Auto merge of #21019 - nikomatsakis:issue-20871-ret-as-assoc-type, r=nrc

Fixes #20871

r? @aturon (at least until we decide definitively if this is a good idea)

Author: bors

src/libcollections/btree/set.rs

@@ -758,7 +758,9 @@ mod test {
         expected: &'b [int],
     }
 
-    impl<'a, 'b, 'c> FnMut(&'c int) -> bool for Counter<'a, 'b> {
+    impl<'a, 'b, 'c> FnMut<(&'c int,)> for Counter<'a, 'b> {
+        type Output = bool;
+
         extern "rust-call" fn call_mut(&mut self, (&x,): (&'c int,)) -> bool {
             assert_eq!(x, self.expected[*self.i]);
             *self.i += 1;

src/libcore/ops.rs

@@ -1117,29 +1117,33 @@ impl<'a, T: ?Sized> DerefMut for &'a mut T {
 #[lang="fn"]
 #[unstable(feature = "core",
            reason = "uncertain about variadic generics, input versus associated types")]
-pub trait Fn<Args,Result> {
+#[cfg(stage0)]
+pub trait Fn<Args,Output> {
     /// This is called when the call operator is used.
-    extern "rust-call" fn call(&self, args: Args) -> Result;
+    extern "rust-call" fn call(&self, args: Args) -> Output;
 }
 
 /// A version of the call operator that takes a mutable receiver.
 #[lang="fn_mut"]
 #[unstable(feature = "core",
            reason = "uncertain about variadic generics, input versus associated types")]
-pub trait FnMut<Args,Result> {
+#[cfg(stage0)]
+pub trait FnMut<Args,Output> {
     /// This is called when the call operator is used.
-    extern "rust-call" fn call_mut(&mut self, args: Args) -> Result;
+    extern "rust-call" fn call_mut(&mut self, args: Args) -> Output;
 }
 
 /// A version of the call operator that takes a by-value receiver.
 #[lang="fn_once"]
 #[unstable(feature = "core",
            reason = "uncertain about variadic generics, input versus associated types")]
-pub trait FnOnce<Args,Result> {
+#[cfg(stage0)]
+pub trait FnOnce<Args,Output> {
     /// This is called when the call operator is used.
-    extern "rust-call" fn call_once(self, args: Args) -> Result;
+    extern "rust-call" fn call_once(self, args: Args) -> Output;
 }
 
+#[cfg(stage0)]
 impl<F: ?Sized, A, R> FnMut<A, R> for F
     where F : Fn<A, R>
 {
@@ -1148,10 +1152,69 @@ impl<F: ?Sized, A, R> FnMut<A, R> for F
     }
 }
 
+#[cfg(stage0)]
 impl<F,A,R> FnOnce<A,R> for F
     where F : FnMut<A,R>
 {
     extern "rust-call" fn call_once(mut self, args: A) -> R {
         self.call_mut(args)
     }
 }
+
+/// A version of the call operator that takes an immutable receiver.
+#[lang="fn"]
+#[unstable(feature = "core",
+           reason = "uncertain about variadic generics, input versus associated types")]
+#[cfg(not(stage0))]
+pub trait Fn<Args> {
+    type Output;
+
+    /// This is called when the call operator is used.
+    extern "rust-call" fn call(&self, args: Args) -> Self::Output;
+}
+
+/// A version of the call operator that takes a mutable receiver.
+#[lang="fn_mut"]
+#[unstable(feature = "core",
+           reason = "uncertain about variadic generics, input versus associated types")]
+#[cfg(not(stage0))]
+pub trait FnMut<Args> {
+    type Output;
+
+    /// This is called when the call operator is used.
+    extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output;
+}
+
+/// A version of the call operator that takes a by-value receiver.
+#[lang="fn_once"]
+#[unstable(feature = "core",
+           reason = "uncertain about variadic generics, input versus associated types")]
+#[cfg(not(stage0))]
+pub trait FnOnce<Args> {
+    type Output;
+
+    /// This is called when the call operator is used.
+    extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
+}
+
+#[cfg(not(stage0))]
+impl<F: ?Sized, A> FnMut<A> for F
+    where F : Fn<A>
+{
+    type Output = <F as Fn<A>>::Output;
+
+    extern "rust-call" fn call_mut(&mut self, args: A) -> <F as Fn<A>>::Output {
+        self.call(args)
+    }
+}
+
+#[cfg(not(stage0))]
+impl<F,A> FnOnce<A> for F
+    where F : FnMut<A>
+{
+    type Output = <F as FnMut<A>>::Output;
+
+    extern "rust-call" fn call_once(mut self, args: A) -> <F as FnMut<A>>::Output {
+        self.call_mut(args)
+    }
+}

src/libcore/str/mod.rs

@@ -461,13 +461,24 @@ delegate_iter!{exact u8 : Bytes<'a>}
 #[derive(Copy, Clone)]
 struct BytesDeref;
 
+#[cfg(stage0)]
 impl<'a> Fn(&'a u8) -> u8 for BytesDeref {
     #[inline]
     extern "rust-call" fn call(&self, (ptr,): (&'a u8,)) -> u8 {
         *ptr
     }
 }
 
