Stabilize the compile_error_macro feature

Stabilizes:

* `compile_error!` as a macro defined by rustc

Closes #40872

Author: alexcrichton

src/doc/unstable-book/src/language-features/compile-error.md

@@ -574,7 +574,7 @@ mod builtin {
     /// For more information, see the [RFC].
     ///
     /// [RFC]: https://github.com/rust-lang/rfcs/blob/master/text/1695-add-error-macro.md
-    #[unstable(feature = "compile_error_macro", issue = "40872")]
+    #[stable(feature = "compile_error_macro", since = "1.20.0")]
     #[macro_export]
     #[cfg(dox)]
     macro_rules! compile_error { ($msg:expr) => ({ /* compiler built-in */ }) }

src/libcore/macros.rs

@@ -249,7 +249,7 @@ pub mod builtin {
     /// For more information, see the [RFC].
     ///
     /// [RFC]: https://github.com/rust-lang/rfcs/blob/master/text/1695-add-error-macro.md
-    #[unstable(feature = "compile_error_macro", issue = "40872")]
+    #[stable(feature = "compile_error_macro", since = "1.20.0")]
     #[macro_export]
     macro_rules! compile_error { ($msg:expr) => ({ /* compiler built-in */ }) }
 

src/libstd/macros.rs

@@ -1041,7 +1041,6 @@ impl<'feat> ExpansionConfig<'feat> {
         fn enable_allow_internal_unstable = allow_internal_unstable,
         fn enable_custom_derive = custom_derive,
         fn proc_macro_enabled = proc_macro,
-        fn enable_compile_error = compile_error,
     }
 }
 

src/libsyntax/ext/expand.rs

@@ -117,7 +117,6 @@ macro_rules! declare_features {
 
 declare_features! (
     (active, asm, "1.0.0", Some(29722)),
-    (active, compile_error, "1.20.0", Some(40872)),
     (active, concat_idents, "1.0.0", Some(29599)),
     (active, link_args, "1.0.0", Some(29596)),
     (active, log_syntax, "1.0.0", Some(29598)),
@@ -445,6 +444,8 @@ declare_features! (
     // Allows the definition of associated constants in `trait` or `impl`
     // blocks.
     (accepted, associated_consts, "1.20.0", Some(29646)),
+    // Usage of the `compile_error!` macro
+    (accepted, compile_error, "1.20.0", Some(40872)),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must
@@ -1040,9 +1041,6 @@ pub const EXPLAIN_LOG_SYNTAX: &'static str =
 pub const EXPLAIN_CONCAT_IDENTS: &'static str =
     "`concat_idents` is not stable enough for use and is subject to change";
 
-pub const EXPLAIN_COMPILE_ERROR: &'static str =
-    "`compile_error` is not stable enough for use and is subject to change";
-
 pub const EXPLAIN_TRACE_MACROS: &'static str =
     "`trace_macros` is not stable enough for use and is subject to change";
 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &'static str =

src/libsyntax/feature_gate.rs

@@ -12,23 +12,13 @@
 
 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,

src/libsyntax_ext/compile_error.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(compile_error)]
-
 fn main() {
     compile_error!("a very descriptive error message"); //~ ERROR: a very descriptive error message
 }