Auto merge of #41847 - alexcrichton:less-unstable-annotations, r=eddyb

rustc: Add a new `-Z force-unstable-if-unmarked` flag

This commit adds a new `-Z` flag to the compiler for use when bootstrapping the
compiler itself. We want to be able to use crates.io crates, but we also want
the usage of such crates to be as ergonomic as possible! To that end compiler
crates are a little tricky in that the crates.io crates are not annotated as
unstable, nor do they expect to pull in unstable dependencies.

To cover all these situations it's intended that the compiler will forever now
bootstrap with `-Z force-unstable-if-unmarked`. This flags serves a dual purpose
of forcing crates.io crates to themselves be unstable while also allowing them
to use other "unstable" crates.io crates. This should mean that adding a
dependency to compiler no longer requires upstream modification with
unstable/staged_api attributes for inclusion!

43 files changed, 201 insertions, 140 deletions

diff --git a/src/bootstrap/bin/rustc.rs b/src/bootstrap/bin/rustc.rs
index 62b7f6cb72e..906c468241a 100644
--- a/src/bootstrap/bin/rustc.rs
+++ b/src/bootstrap/bin/rustc.rs
@@ -194,6 +194,8 @@ fn main() {
                 // do that we pass a weird flag to the compiler to get it to do
                 // so. Note that this is definitely a hack, and we should likely
                 // flesh out rpath support more fully in the future.
+                //
+                // FIXME: remove condition after next stage0
                 if stage != "0" {
                     cmd.arg("-Z").arg("osx-rpath-install-name");
                 }
@@ -218,6 +220,17 @@ fn main() {
             cmd.arg("-Z").arg("unstable-options");
             cmd.arg("-C").arg("target-feature=+crt-static");
         }
+
+        // Force all crates compiled by this compiler to (a) be unstable and (b)
+        // allow the `rustc_private` feature to link to other unstable crates
+        // also in the sysroot.
+        //
+        // FIXME: remove condition after next stage0
+        if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() {
+            if stage != "0" {
+                cmd.arg("-Z").arg("force-unstable-if-unmarked");
+            }
+        }
     }
 
     if verbose > 1 {
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 017d4015134..ea0b521a2ce 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -479,7 +479,8 @@ impl Build {
         // compiled with debuginfo.
         if mode != Mode::Tool {
              cargo.env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string())
-                  .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string());
+                  .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string())
+                  .env("RUSTC_FORCE_UNSTABLE", "1");
         }
 
         // Enable usage of unstable features
@@ -524,7 +525,9 @@ impl Build {
         // the comipiler, libs, and tests are stable and we don't want to make
         // their deps unstable (since this would break the first invariant
         // above).
-        if mode != Mode::Tool {
+        //
+        // FIXME: remove this after next stage0
+        if mode != Mode::Tool && stage == 0 {
             cargo.env("RUSTBUILD_UNSTABLE", "1");
         }
 
diff --git a/src/libarena/lib.rs b/src/libarena/lib.rs
index 321fa2edd56..c4c1635aa2a 100644
--- a/src/libarena/lib.rs
+++ b/src/libarena/lib.rs
@@ -19,7 +19,7 @@
 //! objects of a single type.
 
 #![crate_name = "arena"]
-#![unstable(feature = "rustc_private", issue = "27812")]
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -32,7 +32,7 @@
 #![feature(core_intrinsics)]
 #![feature(dropck_eyepatch)]
 #![feature(generic_param_attrs)]
-#![feature(staged_api)]
+#![cfg_attr(stage0, feature(staged_api))]
 #![cfg_attr(test, feature(test))]
 
 #![allow(deprecated)]
diff --git a/src/libflate/lib.rs b/src/libflate/lib.rs
index 3619be82829..e0bea884f31 100644
--- a/src/libflate/lib.rs
+++ b/src/libflate/lib.rs
@@ -15,7 +15,7 @@
 //! [mz]: https://code.google.com/p/miniz/
 
 #![crate_name = "flate"]
-#![unstable(feature = "rustc_private", issue = "27812")]
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -25,7 +25,7 @@
 #![deny(warnings)]
 
 #![feature(libc)]
-#![feature(staged_api)]
+#![cfg_attr(stage0, feature(staged_api))]
 #![feature(unique)]
 #![cfg_attr(test, feature(rand))]
 
diff --git a/src/libfmt_macros/lib.rs b/src/libfmt_macros/lib.rs
index f5a687de64e..641a42b0818 100644
--- a/src/libfmt_macros/lib.rs
+++ b/src/libfmt_macros/lib.rs
@@ -15,7 +15,7 @@
 //! generated instead.
 
