Implement pinned borrows, part of pin_ergonomics

frank-king · frank-king · commit e627f88f88de · 2025-06-15T10:21:29.000+08:00
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
@@ -898,6 +898,10 @@ pub enum BorrowKind {
     /// The resulting type is either `*const T` or `*mut T`
     /// where `T = typeof($expr)`.
     Raw,
+    /// A pinned borrow, `&pin const $expr` or `&pin mut $expr`.
+    /// The resulting type is either `Pin<&'a T>` or `Pin<&'a mut T>`
+    /// where `T = typeof($expr)` and `'a` is some lifetime.
+    Pin,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Encodable, Decodable, HashStable_Generic)]
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
@@ -357,6 +357,10 @@ impl<'a> State<'a> {
                 self.word_nbsp("raw");
                 self.print_mutability(mutability, true);
             }
+            ast::BorrowKind::Pin => {
+                self.word_nbsp("pin");
+                self.print_mutability(mutability, true);
+            }
         }
         self.print_expr_cond_paren(
             expr,
diff --git a/compiler/rustc_const_eval/src/check_consts/ops.rs b/compiler/rustc_const_eval/src/check_consts/ops.rs
@@ -616,11 +616,13 @@ impl<'tcx> NonConstOp<'tcx> for EscapingMutBorrow {
                 kind: ccx.const_kind(),
                 teach: ccx.tcx.sess.teach(E0764),
             }),
-            hir::BorrowKind::Ref => ccx.dcx().create_err(errors::MutableRefEscaping {
-                span,
-                kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(E0764),
-            }),
+            hir::BorrowKind::Ref | hir::BorrowKind::Pin => {
+                ccx.dcx().create_err(errors::MutableRefEscaping {
+                    span,
+                    kind: ccx.const_kind(),
+                    teach: ccx.tcx.sess.teach(E0764),
+                })
+            }
         }
     }
 }
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
@@ -1339,6 +1339,10 @@ impl<'a> State<'a> {
                 self.word_nbsp("raw");
                 self.print_mutability(mutability, true);
             }
+            hir::BorrowKind::Pin => {
+                self.word_nbsp("pin");
+                self.print_mutability(mutability, true);
+            }
         }
         self.print_expr_cond_paren(expr, expr.precedence() < ExprPrecedence::Prefix);
     }
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
@@ -664,7 +664,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.check_named_place_expr(oprnd);
                 Ty::new_ptr(self.tcx, ty, mutbl)
             }
-            hir::BorrowKind::Ref => {
+            hir::BorrowKind::Ref | hir::BorrowKind::Pin => {
                 // Note: at this point, we cannot say what the best lifetime
                 // is to use for resulting pointer. We want to use the
                 // shortest lifetime possible so as to avoid spurious borrowck
@@ -680,7 +680,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // whose address was taken can actually be made to live as long
                 // as it needs to live.
                 let region = self.next_region_var(infer::BorrowRegion(expr.span));
-                Ty::new_ref(self.tcx, region, ty, mutbl)
+                match kind {
+                    hir::BorrowKind::Ref => Ty::new_ref(self.tcx, region, ty, mutbl),
+                    hir::BorrowKind::Pin => Ty::new_pinned_ref(self.tcx, region, ty, mutbl),
+                    _ => unreachable!(),
+                }
             }
         }
     }
diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs
@@ -479,6 +479,31 @@ impl<'tcx> ThirBuildCx<'tcx> {
                 ExprKind::RawBorrow { mutability, arg: self.mirror_expr(arg) }
             }
 
+            // Make `&pin mut $expr` and `&pin const $expr` into
+            // `Pin { __pointer: &mut $expr }` and `Pin { __pointer: &$expr }`.
+            hir::ExprKind::AddrOf(hir::BorrowKind::Pin, mutbl, arg) => match expr_ty.kind() {
+                &ty::Adt(adt_def, args)
+                    if tcx.is_lang_item(adt_def.did(), rustc_hir::LangItem::Pin) =>
+                {
+                    let arg = self.mirror_expr(arg);
+                    let expr = self.thir.exprs.push(Expr {
+                        temp_lifetime: TempLifetime { temp_lifetime, backwards_incompatible },
+                        ty: args.type_at(0),
+                        span: expr.span,
+                        kind: ExprKind::Borrow { borrow_kind: mutbl.to_borrow_kind(), arg },
+                    });
+                    ExprKind::Adt(Box::new(AdtExpr {
+                        adt_def,
+                        variant_index: FIRST_VARIANT,
+                        args,
+                        fields: Box::new([FieldExpr { name: FieldIdx::from(0u32), expr }]),
+                        user_ty: None,
+                        base: AdtExprBase::None,
+                    }))
+                }
+                _ => span_bug!(expr.span, "unexpected type for pinned borrow: {:?}", expr_ty),
+            },
+
             hir::ExprKind::Block(blk, _) => ExprKind::Block { block: self.mirror_block(blk) },
 
             hir::ExprKind::Assign(lhs, rhs, _) => {
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
@@ -847,14 +847,19 @@ impl<'a> Parser<'a> {
         self.dcx().emit_err(errors::LifetimeInBorrowExpression { span, lifetime_span: lt_span });
     }
 
