From: lcnr <rust@lcnr.de>
Date: Mon, 29 Mar 2021 15:32:20 +0000 (+0200)
Subject: make `Sized` coinductive
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=0f2e45b18f47c9cb93267a82ed685f5d37f79367;p=rust.git

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 de158a15d54..49bb3d03621 100644
--- 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
index 00000000000..7bcd0f1fdaf
--- /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
index 00000000000..212274d2e4b
--- /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(),
+    };
+}