1 files changed, 51 insertions, 0 deletions
diff --git a/vendor/chalk-engine/src/strand.rs b/vendor/chalk-engine/src/strand.rs
new file mode 100644
index 000000000..91196ec94
--- /dev/null
+++ b/vendor/chalk-engine/src/strand.rs
@@ -0,0 +1,51 @@
+use crate::table::AnswerIndex;
+use crate::{ExClause, TableIndex, TimeStamp};
+use std::fmt::Debug;
+
+use chalk_derive::HasInterner;
+use chalk_ir::fold::{Fold, Folder};
+use chalk_ir::interner::Interner;
+use chalk_ir::{Canonical, DebruijnIndex, UniverseMap};
+
+#[derive(Clone, Debug, HasInterner)]
+pub(crate) struct Strand<I: Interner> {
+    pub(super) ex_clause: ExClause<I>,
+
+    /// Index into `ex_clause.subgoals`.
+    pub(crate) selected_subgoal: Option<SelectedSubgoal>,
+
+    pub(crate) last_pursued_time: TimeStamp,
+}
+
+pub(crate) type CanonicalStrand<I> = Canonical<Strand<I>>;
+
+#[derive(Clone, Debug)]
+pub(crate) struct SelectedSubgoal {
+    /// The index of the subgoal in `ex_clause.subgoals`
+    pub(crate) subgoal_index: usize,
+
+    /// The index of the table that we created or found for this subgoal
+    pub(super) subgoal_table: TableIndex,
+
+    /// Index of the answer we should request next from the table
+    pub(crate) answer_index: AnswerIndex,
+
+    /// Maps the universes of the subgoal to the canonical universes
+    /// used in the table
+    pub(crate) universe_map: UniverseMap,
+}
+
+impl<I: Interner> Fold<I> for Strand<I> {
+    type Result = Strand<I>;
+    fn fold_with<E>(
+        self,
+        folder: &mut dyn Folder<I, Error = E>,
+        outer_binder: DebruijnIndex,
+    ) -> Result<Self::Result, E> {
+        Ok(Strand {
+            ex_clause: self.ex_clause.fold_with(folder, outer_binder)?,
+            last_pursued_time: self.last_pursued_time,
+            selected_subgoal: self.selected_subgoal,
+        })
+    }
+}