make `Sized` coinductive

diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index de158a15d54b8563d1c514e287744bf5c24103f7..49bb3d03621f3379a844c8162383b5a8b0ea285a 100644 (file)
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -959,7 +959,10 @@ pub(crate) fn coinductive_match<I>(&mut self, mut cycle: I) -> bool
 
     fn coinductive_predicate(&self, predicate: ty::Predicate<'tcx>) -> bool {
         let result = match predicate.kind().skip_binder() {
-            ty::PredicateKind::Trait(ref data) => self.tcx().trait_is_auto(data.def_id()),
+            ty::PredicateKind::Trait(ref data) => {
+                self.tcx().trait_is_auto(data.def_id())
+                    || self.tcx().lang_items().sized_trait() == Some(data.def_id())
+            }
             ty::PredicateKind::WellFormed(_) => true,
             _ => false,
         };

diff --git a/src/test/ui/sized/coinductive-1.rs b/src/test/ui/sized/coinductive-1.rs
new file mode 100644 (file)
index 0000000..7bcd0f1
--- /dev/null
+++ b/src/test/ui/sized/coinductive-1.rs
@@ -0,0 +1,14 @@
+// check-pass
+struct Node<C: Trait<Self>>(C::Assoc);
+
+trait Trait<T> {
+    type Assoc;
+}
+
+impl<T> Trait<T> for Vec<()> {
+    type Assoc = Vec<T>;
+}
+
+fn main() {
+    let _ = Node::<Vec<()>>(Vec::new());
+}

diff --git a/src/test/ui/sized/coinductive-2.rs b/src/test/ui/sized/coinductive-2.rs
new file mode 100644 (file)
index 0000000..212274d
--- /dev/null
+++ b/src/test/ui/sized/coinductive-2.rs
@@ -0,0 +1,28 @@
+// run-pass
+struct Node<C: CollectionFactory<Self>> {
+    _children: C::Collection,
+}
+
+trait CollectionFactory<T> {
+    type Collection;
+}
+
+impl<T> CollectionFactory<T> for Vec<()> {
+    type Collection = Vec<T>;
+}
+
+trait Collection<T>: Sized {
+    fn push(&mut self, v: T);
+}
+
+impl<T> Collection<T> for Vec<T> {
+    fn push(&mut self, v: T) {
+        self.push(v)
+    }
+}
+
+fn main() {
+    let _ = Node::<Vec<()>> {
+        _children: Vec::new(),
+    };
+}