 #![crate_name = "fmt_macros"]
-#![unstable(feature = "rustc_private", issue = "27812")]
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -25,7 +25,7 @@
        test(attr(deny(warnings))))]
 #![deny(warnings)]
 
-#![feature(staged_api)]
+#![cfg_attr(stage0, feature(staged_api))]
 #![feature(unicode)]
 
 pub use self::Piece::*;
diff --git a/src/libgetopts/lib.rs b/src/libgetopts/lib.rs
index a5cd9fab2cf..c69c68ba59c 100644
--- a/src/libgetopts/lib.rs
+++ b/src/libgetopts/lib.rs
@@ -78,9 +78,9 @@
 //! ```
 
 #![crate_name = "getopts"]
-#![unstable(feature = "rustc_private",
+#![cfg_attr(stage0, unstable(feature = "rustc_private",
             reason = "use the crates.io `getopts` library instead",
-            issue = "27812")]
+            issue = "27812"))]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -91,7 +91,7 @@
 
 #![deny(missing_docs)]
 #![deny(warnings)]
-#![feature(staged_api)]
+#![cfg_attr(stage0, feature(staged_api))]
 
 use self::Name::*;
 use self::HasArg::*;
diff --git a/src/libgraphviz/lib.rs b/src/libgraphviz/lib.rs
index 1b2c7775185..2c6744e7c90 100644
--- a/src/libgraphviz/lib.rs
+++ b/src/libgraphviz/lib.rs
@@ -284,8 +284,8 @@
 //! * [DOT language](http://www.graphviz.org/doc/info/lang.html)
 
 #![crate_name = "graphviz"]
-#![unstable(feature = "rustc_private", issue = "27812")]
-#![feature(staged_api)]
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(staged_api))]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
diff --git a/src/libproc_macro_plugin/lib.rs b/src/libproc_macro_plugin/lib.rs
index a6dad641253..68c5d495918 100644
--- a/src/libproc_macro_plugin/lib.rs
+++ b/src/libproc_macro_plugin/lib.rs
@@ -72,7 +72,7 @@
 //! }
 //! ```
 #![crate_name = "proc_macro_plugin"]
-#![unstable(feature = "rustc_private", issue = "27812")]
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
 #![feature(plugin_registrar)]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
@@ -81,9 +81,9 @@
        html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![deny(warnings)]
 
-#![feature(staged_api)]
+#![cfg_attr(stage0, feature(staged_api))]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
+#![cfg_attr(stage0, feature(rustc_private))]
 
 extern crate rustc_plugin;
 extern crate syntax;
diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index d3954326e7b..5cf26ea8bfc 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -36,15 +35,17 @@
 #![feature(nonzero)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
 #![feature(slice_patterns)]
 #![feature(specialization)]
-#![feature(staged_api)]
 #![feature(unboxed_closures)]
 #![feature(discriminant_value)]
 #![feature(sort_unstable)]
 #![feature(trace_macros)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 #![recursion_limit="128"]
 
