Use ocx.normalize in report_projection_error

Author: spastorino

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -112,6 +112,27 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         self.register_infer_ok_obligations(infer_ok)
     }
 
+    /// Makes `expected <: actual`.
+    ///
+    /// See [`At::trace_exp`] and [`Trace::eq`] for a version of
+    /// this method that only requires `T: Relate<'tcx>`
+    pub fn eq_exp<T>(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        a_is_expected: bool,
+        a: T,
+        b: T,
+    ) -> Result<(), TypeError<'tcx>>
+    where
+        T: ToTrace<'tcx>,
+    {
+        self.infcx
+            .at(cause, param_env)
+            .eq_exp(a_is_expected, a, b)
+            .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
+    }
+
     pub fn eq<T: ToTrace<'tcx>>(
         &self,
         cause: &ObligationCause<'tcx>,

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1576,9 +1576,11 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             return;
         }
 
+        let mut values = None;
+
         self.probe(|_| {
+            let ocx = ObligationCtxt::new_in_snapshot(self);
             let mut err = error.err;
-            let mut values = None;
 
             // try to find the mismatched types to report the error with.
             //
@@ -1588,21 +1590,16 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
                 bound_predicate.skip_binder()
             {
-                let mut selcx = SelectionContext::new(self);
                 let data = self.replace_bound_vars_with_fresh_vars(
                     obligation.cause.span,
                     infer::LateBoundRegionConversionTime::HigherRankedType,
                     bound_predicate.rebind(data),
                 );
-                let mut obligations = vec![];
-                // FIXME(normalization): Change this to use `At::normalize`
-                let normalized_ty = super::normalize_projection_type(
-                    &mut selcx,
+                let normalized_ty = ocx.normalize(
+                    &obligation.cause,
                     obligation.param_env,
-                    data.projection_ty,
-                    obligation.cause.clone(),
-                    0,
-                    &mut obligations,
+                    self.tcx
+                        .mk_projection(data.projection_ty.item_def_id, data.projection_ty.substs),
                 );
 
                 debug!(?obligation.cause, ?obligation.param_env);
@@ -1618,19 +1615,31 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         | ObligationCauseCode::ObjectCastObligation(..)
                         | ObligationCauseCode::OpaqueType
                 );
-                if let Err(new_err) = self.at(&obligation.cause, obligation.param_env).eq_exp(
+                let expected_ty = data.term.ty().unwrap();
+
+                // constrain inference variables a bit more to nested obligations from normalize so
+                // we can have more helpful errors.
+                ocx.select_where_possible();
+
+                if let Err(new_err) = ocx.eq_exp(
+                    &obligation.cause,
+                    obligation.param_env,
                     is_normalized_ty_expected,
                     normalized_ty,
-                    data.term,
+                    expected_ty,
                 ) {
-                    values = Some((data, is_normalized_ty_expected, normalized_ty, data.term));
+                    values = Some((data, is_normalized_ty_expected, normalized_ty, expected_ty));
                     err = new_err;
                 }
             }
 
             let msg = values
                 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
-                    self.maybe_detailed_projection_msg(predicate, normalized_ty, expected_ty)
+                    self.maybe_detailed_projection_msg(
+                        predicate,
+                        normalized_ty.into(),
+                        expected_ty.into(),
+                    )
                 })
                 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
             let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
@@ -1672,11 +1681,11 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 &mut diag,
                 &obligation.cause,
                 secondary_span,
-                values.map(|(_, is_normalized_ty_expected, normalized_ty, term)| {
+                values.map(|(_, is_normalized_ty_expected, normalized_ty, expected_ty)| {
                     infer::ValuePairs::Terms(ExpectedFound::new(
                         is_normalized_ty_expected,
-                        normalized_ty,
-                        term,
+                        normalized_ty.into(),
+                        expected_ty.into(),
                     ))
                 }),
                 err,