Auto merge of #22899 - huonw:macro-stability, r=alexcrichton

Unstable items used in a macro expansion will now always trigger
stability warnings, *unless* the unstable items are directly inside a
macro marked with `#[allow_internal_unstable]`. IOW, the compiler warns
unless the span of the unstable item is a subspan of the definition of a
macro marked with that attribute.

E.g.

    #[allow_internal_unstable]
    macro_rules! foo {
        ($e: expr) => {{
            $e;
            unstable(); // no warning
            only_called_by_foo!();
        }}
    }

    macro_rules! only_called_by_foo {
        () => { unstable() } // warning
    }

    foo!(unstable()) // warning

The unstable inside `foo` is fine, due to the attribute. But the
`unstable` inside `only_called_by_foo` is not, since that macro doesn't
have the attribute, and the `unstable` passed into `foo` is also not
fine since it isn't contained in the macro itself (that is, even though
it is only used directly in the macro).

In the process this makes the stability tracking much more precise,
e.g. previously `println!("{}", unstable())` got no warning, but now it
does. As such, this is a bug fix that may cause [breaking-change]s.

The attribute is definitely feature gated, since it explicitly allows
side-stepping the feature gating system.

---

This updates `thread_local!` macro to use the attribute, since it uses
unstable features internally (initialising a struct with unstable
fields).

Author: bors

src/doc/reference.md

@@ -2555,6 +2555,14 @@ The currently implemented features of the reference compiler are:
                             types, e.g. as the return type of a public function.
                             This capability may be removed in the future.
 
+* `allow_internal_unstable` - Allows `macro_rules!` macros to be tagged with the
+                              `#[allow_internal_unstable]` attribute, designed
+                              to allow `std` macros to call
+                              `#[unstable]`/feature-gated functionality
+                              internally without imposing on callers
+                              (i.e. making them behave like function calls in
+                              terms of encapsulation).
+
 If a feature is promoted to a language feature, then all existing programs will
 start to receive compilation warnings about #[feature] directives which enabled
 the new feature (because the directive is no longer necessary). However, if a

src/libcore/num/mod.rs

@@ -1238,6 +1238,7 @@ pub fn from_f64<A: FromPrimitive>(n: f64) -> Option<A> {
 
 macro_rules! impl_from_primitive {
     ($T:ty, $to_ty:ident) => (
+        #[allow(deprecated)]
         impl FromPrimitive for $T {
             #[inline] fn from_int(n: int) -> Option<$T> { n.$to_ty() }
             #[inline] fn from_i8(n: i8) -> Option<$T> { n.$to_ty() }
@@ -1299,6 +1300,7 @@ macro_rules! impl_num_cast {
     ($T:ty, $conv:ident) => (
         impl NumCast for $T {
             #[inline]
+            #[allow(deprecated)]
             fn from<N: ToPrimitive>(n: N) -> Option<$T> {
                 // `$conv` could be generated using `concat_idents!`, but that
                 // macro seems to be broken at the moment

src/librustc/metadata/creader.rs

@@ -542,6 +542,7 @@ impl<'a> CrateReader<'a> {
                     // overridden in plugin/load.rs
                     export: false,
                     use_locally: false,
+                    allow_internal_unstable: false,
 
                     body: body,
                 });

src/librustc/metadata/macro_import.rs

@@ -166,6 +166,9 @@ impl<'a> MacroLoader<'a> {
                 Some(sel) => sel.contains_key(&name),
             };
             def.export = reexport.contains_key(&name);
+            def.allow_internal_unstable = attr::contains_name(&def.attrs,
+                                                              "allow_internal_unstable");
+            debug!("load_macros: loaded: {:?}", def);
             self.macros.push(def);
         }
 

src/librustc/middle/stability.rs

@@ -362,8 +362,6 @@ pub fn check_item(tcx: &ty::ctxt, item: &ast::Item, warn_about_defns: bool,
 /// Helper for discovering nodes to check for stability
 pub fn check_expr(tcx: &ty::ctxt, e: &ast::Expr,
                   cb: &mut FnMut(ast::DefId, Span, &Option<Stability>)) {
-    if is_internal(tcx, e.span) { return; }
-
     let span;
     let id = match e.node {
         ast::ExprMethodCall(i, _, _) => {
@@ -527,12 +525,13 @@ pub fn check_pat(tcx: &ty::ctxt, pat: &ast::Pat,
 fn maybe_do_stability_check(tcx: &ty::ctxt, id: ast::DefId, span: Span,
                             cb: &mut FnMut(ast::DefId, Span, &Option<Stability>)) {
     if !is_staged_api(tcx, id) { return  }
+    if is_internal(tcx, span) { return }
     let ref stability = lookup(tcx, id);
     cb(id, span, stability);
 }
 
