Skip long-lived pin facts for Unpin places

Author: P8L1

compiler/rustc_borrowck/src/dataflow.rs

@@ -760,7 +760,10 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Pins<'_, 'tcx> {
                 if let mir::Rvalue::Ref(_, mir::BorrowKind::Pinned(_, kind), place) = rhs
                     && matches!(*kind, mir::PinBorrowKind::Persistent)
                 {
-                    self.gen_pins_on_place(state, *place);
+                    let place_ty = place.ty(self.body, self.tcx).ty;
+                    if !place_ty.is_unpin(self.tcx, self.body.typing_env(self.tcx)) {
+                        self.gen_pins_on_place(state, *place);
+                    }
                 }
             }
 

compiler/rustc_borrowck/src/lib.rs

@@ -1274,17 +1274,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
         &self,
         state: &'s BorrowckDomain,
     ) -> Option<&'s MixedBitSet<BorrowIndex>> {
-        // FIXME(pin_ergonomics): borrowck behaviors depend on a safe trait
-        // which should not contain any safety invariants.
-        // if place
-        //     .ty(self.body, self.infcx.tcx)
-        //     .ty
-        //     .is_unpin(self.infcx.tcx, self.body.typing_env(self.infcx.tcx))
-        // {
-        //     None
-        // } else {
         Some(&state.pinned_borrows)
-        // }
     }
 
     #[instrument(level = "debug", skip(self, state))]

tests/ui/pin-ergonomics/borrow-pinned-projection.rs

@@ -6,10 +6,11 @@
 // of `pair.0` until reassignment.
 
 #[pin_v2]
-struct Foo;
+#[derive(Default)]
+struct Foo(std::marker::PhantomPinned);
 
 fn mutable_borrow_of_pinned_projection() {
-    let mut pair = (Foo, Foo);
+    let mut pair = (Foo::default(), Foo::default());
 
     {
         let _pin = &pin mut pair.0;
@@ -21,7 +22,7 @@ fn mutable_borrow_of_pinned_projection() {
 }
 
 fn move_of_pinned_projection() {
-    let mut pair = (Foo, Foo);
+    let mut pair = (Foo::default(), Foo::default());
 
     {
         let _pin = &pin mut pair.0;
@@ -32,4 +33,28 @@ fn move_of_pinned_projection() {
     //~^ ERROR cannot move out of `pair.0` because it is pinned
 }
 
+#[pin_v2]
+struct ContainsUnpinField {
+    field: String,
+    _pin: std::marker::PhantomPinned,
+}
+
+fn pinned_parent_still_blocks_unpin_field_move(mut value: ContainsUnpinField) {
+    {
+        let _ = &pin mut value;
+    }
+
+    let _moved = value.field;
+    //~^ ERROR cannot move out of `value.field` because it is pinned
+}
+
+fn pinned_parent_still_blocks_unpin_field_mut_borrow(mut value: ContainsUnpinField) {
+    {
+        let _ = &pin mut value;
+    }
+
+    let _ = &mut value.field;
+    //~^ ERROR cannot borrow `value.field` as mutable because it is pinned
+}
+
 fn main() {}

tests/ui/pin-ergonomics/borrow-pinned-projection.stderr

@@ -1,5 +1,5 @@
 error: cannot borrow `pair.0` as mutable because it is pinned
-  --> $DIR/borrow-pinned-projection.rs:19:19
+  --> $DIR/borrow-pinned-projection.rs:20:19
    |
 LL |         let _pin = &pin mut pair.0;
    |                    --------------- pin of `pair.0` occurs here
@@ -8,13 +8,31 @@ LL |     let _borrow = &mut pair.0;
    |                   ^^^^^^^^^^^ borrow of `pair.0` as mutable occurs here
 
 error: cannot move out of `pair.0` because it is pinned
-  --> $DIR/borrow-pinned-projection.rs:31:18
+  --> $DIR/borrow-pinned-projection.rs:32:18
    |
 LL |         let _pin = &pin mut pair.0;
    |                    --------------- pin of `pair.0` occurs here
 ...
 LL |     let _moved = pair.0;
    |                  ^^^^^^ move out of `pair.0` occurs here
 
