Rollup merge of #130635 - eholk:pin-reborrow-sugar, r=compiler-errors

Add `&pin (mut|const) T` type position sugar

This adds parser support for `&pin mut T` and `&pin const T` references. These are desugared to `Pin<&mut T>` and `Pin<&T>` in the AST lowering phases.

This PR currently includes #130526 since that one is in the commit queue. Only the most recent commits (bd45002 and following) are new.

Tracking:

- #130494

r? `@compiler-errors`

compiler/rustc_ast/src/ast.rs

@@ -23,7 +23,7 @@ use std::{cmp, fmt, mem};
 
 pub use GenericArgs::*;
 pub use UnsafeSource::*;
-pub use rustc_ast_ir::{Movability, Mutability};
+pub use rustc_ast_ir::{Movability, Mutability, Pinnedness};
 use rustc_data_structures::packed::Pu128;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::stack::ensure_sufficient_stack;
@@ -2161,6 +2161,10 @@ pub enum TyKind {
     Ptr(MutTy),
     /// A reference (`&'a T` or `&'a mut T`).
     Ref(Option<Lifetime>, MutTy),
+    /// A pinned reference (`&'a pin const T` or `&'a pin mut T`).
+    ///
+    /// Desugars into `Pin<&'a T>` or `Pin<&'a mut T>`.
+    PinnedRef(Option<Lifetime>, MutTy),
     /// A bare function (e.g., `fn(usize) -> bool`).
     BareFn(P<BareFnTy>),
     /// The never type (`!`).
@@ -2501,7 +2505,10 @@ impl Param {
             if ident.name == kw::SelfLower {
                 return match self.ty.kind {
                     TyKind::ImplicitSelf => Some(respan(self.pat.span, SelfKind::Value(mutbl))),
-                    TyKind::Ref(lt, MutTy { ref ty, mutbl }) if ty.kind.is_implicit_self() => {
+                    TyKind::Ref(lt, MutTy { ref ty, mutbl })
+                    | TyKind::PinnedRef(lt, MutTy { ref ty, mutbl })
+                        if ty.kind.is_implicit_self() =>
+                    {
                         Some(respan(self.pat.span, SelfKind::Region(lt, mutbl)))
                     }
                     _ => Some(respan(

compiler/rustc_ast/src/mut_visit.rs

@@ -485,7 +485,7 @@ pub fn walk_ty<T: MutVisitor>(vis: &mut T, ty: &mut P<Ty>) {
         }
         TyKind::Slice(ty) => vis.visit_ty(ty),
         TyKind::Ptr(mt) => vis.visit_mt(mt),
-        TyKind::Ref(lt, mt) => {
+        TyKind::Ref(lt, mt) | TyKind::PinnedRef(lt, mt) => {
             visit_opt(lt, |lt| vis.visit_lifetime(lt));
             vis.visit_mt(mt);
         }

compiler/rustc_ast/src/util/classify.rs

@@ -247,7 +247,9 @@ fn type_trailing_braced_mac_call(mut ty: &ast::Ty) -> Option<&ast::MacCall> {
                 break (mac.args.delim == Delimiter::Brace).then_some(mac);
             }
 
-            ast::TyKind::Ptr(mut_ty) | ast::TyKind::Ref(_, mut_ty) => {
+            ast::TyKind::Ptr(mut_ty)
+            | ast::TyKind::Ref(_, mut_ty)
+            | ast::TyKind::PinnedRef(_, mut_ty) => {
                 ty = &mut_ty.ty;
             }
 

compiler/rustc_ast/src/visit.rs

@@ -499,7 +499,8 @@ pub fn walk_ty<'a, V: Visitor<'a>>(visitor: &mut V, typ: &'a Ty) -> V::Result {
     match kind {
         TyKind::Slice(ty) | TyKind::Paren(ty) => try_visit!(visitor.visit_ty(ty)),
         TyKind::Ptr(MutTy { ty, mutbl: _ }) => try_visit!(visitor.visit_ty(ty)),
-        TyKind::Ref(opt_lifetime, MutTy { ty, mutbl: _ }) => {
+        TyKind::Ref(opt_lifetime, MutTy { ty, mutbl: _ })
+        | TyKind::PinnedRef(opt_lifetime, MutTy { ty, mutbl: _ }) => {
             visit_opt!(visitor, visit_lifetime, opt_lifetime, LifetimeCtxt::Ref);
             try_visit!(visitor.visit_ty(ty));
         }

compiler/rustc_ast_ir/src/lib.rs

@@ -79,3 +79,10 @@ impl Mutability {
         matches!(self, Self::Not)
     }
 }
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Copy)]
+#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_NoContext))]
+pub enum Pinnedness {
+    Not,
+    Pinned,
+}

