Auto merge of rust-lang#130633 - eholk:pin-reborrow-self, r=compiler-errors

Add support for reborrowing pinned method receivers

This builds on rust-lang#130526 to add pinned reborrowing for method receivers. This enables the folllowing examples to work:

```rust
#![feature(pin_ergonomics)]
#![allow(incomplete_features)]

use std::pin::Pin;

pub struct Foo;

impl Foo {
    fn foo(self: Pin<&mut Self>) {
    }

    fn baz(self: Pin<&Self>) {
    }
}

pub fn bar(x: Pin<&mut Foo>) {
    x.foo();
    x.foo();

    x.baz(); // Pin<&mut Foo> is downgraded to Pin<&Foo>
}

pub fn baaz(x: Pin<&Foo>) {
    x.baz();
    x.baz();
}
```

This PR includes the original one, which is currently in the commit queue, but the only code changes are in the latest commit (d3c53aa).

rust-lang#130494

r? `@compiler-errors`

Author: bors

Diff for: compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -235,6 +235,23 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                     target,
                 });
             }
+
+            Some(probe::AutorefOrPtrAdjustment::ReborrowPin(mutbl)) => {
+                let region = self.next_region_var(infer::Autoref(self.span));
+
+                target = match target.kind() {
+                    ty::Adt(pin, args) if self.tcx.is_lang_item(pin.did(), hir::LangItem::Pin) => {
+                        let inner_ty = match args[0].expect_ty().kind() {
+                            ty::Ref(_, ty, _) => *ty,
+                            _ => bug!("Expected a reference type for argument to Pin"),
+                        };
+                        Ty::new_pinned_ref(self.tcx, region, inner_ty, mutbl)
+                    }
+                    _ => bug!("Cannot adjust receiver type for reborrowing pin of {target:?}"),
+                };
+
+                adjustments.push(Adjustment { kind: Adjust::ReborrowPin(region, mutbl), target });
+            }
             None => {}
         }
 

Diff for: compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs

@@ -121,16 +121,27 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             mutbl.ref_prefix_str()
                         }
                         Some(probe::AutorefOrPtrAdjustment::ToConstPtr) | None => "",
+                        Some(probe::AutorefOrPtrAdjustment::ReborrowPin(mutbl)) => match mutbl {
+                            hir::Mutability::Mut => "Pin<&mut ",
+                            hir::Mutability::Not => "Pin<&",
+                        },
                     };
                     if let Ok(self_expr) = self.sess().source_map().span_to_snippet(self_expr.span)
                     {
-                        let self_adjusted = if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
+                        let mut self_adjusted =
+                            if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
+                                pick.autoref_or_ptr_adjustment
+                            {
+                                format!("{derefs}{self_expr} as *const _")
+                            } else {
+                                format!("{autoref}{derefs}{self_expr}")
+                            };
+
+                        if let Some(probe::AutorefOrPtrAdjustment::ReborrowPin(_)) =
                             pick.autoref_or_ptr_adjustment
                         {
-                            format!("{derefs}{self_expr} as *const _")
-                        } else {
-                            format!("{autoref}{derefs}{self_expr}")
-                        };
+                            self_adjusted.push('>');
+                        }
 
                         lint.span_suggestion(
                             sp,
@@ -400,6 +411,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let autoref = match pick.autoref_or_ptr_adjustment {
             Some(probe::AutorefOrPtrAdjustment::Autoref { mutbl, .. }) => mutbl.ref_prefix_str(),
             Some(probe::AutorefOrPtrAdjustment::ToConstPtr) | None => "",
+            Some(probe::AutorefOrPtrAdjustment::ReborrowPin(mutbl)) => match mutbl {
+                hir::Mutability::Mut => "Pin<&mut ",
+                hir::Mutability::Not => "Pin<&",
+            },
         };
 
         let (expr_text, precise) = if let Some(expr_text) = expr
@@ -412,14 +427,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ("(..)".to_string(), false)
         };
 
-        let adjusted_text = if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
+        let mut adjusted_text = if let Some(probe::AutorefOrPtrAdjustment::ToConstPtr) =
             pick.autoref_or_ptr_adjustment
         {
             format!("{derefs}{expr_text} as *const _")
         } else {
             format!("{autoref}{derefs}{expr_text}")
         };
 
+        if let Some(probe::AutorefOrPtrAdjustment::ReborrowPin(_)) = pick.autoref_or_ptr_adjustment
+        {
+            adjusted_text.push('>');
+        }
+
         (adjusted_text, precise)
     }
 }