 extern crate arena;
diff --git a/src/librustc/middle/cstore.rs b/src/librustc/middle/cstore.rs
index da899a9130c..569b1aeeb09 100644
--- a/src/librustc/middle/cstore.rs
+++ b/src/librustc/middle/cstore.rs
@@ -233,7 +233,6 @@ pub trait CrateStore {
     fn export_macros(&self, cnum: CrateNum);
     fn lang_items(&self, cnum: CrateNum) -> Vec<(DefIndex, usize)>;
     fn missing_lang_items(&self, cnum: CrateNum) -> Vec<lang_items::LangItem>;
-    fn is_staged_api(&self, cnum: CrateNum) -> bool;
     fn is_allocator(&self, cnum: CrateNum) -> bool;
     fn is_panic_runtime(&self, cnum: CrateNum) -> bool;
     fn is_compiler_builtins(&self, cnum: CrateNum) -> bool;
@@ -356,7 +355,6 @@ impl CrateStore for DummyCrateStore {
         { bug!("lang_items") }
     fn missing_lang_items(&self, cnum: CrateNum) -> Vec<lang_items::LangItem>
         { bug!("missing_lang_items") }
-    fn is_staged_api(&self, cnum: CrateNum) -> bool { bug!("is_staged_api") }
     fn dep_kind(&self, cnum: CrateNum) -> DepKind { bug!("is_explicitly_linked") }
     fn export_macros(&self, cnum: CrateNum) { bug!("export_macros") }
     fn is_allocator(&self, cnum: CrateNum) -> bool { bug!("is_allocator") }
diff --git a/src/librustc/middle/stability.rs b/src/librustc/middle/stability.rs
index 198f7420f5d..d74877e355a 100644
--- a/src/librustc/middle/stability.rs
+++ b/src/librustc/middle/stability.rs
@@ -13,12 +13,12 @@
 
 pub use self::StabilityLevel::*;
 
-use hir::map as hir_map;
 use lint;
 use hir::def::Def;
 use hir::def_id::{CrateNum, CRATE_DEF_INDEX, DefId, DefIndex, LOCAL_CRATE};
 use ty::{self, TyCtxt};
 use middle::privacy::AccessLevels;
+use session::Session;
 use syntax::symbol::Symbol;
 use syntax_pos::{Span, DUMMY_SP};
 use syntax::ast;
@@ -123,7 +123,7 @@ impl<'a, 'tcx: 'a> Annotator<'a, 'tcx> {
                    item_sp: Span, kind: AnnotationKind, visit_children: F)
         where F: FnOnce(&mut Self)
     {
-        if self.index.staged_api[&LOCAL_CRATE] && self.tcx.sess.features.borrow().staged_api {
+        if self.index.staged_api[&LOCAL_CRATE] {
             debug!("annotate(id = {:?}, attrs = {:?})", id, attrs);
             if let Some(..) = attr::find_deprecation(self.tcx.sess.diagnostic(), attrs, item_sp) {
                 self.tcx.sess.span_err(item_sp, "`#[deprecated]` cannot be used in staged api, \
@@ -390,20 +390,36 @@ impl<'a, 'tcx> Index<'tcx> {
             parent_depr: None,
             in_trait_impl: false,
         };
+
+        // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
+        // a parent stability annotation which indicates that this is private
+        // with the `rustc_private` feature. This is intended for use when
+        // compiling librustc crates themselves so we can leverage crates.io
+        // while maintaining the invariant that all sysroot crates are unstable
+        // by default and are unable to be used.
+        if tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
+            let reason = "this crate is being loaded from the sysroot, and \
+                          unstable location; did you mean to load this crate \
+                          from crates.io via `Cargo.toml` instead?";
+            let stability = tcx.intern_stability(Stability {
+                level: attr::StabilityLevel::Unstable {
+                    reason: Some(Symbol::intern(reason)),
+                    issue: 27812,
+                },
+                feature: Symbol::intern("rustc_private"),
+                rustc_depr: None,
+            });
+            annotator.parent_stab = Some(stability);
+        }
+
         annotator.annotate(ast::CRATE_NODE_ID, &krate.attrs, krate.span, AnnotationKind::Required,
                            |v| intravisit::walk_crate(v, krate));
     }
 
-    pub fn new(hir_map: &hir_map::Map) -> Index<'tcx> {
-        let krate = hir_map.krate();
-
-        let mut is_staged_api = false;
-        for attr in &krate.attrs {
-            if attr.path == "stable" || attr.path == "unstable" {
-                is_staged_api = true;
-                break
-            }
-        }
+    pub fn new(sess: &Session) -> Index<'tcx> {
+        let is_staged_api =
+            sess.opts.debugging_opts.force_unstable_if_unmarked ||
+            sess.features.borrow().staged_api;
 
         let mut staged_api = FxHashMap();
         staged_api.insert(LOCAL_CRATE, is_staged_api);
@@ -496,8 +512,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             }
         }
 
