Auto merge of #729 - henrikhorluck:std-controlflow, r=matthewjasper

Replace `ControlFlow` with version in std

- Since Rust 1.55, `ControlFlow` is now available in std
- Some functions are not available in std yet, and the functional
  equivalents have been used (e.g. `ControlFlow::Break(())` instead of
  `ControlFlow::BREAK`, etc.)

Closes #725

chalk-derive/src/lib.rs

@@ -181,14 +181,14 @@ fn derive_any_visit(
                 &self,
                 visitor: &mut dyn ::chalk_ir::visit::Visitor < 'i, #interner, BreakTy = B >,
                 outer_binder: ::chalk_ir::DebruijnIndex,
-            ) -> ::chalk_ir::visit::ControlFlow<B>
+            ) -> std::ops::ControlFlow<B>
             where
                 #interner: 'i
             {
                 match *self {
                     #body
                 }
-                ::chalk_ir::visit::ControlFlow::CONTINUE
+                std::ops::ControlFlow::Continue(())
             }
         },
     )

chalk-engine/src/lib.rs

@@ -58,11 +58,11 @@ use std::usize;
 
 use chalk_derive::{Fold, HasInterner, Visit};
 use chalk_ir::interner::Interner;
-use chalk_ir::visit::ControlFlow;
 use chalk_ir::{
     AnswerSubst, Canonical, ConstrainedSubst, Constraint, DebruijnIndex, Goal, InEnvironment,
     Substitution,
 };
+use std::ops::ControlFlow;
 
 pub mod context;
 mod derived;

chalk-ir/src/lib.rs

@@ -9,9 +9,10 @@ extern crate self as chalk_ir;
 use crate::cast::{Cast, CastTo, Caster};
 use crate::fold::shift::Shift;
 use crate::fold::{Fold, Folder, Subst, SuperFold};
-use crate::visit::{ControlFlow, SuperVisit, Visit, VisitExt, Visitor};
+use crate::visit::{SuperVisit, Visit, VisitExt, Visitor};
 use chalk_derive::{Fold, HasInterner, SuperVisit, Visit, Zip};
 use std::marker::PhantomData;
+use std::ops::ControlFlow;
 
 pub use crate::debug::SeparatorTraitRef;
 #[macro_use(bitflags)]

chalk-ir/src/visit.rs

@@ -1,5 +1,6 @@
 //! Traits for visiting bits of IR.
 use std::fmt::Debug;
+use std::ops::ControlFlow;
 
 use crate::{
     BoundVar, Const, ConstValue, DebruijnIndex, DomainGoal, Goal, InferenceVar, Interner, Lifetime,
@@ -12,59 +13,15 @@ pub mod visitors;
 
 pub use visitors::VisitExt;
 
-/// An copy of the unstable `std::ops::ControlFlow` for use in Chalk visitors.
-pub enum ControlFlow<B, C = ()> {
-    /// Continue in the loop, using the given value for the next iteration
-    Continue(C),
-    /// Exit the loop, yielding the given value
-    Break(B),
-}
-
-impl<B, C> ControlFlow<B, C> {
-    /// Returns `true` if this is a `Break` variant.
-    #[inline]
-    pub fn is_break(&self) -> bool {
-        matches!(*self, ControlFlow::Break(_))
-    }
-
-    /// Returns `true` if this is a `Continue` variant.
-    #[inline]
-    pub fn is_continue(&self) -> bool {
-        matches!(*self, ControlFlow::Continue(_))
-    }
-
-    /// Converts the `ControlFlow` into an `Option` which is `Some`
-    /// if the `ControlFlow` was `Break` and `None` otherwise.
-    #[inline]
-    pub fn break_value(self) -> Option<B> {
-        match self {
-            ControlFlow::Continue(..) => None,
-            ControlFlow::Break(x) => Some(x),
-        }
-    }
-}
-
-impl<B> ControlFlow<B, ()> {
-    /// It's frequently the case that there's no value needed with `Continue`,
-    /// so this provides a way to avoid typing `(())`, if you prefer it.
-    pub const CONTINUE: Self = ControlFlow::Continue(());
-}
-
-impl<C> ControlFlow<(), C> {
-    /// APIs like `try_for_each` don't need values with `Break`,
-    /// so this provides a way to avoid typing `(())`, if you prefer it.
-    pub const BREAK: Self = ControlFlow::Break(());
-}
-
 /// Unwraps a `ControlFlow` or propagates its `Break` value.
 /// This replaces the `Try` implementation that would be used
 /// with `std::ops::ControlFlow`.
 #[macro_export]
 macro_rules! try_break {
     ($expr:expr) => {
         match $expr {
-            $crate::visit::ControlFlow::Continue(c) => c,
-            $crate::visit::ControlFlow::Break(b) => return $crate::visit::ControlFlow::Break(b),
+            std::ops::ControlFlow::Continue(c) => c,
+            std::ops::ControlFlow::Break(b) => return std::ops::ControlFlow::Break(b),
         }
     };
 }
@@ -174,7 +131,7 @@ where
                 bound_var, outer_binder
             )
         } else {
-            ControlFlow::CONTINUE
+            ControlFlow::Continue(())
         }
     }
 