Diff for: compiler/rustc_hir_typeck/src/method/probe.rs

@@ -136,7 +136,7 @@ enum ProbeResult {
 /// `mut`), or it has type `*mut T` and we convert it to `*const T`.
 #[derive(Debug, PartialEq, Copy, Clone)]
 pub(crate) enum AutorefOrPtrAdjustment {
-    /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it.
+    /// Receiver has type `T`, add `&` or `&mut` (if `T` is `mut`), and maybe also "unsize" it.
     /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing.
     Autoref {
         mutbl: hir::Mutability,
@@ -147,13 +147,17 @@ pub(crate) enum AutorefOrPtrAdjustment {
     },
     /// Receiver has type `*mut T`, convert to `*const T`
     ToConstPtr,
+
+    /// Reborrow a `Pin<&mut T>` or `Pin<&T>`.
+    ReborrowPin(hir::Mutability),
 }
 
 impl AutorefOrPtrAdjustment {
     fn get_unsize(&self) -> bool {
         match self {
             AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize,
             AutorefOrPtrAdjustment::ToConstPtr => false,
+            AutorefOrPtrAdjustment::ReborrowPin(_) => false,
         }
     }
 }
@@ -1109,6 +1113,13 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                                 unstable_candidates.as_deref_mut(),
                             )
                         })
+                        .or_else(|| {
+                            self.pick_reborrow_pin_method(
+                                step,
+                                self_ty,
+                                unstable_candidates.as_deref_mut(),
+                            )
+                        })
                     })
             })
     }
@@ -1133,13 +1144,28 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             r.map(|mut pick| {
                 pick.autoderefs = step.autoderefs;
 
-                // Insert a `&*` or `&mut *` if this is a reference type:
-                if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() {
-                    pick.autoderefs += 1;
-                    pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
-                        mutbl,
-                        unsize: pick.autoref_or_ptr_adjustment.is_some_and(|a| a.get_unsize()),
-                    })
+                match *step.self_ty.value.value.kind() {
+                    // Insert a `&*` or `&mut *` if this is a reference type:
+                    ty::Ref(_, _, mutbl) => {
+                        pick.autoderefs += 1;
+                        pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref {
+                            mutbl,
+                            unsize: pick.autoref_or_ptr_adjustment.is_some_and(|a| a.get_unsize()),
+                        })
+                    }
+
+                    ty::Adt(def, args)
+                        if self.tcx.features().pin_ergonomics
+                            && self.tcx.is_lang_item(def.did(), hir::LangItem::Pin) =>
+                    {
+                        // make sure this is a pinned reference (and not a `Pin<Box>` or something)
+                        if let ty::Ref(_, _, mutbl) = args[0].expect_ty().kind() {
+                            pick.autoref_or_ptr_adjustment =
+                                Some(AutorefOrPtrAdjustment::ReborrowPin(*mutbl));
+                        }
+                    }
+
+                    _ => (),
                 }
 
                 pick
@@ -1170,6 +1196,43 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         })
     }
 
+    /// Looks for applicable methods if we reborrow a `Pin<&mut T>` as a `Pin<&T>`.
+    #[instrument(level = "debug", skip(self, step, unstable_candidates))]
+    fn pick_reborrow_pin_method(
+        &self,
+        step: &CandidateStep<'tcx>,
+        self_ty: Ty<'tcx>,
+        unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>,
+    ) -> Option<PickResult<'tcx>> {
+        if !self.tcx.features().pin_ergonomics {
+            return None;
+        }
+
+        // make sure self is a Pin<&mut T>
+        let inner_ty = match self_ty.kind() {
+            ty::Adt(def, args) if self.tcx.is_lang_item(def.did(), hir::LangItem::Pin) => {
+                match args[0].expect_ty().kind() {
+                    ty::Ref(_, ty, hir::Mutability::Mut) => *ty,
+                    _ => {
+                        return None;
+                    }
+                }
+            }
+            _ => return None,
+        };
+
+        let region = self.tcx.lifetimes.re_erased;
+        let autopin_ty = Ty::new_pinned_ref(self.tcx, region, inner_ty, hir::Mutability::Not);
+        self.pick_method(autopin_ty, unstable_candidates).map(|r| {
+            r.map(|mut pick| {
+                pick.autoderefs = step.autoderefs;
+                pick.autoref_or_ptr_adjustment =
+                    Some(AutorefOrPtrAdjustment::ReborrowPin(hir::Mutability::Not));
+                pick
+            })
+        })
+    }
+
     /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a
     /// special case for this is because going from `*mut T` to `*const T` with autoderefs and
     /// autorefs would require dereferencing the pointer, which is not safe.

