Add compile_fail test for boxed Local (#275)

tests/compile_fail/boxed_local.rs

@@ -0,0 +1,18 @@
+// Copyright 2019-2020 the Deno authors. All rights reserved. MIT license.
+use rusty_v8 as v8;
+
+pub fn main() {
+  let mut isolate = v8::Isolate::new(mock());
+  let mut root_hs = v8::HandleScope::new(&mut isolate);
+  let root_hs = root_hs.enter();
+
+  let _boxed = {
+    let mut hs = v8::HandleScope::new(root_hs);
+    let hs = hs.enter();
+    Box::new(v8::Integer::new(hs, 123))
+  };
+}
+
+fn mock<T>() -> T {
+  unimplemented!()
+}

tests/compile_fail/boxed_local.stderr

@@ -0,0 +1,11 @@
+error[E0597]: `hs` does not live long enough
+  --> $DIR/boxed_local.rs:11:14
+   |
+9  |   let _boxed = {
+   |       ------ borrow later stored here
+10 |     let mut hs = v8::HandleScope::new(root_hs);
+11 |     let hs = hs.enter();
+   |              ^^ borrowed value does not live long enough
+12 |     Box::new(v8::Integer::new(hs, 123))
+13 |   };
+   |   - `hs` dropped here while still borrowed

tests/test_ui.rs

@@ -8,6 +8,7 @@ fn ui() {
   env::set_var("DENO_TRYBUILD", "1");
 
   let t = trybuild::TestCases::new();
+  t.compile_fail("tests/compile_fail/boxed_local.rs");
   t.compile_fail("tests/compile_fail/handle_scope_escape_lifetime.rs");
   t.compile_fail("tests/compile_fail/handle_scope_lifetimes.rs");
   t.compile_fail("tests/compile_fail/try_catch_lifetimes.rs");