Add compile_error!

Related to #40872

src/libcore/macros.rs

@@ -562,6 +562,17 @@ macro_rules! unimplemented {
 ///
 /// For more information, see documentation for `std`'s macros.
 mod builtin {
+
+    /// Unconditionally causes compilation to fail with the given error message when encountered.
+    ///
+    /// 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")]
+    #[macro_export]
+    #[cfg(dox)]
+    macro_rules! compile_error { ($msg:expr) => ({ /* compiler built-in */ }) }
+
     /// The core macro for formatted string creation & output.
     ///
     /// For more information, see the documentation for [`std::format_args!`].

src/libstd/macros.rs

@@ -238,6 +238,16 @@ macro_rules! assert_approx_eq {
 /// into libsyntax itself.
 #[cfg(dox)]
 pub mod builtin {
+
+    /// Unconditionally causes compilation to fail with the given error message when encountered.
+    ///
+    /// 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")]
+    #[macro_export]
+    macro_rules! compile_error { ($msg:expr) => ({ /* compiler built-in */ }) }
+
     /// The core macro for formatted string creation & output.
     ///
     /// This macro produces a value of type [`fmt::Arguments`]. This value can be

src/libsyntax/ext/expand.rs

@@ -1065,6 +1065,7 @@ 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/feature_gate.rs

@@ -111,6 +111,7 @@ 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)),
@@ -1008,6 +1009,9 @@ 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_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)
+}

src/libsyntax_ext/lib.rs

@@ -34,6 +34,7 @@ extern crate rustc_errors as errors;
 
 mod asm;
 mod cfg;
+mod compile_error;
 mod concat;
 mod concat_idents;
 mod env;
@@ -109,6 +110,7 @@ pub fn register_builtins(resolver: &mut syntax::ext::base::Resolver,
         option_env: env::expand_option_env,
         log_syntax: log_syntax::expand_syntax_ext,
         trace_macros: trace_macros::expand_trace_macros,
+        compile_error: compile_error::expand_compile_error,
     }
 
     // format_args uses `unstable` things internally.

src/test/compile-fail/compile_error_macro.rs

@@ -0,0 +1,15 @@
+// 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(compile_error)]
+
+fn main() {
+    compile_error!("a very descriptive error message"); //~ ERROR: a very descriptive error message
+}

src/test/compile-fail/feature-gate-compile_error.rs

@@ -0,0 +1,13 @@
+// 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.
+
+fn main() {
+    compile_error!("test"); //~ ERROR: `compile_error` is not stable enough
+}