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evaluation.py
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evaluation.py
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# SPDX-Copyright: Copyright (c) Capital One Services, LLC
# SPDX-License-Identifier: Apache-2.0
# Copyright 2020 Capital One Services, LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and limitations under the License.
"""
CEL Interpreter using the AST directly.
The general idea is to map CEL operators to Python operators and push the
real work off to Python objects defined by the :py:mod:`celpy.celtypes` module.
CEL operator "+" is implemented by "_+_" function. We map this to :py:func:`operator.add`.
This will then look for `__add__()` methods in the various :py:class:`celpy.celtypes.CELType`
types.
In order to deal gracefully with missing and incomplete data,
exceptions are turned into first-class :py:class:`Result` objects.
They're not raised directly, but instead saved as part of the evaluation so that
short-circuit operators can ignore the exceptions.
This means that Python exceptions like :exc:`TypeError`, :exc:`IndexError`, and :exc:`KeyError`
are caught and transformed into :exc:`CELEvalError` objects.
The :py:class:`Resut` type hint is a union of the various values that are encountered
during evaluation. It's a union of the :py:class:`celpy.celtypes.CELTypes` type and the
:exc:`CELEvalError` exception.
"""
import collections
import logging
import operator
import re
import sys
from functools import reduce, wraps
from typing import (Any, Callable, Dict, Iterable, Iterator, List, Mapping,
Match, Optional, Sequence, Sized, Tuple, Type, TypeVar,
Union, cast)
import lark
import lark.visitors
import celpy.celtypes
from celpy.celparser import tree_dump
# A CEL type annotation. Used in an environment to describe objects as well as functions.
# This is a list of types, plus Callable for conversion functions.
Annotation = Union[
celpy.celtypes.CELType,
Callable[..., celpy.celtypes.Value], # Conversion functions and protobuf message type
Type[celpy.celtypes.FunctionType], # Concrete class for annotations
]
logger = logging.getLogger("evaluation")
class CELSyntaxError(Exception):
"""CEL Syntax error -- the AST did not have the expected structure."""
def __init__(self, arg: Any, line: Optional[int] = None, column: Optional[int] = None) -> None:
super().__init__(arg)
self.line = line
self.column = column
class CELUnsupportedError(Exception):
"""Feature unsupported by this implementation of CEL."""
def __init__(self, arg: Any, line: int, column: int) -> None:
super().__init__(arg)
self.line = line
self.column = column
class CELEvalError(Exception):
"""CEL evaluation problem. This can be saved as a temporary value for later use.
This is politely ignored by logic operators to provide commutative short-circuit.
We provide operator-like special methods so an instance of an error
returns itself when operated on.
"""
def __init__(
self,
*args: Any,
tree: Optional[lark.Tree] = None,
token: Optional[lark.Token] = None) -> None:
super().__init__(*args)
self.tree = tree
self.token = token
self.line: Optional[int] = None
self.column: Optional[int] = None
if self.tree:
self.line = self.tree.meta.line
self.column = self.tree.meta.column
if self.token:
self.line = self.token.line
self.column = self.token.column
def __repr__(self) -> str:
cls = self.__class__.__name__
if self.tree and self.token:
# This is rare
return (
f"{cls}(*{self.args}, tree={tree_dump(self.tree)!r}, token={self.token!r})"
) # pragma: no cover
elif self.tree:
return f"{cls}(*{self.args}, tree={tree_dump(self.tree)!r})" # pragma: no cover
else:
