Auto merge of #143545 - compiler-errors:coroutine-obl, r=<try>

[experiment] Consider WF of coroutine witness when proving outlives assumptions

This needs to be majorly cleaned up

---

cc #110338

Consider, for example:

```rust
use std::future::Future;

trait Client {
    type Connecting<'a>: Future + Send
    where
        Self: 'a;
    fn connect(&'_ self) -> Self::Connecting<'_>;
}

fn call_connect<C>(c: &'_ C) -> impl Future + Send
where
    C: Client + Send + Sync,
{
    async move { c.connect().await }
}
```

Author: rust-bors[bot]

compiler/rustc_borrowck/src/type_check/constraint_conversion.rs

@@ -70,9 +70,13 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
 
     #[instrument(skip(self), level = "debug")]
     pub(super) fn convert_all(&mut self, query_constraints: &QueryRegionConstraints<'tcx>) {
-        let QueryRegionConstraints { outlives } = query_constraints;
+        let QueryRegionConstraints { outlives, assumptions } = query_constraints;
 
         for &(predicate, constraint_category) in outlives {
+            if assumptions.contains(&predicate) {
+                continue;
+            }
+
             self.convert(predicate, constraint_category);
         }
     }
@@ -270,7 +274,8 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         match self.param_env.and(DeeplyNormalize { value: ty }).fully_perform(self.infcx, self.span)
         {
             Ok(TypeOpOutput { output: ty, constraints, .. }) => {
-                if let Some(QueryRegionConstraints { outlives }) = constraints {
+                // FIXME(higher_ranked_auto): WTF
+                if let Some(QueryRegionConstraints { outlives, assumptions: _ }) = constraints {
                     next_outlives_predicates.extend(outlives.iter().copied());
                 }
                 ty

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -131,6 +131,11 @@ pub(crate) fn type_check<'tcx>(
         pre_obligations.is_empty(),
         "there should be no incoming region obligations = {pre_obligations:#?}",
     );
+    let pre_assumptions = infcx.take_registered_region_assumptions();
+    assert!(
+        pre_assumptions.is_empty(),
+        "there should be no incoming region assumptions = {pre_assumptions:#?}",
+    );
 
     debug!(?normalized_inputs_and_output);
 

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -115,6 +115,7 @@ impl<'tcx> InferCtxt<'tcx> {
         }
 
         let region_obligations = self.take_registered_region_obligations();
+        let region_assumptions = self.take_registered_region_assumptions();
         debug!(?region_obligations);
         let region_constraints = self.with_region_constraints(|region_constraints| {
             make_query_region_constraints(
@@ -123,6 +124,7 @@ impl<'tcx> InferCtxt<'tcx> {
                     .iter()
                     .map(|r_o| (r_o.sup_type, r_o.sub_region, r_o.origin.to_constraint_category())),
                 region_constraints,
+                region_assumptions,
             )
         });
         debug!(?region_constraints);
@@ -174,6 +176,11 @@ impl<'tcx> InferCtxt<'tcx> {
             self.register_outlives_constraint(predicate, cause);
         }
 
+        for assumption in &query_response.value.region_constraints.assumptions {
+            let assumption = instantiate_value(self.tcx, &result_args, *assumption);
+            self.register_region_assumption(assumption);
+        }
+
         let user_result: R =
             query_response.instantiate_projected(self.tcx, &result_args, |q_r| q_r.value.clone());
 
@@ -297,6 +304,16 @@ impl<'tcx> InferCtxt<'tcx> {
             }),
         );
 
+        // FIXME(higher_ranked_auto): Optimize?
+        output_query_region_constraints.assumptions.extend(
+            query_response
+                .value
+                .region_constraints
+                .assumptions
+                .iter()
+                .map(|&r_c| instantiate_value(self.tcx, &result_args, r_c)),
+        );
+
         let user_result: R =
             query_response.instantiate_projected(self.tcx, &result_args, |q_r| q_r.value.clone());
 
@@ -572,6 +589,7 @@ pub fn make_query_region_constraints<'tcx>(
     tcx: TyCtxt<'tcx>,
     outlives_obligations: impl Iterator<Item = (Ty<'tcx>, ty::Region<'tcx>, ConstraintCategory<'tcx>)>,
     region_constraints: &RegionConstraintData<'tcx>,
+    assumptions: Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>>,
 ) -> QueryRegionConstraints<'tcx> {
     let RegionConstraintData { constraints, verifys } = region_constraints;
 