@@ -194,7 +151,7 @@ where
         if self.forbid_free_placeholders() {
             panic!("unexpected placeholder type `{:?}`", universe)
         } else {
-            ControlFlow::CONTINUE
+            ControlFlow::Continue(())
         }
     }
 
@@ -224,7 +181,7 @@ where
         if self.forbid_inference_vars() {
             panic!("unexpected inference type `{:?}`", var)
         } else {
-            ControlFlow::CONTINUE
+            ControlFlow::Continue(())
         }
     }
 
@@ -298,7 +255,7 @@ where
                 if let Some(_) = bound_var.shifted_out_to(outer_binder) {
                     visitor.visit_free_var(*bound_var, outer_binder)
                 } else {
-                    ControlFlow::CONTINUE
+                    ControlFlow::Continue(())
                 }
             }
             TyKind::Dyn(clauses) => clauses.visit_with(visitor, outer_binder),
@@ -311,7 +268,7 @@ where
                 substitution.visit_with(visitor, outer_binder)
             }
             TyKind::Scalar(scalar) => scalar.visit_with(visitor, outer_binder),
-            TyKind::Str => ControlFlow::CONTINUE,
+            TyKind::Str => ControlFlow::Continue(()),
             TyKind::Tuple(arity, substitution) => {
                 try_break!(arity.visit_with(visitor, outer_binder));
                 substitution.visit_with(visitor, outer_binder)
@@ -334,7 +291,7 @@ where
                 try_break!(mutability.visit_with(visitor, outer_binder));
                 ty.visit_with(visitor, outer_binder)
             }
-            TyKind::Never => ControlFlow::CONTINUE,
+            TyKind::Never => ControlFlow::Continue(()),
             TyKind::Array(ty, const_) => {
                 try_break!(ty.visit_with(visitor, outer_binder));
                 const_.visit_with(visitor, outer_binder)
@@ -352,7 +309,7 @@ where
                 substitution.visit_with(visitor, outer_binder)
             }
             TyKind::Foreign(foreign_ty) => foreign_ty.visit_with(visitor, outer_binder),
-            TyKind::Error => ControlFlow::CONTINUE,
+            TyKind::Error => ControlFlow::Continue(()),
         }
     }
 }
@@ -385,15 +342,15 @@ impl<I: Interner> SuperVisit<I> for Lifetime<I> {
                 if let Some(_) = bound_var.shifted_out_to(outer_binder) {
                     visitor.visit_free_var(*bound_var, outer_binder)
                 } else {
-                    ControlFlow::CONTINUE
+                    ControlFlow::Continue(())
                 }
             }
             LifetimeData::InferenceVar(var) => visitor.visit_inference_var(*var, outer_binder),
             LifetimeData::Placeholder(universe) => {
                 visitor.visit_free_placeholder(*universe, outer_binder)
             }
             LifetimeData::Static | LifetimeData::Empty(_) | LifetimeData::Erased => {
-                ControlFlow::CONTINUE
+                ControlFlow::Continue(())
             }
             LifetimeData::Phantom(void, ..) => match *void {},
         }
@@ -428,14 +385,14 @@ impl<I: Interner> SuperVisit<I> for Const<I> {
                 if let Some(_) = bound_var.shifted_out_to(outer_binder) {
                     visitor.visit_free_var(*bound_var, outer_binder)
                 } else {
-                    ControlFlow::CONTINUE
+                    ControlFlow::Continue(())
                 }
             }
             ConstValue::InferenceVar(var) => visitor.visit_inference_var(*var, outer_binder),
             ConstValue::Placeholder(universe) => {
                 visitor.visit_free_placeholder(*universe, outer_binder)
             }
-            ConstValue::Concrete(_) => ControlFlow::CONTINUE,
+            ConstValue::Concrete(_) => ControlFlow::Continue(()),
         }
     }
 }

