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Waylon Walker 2022-03-31 20:20:07 -05:00
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from contextlib import contextmanager
from collections import defaultdict
from typing import Dict, List, Set, Iterator, Union, Optional, Tuple, cast
from typing_extensions import DefaultDict, TypeAlias as _TypeAlias
from mypy.types import (
Type, AnyType, PartialType, UnionType, TypeOfAny, NoneType, get_proper_type
)
from mypy.subtypes import is_subtype
from mypy.join import join_simple
from mypy.sametypes import is_same_type
from mypy.erasetype import remove_instance_last_known_values
from mypy.nodes import Expression, Var, RefExpr
from mypy.literals import Key, literal, literal_hash, subkeys
from mypy.nodes import IndexExpr, MemberExpr, AssignmentExpr, NameExpr
BindableExpression: _TypeAlias = Union[IndexExpr, MemberExpr, AssignmentExpr, NameExpr]
class Frame:
"""A Frame represents a specific point in the execution of a program.
It carries information about the current types of expressions at
that point, arising either from assignments to those expressions
or the result of isinstance checks. It also records whether it is
possible to reach that point at all.
This information is not copied into a new Frame when it is pushed
onto the stack, so a given Frame only has information about types
that were assigned in that frame.
"""
def __init__(self, id: int, conditional_frame: bool = False) -> None:
self.id = id
self.types: Dict[Key, Type] = {}
self.unreachable = False
self.conditional_frame = conditional_frame
# Should be set only if we're entering a frame where it's not
# possible to accurately determine whether or not contained
# statements will be unreachable or not.
#
# Long-term, we should improve mypy to the point where we no longer
# need this field.
self.suppress_unreachable_warnings = False
Assigns = DefaultDict[Expression, List[Tuple[Type, Optional[Type]]]]
class ConditionalTypeBinder:
"""Keep track of conditional types of variables.
NB: Variables are tracked by literal expression, so it is possible
to confuse the binder; for example,
```
class A:
a = None # type: Union[int, str]
x = A()
lst = [x]
reveal_type(x.a) # Union[int, str]
x.a = 1
reveal_type(x.a) # int
reveal_type(lst[0].a) # Union[int, str]
lst[0].a = 'a'
reveal_type(x.a) # int
reveal_type(lst[0].a) # str
```
"""
# Stored assignments for situations with tuple/list lvalue and rvalue of union type.
# This maps an expression to a list of bound types for every item in the union type.
type_assignments: Optional[Assigns] = None
def __init__(self) -> None:
self.next_id = 1
# The stack of frames currently used. These map
# literal_hash(expr) -- literals like 'foo.bar' --
# to types. The last element of this list is the
# top-most, current frame. Each earlier element
# records the state as of when that frame was last
# on top of the stack.
self.frames = [Frame(self._get_id())]
# For frames higher in the stack, we record the set of
# Frames that can escape there, either by falling off
# the end of the frame or by a loop control construct
# or raised exception. The last element of self.frames
# has no corresponding element in this list.
self.options_on_return: List[List[Frame]] = []
# Maps literal_hash(expr) to get_declaration(expr)
# for every expr stored in the binder
self.declarations: Dict[Key, Optional[Type]] = {}
# Set of other keys to invalidate if a key is changed, e.g. x -> {x.a, x[0]}
# Whenever a new key (e.g. x.a.b) is added, we update this
self.dependencies: Dict[Key, Set[Key]] = {}
# Whether the last pop changed the newly top frame on exit
self.last_pop_changed = False
self.try_frames: Set[int] = set()
self.break_frames: List[int] = []
self.continue_frames: List[int] = []
def _get_id(self) -> int:
self.next_id += 1
return self.next_id
def _add_dependencies(self, key: Key, value: Optional[Key] = None) -> None:
if value is None:
value = key
else:
self.dependencies.setdefault(key, set()).add(value)
for elt in subkeys(key):
self._add_dependencies(elt, value)
def push_frame(self, conditional_frame: bool = False) -> Frame:
"""Push a new frame into the binder."""
f = Frame(self._get_id(), conditional_frame)
self.frames.append(f)
self.options_on_return.append([])
return f
def _put(self, key: Key, type: Type, index: int = -1) -> None:
self.frames[index].types[key] = type
def _get(self, key: Key, index: int = -1) -> Optional[Type]:
if index < 0:
index += len(self.frames)
for i in range(index, -1, -1):
if key in self.frames[i].types:
return self.frames[i].types[key]
return None
def put(self, expr: Expression, typ: Type) -> None:
if not isinstance(expr, (IndexExpr, MemberExpr, AssignmentExpr, NameExpr)):
return
if not literal(expr):
return
key = literal_hash(expr)
assert key is not None, 'Internal error: binder tried to put non-literal'
if key not in self.declarations:
self.declarations[key] = get_declaration(expr)
self._add_dependencies(key)
self._put(key, typ)
def unreachable(self) -> None:
self.frames[-1].unreachable = True
def suppress_unreachable_warnings(self) -> None:
self.frames[-1].suppress_unreachable_warnings = True
def get(self, expr: Expression) -> Optional[Type]:
key = literal_hash(expr)
assert key is not None, 'Internal error: binder tried to get non-literal'
return self._get(key)
def is_unreachable(self) -> bool:
# TODO: Copy the value of unreachable into new frames to avoid
# this traversal on every statement?
return any(f.unreachable for f in self.frames)
def is_unreachable_warning_suppressed(self) -> bool:
# TODO: See todo in 'is_unreachable'
return any(f.suppress_unreachable_warnings for f in self.frames)
def cleanse(self, expr: Expression) -> None:
"""Remove all references to a Node from the binder."""
key = literal_hash(expr)
assert key is not None, 'Internal error: binder tried cleanse non-literal'
self._cleanse_key(key)
def _cleanse_key(self, key: Key) -> None:
"""Remove all references to a key from the binder."""
for frame in self.frames:
if key in frame.types:
del frame.types[key]
def update_from_options(self, frames: List[Frame]) -> bool:
"""Update the frame to reflect that each key will be updated
as in one of the frames. Return whether any item changes.
If a key is declared as AnyType, only update it if all the
options are the same.
"""
frames = [f for f in frames if not f.unreachable]
changed = False
keys = set(key for f in frames for key in f.types)
for key in keys:
current_value = self._get(key)
resulting_values = [f.types.get(key, current_value) for f in frames]
if any(x is None for x in resulting_values):
# We didn't know anything about key before
# (current_value must be None), and we still don't
# know anything about key in at least one possible frame.
continue
type = resulting_values[0]
assert type is not None
declaration_type = get_proper_type(self.declarations.get(key))
if isinstance(declaration_type, AnyType):
# At this point resulting values can't contain None, see continue above
if not all(is_same_type(type, cast(Type, t)) for t in resulting_values[1:]):
type = AnyType(TypeOfAny.from_another_any, source_any=declaration_type)
else:
for other in resulting_values[1:]:
assert other is not None
type = join_simple(self.declarations[key], type, other)
if current_value is None or not is_same_type(type, current_value):
self._put(key, type)
changed = True
self.frames[-1].unreachable = not frames
return changed
def pop_frame(self, can_skip: bool, fall_through: int) -> Frame:
"""Pop a frame and return it.
See frame_context() for documentation of fall_through.
"""
if fall_through > 0:
self.allow_jump(-fall_through)
result = self.frames.pop()
options = self.options_on_return.pop()
if can_skip:
options.insert(0, self.frames[-1])
self.last_pop_changed = self.update_from_options(options)
return result
@contextmanager
def accumulate_type_assignments(self) -> 'Iterator[Assigns]':
"""Push a new map to collect assigned types in multiassign from union.
If this map is not None, actual binding is deferred until all items in
the union are processed (a union of collected items is later bound
manually by the caller).
"""
old_assignments = None
if self.type_assignments is not None:
old_assignments = self.type_assignments
self.type_assignments = defaultdict(list)
yield self.type_assignments
self.type_assignments = old_assignments
def assign_type(self, expr: Expression,
type: Type,
declared_type: Optional[Type],
restrict_any: bool = False) -> None:
# We should erase last known value in binder, because if we are using it,
# it means that the target is not final, and therefore can't hold a literal.
type = remove_instance_last_known_values(type)
type = get_proper_type(type)
declared_type = get_proper_type(declared_type)
if self.type_assignments is not None:
# We are in a multiassign from union, defer the actual binding,
# just collect the types.
self.type_assignments[expr].append((type, declared_type))
return
if not isinstance(expr, (IndexExpr, MemberExpr, NameExpr)):
return None
if not literal(expr):
return
self.invalidate_dependencies(expr)
if declared_type is None:
# Not sure why this happens. It seems to mainly happen in
# member initialization.
return
if not is_subtype(type, declared_type):
# Pretty sure this is only happens when there's a type error.
# Ideally this function wouldn't be called if the
# expression has a type error, though -- do other kinds of
# errors cause this function to get called at invalid
# times?
return
enclosing_type = get_proper_type(self.most_recent_enclosing_type(expr, type))
if isinstance(enclosing_type, AnyType) and not restrict_any:
# If x is Any and y is int, after x = y we do not infer that x is int.
# This could be changed.
# Instead, since we narrowed type from Any in a recent frame (probably an
# isinstance check), but now it is reassigned, we broaden back
# to Any (which is the most recent enclosing type)
self.put(expr, enclosing_type)