-error: aborting due to 2 previous errors
+error: cannot move out of `value.field` because it is pinned
+  --> $DIR/borrow-pinned-projection.rs:47:18
+   |
+LL |         let _ = &pin mut value;
+   |                 -------------- pin of `value` occurs here
+...
+LL |     let _moved = value.field;
+   |                  ^^^^^^^^^^^ move out of `value.field` occurs here
+
+error: cannot borrow `value.field` as mutable because it is pinned
+  --> $DIR/borrow-pinned-projection.rs:56:13
+   |
+LL |         let _ = &pin mut value;
+   |                 -------------- pin of `value` occurs here
+...
+LL |     let _ = &mut value.field;
+   |             ^^^^^^^^^^^^^^^^ borrow of `value.field` as mutable occurs here
+
+error: aborting due to 4 previous errors
 

tests/ui/pin-ergonomics/borrow-unpin.rs

@@ -2,8 +2,8 @@
 #![feature(pin_ergonomics)]
 #![allow(dead_code, incomplete_features)]
 
-// This test ensures that the place cannot be mutably borrowed or moved after pinned
-// no matter if `place` is `Unpin` or not.
+// This test ensures `!Unpin` places cannot be mutably borrowed or moved after pinning.
+// `Unpin` places still obey ordinary borrow rules, but expired `&pin` borrows do not pin.
 
 use std::marker::PhantomPinned;
 use std::pin::Pin;
@@ -27,7 +27,7 @@ fn foo_move(_: Foo) {}
 fn immutable_pin_mut_then_move() {
     let mut foo = Foo::default();
     foo_pin_mut(&pin mut foo); // ok
-    foo_move(foo); //~ ERROR cannot move out of `foo` because it is pinned
+    foo_move(foo); //[pinned]~ ERROR cannot move out of `foo` because it is pinned
 
     let mut foo = Foo::default();
     let x = &pin mut foo;
@@ -38,7 +38,7 @@ fn immutable_pin_mut_then_move() {
 fn pin_mut_then_move() {
     let mut foo = Foo::default();
     foo_pin_mut(&pin mut foo); // ok
-    foo_move(foo); //~ ERROR cannot move out of `foo` because it is pinned
+    foo_move(foo); //[pinned]~ ERROR cannot move out of `foo` because it is pinned
 
     let mut foo = Foo::default();
     let x = &pin mut foo; // ok
@@ -49,7 +49,7 @@ fn pin_mut_then_move() {
 fn pin_ref_then_move() {
     let foo = Foo::default();
     foo_pin_ref(&pin const foo); // ok
-    foo_move(foo); //~ ERROR cannot move out of `foo` because it is pinned
+    foo_move(foo); //[pinned]~ ERROR cannot move out of `foo` because it is pinned
 
     let foo = Foo::default();
     let x = &pin const foo; // ok

tests/ui/pin-ergonomics/borrow-unpin.unpin.stderr

@@ -1,11 +1,3 @@
-error: cannot move out of `foo` because it is pinned
-  --> $DIR/borrow-unpin.rs:30:14
-   |
-LL |     foo_pin_mut(&pin mut foo); // ok
-   |                 ------------ pin of `foo` occurs here
-LL |     foo_move(foo);
-   |              ^^^ move out of `foo` occurs here
-
 error[E0505]: cannot move out of `foo` because it is borrowed
   --> $DIR/borrow-unpin.rs:34:14
    |
@@ -27,14 +19,6 @@ LL | struct Foo;
 LL |     let x = &pin mut foo;
    |                      --- you could clone this value
 
-error: cannot move out of `foo` because it is pinned
-  --> $DIR/borrow-unpin.rs:41:14
-   |
-LL |     foo_pin_mut(&pin mut foo); // ok
-   |                 ------------ pin of `foo` occurs here
-LL |     foo_move(foo);
-   |              ^^^ move out of `foo` occurs here
-
 error[E0505]: cannot move out of `foo` because it is borrowed
   --> $DIR/borrow-unpin.rs:45:14
    |
@@ -56,14 +40,6 @@ LL | struct Foo;
 LL |     let x = &pin mut foo; // ok
    |                      --- you could clone this value
 
-error: cannot move out of `foo` because it is pinned
-  --> $DIR/borrow-unpin.rs:52:14
-   |
-LL |     foo_pin_ref(&pin const foo); // ok
-   |                 -------------- pin of `foo` occurs here
-LL |     foo_move(foo);
-   |              ^^^ move out of `foo` occurs here
-
 error[E0505]: cannot move out of `foo` because it is borrowed
   --> $DIR/borrow-unpin.rs:56:14
    |
@@ -125,7 +101,7 @@ LL |     foo_pin_ref(&pin const foo);
 LL |     foo_pin_mut(x);
    |                 - mutable borrow later used here
 
