[WIP] -Zhigher-ranked-assumptions-v2

compiler/rustc_borrowck/src/constraints/mod.rs

@@ -96,8 +96,8 @@ impl<'tcx> fmt::Debug for OutlivesConstraint<'tcx> {
     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
             formatter,
-            "({:?}: {:?}) due to {:?} ({:?}) ({:?})",
-            self.sup, self.sub, self.locations, self.variance_info, self.category,
+            "({:?}: {:?}) due to {:?} ({:?}) ({:?}) (span: {:?})",
+            self.sup, self.sub, self.locations, self.variance_info, self.category, self.span,
         )
     }
 }

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -57,7 +57,8 @@ impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> {
             ConstraintCategory::OpaqueType => "opaque type ",
             ConstraintCategory::ClosureUpvar(_) => "closure capture ",
             ConstraintCategory::Usage => "this usage ",
-            ConstraintCategory::Predicate(_)
+            ConstraintCategory::SolverRegionConstraint(_)
+            | ConstraintCategory::Predicate(_)
             | ConstraintCategory::Boring
             | ConstraintCategory::BoringNoLocation
             | ConstraintCategory::Internal
@@ -473,6 +474,14 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         let errci = ErrorConstraintInfo { fr, outlived_fr, category, span: cause.span };
 
         let mut diag = match (category, fr_is_local, outlived_fr_is_local) {
+            (ConstraintCategory::SolverRegionConstraint(span), _, _) => {
+                let mut d = self.dcx().struct_span_err(
+                    span,
+                    "unsatisfied lifetime constraint from -Zassumptions-on-binders :3",
+                );
+                d.note("meoow :c");
+                d
+            }
             (ConstraintCategory::Return(kind), true, false) if self.is_closure_fn_mut(fr) => {
                 self.report_fnmut_error(&errci, kind)
             }

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -1479,6 +1479,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 // This loop is cold and runs at the end, which is why we delay
                 // `OutlivesConstraint` construction until now.
                 loop {
+                    let ctx = &context[p];
+                    debug!(?ctx);
                     match context[p] {
                         Trace::FromGraph(c) => {
                             p = c.sup;
@@ -1793,6 +1795,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 // the `'region: 'static` constraints introduced by placeholder outlives.
                 ConstraintCategory::Internal => 7,
                 ConstraintCategory::OutlivesUnnameablePlaceholder(_) => 8,
+                ConstraintCategory::SolverRegionConstraint(_) => 9,
             };
 
             debug!("constraint {constraint:?} category: {category:?}, interest: {interest:?}");

compiler/rustc_borrowck/src/type_check/free_region_relations.rs

@@ -26,7 +26,7 @@ pub(crate) struct UniversalRegionRelations<'tcx> {
     /// Stores the outlives relations that are known to hold from the
     /// implied bounds, in-scope where-clauses, and that sort of
     /// thing.
-    outlives: TransitiveRelation<RegionVid>,
+    pub(crate) outlives: TransitiveRelation<RegionVid>,
 
     /// This is the `<=` relation; that is, if `a: b`, then `b <= a`,
     /// and we store that here. This is useful when figuring out how

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -173,6 +173,23 @@ pub(crate) fn type_check<'tcx>(
 
     let polonius_context = typeck.polonius_context;
 
+    let mut converter = constraint_conversion::ConstraintConversion::new(
+        typeck.infcx,
+        typeck.universal_regions,
+        typeck.region_bound_pairs,
+        typeck.known_type_outlives_obligations,
+        Locations::All(rustc_span::DUMMY_SP),
+        rustc_span::DUMMY_SP,
+        ConstraintCategory::Boring,
+        typeck.constraints,
+    );
+    typeck.infcx.destructure_solver_region_constraints_for_borrowck(
+        &mut converter,
+        typeck.known_type_outlives_obligations,
+        universal_region_relations.outlives.clone(),
+        infcx.tcx.def_span(infcx.root_def_id),
+    );
+
     // In case type check encountered an error region, we suppress unhelpful extra
     // errors in by clearing out all outlives bounds that we may end up checking.
     if let Some(guar) = universal_region_relations.universal_regions.encountered_re_error() {

