Rollup merge of #107061 - compiler-errors:new-solver-new-candidates-3, r=lcnr

Implement some more new solver candidates and fix some bugs

First, fix some bugs:

1. `IndexVec::drain_enumerated(a..b)` does not give us an iterator of index keys + items enumerated from `a..b`, but from `0..(b-a)`... That caused a bug. See first commit for the fix.
2. Implement the `_: Trait` ambiguity hack. I put it in assemble, let me know if it should live elsewhere. This is important, since we otherwise consider `_: Sized` to have no solutions, and nothing passes!
3. Swap `Ambiguity` and `Unimplemented` cases for the new solver. Sorry for accidentally swapping them 😄
4. Check GATs' own predicates during projection confirmation.

Then implement a few builtin traits:

5. Implement `PointerSized`. Pretty independent.
6. Implement `Fn` family of traits for fnptr, fndef, and closures. Closures are currently broken because `FulfillCtxt::relationships` is intentionally left unimplemented. See comment in the test.

r? ```@lcnr```

Author: compiler-errors

compiler/rustc_index/src/vec.rs

@@ -207,7 +207,12 @@ impl<I: Idx, T> IndexVec<I, T> {
         &'a mut self,
         range: R,
     ) -> impl Iterator<Item = (I, T)> + 'a {
-        self.raw.drain(range).enumerate().map(|(n, t)| (I::new(n), t))
+        let begin = match range.start_bound() {
+            std::ops::Bound::Included(i) => *i,
+            std::ops::Bound::Excluded(i) => i.checked_add(1).unwrap(),
+            std::ops::Bound::Unbounded => 0,
+        };
+        self.raw.drain(range).enumerate().map(move |(n, t)| (I::new(begin + n), t))
     }
 
     #[inline]

compiler/rustc_trait_selection/src/solve/assembly.rs

@@ -1,7 +1,7 @@
 //! Code shared by trait and projection goals for candidate assembly.
 
 use super::infcx_ext::InferCtxtExt;
-use super::{CanonicalResponse, EvalCtxt, Goal, QueryResult};
+use super::{CanonicalResponse, Certainty, EvalCtxt, Goal, MaybeCause, QueryResult};
 use rustc_hir::def_id::DefId;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::util::elaborate_predicates;
@@ -79,7 +79,7 @@ pub(super) enum CandidateSource {
     AliasBound(usize),
 }
 
-pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy {
+pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy + Eq {
     fn self_ty(self) -> Ty<'tcx>;
 
     fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self;
@@ -117,13 +117,43 @@ pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx>;
+
+    fn consider_builtin_pointer_sized_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
+
+    fn consider_builtin_fn_trait_candidates(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        kind: ty::ClosureKind,
+    ) -> QueryResult<'tcx>;
+
+    fn consider_builtin_tuple_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {
     pub(super) fn assemble_and_evaluate_candidates<G: GoalKind<'tcx>>(
         &mut self,
         goal: Goal<'tcx, G>,
     ) -> Vec<Candidate<'tcx>> {
+        debug_assert_eq!(goal, self.infcx.resolve_vars_if_possible(goal));
+
+        // HACK: `_: Trait` is ambiguous, because it may be satisfied via a builtin rule,
+        // object bound, alias bound, etc. We are unable to determine this until we can at
+        // least structually resolve the type one layer.
+        if goal.predicate.self_ty().is_ty_var() {
+            return vec![Candidate {
+                source: CandidateSource::BuiltinImpl,
+                result: self
+                    .make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity))
+                    .unwrap(),
+            }];
+        }
+
         let mut candidates = Vec::new();
 
         self.assemble_candidates_after_normalizing_self_ty(goal, &mut candidates);
@@ -169,6 +199,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
                 Ok((_, certainty)) => certainty,
                 Err(NoSolution) => return,
             };
+            let normalized_ty = self.infcx.resolve_vars_if_possible(normalized_ty);
 
             // NOTE: Alternatively we could call `evaluate_goal` here and only have a `Normalized` candidate.
             // This doesn't work as long as we use `CandidateSource` in winnowing.
@@ -224,6 +255,12 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             || lang_items.clone_trait() == Some(trait_def_id)
         {
             G::consider_builtin_copy_clone_candidate(self, goal)
+        } else if lang_items.pointer_sized() == Some(trait_def_id) {
+            G::consider_builtin_pointer_sized_candidate(self, goal)
+        } else if let Some(kind) = self.tcx().fn_trait_kind_from_def_id(trait_def_id) {
+            G::consider_builtin_fn_trait_candidates(self, goal, kind)
+        } else if lang_items.tuple_trait() == Some(trait_def_id) {
+            G::consider_builtin_tuple_candidate(self, goal)
         } else {
             Err(NoSolution)
         };