@@ -604,5 +622,5 @@ pub fn make_query_region_constraints<'tcx>(
         }))
         .collect();
 
-    QueryRegionConstraints { outlives }
+    QueryRegionConstraints { outlives, assumptions }
 }

compiler/rustc_infer/src/infer/mod.rs

@@ -149,6 +149,9 @@ pub struct InferCtxtInner<'tcx> {
     /// that all type inference variables have been bound and so forth.
     region_obligations: Vec<TypeOutlivesConstraint<'tcx>>,
 
+    /// UwU
+    region_assumptions: Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>>,
+
     /// Caches for opaque type inference.
     opaque_type_storage: OpaqueTypeStorage<'tcx>,
 }
@@ -164,7 +167,8 @@ impl<'tcx> InferCtxtInner<'tcx> {
             int_unification_storage: Default::default(),
             float_unification_storage: Default::default(),
             region_constraint_storage: Some(Default::default()),
-            region_obligations: vec![],
+            region_obligations: Default::default(),
+            region_assumptions: Default::default(),
             opaque_type_storage: Default::default(),
         }
     }
@@ -174,6 +178,11 @@ impl<'tcx> InferCtxtInner<'tcx> {
         &self.region_obligations
     }
 
+    #[inline]
+    pub fn region_assumptions(&self) -> &[ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>] {
+        &self.region_assumptions
+    }
+
     #[inline]
     pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
         self.projection_cache.with_log(&mut self.undo_log)

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

@@ -60,7 +60,7 @@ impl<'tcx> InferCtxt<'tcx> {
             assert!(
                 self.tainted_by_errors().is_some() || inner.region_obligations.is_empty(),
                 "region_obligations not empty: {:#?}",
-                inner.region_obligations
+                inner.region_obligations,
             );
             assert!(!UndoLogs::<UndoLog<'_>>::in_snapshot(&inner.undo_log));
             inner.region_constraint_storage.take().expect("regions already resolved")
@@ -93,6 +93,11 @@ impl<'tcx> InferCtxt<'tcx> {
             "region_obligations not empty: {:#?}",
             self.inner.borrow().region_obligations
         );
+        assert!(
+            self.inner.borrow().region_assumptions.is_empty(),
+            "region_assumptions not empty: {:#?}",
+            self.inner.borrow().region_assumptions
+        );
 
         self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
     }

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

@@ -169,6 +169,21 @@ impl<'tcx> InferCtxt<'tcx> {
         std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
+    pub fn register_region_assumption(
+        &self,
+        assumption: ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
+    ) {
+        let mut inner = self.inner.borrow_mut();
+        inner.undo_log.push(UndoLog::PushRegionAssumption);
+        inner.region_assumptions.push(assumption);
+    }
+
+    pub fn take_registered_region_assumptions(
+        &self,
+    ) -> Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>> {
+        std::mem::take(&mut self.inner.borrow_mut().region_assumptions)
+    }
+
     /// Process the region obligations that must be proven (during
     /// `regionck`) for the given `body_id`, given information about
     /// the region bounds in scope and so forth.
@@ -189,6 +204,7 @@ impl<'tcx> InferCtxt<'tcx> {
             -> Result<PolyTypeOutlivesPredicate<'tcx>, NoSolution>,
     ) -> Result<(), (PolyTypeOutlivesPredicate<'tcx>, SubregionOrigin<'tcx>)> {
         assert!(!self.in_snapshot(), "cannot process registered region obligations in a snapshot");
+        let assumptions = self.take_registered_region_assumptions();
 
         // Must loop since the process of normalizing may itself register region obligations.
         for iteration in 0.. {
@@ -207,6 +223,10 @@ impl<'tcx> InferCtxt<'tcx> {
             }
 
             for TypeOutlivesConstraint { sup_type, sub_region, origin } in my_region_obligations {
+                if assumptions.contains(&ty::OutlivesPredicate(sup_type.into(), sub_region)) {
+                    continue;
+                }
+
                 let outlives = ty::Binder::dummy(ty::OutlivesPredicate(sup_type, sub_region));
                 let ty::OutlivesPredicate(sup_type, sub_region) =
                     deeply_normalize_ty(outlives, origin.clone())

