Add regression test for #143128

Author: GuillaumeGomez

tests/ui/closures/missing-body.rs

@@ -0,0 +1,7 @@
+// Checks that the compiler complains about the missing closure body and does not
+// crash.
+// This is a regression test for <https://github.com/rust-lang/rust/issues/143128>.
+
+fn main() { |b: [str; _]| {}; }
+//~^ ERROR the placeholder `_` is not allowed within types on item signatures for closures
+//~| ERROR the size for values of type `str` cannot be known at compilation time

tests/ui/closures/missing-body.stderr

@@ -0,0 +1,19 @@
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for closures
+  --> $DIR/missing-body.rs:5:23
+   |
+LL | fn main() { |b: [str; _]| {}; }
+   |                       ^ not allowed in type signatures
+
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/missing-body.rs:5:17
+   |
+LL | fn main() { |b: [str; _]| {}; }
+   |                 ^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+   = note: slice and array elements must have `Sized` type
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0121, E0277.
+For more information about an error, try `rustc --explain E0121`.