# Some unit tests do not provide a mock tree.
return f"{cls}(*{self.args})" # pragma: no cover
def with_traceback(self, tb: Any) -> 'CELEvalError':
return super().with_traceback(tb)
def __neg__(self) -> 'CELEvalError':
return self
def __add__(self, other: Any) -> 'CELEvalError':
return self
def __sub__(self, other: Any) -> 'CELEvalError':
return self
def __mul__(self, other: Any) -> 'CELEvalError':
return self
def __truediv__(self, other: Any) -> 'CELEvalError':
return self
def __floordiv__(self, other: Any) -> 'CELEvalError':
return self
def __mod__(self, other: Any) -> 'CELEvalError':
return self
def __pow__(self, other: Any) -> 'CELEvalError':
return self
def __radd__(self, other: Any) -> 'CELEvalError':
return self
def __rsub__(self, other: Any) -> 'CELEvalError':
return self
def __rmul__(self, other: Any) -> 'CELEvalError':
return self
def __rtruediv__(self, other: Any) -> 'CELEvalError':
return self
def __rfloordiv__(self, other: Any) -> 'CELEvalError':
return self
def __rmod__(self, other: Any) -> 'CELEvalError':
return self
def __rpow__(self, other: Any) -> 'CELEvalError':
return self
def __eq__(self, other: Any) -> bool:
if isinstance(other, CELEvalError):
return self.args == other.args
return NotImplemented
def __call__(self, *args: Any) -> 'CELEvalError':
return self
# The interim results extends celtypes to include itermediate CELEvalError exception objects.
# These can be deferred as part of commutative logical_and and logical_or operations.
# It includes the responses to type() queries, also.
Result = Union[
celpy.celtypes.Value,
CELEvalError,
celpy.celtypes.CELType,
]
# The various functions that apply to CEL data.
# The evaluator's functions expand on the CELTypes to include CELEvalError and the
# celpy.celtypes.CELType union type, also.
CELFunction = Callable[..., Result]
# A combination of a CELType result or a function resulting from identifier evaluation.
Result_Function = Union[
Result,
CELFunction,
]
Exception_Filter = Union[Type[BaseException], Sequence[Type[BaseException]]]
TargetFunc = TypeVar('TargetFunc', bound=CELFunction)
def eval_error(new_text: str, exc_class: Exception_Filter) -> Callable[[TargetFunc], TargetFunc]:
"""
Wrap a function to transform native Python exceptions to CEL CELEvalError values.
Any exception of the given class is replaced with the new CELEvalError object.
:param new_text: Text of the exception, e.g., "divide by zero", "no such overload")
this is the return value if the :exc:`CELEvalError` becomes the result.
:param exc_class: A Python exception class to match, e.g. ZeroDivisionError,
or a sequence of exception classes (e.g. (ZeroDivisionError, ValueError))
:return: A decorator that can be applied to a function
to map Python exceptions to :exc:`CELEvalError` instances.
This is used in the ``all()`` and ``exists()`` macros to silently ignore TypeError exceptions.
"""
def concrete_decorator(function: TargetFunc) -> TargetFunc:
@wraps(function)
def new_function(*args: celpy.celtypes.Value, **kwargs: celpy.celtypes.Value) -> Result:
try:
return function(*args, **kwargs)
except exc_class as ex: # type: ignore[misc]
logger.debug("%s(*%s, **%s) --> %s", function.__name__, args, kwargs, ex)
_, _, tb = sys.exc_info()
value = CELEvalError(new_text, ex.__class__, ex.args).with_traceback(tb)
value.__cause__ = ex
return value
except Exception:
logger.error("%s(*%s, **%s)", function.__name__, args, kwargs)
raise
return cast(TargetFunc, new_function)
return concrete_decorator
def boolean(
function: Callable[..., celpy.celtypes.Value]) -> Callable[..., celpy.celtypes.BoolType]:
"""
Wraps boolean operators to create CEL BoolType results.
:param function: One of the operator.lt, operator.gt, etc. comparison functions
:return: Decorated function with type coercion.
"""
@wraps(function)
def bool_function(a: celpy.celtypes.Value, b: celpy.celtypes.Value) -> celpy.celtypes.BoolType:
result = function(a, b)
if result == NotImplemented:
return cast(celpy.celtypes.BoolType, result)
return celpy.celtypes.BoolType(bool(result))
return bool_function
def operator_in(item: Result, container: Result) -> Result:
"""
CEL contains test; ignores type errors.
During evaluation of ``'elem' in [1, 'elem', 2]``,
CEL will raise internal exceptions for ``'elem' == 1`` and ``'elem' == 2``.
The :exc:`TypeError` exceptions are gracefully ignored.
