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[red-knot] AnnAssign with no RHS is not a Definition (#13247)

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My plan for handling declared types is to introduce a `Declaration` in
addition to `Definition`. A `Declaration` is an annotation of a name
with a type; a `Definition` is an actual runtime assignment of a value
to a name. A few things (an annotated function parameter, an
annotated-assignment with an RHS) are both a `Definition` and a
`Declaration`.

This more cleanly separates type inference (only cares about
`Definition`) from declared types (only impacted by a `Declaration`),
and I think it will work out better than trying to squeeze everything
into `Definition`. One of the tests in this PR
(`annotation_only_assignment_transparent_to_local_inference`)
demonstrates one reason why. The statement `x: int` should have no
effect on local inference of the type of `x`; whatever the locally
inferred type of `x` was before `x: int` should still be the inferred
type after `x: int`. This is actually quite hard to do if `x: int` is
considered a `Definition`, because a core assumption of the use-def map
is that a `Definition` replaces the previous value. To achieve this
would require some hackery to effectively treat `x: int` sort of as if
it were `x: int = x`, but it's not really even equivalent to that, so
this approach gets quite ugly.

As a first step in this plan, this PR stops treating AnnAssign with no
RHS as a `Definition`, which fixes behavior in a couple added tests.

This actually makes things temporarily worse for the ellipsis-type test,
since it is defined in typeshed only using annotated assignments with no
RHS. This will be fixed properly by the upcoming addition of
declarations, which should also treat a declared type as sufficient to
import a name, at least from a stub.
This commit is contained in:
Carl Meyer 2024-09-05 08:55:00 -07:00 • committed by GitHub
parent 65cc6ec41d
commit 2a3775e525
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3 changed files with 68 additions and 25 deletions
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30
crates/red_knot_python_semantic/src/semantic_index/builder.rs
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@ -498,7 +498,6 @@ where
}
ast::Stmt::AnnAssign(node) => {
debug_assert!(self.current_assignment.is_none());
// TODO deferred annotation visiting
self.visit_expr(&node.annotation);
if let Some(value) = &node.value {
self.visit_expr(value);
@ -633,21 +632,22 @@ where
match expr {
ast::Expr::Name(name_node @ ast::ExprName { id, ctx, .. }) => {
let mut flags = match ctx {
ast::ExprContext::Load => SymbolFlags::IS_USED,
ast::ExprContext::Store => SymbolFlags::IS_DEFINED,
ast::ExprContext::Del => SymbolFlags::IS_DEFINED,
ast::ExprContext::Invalid => SymbolFlags::empty(),
let flags = match (ctx, self.current_assignment) {
(ast::ExprContext::Store, Some(CurrentAssignment::AugAssign(_))) => {
// For augmented assignment, the target expression is also used.
SymbolFlags::IS_DEFINED | SymbolFlags::IS_USED
}
(ast::ExprContext::Store, Some(CurrentAssignment::AnnAssign(ann_assign)))
if ann_assign.value.is_none() =>
{
// An annotated assignment that doesn't assign a value is not a Definition
SymbolFlags::empty()
}
(ast::ExprContext::Load, _) => SymbolFlags::IS_USED,
(ast::ExprContext::Store, _) => SymbolFlags::IS_DEFINED,
(ast::ExprContext::Del, _) => SymbolFlags::IS_DEFINED,
(ast::ExprContext::Invalid, _) => SymbolFlags::empty(),
};
if matches!(
self.current_assignment,
Some(CurrentAssignment::AugAssign(_))
) && !ctx.is_invalid()
{
// For augmented assignment, the target expression is also used, so we should
// record that as a use.
flags |= SymbolFlags::IS_USED;
}
let symbol = self.add_or_update_symbol(id.clone(), flags);
if flags.contains(SymbolFlags::IS_DEFINED) {
match self.current_assignment {