency from {cls.__name__}"
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)
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try:
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return node._metadata[key]
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except KeyError as err:
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if default is not _UNDEFINED_DEFAULT:
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return default
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else:
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raise err
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