-        let is_staged_api = *self.stability.borrow_mut().staged_api.entry(def_id.krate)
-            .or_insert_with(|| self.sess.cstore.is_staged_api(def_id.krate));
+        let is_staged_api = self.lookup_stability(DefId {
+            index: CRATE_DEF_INDEX,
+            ..def_id
+        }).is_some();
         if !is_staged_api {
             return;
         }
@@ -530,15 +548,32 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
         match stability {
             Some(&Stability { level: attr::Unstable {ref reason, issue}, ref feature, .. }) => {
-                if !self.stability.borrow().active_features.contains(feature) {
-                    let msg = match *reason {
-                        Some(ref r) => format!("use of unstable library feature '{}': {}",
-                                               feature.as_str(), &r),
-                        None => format!("use of unstable library feature '{}'", &feature)
-                    };
-                    emit_feature_err(&self.sess.parse_sess, &feature.as_str(), span,
-                                     GateIssue::Library(Some(issue)), &msg);
+                if self.stability.borrow().active_features.contains(feature) {
+                    return
                 }
+
+                // When we're compiling the compiler itself we may pull in
+                // crates from crates.io, but those crates may depend on other
+                // crates also pulled in from crates.io. We want to ideally be
+                // able to compile everything without requiring upstream
+                // modifications, so in the case that this looks like a
+                // rustc_private crate (e.g. a compiler crate) and we also have
+                // the `-Z force-unstable-if-unmarked` flag present (we're
+                // compiling a compiler crate), then let this missing feature
+                // annotation slide.
+                if *feature == "rustc_private" && issue == 27812 {
+                    if self.sess.opts.debugging_opts.force_unstable_if_unmarked {
+                        return
+                    }
+                }
+
+                let msg = match *reason {
+                    Some(ref r) => format!("use of unstable library feature '{}': {}",
+                                           feature.as_str(), &r),
+                    None => format!("use of unstable library feature '{}'", &feature)
+                };
+                emit_feature_err(&self.sess.parse_sess, &feature.as_str(), span,
+                                 GateIssue::Library(Some(issue)), &msg);
             }
             Some(_) => {
                 // Stable APIs are always ok to call and deprecated APIs are
@@ -658,7 +693,7 @@ pub fn check_unused_or_stable_features<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
 
     let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
 
-    if tcx.stability.borrow().staged_api[&LOCAL_CRATE] && tcx.sess.features.borrow().staged_api {
+    if tcx.stability.borrow().staged_api[&LOCAL_CRATE] {
         let krate = tcx.hir.krate();
         let mut missing = MissingStabilityAnnotations {
             tcx: tcx,
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 75bc940625d..884a71f0d32 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -1027,6 +1027,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "add a source pattern to the file path remapping config"),
     remap_path_prefix_to: Vec<String> = (vec![], parse_string_push, [TRACKED],
         "add a mapping target to the file path remapping config"),
+    force_unstable_if_unmarked: bool = (false, parse_bool, [TRACKED],
+        "force all crates to be `rustc_private` unstable"),
 }
 
 pub fn default_lib_output() -> CrateType {
diff --git a/src/librustc_back/lib.rs b/src/librustc_back/lib.rs
index 6679cc73029..69eabfe2ac0 100644
--- a/src/librustc_back/lib.rs
+++ b/src/librustc_back/lib.rs
@@ -22,7 +22,6 @@
 //! build speedups.
 
