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[red-knot] Consider all definitions after terminal statements unreachable (#15676)

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`FlowSnapshot` now tracks a `reachable` bool, which indicates whether we
have encountered a terminal statement on that control flow path. When
merging flow states together, we skip any that have been marked
unreachable. This ensures that bindings that can only be reached through
unreachable paths are not considered visible.

## Test Plan

The new mdtests failed (with incorrect `reveal_type` results, and
spurious `possibly-unresolved-reference` errors) before adding the new
visibility constraints.

---------

Co-authored-by: Carl Meyer <carl@astral.sh>
This commit is contained in:
Douglas Creager 2025-01-29 14:06:57 -05:00 • committed by GitHub
parent e1c9d10863
commit 15d886a502
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4 changed files with 686 additions and 22 deletions
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26
crates/red_knot_python_semantic/src/semantic_index/builder.rs
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@ -368,6 +368,12 @@ impl<'db> SemanticIndexBuilder<'db> {
.record_visibility_constraint(VisibilityConstraint::VisibleIf(constraint))
}
/// Records that all remaining statements in the current block are unreachable, and therefore
/// not visible.
fn mark_unreachable(&mut self) {
self.current_use_def_map_mut().mark_unreachable();
}
/// Records a [`VisibilityConstraint::Ambiguous`] constraint.
fn record_ambiguous_visibility(&mut self) -> ScopedVisibilityConstraintId {
self.current_use_def_map_mut()
@ -1019,11 +1025,6 @@ where
}
self.visit_body(body);
}
ast::Stmt::Break(_) => {
if self.loop_state().is_inside() {
self.loop_break_states.push(self.flow_snapshot());
}
}
ast::Stmt::For(
for_stmt @ ast::StmtFor {
@ -1270,6 +1271,21 @@ where
// - https://github.com/astral-sh/ruff/pull/13633#discussion_r1788626702
self.visit_body(finalbody);
}
ast::Stmt::Raise(_) | ast::Stmt::Return(_) | ast::Stmt::Continue(_) => {
walk_stmt(self, stmt);
// Everything in the current block after a terminal statement is unreachable.
self.mark_unreachable();
}
ast::Stmt::Break(_) => {
if self.loop_state().is_inside() {
self.loop_break_states.push(self.flow_snapshot());
}
// Everything in the current block after a terminal statement is unreachable.
self.mark_unreachable();
}
_ => {
walk_stmt(self, stmt);
}