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# Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
from enum import auto, Enum
from typing import Optional, Sequence
import libcst as cst
from libcst.metadata.base_provider import BatchableMetadataProvider
class ExpressionContext(Enum):
"""Used in :class:`ExpressionContextProvider` to represent context of a variable
reference."""
#: Load the value of a variable reference.
#:
#: >>> libcst.MetadataWrapper(libcst.parse_module("a")).resolve(libcst.ExpressionContextProvider)
#: mappingproxy({Name(
#: value='a',
#: lpar=[],
#: rpar=[],
#: ): <ExpressionContext.LOAD: 1>})
LOAD = auto()
#: Store a value to a variable reference by :class:`~libcst.Assign` (``=``),
#: :class:`~libcst.AugAssign` (e.g. ``+=``, ``-=``, etc), or
#: :class:`~libcst.AnnAssign`.
#:
#: >>> libcst.MetadataWrapper(libcst.parse_module("a = b")).resolve(libcst.ExpressionContextProvider)
#: mappingproxy({Name(
#: value='a',
#: lpar=[],
#: rpar=[],
#: ): <ExpressionContext.STORE: 2>, Name(
#: value='b',
#: lpar=[],
#: rpar=[],
#: ): <ExpressionContext.LOAD: 1>})
STORE = auto()
#: Delete value of a variable reference by ``del``.
#:
#: >>> libcst.MetadataWrapper(libcst.parse_module("del a")).resolve(libcst.ExpressionContextProvider)
#: mappingproxy({Name(
#: value='a',
#: lpar=[],
#: rpar=[],
#: ): < ExpressionContext.DEL: 3 >})
DEL = auto()
class ExpressionContextVisitor(cst.CSTVisitor):
def __init__(
self, provider: "ExpressionContextProvider", context: ExpressionContext
) -> None:
self.provider = provider
self.context = context
def visit_Assign(self, node: cst.Assign) -> bool:
for target in node.targets:
target.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.value.visit(self)
return False
def visit_AnnAssign(self, node: cst.AnnAssign) -> bool:
node.target.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.annotation.visit(self)
value = node.value
if value:
value.visit(self)
return False
def visit_AugAssign(self, node: cst.AugAssign) -> bool:
node.target.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.value.visit(self)
return False
def visit_NamedExpr(self, node: cst.NamedExpr) -> bool:
node.target.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.value.visit(self)
return False
def visit_Name(self, node: cst.Name) -> bool:
self.provider.set_metadata(node, self.context)
return False
def visit_AsName(self, node: cst.AsName) -> Optional[bool]:
node.name.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
return False
def visit_CompFor(self, node: cst.CompFor) -> bool:
node.target.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.iter.visit(self)
for i in node.ifs:
i.visit(self)
inner_for_in = node.inner_for_in
if inner_for_in:
inner_for_in.visit(self)
return False
def visit_For(self, node: cst.For) -> bool:
node.target.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.iter.visit(self)
node.body.visit(self)
orelse = node.orelse
if orelse:
orelse.visit(self)
return False
def visit_Del(self, node: cst.Del) -> bool:
node.target.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.DEL)
)
return False
def visit_Attribute(self, node: cst.Attribute) -> bool:
self.provider.set_metadata(node, self.context)
node.value.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.LOAD)
)
# don't visit attr (Name), so attr has no context
return False
def visit_Subscript(self, node: cst.Subscript) -> bool:
self.provider.set_metadata(node, self.context)
node.value.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.LOAD)
)
slice = node.slice
if isinstance(slice, Sequence):
for sli in slice:
sli.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.LOAD)
)
else:
slice.visit(ExpressionContextVisitor(self.provider, ExpressionContext.LOAD))
return False
def visit_Tuple(self, node: cst.Tuple) -> Optional[bool]:
self.provider.set_metadata(node, self.context)
def visit_List(self, node: cst.List) -> Optional[bool]:
self.provider.set_metadata(node, self.context)
def visit_StarredElement(self, node: cst.StarredElement) -> Optional[bool]:
self.provider.set_metadata(node, self.context)
def visit_ClassDef(self, node: cst.ClassDef) -> Optional[bool]:
node.name.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.body.visit(self)
for base in node.bases:
base.visit(self)
for keyword in node.keywords:
keyword.visit(self)
for decorator in node.decorators:
decorator.visit(self)
return False
def visit_FunctionDef(self, node: cst.FunctionDef) -> Optional[bool]:
node.name.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
node.params.visit(self)
node.body.visit(self)
for decorator in node.decorators:
decorator.visit(self)
returns = node.returns
if returns:
returns.visit(self)
return False
def visit_Param(self, node: cst.Param) -> Optional[bool]:
node.name.visit(
ExpressionContextVisitor(self.provider, ExpressionContext.STORE)
)
annotation = node.annotation
if annotation:
annotation.visit(self)
default = node.default
if default:
default.visit(self)
return False
class ExpressionContextProvider(BatchableMetadataProvider[ExpressionContext]):
"""
Provides :class:`ExpressionContext` metadata (mimics the `expr_context
<https://docs.python.org/3/library/ast.html>`__ in ast) for the
following node types:
:class:`~libcst.Attribute`, :class:`~libcst.Subscript`,
:class:`~libcst.StarredElement` , :class:`~libcst.List`,
:class:`~libcst.Tuple` and :class:`~libcst.Name`.
Note that a :class:`~libcst.Name` may not always have context because of the differences between
ast and LibCST. E.g. :attr:`~libcst.Attribute.attr` is a :class:`~libcst.Name` in LibCST
but a str in ast. To honor ast implementation, we don't assign context to
:attr:`~libcst.Attribute.attr`.
Three context types :attr:`ExpressionContext.STORE`,
:attr:`ExpressionContext.LOAD` and :attr:`ExpressionContext.DEL` are provided.
"""
def visit_Module(self, node: cst.Module) -> Optional[bool]:
node.visit(ExpressionContextVisitor(self, ExpressionContext.LOAD))
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