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This change starts denying `*T` in the parser. All code using `*T` should ensure
that the FFI call does indeed take `const T*` on the other side before renaming
the type to `*const T`.

Otherwise, all code can rename `*T` to `*const T`.

[breaking-change]

src/libsyntax/parse/parser.rs

@@ -1448,7 +1448,11 @@ impl<'a> Parser<'a> {
         } else if self.eat_keyword(keywords::Const) {
             MutImmutable
         } else {
-            // NOTE: after a stage0 snap this should turn into a span_err.
+            let span = self.last_span;
+            self.span_err(span,
+                          "bare raw pointers are no longer allowed, you should \
+                           likely use `*mut T`, but otherwise `*T` is now \
+                           known as `*const T`");
             MutImmutable
         };
         let t = self.parse_ty(true);