Suggest as_mut when Pin<T> is used after move

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -235,11 +235,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                                 );
                             }
                         }
-                        FnSelfUseKind::Normal {
-                            self_arg,
-                            implicit_into_iter,
-                            is_option_or_result,
-                        } => {
+                        FnSelfUseKind::Normal { self_arg, implicit_into_iter, self_name } => {
                             if implicit_into_iter {
                                 err.span_label(
                                     fn_call_span,
@@ -287,14 +283,27 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                                     ),
                                 );
                             }
-                            if is_option_or_result && maybe_reinitialized_locations.is_empty() {
-                                err.span_suggestion_verbose(
-                                    fn_call_span.shrink_to_lo(),
-                                    "consider calling `.as_ref()` to borrow the type's contents",
-                                    "as_ref().".to_string(),
-                                    Applicability::MachineApplicable,
-                                );
+
+                            let borrow_method = match self_name {
+                                Some(sym::Option | sym::Result) => Some("as_ref"),
+                                Some(sym::Pin) => Some("as_mut"),
+                                _ => None,
+                            };
+
+                            if let Some(borrow_method) = borrow_method {
+                                if maybe_reinitialized_locations.is_empty() {
+                                    err.span_suggestion_verbose(
+                                        fn_call_span.shrink_to_lo(),
+                                        &format!(
+                                            "consider calling `.{}()` to borrow the type's contents",
+                                            borrow_method,
+                                        ),
+                                        format!("{}().", borrow_method),
+                                        Applicability::MachineApplicable,
+                                    );
+                                }
                             }
+
                             // Avoid pointing to the same function in multiple different
                             // error messages.
                             if span != DUMMY_SP && self.fn_self_span_reported.insert(self_arg.span)

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -13,7 +13,11 @@ use rustc_middle::mir::{
 use rustc_middle::ty::print::Print;
 use rustc_middle::ty::{self, DefIdTree, Instance, Ty, TyCtxt};
 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
-use rustc_span::{hygiene::DesugaringKind, symbol::sym, Span};
+use rustc_span::{
+    hygiene::DesugaringKind,
+    symbol::{sym, Symbol},
+    Span,
+};
 use rustc_target::abi::VariantIdx;
 
 use super::borrow_set::BorrowData;
@@ -577,9 +581,8 @@ pub(super) enum FnSelfUseKind<'tcx> {
     Normal {
         self_arg: Ident,
         implicit_into_iter: bool,
-        /// Whether the self type of the method call has an `.as_ref()` method.
         /// Used for better diagnostics.
-        is_option_or_result: bool,
+        self_name: Option<Symbol>,
     },
     /// A call to `FnOnce::call_once`, desugared from `my_closure(a, b, c)`
     FnOnceCall,
@@ -948,18 +951,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             let kind = kind.unwrap_or_else(|| {
                 // This isn't a 'special' use of `self`
                 debug!("move_spans: method_did={:?}, fn_call_span={:?}", method_did, fn_call_span);
+
                 let implicit_into_iter = Some(method_did) == tcx.lang_items().into_iter_fn()
                     && fn_call_span.desugaring_kind() == Some(DesugaringKind::ForLoop);
-                let parent_self_ty = parent
-                    .filter(|did| tcx.def_kind(*did) == rustc_hir::def::DefKind::Impl)
-                    .and_then(|did| match tcx.type_of(did).kind() {
-                        ty::Adt(def, ..) => Some(def.did),
-                        _ => None,
-                    });
-                let is_option_or_result = parent_self_ty.map_or(false, |def_id| {
-                    matches!(tcx.get_diagnostic_name(def_id), Some(sym::Option | sym::Result))
-                });
-                FnSelfUseKind::Normal { self_arg, implicit_into_iter, is_option_or_result }
+
+                let self_name = self.body.local_decls[target_temp]
+                    .ty
+                    .ty_adt_def()
+                    .and_then(|def| tcx.get_diagnostic_name(def.did));
+
+                FnSelfUseKind::Normal { self_arg, implicit_into_iter, self_name }
             });
 
             return FnSelfUse {

library/core/src/pin.rs

@@ -402,6 +402,7 @@ use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Receiver};
 // See <https://internals.rust-lang.org/t/unsoundness-in-pin/11311> for more details.
 #[stable(feature = "pin", since = "1.33.0")]
 #[lang = "pin"]
+#[rustc_diagnostic_item = "Pin"]
 #[fundamental]
 #[repr(transparent)]
 #[derive(Copy, Clone)]

src/test/ui/suggestions/pin-content-move.rs

@@ -0,0 +1,23 @@
+use std::pin::Pin;
+
+struct Foo;
+
+impl Foo {
+    fn foo(self: Pin<&mut Self>) {}
+}
+
+fn main() {
+    let mut foo = Foo;
+    let foo = Pin::new(&mut foo);
+    foo.foo();
+    //~^ HELP consider calling `.as_mut()` to borrow the type's contents
+    foo.foo();
+    //~^ ERROR use of moved value
+
+    let mut x = 1;
+    let mut x = Pin::new(&mut x);
+    x.get_mut();
+    //~^ HELP consider calling `.as_mut()` to borrow the type's contents
+    x.get_mut();
+    //~^ ERROR use of moved value
+}

src/test/ui/suggestions/pin-content-move.stderr

@@ -0,0 +1,45 @@
+error[E0382]: use of moved value: `foo`
+  --> $DIR/pin-content-move.rs:14:5
+   |
+LL |     let foo = Pin::new(&mut foo);
+   |         --- move occurs because `foo` has type `Pin<&mut Foo>`, which does not implement the `Copy` trait
+LL |     foo.foo();
+   |         ----- `foo` moved due to this method call
+LL |
+LL |     foo.foo();
+   |     ^^^ value used here after move
+   |
+note: this function takes ownership of the receiver `self`, which moves `foo`
+  --> $DIR/pin-content-move.rs:6:12
+   |
+LL |     fn foo(self: Pin<&mut Self>) {}
+   |            ^^^^
+help: consider calling `.as_mut()` to borrow the type's contents
+   |
+LL |     foo.as_mut().foo();
+   |         +++++++++
+
+error[E0382]: use of moved value: `x`
+  --> $DIR/pin-content-move.rs:21:5
+   |
+LL |     let mut x = Pin::new(&mut x);
+   |         ----- move occurs because `x` has type `Pin<&mut i32>`, which does not implement the `Copy` trait
+LL |     x.get_mut();
+   |       --------- `x` moved due to this method call
+LL |
+LL |     x.get_mut();
+   |     ^ value used here after move
+   |
+note: this function takes ownership of the receiver `self`, which moves `x`
+  --> $SRC_DIR/core/src/pin.rs:LL:COL
+   |
+LL |     pub const fn get_mut(self) -> &'a mut T
+   |                          ^^^^
+help: consider calling `.as_mut()` to borrow the type's contents
+   |
+LL |     x.as_mut().get_mut();
+   |       +++++++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0382`.