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Support making a variable Optional in an else branch #11002

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Merged
msullivan merged 7 commits into from
Aug 27, 2021
Merged

Support making a variable Optional in an else branch #11002

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eecc3b3
Support making a variable Optional in an else branch
msullivan Aug 20, 2021
bfd3727
Don't update the type if it is Any
msullivan Aug 20, 2021
5859a79
thread outer_if_frame in and rename it
msullivan Aug 20, 2021
08f09ea
sure, some more tests
msullivan Aug 20, 2021
2b24306
try it with try/loops
msullivan Aug 20, 2021
4817560
Implement most of the tests that Jukka requested
msullivan Aug 25, 2021
804f52e
tweaks
msullivan Aug 26, 2021
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21 changes: 15 additions & 6 deletions mypy/binder.py
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Original file line number Diff line number Diff line change
Expand Up @@ -31,9 +31,11 @@ class Frame:
that were assigned in that frame.
"""

def __init__(self) -> None:
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
Expand Down Expand Up @@ -72,13 +74,15 @@ class A:
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.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
Expand All @@ -101,6 +105,10 @@ def __init__(self) -> None:
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
Expand All @@ -109,9 +117,9 @@ def _add_dependencies(self, key: Key, value: Optional[Key] = None) -> None:
for elt in subkeys(key):
self._add_dependencies(elt, value)

def push_frame(self) -> Frame:
def push_frame(self, conditional_frame: bool = False) -> Frame:
"""Push a new frame into the binder."""
f = Frame()
f = Frame(self._get_id(), conditional_frame)
self.frames.append(f)
self.options_on_return.append([])
return f
Expand Down Expand Up @@ -349,7 +357,7 @@ def allow_jump(self, index: int) -> None:
# so make sure the index is positive
if index < 0:
index += len(self.options_on_return)
frame = Frame()
frame = Frame(self._get_id())
for f in self.frames[index + 1:]:
frame.types.update(f.types)
if f.unreachable:
Expand All @@ -367,6 +375,7 @@ def handle_continue(self) -> None:
@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.

Expand Down Expand Up @@ -401,7 +410,7 @@ def frame_context(self, *, can_skip: bool, fall_through: int = 1,
if try_frame:
self.try_frames.add(len(self.frames) - 1)

new_frame = self.push_frame()
new_frame = self.push_frame(conditional_frame)
if try_frame:
# An exception may occur immediately
self.allow_jump(-1)
Expand Down
48 changes: 43 additions & 5 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,14 +22,14 @@
Context, Decorator, PrintStmt, BreakStmt, PassStmt, ContinueStmt,
ComparisonExpr, StarExpr, EllipsisExpr, RefExpr, PromoteExpr,
Import, ImportFrom, ImportAll, ImportBase, TypeAlias,
ARG_POS, ARG_STAR, LITERAL_TYPE, MDEF, GDEF,
ARG_POS, ARG_STAR, LITERAL_TYPE, LDEF, MDEF, GDEF,
CONTRAVARIANT, COVARIANT, INVARIANT, TypeVarExpr, AssignmentExpr,
is_final_node,
ARG_NAMED)
from mypy import nodes
from mypy import operators
from mypy.literals import literal, literal_hash, Key
from mypy.typeanal import has_any_from_unimported_type, check_for_explicit_any
from mypy.typeanal import has_any_from_unimported_type, check_for_explicit_any, make_optional_type
from mypy.types import (
Type, AnyType, CallableType, FunctionLike, Overloaded, TupleType, TypedDictType,
Instance, NoneType, strip_type, TypeType, TypeOfAny,
Expand Down Expand Up @@ -203,6 +203,14 @@ class TypeChecker(NodeVisitor[None], CheckerPluginInterface):
# directly or indirectly.
module_refs: Set[str]

# A map from variable nodes to a snapshot of the frame ids of the
# frames that were active when the variable was declared. This can
# be used to determine nearest common ancestor frame of a variable's
# declaration and the current frame, which lets us determine if it
# was declared in a different branch of the same `if` statement
# (if that frame is a conditional_frame).
var_decl_frames: Dict[Var, Set[int]]