 fn is_internal(tcx: &ty::ctxt, span: Span) -> bool {
-    tcx.sess.codemap().span_is_internal(span)
+    tcx.sess.codemap().span_allows_unstable(span)
 }
 
 fn is_staged_api(tcx: &ty::ctxt, id: DefId) -> bool {

src/librustc/plugin/registry.rs

@@ -81,8 +81,12 @@ impl<'a> Registry<'a> {
     /// This is the most general hook into `libsyntax`'s expansion behavior.
     pub fn register_syntax_extension(&mut self, name: ast::Name, extension: SyntaxExtension) {
         self.syntax_exts.push((name, match extension {
-            NormalTT(ext, _) => NormalTT(ext, Some(self.krate_span)),
-            IdentTT(ext, _) => IdentTT(ext, Some(self.krate_span)),
+            NormalTT(ext, _, allow_internal_unstable) => {
+                NormalTT(ext, Some(self.krate_span), allow_internal_unstable)
+            }
+            IdentTT(ext, _, allow_internal_unstable) => {
+                IdentTT(ext, Some(self.krate_span), allow_internal_unstable)
+            }
             Decorator(ext) => Decorator(ext),
             Modifier(ext) => Modifier(ext),
             MultiModifier(ext) => MultiModifier(ext),
@@ -99,7 +103,8 @@ impl<'a> Registry<'a> {
     /// It builds for you a `NormalTT` that calls `expander`,
     /// and also takes care of interning the macro's name.
     pub fn register_macro(&mut self, name: &str, expander: MacroExpanderFn) {
-        self.register_syntax_extension(token::intern(name), NormalTT(Box::new(expander), None));
+        self.register_syntax_extension(token::intern(name),
+                                       NormalTT(Box::new(expander), None, false));
     }
 
     /// Register a compiler lint pass.

src/librustc_driver/driver.rs

@@ -493,12 +493,16 @@ pub fn phase_2_configure_and_expand(sess: &Session,
         }
     );
 
-    // Needs to go *after* expansion to be able to check the results of macro expansion.
-    time(time_passes, "complete gated feature checking", (), |_| {
+    // Needs to go *after* expansion to be able to check the results
+    // of macro expansion.  This runs before #[cfg] to try to catch as
+    // much as possible (e.g. help the programmer avoid platform
+    // specific differences)
+    time(time_passes, "complete gated feature checking 1", (), |_| {
         let features =
             syntax::feature_gate::check_crate(sess.codemap(),
-                                          &sess.parse_sess.span_diagnostic,
-                                          &krate);
+                                              &sess.parse_sess.span_diagnostic,
+                                              &krate,
+                                              true);
         *sess.features.borrow_mut() = features;
         sess.abort_if_errors();
     });
@@ -521,6 +525,19 @@ pub fn phase_2_configure_and_expand(sess: &Session,
     time(time_passes, "checking that all macro invocations are gone", &krate, |krate|
          syntax::ext::expand::check_for_macros(&sess.parse_sess, krate));
 
+    // One final feature gating of the true AST that gets compiled
+    // later, to make sure we've got everything (e.g. configuration
+    // can insert new attributes via `cfg_attr`)
+    time(time_passes, "complete gated feature checking 2", (), |_| {
+        let features =
+            syntax::feature_gate::check_crate(sess.codemap(),
+                                              &sess.parse_sess.span_diagnostic,
+                                              &krate,
+                                              false);
+        *sess.features.borrow_mut() = features;
+        sess.abort_if_errors();
+    });
+
     Some(krate)
 }
 

src/libstd/lib.rs

@@ -125,6 +125,7 @@
 #![feature(hash)]
 #![feature(int_uint)]
 #![feature(unique)]
+#![feature(allow_internal_unstable)]
 #![cfg_attr(test, feature(test, rustc_private))]
 
 // Don't link to std. We are std.

src/libstd/sys/common/thread_local.rs

@@ -55,6 +55,7 @@
 //! ```
 
 #![allow(non_camel_case_types)]
+#![unstable(feature = "thread_local_internals")]
 
 use prelude::v1::*;
 
@@ -84,17 +85,14 @@ use sys::thread_local as imp;
 ///     KEY.set(1 as *mut u8);
 /// }
 /// ```
-#[stable(feature = "rust1", since = "1.0.0")]
 pub struct StaticKey {
     /// Inner static TLS key (internals), created with by `INIT_INNER` in this
     /// module.
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub inner: StaticKeyInner,
     /// Destructor for the TLS value.
     ///
     /// See `Key::new` for information about when the destructor runs and how
     /// it runs.
-    #[stable(feature = "rust1", since = "1.0.0")]
     pub dtor: Option<unsafe extern fn(*mut u8)>,
 }
 