During evaluation of ``'elem' in [1u, 'str', 2, b'bytes']``, however,
CEL will raise internal exceptions every step of the way, and an exception
value is the final result. (Not ``False`` from the one non-exceptional comparison.)
It would be nice to make use of the following::
eq_test = eval_error("no such overload", TypeError)(lambda x, y: x == y)
It seems like ``next(iter(filter(lambda x: eq_test(c, x) for c in container))))``
would do it. But. It's not quite right for the job.
There need to be three results, something :py:func:`filter` doesn't handle.
These are the chocies:
- True. There was a item found. Exceptions may or may not have been found.
- False. No item found AND no expceptions.
- CELEvalError. No item found AND at least one exception.
To an extent this is a little like the ``exists()`` macro.
We can think of ``container.contains(item)`` as ``container.exists(r, r == item)``.
However, exists() tends to silence exceptions, where this can expost them.
.. todo:: This may be better done as
``reduce(logical_or, (item == c for c in container), BoolType(False))``
"""
result: Result = celpy.celtypes.BoolType(False)
for c in cast(Iterable[Result], container):
try:
if c == item:
return celpy.celtypes.BoolType(True)
except TypeError as ex:
logger.debug("operator_in(%s, %s) --> %s", item, container, ex)
result = CELEvalError("no such overload", ex.__class__, ex.args)
logger.debug("operator_in(%r, %r) = %r", item, container, result)
return result
def function_size(container: Result) -> Result:
"""
The size() function applied to a Value. Delegate to Python's :py:func:`len`.
(string) -> int string length
(bytes) -> int bytes length
(list(A)) -> int list size
(map(A, B)) -> int map size
For other types, this will raise a Python :exc:`TypeError`.
(This is captured and becomes an :exc:`CELEvalError` Result.)
.. todo:: check container type for celpy.celtypes.StringType, celpy.celtypes.BytesType,
celpy.celtypes.ListType and celpy.celtypes.MapType
"""
if container is None:
return celpy.celtypes.IntType(0)
sized_container = cast(Sized, container)
result = celpy.celtypes.IntType(len(sized_container))
logger.debug("function_size(%r) = %r", container, result)
return result
# User-defined functions can override items in this mapping.
base_functions: Mapping[str, CELFunction] = {
"!_": celpy.celtypes.logical_not,
"-_": operator.neg,
"_+_": operator.add,
"_-_": operator.sub,
"_*_": operator.mul,
"_/_": operator.truediv,
"_%_": operator.mod,
"_<_": boolean(operator.lt),
"_<=_": boolean(operator.le),
"_>=_": boolean(operator.ge),
"_>_": boolean(operator.gt),
"_==_": boolean(operator.eq),
"_!=_": boolean(operator.ne),
"_in_": operator_in,
"_||_": celpy.celtypes.logical_or,
"_&&_": celpy.celtypes.logical_and,
"_?_:_": celpy.celtypes.logical_condition,
"_[_]": operator.getitem,
"size": function_size,
# StringType methods
"endsWith": lambda s, text: celpy.celtypes.BoolType(s.endswith(text)),
"startsWith": lambda s, text: celpy.celtypes.BoolType(s.startswith(text)),
"matches": lambda s, pattern: celpy.celtypes.BoolType(re.search(pattern, s) is not None),
"contains": lambda s, text: celpy.celtypes.BoolType(text in s),
# TimestampType methods. Type details are redundant, but required because of the lambdas
"getDate": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getDate(tz_name)),
"getDayOfMonth": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getDayOfMonth(tz_name)),
"getDayOfWeek": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getDayOfWeek(tz_name)),
"getDayOfYear": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getDayOfYear(tz_name)),
"getFullYear": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getFullYear(tz_name)),
"getMonth": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getMonth(tz_name)),
# TimestampType and DurationType methods
"getHours": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getHours(tz_name)),
"getMilliseconds": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getMilliseconds(tz_name)),
"getMinutes": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getMinutes(tz_name)),
"getSeconds": lambda ts, tz_name=None: celpy.celtypes.IntType(ts.getSeconds(tz_name)),
# type conversion functions
"bool": celpy.celtypes.BoolType,
"bytes": celpy.celtypes.BytesType,
"double": celpy.celtypes.DoubleType,
"duration": celpy.celtypes.DurationType,
"int": celpy.celtypes.IntType,
"list": celpy.celtypes.ListType, # https://github.com/google/cel-spec/issues/123
"map": celpy.celtypes.MapType,
"null_type": type(None),
"string": celpy.celtypes.StringType,
"timestamp": celpy.celtypes.TimestampType,
"uint": celpy.celtypes.UintType,
"type": type,
}
class Referent:
"""
A Name can refer to any of the following things:
- Annotations -- initially most names are these
or a CELFunction that may implement a type.
