Mark non-static generators as always Unpin

Author: Nemo157

src/librustc/traits/select.rs

@@ -2017,12 +2017,24 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                     // the auto impl might apply, we don't know
                     candidates.ambiguous = true;
                 }
-                ty::Generator(_, _, hir::GeneratorMovability::Static)
+                ty::Generator(_, _, movability)
                     if self.tcx().lang_items().unpin_trait() == Some(def_id) =>
                 {
-                    // Immovable generators are never `Unpin`, so suppress the
-                    // normal auto-impl candidate for it.
+                    match movability {
+                        hir::GeneratorMovability::Static => {
+                            // Immovable generators are never `Unpin`, so
+                            // suppress the normal auto-impl candidate for it.
+                        }
+                        hir::GeneratorMovability::Movable => {
+                            // Movable generators are always `Unpin`, so add an
+                            // unconditional builtin candidate.
+                            candidates.vec.push(BuiltinCandidate {
+                                has_nested: false,
+                            });
+                        }
+                    }
                 }
+
                 _ => candidates.vec.push(AutoImplCandidate(def_id.clone())),
             }
         }

src/test/run-pass/generator/auxiliary/xcrate.rs

@@ -11,7 +11,7 @@ pub fn foo() -> impl Generator<Yield = (), Return = ()> {
     }
 }
 
-pub fn bar<T: Unpin + 'static>(t: T) -> Box<Generator<Yield = T, Return = ()> + Unpin> {
+pub fn bar<T: 'static>(t: T) -> Box<Generator<Yield = T, Return = ()> + Unpin> {
     Box::new(|| {
         yield t;
     })

src/test/run-pass/generator/non-static-is-unpin.rs

@@ -0,0 +1,18 @@
+// run-pass
+
+#![feature(generators, generator_trait)]
+
+use std::marker::{PhantomPinned, Unpin};
+
+fn assert_unpin<G: Unpin>(_: G) {
+}
+
+fn main() {
+    // Even though this generator holds a `PhantomPinned` in its environment, it
+    // remains `Unpin`.
+    assert_unpin(|| {
+        let pinned = PhantomPinned;
+        yield;
+        drop(pinned);
+    });
+}