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Merge #11623

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11623: fix: Add type variable table to InferenceTableSnapshot r=flodiebold a=tysg

Fixes #11601. 

I observed that removing the `rollback` line in 6fc3d3aa4c fixes the issue.  

Looking at the stacktrace, I believe not restoring `type_variable_table` causes `type_variable_table` and `var_unification_table` to go out of sync, then when `hir_ty::infer::unify::InferenceTable::new_var` tries to extend `type_variable_table` to be the same length as `var_unification_table`, problems will arise.

However, I cannot pinpoint exactly how or where the vector capacity overflow happens, so my understanding might not be correct after all. 

Co-authored-by: Tianyi Song <42670338+tysg@users.noreply.github.com>
This commit is contained in:
bors[bot] 2022-03-05 10:32:07 +00:00 committed by GitHub
commit 79a7ba0bdf
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1 changed files with 6 additions and 3 deletions
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9
crates/hir_ty/src/infer/unify.rs
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@ -140,7 +140,8 @@ pub(crate) struct InferenceTable<'a> {
pub(crate) struct InferenceTableSnapshot {
var_table_snapshot: chalk_solve::infer::InferenceSnapshot<Interner>,
// FIXME: snapshot type_variable_table, pending_obligations?
// FIXME: snapshot pending_obligations?
type_variable_table_snapshot: Vec<TypeVariableData>,
}
impl<'a> InferenceTable<'a> {
@ -356,12 +357,14 @@ impl<'a> InferenceTable<'a> {
}
pub(crate) fn snapshot(&mut self) -> InferenceTableSnapshot {
let snapshot = self.var_unification_table.snapshot();
InferenceTableSnapshot { var_table_snapshot: snapshot }
let var_table_snapshot = self.var_unification_table.snapshot();
let type_variable_table_snapshot = self.type_variable_table.clone();
InferenceTableSnapshot { var_table_snapshot, type_variable_table_snapshot }
}
pub(crate) fn rollback_to(&mut self, snapshot: InferenceTableSnapshot) {
self.var_unification_table.rollback_to(snapshot.var_table_snapshot);
self.type_variable_table = snapshot.type_variable_table_snapshot;
}
/// Checks an obligation without registering it. Useful mostly to check