Must be provided as part of the initialization.
- NameContainer -- some names are these. This is true
when the name is *not* provided as part of the initialization because
we discovered the name during type or environment binding.
- celpy.celtypes.Value -- many annotations also have values.
These are provided **after** Annotations, and require them.
- CELEvalError -- This seems unlikely, but we include it because it's possible.
- Functions -- All of the type conversion functions are names in a NameContainer.
A name can be ambiguous and refer to both a nested ``NameContainer`` as well
as a ``celpy.celtypes.Value`` (usually a MapType instance.)
Object ``b`` has two possible meanings:
- ``b.c`` is a NameContainer for ``c``, a string.
- ``b`` is a mapping, and ``b.c`` is syntax sugar for ``b['c']``.
The "longest name" rule means that the useful value is the "c" object
in the nested ``NameContainer``.
The syntax sugar interpretation is done in the rare case we can't find the ``NameContainer``.
>>> nc = NameContainer("c", celpy.celtypes.StringType)
>>> b = Referent(celpy.celtypes.MapType)
>>> b.value = celpy.celtypes.MapType({"c": "oops"})
>>> b.value == celpy.celtypes.MapType({"c": "oops"})
True
>>> b.container = nc
>>> b.value == nc
True
In effect, this class is
::
Referent = Union[
Annotation,
celpy.celtypes.Value,
CELEvalError,
CELFunction,
]
"""
def __init__(
self,
ref_to: Optional[Annotation] = None
# Union[
# None, Annotation, celpy.celtypes.Value, CELEvalError,
# CELFunction, 'NameContainer'
# ] = None
) -> None:
self.annotation: Optional[Annotation] = None
self.container: Optional['NameContainer'] = None
self._value: Union[
None, Annotation, celpy.celtypes.Value, CELEvalError, CELFunction,
'NameContainer'] = None
self._value_set = False
if ref_to:
self.annotation = ref_to
def __repr__(self) -> str:
return (
f"{self.__class__.__name__}(annotation={self.annotation!r}, "
f"container={self.container!r}, "
f"_value={self._value!r})"
)
@property
def value(self) -> Union[
Annotation, celpy.celtypes.Value, CELEvalError, CELFunction, 'NameContainer']:
"""
The longest-path rule means we prefer ``NameContainer`` over any locally defined value.
Otherwise, we'll provide a value if there is one.
Finally, we'll provide the annotation if there's no value.
:return:
"""
if self.container is not None:
return self.container
elif self._value_set:
return self._value
else:
# Not part of a namespace path. Nor was a value set.
return self.annotation
@value.setter
def value(
self,
ref_to: Union[
Annotation, celpy.celtypes.Value, CELEvalError, CELFunction, 'NameContainer']
) -> None:
self._value = ref_to
self._value_set = True
def clone(self) -> "Referent":
new = Referent(self.annotation)
new.container = self.container
new._value = self._value
new._value_set = self._value_set
return new
# A name resolution context is a mapping from an identifer to a Value or a ``NameContainer``.
# This reflects some murkiness in the name resolution algorithm that needs to be cleaned up.
Context = Mapping[str, Union[Result, "NameContainer"]]
# Copied from cel.lark
IDENT = r"[_a-zA-Z][_a-zA-Z0-9]*"
class NameContainer(Dict[str, Referent]):
"""
A namespace that fulfills the CEL name resolution requirement.
