1 files changed, 66 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/traits/solve.rs b/compiler/rustc_middle/src/traits/solve.rs
new file mode 100644
index 000000000..bd43867a3
--- /dev/null
+++ b/compiler/rustc_middle/src/traits/solve.rs
@@ -0,0 +1,66 @@
+use std::ops::ControlFlow;
+
+use rustc_data_structures::intern::Interned;
+
+use crate::infer::canonical::QueryRegionConstraints;
+use crate::ty::{
+    FallibleTypeFolder, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable, TypeVisitor,
+};
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
+pub struct ExternalConstraints<'tcx>(pub(crate) Interned<'tcx, ExternalConstraintsData<'tcx>>);
+
+impl<'tcx> std::ops::Deref for ExternalConstraints<'tcx> {
+    type Target = ExternalConstraintsData<'tcx>;
+
+    fn deref(&self) -> &Self::Target {
+        &*self.0
+    }
+}
+
+/// Additional constraints returned on success.
+#[derive(Debug, PartialEq, Eq, Clone, Hash, Default, TypeFoldable, TypeVisitable)]
+pub struct ExternalConstraintsData<'tcx> {
+    // FIXME: implement this.
+    pub region_constraints: QueryRegionConstraints<'tcx>,
+    pub opaque_types: Vec<(Ty<'tcx>, Ty<'tcx>)>,
+}
+
+// FIXME: Having to clone `region_constraints` for folding feels bad and
+// probably isn't great wrt performance.
+//
+// Not sure how to fix this, maybe we should also intern `opaque_types` and
+// `region_constraints` here or something.
+impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
+    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
+        self,
+        folder: &mut F,
+    ) -> Result<Self, F::Error> {
+        Ok(FallibleTypeFolder::interner(folder).mk_external_constraints(ExternalConstraintsData {
+            region_constraints: self.region_constraints.clone().try_fold_with(folder)?,
+            opaque_types: self
+                .opaque_types
+                .iter()
+                .map(|opaque| opaque.try_fold_with(folder))
+                .collect::<Result<_, F::Error>>()?,
+        }))
+    }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        TypeFolder::interner(folder).mk_external_constraints(ExternalConstraintsData {
+            region_constraints: self.region_constraints.clone().fold_with(folder),
+            opaque_types: self.opaque_types.iter().map(|opaque| opaque.fold_with(folder)).collect(),
+        })
+    }
+}
+
+impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
+    fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(
+        &self,
+        visitor: &mut V,
+    ) -> std::ops::ControlFlow<V::BreakTy> {
+        self.region_constraints.visit_with(visitor)?;
+        self.opaque_types.visit_with(visitor)?;
+        ControlFlow::Continue(())
+    }
+}