@@ -131,7 +129,6 @@ pub struct Key {
 /// Constant initialization value for static TLS keys.
 ///
 /// This value specifies no destructor by default.
-#[stable(feature = "rust1", since = "1.0.0")]
 pub const INIT: StaticKey = StaticKey {
     inner: INIT_INNER,
     dtor: None,
@@ -140,7 +137,6 @@ pub const INIT: StaticKey = StaticKey {
 /// Constant initialization value for the inner part of static TLS keys.
 ///
 /// This value allows specific configuration of the destructor for a TLS key.
-#[stable(feature = "rust1", since = "1.0.0")]
 pub const INIT_INNER: StaticKeyInner = StaticKeyInner {
     key: atomic::ATOMIC_USIZE_INIT,
 };

src/libstd/thread_local/mod.rs

@@ -45,7 +45,7 @@ pub mod scoped;
 
 // Sure wish we had macro hygiene, no?
 #[doc(hidden)]
-#[stable(feature = "rust1", since = "1.0.0")]
+#[unstable(feature = "thread_local_internals")]
 pub mod __impl {
     pub use super::imp::Key as KeyInner;
     pub use super::imp::destroy_value;
@@ -117,6 +117,7 @@ pub struct Key<T> {
 /// Declare a new thread local storage key of type `std::thread_local::Key`.
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[allow_internal_unstable]
 macro_rules! thread_local {
     (static $name:ident: $t:ty = $init:expr) => (
         static $name: ::std::thread_local::Key<$t> = {
@@ -176,6 +177,7 @@ macro_rules! thread_local {
 
 #[macro_export]
 #[doc(hidden)]
+#[allow_internal_unstable]
 macro_rules! __thread_local_inner {
     (static $name:ident: $t:ty = $init:expr) => (
         #[cfg_attr(all(any(target_os = "macos", target_os = "linux"),
@@ -337,22 +339,22 @@ mod imp {
     use ptr;
 
     #[doc(hidden)]
-    #[stable(since = "1.0.0", feature = "rust1")]
+    #[unstable(feature = "thread_local_internals")]
     pub struct Key<T> {
         // Place the inner bits in an `UnsafeCell` to currently get around the
         // "only Sync statics" restriction. This allows any type to be placed in
         // the cell.
         //
         // Note that all access requires `T: 'static` so it can't be a type with
         // any borrowed pointers still.
-        #[stable(since = "1.0.0", feature = "rust1")]
+        #[unstable(feature = "thread_local_internals")]
         pub inner: UnsafeCell<T>,
 
         // Metadata to keep track of the state of the destructor. Remember that
         // these variables are thread-local, not global.
-        #[stable(since = "1.0.0", feature = "rust1")]
+        #[unstable(feature = "thread_local_internals")]
         pub dtor_registered: UnsafeCell<bool>, // should be Cell
-        #[stable(since = "1.0.0", feature = "rust1")]
+        #[unstable(feature = "thread_local_internals")]
         pub dtor_running: UnsafeCell<bool>, // should be Cell
     }
 
@@ -455,7 +457,7 @@ mod imp {
     }
 
     #[doc(hidden)]
-    #[stable(feature = "rust1", since = "1.0.0")]
+    #[unstable(feature = "thread_local_internals")]
     pub unsafe extern fn destroy_value<T>(ptr: *mut u8) {
         let ptr = ptr as *mut Key<T>;
         // Right before we run the user destructor be sure to flag the
@@ -477,15 +479,15 @@ mod imp {
     use sys_common::thread_local::StaticKey as OsStaticKey;
 
     #[doc(hidden)]
-    #[stable(since = "1.0.0", feature = "rust1")]
+    #[unstable(feature = "thread_local_internals")]
     pub struct Key<T> {
         // Statically allocated initialization expression, using an `UnsafeCell`
         // for the same reasons as above.
-        #[stable(since = "1.0.0", feature = "rust1")]
+        #[unstable(feature = "thread_local_internals")]
         pub inner: UnsafeCell<T>,
 
         // OS-TLS key that we'll use to key off.
-        #[stable(since = "1.0.0", feature = "rust1")]
+        #[unstable(feature = "thread_local_internals")]
         pub os: OsStaticKey,
     }
 
@@ -528,7 +530,7 @@ mod imp {
     }
 
     #[doc(hidden)]
-    #[stable(feature = "rust1", since = "1.0.0")]
+    #[unstable(feature = "thread_local_internals")]
     pub unsafe extern fn destroy_value<T: 'static>(ptr: *mut u8) {
         // The OS TLS ensures that this key contains a NULL value when this
         // destructor starts to run. We set it back to a sentinel value of 1 to