::
Scenario: "qualified_identifier_resolution_unchecked"
"namespace resolution should try to find the longest prefix for the evaluator."
NameContainer instances can be chained (via parent) to create a sequence of searchable
locations for a name.
- Local-most is an Activation with local variables within a macro.
These are part of a nested chain of Activations for each macro. Each local activation
is a child with a reference to the parent Activation.
- Parent of any local Activation is the overall Activation for this CEL evaluation.
The overall Activation contains a number of NameContainers:
- The global variable bindings.
- Bindings of function definitions. This is the default set of functions for CEL
plus any add-on functions introduced by C7N.
- The run-time annotations from the environment. There are two kinds:
- Protobuf message definitions. These are types, really.
- Annotations for global variables. The annotations tend to be hidden by the values.
They're in the lookup chain to simplify access to protobuf messages.
- The environment also provides the built-in type names and aliases for the
:mod:`celtypes` package of built-in types.
This means name resolution marches from local-most to remote-most, searching for a binding.
The global variable bindings have a local-most value and a more remote annotation.
The annotations (i.e. protobuf message types) have only a fairly remote annotation without
a value.
Structure.
A NameContainer is a mapping from names to Referents.
A Referent can be one of three things.
- A NameContainer further down the path
- An Annotation
- An Annotation with a value.
Loading Names.
There are several "phases" to building the chain of ``NameContainer`` instances.
1. The ``Activation`` creates the initial ``name : annotation`` bindings.
Generally, the names are type names, like "int", bound to :py:class:`celtypes.IntType`.
In some cases, the name is a future variable name, "resource",
bound to :py:class:`celtypes.MapType`.
2. The ``Activation`` creates a second ``NameContainer`` that has variable names.
This has a reference back to the parent to resolve names that are types.
This involves decomposing the paths of names to make a tree of nested ``NameContainers``.
Upper-level containers don't (necessarily) have types or values -- they're merely
``NameContainer`` along the path to the target names.
Resolving Names.
See https://github.com/google/cel-spec/blob/master/doc/langdef.md#name-resolution
There are three cases required in the :py:class:`Evaluator` engine.
- Variables and Functions. These are ``Result_Function`` instances: i.e., ordinary values.
- ``Name.Name`` can be navigation into a protobuf package, when ``Name`` is protobuf package.
The idea is to locate the longest possible match.
If a.b is a name to be resolved in the context of a protobuf declaration with scope A.B,
then resolution is attempted, in order, as A.B.a.b, A.a.b, and finally a.b.
To override this behavior, one can use .a.b;
this name will only be attempted to be resolved in the root scope, i.e. as a.b.
- ``Name.Name`` can be syntactic sugar for indexing into a mapping when ``Name`` is a value of
``MapType`` or a ``MessageType``. It's evaluated as if it was ``Name["Name"]``.
This is a fall-back plan if the previous resolution failed.
The longest chain of nested packages *should* be resolved first.
This will happen when each name is a ``NameContainer`` object containing
other ``NameContainer`` objects.
The chain of evaluations for ``IDENT . IDENT . IDENT`` is (in effect)
::
member_dot(member_dot(primary(IDENT), IDENT), IDENT)
This makes the ``member_dot` processing left associative.
The ``primary(IDENT)`` resolves to a CEL object of some kind.
Once the ``primary(IDENT)`` has been resolved, it establishes a context
for subsequent ``member_dot`` methods.
- If this is a ``MapType`` or a ``MessageType`` with an object,
then ``member_dot`` will pluck out a field value and return this.
- If this is a ``NameContainer`` or a ``PackageType`` then the ``member_dot``
will pluck out a sub-package or ``EnumType`` or ``MessageType``
and return the type object instead of a value.
At some point a ``member_object`` production will build an object from the type.
The evaluator's :meth:`ident_value` method resolves the identifier into the ``Referent``.
Acceptance Test Case
We have two names
- `a.b` -> NameContainer in which c = "yeah". (i.e., a.b.c : "yeah")
- `a.b` -> Mapping with {"c": "oops"}.
