Rollup merge of #110259 - ndrewxie:issue-109964-fix-gitstuff, r=cjgillot

Added diagnostic for pin! macro in addition to Box::pin if Unpin isn't implemented

I made a PR earlier, but accidentally renamed a branch and that deleted the PR... sorry for the duplicate

Currently, if an operation on `Pin<T>` is performed that requires `T` to implement `Unpin`, the diagnostic suggestion is to use `Box::pin` ("note: consider using `Box::pin`").

This PR suggests pin! as well, as that's another valid way of pinning a value, and avoids a heap allocation. Appropriate diagnostic suggestions were included to highlight the difference in semantics (local pinning for pin! vs non-local for Box::pin).

Fixes #109964

library/core/src/marker.rs

@@ -823,7 +823,7 @@ unsafe impl<T: ?Sized> Freeze for &mut T {}
 /// [`pin` module]: crate::pin
 #[stable(feature = "pin", since = "1.33.0")]
 #[rustc_on_unimplemented(
-    note = "consider using `Box::pin`",
+    note = "consider using the `pin!` macro\nconsider using `Box::pin` if you need to access the pinned value outside of the current scope",
     message = "`{Self}` cannot be unpinned"
 )]
 #[lang = "unpin"]

tests/ui/async-await/pin-needed-to-poll-2.stderr

@@ -6,7 +6,8 @@ LL |         Pin::new(&mut self.sleep).poll(cx)
    |         |
    |         required by a bound introduced by this call
    |
-   = note: consider using `Box::pin`
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
 note: required because it appears within the type `Sleep`
   --> $DIR/pin-needed-to-poll-2.rs:8:8
    |

tests/ui/generator/static-not-unpin.stderr

@@ -6,7 +6,8 @@ LL |     assert_unpin(generator);
    |     |
    |     required by a bound introduced by this call
    |
-   = note: consider using `Box::pin`
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
 note: required by a bound in `assert_unpin`
   --> $DIR/static-not-unpin.rs:7:20
    |

tests/ui/suggestions/expected-boxed-future-isnt-pinned.stderr

@@ -50,7 +50,8 @@ LL |     Pin::new(x)
    |     |
    |     required by a bound introduced by this call
    |
-   = note: consider using `Box::pin`
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
 note: required by a bound in `Pin::<P>::new`
   --> $SRC_DIR/core/src/pin.rs:LL:COL
 
@@ -62,7 +63,8 @@ LL |     Pin::new(Box::new(x))
    |     |
    |     required by a bound introduced by this call
    |
-   = note: consider using `Box::pin`
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
 note: required by a bound in `Pin::<P>::new`
   --> $SRC_DIR/core/src/pin.rs:LL:COL
 

tests/ui/suggestions/issue-84973-blacklist.stderr

@@ -39,7 +39,8 @@ LL |     f_unpin(static || { yield; });
    |     |
    |     required by a bound introduced by this call
    |
-   = note: consider using `Box::pin`
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
 note: required by a bound in `f_unpin`
   --> $DIR/issue-84973-blacklist.rs:8:15
    |

tests/ui/suggestions/suggest-pin-macro.rs

@@ -0,0 +1,23 @@
+use std::pin::Pin;
+use std::marker::PhantomPinned;
+
+#[derive(Debug)]
+struct Test {
+    _marker: PhantomPinned,
+}
+impl Test {
+    fn new() -> Self {
+        Test {
+            _marker: PhantomPinned, // This makes our type `!Unpin`
+        }
+    }
+}
+
+fn dummy(_: &mut Test) {}
+
+pub fn main() {
+    let mut test1 = Test::new();
+    let mut test1 = unsafe { Pin::new_unchecked(&mut test1) };
+
+    dummy(test1.get_mut()); //~ ERROR E0277
+}

tests/ui/suggestions/suggest-pin-macro.stderr

@@ -0,0 +1,19 @@
+error[E0277]: `PhantomPinned` cannot be unpinned
+  --> $DIR/suggest-pin-macro.rs:22:17
+   |
+LL |     dummy(test1.get_mut());
+   |                 ^^^^^^^ within `Test`, the trait `Unpin` is not implemented for `PhantomPinned`
+   |
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
+note: required because it appears within the type `Test`
+  --> $DIR/suggest-pin-macro.rs:5:8
+   |
+LL | struct Test {
+   |        ^^^^
+note: required by a bound in `Pin::<&'a mut T>::get_mut`
+  --> $SRC_DIR/core/src/pin.rs:LL:COL
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/typeck/issue-90164.stderr

@@ -6,7 +6,8 @@ LL |     copy(r, w);
    |     |
    |     required by a bound introduced by this call
    |
-   = note: consider using `Box::pin`
+   = note: consider using the `pin!` macro
+           consider using `Box::pin` if you need to access the pinned value outside of the current scope
 note: required by a bound in `copy`
   --> $DIR/issue-90164.rs:1:12
    |