Auto merge of rust-lang#118751 - lcnr:writeback-change, r=<try>

refactor writeback: emit normalization errors with new solver

implements rust-lang#118725 (comment)

r? `@compiler-errors` `@BoxyUwU` whoever comes first n stuff

Author: bors

Diff for: compiler/rustc_hir_typeck/src/lib.rs

@@ -283,8 +283,6 @@ fn typeck_with_fallback<'tcx>(
 
     fcx.check_asms();
 
-    fcx.infcx.skip_region_resolution();
-
     let typeck_results = fcx.resolve_type_vars_in_body(body);
 
     // Consistency check our TypeckResults instance can hold all ItemLocalIds

Diff for: compiler/rustc_hir_typeck/src/writeback.rs

@@ -8,12 +8,16 @@ use rustc_errors::{ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
+use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCoercion};
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::visit::TypeVisitableExt;
+use rustc_middle::ty::TypeSuperFoldable;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
+use rustc_trait_selection::solve;
+use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 
 use std::mem;
 
@@ -695,24 +699,22 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
         }
     }
 
-    fn resolve<T>(&mut self, x: T, span: &dyn Locatable) -> T
+    fn resolve<T>(&mut self, value: T, span: &dyn Locatable) -> T
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        let mut resolver = Resolver::new(self.fcx, span, self.body);
-        let x = x.fold_with(&mut resolver);
-        if cfg!(debug_assertions) && x.has_infer() {
-            span_bug!(span.to_span(self.fcx.tcx), "writeback: `{:?}` has inference variables", x);
-        }
+        let value = self.fcx.resolve_vars_if_possible(value);
+        let value = value.fold_with(&mut Resolver::new(self.fcx, span, self.body));
+        assert!(!value.has_infer());
 
         // We may have introduced e.g. `ty::Error`, if inference failed, make sure
         // to mark the `TypeckResults` as tainted in that case, so that downstream
         // users of the typeck results don't produce extra errors, or worse, ICEs.
-        if let Some(e) = resolver.replaced_with_error {
-            self.typeck_results.tainted_by_errors = Some(e);
+        if let Err(guar) = value.error_reported() {
+            self.typeck_results.tainted_by_errors = Some(guar);
         }
 
-        x
+        value
     }
 }
 
@@ -732,15 +734,13 @@ impl Locatable for hir::HirId {
     }
 }
 
-/// The Resolver. This is the type folding engine that detects
-/// unresolved types and so forth.
 struct Resolver<'cx, 'tcx> {
     fcx: &'cx FnCtxt<'cx, 'tcx>,
     span: &'cx dyn Locatable,
     body: &'tcx hir::Body<'tcx>,
-
-    /// Set to `Some` if any `Ty` or `ty::Const` had to be replaced with an `Error`.
-    replaced_with_error: Option<ErrorGuaranteed>,
+    /// Whether we should normalize using the new solver, disabled
+    /// both when using the old solver and when resolving predicates.
+    should_normalize: bool,
 }
 
 impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
@@ -749,7 +749,7 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
         span: &'cx dyn Locatable,
         body: &'tcx hir::Body<'tcx>,
     ) -> Resolver<'cx, 'tcx> {
-        Resolver { fcx, span, body, replaced_with_error: None }
+        Resolver { fcx, span, body, should_normalize: fcx.next_trait_solver() }
     }
 
     fn report_error(&self, p: impl Into<ty::GenericArg<'tcx>>) -> ErrorGuaranteed {
@@ -768,64 +768,73 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
                 .emit(),
         }
     }
+
+    fn handle_term<T>(
+        &mut self,
+        value: T,
+        outer_exclusive_binder: impl FnOnce(T) -> ty::DebruijnIndex,
+        new_err: impl Fn(TyCtxt<'tcx>, ErrorGuaranteed) -> T,
+    ) -> T
+    where
+        T: Into<ty::GenericArg<'tcx>> + Copy,
+        T: TypeFoldable<TyCtxt<'tcx>>,
+        T: TypeSuperFoldable<TyCtxt<'tcx>>,
+    {
+        let tcx = self.fcx.tcx;
+        // We must deeply normalize in the new solver, since later lints
+        // expect that types that show up in the typeck are fully
+        // normalized.
+        let value = if self.should_normalize {
+            let body_id = tcx.hir().body_owner_def_id(self.body.id());
+            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| {
+                    let guar = self.fcx.err_ctxt().report_fulfillment_errors(errors);
+                    new_err(tcx, guar)
+                },
+            )
+        } else {
+            value
+        };
+
+        if value.has_non_region_infer() {
+            let guar = self.report_error(value);
+            new_err(tcx, guar)
+        } else {
+            tcx.fold_regions(value, |_, _| tcx.lifetimes.re_erased)
+        }
+    }
 }
 
 impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Resolver<'cx, 'tcx> {
     fn interner(&self) -> TyCtxt<'tcx> {
         self.fcx.tcx
     }
 
-    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        let tcx = self.fcx.tcx;
-        match self.fcx.fully_resolve(t) {
-            Ok(t) if self.fcx.next_trait_solver() => {
-                // We must normalize erasing regions here, since later lints
-                // expect that types that show up in the typeck are fully
-                // normalized.
-                if let Ok(t) = tcx.try_normalize_erasing_regions(self.fcx.param_env, t) {
-                    t
-                } else {
-                    tcx.fold_regions(t, |_, _| tcx.lifetimes.re_erased)
-                }
-            }
-            Ok(t) => {
-                // Do not anonymize late-bound regions
-                // (e.g. keep `for<'a>` named `for<'a>`).
-                // This allows NLL to generate error messages that
-                // refer to the higher-ranked lifetime names written by the user.
-                tcx.fold_regions(t, |_, _| tcx.lifetimes.re_erased)
-            }
-            Err(_) => {
-                debug!("Resolver::fold_ty: input type `{:?}` not fully resolvable", t);
-                let e = self.report_error(t);
-                self.replaced_with_error = Some(e);
-                Ty::new_error(self.fcx.tcx, e)
-            }
-        }
-    }
-
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         debug_assert!(!r.is_bound(), "Should not be resolving bound region.");
         self.fcx.tcx.lifetimes.re_erased
     }
 
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        self.handle_term(ty, Ty::outer_exclusive_binder, Ty::new_error)
+    }
+
     fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
-        match self.fcx.fully_resolve(ct) {
-            Ok(ct) => self.fcx.tcx.erase_regions(ct),
-            Err(_) => {
-                debug!("Resolver::fold_const: input const `{:?}` not fully resolvable", ct);
-                let e = self.report_error(ct);
-                self.replaced_with_error = Some(e);
-                ty::Const::new_error(self.fcx.tcx, e, ct.ty())
-            }
-        }
+        self.handle_term(ct, ty::Const::outer_exclusive_binder, |tcx, guar| {
+            ty::Const::new_error(tcx, guar, ct.ty())
+        })
     }
-}
 
-///////////////////////////////////////////////////////////////////////////
-// During type check, we store promises with the result of trait
-// lookup rather than the actual results (because the results are not
-// necessarily available immediately). These routines unwind the
-// promises. It is expected that we will have already reported any
-// errors that may be encountered, so if the promises store an error,
-// a dummy result is returned.
+    fn fold_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
+        // Do not normalize predicates in the new solver. The new solver is
+        // supposed to handle unnormalized predicates and incorrectly normalizing
+        // them can be unsound, e.g. for `WellFormed` predicates.
+        let prev = mem::replace(&mut self.should_normalize, false);
+        let predicate = predicate.super_fold_with(self);
+        self.should_normalize = prev;
+        predicate
+    }
+}

Diff for: compiler/rustc_infer/src/infer/outlives/mod.rs

@@ -3,7 +3,7 @@ use self::env::OutlivesEnvironment;
 use super::region_constraints::RegionConstraintData;
 use super::{InferCtxt, RegionResolutionError};
 use crate::infer::free_regions::RegionRelations;
-use crate::infer::lexical_region_resolve::{self, LexicalRegionResolutions};
+use crate::infer::lexical_region_resolve;
 use rustc_middle::traits::query::OutlivesBound;
 use rustc_middle::ty;
 
