implementing fallible allocation API (try_reserve) for Vec, String and HashMap

src/test/ui/feature-gate-try_reserve.rs

@@ -0,0 +1,14 @@
+// Copyright 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.
+
+fn main() {
+    let v = Vec::new();
+    v.try_reserve(10); //~ ERROR: use of unstable library feature 'try_reserve'
+}

src/test/ui/feature-gate-try_reserve.stderr

@@ -0,0 +1,11 @@
+error[E0658]: use of unstable library feature 'try_reserve': new API (see issue #48043)
+  --> $DIR/feature-gate-try_reserve.rs:13:7
+   |
+LL |     v.try_reserve(10); //~ ERROR: use of unstable library feature 'try_reserve'
+   |       ^^^^^^^^^^^
+   |
+   = help: add #![feature(try_reserve)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+If you want more information on this error, try using "rustc --explain E0658"