fn pointers don't implement Fn/FnMut/FnOnce traits if its return type is unsized

3 files changed, 64 insertions, 0 deletions

diff --git a/src/test/ui/function-pointer/sized-ret-with-binder.rs b/src/test/ui/function-pointer/sized-ret-with-binder.rs
new file mode 100644
index 00000000000..104ac4d222e
--- /dev/null
+++ b/src/test/ui/function-pointer/sized-ret-with-binder.rs
@@ -0,0 +1,15 @@
+// check-pass
+
+#![feature(unboxed_closures)]
+
+fn is_fn<T: for<'a> Fn<(&'a (),)>>() {}
+fn is_fn2<T: for<'a, 'b> Fn<(&'a &'b (),)>>() {}
+
+struct Outlives<'a, 'b>(std::marker::PhantomData<&'a &'b ()>);
+
+fn main() {
+    is_fn::<for<'a> fn(&'a ()) -> &'a ()>();
+    is_fn::<for<'a> fn(&'a ()) -> &'a dyn std::fmt::Debug>();
+    is_fn2::<for<'a, 'b> fn(&'a &'b ()) -> Outlives<'a, 'b>>();
+    is_fn2::<for<'a, 'b> fn(&'a &'b ()) -> (&'a (), &'a ())>();
+}
diff --git a/src/test/ui/function-pointer/unsized-ret.rs b/src/test/ui/function-pointer/unsized-ret.rs
new file mode 100644
index 00000000000..60af5769d6d
--- /dev/null
+++ b/src/test/ui/function-pointer/unsized-ret.rs
@@ -0,0 +1,14 @@
+#![feature(fn_traits)]
+#![feature(unboxed_closures)]
+
+fn foo<F: Fn<T>, T>(f: Option<F>, t: T) {
+    let y = (f.unwrap()).call(t);
+}
+
+fn main() {
+    foo::<fn() -> str, _>(None, ());
+    //~^ ERROR the size for values of type `str` cannot be known at compilation time
+
+    foo::<for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a), _>(None, (&(),));
+    //~^ ERROR the size for values of type `(dyn std::fmt::Display + 'a)` cannot be known at compilation time
+}
diff --git a/src/test/ui/function-pointer/unsized-ret.stderr b/src/test/ui/function-pointer/unsized-ret.stderr
new file mode 100644
index 00000000000..bec3e2aa3fe
--- /dev/null
+++ b/src/test/ui/function-pointer/unsized-ret.stderr
@@ -0,0 +1,35 @@
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/unsized-ret.rs:9:27
+   |
+LL |     foo::<fn() -> str, _>(None, ());
+   |     --------------------- ^^^^ doesn't have a size known at compile-time
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: within `fn() -> str`, the trait `Sized` is not implemented for `str`
+   = note: required because it appears within the type `fn() -> str`
+note: required by a bound in `foo`
+  --> $DIR/unsized-ret.rs:4:11
+   |
+LL | fn foo<F: Fn<T>, T>(f: Option<F>, t: T) {
+   |           ^^^^^ required by this bound in `foo`
+
+error[E0277]: the size for values of type `(dyn std::fmt::Display + 'a)` cannot be known at compilation time
+  --> $DIR/unsized-ret.rs:12:66
+   |
+LL |     foo::<for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a), _>(None, (&(),));
+   |     ------------------------------------------------------------ ^^^^ doesn't have a size known at compile-time
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: within `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`, the trait `for<'a> Sized` is not implemented for `(dyn std::fmt::Display + 'a)`
+   = note: required because it appears within the type `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`
+note: required by a bound in `foo`
+  --> $DIR/unsized-ret.rs:4:11
+   |
+LL | fn foo<F: Fn<T>, T>(f: Option<F>, t: T) {
+   |           ^^^^^ required by this bound in `foo`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.