# Plugin that provides special type checking rules for specific library
# functions such as open(), etc.
plugin: Plugin
Expand All @@ -229,6 +237,7 @@ def __init__(self, errors: Errors, modules: Dict[str, MypyFile], options: Option
self.dynamic_funcs = []
self.partial_types = []
self.partial_reported = set()
self.var_decl_frames = {}
self.deferred_nodes = []
self.type_map = {}
self.module_refs = set()
Expand Down Expand Up @@ -411,7 +420,7 @@ def accept_loop(self, body: Statement, else_body: Optional[Statement] = None, *,
Then check the else_body.
"""
# The outer frame accumulates the results of all iterations
with self.binder.frame_context(can_skip=False):
with self.binder.frame_context(can_skip=False, conditional_frame=True):
while True:
with self.binder.frame_context(can_skip=True,
break_frame=2, continue_frame=1):
Expand Down Expand Up @@ -2167,6 +2176,31 @@ def check_assignment(self, lvalue: Lvalue, rvalue: Expression, infer_lvalue_type
rvalue_type, lvalue_type, infer_lvalue_type = self.check_member_assignment(
instance_type, lvalue_type, rvalue, context=rvalue)
else:
# Hacky special case for assigning a literal None
# to a variable defined in a previous if
# branch. When we detect this, we'll go back and
# make the type optional. This is somewhat
# unpleasant, and a generalization of this would
# be an improvement!
if (is_literal_none(rvalue) and
isinstance(lvalue, NameExpr) and
lvalue.kind == LDEF and
isinstance(lvalue.node, Var) and
lvalue.node.type and
lvalue.node in self.var_decl_frames and
not isinstance(get_proper_type(lvalue_type), AnyType)):
decl_frame_map = self.var_decl_frames[lvalue.node]
# Check if the nearest common ancestor frame for the definition site
# and the current site is the enclosing frame of an if/elif/else block.
has_if_ancestor = False
for frame in reversed(self.binder.frames):
if frame.id in decl_frame_map:
has_if_ancestor = frame.conditional_frame
break
if has_if_ancestor:
lvalue_type = make_optional_type(lvalue_type)
self.set_inferred_type(lvalue.node, lvalue, lvalue_type)

rvalue_type = self.check_simple_assignment(lvalue_type, rvalue, context=rvalue,
code=codes.ASSIGNMENT)

Expand Down Expand Up @@ -2992,6 +3026,9 @@ def set_inferred_type(self, var: Var, lvalue: Lvalue, type: Type) -> None:
if var and not self.current_node_deferred:
var.type = type
var.is_inferred = True
if var not in self.var_decl_frames:
# Used for the hack to improve optional type inference in conditionals
self.var_decl_frames[var] = {frame.id for frame in self.binder.frames}
if isinstance(lvalue, MemberExpr) and self.inferred_attribute_types is not None:
# Store inferred attribute type so that we can check consistency afterwards.
if lvalue.def_var is not None:
Expand Down Expand Up @@ -3298,7 +3335,7 @@ def visit_if_stmt(self, s: IfStmt) -> None:
"""Type check an if statement."""
# This frame records the knowledge from previous if/elif clauses not being taken.
# Fall-through to the original frame is handled explicitly in each block.
with self.binder.frame_context(can_skip=False, fall_through=0):
with self.binder.frame_context(can_skip=False, conditional_frame=True, fall_through=0):
for e, b in zip(s.expr, s.body):
t = get_proper_type(self.expr_checker.accept(e))

Expand Down Expand Up @@ -3437,7 +3474,7 @@ def visit_try_without_finally(self, s: TryStmt, try_frame: bool) -> None:
# was the top frame on entry.
with self.binder.frame_context(can_skip=False, fall_through=2, try_frame=try_frame):
# This frame receives exit via exception, and runs exception handlers
with self.binder.frame_context(can_skip=False, fall_through=2):
with self.binder.frame_context(can_skip=False, conditional_frame=True, fall_through=2):
# Finally, the body of the try statement
with self.binder.frame_context(can_skip=False, fall_through=2, try_frame=True):
self.accept(s.body)
Expand Down Expand Up @@ -4920,6 +4957,7 @@ def handle_partial_var_type(
if is_local or not self.options.allow_untyped_globals:
self.msg.need_annotation_for_var(node, context,
self.options.python_version)
self.partial_reported.add(node)
else:
# Defer the node -- we might get a better type in the outer scope
self.handle_cannot_determine_type(node.name, context)
Expand Down
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