-    /// Parse `mut?` or `raw [ const | mut ]`.
+    /// Parse `mut?` or `[ raw | pin ] [ const | mut ]`.
     fn parse_borrow_modifiers(&mut self) -> (ast::BorrowKind, ast::Mutability) {
         if self.check_keyword(exp!(Raw)) && self.look_ahead(1, Token::is_mutability) {
             // `raw [ const | mut ]`.
             let found_raw = self.eat_keyword(exp!(Raw));
             assert!(found_raw);
             let mutability = self.parse_const_or_mut().unwrap();
             (ast::BorrowKind::Raw, mutability)
+        } else if let Some((ast::Pinnedness::Pinned, mutbl)) = self.parse_pin_and_mut() {
+            // `pin [ const | mut ]`.
+            // `pin` has been gated in `self.parse_pin_and_mut()` so we don't
+            // need to gate it here.
+            (ast::BorrowKind::Pin, mutbl)
         } else {
             // `mut?`
             (ast::BorrowKind::Ref, self.parse_mutability())
diff --git a/src/tools/rustfmt/src/expr.rs b/src/tools/rustfmt/src/expr.rs
@@ -2289,8 +2289,10 @@ fn rewrite_expr_addrof(
 ) -> RewriteResult {
     let operator_str = match (mutability, borrow_kind) {
         (ast::Mutability::Not, ast::BorrowKind::Ref) => "&",
+        (ast::Mutability::Not, ast::BorrowKind::Pin) => "&pin const ",
         (ast::Mutability::Not, ast::BorrowKind::Raw) => "&raw const ",
         (ast::Mutability::Mut, ast::BorrowKind::Ref) => "&mut ",
+        (ast::Mutability::Mut, ast::BorrowKind::Pin) => "&pin mut ",
         (ast::Mutability::Mut, ast::BorrowKind::Raw) => "&raw mut ",
     };
     rewrite_unary_prefix(context, operator_str, expr, shape)
diff --git a/src/tools/rustfmt/tests/source/pin_sugar.rs b/src/tools/rustfmt/tests/source/pin_sugar.rs
@@ -18,3 +18,13 @@ impl Foo {
 mut self) {}
     fn i(&pin      mut   self) {}
 }
+
+fn borrows() {
+    let mut foo = 0_i32;
+    let x: Pin<&mut _> = & pin 
+    mut    foo;
+
+    let x: Pin<&_> = &
+    pin                const 
+    foo;
+}
diff --git a/src/tools/rustfmt/tests/target/pin_sugar.rs b/src/tools/rustfmt/tests/target/pin_sugar.rs
@@ -16,3 +16,10 @@ impl Foo {
     fn h<'a>(&'a pin mut self) {}
     fn i(&pin mut self) {}
 }
+
+fn borrows() {
+    let mut foo = 0_i32;
+    let x: Pin<&mut _> = &pin mut foo;
+
+    let x: Pin<&_> = &pin const foo;
+}
diff --git a/tests/pretty/pin-ergonomics-hir.pp b/tests/pretty/pin-ergonomics-hir.pp
@@ -0,0 +1,43 @@
+//@ pretty-compare-only
+//@ pretty-mode:hir
+//@ pp-exact:pin-ergonomics-hir.pp
+
+#![feature(pin_ergonomics)]#![allow(dead_code, incomplete_features)]
+#[prelude_import]
+use ::std::prelude::rust_2015::*;
+#[macro_use]
+extern crate std;
+
+use std::pin::Pin;
+
+struct Foo;
+
+impl Foo {
+    fn baz(&mut self) { }
+
+    fn baz_const(&self) { }
+
+    fn baz_lt<'a>(&mut self) { }
+
+    fn baz_const_lt(&self) { }
+}
+
+fn foo(_: Pin<&'_ mut Foo>) { }
+fn foo_lt<'a>(_: Pin<&'a mut Foo>) { }
+
+fn foo_const(_: Pin<&'_ Foo>) { }
+fn foo_const_lt(_: Pin<&'_ Foo>) { }
+
+fn bar() {
+    let mut x: Pin<&mut _> = &pin mut Foo;
+    foo(x.as_mut());
+    foo(x.as_mut());
+    foo_const(x);
+
+    let x: Pin<&_> = &pin const Foo;
+
+    foo_const(x);
+    foo_const(x);
+}
+
+fn main() { }
diff --git a/tests/pretty/pin-ergonomics-hir.rs b/tests/pretty/pin-ergonomics-hir.rs
@@ -0,0 +1,40 @@
+//@ pretty-compare-only
+//@ pretty-mode:hir
+//@ pp-exact:pin-ergonomics-hir.pp
+
+#![feature(pin_ergonomics)]
+#![allow(dead_code, incomplete_features)]
+
+use std::pin::Pin;
+
+struct Foo;
+
+impl Foo {
+    fn baz(&mut self) { }
+
+    fn baz_const(&self) { }
+
+    fn baz_lt<'a>(&mut self) { }
+
+    fn baz_const_lt(&self) { }
+}
+
+fn foo(_: Pin<&'_ mut Foo>) { }
+fn foo_lt<'a>(_: Pin<&'a mut Foo>) { }
+
+fn foo_const(_: Pin<&'_ Foo>) { }
+fn foo_const_lt(_: Pin<&'_ Foo>) { }
+
+fn bar() {
+    let mut x: Pin<&mut _> = &pin mut Foo;
+    foo(x.as_mut());
+    foo(x.as_mut());
+    foo_const(x);
+
+    let x: Pin<&_> = &pin const Foo;
+
+    foo_const(x);
+    foo_const(x);
+}
+
+fn main() { }
diff --git a/tests/pretty/pin-ergonomics.rs b/tests/pretty/pin-ergonomics.rs
@@ -3,6 +3,8 @@
 #![feature(pin_ergonomics)]
 #![allow(dead_code, incomplete_features)]
 