@@ -37,32 +37,6 @@ pub fn explicit_outlives_bounds<'tcx>(
 }
 
 impl<'tcx> InferCtxt<'tcx> {
-    pub fn skip_region_resolution(&self) {
-        let (var_infos, _) = {
-            let mut inner = self.inner.borrow_mut();
-            let inner = &mut *inner;
-            // Note: `inner.region_obligations` may not be empty, because we
-            // didn't necessarily call `process_registered_region_obligations`.
-            // This is okay, because that doesn't introduce new vars.
-            inner
-                .region_constraint_storage
-                .take()
-                .expect("regions already resolved")
-                .with_log(&mut inner.undo_log)
-                .into_infos_and_data()
-        };
-
-        let lexical_region_resolutions = LexicalRegionResolutions {
-            values: rustc_index::IndexVec::from_elem_n(
-                crate::infer::lexical_region_resolve::VarValue::Value(self.tcx.lifetimes.re_erased),
-                var_infos.len(),
-            ),
-        };
-
-        let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
-        assert!(old_value.is_none());
-    }
-
     /// Process the region constraints and return any errors that
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use

Diff for: compiler/rustc_trait_selection/src/solve/mod.rs

@@ -42,9 +42,8 @@ mod trait_goals;
 
 pub use eval_ctxt::{EvalCtxt, GenerateProofTree, InferCtxtEvalExt, InferCtxtSelectExt};
 pub use fulfill::FulfillmentCtxt;
-pub(crate) use normalize::{
-    deeply_normalize, deeply_normalize_for_diagnostics, deeply_normalize_with_skipped_universes,
-};
+pub(crate) use normalize::deeply_normalize_for_diagnostics;
+pub use normalize::{deeply_normalize, deeply_normalize_with_skipped_universes};
 
 #[derive(Debug, Clone, Copy)]
 enum SolverMode {

Diff for: compiler/rustc_trait_selection/src/solve/normalize.rs

@@ -17,7 +17,7 @@ use super::FulfillmentCtxt;
 
 /// Deeply normalize all aliases in `value`. This does not handle inference and expects
 /// its input to be already fully resolved.
-pub(crate) fn deeply_normalize<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
+pub fn deeply_normalize<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
     at: At<'_, 'tcx>,
     value: T,
 ) -> Result<T, Vec<FulfillmentError<'tcx>>> {
@@ -31,7 +31,7 @@ pub(crate) fn deeply_normalize<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
 /// 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.
-pub(crate) fn deeply_normalize_with_skipped_universes<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
+pub fn deeply_normalize_with_skipped_universes<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
     at: At<'_, 'tcx>,
     value: T,
     universes: Vec<Option<UniverseIndex>>,

Diff for: tests/ui/traits/new-solver/alias-bound-unsound.rs

@@ -27,5 +27,6 @@ fn main() {
     //~| ERROR overflow evaluating the requirement `<() as Foo>::Item well-formed`
     //~| ERROR overflow evaluating the requirement `String <: <() as Foo>::Item`
     //~| ERROR overflow evaluating the requirement `&<() as Foo>::Item well-formed`
+    //~| ERROR overflow evaluating the requirement `<() as Foo>::Item normalizes-to _`
     println!("{x}");
 }

Diff for: tests/ui/traits/new-solver/alias-bound-unsound.stderr

@@ -52,6 +52,15 @@ LL |     drop(<() as Foo>::copy_me(&x));
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
 
-error: aborting due to 6 previous errors
+error[E0275]: overflow evaluating the requirement `<() as Foo>::Item normalizes-to _`
+  --> $DIR/alias-bound-unsound.rs:24:10
+   |
+LL |     drop(<() as Foo>::copy_me(&x));
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 7 previous errors
 
 For more information about this error, try `rustc --explain E0275`.

Diff for: tests/ui/traits/new-solver/generalize/generalize-proj-new-universe-index-2.rs

@@ -1,7 +1,5 @@
 // compile-flags: -Ztrait-solver=next
 // known-bug: trait-system-refactor-initiative#60
-// dont-check-failure-status
-// dont-check-compiler-stderr
 
 // Generalizing a projection containing an inference variable
 // which cannot be named by the `root_vid` can result in ambiguity.

