convert region-liveness-drop{-,-no-}may-dangle.rs into ui tests

The "match exact bits of CFG" approach was fragile and uninformative.

src/test/ui/nll/drop-may-dangle.rs

@@ -0,0 +1,46 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Basic test for liveness constraints: the region (`R1`) that appears
+// in the type of `p` includes the points after `&v[0]` up to (but not
+// including) the call to `use_x`. The `else` branch is not included.
+
+// compile-flags:-Znll -Zborrowck=mir
+// must-compile-successfully
+
+#![allow(warnings)]
+#![feature(dropck_eyepatch)]
+#![feature(generic_param_attrs)]
+
+fn use_x(_: usize) -> bool { true }
+
+fn main() {
+    let mut v = [1, 2, 3];
+    let p: WrapMayDangle<& /* R4 */ usize> = WrapMayDangle { value: &v[0] };
+    if true {
+        // `p` will get dropped at end of this block. However, because of
+        // the `#[may_dangle]` attribute, we do not need to consider R4
+        // live after this point.
+        use_x(*p.value);
+    } else {
+        v[0] += 1;
+        use_x(22);
+    }
+
+    v[0] += 1;
+}
+
+struct WrapMayDangle<T> {
+    value: T
+}
+
+unsafe impl<#[may_dangle] T> Drop for WrapMayDangle<T> {
+    fn drop(&mut self) { }
+}

src/test/ui/nll/drop-no-may-dangle.rs

@@ -0,0 +1,43 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Basic test for liveness constraints: the region (`R1`) that appears
+// in the type of `p` must include everything until `p` is dropped
+// because of destructor. (Note that the stderr also identifies this
+// destructor in the error message.)
+
+// compile-flags:-Znll -Zborrowck=mir -Znll-dump-cause
+
+#![allow(warnings)]
+#![feature(dropck_eyepatch)]
+#![feature(generic_param_attrs)]
+
+fn use_x(_: usize) -> bool { true }
+
+fn main() {
+    let mut v = [1, 2, 3];
+    let p: WrapMayNotDangle<&usize> = WrapMayNotDangle { value: &v[0] };
+    if true {
+        use_x(*p.value);
+    } else {
+        use_x(22);
+        v[0] += 1; //~ ERROR cannot assign to `v[..]` because it is borrowed
+    }
+
+    v[0] += 1; //~ ERROR cannot assign to `v[..]` because it is borrowed
+}
+
+struct WrapMayNotDangle<T> {
+    value: T
+}
+
+impl<T> Drop for WrapMayNotDangle<T> {
+    fn drop(&mut self) { }
+}

src/test/ui/nll/drop-no-may-dangle.stderr

@@ -0,0 +1,25 @@
+error[E0506]: cannot assign to `v[..]` because it is borrowed
+  --> $DIR/drop-no-may-dangle.rs:31:9
+   |
+26 |     let p: WrapMayNotDangle<&usize> = WrapMayNotDangle { value: &v[0] };
+   |                                                                 ----- borrow of `v[..]` occurs here
+...
+31 |         v[0] += 1; //~ ERROR cannot assign to `v[..]` because it is borrowed
+   |         ^^^^^^^^^ assignment to borrowed `v[..]` occurs here
+...
+35 | }
+   |  - borrow later used here, when `p` is dropped
+
+error[E0506]: cannot assign to `v[..]` because it is borrowed
+  --> $DIR/drop-no-may-dangle.rs:34:5
+   |
+26 |     let p: WrapMayNotDangle<&usize> = WrapMayNotDangle { value: &v[0] };
+   |                                                                 ----- borrow of `v[..]` occurs here
+...
+34 |     v[0] += 1; //~ ERROR cannot assign to `v[..]` because it is borrowed
+   |     ^^^^^^^^^ assignment to borrowed `v[..]` occurs here
+35 | }
+   |  - borrow later used here, when `p` is dropped
+
+error: aborting due to 2 previous errors
+