Add compile_error!

Related to #40872

src/libsyntax_ext/compile_error.rs

@@ -0,0 +1,40 @@
+// Copyright 2012-2017 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.
+
+// The compiler code necessary to support the compile_error! extension.
+
+use syntax::ext::base::*;
+use syntax::ext::base;
+use syntax::feature_gate;
+use syntax_pos::Span;
+use syntax::tokenstream;
+
+pub fn expand_compile_error<'cx>(cx: &'cx mut ExtCtxt,
+                              sp: Span,
+                              tts: &[tokenstream::TokenTree])
+                              -> Box<base::MacResult + 'cx> {
+    if !cx.ecfg.enable_compile_error() {
+        feature_gate::emit_feature_err(&cx.parse_sess,
+                                       "compile_error",
+                                       sp,
+                                       feature_gate::GateIssue::Language,
+                                       feature_gate::EXPLAIN_COMPILE_ERROR);
+        return DummyResult::expr(sp);
+    }
+
+    let var = match get_single_str_from_tts(cx, sp, tts, "compile_error!") {
+        None => return DummyResult::expr(sp),
+        Some(v) => v,
+    };
+
+    cx.span_err(sp, &var);
+
+    DummyResult::any(sp)
+}