 #![crate_name = "rustc_back"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -34,10 +33,12 @@
 #![feature(const_fn)]
 #![feature(libc)]
 #![feature(rand)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![cfg_attr(test, feature(rand))]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate syntax;
 extern crate libc;
 extern crate serialize;
diff --git a/src/librustc_bitflags/lib.rs b/src/librustc_bitflags/lib.rs
index edd474b2e9e..23558d82883 100644
--- a/src/librustc_bitflags/lib.rs
+++ b/src/librustc_bitflags/lib.rs
@@ -11,11 +11,11 @@
 
 #![crate_name = "rustc_bitflags"]
 #![feature(associated_consts)]
-#![feature(staged_api)]
 #![crate_type = "rlib"]
 #![no_std]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![deny(warnings)]
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 //! A typesafe bitmask flag generator.
 
diff --git a/src/librustc_borrowck/lib.rs b/src/librustc_borrowck/lib.rs
index a1d3357faf5..61732680897 100644
--- a/src/librustc_borrowck/lib.rs
+++ b/src/librustc_borrowck/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_name = "rustc_borrowck"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -21,10 +20,13 @@
 
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(associated_consts)]
 #![feature(nonzero)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;
 extern crate syntax_pos;
diff --git a/src/librustc_const_eval/lib.rs b/src/librustc_const_eval/lib.rs
index fa3161a8604..8142829e816 100644
--- a/src/librustc_const_eval/lib.rs
+++ b/src/librustc_const_eval/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc_const_eval"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -23,8 +22,6 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![deny(warnings)]
 
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_patterns)]
 #![feature(box_patterns)]
@@ -32,6 +29,10 @@
 #![feature(const_fn)]
 #![feature(i128_type)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate arena;
 #[macro_use] extern crate syntax;
 #[macro_use] extern crate log;
diff --git a/src/librustc_const_math/lib.rs b/src/librustc_const_math/lib.rs
index b7833a54403..528170781ea 100644
--- a/src/librustc_const_math/lib.rs
+++ b/src/librustc_const_math/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc_const_math"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -23,12 +22,14 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![deny(warnings)]
 
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(const_fn)]
 #![feature(i128)]
 #![feature(i128_type)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate syntax;
 
 extern crate serialize as rustc_serialize; // used by deriving
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 00c46d992bf..c254dfc48d2 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -17,7 +17,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc_data_structures"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -28,8 +27,6 @@
 #![feature(shared)]
 #![feature(collections_range)]
 #![feature(nonzero)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(unboxed_closures)]
 #![feature(fn_traits)]
 #![feature(untagged_unions)]
@@ -42,6 +39,10 @@
 #![feature(manually_drop)]
 #![feature(struct_field_attributes)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 #![cfg_attr(unix, feature(libc))]
 #![cfg_attr(test, feature(test))]
 
diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs
index 5f14890665c..8fddbe110b0 100644
--- a/src/librustc_driver/driver.rs
+++ b/src/librustc_driver/driver.rs
@@ -882,7 +882,7 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
               "static item recursion checking",
               || static_recursion::check_crate(sess, &hir_map))?;
 
-    let index = stability::Index::new(&hir_map);
+    let index = stability::Index::new(&sess);
 
     let mut local_providers = ty::maps::Providers::default();
     borrowck::provide(&mut local_providers);
diff --git a/src/librustc_driver/lib.rs b/src/librustc_driver/lib.rs
index eef3b38a8b5..024fc546a15 100644
--- a/src/librustc_driver/lib.rs
+++ b/src/librustc_driver/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc_driver"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -28,9 +27,11 @@
 #![feature(libc)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
 #![feature(set_stdio)]
-#![feature(staged_api)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 extern crate arena;
 extern crate getopts;
diff --git a/src/librustc_driver/test.rs b/src/librustc_driver/test.rs
index 8b95be00fa7..3b4f2560fc5 100644
--- a/src/librustc_driver/test.rs
+++ b/src/librustc_driver/test.rs
@@ -138,7 +138,7 @@ fn test_env<F>(source_string: &str,
     // run just enough stuff to build a tcx:
     let lang_items = lang_items::collect_language_items(&sess, &hir_map);
     let named_region_map = resolve_lifetime::krate(&sess, &hir_map);
-    let index = stability::Index::new(&hir_map);
+    let index = stability::Index::new(&sess);
     TyCtxt::create_and_enter(&sess,
                              ty::maps::Providers::default(),
                              ty::maps::Providers::default(),
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index db8c9ac306b..0f2e1669a47 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_name = "rustc_errors"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -19,11 +18,13 @@
 
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(range_contains)]
 #![feature(libc)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate term;
 extern crate libc;
 extern crate serialize as rustc_serialize;
diff --git a/src/librustc_incremental/lib.rs b/src/librustc_incremental/lib.rs
index 95f0a96fdf9..70f967d50b0 100644
--- a/src/librustc_incremental/lib.rs
+++ b/src/librustc_incremental/lib.rs
@@ -11,7 +11,6 @@
 //! Support for serializing the dep-graph and reloading it.
 
