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Commit8c14cba

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Propagate type narrowing to nested functions (#15133)
Fixes#2608.Use the heuristic suggested in#2608 and allow narrowed types ofvariables (but not attributes) to be propagated to nested functions ifthe variable is not assigned to after the definition of the nestedfunction in the outer function.Since we don't have a full control flow graph, we simply look forassignments that are textually after the nested function in the outerfunction. This can result in false negatives (at least in loops) andfalse positives (in if statements, and if the assigned type is narrowenough), but I expect these to be rare and not a significant issue. Typenarrowing is already unsound, and the additional unsoundness seemsminor, while the usability benefit is big.This doesn't do the right thing for nested classes yet. I'll create anissue to track that.---------Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
1 parentd71ece8 commit8c14cba

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8 files changed

+518
-5
lines changed

8 files changed

+518
-5
lines changed

‎mypy/binder.py‎

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -51,6 +51,9 @@ def __init__(self, id: int, conditional_frame: bool = False) -> None:
5151
# need this field.
5252
self.suppress_unreachable_warnings=False
5353

54+
def__repr__(self)->str:
55+
returnf"Frame({self.id},{self.types},{self.unreachable},{self.conditional_frame})"
56+
5457

5558
Assigns=DefaultDict[Expression,List[Tuple[Type,Optional[Type]]]]
5659

@@ -63,7 +66,7 @@ class ConditionalTypeBinder:
6366
6467
```
6568
class A:
66-
a = None # type: Union[int, str]
69+
a: Union[int, str] = None
6770
x = A()
6871
lst = [x]
6972
reveal_type(x.a) # Union[int, str]
@@ -446,6 +449,7 @@ def top_frame_context(self) -> Iterator[Frame]:
446449
assertlen(self.frames)==1
447450
yieldself.push_frame()
448451
self.pop_frame(True,0)
452+
assertlen(self.frames)==1
449453

450454

451455
defget_declaration(expr:BindableExpression)->Type|None:

‎mypy/checker.py‎

Lines changed: 114 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -26,7 +26,7 @@
2626

2727
importmypy.checkexpr
2828
frommypyimporterrorcodesascodes,message_registry,nodes,operators
29-
frommypy.binderimportConditionalTypeBinder,get_declaration
29+
frommypy.binderimportConditionalTypeBinder,Frame,get_declaration
3030
frommypy.checkmemberimport (
3131
MemberContext,
3232
analyze_decorator_or_funcbase_access,
@@ -41,7 +41,7 @@
4141
frommypy.errorsimportErrors,ErrorWatcher,report_internal_error
4242
frommypy.expandtypeimportexpand_self_type,expand_type,expand_type_by_instance
4343
frommypy.joinimportjoin_types
44-
frommypy.literalsimportKey,literal,literal_hash
44+
frommypy.literalsimportKey,extract_var_from_literal_hash,literal,literal_hash
4545
frommypy.maptypeimportmap_instance_to_supertype
4646
frommypy.meetimportis_overlapping_erased_types,is_overlapping_types
4747
frommypy.message_registryimportErrorMessage
@@ -134,6 +134,7 @@
134134
is_final_node,
135135
)
136136
frommypy.optionsimportOptions
137+
frommypy.patternsimportAsPattern,StarredPattern
137138
frommypy.pluginimportCheckerPluginInterface,Plugin
138139
frommypy.scopeimportScope
139140
frommypy.semanalimportis_trivial_body,refers_to_fullname,set_callable_name
@@ -151,7 +152,7 @@
151152
restrict_subtype_away,
152153
unify_generic_callable,
153154
)
154-
frommypy.traverserimportall_return_statements,has_return_statement
