Mark static generators as !Unpin

Author: Nemo157

src/libcore/marker.rs

@@ -627,6 +627,7 @@ unsafe impl<T: ?Sized> Freeze for &mut T {}
 /// [`Pin`]: ../pin/struct.Pin.html
 /// [`pin module`]: ../../std/pin/index.html
 #[stable(feature = "pin", since = "1.33.0")]
+#[cfg_attr(not(stage0), lang = "unpin")]
 pub auto trait Unpin {}
 
 /// A marker type which does not implement `Unpin`.

src/librustc/middle/lang_items.rs

@@ -299,6 +299,7 @@ language_item_table! {
 
     GeneratorStateLangItem,      "generator_state",    gen_state,               Target::Enum;
     GeneratorTraitLangItem,      "generator",          gen_trait,               Target::Trait;
+    UnpinTraitLangItem,          "unpin",              unpin_trait,             Target::Trait;
 
     EqTraitLangItem,             "eq",                 eq_trait,                Target::Trait;
     PartialOrdTraitLangItem,     "partial_ord",        partial_ord_trait,       Target::Trait;

src/librustc/traits/select.rs

@@ -2017,6 +2017,12 @@ 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)
+                    if self.tcx().lang_items().unpin_trait() == Some(def_id) =>
+                {
+                    // Immovable generators are never `Unpin`, so suppress the
+                    // normal auto-impl candidate for it.
+                }
                 _ => candidates.vec.push(AutoImplCandidate(def_id.clone())),
             }
         }

src/test/ui/generator/static-not-unpin.rs

@@ -0,0 +1,13 @@
+#![feature(generators)]
+
+use std::marker::Unpin;
+
+fn assert_unpin<T: Unpin>(_: T) {
+}
+
+fn main() {
+    let mut generator = static || {
+        yield;
+    };
+    assert_unpin(generator); //~ ERROR std::marker::Unpin` is not satisfied
+}

src/test/ui/generator/static-not-unpin.stderr

@@ -0,0 +1,15 @@
+error[E0277]: the trait bound `[static generator@$DIR/static-not-unpin.rs:9:25: 11:6 _]: std::marker::Unpin` is not satisfied
+  --> $DIR/static-not-unpin.rs:12:5
+   |
+LL |     assert_unpin(generator); //~ ERROR std::marker::Unpin` is not satisfied
+   |     ^^^^^^^^^^^^ the trait `std::marker::Unpin` is not implemented for `[static generator@$DIR/static-not-unpin.rs:9:25: 11:6 _]`
+   |
+note: required by `assert_unpin`
+  --> $DIR/static-not-unpin.rs:5:1
+   |
+LL | fn assert_unpin<T: Unpin>(_: T) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.