Use ops::ControlFlow in graph::iterate

compiler/rustc_data_structures/src/graph/iterate/mod.rs

@@ -87,11 +87,8 @@ where
 }
 
 /// Allows searches to terminate early with a value.
-#[derive(Clone, Copy, Debug)]
-pub enum ControlFlow<T> {
-    Break(T),
-    Continue,
-}
+// FIXME (#75744): remove the alias once the generics are in a better order and `C=()`.
+pub type ControlFlow<T> = std::ops::ControlFlow<(), T>;
 
 /// The status of a node in the depth-first search.
 ///
@@ -260,12 +257,12 @@ where
         _node: G::Node,
         _prior_status: Option<NodeStatus>,
     ) -> ControlFlow<Self::BreakVal> {
-        ControlFlow::Continue
+        ControlFlow::CONTINUE
     }
 
     /// Called after all nodes reachable from this one have been examined.
     fn node_settled(&mut self, _node: G::Node) -> ControlFlow<Self::BreakVal> {
-        ControlFlow::Continue
+        ControlFlow::CONTINUE
     }
 
     /// Behave as if no edges exist from `source` to `target`.
@@ -290,7 +287,7 @@ where
     ) -> ControlFlow<Self::BreakVal> {
         match prior_status {
             Some(NodeStatus::Visited) => ControlFlow::Break(()),
-            _ => ControlFlow::Continue,
+            _ => ControlFlow::CONTINUE,
         }
     }
 }

compiler/rustc_data_structures/src/lib.rs

@@ -8,6 +8,7 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![allow(incomplete_features)]
+#![feature(control_flow_enum)]
 #![feature(in_band_lifetimes)]
 #![feature(unboxed_closures)]
 #![feature(generators)]

compiler/rustc_mir_build/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(box_syntax)]
 #![feature(const_fn)]
 #![feature(const_panic)]
+#![feature(control_flow_enum)]
 #![feature(crate_visibility_modifier)]
 #![feature(bool_to_option)]
 #![feature(or_patterns)]

compiler/rustc_mir_build/src/lints.rs

@@ -117,7 +117,7 @@ impl<'mir, 'tcx> TriColorVisitor<&'mir Body<'tcx>> for Search<'mir, 'tcx> {
             // A diverging InlineAsm is treated as non-recursing
             TerminatorKind::InlineAsm { destination, .. } => {
                 if destination.is_some() {
-                    ControlFlow::Continue
+                    ControlFlow::CONTINUE
                 } else {
                     ControlFlow::Break(NonRecursive)
                 }
@@ -131,7 +131,7 @@ impl<'mir, 'tcx> TriColorVisitor<&'mir Body<'tcx>> for Search<'mir, 'tcx> {
             | TerminatorKind::FalseEdge { .. }
             | TerminatorKind::FalseUnwind { .. }
             | TerminatorKind::Goto { .. }
-            | TerminatorKind::SwitchInt { .. } => ControlFlow::Continue,
+            | TerminatorKind::SwitchInt { .. } => ControlFlow::CONTINUE,
         }
     }
 
@@ -144,7 +144,7 @@ impl<'mir, 'tcx> TriColorVisitor<&'mir Body<'tcx>> for Search<'mir, 'tcx> {
             }
         }
 
-        ControlFlow::Continue
+        ControlFlow::CONTINUE
     }
 
     fn ignore_edge(&mut self, bb: BasicBlock, target: BasicBlock) -> bool {

library/core/src/iter/adapters/mod.rs

@@ -1273,7 +1273,7 @@ where
         ) -> impl FnMut((), T) -> ControlFlow<(), B> + '_ {
             move |(), x| match f(x) {
                 Some(x) => ControlFlow::Break(x),
-                None => ControlFlow::Continue(()),
+                None => ControlFlow::CONTINUE,
             }
         }
 

library/core/src/iter/traits/double_ended.rs

@@ -310,7 +310,7 @@ pub trait DoubleEndedIterator: Iterator {
             mut predicate: impl FnMut(&T) -> bool,
         ) -> impl FnMut((), T) -> ControlFlow<(), T> {
             move |(), x| {
-                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::Continue(()) }
+                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::CONTINUE }
             }
         }
 

library/core/src/ops/control_flow.rs

@@ -65,3 +65,10 @@ impl<R: Try> ControlFlow<R::Ok, R> {
         }
     }
 }
+
+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.
+    #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
+    pub const CONTINUE: Self = ControlFlow::Continue(());
+}