+use std::pin::Pin;
+
 struct Foo;
 
 impl Foo {
@@ -21,4 +23,16 @@ fn foo_lt<'a>(_: &'a pin mut Foo) {}
 fn foo_const(_: &pin const Foo) {}
 fn foo_const_lt(_: &'_ pin const Foo) {}
 
+fn bar() {
+    let mut x: Pin<&mut _> = &pin mut Foo;
+    foo(x.as_mut());
+    foo(x.as_mut());
+    foo_const(x);
+
+    let x: Pin<&_> = &pin const Foo;
+
+    foo_const(x);
+    foo_const(x);
+}
+
 fn main() {}
diff --git a/tests/ui/async-await/pin-ergonomics/borrow-mut-xor-share.rs b/tests/ui/async-await/pin-ergonomics/borrow-mut-xor-share.rs
@@ -0,0 +1,59 @@
+#![feature(pin_ergonomics)]
+#![allow(dead_code, incomplete_features)]
+
+// Makes sure `&pin mut place` and `&pin const place` cannot violate the mut-xor-share rules.
+
+use std::pin::Pin;
+
+struct Foo;
+
+fn foo_mut(_: &mut Foo) {
+}
+
+fn foo_ref(_: &Foo) {
+}
+
+fn foo_pin_mut(_: Pin<&mut Foo>) {
+}
+
+fn foo_pin_ref(_: Pin<&Foo>) {
+}
+
+fn bar() {
+    let foo = Foo;
+    foo_pin_mut(&pin mut foo); //~ ERROR cannot borrow `foo` as mutable, as it is not declared as mutable
+
+    let mut foo = Foo;
+    let x = &pin mut foo;
+    foo_pin_ref(&pin const foo); //~ ERROR cannot borrow `foo` as immutable because it is also borrowed as mutable
+    foo_pin_mut(&pin mut foo); //~ ERROR cannot borrow `foo` as mutable more than once at a time
+    foo_ref(&foo); //~ ERROR cannot borrow `foo` as immutable because it is also borrowed as mutable
+    foo_mut(&mut foo); //~ ERROR cannot borrow `foo` as mutable more than once at a time
+
+    foo_pin_mut(x);
+
+    let mut foo = Foo;
+    let x = &pin const foo;
+    foo_pin_ref(&pin const foo); // ok
+    foo_pin_mut(&pin mut foo); //~ ERROR cannot borrow `foo` as mutable because it is also borrowed as immutable
+    foo_ref(&foo); // ok
+    foo_mut(&mut foo); //~ ERROR cannot borrow `foo` as mutable because it is also borrowed as immutable
+
+    foo_pin_ref(x);
+
+    let mut foo = Foo;
+    let x = &mut foo;
+    foo_pin_ref(&pin const foo); //~ ERROR cannot borrow `foo` as immutable because it is also borrowed as mutable
+    foo_pin_mut(&pin mut foo); //~ ERROR cannot borrow `foo` as mutable more than once at a time
+
+    foo_mut(x);
+
+    let mut foo = Foo;
+    let x = &foo;
+    foo_pin_ref(&pin const foo); // ok
+    foo_pin_mut(&pin mut foo); //~ ERROR cannot borrow `foo` as mutable because it is also borrowed as immutable
+
+    foo_ref(x);
+}
+
+fn main() {}
diff --git a/tests/ui/async-await/pin-ergonomics/borrow-mut-xor-share.stderr b/tests/ui/async-await/pin-ergonomics/borrow-mut-xor-share.stderr
diff --git a/tests/ui/async-await/pin-ergonomics/borrow.rs b/tests/ui/async-await/pin-ergonomics/borrow.rs
diff --git a/tests/ui/feature-gates/feature-gate-pin_ergonomics.rs b/tests/ui/feature-gates/feature-gate-pin_ergonomics.rs
diff --git a/tests/ui/feature-gates/feature-gate-pin_ergonomics.stderr b/tests/ui/feature-gates/feature-gate-pin_ergonomics.stderr