chalk-ir/src/visit/boring_impls.rs

@@ -26,7 +26,7 @@ where
     for e in it {
         try_break!(e.visit_with(visitor, outer_binder));
     }
-    ControlFlow::CONTINUE
+    ControlFlow::Continue(())
 }
 
 impl<T: Visit<I>, I: Interner> Visit<I> for &T {
@@ -104,7 +104,7 @@ macro_rules! tuple_visit {
                 $(
                     try_break!($n.visit_with(visitor, outer_binder));
                 )*
-                ControlFlow::CONTINUE
+                ControlFlow::Continue(())
             }
         }
     }
@@ -126,7 +126,7 @@ impl<T: Visit<I>, I: Interner> Visit<I> for Option<T> {
     {
         match self {
             Some(e) => e.visit_with(visitor, outer_binder),
-            None => ControlFlow::CONTINUE,
+            None => ControlFlow::Continue(()),
         }
     }
 }
@@ -186,7 +186,7 @@ macro_rules! const_visit {
             where
                 I: 'i,
             {
-                ControlFlow::CONTINUE
+                ControlFlow::Continue(())
             }
         }
     };
@@ -220,7 +220,7 @@ macro_rules! id_visit {
             where
                 I: 'i,
             {
-                ControlFlow::CONTINUE
+                ControlFlow::Continue(())
             }
         }
     };
@@ -305,6 +305,6 @@ impl<I: Interner> Visit<I> for PhantomData<I> {
     where
         I: 'i,
     {
-        ControlFlow::CONTINUE
+        ControlFlow::Continue(())
     }
 }

chalk-ir/src/visit/visitors.rs

@@ -6,11 +6,11 @@ use crate::{BoundVar, ControlFlow, DebruijnIndex, Interner, Visit, Visitor};
 pub trait VisitExt<I: Interner>: Visit<I> {
     /// Check whether there are free (non-bound) variables.
     fn has_free_vars(&self, interner: &I) -> bool {
-        self.visit_with(
+        let flow = self.visit_with(
             &mut FindFreeVarsVisitor { interner },
             DebruijnIndex::INNERMOST,
-        )
-        .is_break()
+        );
+        matches!(flow, ControlFlow::Break(_))
     }
 }
 
@@ -36,6 +36,6 @@ impl<'i, I: Interner> Visitor<'i, I> for FindFreeVarsVisitor<'i, I> {
         _bound_var: BoundVar,
         _outer_binder: DebruijnIndex,
     ) -> ControlFlow<()> {
-        ControlFlow::BREAK
+        ControlFlow::Break(())
     }
 }

chalk-solve/src/clauses/builtin_traits/unsize.rs

@@ -1,13 +1,14 @@
 use std::collections::HashSet;
 use std::iter;
+use std::ops::ControlFlow;
 