# As a special case, when assigning Any to a variable with a
# declared Optional type that has been narrowed to None,
# replace all the Nones in the declared Union type with Any.
# This overrides the normal behavior of ignoring Any assignments to variables
# in order to prevent false positives.
# (See discussion in #3526)
elif (isinstance(type, AnyType)
and isinstance(declared_type, UnionType)
and any(isinstance(get_proper_type(item), NoneType) for item in declared_type.items)
and isinstance(get_proper_type(self.most_recent_enclosing_type(expr, NoneType())),
NoneType)):
# Replace any Nones in the union type with Any
new_items = [type if isinstance(get_proper_type(item), NoneType) else item
for item in declared_type.items]
self.put(expr, UnionType(new_items))
elif (isinstance(type, AnyType)
and not (isinstance(declared_type, UnionType)
and any(isinstance(get_proper_type(item), AnyType)
for item in declared_type.items))):
# Assigning an Any value doesn't affect the type to avoid false negatives, unless
# there is an Any item in a declared union type.
self.put(expr, declared_type)
else:
self.put(expr, type)
for i in self.try_frames:
# XXX This should probably not copy the entire frame, but
# just copy this variable into a single stored frame.
self.allow_jump(i)
def invalidate_dependencies(self, expr: BindableExpression) -> None:
"""Invalidate knowledge of types that include expr, but not expr itself.
For example, when expr is foo.bar, invalidate foo.bar.baz.
It is overly conservative: it invalidates globally, including
in code paths unreachable from here.
"""
key = literal_hash(expr)
assert key is not None
for dep in self.dependencies.get(key, set()):
self._cleanse_key(dep)
def most_recent_enclosing_type(self, expr: BindableExpression, type: Type) -> Optional[Type]:
type = get_proper_type(type)
if isinstance(type, AnyType):
return get_declaration(expr)
key = literal_hash(expr)
assert key is not None
enclosers = ([get_declaration(expr)] +
[f.types[key] for f in self.frames
if key in f.types and is_subtype(type, f.types[key])])
return enclosers[-1]
def allow_jump(self, index: int) -> None:
# self.frames and self.options_on_return have different lengths
# so make sure the index is positive
if index < 0:
index += len(self.options_on_return)
frame = Frame(self._get_id())
for f in self.frames[index + 1:]:
frame.types.update(f.types)
if f.unreachable:
frame.unreachable = True
self.options_on_return[index].append(frame)
def handle_break(self) -> None:
self.allow_jump(self.break_frames[-1])
self.unreachable()
def handle_continue(self) -> None:
self.allow_jump(self.continue_frames[-1])
self.unreachable()
@contextmanager
def frame_context(self, *, can_skip: bool, fall_through: int = 1,
break_frame: int = 0, continue_frame: int = 0,
conditional_frame: bool = False,
try_frame: bool = False) -> Iterator[Frame]:
"""Return a context manager that pushes/pops frames on enter/exit.
If can_skip is True, control flow is allowed to bypass the
newly-created frame.
If fall_through > 0, then it will allow control flow that
falls off the end of the frame to escape to its ancestor
`fall_through` levels higher. Otherwise control flow ends
at the end of the frame.
If break_frame > 0, then 'break' statements within this frame
will jump out to the frame break_frame levels higher than the
frame created by this call to frame_context. Similarly for
continue_frame and 'continue' statements.
If try_frame is true, then execution is allowed to jump at any
point within the newly created frame (or its descendants) to
its parent (i.e., to the frame that was on top before this
call to frame_context).
After the context manager exits, self.last_pop_changed indicates
whether any types changed in the newly-topmost frame as a result
of popping this frame.
"""
assert len(self.frames) > 1
if break_frame:
self.break_frames.append(len(self.frames) - break_frame)
if continue_frame:
self.continue_frames.append(len(self.frames) - continue_frame)
if try_frame:
self.try_frames.add(len(self.frames) - 1)
new_frame = self.push_frame(conditional_frame)
if try_frame:
# An exception may occur immediately
self.allow_jump(-1)
yield new_frame
self.pop_frame(can_skip, fall_through)
if break_frame:
self.break_frames.pop()
if continue_frame:
self.continue_frames.pop()
if try_frame:
self.try_frames.remove(len(self.frames) - 1)
@contextmanager
def top_frame_context(self) -> Iterator[Frame]:
"""A variant of frame_context for use at the top level of
a namespace (module, function, or class).
"""
assert len(self.frames) == 1
yield self.push_frame()
self.pop_frame(True, 0)
def get_declaration(expr: BindableExpression) -> Optional[Type]:
if isinstance(expr, RefExpr) and isinstance(expr.node, Var):
type = get_proper_type(expr.node.type)
if not isinstance(type, PartialType):
return type
return None