Implement Min trait in new solver

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -122,7 +122,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
 
         let identity_args = ty::GenericArgs::identity_for_item(tcx, def_id);
         let preds = tcx.explicit_predicates_of(parent);
-        predicates.extend(preds.instantiate_own(tcx, identity_args));
+
         if let ty::AssocItemContainer::TraitContainer = tcx.associated_item(def_id).container {
             // for traits, emit `type Effects: TyCompat<<(T1::Effects, ..) as Min>::Output>`
             // TODO do the same for impls

compiler/rustc_middle/src/ty/context.rs

@@ -598,6 +598,11 @@ fn trait_lang_item_to_lang_item(lang_item: TraitSolverLangItem) -> LangItem {
         TraitSolverLangItem::Destruct => LangItem::Destruct,
         TraitSolverLangItem::DiscriminantKind => LangItem::DiscriminantKind,
         TraitSolverLangItem::DynMetadata => LangItem::DynMetadata,
+        TraitSolverLangItem::EffectsMaybe => LangItem::EffectsMaybe,
+        TraitSolverLangItem::EffectsMin => LangItem::EffectsMin,
+        TraitSolverLangItem::EffectsMinOutput => LangItem::EffectsMinOutput,
+        TraitSolverLangItem::EffectsNoRuntime => LangItem::EffectsNoRuntime,
+        TraitSolverLangItem::EffectsRuntime => LangItem::EffectsRuntime,
         TraitSolverLangItem::FnPtrTrait => LangItem::FnPtrTrait,
         TraitSolverLangItem::FusedIterator => LangItem::FusedIterator,
         TraitSolverLangItem::Future => LangItem::Future,

compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs

@@ -269,6 +269,11 @@ where
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
     ) -> Vec<Candidate<I>>;
+
+    fn consider_builtin_effects_min_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution>;
 }
 
 impl<D, I> EvalCtxt<'_, D>
@@ -420,6 +425,8 @@ where
             G::consider_builtin_destruct_candidate(self, goal)
         } else if cx.is_lang_item(trait_def_id, TraitSolverLangItem::TransmuteTrait) {
             G::consider_builtin_transmute_candidate(self, goal)
+        } else if tcx.is_lang_item(trait_def_id, TraitSolverLangItem::EffectsMin) {
+            G::consider_builtin_effects_min_candidate(self, goal)
         } else {
             Err(NoSolution)
         };

compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs

@@ -864,6 +864,65 @@ where
     ) -> Result<Candidate<I>, NoSolution> {
         panic!("`BikeshedIntrinsicFrom` does not have an associated type: {:?}", goal)
     }
+
+    fn consider_builtin_effects_min_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        let ty::Tuple(types) = goal.predicate.self_ty().kind() else {
+            return Err(NoSolution);
+        };
+
+
+        let cx = ecx.cx();
+
+        let mut first_non_maybe = None;
+        let mut non_maybe_count = 0;
+        for ty in types {
+            if !matches!(ty::EffectKind::try_from_ty(cx, ty), Some(ty::EffectKind::Maybe)) {
+                first_non_maybe.get_or_insert(ty);
+                non_maybe_count += 1;
+            }
+        }
+
+        match non_maybe_count {
+            0 => {
+                let ty = ty::EffectKind::Maybe.to_ty(cx);
+                ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
+                    ecx.instantiate_normalizes_to_term(goal, ty.into());
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                })
+            }
+            1 => {
+                let ty = first_non_maybe.unwrap();
+                ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
+                    ecx.instantiate_normalizes_to_term(goal, ty.into());
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                })
+            }
+            _ => {
+                let mut min = ty::EffectKind::Maybe;
+
+                for ty in types {
+                    let Some(kind) = ty::EffectKind::try_from_ty(cx, ty) else {
+                        return Err(NoSolution);
+                    };
+        
+                    let Some(result) = ty::EffectKind::min(min, kind) else {
+                        return Err(NoSolution);
+                    };
+        
+                    min = result;
+                }
+
+                let ty = min.to_ty(cx);
+                ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
+                    ecx.instantiate_normalizes_to_term(goal, ty.into());
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                })
+            }
+        }
+    }
 }
 
 impl<D, I> EvalCtxt<'_, D>

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -702,6 +702,47 @@ where
             }
         })
     }
+
+    fn consider_builtin_effects_min_candidate(
+        ecx: &mut EvalCtxt<'_, D>,
+        goal: Goal<I, Self>,
+    ) -> Result<Candidate<I>, NoSolution> {
+        if goal.predicate.polarity != ty::PredicatePolarity::Positive {
+            return Err(NoSolution);
+        }
+
+        let ty::Tuple(types) = goal.predicate.self_ty().kind() else {
+            return Err(NoSolution);
+        };
+
+        let cx = ecx.cx();
+        let maybe_count = types
+            .into_iter()
+            .filter_map(|ty| ty::EffectKind::try_from_ty(cx, ty))
+            .filter(|&ty| ty == ty::EffectKind::Maybe)
+            .count();
+
+        // Don't do concrete type check unless there are more than one type that will influence the result.
+        // This would allow `(Maybe, T): Min` pass even if we know nothing about `T`.
+        if types.len() - maybe_count > 1 {
+            let mut min = ty::EffectKind::Maybe;
+
+            for ty in types {
+                let Some(kind) = ty::EffectKind::try_from_ty(ecx.cx(), ty) else {
+                    return Err(NoSolution);
+                };
+    
+                let Some(result) = ty::EffectKind::min(min, kind) else {
+                    return Err(NoSolution);
+                };
+    
+                min = result;
+            }
+        }
+
+        ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc)
+            .enter(|ecx| ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes))
+    }
 }
 