Diff for: tests/ui/traits/new-solver/generalize/generalize-proj-new-universe-index-2.stderr

@@ -1,17 +1,8 @@
-error[E0284]: type annotations needed: cannot satisfy `<<Leaf as WithAssoc<_>>::Assoc as Id>::Assoc == <<Leaf as WithAssoc<_>>::Assoc as Id>::Assoc`
+error[E0284]: type annotations needed: cannot satisfy `<<Rigid as IdHigherRankedBound>::Assoc as WithAssoc<<Wrapper<Leaf> as Id>::Assoc>>::Assoc normalizes-to <<Leaf as WithAssoc<_>>::Assoc as Id>::Assoc`
   --> $DIR/generalize-proj-new-universe-index-2.rs:74:5
    |
 LL |     bound::<<Rigid as IdHigherRankedBound>::Assoc, <Wrapper<Leaf> as Id>::Assoc, _>()
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot satisfy `<<Leaf as WithAssoc<_>>::Assoc as Id>::Assoc == <<Leaf as WithAssoc<_>>::Assoc as Id>::Assoc`
-   |
-note: required by a bound in `bound`
-  --> $DIR/generalize-proj-new-universe-index-2.rs:69:21
-   |
-LL | fn bound<T: ?Sized, U: ?Sized, V: ?Sized>()
-   |    ----- required by a bound in this function
-LL | where
-LL |     T: WithAssoc<U, Assoc = V>,
-   |                     ^^^^^^^^^ required by this bound in `bound`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot satisfy `<<Rigid as IdHigherRankedBound>::Assoc as WithAssoc<<Wrapper<Leaf> as Id>::Assoc>>::Assoc normalizes-to <<Leaf as WithAssoc<_>>::Assoc as Id>::Assoc`
 
 error: aborting due to 1 previous error
 

Diff for: tests/ui/traits/new-solver/overflow/recursive-self-normalization-2.rs

@@ -1,4 +1,3 @@
-//~ ERROR overflow
 // compile-flags: -Ztrait-solver=next
 
 trait Foo1 {
@@ -15,6 +14,7 @@ fn needs_bar<S: Bar>() {}
 fn test<T: Foo1<Assoc1 = <T as Foo2>::Assoc2> + Foo2<Assoc2 = <T as Foo1>::Assoc1>>() {
     needs_bar::<T::Assoc1>();
     //~^ ERROR overflow evaluating the requirement `<T as Foo1>::Assoc1: Bar`
+    //~| ERROR overflow evaluating the requirement `<T as Foo2>::Assoc2`
 }
 
 fn main() {}

Diff for: tests/ui/traits/new-solver/overflow/recursive-self-normalization-2.stderr

@@ -1,17 +1,21 @@
 error[E0275]: overflow evaluating the requirement `<T as Foo1>::Assoc1: Bar`
-  --> $DIR/recursive-self-normalization-2.rs:16:17
+  --> $DIR/recursive-self-normalization-2.rs:15:17
    |
 LL |     needs_bar::<T::Assoc1>();
    |                 ^^^^^^^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`recursive_self_normalization_2`)
 note: required by a bound in `needs_bar`
-  --> $DIR/recursive-self-normalization-2.rs:13:17
+  --> $DIR/recursive-self-normalization-2.rs:12:17
    |
 LL | fn needs_bar<S: Bar>() {}
    |                 ^^^ required by this bound in `needs_bar`
 
 error[E0275]: overflow evaluating the requirement `<T as Foo2>::Assoc2`
+  --> $DIR/recursive-self-normalization-2.rs:15:5
+   |
+LL |     needs_bar::<T::Assoc1>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`recursive_self_normalization_2`)
 

Diff for: tests/ui/traits/new-solver/overflow/recursive-self-normalization.rs

@@ -1,4 +1,3 @@
-//~ ERROR overflow evaluating the requirement `<T as Foo>::Assoc` [E0275]
 // compile-flags: -Ztrait-solver=next
 
 trait Foo {
@@ -11,6 +10,7 @@ fn needs_bar<S: Bar>() {}
 fn test<T: Foo<Assoc = <T as Foo>::Assoc>>() {
     needs_bar::<T::Assoc>();
     //~^ ERROR overflow evaluating the requirement `<T as Foo>::Assoc: Bar`
+    //~| ERROR overflow evaluating the requirement `<T as Foo>::Assoc` [E0275]
 }
 
 fn main() {}