 #![crate_name = "rustc_incremental"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -19,12 +18,14 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![deny(warnings)]
 
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(rand)]
 #![feature(conservative_impl_trait)]
 #![feature(sort_unstable)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate graphviz;
 #[macro_use] extern crate rustc;
 extern crate rustc_data_structures;
diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 53ea3a8333f..2d0b5a6a51c 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -20,7 +20,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc_lint"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -34,9 +33,11 @@
 #![feature(i128_type)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
 #![feature(slice_patterns)]
-#![feature(staged_api)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 #[macro_use]
 extern crate syntax;
diff --git a/src/librustc_llvm/lib.rs b/src/librustc_llvm/lib.rs
index c9b3a7ff3f3..790d493f191 100644
--- a/src/librustc_llvm/lib.rs
+++ b/src/librustc_llvm/lib.rs
@@ -14,7 +14,6 @@
 #![allow(dead_code)]
 
 #![crate_name = "rustc_llvm"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -27,10 +26,12 @@
 #![feature(concat_idents)]
 #![feature(libc)]
 #![feature(link_args)]
-#![feature(staged_api)]
-#![feature(rustc_private)]
 #![feature(static_nobundle)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate libc;
 #[macro_use]
 #[no_link]
diff --git a/src/librustc_metadata/cstore.rs b/src/librustc_metadata/cstore.rs
index 8d53e7d49ee..c12b4209675 100644
--- a/src/librustc_metadata/cstore.rs
+++ b/src/librustc_metadata/cstore.rs
@@ -269,15 +269,6 @@ impl CrateMetadata {
         self.root.disambiguator
     }
 
-    pub fn is_staged_api(&self, dep_graph: &DepGraph) -> bool {
-        for attr in self.get_item_attrs(CRATE_DEF_INDEX, dep_graph).iter() {
-            if attr.path == "stable" || attr.path == "unstable" {
-                return true;
-            }
-        }
-        false
-    }
-
     pub fn is_allocator(&self, dep_graph: &DepGraph) -> bool {
         let attrs = self.get_item_attrs(CRATE_DEF_INDEX, dep_graph);
         attr::contains_name(&attrs, "allocator")
diff --git a/src/librustc_metadata/cstore_impl.rs b/src/librustc_metadata/cstore_impl.rs
index f3fb427fed6..dbf3e94832f 100644
--- a/src/librustc_metadata/cstore_impl.rs
+++ b/src/librustc_metadata/cstore_impl.rs
@@ -229,11 +229,6 @@ impl CrateStore for cstore::CStore {
         self.get_crate_data(cnum).get_missing_lang_items(&self.dep_graph)
     }
 
-    fn is_staged_api(&self, cnum: CrateNum) -> bool
-    {
-        self.get_crate_data(cnum).is_staged_api(&self.dep_graph)
-    }
-
     fn is_allocator(&self, cnum: CrateNum) -> bool
     {
         self.get_crate_data(cnum).is_allocator(&self.dep_graph)
diff --git a/src/librustc_metadata/lib.rs b/src/librustc_metadata/lib.rs
index 90eb2bc0f6a..27555f49e57 100644
--- a/src/librustc_metadata/lib.rs
+++ b/src/librustc_metadata/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_name = "rustc_metadata"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -24,10 +23,12 @@
 #![feature(proc_macro_internals)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
 #![feature(specialization)]
-#![feature(staged_api)]
 #![feature(discriminant_value)]
+#![feature(rustc_private)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 #[macro_use]
 extern crate log;
diff --git a/src/librustc_mir/lib.rs b/src/librustc_mir/lib.rs
index 5fa56bac137..014705bf32f 100644
--- a/src/librustc_mir/lib.rs
+++ b/src/librustc_mir/lib.rs
@@ -18,18 +18,19 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![deny(warnings)]
-#![unstable(feature = "rustc_private", issue = "27812")]
 