This means any given name can have as many as three meanings:
- Primarily as a NameContainer. This resolves name.name.name to find the longest
namespace possible.
- Secondarily as a Mapping. This will be a fallback when name.name.name is really
syntactic sugar for name.name['name'].
- Finally as a type annotation.
"""
ident_pat = re.compile(IDENT)
extended_name_path = re.compile(f"^\\.?{IDENT}(?:\\.{IDENT})*$")
logger = logging.getLogger("NameContainer")
def __init__(
self,
name: Optional[str] = None,
ref_to: Optional[Referent] = None,
parent: Optional['NameContainer'] = None
) -> None:
if name and ref_to:
super().__init__({name: ref_to})
else:
super().__init__()
self.parent: Optional[NameContainer] = parent
def load_annotations(
self,
names: Mapping[str, Annotation],
) -> None:
"""
Used by an ``Activation`` to build a container used to resolve
long path names into nested NameContainers.
Sets annotations for all supplied identifiers.
``{"name1.name2": annotation}`` becomes two things:
1. nc2 = NameContainer({"name2" : Referent(annotation)})
2. nc1 = NameContainer({"name1" : Referent(nc2)})
:param names: A dictionary of {"name1.name1....": Referent, ...} items.
"""
for name, refers_to in names.items():
self.logger.info("load_annotations %r : %r", name, refers_to)
if not self.extended_name_path.match(name):
raise ValueError(f"Invalid name {name}")
context = self
# Expand "name1.name2....": refers_to into ["name1", "name2", ...]: refers_to
*path, final = self.ident_pat.findall(name)
for name in path:
ref = context.setdefault(name, Referent())
if ref.container is None:
ref.container = NameContainer(parent=self.parent)
context = ref.container
context.setdefault(final, Referent(refers_to))
def load_values(self, values: Context) -> None:
"""Update annotations with actual values."""
for name, refers_to in values.items():
self.logger.info("load_values %r : %r", name, refers_to)
if not self.extended_name_path.match(name):
raise ValueError(f"Invalid name {name}")
context = self
# Expand "name1.name2....": refers_to into ["name1", "name2", ...]: refers_to
# Update NameContainer("name1", NameContainer("name2", NameContainer(..., refers_to)))
*path, final = self.ident_pat.findall(name)
for name in path:
ref = context.setdefault(name, Referent())
if ref.container is None:
ref.container = NameContainer(parent=self.parent)
context = ref.container
context.setdefault(final, Referent()) # No annotation.
context[final].value = refers_to
class NotFound(Exception):
"""
Raised locally when a name is not found in the middle of package search.
We can't return ``None`` from find_name because that's a valid value.
"""
pass
@staticmethod
def dict_find_name(some_dict: Dict[str, Referent], path: List[str]) -> Result:
"""
Extension to navgiate into mappings, messages, and packages.
:param some_dict: An instance of a MapType, MessageType, or PackageType.
:param path: names to follow into the structure.
:returns: Value found down inside the structure.
"""
if path:
head, *tail = path
try:
return NameContainer.dict_find_name(
cast(Dict[str, Referent], some_dict[head]),
tail)
except KeyError:
NameContainer.logger.debug("%r not found in %s", head, some_dict.keys())
raise NameContainer.NotFound(path)
else:
return cast(Result, some_dict)
def find_name(self, path: List[str]) -> Union["NameContainer", Result]:
"""
Find the name by searching down through nested packages or raise NotFound.
This is a kind of in-order tree walk of contained packages.
"""
if path:
head, *tail = path
try:
sub_context = self[head].value
except KeyError:
self.logger.debug("%r not found in %s", head, self.keys())
raise NameContainer.NotFound(path)
if isinstance(sub_context, NameContainer):
return sub_context.find_name(tail)
elif isinstance(
sub_context,
(celpy.celtypes.MessageType, celpy.celtypes.MapType,
celpy.celtypes.PackageType, dict)
):
# Out of defined NameContainers, moving into Values: Messages, Mappings or Packages
# Make a fake Referent return value.
item: Union["NameContainer", Result] = NameContainer.dict_find_name(
cast(Dict[str, Referent], sub_context),
tail
)
return item
else:
# Fully matched. No more Referents with NameContainers or Referents with Mappings.
return cast(NameContainer, sub_context)
else:
# Fully matched. This NameContainer is what we were looking for.
return self
def parent_iter(self) -> Iterator['NameContainer']:
"""Yield this NameContainer and all of its parents to create a flat list."""
yield self
if self.parent is not None:
yield from self.parent.parent_iter()
def resolve_name(
self,
package: Optional[str],
name: str
) -> Referent:
"""
Search with less and less package prefix until we find the thing.
