Auto merge of #39087 - nrc:qquote-empty-delim, r=jseyfried

proc macros/qquote: Handle empty delimited tokens

r? @jseyfried

src/test/run-pass-fulldeps/auxiliary/hello_macro.rs

@@ -0,0 +1,35 @@
+// Copyright 2017 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.
+
+#![feature(plugin)]
+#![feature(plugin_registrar)]
+#![feature(rustc_private)]
+#![plugin(proc_macro_plugin)]
+
+extern crate rustc_plugin;
+extern crate proc_macro_tokens;
+extern crate syntax;
+
+use syntax::ext::proc_macro_shim::prelude::*;
+use proc_macro_tokens::prelude::*;
+
+use rustc_plugin::Registry;
+
+#[plugin_registrar]
+pub fn plugin_registrar(reg: &mut Registry) {
+    reg.register_macro("hello", hello);
+}
+
+// This macro is not very interesting, but it does contain delimited tokens with
+// no content - `()` and `{}` - which has caused problems in the past.
+fn hello<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Box<MacResult + 'cx> {
+    let output = qquote!({ fn hello() {} hello(); });
+    build_block_emitter(cx, sp, output)
+}

src/test/run-pass-fulldeps/macro-quote-empty-delims.rs

@@ -0,0 +1,22 @@
+// Copyright 2012-2014 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.
+
+// Test that a macro can emit delimiters with nothing inside - `()`, `{}`
+
+// aux-build:hello_macro.rs
+// ignore-stage1
+
+#![feature(plugin)]
+#![feature(rustc_private)]
+#![plugin(hello_macro)]
+
+fn main() {
+    hello!();
+}