 #![feature(associated_consts)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(i128_type)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(placement_in_syntax)]
 #![feature(collection_placement)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 #[macro_use] extern crate log;
 extern crate graphviz as dot;
 #[macro_use]
diff --git a/src/librustc_passes/lib.rs b/src/librustc_passes/lib.rs
index 22566c813d8..97f0022b8db 100644
--- a/src/librustc_passes/lib.rs
+++ b/src/librustc_passes/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc_passes"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -24,8 +23,10 @@
 #![deny(warnings)]
 
 #![feature(rustc_diagnostic_macros)]
-#![feature(staged_api)]
-#![feature(rustc_private)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 #[macro_use]
 extern crate rustc;
diff --git a/src/librustc_platform_intrinsics/lib.rs b/src/librustc_platform_intrinsics/lib.rs
index dd2d60a1d22..21dd360c9bb 100644
--- a/src/librustc_platform_intrinsics/lib.rs
+++ b/src/librustc_platform_intrinsics/lib.rs
@@ -9,10 +9,10 @@
 // except according to those terms.
 
 #![crate_name = "rustc_platform_intrinsics"]
-#![unstable(feature = "rustc_private", issue = "27812")]
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
-#![feature(staged_api)]
+#![cfg_attr(stage0, feature(staged_api))]
 #![deny(warnings)]
 #![allow(bad_style)]
 
diff --git a/src/librustc_plugin/lib.rs b/src/librustc_plugin/lib.rs
index 8aa680ca12d..16ab593e47a 100644
--- a/src/librustc_plugin/lib.rs
+++ b/src/librustc_plugin/lib.rs
@@ -51,7 +51,6 @@
 //! for more examples.
 
 #![crate_name = "rustc_plugin"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -59,9 +58,11 @@
        html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![deny(warnings)]
 
-#![feature(staged_api)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 #[macro_use] extern crate syntax;
 
diff --git a/src/librustc_privacy/lib.rs b/src/librustc_privacy/lib.rs
index f63102433c1..2ced61f5753 100644
--- a/src/librustc_privacy/lib.rs
+++ b/src/librustc_privacy/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_name = "rustc_privacy"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -18,8 +17,10 @@
 #![deny(warnings)]
 
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 extern crate rustc;
 #[macro_use] extern crate syntax;
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index ac556270886..ee72aee042e 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_name = "rustc_resolve"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -19,8 +18,10 @@
 
 #![feature(associated_consts)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 #[macro_use]
 extern crate log;
diff --git a/src/librustc_save_analysis/lib.rs b/src/librustc_save_analysis/lib.rs
index fd6898d19d8..cc98754f610 100644
--- a/src/librustc_save_analysis/lib.rs
+++ b/src/librustc_save_analysis/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_name = "rustc_save_analysis"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -19,8 +18,10 @@
 
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 #[macro_use] extern crate rustc;
 
diff --git a/src/librustc_trans/lib.rs b/src/librustc_trans/lib.rs
index 111c2547721..ff094d04c84 100644
--- a/src/librustc_trans/lib.rs
+++ b/src/librustc_trans/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "rustc_trans"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -33,12 +32,14 @@
 #![feature(libc)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
 #![feature(slice_patterns)]
-#![feature(staged_api)]
 #![feature(unicode)]
 #![feature(conservative_impl_trait)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 use rustc::dep_graph::WorkProduct;
 use syntax_pos::symbol::Symbol;
 
diff --git a/src/librustc_typeck/lib.rs b/src/librustc_typeck/lib.rs
index 84de4ff2b7b..99ee1cff7fd 100644
--- a/src/librustc_typeck/lib.rs
+++ b/src/librustc_typeck/lib.rs
@@ -64,7 +64,6 @@ This API is completely unstable and subject to change.
 */
 
