Remove *most* mentions of phantom fns and variance on traits. Leave some

comments and also leave the entries in the variance tables for now.

Author: nikomatsakis

src/libcore/marker.rs

@@ -276,12 +276,15 @@ macro_rules! impls{
 #[unstable(feature = "core", reason = "deprecated")]
 #[deprecated(since = "1.0.0", reason = "No longer needed")]
 #[allow(deprecated)]
+#[cfg(stage0)]
 pub trait MarkerTrait : PhantomFn<Self,Self> { }
-//                                    ~~~~~ <-- FIXME(#22806)?
-//
-// Marker trait has been made invariant so as to avoid inf recursion,
-// but we should ideally solve the underlying problem. That's a bit
-// complicated.
+
+/// `MarkerTrait` is deprecated and no longer needed.
+#[unstable(feature = "core", reason = "deprecated")]
+#[deprecated(since = "1.0.0", reason = "No longer needed")]
+#[allow(deprecated)]
+#[cfg(not(stage0))]
+pub trait MarkerTrait { }
 
 #[allow(deprecated)]
 impl<T:?Sized> MarkerTrait for T { }
@@ -290,7 +293,20 @@ impl<T:?Sized> MarkerTrait for T { }
 #[lang="phantom_fn"]
 #[unstable(feature = "core", reason = "deprecated")]
 #[deprecated(since = "1.0.0", reason = "No longer needed")]
-pub trait PhantomFn<A:?Sized,R:?Sized=()> { }
+#[cfg(stage0)]
+pub trait PhantomFn<A:?Sized,R:?Sized=()> {
+}
+
+/// `PhantomFn` is a deprecated marker trait that is no longer needed.
+#[unstable(feature = "core", reason = "deprecated")]
+#[deprecated(since = "1.0.0", reason = "No longer needed")]
+#[cfg(not(stage0))]
+pub trait PhantomFn<A:?Sized,R:?Sized=()> {
+}
+
+#[allow(deprecated)]
+#[cfg(not(stage0))]
+impl<A:?Sized,R:?Sized,T:?Sized> PhantomFn<A,R> for T { }
 
 /// `PhantomData<T>` allows you to describe that a type acts as if it stores a value of type `T`,
 /// even though it does not. This allows you to inform the compiler about certain safety properties

src/librustc/middle/lang_items.rs

@@ -321,7 +321,6 @@ lets_do_this! {
     ExchangeHeapLangItem,            "exchange_heap",           exchange_heap;
     OwnedBoxLangItem,                "owned_box",               owned_box;
 
-    PhantomFnItem,                   "phantom_fn",              phantom_fn;
     PhantomDataItem,                 "phantom_data",            phantom_data;
 
     // Deprecated:

src/librustc/middle/traits/object_safety.rs

@@ -138,11 +138,10 @@ fn supertraits_reference_self<'tcx>(tcx: &ty::ctxt<'tcx>,
             match predicate {
                 ty::Predicate::Trait(ref data) => {
                     // In the case of a trait predicate, we can skip the "self" type.
-                    Some(data.def_id()) != tcx.lang_items.phantom_fn() &&
-                        data.0.trait_ref.substs.types.get_slice(TypeSpace)
-                                                     .iter()
-                                                     .cloned()
-                                                     .any(is_self)
+                    data.0.trait_ref.substs.types.get_slice(TypeSpace)
+                                                 .iter()
+                                                 .cloned()
+                                                 .any(is_self)
                 }
                 ty::Predicate::Projection(..) |
                 ty::Predicate::TypeOutlives(..) |

src/librustc/middle/traits/select.rs

@@ -836,14 +836,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             ambiguous: false
         };
 
-        // Check for the `PhantomFn` trait. This is really just a
-        // special annotation that is *always* considered to match, no
-        // matter what the type parameters are etc.
-        if self.tcx().lang_items.phantom_fn() == Some(obligation.predicate.def_id()) {
-            candidates.vec.push(PhantomFnCandidate);
-            return Ok(candidates);
-        }
-
         // Other bounds. Consider both in-scope bounds from fn decl
         // and applicable impls. There is a certain set of precedence rules here.
 

src/librustc_typeck/check/wf.rs

@@ -117,15 +117,10 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
 
                 self.check_variances_for_type_defn(item, ast_generics);
             }
-            ast::ItemTrait(_, ref ast_generics, _, ref items) => {
+            ast::ItemTrait(_, _, _, ref items) => {
                 let trait_predicates =
                     ty::lookup_predicates(ccx.tcx, local_def(item.id));
-                reject_non_type_param_bounds(
-                    ccx.tcx,
-                    item.span,
-                    &trait_predicates);
-                self.check_variances(item, ast_generics, &trait_predicates,
-                                     self.tcx().lang_items.phantom_fn());
+                reject_non_type_param_bounds(ccx.tcx, item.span, &trait_predicates);
                 if ty::trait_has_default_impl(ccx.tcx, local_def(item.id)) {
                     if !items.is_empty() {
                         ccx.tcx.sess.span_err(
@@ -287,30 +282,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
                                      ast_generics: &ast::Generics)
     {
         let item_def_id = local_def(item.id);
-        let predicates = ty::lookup_predicates(self.tcx(), item_def_id);
-        self.check_variances(item,
-                             ast_generics,
-                             &predicates,
-                             self.tcx().lang_items.phantom_data());
-    }
-
-    fn check_variances(&self,
-                       item: &ast::Item,
-                       ast_generics: &ast::Generics,
-                       ty_predicates: &ty::GenericPredicates<'tcx>,
-                       suggested_marker_id: Option<ast::DefId>)
-    {
-        let variance_lang_items = &[
-            self.tcx().lang_items.phantom_fn(),
-            self.tcx().lang_items.phantom_data(),
-        ];
-
-        let item_def_id = local_def(item.id);
-        let is_lang_item = variance_lang_items.iter().any(|n| *n == Some(item_def_id));
-        if is_lang_item {
-            return;
-        }
-
+        let ty_predicates = ty::lookup_predicates(self.tcx(), item_def_id);
         let variances = ty::item_variances(self.tcx(), item_def_id);
 
         let mut constrained_parameters: HashSet<_> =
@@ -331,7 +303,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
                 continue;
             }
             let span = self.ty_param_span(ast_generics, item, space, index);
-            self.report_bivariance(span, param_ty.name, suggested_marker_id);
+            self.report_bivariance(span, param_ty.name);
         }
 
         for (space, index, &variance) in variances.regions.iter_enumerated() {
@@ -342,7 +314,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
             assert_eq!(space, TypeSpace);
             let span = ast_generics.lifetimes[index].lifetime.span;
             let name = ast_generics.lifetimes[index].lifetime.name;
-            self.report_bivariance(span, name, suggested_marker_id);
+            self.report_bivariance(span, name);
         }
     }
 
@@ -377,14 +349,14 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
 
     fn report_bivariance(&self,
                          span: Span,
-                         param_name: ast::Name,
-                         suggested_marker_id: Option<ast::DefId>)
+                         param_name: ast::Name)
     {
         self.tcx().sess.span_err(
             span,
             &format!("parameter `{}` is never used",
                      param_name.user_string(self.tcx())));
 
+        let suggested_marker_id = self.tcx().lang_items.phantom_data();
         match suggested_marker_id {
             Some(def_id) => {
                 self.tcx().sess.fileline_help(