155+
frommypy.traverserimportTraverserVisitor,all_return_statements,has_return_statement
155156
frommypy.treetransformimportTransformVisitor
156157
frommypy.typeanalimportcheck_for_explicit_any,has_any_from_unimported_type,make_optional_type
157158
frommypy.typeopsimport (
@@ -1207,6 +1208,20 @@ def check_func_def(
12071208

12081209
# Type check body in a new scope.
12091210
withself.binder.top_frame_context():
1211+
# Copy some type narrowings from an outer function when it seems safe enough
1212+
# (i.e. we can't find an assignment that might change the type of the
1213+
# variable afterwards).
1214+
new_frame:Frame|None=None
1215+
forframeinold_binder.frames:
1216+
forkey,narrowed_typeinframe.types.items():
1217+
key_var=extract_var_from_literal_hash(key)
1218+
ifkey_varisnotNoneandnotself.is_var_redefined_in_outer_context(
1219+
key_var,defn.line
1220+
):
1221+
# It seems safe to propagate the type narrowing to a nested scope.
1222+
ifnew_frameisNone:
1223+
new_frame=self.binder.push_frame()
1224+
new_frame.types[key]=narrowed_type
12101225
withself.scope.push_function(defn):
12111226
# We suppress reachability warnings when we use TypeVars with value
12121227
# restrictions: we only want to report a warning if a certain statement is
@@ -1218,6 +1233,8 @@ def check_func_def(
12181233
self.binder.suppress_unreachable_warnings()
12191234
self.accept(item.body)
12201235
unreachable=self.binder.is_unreachable()
1236+
ifnew_frameisnotNone:
1237+
self.binder.pop_frame(True,0)
12211238

12221239
ifnotunreachable:
12231240
ifdefn.is_generatororis_named_instance(
@@ -1310,6 +1327,23 @@ def check_func_def(
13101327

13111328
self.binder=old_binder
13121329

1330+
defis_var_redefined_in_outer_context(self,v:Var,after_line:int)->bool:
1331+
"""Can the variable be assigned to at module top level or outer function?
1332+
1333+
Note that this doesn't do a full CFG analysis but uses a line number based
1334+
heuristic that isn't correct in some (rare) cases.
1335+
"""
1336+
outers=self.tscope.outer_functions()
1337+
ifnotouters:
1338+
# Top-level function -- outer context is top level, and we can't reason about
1339+
# globals
1340+
returnTrue
1341+
forouterinouters:
1342+
ifisinstance(outer,FuncDef):
1343+
iffind_last_var_assignment_line(outer.body,v)>=after_line:
1344+
returnTrue
1345+
returnFalse
1346+
13131347
defcheck_unbound_return_typevar(self,typ:CallableType)->None:
13141348
"""Fails when the return typevar is not defined in arguments."""
13151349
ifisinstance(typ.ret_type,TypeVarType)andtyp.ret_typeintyp.variables:
@@ -7629,3 +7663,80 @@ def collapse_walrus(e: Expression) -> Expression:
76297663
ifisinstance(e,AssignmentExpr):
76307664
returne.target
76317665
returne
7666+
7667+
7668+
deffind_last_var_assignment_line(n:Node,v:Var)->int:
7669+
"""Find the highest line number of a potential assignment to variable within node.
7670+
7671+
This supports local and global variables.
7672+
7673+
Return -1 if no assignment was found.
7674+
"""
7675+
visitor=VarAssignVisitor(v)
7676+
n.accept(visitor)
7677+
returnvisitor.last_line
7678+
7679+
7680+
classVarAssignVisitor(TraverserVisitor):
7681+
def__init__(self,v:Var)->None:
7682+
self.last_line=-1
7683+
self.lvalue=False
7684+
self.var_node=v
7685+
7686+
defvisit_assignment_stmt(self,s:AssignmentStmt)->None:
7687+
self.lvalue=True
7688+
forlvins.lvalues:
7689+
lv.accept(self)
7690+
self.lvalue=False
7691+
7692+
defvisit_name_expr(self,e:NameExpr)->None:
7693+
