Rollup merge of rust-lang#71710 - workingjubilee:jubilee-readd-test, r=nikomatsakis

Test for zero-sized function items not ICEing

Closes rust-lang#30276.
Again.
Please give rustcake with no icing!

Author: Dylan-DPC

src/test/ui/unsized-locals/issue-30276-feature-flagged.rs

@@ -0,0 +1,7 @@
+#![feature(unsized_locals)]
+
+struct Test([i32]);
+
+fn main() {
+    let _x: fn(_) -> Test = Test;
+} //~^the size for values of type `[i32]` cannot be known at compilation time

src/test/ui/unsized-locals/issue-30276-feature-flagged.stderr

@@ -0,0 +1,14 @@
+error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
+  --> $DIR/issue-30276-feature-flagged.rs:6:29
+   |
+LL |     let _x: fn(_) -> Test = Test;
+   |                             ^^^^ doesn't have a size known at compile-time
+   |
+   = help: within `Test`, the trait `std::marker::Sized` is not implemented for `[i32]`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: required because it appears within the type `Test`
+   = note: the return type of a function must have a statically known size
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/unsized-locals/issue-30276.rs

@@ -0,0 +1,5 @@
+struct Test([i32]);
+
+fn main() {
+    let _x: fn(_) -> Test = Test;
+} //~^the size for values of type `[i32]` cannot be known at compilation time

src/test/ui/unsized-locals/issue-30276.stderr

@@ -0,0 +1,14 @@
+error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
+  --> $DIR/issue-30276.rs:4:29
+   |
+LL |     let _x: fn(_) -> Test = Test;
+   |                             ^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `std::marker::Sized` is not implemented for `[i32]`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: all function arguments must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.