compiler/rustc_infer/src/infer/snapshot/undo_log.rs

@@ -27,6 +27,7 @@ pub(crate) enum UndoLog<'tcx> {
     RegionUnificationTable(sv::UndoLog<ut::Delegate<RegionVidKey<'tcx>>>),
     ProjectionCache(traits::UndoLog<'tcx>),
     PushTypeOutlivesConstraint,
+    PushRegionAssumption,
 }
 
 macro_rules! impl_from {
@@ -75,6 +76,9 @@ impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> {
             UndoLog::PushTypeOutlivesConstraint => {
                 self.region_obligations.pop();
             }
+            UndoLog::PushRegionAssumption => {
+                self.region_assumptions.pop();
+            }
         }
     }
 }

compiler/rustc_middle/src/infer/canonical.rs

@@ -81,13 +81,14 @@ pub struct QueryResponse<'tcx, R> {
 #[derive(HashStable, TypeFoldable, TypeVisitable)]
 pub struct QueryRegionConstraints<'tcx> {
     pub outlives: Vec<QueryOutlivesConstraint<'tcx>>,
+    pub assumptions: Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>>,
 }
 
 impl QueryRegionConstraints<'_> {
-    /// Represents an empty (trivially true) set of region
-    /// constraints.
+    /// Represents an empty (trivially true) set of region constraints.
+    // FIXME(higher_ranked_auto): This could still just be true if there are only assumptions?
     pub fn is_empty(&self) -> bool {
-        self.outlives.is_empty()
+        self.outlives.is_empty() && self.assumptions.is_empty()
     }
 }
 

compiler/rustc_middle/src/query/mod.rs

@@ -988,7 +988,7 @@ rustc_queries! {
     }
 
     query coroutine_hidden_types(
-        def_id: DefId
+        def_id: DefId,
     ) -> ty::EarlyBinder<'tcx, ty::Binder<'tcx, ty::CoroutineWitnessTypes<TyCtxt<'tcx>>>> {
         desc { "looking up the hidden types stored across await points in a coroutine" }
     }

compiler/rustc_middle/src/ty/context.rs

@@ -162,6 +162,8 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     type BoundRegion = ty::BoundRegion;
     type PlaceholderRegion = ty::PlaceholderRegion;
 
+    type RegionAssumptions = &'tcx ty::List<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>>;
+
     type ParamEnv = ty::ParamEnv<'tcx>;
     type Predicate = Predicate<'tcx>;
 
@@ -874,6 +876,7 @@ pub struct CtxtInterners<'tcx> {
     offset_of: InternedSet<'tcx, List<(VariantIdx, FieldIdx)>>,
     valtree: InternedSet<'tcx, ty::ValTreeKind<'tcx>>,
     patterns: InternedSet<'tcx, List<ty::Pattern<'tcx>>>,
+    outlives: InternedSet<'tcx, List<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>>>,
 }
 
 impl<'tcx> CtxtInterners<'tcx> {
@@ -911,6 +914,7 @@ impl<'tcx> CtxtInterners<'tcx> {
             offset_of: InternedSet::with_capacity(N),
             valtree: InternedSet::with_capacity(N),
             patterns: InternedSet::with_capacity(N),
+            outlives: InternedSet::with_capacity(N),
         }
     }
 
@@ -2692,6 +2696,7 @@ slice_interners!(
     captures: intern_captures(&'tcx ty::CapturedPlace<'tcx>),
     offset_of: pub mk_offset_of((VariantIdx, FieldIdx)),
     patterns: pub mk_patterns(Pattern<'tcx>),
+    outlives: pub mk_outlives(ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>),
 );
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -3107,6 +3112,17 @@ impl<'tcx> TyCtxt<'tcx> {
         T::collect_and_apply(iter, |xs| self.mk_bound_variable_kinds(xs))
     }
 
+    pub fn mk_outlives_from_iter<I, T>(self, iter: I) -> T::Output
+    where
+        I: Iterator<Item = T>,
+        T: CollectAndApply<
+                ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
+                &'tcx ty::List<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>>,
+            >,
+    {
+        T::collect_and_apply(iter, |xs| self.mk_outlives(xs))
+    }
+
     /// Emit a lint at `span` from a lint struct (some type that implements `LintDiagnostic`,
     /// typically generated by `#[derive(LintDiagnostic)]`).
     #[track_caller]