ifself.lvalueande.nodeisself.var_node:
7694+
self.last_line=max(self.last_line,e.line)
7695+
7696+
defvisit_member_expr(self,e:MemberExpr)->None:
7697+
old_lvalue=self.lvalue
7698+
self.lvalue=False
7699+
super().visit_member_expr(e)
7700+
self.lvalue=old_lvalue
7701+
7702+
defvisit_index_expr(self,e:IndexExpr)->None:
7703+
old_lvalue=self.lvalue
7704+
self.lvalue=False
7705+
super().visit_index_expr(e)
7706+
self.lvalue=old_lvalue
7707+
7708+
defvisit_with_stmt(self,s:WithStmt)->None:
7709+
self.lvalue=True
7710+
forlvins.target:
7711+
iflvisnotNone:
7712+
lv.accept(self)
7713+
self.lvalue=False
7714+
s.body.accept(self)
7715+
7716+
defvisit_for_stmt(self,s:ForStmt)->None:
7717+
self.lvalue=True
7718+
s.index.accept(self)
7719+
self.lvalue=False
7720+
s.body.accept(self)
7721+
ifs.else_body:
7722+
s.else_body.accept(self)
7723+
7724+
defvisit_assignment_expr(self,e:AssignmentExpr)->None:
7725+
self.lvalue=True
7726+
e.target.accept(self)
7727+
self.lvalue=False
7728+
e.value.accept(self)
7729+
7730+
defvisit_as_pattern(self,p:AsPattern)->None:
7731+
ifp.patternisnotNone:
7732+
p.pattern.accept(self)
7733+
ifp.nameisnotNone:
7734+
self.lvalue=True
7735+
p.name.accept(self)
7736+
self.lvalue=False
7737+
7738+
defvisit_starred_pattern(self,p:StarredPattern)->None:
7739+
ifp.captureisnotNone:
7740+
self.lvalue=True
7741+
p.capture.accept(self)
7742+
self.lvalue=False

‎mypy/fastparse.py‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1766,7 +1766,8 @@ def visit_MatchStar(self, n: MatchStar) -> StarredPattern:
17661766
ifn.nameisNone:
17671767
node=StarredPattern(None)
17681768
else:
1769-
node=StarredPattern(NameExpr(n.name))
1769+
name=self.set_line(NameExpr(n.name),n)
1770+
node=StarredPattern(name)
17701771

17711772
returnself.set_line(node,n)
17721773

‎mypy/literals.py‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -139,6 +139,16 @@ def literal_hash(e: Expression) -> Key | None:
139139
returne.accept(_hasher)
140140

141141

142+
defextract_var_from_literal_hash(key:Key)->Var|None:
143+
"""If key refers to a Var node, return it.
144+
145+
Return None otherwise.
146+
"""
147+
iflen(key)==2andkey[0]=="Var"andisinstance(key[1],Var):
148+
returnkey[1]
149+
returnNone
150+
151+
142152
class_Hasher(ExpressionVisitor[Optional[Key]]):
143153
defvisit_int_expr(self,e:IntExpr)->Key:
144154
return ("Literal",e.value)

‎mypy/scope.py‎

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,7 @@ def __init__(self) -> None:
2121
self.module:str|None=None
2222
self.classes:list[TypeInfo]= []
2323
self.function:FuncBase|None=None
24+
self.functions:list[FuncBase]= []
2425
# Number of nested scopes ignored (that don't get their own separate targets)
2526
self.ignored=0
2627

@@ -65,19 +66,24 @@ def module_scope(self, prefix: str) -> Iterator[None]:
6566

6667
@contextmanager
6768
deffunction_scope(self,fdef:FuncBase)->Iterator[None]:
69+
self.functions.append(fdef)
6870
ifnotself.function:
6971
self.function=fdef
7072
else:
7173
# Nested functions are part of the topmost function target.
7274
self.ignored+=1
7375
yield
76+
self.functions.pop()
7477
ifself.ignored:
7578
# Leave a scope that's included in the enclosing target.
7679
self.ignored-=1
7780
else:
7881
assertself.function
7982
self.function=None
8083

84+
defouter_functions(self)->list[FuncBase]:
85+
returnself.functions[:-1]
86+
8187
defenter_class(self,info:TypeInfo)->None:
8288
"""Enter a class target scope."""
8389
ifnotself.function:

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