Resolution works as follows.
If a.b is a name to be resolved in the context of a protobuf declaration with scope A.B,
then resolution is attempted, in order, as
1. A.B.a.b. (Search for "a" in paackage "A.B"; the ".b" is handled separately.)
2. A.a.b. (Search for "a" in paackage "A"; the ".b" is handled separately.)
3. (finally) a.b. (Search for "a" in paackage None; the ".b" is handled separately.)
To override this behavior, one can use .a.b;
this name will only be attempted to be resolved in the root scope, i.e. as a.b.
We Start with the longest package name, a ``List[str]`` assigned to ``target``.
Given a target, search through this ``NameContainer`` and all parents in the
:meth:`parent_iter` iterable.
The first name we find in the parent sequence is the goal.
This is because values are first, type annotations are laast.
If we can't find the identifier with given package target,
truncate the package name from the end to create a new target and try again.
This is a bottom-up look that favors the longest name.
:param package: Prefix string "name.name.name"
:param name: The variable we're looking for
:return: Name resolution as a Rereferent, often a value, but maybe a package or an
annotation.
"""
self.logger.info(
"resolve_name(%r.%r) in %s, parent=%s", package, name, self.keys, self.parent
)
# Longest Name
if package:
target = self.ident_pat.findall(package) + [""]
else:
target = [""]
# Pool of matches
matches: List[Tuple[List[str], Union["NameContainer", Result]]] = []
# Target has an extra item to make the len non-zero.
while not matches and target:
target = target[:-1]
for p in self.parent_iter():
try:
package_ident: List[str] = target + [name]
match: Union["NameContainer", Result] = p.find_name(package_ident)
matches.append((package_ident, match))
except NameContainer.NotFound:
# No matches; move to the parent and try again.
pass
self.logger.debug("resolve_name: target=%s+[%r], matches=%s", target, name, matches)
if not matches:
raise KeyError(name)
# This feels hackish -- it should be the first referent value.
# Find the longest name match.p
path, value = max(matches, key=lambda path_value: len(path_value[0]))
return cast(Referent, value)
def clone(self) -> 'NameContainer':
new = NameContainer(parent=self.parent)
for k, v in self.items():
new[k] = v.clone()
return new
def __repr__(self) -> str:
return f"{self.__class__.__name__}({dict(self)}, parent={self.parent})"
class Activation:
"""
Namespace with variable bindings and type name ("annotation") bindings.
.. rubric:: Life and Content
An Activation is created by an Environment and contains the annotations
(and a package name) from that Environment. Variables are loaded into the
activation for evaluation.
A nested Activation is created each time we evaluate a macro.
An Activation contains a ``NameContainer`` instance to resolve identifers.
(This may be a needless distinction and the two classes could, perhaps, be combined.)
.. todo:: The environment's annotations are type names used for protobuf.
.. rubric:: Chaining/Nesting
Activations can form a chain so locals are checked first.
Activations can nest via macro evaluation, creating transient local variables.
::
``"[2, 4, 6].map(n, n / 2)"``
means nested activations with ``n`` bound to 2, 4, and 6 respectively.
The resulting objects then form a resulting list.
This is used by an :py:class:`Evaluator` as follows::
sub_activation: Activation = self.activation.nested_activation()
sub_eval: Evaluator = self.sub_eval(sub_activation)
sub_eval_partial: Callable[[Value], Value] = sub_eval.partial(
tree_for_variable, tree_for_expression)
push(celtypes.ListType(map(sub_eval_partial, pop()))
The ``localized_eval()`` creates a new :py:class:`Activation`
and an associated :py:class:`Evaluator` for this nested activation context.