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -52,7 +52,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
             .drain(..)
             .map(|obligation| FulfillmentError {
                 obligation: obligation.clone(),
-                code: FulfillmentErrorCode::CodeSelectionError(SelectionError::Unimplemented),
+                code: FulfillmentErrorCode::CodeAmbiguity,
                 root_obligation: obligation,
             })
             .collect()
@@ -75,7 +75,9 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
                     Err(NoSolution) => {
                         errors.push(FulfillmentError {
                             obligation: obligation.clone(),
-                            code: FulfillmentErrorCode::CodeAmbiguity,
+                            code: FulfillmentErrorCode::CodeSelectionError(
+                                SelectionError::Unimplemented,
+                            ),
                             root_obligation: obligation,
                         });
                         continue;

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -2,6 +2,7 @@ use crate::traits::{specialization_graph, translate_substs};
 
 use super::assembly::{self, Candidate, CandidateSource};
 use super::infcx_ext::InferCtxtExt;
+use super::trait_goals::structural_traits;
 use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::DefKind;
@@ -11,9 +12,9 @@ use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::specialization_graph::LeafDef;
 use rustc_infer::traits::Reveal;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
-use rustc_middle::ty::TypeVisitable;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor};
+use rustc_middle::ty::{ToPredicate, TypeVisitable};
 use rustc_span::DUMMY_SP;
 use std::iter;
 use std::ops::ControlFlow;
@@ -351,6 +352,46 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
     ) -> QueryResult<'tcx> {
         bug!("`Copy`/`Clone` does not have an associated type: {:?}", goal);
     }
+
+    fn consider_builtin_pointer_sized_candidate(
+        _ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        bug!("`PointerSized` does not have an associated type: {:?}", goal);
+    }
+
+    fn consider_builtin_fn_trait_candidates(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        goal_kind: ty::ClosureKind,
+    ) -> QueryResult<'tcx> {
+        if let Some(tupled_inputs_and_output) =
+            structural_traits::extract_tupled_inputs_and_output_from_callable(
+                ecx.tcx(),
+                goal.predicate.self_ty(),
+                goal_kind,
+            )?
+        {
+            let pred = tupled_inputs_and_output
+                .map_bound(|(inputs, output)| ty::ProjectionPredicate {
+                    projection_ty: ecx
+                        .tcx()
+                        .mk_alias_ty(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]),
+                    term: output.into(),
+                })
+                .to_predicate(ecx.tcx());
+            Self::consider_assumption(ecx, goal, pred)
+        } else {
+            ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity))
+        }
+    }
+
+    fn consider_builtin_tuple_candidate(
+        _ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        bug!("`Tuple` does not have an associated type: {:?}", goal);
+    }
 }
 
 /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -4,16 +4,16 @@ use std::iter;
 
 use super::assembly::{self, Candidate, CandidateSource};
 use super::infcx_ext::InferCtxtExt;
-use super::{EvalCtxt, Goal, QueryResult};
+use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult};
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
-use rustc_middle::ty::TraitPredicate;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
+use rustc_middle::ty::{TraitPredicate, TypeVisitable};
 use rustc_span::DUMMY_SP;
 
-mod structural_traits;
+pub mod structural_traits;
 
 impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
     fn self_ty(self) -> Ty<'tcx> {
@@ -127,6 +127,64 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
             structural_traits::instantiate_constituent_tys_for_copy_clone_trait,
         )
     }
+
+    fn consider_builtin_pointer_sized_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        if goal.predicate.self_ty().has_non_region_infer() {
+            return ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity));
+        }
+
+        let tcx = ecx.tcx();
+        let self_ty = tcx.erase_regions(goal.predicate.self_ty());
+
+        if let Ok(layout) = tcx.layout_of(goal.param_env.and(self_ty))
+            &&  let usize_layout = tcx.layout_of(ty::ParamEnv::empty().and(tcx.types.usize)).unwrap().layout
+            && layout.layout.size() == usize_layout.size()
+            && layout.layout.align().abi == usize_layout.align().abi
+        {
+            // FIXME: We could make this faster by making a no-constraints response
+            ecx.make_canonical_response(Certainty::Yes)
+        } else {
+            Err(NoSolution)
+        }
+    }
+
+    fn consider_builtin_fn_trait_candidates(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        goal_kind: ty::ClosureKind,
+    ) -> QueryResult<'tcx> {
+        if let Some(tupled_inputs_and_output) =
+            structural_traits::extract_tupled_inputs_and_output_from_callable(
+                ecx.tcx(),
+                goal.predicate.self_ty(),
+                goal_kind,
+            )?
+        {
+            let pred = tupled_inputs_and_output
+                .map_bound(|(inputs, _)| {
+                    ecx.tcx()
+                        .mk_trait_ref(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs])
+                })
+                .to_predicate(ecx.tcx());
+            Self::consider_assumption(ecx, goal, pred)
+        } else {
+            ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity))
+        }
+    }
+
+    fn consider_builtin_tuple_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        if let ty::Tuple(..) = goal.predicate.self_ty().kind() {
+            ecx.make_canonical_response(Certainty::Yes)
+        } else {
+            Err(NoSolution)
+        }
+    }
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {

compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs

@@ -1,6 +1,6 @@
 use rustc_hir::{Movability, Mutability};
 use rustc_infer::{infer::InferCtxt, traits::query::NoSolution};
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 
 // Calculates the constituent types of a type for `auto trait` purposes.
 //
@@ -30,10 +30,7 @@ pub(super) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
         | ty::Foreign(..)
         | ty::Alias(ty::Projection, ..)
         | ty::Bound(..)
-        | ty::Infer(ty::TyVar(_)) => {
-            // FIXME: Do we need to mark anything as ambiguous here? Yeah?
-            Err(NoSolution)
-        }
+        | ty::Infer(ty::TyVar(_)) => Err(NoSolution),
 
         ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => bug!(),
 
@@ -101,9 +98,8 @@ pub(super) fn instantiate_constituent_tys_for_sized_trait<'tcx>(
         | ty::Dynamic(..)
         | ty::Foreign(..)
         | ty::Alias(..)
-        | ty::Param(_) => Err(NoSolution),
-
-        ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
+        | ty::Param(_)
+        | ty::Infer(ty::TyVar(_)) => Err(NoSolution),
 
         ty::Placeholder(..)
         | ty::Bound(..)
@@ -151,9 +147,8 @@ pub(super) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
         | ty::Ref(_, _, Mutability::Mut)
         | ty::Adt(_, _)
         | ty::Alias(_, _)
-        | ty::Param(_) => Err(NoSolution),
-
-        ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
+        | ty::Param(_)
+        | ty::Infer(ty::TyVar(_)) => Err(NoSolution),
 
         ty::Placeholder(..)
         | ty::Bound(..)
@@ -177,3 +172,52 @@ pub(super) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
         }
     }
 }
+
+pub(crate) fn extract_tupled_inputs_and_output_from_callable<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    self_ty: Ty<'tcx>,
+    goal_kind: ty::ClosureKind,
+) -> Result<Option<ty::Binder<'tcx, (Ty<'tcx>, Ty<'tcx>)>>, NoSolution> {
+    match *self_ty.kind() {
+        ty::FnDef(def_id, substs) => Ok(Some(
+            tcx.bound_fn_sig(def_id)
+                .subst(tcx, substs)
+                .map_bound(|sig| (tcx.mk_tup(sig.inputs().iter()), sig.output())),
+        )),
+        ty::FnPtr(sig) => {
+            Ok(Some(sig.map_bound(|sig| (tcx.mk_tup(sig.inputs().iter()), sig.output()))))
+        }
+        ty::Closure(_, substs) => {
+            let closure_substs = substs.as_closure();
+            match closure_substs.kind_ty().to_opt_closure_kind() {
+                Some(closure_kind) if closure_kind.extends(goal_kind) => {}
+                None => return Ok(None),
+                _ => return Err(NoSolution),
+            }
+            Ok(Some(closure_substs.sig().map_bound(|sig| (sig.inputs()[0], sig.output()))))
+        }
+        ty::Bool
+        | ty::Char
+        | ty::Int(_)
+        | ty::Uint(_)
+        | ty::Float(_)
+        | ty::Adt(_, _)
+        | ty::Foreign(_)
+        | ty::Str
+        | ty::Array(_, _)
+        | ty::Slice(_)
+        | ty::RawPtr(_)
+        | ty::Ref(_, _, _)
+        | ty::Dynamic(_, _, _)
+        | ty::Generator(_, _, _)
+        | ty::GeneratorWitness(_)
+        | ty::Never
+        | ty::Tuple(_)
+        | ty::Alias(_, _)
+        | ty::Param(_)
+        | ty::Placeholder(_)
+        | ty::Bound(_, _)
+        | ty::Infer(_)
+        | ty::Error(_) => Err(NoSolution),
+    }
+}

tests/ui/traits/new-solver/fn-trait-closure.rs

@@ -0,0 +1,15 @@
+// compile-flags: -Ztrait-solver=next
+// known-bug: unknown
+// failure-status: 101
+// dont-check-compiler-stderr
+
+// This test will fail until we fix `FulfillmentCtxt::relationships`. That's
+// because we create a type variable for closure upvar types, which is not
+// constrained until after we try to do fallback on diverging type variables.
+// Thus, we will call that function, which is unimplemented.
+
+fn require_fn(_: impl Fn() -> i32) {}
+
+fn main() {
+    require_fn(|| -> i32 { 1i32 });
+}

tests/ui/traits/new-solver/fn-trait.rs

@@ -0,0 +1,13 @@
+// compile-flags: -Ztrait-solver=next
+// check-pass
+
+fn require_fn(_: impl Fn() -> i32) {}
+
+fn f() -> i32 {
+    1i32
+}
+
+fn main() {
+    require_fn(f);
+    require_fn(f as fn() -> i32);
+}