 impl<D, I> EvalCtxt<'_, D>

compiler/rustc_type_ir/src/effects.rs

@@ -0,0 +1,56 @@
+use crate::lang_items::TraitSolverLangItem::{EffectsMaybe, EffectsRuntime, EffectsNoRuntime};
+use crate::Interner;
+use crate::inherent::{AdtDef, IntoKind, Ty};
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum EffectKind {
+    Maybe,
+    Runtime,
+    NoRuntime,
+}
+
+impl EffectKind {
+    pub fn try_from_def_id<I: Interner>(tcx: I, def_id: I::DefId) -> Option<EffectKind> {
+        if tcx.is_lang_item(def_id, EffectsMaybe) {
+            Some(EffectKind::Maybe)
+        } else if tcx.is_lang_item(def_id, EffectsRuntime) {
+            Some(EffectKind::Runtime)
+        } else if tcx.is_lang_item(def_id, EffectsNoRuntime) {
+            Some(EffectKind::NoRuntime)
+        } else {
+            None
+        }
+    }
+
+    pub fn to_def_id<I: Interner>(self, tcx: I) -> I::DefId {
+        let lang_item = match self {
+            EffectKind::Maybe => EffectsMaybe,
+            EffectKind::NoRuntime => EffectsNoRuntime,
+            EffectKind::Runtime => EffectsRuntime,
+        };
+
+        tcx.require_lang_item(lang_item)
+    }
+
+    pub fn try_from_ty<I: Interner>(tcx: I, ty: I::Ty) -> Option<EffectKind> {
+        if let crate::Adt(def, _) = ty.kind() {
+            Self::try_from_def_id(tcx, def.def_id())
+        } else {
+            None
+        }
+    }
+
+    pub fn to_ty<I: Interner>(self, tcx: I) -> I::Ty {
+        I::Ty::new_adt(tcx, tcx.adt_def(self.to_def_id(tcx)), Default::default())
+    }
+
+    pub fn min(a: Self, b: Self) -> Option<Self> {
+        use EffectKind::*;
+        match (a, b) {
+            (Maybe, x) | (x, Maybe) => Some(x),
+            (Runtime, Runtime) => Some(Runtime),
+            (NoRuntime, NoRuntime) => Some(NoRuntime),
+            (Runtime, NoRuntime) | (NoRuntime, Runtime) => None,
+        }
+    }
+}

compiler/rustc_type_ir/src/lang_items.rs

@@ -17,6 +17,11 @@ pub enum TraitSolverLangItem {
     Destruct,
     DiscriminantKind,
     DynMetadata,
+    EffectsMaybe,
+    EffectsMin,
+    EffectsMinOutput,
+    EffectsNoRuntime,
+    EffectsRuntime,
     FnPtrTrait,
     FusedIterator,
     Future,

compiler/rustc_type_ir/src/lib.rs

@@ -35,6 +35,7 @@ mod macros;
 mod binder;
 mod canonical;
 mod const_kind;
+mod effects;
 mod flags;
 mod generic_arg;
 mod interner;
@@ -51,6 +52,7 @@ pub use canonical::*;
 #[cfg(feature = "nightly")]
 pub use codec::*;
 pub use const_kind::*;
+pub use effects::*;
 pub use flags::*;
 pub use generic_arg::*;
 pub use interner::*;

library/core/src/marker.rs

@@ -1054,14 +1054,15 @@ pub mod effects {
 
     #[lang = "EffectsTyCompat"]
     #[marker]
-    pub trait TyCompat<T> {}
+    pub trait TyCompat<T: ?Sized> {}
 
-    impl<T> TyCompat<T> for T {}
+    impl<T: ?Sized> TyCompat<T> for T {}
-    impl<T> TyCompat<T> for Maybe {}
+    impl<T: ?Sized> TyCompat<T> for Maybe {}
+    impl<T: ?Sized> TyCompat<Maybe> for T {}
 
     #[lang = "EffectsMin"]
     pub trait Min {
         #[lang = "EffectsMinOutput"]
-        type Output;
+        type Output: ?Sized;
     }
 }

tests/ui/rfcs/rfc-2632-const-trait-impl/trait-where-clause-run.rs

@@ -1,4 +1,5 @@
 //@ run-pass
+//@ compile-flags: -Znext-solver
 
 #![feature(const_trait_impl, effects)] //~ WARN the feature `effects` is incomplete