Remove impl trait names and move bits of await into a function

src/librustc/hir/lowering.rs

@@ -877,7 +877,7 @@ impl<'a> LoweringContext<'a> {
 
         let unstable_span = self.allow_internal_unstable(CompilerDesugaringKind::Async, span);
         let gen_future = self.expr_std_path(
-            unstable_span, &["future", "future_from_generator"], None, ThinVec::new());
+            unstable_span, &["future", "from_generator"], None, ThinVec::new());
         hir::ExprCall(P(gen_future), hir_vec![generator])
     }
 
@@ -1173,11 +1173,8 @@ impl<'a> LoweringContext<'a> {
                 let span = t.span;
                 match itctx {
                     ImplTraitContext::Existential(fn_def_id) => {
-                        // Set the name to `impl Bound1 + Bound2`
-                        let exist_ty_name = Symbol::intern(&pprust::ty_to_string(t));
                         self.lower_existential_impl_trait(
-                            span, fn_def_id, exist_ty_name,
-                            |this| this.lower_param_bounds(bounds, itctx))
+                            span, fn_def_id, |this| this.lower_param_bounds(bounds, itctx))
                     }
                     ImplTraitContext::Universal(def_id) => {
                         let def_node_id = self.next_id().node_id;
@@ -1245,7 +1242,6 @@ impl<'a> LoweringContext<'a> {
         &mut self,
         span: Span,
         fn_def_id: DefId,
-        exist_ty_name: Name,
         lower_bounds: impl FnOnce(&mut LoweringContext) -> hir::GenericBounds,
     ) -> hir::Ty_ {
         // We need to manually repeat the code of `next_id` because the lowering
@@ -1307,7 +1303,7 @@ impl<'a> LoweringContext<'a> {
             let exist_ty_item = hir::Item {
                 id: exist_ty_id.node_id,
                 hir_id: exist_ty_id.hir_id,
-                name: exist_ty_name,
+                name: keywords::Invalid.name(),
                 attrs: Default::default(),
                 node: exist_ty_item_kind,
                 vis: hir::Visibility::Inherited,
@@ -2090,19 +2086,13 @@ impl<'a> LoweringContext<'a> {
             lifetime_collector.output_lifetime
         };
 
-        let output_ty_name_owned;
-        let (output_ty_name, span) = match output {
-            FunctionRetTy::Ty(ty) => {
-                output_ty_name_owned = pprust::ty_to_string(ty);
-                (&*output_ty_name_owned, ty.span)
-            },
-            FunctionRetTy::Default(span) => ("()", *span),
+        let span = match output {
+            FunctionRetTy::Ty(ty) => ty.span,
+            FunctionRetTy::Default(span) => *span,
         };
 
-        // FIXME(cramertj) add lifetimes (see FIXME below) to the name
-        let exist_ty_name = Symbol::intern(&format!("impl Future<Output = {}>", output_ty_name));
         let impl_trait_ty = self.lower_existential_impl_trait(
-            span, fn_def_id, exist_ty_name, |this| {
+            span, fn_def_id, |this| {
             let output_ty = match output {
                 FunctionRetTy::Ty(ty) =>
                     this.lower_ty(ty, ImplTraitContext::Existential(fn_def_id)),

src/libstd/future.rs

@@ -26,7 +26,7 @@ pub use core::future::*;
 /// This function returns a `GenFuture` underneath, but hides it in `impl Trait` to give
 /// better error messages (`impl Future` rather than `GenFuture<[closure.....]>`).
 #[unstable(feature = "gen_future", issue = "50547")]
-pub fn future_from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T::Return> {
+pub fn from_generator<T: Generator<Yield = ()>>(x: T) -> impl Future<Output = T::Return> {
     GenFuture(x)
 }
 
@@ -71,19 +71,22 @@ where
     F: FnOnce() -> R
 {
     let old_cx = TLS_CX.with(|tls_cx| {
-        let old_cx = tls_cx.get();
-        tls_cx.set(NonNull::new(
-                cx as *mut task::Context as *mut () as *mut task::Context<'static>));
-        old_cx
+        tls_cx.replace(NonNull::new(
+            cx
+                as *mut task::Context
+                as *mut ()
+                as *mut task::Context<'static>
+        ))
     });
     let _reset_cx = SetOnDrop(old_cx);
-    let res = f();
-    res
+    f()
 }
 
 #[unstable(feature = "gen_future", issue = "50547")]
 /// Retrieves the thread-local task context used by async/await futures.
 ///
+/// This function acquires exclusive access to the task context.
+///
 /// Panics if no task has been set or if the task context has already been
 /// retrived by a surrounding call to get_task_cx.
 pub fn get_task_cx<F, R>(f: F) -> R
@@ -91,11 +94,9 @@ where
     F: FnOnce(&mut task::Context) -> R
 {
     let cx_ptr = TLS_CX.with(|tls_cx| {
-        let cx_ptr = tls_cx.get();
         // Clear the entry so that nested `with_get_cx` calls
         // will fail or set their own value.
-        tls_cx.set(None);
-        cx_ptr
+        tls_cx.replace(None)
     });
     let _reset_cx = SetOnDrop(cx_ptr);
 
@@ -104,3 +105,12 @@ where
         Please file an issue on https://github.com/rust-lang/rust.");
     unsafe { f(cx_ptr.as_mut()) }
 }
+
+#[unstable(feature = "gen_future", issue = "50547")]
+/// Polls a future in the current thread-local task context.
+pub fn poll_in_task_cx<F>(f: &mut PinMut<F>) -> Poll<F::Output>
+where
+    F: Future
+{
+    get_task_cx(|cx| f.reborrow().poll(cx))
+}

src/libstd/macros.rs

@@ -222,9 +222,7 @@ macro_rules! await {
         let mut pinned = $e;
         let mut pinned = unsafe { $crate::mem::PinMut::new_unchecked(&mut pinned) };
         loop {
-            match $crate::future::get_task_cx(|cx|
-                $crate::future::Future::poll(pinned.reborrow(), cx))
-            {
+            match $crate::future::poll_in_task_cx(&mut pinned) {
                 // FIXME(cramertj) prior to stabilizing await, we have to ensure that this
                 // can't be used to create a generator on stable via `|| await!()`.
                 $crate::task::Poll::Pending => yield,