Diff for: compiler/rustc_middle/src/ty/sty.rs

@@ -584,6 +584,16 @@ impl<'tcx> Ty<'tcx> {
         Ty::new_ref(tcx, r, ty, hir::Mutability::Not)
     }
 
+    pub fn new_pinned_ref(
+        tcx: TyCtxt<'tcx>,
+        r: Region<'tcx>,
+        ty: Ty<'tcx>,
+        mutbl: ty::Mutability,
+    ) -> Ty<'tcx> {
+        let pin = tcx.adt_def(tcx.require_lang_item(LangItem::Pin, None));
+        Ty::new_adt(tcx, pin, tcx.mk_args(&[Ty::new_ref(tcx, r, ty, mutbl).into()]))
+    }
+
     #[inline]
     pub fn new_ptr(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, mutbl: ty::Mutability) -> Ty<'tcx> {
         Ty::new(tcx, ty::RawPtr(ty, mutbl))

Diff for: tests/ui/async-await/pin-reborrow-self.rs

@@ -1,24 +1,33 @@
 //@ check-pass
-//@ignore-test
-
-// Currently ignored due to self reborrowing not being implemented for Pin
 
 #![feature(pin_ergonomics)]
 #![allow(incomplete_features)]
 
 use std::pin::Pin;
 
-struct Foo;
+pub struct Foo;
 
 impl Foo {
     fn foo(self: Pin<&mut Self>) {
     }
+
+    fn baz(self: Pin<&Self>) {
+    }
 }
 
-fn bar(x: Pin<&mut Foo>) {
+pub fn bar(x: Pin<&mut Foo>) {
     x.foo();
     x.foo(); // for this to work we need to automatically reborrow,
              // as if the user had written `x.as_mut().foo()`.
+
+    Foo::baz(x);
+
+    x.baz();
+}
+
+pub fn baaz(x: Pin<&Foo>) {
+    x.baz();
+    x.baz();
 }
 
 fn main() {}

Diff for: tests/ui/feature-gates/feature-gate-pin_ergonomics.rs

@@ -4,6 +4,11 @@ use std::pin::Pin;
 
 struct Foo;
 
+impl Foo {
+    fn foo(self: Pin<&mut Self>) {
+    }
+}
+
 fn foo(_: Pin<&mut Foo>) {
 }
 
@@ -12,4 +17,9 @@ fn bar(mut x: Pin<&mut Foo>) {
     foo(x); //~ ERROR use of moved value: `x`
 }
 
+fn baz(mut x: Pin<&mut Foo>) {
+    x.foo();
+    x.foo(); //~ ERROR use of moved value: `x`
+}
+
 fn main() {}

Diff for: tests/ui/feature-gates/feature-gate-pin_ergonomics.stderr

@@ -1,5 +1,5 @@
 error[E0382]: use of moved value: `x`
-  --> $DIR/feature-gate-pin_ergonomics.rs:12:9
+  --> $DIR/feature-gate-pin_ergonomics.rs:17:9
    |
 LL | fn bar(mut x: Pin<&mut Foo>) {
    |        ----- move occurs because `x` has type `Pin<&mut Foo>`, which does not implement the `Copy` trait
@@ -9,13 +9,33 @@ LL |     foo(x);
    |         ^ value used here after move
    |
 note: consider changing this parameter type in function `foo` to borrow instead if owning the value isn't necessary
-  --> $DIR/feature-gate-pin_ergonomics.rs:7:11
+  --> $DIR/feature-gate-pin_ergonomics.rs:12:11
    |
 LL | fn foo(_: Pin<&mut Foo>) {
    |    ---    ^^^^^^^^^^^^^ this parameter takes ownership of the value
    |    |
    |    in this function
 
-error: aborting due to 1 previous error
+error[E0382]: use of moved value: `x`
+  --> $DIR/feature-gate-pin_ergonomics.rs:22:5
+   |
+LL | fn baz(mut x: Pin<&mut Foo>) {
+   |        ----- move occurs because `x` has type `Pin<&mut Foo>`, which does not implement the `Copy` trait
+LL |     x.foo();
+   |       ----- `x` moved due to this method call
+LL |     x.foo();
+   |     ^ value used here after move
+   |
+note: `Foo::foo` takes ownership of the receiver `self`, which moves `x`
+  --> $DIR/feature-gate-pin_ergonomics.rs:8:12
+   |
+LL |     fn foo(self: Pin<&mut Self>) {
+   |            ^^^^
+help: consider reborrowing the `Pin` instead of moving it
+   |
+LL |     x.as_mut().foo();
+   |      +++++++++
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0382`.