 use crate::clauses::ClauseBuilder;
 use crate::rust_ir::AdtKind;
 use crate::{Interner, RustIrDatabase, TraitRef, WellKnownTrait};
 use chalk_ir::{
     cast::Cast,
     interner::HasInterner,
-    visit::{ControlFlow, SuperVisit, Visit, Visitor},
+    visit::{SuperVisit, Visit, Visitor},
     Binders, Const, ConstValue, DebruijnIndex, DomainGoal, DynTy, EqGoal, Goal, LifetimeOutlives,
     QuantifiedWhereClauses, Substitution, TraitId, Ty, TyKind, TypeOutlives, WhereClause,
 };
@@ -34,7 +35,7 @@ impl<'a, I: Interner> Visitor<'a, I> for UnsizeParameterCollector<'a, I> {
                 if bound_var.debruijn.shifted_in() == outer_binder {
                     self.parameters.insert(bound_var.index);
                 }
-                ControlFlow::CONTINUE
+                ControlFlow::Continue(())
             }
             _ => ty.super_visit_with(self, outer_binder),
         }
@@ -49,7 +50,7 @@ impl<'a, I: Interner> Visitor<'a, I> for UnsizeParameterCollector<'a, I> {
                 self.parameters.insert(bound_var.index);
             }
         }
-        ControlFlow::CONTINUE
+        ControlFlow::Continue(())
     }
 
     fn interner(&self) -> &'a I {
@@ -90,9 +91,9 @@ impl<'a, 'p, I: Interner> Visitor<'a, I> for ParameterOccurenceCheck<'a, 'p, I>
                 if bound_var.debruijn.shifted_in() == outer_binder
                     && self.parameters.contains(&bound_var.index)
                 {
-                    ControlFlow::BREAK
+                    ControlFlow::Break(())
                 } else {
-                    ControlFlow::CONTINUE
+                    ControlFlow::Continue(())
                 }
             }
             _ => ty.super_visit_with(self, outer_binder),
@@ -107,12 +108,12 @@ impl<'a, 'p, I: Interner> Visitor<'a, I> for ParameterOccurenceCheck<'a, 'p, I>
                 if bound_var.debruijn.shifted_in() == outer_binder
                     && self.parameters.contains(&bound_var.index)
                 {
-                    ControlFlow::BREAK
+                    ControlFlow::Break(())
                 } else {
-                    ControlFlow::CONTINUE
+                    ControlFlow::Continue(())
                 }
             }
-            _ => ControlFlow::CONTINUE,
+            _ => ControlFlow::Continue(()),
         }
     }
 
@@ -130,8 +131,9 @@ fn uses_outer_binder_params<I: Interner>(
         interner,
         parameters,
     };
-    v.visit_with(&mut visitor, DebruijnIndex::INNERMOST)
-        .is_break()
+
+    let flow = v.visit_with(&mut visitor, DebruijnIndex::INNERMOST);
+    matches!(flow, ControlFlow::Break(_))
 }
 
 fn principal_id<'a, I: Interner>(

chalk-solve/src/clauses/env_elaborator.rs

@@ -8,9 +8,10 @@ use crate::RustIrDatabase;
 use crate::Ty;
 use crate::{debug_span, TyKind};
 use chalk_ir::interner::Interner;
-use chalk_ir::visit::{ControlFlow, Visit, Visitor};
+use chalk_ir::visit::{Visit, Visitor};
 use chalk_ir::{DebruijnIndex, Environment};
 use rustc_hash::FxHashSet;
+use std::ops::ControlFlow;
 use tracing::instrument;
 
 /// When proving a `FromEnv` goal, we elaborate all `FromEnv` goals
@@ -71,7 +72,7 @@ impl<'me, 'builder, I: Interner> Visitor<'me, I> for EnvElaborator<'me, 'builder
                     .unwrap()
             }
         }
-        ControlFlow::CONTINUE
+        ControlFlow::Continue(())
     }
 
     fn visit_domain_goal(
@@ -95,12 +96,12 @@ impl<'me, 'builder, I: Interner> Visitor<'me, I> for EnvElaborator<'me, 'builder
                             .associated_ty_data(associated_ty_id)
                             .to_program_clauses(self.builder, self.environment);
                     }
-                    ControlFlow::CONTINUE
+                    ControlFlow::Continue(())
                 }
                 FromEnv::Ty(ty) => ty.visit_with(self, outer_binder),
             }
         } else {
-            ControlFlow::CONTINUE
+            ControlFlow::Continue(())
         }
     }
 }