It uses the :py:class:`Evaluator.visit` method to evaluate the given expression for
a new object bound to the given variable.
.. rubric:: Namespace Creation
We expand ``{"a.b.c": 42}`` to create nested namespaces: ``{"a": {"b": {"c": 42}}}``.
This depends on two syntax rules to define the valid names::
member : primary
| member "." IDENT ["(" [exprlist] ")"]
primary : ["."] IDENT ["(" [exprlist] ")"]
Ignore the ``["(" [exprlist] ")"]`` options used for member functions.
We have members and primaries, both of which depend on the following lexical rule::
IDENT : /[_a-zA-Z][_a-zA-Z0-9]*/
Name expansion is handled in order of length. Here's why::
Scenario: "qualified_identifier_resolution_unchecked"
"namespace resolution should try to find the longest prefix for the evaluator."
Most names start with ``IDENT``, but a primary can start with ``.``.
"""
def __init__(
self,
annotations: Optional[Mapping[str, Annotation]] = None,
package: Optional[str] = None,
vars: Optional[Context] = None,
parent: Optional['Activation'] = None,
) -> None:
"""
Create an Activation.
The annotations are loaded first. The variables are loaded second, and placed
in front of the annotations in the chain of name resolutions. Values come before
annotations.
:param annotations: Variables and type annotations.
Annotations are loaded first to serve as defaults to create a parent NameContainer.
:param package: The package name to assume as a prefix for name resolution.
:param vars: Variables and their values, loaded to update the NameContainer.
:param parent: A parent activation in the case of macro evaluations.
"""
logger.info(
"Activation(annotations=%r, package=%r, vars=%r, "
"parent=%s)", annotations, package, vars, parent
)
# Seed the annotation identifiers for this activation.
self.identifiers: NameContainer = NameContainer(
parent=parent.identifiers if parent else None
)
if annotations is not None:
self.identifiers.load_annotations(annotations)
# The name of the run-time package -- an assumed prefix for name resolution
self.package = package
# Create a child NameContainer with variables (if any.)
if vars is None:
pass
elif isinstance(vars, Activation): # pragma: no cover
# Deprecated legacy feature.
raise NotImplementedError("Use Activation.clone()")
else:
# Set values from a dictionary of names and values.
self.identifiers.load_values(vars)
def clone(self) -> "Activation":
"""
Create a clone of this activation with a deep copy of the identifiers.
"""
clone = Activation()
clone.package = self.package
clone.identifiers = self.identifiers.clone()
return clone
def nested_activation(
self,
annotations: Optional[Mapping[str, Annotation]] = None,
vars: Optional[Context] = None
) -> 'Activation':
"""
Create a nested sub-Activation that chains to the current activation.
The sub-activations don't have the same implied package context,
:param annotations: Variable type annotations
:param vars: Variables with literals to be converted to the desired types.
:return: An ``Activation`` that chains to this Activation.
"""
new = Activation(
annotations=annotations,
vars=vars,
parent=self,
package=self.package
)
return new
def resolve_variable(self, name: str) -> Union[Result, NameContainer]:
"""Find the object referred to by the name.
An Activation usually has a chain of NameContainers to be searched.
A variable can refer to an annotation and/or a value and/or a nested
container. Most of the time, we want the `value` attribute of the Referent.
This can be a Result (a Union[Value, CelType])
"""
container_or_value = self.identifiers.resolve_name(self.package, str(name))
return cast(Union[Result, NameContainer], container_or_value)
def __repr__(self) -> str:
return (
f"{self.__class__.__name__}"
f"(annotations={self.identifiers.parent!r}, "
f"package={self.package!r}, "
f"vars={self.identifiers!r}, "
f"parent={self.identifiers.parent})"
)
class FindIdent(lark.visitors.Visitor_Recursive):
"""Locate the ident token at the bottom of an AST.
This is needed to find the bind variable for macros.
It works by doing a "visit" on the entire tree, but saving
the details of the ``ident`` nodes only.