1 files changed, 109 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs
new file mode 100644
index 000000000..a6240666e
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs
@@ -0,0 +1,109 @@
+use std::mem;
+
+use rustc_data_structures::fx::FxHashMap;
+use rustc_infer::{
+    infer::InferCtxt,
+    traits::{
+        query::NoSolution, FulfillmentError, FulfillmentErrorCode, PredicateObligation,
+        SelectionError, TraitEngine,
+    },
+};
+use rustc_middle::ty;
+
+use super::{search_graph, Certainty, EvalCtxt};
+
+/// A trait engine using the new trait solver.
+///
+/// This is mostly identical to how `evaluate_all` works inside of the
+/// solver, except that the requirements are slightly different.
+///
+/// Unlike `evaluate_all` it is possible to add new obligations later on
+/// and we also have to track diagnostics information by using `Obligation`
+/// instead of `Goal`.
+///
+/// It is also likely that we want to use slightly different datastructures
+/// here as this will have to deal with far more root goals than `evaluate_all`.
+pub struct FulfillmentCtxt<'tcx> {
+    obligations: Vec<PredicateObligation<'tcx>>,
+}
+
+impl<'tcx> FulfillmentCtxt<'tcx> {
+    pub fn new() -> FulfillmentCtxt<'tcx> {
+        FulfillmentCtxt { obligations: Vec::new() }
+    }
+}
+
+impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
+    fn register_predicate_obligation(
+        &mut self,
+        _infcx: &InferCtxt<'tcx>,
+        obligation: PredicateObligation<'tcx>,
+    ) {
+        self.obligations.push(obligation);
+    }
+
+    fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
+        let errors = self.select_where_possible(infcx);
+        if !errors.is_empty() {
+            return errors;
+        }
+
+        self.obligations
+            .drain(..)
+            .map(|obligation| FulfillmentError {
+                obligation: obligation.clone(),
+                code: FulfillmentErrorCode::CodeAmbiguity,
+                root_obligation: obligation,
+            })
+            .collect()
+    }
+
+    fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
+        let mut errors = Vec::new();
+        for i in 0.. {
+            if !infcx.tcx.recursion_limit().value_within_limit(i) {
+                unimplemented!("overflowed on pending obligations: {:?}", self.obligations);
+            }
+
+            let mut has_changed = false;
+            for obligation in mem::take(&mut self.obligations) {
+                let goal = obligation.clone().into();
+                let search_graph = &mut search_graph::SearchGraph::new(infcx.tcx);
+                let mut ecx = EvalCtxt::new_outside_solver(infcx, search_graph);
+                let (changed, certainty) = match ecx.evaluate_goal(goal) {
+                    Ok(result) => result,
+                    Err(NoSolution) => {
+                        errors.push(FulfillmentError {
+                            obligation: obligation.clone(),
+                            code: FulfillmentErrorCode::CodeSelectionError(
+                                SelectionError::Unimplemented,
+                            ),
+                            root_obligation: obligation,
+                        });
+                        continue;
+                    }
+                };
+
+                has_changed |= changed;
+                match certainty {
+                    Certainty::Yes => {}
+                    Certainty::Maybe(_) => self.obligations.push(obligation),
+                }
+            }
+
+            if !has_changed {
+                break;
+            }
+        }
+
+        errors
+    }
+
+    fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
+        self.obligations.clone()
+    }
+
+    fn relationships(&mut self) -> &mut FxHashMap<ty::TyVid, ty::FoundRelationships> {
+        unimplemented!("Should be moved out of `TraitEngine`")
+    }
+}