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -197,7 +197,7 @@ where
 
     lint_redundant_lifetimes(tcx, body_def_id, &outlives_env);
 
-    let errors = infcx.resolve_regions_with_outlives_env(&outlives_env);
+    let errors = infcx.resolve_regions_with_outlives_env(&outlives_env, tcx.def_span(body_def_id));
     if errors.is_empty() {
         return Ok(());
     }
@@ -211,7 +211,8 @@ where
         // the implied bounds hack if this contains `bevy_ecs`'s `ParamSet` type.
         false,
     );
-    let errors_compat = infcx_compat.resolve_regions_with_outlives_env(&outlives_env);
+    let errors_compat =
+        infcx_compat.resolve_regions_with_outlives_env(&outlives_env, tcx.def_span(body_def_id));
     if errors_compat.is_empty() {
         // FIXME: Once we fix bevy, this would be the place to insert a warning
         // to upgrade bevy.

compiler/rustc_infer/src/infer/at.rs

@@ -81,6 +81,9 @@ impl<'tcx> InferCtxt<'tcx> {
             reported_signature_mismatch: self.reported_signature_mismatch.clone(),
             tainted_by_errors: self.tainted_by_errors.clone(),
             universe: self.universe.clone(),
+            placeholder_assumptions_for_next_solver: self
+                .placeholder_assumptions_for_next_solver
+                .clone(),
             next_trait_solver: self.next_trait_solver,
             obligation_inspector: self.obligation_inspector.clone(),
         }
@@ -106,6 +109,9 @@ impl<'tcx> InferCtxt<'tcx> {
             reported_signature_mismatch: self.reported_signature_mismatch.clone(),
             tainted_by_errors: self.tainted_by_errors.clone(),
             universe: self.universe.clone(),
+            placeholder_assumptions_for_next_solver: self
+                .placeholder_assumptions_for_next_solver
+                .clone(),
             next_trait_solver: self.next_trait_solver,
             obligation_inspector: self.obligation_inspector.clone(),
         };

compiler/rustc_infer/src/infer/context.rs

@@ -22,6 +22,10 @@ impl<'tcx> rustc_type_ir::InferCtxtLike for InferCtxt<'tcx> {
         self.next_trait_solver
     }
 
+    fn higher_ranked_assumptions_v2(&self) -> bool {
+        self.tcx.sess.opts.unstable_opts.higher_ranked_assumptions_v2
+    }
+
     fn typing_mode(&self) -> ty::TypingMode<'tcx> {
         self.typing_mode()
     }
@@ -34,6 +38,40 @@ impl<'tcx> rustc_type_ir::InferCtxtLike for InferCtxt<'tcx> {
         self.create_next_universe()
     }
 
+    fn insert_placeholder_assumptions(
+        &self,
+        u: ty::UniverseIndex,
+        assumptions: Option<rustc_type_ir::region_constraint::Assumptions<TyCtxt<'tcx>>>,
+    ) {
+        self.placeholder_assumptions_for_next_solver.borrow_mut().insert(u, assumptions);
+    }
+
+    fn get_placeholder_assumptions(
+        &self,
+        u: ty::UniverseIndex,
+    ) -> Option<rustc_type_ir::region_constraint::Assumptions<TyCtxt<'tcx>>> {
+        self.placeholder_assumptions_for_next_solver.borrow().get(&u).unwrap().as_ref().cloned()
+    }
+
+    fn get_solver_region_constraint(
+        &self,
+    ) -> rustc_type_ir::region_constraint::RegionConstraint<TyCtxt<'tcx>> {
+        self.inner.borrow().solver_region_constraint_storage.get_constraint()
+    }
+
+    fn overwrite_solver_region_constraint(
+        &self,
+        constraint: rustc_type_ir::region_constraint::RegionConstraint<TyCtxt<'tcx>>,
+    ) {
+        let mut inner = self.inner.borrow_mut();
+        use rustc_data_structures::undo_log::UndoLogs;
+
+        use crate::infer::UndoLog;
+        let old_constraint = inner.solver_region_constraint_storage.get_constraint();
+        inner.undo_log.push(UndoLog::OverwriteSolverRegionConstraint { old_constraint });
+        inner.solver_region_constraint_storage.overwrite_solver_region_constraint(constraint);
+    }
+
     fn universe_of_ty(&self, vid: ty::TyVid) -> Option<ty::UniverseIndex> {
         match self.try_resolve_ty_var(vid) {
             Err(universe) => Some(universe),
@@ -272,6 +310,18 @@ impl<'tcx> rustc_type_ir::InferCtxtLike for InferCtxt<'tcx> {
         );
     }
 
