From f6b8e2be8da317318eb3639681f6cd3bec20a355 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Wed, 3 Feb 2021 18:51:14 +0100
Subject: [PATCH] Rollup merge of #81532 - estebank:ice-ice-baby, r=pnkfelix

Remove incorrect `delay_span_bug`

The following code is supposed to compile

```rust
use std::ops::BitOr;

pub trait IntWrapper {
    type InternalStorage;
}

impl<T> BitOr for dyn IntWrapper<InternalStorage = T>
where
    Self: Sized,
    T: BitOr + BitOr<Output = T>,
{
    type Output = Self;
    fn bitor(self, _other: Self) -> Self {
        todo!()
    }
}
```

Before this change it would ICE. In #70998 the removed logic was added
to provide better suggestions, and the `delay_span_bug` guard was added
to  protect against a potential logic error when returning traits. As it
happens, there are cases, like the one above, where traits can indeed be
returned, so valid code was being rejected.

Fix (but not close) #80207.
---
 compiler/rustc_typeck/src/check/check.rs      |  1 -
 .../ui/typeck/issue-80207-unsized-return.rs   | 20 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/typeck/issue-80207-unsized-return.rs

diff --git a/compiler/rustc_typeck/src/check/check.rs b/compiler/rustc_typeck/src/check/check.rs
index ec7369fd3e8e..d235ad21c7b9 100644
--- a/compiler/rustc_typeck/src/check/check.rs
+++ b/compiler/rustc_typeck/src/check/check.rs
@@ -188,7 +188,6 @@ pub(super) fn check_fn<'a, 'tcx>(
         // possible cases.
         fcx.check_expr(&body.value);
         fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
-        tcx.sess.delay_span_bug(decl.output.span(), "`!Sized` return type");
     } else {
         fcx.require_type_is_sized(declared_ret_ty, decl.output.span(), traits::SizedReturnType);
         fcx.check_return_expr(&body.value);
diff --git a/src/test/ui/typeck/issue-80207-unsized-return.rs b/src/test/ui/typeck/issue-80207-unsized-return.rs
new file mode 100644
index 000000000000..75430da14823
--- /dev/null
+++ b/src/test/ui/typeck/issue-80207-unsized-return.rs
@@ -0,0 +1,20 @@
+// check-pass
+
+trait Foo {
+    fn do_stuff() -> Self;
+}
+
+trait Bar {
+    type Output;
+}
+
+impl<T> Foo for dyn Bar<Output = T>
+where
+    Self: Sized,
+{
+    fn do_stuff() -> Self {
+        todo!()
+    }
+}
+
+fn main() {}