Continue folding if deep normalizer fails

compiler/rustc_trait_selection/src/solve/normalize.rs

@@ -10,7 +10,7 @@ use rustc_infer::traits::{FulfillmentError, Obligation, TraitEngine};
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::traits::{ObligationCause, Reveal};
 use rustc_middle::ty::{self, AliasTy, Ty, TyCtxt, UniverseIndex};
-use rustc_middle::ty::{FallibleTypeFolder, TypeSuperFoldable};
+use rustc_middle::ty::{FallibleTypeFolder, TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::{TypeFoldable, TypeVisitableExt};
 
 use super::FulfillmentCtxt;
@@ -42,19 +42,6 @@ pub(crate) fn deeply_normalize_with_skipped_universes<'tcx, T: TypeFoldable<TyCt
     value.try_fold_with(&mut folder)
 }
 
-// Deeply normalize a value and return it
-pub(crate) fn deeply_normalize_for_diagnostics<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
-    infcx: &InferCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    t: T,
-) -> T {
-    infcx
-        .commit_if_ok(|_| {
-            deeply_normalize(infcx.at(&ObligationCause::dummy(), param_env), t.clone())
-        })
-        .unwrap_or(t)
-}
-
 struct NormalizationFolder<'me, 'tcx> {
     at: At<'me, 'tcx>,
     fulfill_cx: FulfillmentCtxt<'tcx>,
@@ -244,3 +231,42 @@ impl<'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for NormalizationFolder<'_, 'tcx> {
         }
     }
 }
+
+// Deeply normalize a value and return it
+pub(crate) fn deeply_normalize_for_diagnostics<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
+    infcx: &InferCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    t: T,
+) -> T {
+    t.clone().fold_with(&mut DeeplyNormalizeForDiagnosticsFolder {
+        at: infcx.at(&ObligationCause::dummy(), param_env),
+    })
+}
+
+struct DeeplyNormalizeForDiagnosticsFolder<'a, 'tcx> {
+    at: At<'a, 'tcx>,
+}
+
+impl<'tcx> TypeFolder<TyCtxt<'tcx>> for DeeplyNormalizeForDiagnosticsFolder<'_, 'tcx> {
+    fn interner(&self) -> TyCtxt<'tcx> {
+        self.at.infcx.tcx
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        deeply_normalize_with_skipped_universes(
+            self.at,
+            ty,
+            vec![None; ty.outer_exclusive_binder().as_usize()],
+        )
+        .unwrap_or_else(|_| ty.super_fold_with(self))
+    }
+
+    fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
+        deeply_normalize_with_skipped_universes(
+            self.at,
+            ct,
+            vec![None; ct.outer_exclusive_binder().as_usize()],
+        )
+        .unwrap_or_else(|_| ct.super_fold_with(self))
+    }
+}

tests/ui/coherence/normalize-for-errors.current.stderr

@@ -1,11 +1,11 @@
-error[E0119]: conflicting implementations of trait `MyTrait` for type `Box<(MyType,)>`
+error[E0119]: conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>, _)`
   --> $DIR/normalize-for-errors.rs:17:1
    |
-LL | impl<T: Copy> MyTrait for T {}
-   | --------------------------- first implementation here
+LL | impl<T: Copy, S: Iterator> MyTrait<S> for (T, S::Item) {}
+   | ------------------------------------------------------ first implementation here
 LL |
-LL | impl MyTrait for Box<<(MyType,) as Mirror>::Assoc> {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<(MyType,)>`
+LL | impl<S: Iterator> MyTrait<S> for (Box<<(MyType,) as Mirror>::Assoc>, S::Item) {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(Box<(MyType,)>, _)`
    |
    = note: upstream crates may add a new impl of trait `std::marker::Copy` for type `std::boxed::Box<(MyType,)>` in future versions
 

tests/ui/coherence/normalize-for-errors.next.stderr

@@ -1,11 +1,11 @@
-error[E0119]: conflicting implementations of trait `MyTrait` for type `Box<(MyType,)>`
+error[E0119]: conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>, <_ as Iterator>::Item)`
   --> $DIR/normalize-for-errors.rs:17:1
    |
-LL | impl<T: Copy> MyTrait for T {}
-   | --------------------------- first implementation here
+LL | impl<T: Copy, S: Iterator> MyTrait<S> for (T, S::Item) {}
+   | ------------------------------------------------------ first implementation here
 LL |
-LL | impl MyTrait for Box<<(MyType,) as Mirror>::Assoc> {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<(MyType,)>`
+LL | impl<S: Iterator> MyTrait<S> for (Box<<(MyType,) as Mirror>::Assoc>, S::Item) {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(Box<(MyType,)>, <_ as Iterator>::Item)`
    |
    = note: upstream crates may add a new impl of trait `std::marker::Copy` for type `std::boxed::Box<(MyType,)>` in future versions
 

tests/ui/coherence/normalize-for-errors.rs

@@ -2,8 +2,7 @@
 //[next] compile-flags: -Ztrait-solver=next
 
 struct MyType;
-trait MyTrait {
-}
+trait MyTrait<S> {}
 
 trait Mirror {
     type Assoc;
@@ -12,11 +11,11 @@ impl<T> Mirror for T {
     type Assoc = T;
 }
 
-impl<T: Copy> MyTrait for T {}
+impl<T: Copy, S: Iterator> MyTrait<S> for (T, S::Item) {}
 //~^ NOTE first implementation here
-impl MyTrait for Box<<(MyType,) as Mirror>::Assoc> {}
-//~^ ERROR conflicting implementations of trait `MyTrait` for type `Box<(MyType,)>`
-//~| NOTE conflicting implementation for `Box<(MyType,)>
+impl<S: Iterator> MyTrait<S> for (Box<<(MyType,) as Mirror>::Assoc>, S::Item) {}
+//~^ ERROR conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>,
+//~| NOTE conflicting implementation for `(Box<(MyType,)>,
 //~| NOTE upstream crates may add a new impl of trait `std::marker::Copy` for type `std::boxed::Box<(MyType,)>` in future versions
 
 fn main() {}