Original file line number	Diff line number	Diff line change
`@@ -357,6 +357,10 @@ impl<'a> State<'a> {`
`357`	`357`	`self.word_nbsp("raw");`
`358`	`358`	`self.print_mutability(mutability, true);`
`359`	`359`	`}`
	`360`	`+ ast::BorrowKind::Pin => {`
	`361`	`+ self.word_nbsp("pin");`
	`362`	`+ self.print_mutability(mutability, true);`
	`363`	`+ }`
`360`	`364`	`}`
`361`	`365`	`self.print_expr_cond_paren(`
`362`	`366`	`expr,`
Original file line number	Diff line number	Diff line change
`@@ -616,11 +616,13 @@ impl<'tcx> NonConstOp<'tcx> for EscapingMutBorrow {`
`616`	`616`	`kind: ccx.const_kind(),`
`617`	`617`	`teach: ccx.tcx.sess.teach(E0764),`
`618`	`618`	`}),`
`619`		`- hir::BorrowKind::Ref => ccx.dcx().create_err(errors::MutableRefEscaping {`
`620`		`- span,`
`621`		`- kind: ccx.const_kind(),`
`622`		`- teach: ccx.tcx.sess.teach(E0764),`
`623`		`- }),`
	`619`	`+ hir::BorrowKind::Ref \| hir::BorrowKind::Pin => {`
	`620`	`+ ccx.dcx().create_err(errors::MutableRefEscaping {`
	`621`	`+ span,`
	`622`	`+ kind: ccx.const_kind(),`
	`623`	`+ teach: ccx.tcx.sess.teach(E0764),`
	`624`	`+ })`
	`625`	`+ }`
`624`	`626`	`}`
`625`	`627`	`}`
`626`	`628`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1339,6 +1339,10 @@ impl<'a> State<'a> {`
`1339`	`1339`	`self.word_nbsp("raw");`
`1340`	`1340`	`self.print_mutability(mutability, true);`
`1341`	`1341`	`}`
	`1342`	`+ hir::BorrowKind::Pin => {`
	`1343`	`+ self.word_nbsp("pin");`
	`1344`	`+ self.print_mutability(mutability, true);`
	`1345`	`+ }`
`1342`	`1346`	`}`
`1343`	`1347`	`self.print_expr_cond_paren(expr, expr.precedence() < ExprPrecedence::Prefix);`
`1344`	`1348`	`}`
Original file line number	Diff line number	Diff line change
`@@ -664,7 +664,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {`
`664`	`664`	`self.check_named_place_expr(oprnd);`
`665`	`665`	`Ty::new_ptr(self.tcx, ty, mutbl)`
`666`	`666`	`}`
`667`		`- hir::BorrowKind::Ref => {`
	`667`	`+ hir::BorrowKind::Ref \| hir::BorrowKind::Pin => {`
`668`	`668`	`// Note: at this point, we cannot say what the best lifetime`
`669`	`669`	`// is to use for resulting pointer. We want to use the`
`670`	`670`	`// shortest lifetime possible so as to avoid spurious borrowck`
`@@ -680,7 +680,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {`
`680`	`680`	`// whose address was taken can actually be made to live as long`
`681`	`681`	`// as it needs to live.`
`682`	`682`	`let region = self.next_region_var(infer::BorrowRegion(expr.span));`
`683`		`- Ty::new_ref(self.tcx, region, ty, mutbl)`
	`683`	`+ match kind {`
	`684`	`+ hir::BorrowKind::Ref => Ty::new_ref(self.tcx, region, ty, mutbl),`
	`685`	`+ hir::BorrowKind::Pin => Ty::new_pinned_ref(self.tcx, region, ty, mutbl),`
	`686`	`+ _ => unreachable!(),`
	`687`	`+ }`
`684`	`688`	`}`
`685`	`689`	`}`
`686`	`690`	`}`