Add comment about ruby_style_closure status

Author: Sasha Pourcelot

src/test/ui/expr/malformed_closure/ruby_style_closure.rs

@@ -1,3 +1,11 @@
+// Part of issue #27300.
+// The problem here is that ruby-style closures are parsed as blocks whose
+// first statement is a closure. See the issue for more details:
+// https://github.com/rust-lang/rust/issues/27300
+
+// Note: this test represents what the compiler currently emits. The error
+// message will be improved later.
+
 fn main() {
     let p = Some(45).and_then({
         //~^ expected a `FnOnce<({integer},)>` closure, found `Option<_>`

src/test/ui/expr/malformed_closure/ruby_style_closure.stderr

@@ -1,11 +1,11 @@
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/ruby_style_closure.rs:5:14
+  --> $DIR/ruby_style_closure.rs:13:14
    |
 LL |         Some(x * 2)
    |              ^ not found in this scope
 
 error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
-  --> $DIR/ruby_style_closure.rs:2:22
+  --> $DIR/ruby_style_closure.rs:10:22
    |
 LL |     let p = Some(45).and_then({
    |                      ^^^^^^^^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`