 #![crate_name = "rustc_typeck"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -81,8 +80,10 @@ This API is completely unstable and subject to change.
 #![feature(never_type)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 1156fadf8c0..d89fa547a89 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_name = "rustdoc"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -21,14 +20,16 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(libc)]
-#![feature(rustc_private)]
 #![feature(set_stdio)]
 #![feature(slice_patterns)]
-#![feature(staged_api)]
 #![feature(test)]
 #![feature(unicode)]
 #![feature(vec_remove_item)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate arena;
 extern crate getopts;
 extern crate env_logger;
diff --git a/src/libserialize/lib.rs b/src/libserialize/lib.rs
index 2b31e2f4108..4eb2cad5c91 100644
--- a/src/libserialize/lib.rs
+++ b/src/libserialize/lib.rs
@@ -15,9 +15,9 @@ Core encoding and decoding interfaces.
 */
 
 #![crate_name = "serialize"]
-#![unstable(feature = "rustc_private",
+#![cfg_attr(stage0, unstable(feature = "rustc_private",
             reason = "deprecated in favor of rustc-serialize on crates.io",
-            issue = "27812")]
+            issue = "27812"))]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -32,7 +32,7 @@ Core encoding and decoding interfaces.
 #![feature(core_intrinsics)]
 #![feature(i128_type)]
 #![feature(specialization)]
-#![feature(staged_api)]
+#![cfg_attr(stage0, feature(staged_api))]
 #![cfg_attr(test, feature(test))]
 
 extern crate collections;
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 89c67b88cbd..32dafcdb582 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "syntax"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -24,12 +23,14 @@
        test(attr(deny(warnings))))]
 #![deny(warnings)]
 
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(unicode)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(i128_type)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 extern crate serialize;
 #[macro_use] extern crate log;
 #[macro_use] extern crate bitflags;
diff --git a/src/libsyntax_ext/lib.rs b/src/libsyntax_ext/lib.rs
index e35e79df585..60f5d24ac97 100644
--- a/src/libsyntax_ext/lib.rs
+++ b/src/libsyntax_ext/lib.rs
@@ -11,7 +11,6 @@
 //! Syntax extensions in the Rust compiler.
 
 #![crate_name = "syntax_ext"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -20,8 +19,10 @@
 #![deny(warnings)]
 
 #![feature(proc_macro_internals)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
+
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
 
 extern crate fmt_macros;
 extern crate log;
diff --git a/src/libsyntax_pos/lib.rs b/src/libsyntax_pos/lib.rs
index eb86a8e1379..25f74aeecf4 100644
--- a/src/libsyntax_pos/lib.rs
+++ b/src/libsyntax_pos/lib.rs
@@ -15,7 +15,6 @@
 //! This API is completely unstable and subject to change.
 
 #![crate_name = "syntax_pos"]
-#![unstable(feature = "rustc_private", issue = "27812")]
 #![crate_type = "dylib"]
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -27,10 +26,12 @@
 #![feature(custom_attribute)]
 #![feature(optin_builtin_traits)]
 #![allow(unused_attributes)]
-#![feature(rustc_private)]
-#![feature(staged_api)]
 #![feature(specialization)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(rustc_private))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 use std::cell::{Cell, RefCell};
 use std::ops::{Add, Sub};
 use std::rc::Rc;
diff --git a/src/libterm/lib.rs b/src/libterm/lib.rs
index 370757c0609..eb0ee6ba154 100644
--- a/src/libterm/lib.rs
+++ b/src/libterm/lib.rs
@@ -41,9 +41,6 @@
 //! [ti]: https://en.wikipedia.org/wiki/Terminfo
 
 #![crate_name = "term"]
-#![unstable(feature = "rustc_private",
-            reason = "use the crates.io `term` library instead",
-            issue = "27812")]
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
@@ -54,13 +51,15 @@
 #![deny(missing_docs)]
 #![deny(warnings)]
 
-#![feature(box_syntax)]
 #![feature(staged_api)]
 #![cfg_attr(windows, feature(libc))]
 // Handle rustfmt skips
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
 
+#![cfg_attr(stage0, unstable(feature = "rustc_private", issue = "27812"))]
+#![cfg_attr(stage0, feature(staged_api))]
+
 use std::io::prelude::*;
 
 pub use terminfo::TerminfoTerminal;