+#[cfg(not(stage0))]
+impl<'a> Fn<(&'a u8,)> for BytesDeref {
+    type Output = u8;
+
+    #[inline]
+    extern "rust-call" fn call(&self, (ptr,): (&'a u8,)) -> u8 {
+        *ptr
+    }
+}
+
 /// An iterator over the substrings of a string, separated by `sep`.
 #[derive(Clone)]
 struct CharSplits<'a, Sep> {

src/librustc/middle/astencode.rs

@@ -904,8 +904,8 @@ impl<'a, 'tcx> rbml_writer_helpers<'tcx> for Encoder<'a> {
                             try!(this.emit_struct_field("method_num", 0, |this| {
                                 this.emit_uint(o.method_num)
                             }));
-                            try!(this.emit_struct_field("real_index", 0, |this| {
-                                this.emit_uint(o.real_index)
+                            try!(this.emit_struct_field("vtable_index", 0, |this| {
+                                this.emit_uint(o.vtable_index)
                             }));
                             Ok(())
                         })
@@ -1492,8 +1492,8 @@ impl<'a, 'tcx> rbml_decoder_decoder_helpers<'tcx> for reader::Decoder<'a> {
                                             this.read_uint()
                                         }).unwrap()
                                     },
-                                    real_index: {
-                                        this.read_struct_field("real_index", 3, |this| {
+                                    vtable_index: {
+                                        this.read_struct_field("vtable_index", 3, |this| {
                                             this.read_uint()
                                         }).unwrap()
                                     },

src/librustc/middle/traits/error_reporting.rs

@@ -408,7 +408,7 @@ fn note_obligation_cause_code<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
         }
         ObligationCauseCode::CompareImplMethodObligation => {
             span_note!(tcx.sess, cause_span,
-                      "the requirement `{}` appears on the impl method\
+                      "the requirement `{}` appears on the impl method \
                       but not on the corresponding trait method",
                       predicate.user_string(infcx.tcx));
         }

src/librustc/middle/traits/mod.rs

@@ -18,7 +18,7 @@ pub use self::ObligationCauseCode::*;
 use middle::mem_categorization::Typer;
 use middle::subst;
 use middle::ty::{self, Ty};
-use middle::infer::InferCtxt;
+use middle::infer::{self, InferCtxt};
 use std::slice::Iter;
 use std::rc::Rc;
 use syntax::ast;
@@ -392,6 +392,65 @@ pub fn type_known_to_meet_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
     }
 }
 
+pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvironment<'a,'tcx>,
+                                             cause: ObligationCause<'tcx>)
+                                             -> ty::ParameterEnvironment<'a,'tcx>
+{
+    match normalize_param_env(&unnormalized_env, cause) {
+        Ok(p) => p,
+        Err(errors) => {
+            // I'm not wild about reporting errors here; I'd prefer to
+            // have the errors get reported at a defined place (e.g.,
+            // during typeck). Instead I have all parameter
+            // environments, in effect, going through this function
+            // and hence potentially reporting errors. This ensurse of
+            // course that we never forget to normalize (the
+            // alternative seemed like it would involve a lot of
+            // manual invocations of this fn -- and then we'd have to
+            // deal with the errors at each of those sites).
+            //
+            // In any case, in practice, typeck constructs all the
+            // parameter environments once for every fn as it goes,
+            // and errors will get reported then; so after typeck we
+            // can be sure that no errors should occur.
+            let infcx = infer::new_infer_ctxt(unnormalized_env.tcx);
+            report_fulfillment_errors(&infcx, &errors);
+
+            // Normalized failed? use what they gave us, it's better than nothing.
+            unnormalized_env
+        }
+    }
+}
+
+pub fn normalize_param_env<'a,'tcx>(param_env: &ty::ParameterEnvironment<'a,'tcx>,
+                                    cause: ObligationCause<'tcx>)
+                                    -> Result<ty::ParameterEnvironment<'a,'tcx>,
+                                              Vec<FulfillmentError<'tcx>>>
+{
+    let tcx = param_env.tcx;
+
+    debug!("normalize_param_env(param_env={})",
+           param_env.repr(tcx));
+
+    let predicates: Vec<ty::Predicate<'tcx>> = {
+        let infcx = infer::new_infer_ctxt(tcx);
+        let mut selcx = &mut SelectionContext::new(&infcx, param_env);
+        let mut fulfill_cx = FulfillmentContext::new();
+        let Normalized { value: predicates, obligations } =
+            project::normalize(selcx, cause, &param_env.caller_bounds);
+        for obligation in obligations.into_iter() {
+            fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
+        }
+        try!(fulfill_cx.select_all_or_error(selcx.infcx(), param_env));
+        predicates.iter().map(|p| infcx.resolve_type_vars_if_possible(p)).collect()
+    };
+
+    debug!("normalize_param_env: predicates={}",
+           predicates.repr(tcx));
+
+    Ok(param_env.with_caller_bounds(predicates))
+}
+
 impl<'tcx,O> Obligation<'tcx,O> {
     pub fn new(cause: ObligationCause<'tcx>,
                trait_ref: O)

src/librustc/middle/traits/object_safety.rs

@@ -122,17 +122,15 @@ fn trait_has_sized_self<'tcx>(tcx: &ty::ctxt<'tcx>,
                               trait_def_id: ast::DefId)
                               -> bool
 {
-    let trait_def = ty::lookup_trait_def(tcx, trait_def_id);
-    let param_env = ty::construct_parameter_environment(tcx,
-                                                        &trait_def.generics,
-                                                        ast::DUMMY_NODE_ID);
-    let predicates = param_env.caller_bounds.predicates.as_slice().to_vec();
     let sized_def_id = match tcx.lang_items.sized_trait() {
         Some(def_id) => def_id,
         None => { return false; /* No Sized trait, can't require it! */ }
     };
 
     // Search for a predicate like `Self : Sized` amongst the trait bounds.
+    let trait_def = ty::lookup_trait_def(tcx, trait_def_id);
+    let free_substs = ty::construct_free_substs(tcx, &trait_def.generics, ast::DUMMY_NODE_ID);
+    let predicates = trait_def.generics.to_bounds(tcx, &free_substs).predicates.into_vec();
     elaborate_predicates(tcx, predicates)
         .any(|predicate| {
             match predicate {