Collect and resolve ambiguous obligations from normalizing in writeback

Author: compiler-errors

compiler/rustc_hir_typeck/src/writeback.rs

@@ -8,6 +8,7 @@ use rustc_data_structures::unord::ExtendUnord;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::intravisit::{self, InferKind, Visitor};
 use rustc_hir::{self as hir, AmbigArg, HirId};
+use rustc_infer::traits::solve::Goal;
 use rustc_middle::span_bug;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCoercion};
@@ -730,8 +731,36 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
         let value = self.fcx.resolve_vars_if_possible(value);
-        let value =
-            value.fold_with(&mut Resolver::new(self.fcx, span, self.body, should_normalize));
+        let mut goals = vec![];
+        let value = value.fold_with(&mut Resolver::new(
+            self.fcx,
+            span,
+            self.body,
+            should_normalize,
+            &mut goals,
+        ));
+
+        // Ensure that we resolve goals we get from normalizing coroutine interiors,
+        // but we shouldn't expect those goals to need normalizing (or else we'd get
+        // into a somewhat awkward fixpoint situation, and we don't need it anyways).
+        let mut unexpected_goals = vec![];
+        self.typeck_results.coroutine_stalled_predicates.extend(
+            goals
+                .into_iter()
+                .map(|pred| {
+                    self.fcx.resolve_vars_if_possible(pred).fold_with(&mut Resolver::new(
+                        self.fcx,
+                        span,
+                        self.body,
+                        false,
+                        &mut unexpected_goals,
+                    ))
+                })
+                // FIXME: throwing away the param-env :(
+                .map(|goal| (goal.predicate, self.fcx.misc(span.to_span(self.fcx.tcx)))),
+        );
+        assert_eq!(unexpected_goals, vec![]);
+
         assert!(!value.has_infer());
 
         // We may have introduced e.g. `ty::Error`, if inference failed, make sure
@@ -768,6 +797,7 @@ struct Resolver<'cx, 'tcx> {
     /// Whether we should normalize using the new solver, disabled
     /// both when using the old solver and when resolving predicates.
     should_normalize: bool,
+    nested_goals: &'cx mut Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
 }
 
 impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
@@ -776,8 +806,9 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
         span: &'cx dyn Locatable,
         body: &'tcx hir::Body<'tcx>,
         should_normalize: bool,
+        nested_goals: &'cx mut Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
     ) -> Resolver<'cx, 'tcx> {
-        Resolver { fcx, span, body, should_normalize }
+        Resolver { fcx, span, body, nested_goals, should_normalize }
     }
 
     fn report_error(&self, p: impl Into<ty::GenericArg<'tcx>>) -> ErrorGuaranteed {
@@ -814,12 +845,18 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
             let cause = ObligationCause::misc(self.span.to_span(tcx), body_id);
             let at = self.fcx.at(&cause, self.fcx.param_env);
             let universes = vec![None; outer_exclusive_binder(value).as_usize()];
-            solve::deeply_normalize_with_skipped_universes(at, value, universes).unwrap_or_else(
-                |errors| {
+            match solve::deeply_normalize_with_skipped_universes_and_ambiguous_goals(
+                at, value, universes,
+            ) {
+                Ok((value, goals)) => {
+                    self.nested_goals.extend(goals);
+                    value
+                }
+                Err(errors) => {
                     let guar = self.fcx.err_ctxt().report_fulfillment_errors(errors);
                     new_err(tcx, guar)
-                },
-            )
+                }
+            }
         } else {
             value
         };

compiler/rustc_trait_selection/src/solve.rs

@@ -9,5 +9,8 @@ mod select;
 pub(crate) use delegate::SolverDelegate;
 pub use fulfill::{FulfillmentCtxt, NextSolverError};
 pub(crate) use normalize::deeply_normalize_for_diagnostics;
-pub use normalize::{deeply_normalize, deeply_normalize_with_skipped_universes};
+pub use normalize::{
+    deeply_normalize, deeply_normalize_with_skipped_universes,
+    deeply_normalize_with_skipped_universes_and_ambiguous_goals,
+};
 pub use select::InferCtxtSelectExt;

compiler/rustc_trait_selection/src/solve/normalize.rs

@@ -5,6 +5,7 @@ use std::marker::PhantomData;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::infer::at::At;
+use rustc_infer::traits::solve::Goal;
 use rustc_infer::traits::{FromSolverError, Obligation, TraitEngine};
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::{
@@ -41,15 +42,46 @@ pub fn deeply_normalize_with_skipped_universes<'tcx, T, E>(
     value: T,
     universes: Vec<Option<UniverseIndex>>,
 ) -> Result<T, Vec<E>>
+where
+    T: TypeFoldable<TyCtxt<'tcx>>,
+    E: FromSolverError<'tcx, NextSolverError<'tcx>>,
+{
+    let (value, goals) =
+        deeply_normalize_with_skipped_universes_and_ambiguous_goals(at, value, universes)?;
+    assert_eq!(goals, vec![]);
+
+    Ok(value)
+}
+
+/// Deeply normalize all aliases in `value`. This does not handle inference and expects
+/// its input to be already fully resolved.
+///
+/// Additionally takes a list of universes which represents the binders which have been
+/// entered before passing `value` to the function. This is currently needed for
+/// `normalize_erasing_regions`, which skips binders as it walks through a type.
+///
+/// TODO: doc
+pub fn deeply_normalize_with_skipped_universes_and_ambiguous_goals<'tcx, T, E>(
+    at: At<'_, 'tcx>,
+    value: T,
+    universes: Vec<Option<UniverseIndex>>,
+) -> Result<(T, Vec<Goal<'tcx, ty::Predicate<'tcx>>>), Vec<E>>
 where
     T: TypeFoldable<TyCtxt<'tcx>>,
     E: FromSolverError<'tcx, NextSolverError<'tcx>>,
 {
     let fulfill_cx = FulfillmentCtxt::new(at.infcx);
     let mut folder =
         NormalizationFolder { at, fulfill_cx, depth: 0, universes, _errors: PhantomData };
-
-    value.try_fold_with(&mut folder)
+    let value = value.try_fold_with(&mut folder)?;
+    let goals = folder
+        .fulfill_cx
+        .drain_unstalled_obligations(at.infcx)
+        .into_iter()
+        .map(|obl| obl.as_goal())
+        .collect();
+    let errors = folder.fulfill_cx.select_all_or_error(at.infcx);
+    if errors.is_empty() { Ok((value, goals)) } else { Err(errors) }
 }
 
 struct NormalizationFolder<'me, 'tcx, E> {