+    fn register_solver_region_constraint(
+        &self,
+        c: rustc_type_ir::region_constraint::RegionConstraint<TyCtxt<'tcx>>,
+    ) {
+        let mut inner = self.inner.borrow_mut();
+        use rustc_data_structures::undo_log::UndoLogs;
+
+        use crate::infer::UndoLog;
+        inner.undo_log.push(UndoLog::PushSolverRegionConstraint);
+        inner.solver_region_constraint_storage.push(c);
+    }
+
     fn register_ty_outlives(&self, ty: Ty<'tcx>, r: ty::Region<'tcx>, span: Span) {
         self.register_type_outlives_constraint(ty, r, &ObligationCause::dummy_with_span(span));
     }

compiler/rustc_infer/src/infer/mod.rs

@@ -123,6 +123,9 @@ pub struct InferCtxtInner<'tcx> {
     /// region constraints would've been added.
     region_constraint_storage: Option<RegionConstraintStorage<'tcx>>,
 
+    /// Used by the next solver when `-Zhigher-ranked-assumptions=v2` is set.
+    solver_region_constraint_storage: SolverRegionConstraintStorage<'tcx>,
+
     /// A set of constraints that regionck must validate.
     ///
     /// Each constraint has the form `T:'a`, meaning "some type `T` must
@@ -170,6 +173,7 @@ impl<'tcx> InferCtxtInner<'tcx> {
             float_unification_storage: Default::default(),
             float_origin_origin_storage: Default::default(),
             region_constraint_storage: Some(Default::default()),
+            solver_region_constraint_storage: SolverRegionConstraintStorage::new(),
             region_obligations: Default::default(),
             region_assumptions: Default::default(),
             hir_typeck_potentially_region_dependent_goals: Default::default(),
@@ -314,6 +318,16 @@ pub struct InferCtxt<'tcx> {
     /// bound.
     universe: Cell<ty::UniverseIndex>,
 
+    /// List of assumed wellformed types which we can derive implied
+    /// bounds on a `for<...>` from. Only used unstabley and by the
+    /// new solver.
+    placeholder_assumptions_for_next_solver: RefCell<
+        FxIndexMap<
+            ty::UniverseIndex,
+            Option<rustc_type_ir::region_constraint::Assumptions<TyCtxt<'tcx>>>,
+        >,
+    >,
+
     next_trait_solver: bool,
 
     pub obligation_inspector: Cell<Option<ObligationInspector<'tcx>>>,
@@ -396,6 +410,10 @@ pub enum SubregionOrigin<'tcx> {
     },
 
     AscribeUserTypeProvePredicate(Span),
+
+    // FIXME(-Zhigher-ranked-assumptions-v2): this is a temporary hack until we support
+    // proper diagnostics for solver region constraints.
+    SolverRegionConstraint(Span),
 }
 
