remove attempts to encode macro's instability from implementation.

Author: pnkfelix

src/libcore/macros.rs

@@ -12,7 +12,7 @@
 #[cfg(stage0)]
 #[macro_export]
 macro_rules! __unstable_rustc_ensure_not_fmt_string_literal {
-    ($name:expr, $e:expr) => { ((), $e) }
+    ($name:expr, $e:expr) => { $e }
 }
 
 /// Entry point of task panic, for details, see std::macros
@@ -23,7 +23,7 @@ macro_rules! panic {
     );
     ($msg:expr) => ({
         static _MSG_FILE_LINE: (&'static str, &'static str, u32) =
-            (__unstable_rustc_ensure_not_fmt_string_literal!("unary `panic!`", $msg).1,
+            (__unstable_rustc_ensure_not_fmt_string_literal!("unary `panic!`", $msg),
              file!(), line!());
         ::core::panicking::panic(&_MSG_FILE_LINE)
     });

src/libstd/macros.rs

@@ -21,7 +21,7 @@
 #[macro_export]
 #[allow_internal_unstable]
 macro_rules! __unstable_rustc_ensure_not_fmt_string_literal {
-    ($name:expr, $e:expr) => { ((), $e) }
+    ($name:expr, $e:expr) => { $e }
 }
 
 /// The entry point for panic of Rust tasks.
@@ -53,7 +53,7 @@ macro_rules! panic {
     });
     ($msg:expr) => ({
         $crate::rt::begin_unwind(
-            __unstable_rustc_ensure_not_fmt_string_literal!("unary `panic!`", $msg).1, {
+            __unstable_rustc_ensure_not_fmt_string_literal!("unary `panic!`", $msg), {
             // static requires less code at runtime, more constant data
             static _FILE_LINE: (&'static str, usize) = (file!(), line!() as usize);
             &_FILE_LINE
@@ -100,7 +100,7 @@ macro_rules! panic {
     });
     ($msg:expr) => ({
         $crate::rt::begin_unwind(
-            __unstable_rustc_ensure_not_fmt_string_literal!("unary `panic!`", $msg).1, {
+            __unstable_rustc_ensure_not_fmt_string_literal!("unary `panic!`", $msg), {
                 // static requires less code at runtime, more constant data
                 static _FILE_LINE: (&'static str, u32) = (file!(), line!());
                 &_FILE_LINE

src/libsyntax/ext/format.rs

@@ -701,39 +701,6 @@ pub fn ensure_not_fmt_string_literal<'cx>(cx: &'cx mut ExtCtxt,
         }
     };
 
-    let unstable_marker = cx.expr_path(cx.path_global(sp, vec![
-        cx.ident_of_std("core"),
-        cx.ident_of("fmt"),
-        cx.ident_of("ENSURE_NOT_FMT_STRING_LITERAL_IS_UNSTABLE")]));
-
-    // Total hack: We do not (yet) have hygienic-marking of stabilty.
-    // Thus an unstable macro (like `ensure_not_fmt_string!`) can leak
-    // through another macro (like `panic!`), where the latter is just
-    // using the former as an implementation detail.
-    //
-    // The `#[allow_internal_unstable]` system does not suffice to
-    // address this; it explicitly (as described on Issue #22899)
-    // disallows the use of unstable functionality via a helper macro
-    // like `ensure_not_fmt_string!`, by design.
-    //
-    // So, the hack: the `ensure_not_fmt_string!` macro has just one
-    // stable client: `panic!`.  So we give `panic!` a backdoor: we
-    // allow its name literal string to give it stable access. Any
-    // other argument that is passed in will cause us to emit the
-    // unstable-marker, which will then be checked against the enabled
-    // feature-set.
-    //
-    // This, combined with the awkward actual name of the unstable
-    // macro (hint: the real name is far more awkward than the one
-    // given in this comment) should suffice to ensure that people do
-    // not accidentally commit to using it.
-    let marker = if name == "unary `panic!`" {
-        cx.expr_tuple(sp, vec![]) // i.e. `()`
-    } else {
-        unstable_marker
-    };
-    let expr = cx.expr_tuple(sp, vec![marker, expr]);
-
     MacEager::expr(expr)
 }