-error: aborting due to 10 previous errors
+error: aborting due to 7 previous errors
 
 Some errors have detailed explanations: E0499, E0502, E0505.
 For more information about an error, try `rustc --explain E0499`.

tests/ui/pin-ergonomics/borrow.rs

@@ -4,22 +4,24 @@
 // Makes sure we can handle `&pin mut place` and `&pin const place` as sugar for
 // `std::pin::pin!(place)` and `Pin::new(&place)`.
 
+use std::marker::PhantomPinned;
 use std::pin::Pin;
 
 #[pin_v2]
-struct Foo;
+#[derive(Default)]
+struct Foo(PhantomPinned);
 
 fn foo_pin_mut(_: Pin<&mut Foo>) {}
 
 fn foo_pin_ref(_: Pin<&Foo>) {}
 
 fn bar() {
-    let mut x: Pin<&mut _> = &pin mut Foo;
+    let mut x: Pin<&mut _> = &pin mut Foo::default();
     foo_pin_mut(x.as_mut());
     foo_pin_mut(x.as_mut());
     foo_pin_ref(x);
 
-    let x: Pin<&_> = &pin const Foo;
+    let x: Pin<&_> = &pin const Foo::default();
 
     foo_pin_ref(x);
     foo_pin_ref(x);
@@ -32,7 +34,7 @@ fn baz(mut x: Foo, mut y: Foo) {
     let _x = &mut x; //~ ERROR cannot borrow `x` as mutable because it is pinned
     let _x = x; //~ ERROR cannot move out of `x` because it is pinned
 
-    x = Foo;
+    x = Foo::default();
     let _x = &mut x; // ok
 
     {

tests/ui/pin-ergonomics/borrow.stderr

@@ -1,5 +1,5 @@
 error: cannot borrow `x` as mutable because it is pinned
-  --> $DIR/borrow.rs:32:14
+  --> $DIR/borrow.rs:34:14
    |
 LL |         let _x = &pin mut x;
    |                  ---------- pin of `x` occurs here
@@ -8,7 +8,7 @@ LL |     let _x = &mut x;
    |              ^^^^^^ borrow of `x` as mutable occurs here
 
 error: cannot move out of `x` because it is pinned
-  --> $DIR/borrow.rs:33:14
+  --> $DIR/borrow.rs:35:14
    |
 LL |         let _x = &pin mut x;
    |                  ---------- pin of `x` occurs here
@@ -17,7 +17,7 @@ LL |     let _x = x;
    |              ^ move out of `x` occurs here
 
 error: cannot borrow `y` as mutable because it is pinned
-  --> $DIR/borrow.rs:41:14
+  --> $DIR/borrow.rs:43:14
    |
 LL |         let _y = &pin const y;
    |                  ------------ pin of `y` occurs here
@@ -26,7 +26,7 @@ LL |     let _y = &mut y;
    |              ^^^^^^ borrow of `y` as mutable occurs here
 
 error: cannot move out of `y` because it is pinned
-  --> $DIR/borrow.rs:42:14
+  --> $DIR/borrow.rs:44:14
    |
 LL |         let _y = &pin const y;
    |                  ------------ pin of `y` occurs here

tests/ui/pin-ergonomics/direct-borrow-requires-pin-v2.rs

@@ -80,4 +80,28 @@ fn direct_pin_mut_drop_generic(mut input: DropGenericAdt<NotUnpin>) {
     //~^ ERROR cannot directly pin a type that is not structurally pinnable
 }
 
+fn direct_pin_mut_unpin_then_mut_borrow_and_move() {
+    let mut value = UnpinAdt;
+    {
+        let _ = &pin mut value;
+    }
+    let _ = &mut value;
+    let _ = value;
+}
+
+fn direct_pin_const_unpin_then_move() {
+    let value = UnpinAdt;
+    {
+        let _ = &pin const value;
+    }
+    let _ = value;
+}
+
+fn direct_pin_mut_generic_unpin_bound_then_move<T: Unpin>(mut value: T) {
+    {
+        let _ = &pin mut value;
+    }
+    let _ = value;
+}
+
 fn main() {}