 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
@@ -407,6 +425,7 @@ impl<'tcx> SubregionOrigin<'tcx> {
         match self {
             Self::Subtype(type_trace) => type_trace.cause.to_constraint_category(),
             Self::AscribeUserTypeProvePredicate(span) => ConstraintCategory::Predicate(*span),
+            Self::SolverRegionConstraint(span) => ConstraintCategory::SolverRegionConstraint(*span),
             _ => ConstraintCategory::BoringNoLocation,
         }
     }
@@ -606,6 +625,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             reported_signature_mismatch: Default::default(),
             tainted_by_errors: Cell::new(None),
             universe: Cell::new(ty::UniverseIndex::ROOT),
+            placeholder_assumptions_for_next_solver: RefCell::new(Default::default()),
             next_trait_solver,
             obligation_inspector: Cell::new(None),
         }
@@ -1632,6 +1652,7 @@ impl<'tcx> SubregionOrigin<'tcx> {
             SubregionOrigin::CompareImplItemObligation { span, .. } => span,
             SubregionOrigin::AscribeUserTypeProvePredicate(span) => span,
             SubregionOrigin::CheckAssociatedTypeBounds { ref parent, .. } => parent.span(),
+            SubregionOrigin::SolverRegionConstraint(a) => a,
         }
     }
 
@@ -1721,3 +1742,55 @@ impl<'tcx> InferCtxt<'tcx> {
         }
     }
 }
+
+type SolverRegionConstraint<'tcx> =
+    rustc_type_ir::region_constraint::RegionConstraint<TyCtxt<'tcx>>;
+
+#[derive(Clone, Debug)]
+struct SolverRegionConstraintStorage<'tcx>(SolverRegionConstraint<'tcx>);
+
+impl<'tcx> SolverRegionConstraintStorage<'tcx> {
+    fn new() -> Self {
+        SolverRegionConstraintStorage(SolverRegionConstraint::And(Box::new([])))
+    }
+
+    fn get_constraint(&self) -> SolverRegionConstraint<'tcx> {
+        self.0.clone()
+    }
+
+    fn pop(&mut self) -> Option<SolverRegionConstraint<'tcx>> {
+        match &mut self.0 {
+            SolverRegionConstraint::And(and) => {
+                let mut and = core::mem::take(and).into_iter().collect::<Vec<_>>();
+                let popped = and.pop()?;
+                self.0 = SolverRegionConstraint::And(and.into_boxed_slice());
+                Some(popped)
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    #[instrument(level = "debug")]
+    fn push(&mut self, constraint: SolverRegionConstraint<'tcx>) {
+        match &mut self.0 {
+            SolverRegionConstraint::And(and) => {
+                let and = core::mem::take(and)
+                    .into_iter()
+                    .chain([constraint])
+                    .collect::<Vec<_>>()
+                    .into_boxed_slice();
+                self.0 = SolverRegionConstraint::And(and);
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    #[instrument(level = "debug", skip(self))]
+    fn overwrite_solver_region_constraint(&mut self, constraint: SolverRegionConstraint<'tcx>) {
+        if !constraint.is_and() {
+            self.0 = SolverRegionConstraint::And(vec![constraint].into_boxed_slice())
+        } else {
+            self.0 = constraint;
+        }
+    }
+}

compiler/rustc_infer/src/infer/outlives/mod.rs

@@ -5,6 +5,7 @@ use std::iter;
 use rustc_data_structures::undo_log::UndoLogs;
 use rustc_middle::traits::query::{NoSolution, OutlivesBound};
 use rustc_middle::ty;
+use rustc_span::Span;
 use tracing::instrument;
 
 use self::env::OutlivesEnvironment;
@@ -49,8 +50,9 @@ impl<'tcx> InferCtxt<'tcx> {
             ty::PolyTypeOutlivesPredicate<'tcx>,
             SubregionOrigin<'tcx>,
         ) -> Result<ty::PolyTypeOutlivesPredicate<'tcx>, NoSolution>,
+        span: Span,
     ) -> Vec<RegionResolutionError<'tcx>> {
-        match self.process_registered_region_obligations(outlives_env, deeply_normalize_ty) {
+        match self.process_registered_region_obligations(outlives_env, deeply_normalize_ty, span) {
             Ok(()) => {}
             Err((clause, origin)) => {
                 return vec![RegionResolutionError::CannotNormalize(clause, origin)];