compiler/rustc_ast_lowering/src/expr.rs

@@ -640,7 +640,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     self.lower_span(span),
                     Some(self.allow_gen_future.clone()),
                 );
-                let resume_ty = self.make_lang_item_qpath(hir::LangItem::ResumeTy, unstable_span);
+                let resume_ty =
+                    self.make_lang_item_qpath(hir::LangItem::ResumeTy, unstable_span, None);
                 let input_ty = hir::Ty {
                     hir_id: self.next_id(),
                     kind: hir::TyKind::Path(resume_ty),
@@ -2065,7 +2066,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         lang_item: hir::LangItem,
         name: Symbol,
     ) -> hir::Expr<'hir> {
-        let qpath = self.make_lang_item_qpath(lang_item, self.lower_span(span));
+        let qpath = self.make_lang_item_qpath(lang_item, self.lower_span(span), None);
         let path = hir::ExprKind::Path(hir::QPath::TypeRelative(
             self.arena.alloc(self.ty(span, hir::TyKind::Path(qpath))),
             self.arena.alloc(hir::PathSegment::new(

compiler/rustc_ast_lowering/src/lib.rs

@@ -55,8 +55,8 @@ use rustc_errors::{DiagArgFromDisplay, DiagCtxtHandle, StashKey};
 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId, LocalDefIdMap};
 use rustc_hir::{
-    self as hir, ConstArg, GenericArg, HirId, ItemLocalMap, MissingLifetimeKind, ParamName,
-    TraitCandidate,
+    self as hir, ConstArg, GenericArg, HirId, ItemLocalMap, LangItem, MissingLifetimeKind,
+    ParamName, TraitCandidate,
 };
 use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_macros::extension;
@@ -765,8 +765,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         res
     }
 
-    fn make_lang_item_qpath(&mut self, lang_item: hir::LangItem, span: Span) -> hir::QPath<'hir> {
-        hir::QPath::Resolved(None, self.make_lang_item_path(lang_item, span, None))
+    fn make_lang_item_qpath(
+        &mut self,
+        lang_item: hir::LangItem,
+        span: Span,
+        args: Option<&'hir hir::GenericArgs<'hir>>,
+    ) -> hir::QPath<'hir> {
+        hir::QPath::Resolved(None, self.make_lang_item_path(lang_item, span, args))
     }
 
     fn make_lang_item_path(
@@ -1277,6 +1282,32 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let lifetime = self.lower_lifetime(&region);
                 hir::TyKind::Ref(lifetime, self.lower_mt(mt, itctx))
             }
+            TyKind::PinnedRef(region, mt) => {
+                let region = region.unwrap_or_else(|| {
+                    let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
+                        self.resolver.get_lifetime_res(t.id)
+                    {
+                        debug_assert_eq!(start.plus(1), end);
+                        start
+                    } else {
+                        self.next_node_id()
+                    };
+                    let span = self.tcx.sess.source_map().start_point(t.span).shrink_to_hi();
+                    Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
+                });
+                let lifetime = self.lower_lifetime(&region);
+                let kind = hir::TyKind::Ref(lifetime, self.lower_mt(mt, itctx));
+                let span = self.lower_span(t.span);
+                let arg = hir::Ty { kind, span, hir_id: self.next_id() };
+                let args = self.arena.alloc(hir::GenericArgs {
+                    args: self.arena.alloc([hir::GenericArg::Type(self.arena.alloc(arg))]),
+                    constraints: &[],
+                    parenthesized: hir::GenericArgsParentheses::No,
+                    span_ext: span,
+                });
+                let path = self.make_lang_item_qpath(LangItem::Pin, span, Some(args));
+                hir::TyKind::Path(path)
+            }
             TyKind::BareFn(f) => {
                 let generic_params = self.lower_lifetime_binder(t.id, &f.generic_params);
                 hir::TyKind::BareFn(self.arena.alloc(hir::BareFnTy {
@@ -1845,10 +1876,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     // Given we are only considering `ImplicitSelf` types, we needn't consider
                     // the case where we have a mutable pattern to a reference as that would
                     // no longer be an `ImplicitSelf`.
-                    TyKind::Ref(_, mt) if mt.ty.kind.is_implicit_self() => match mt.mutbl {
-                        hir::Mutability::Not => hir::ImplicitSelfKind::RefImm,
-                        hir::Mutability::Mut => hir::ImplicitSelfKind::RefMut,
-                    },
+                    TyKind::Ref(_, mt) | TyKind::PinnedRef(_, mt)
+                        if mt.ty.kind.is_implicit_self() =>
+                    {
+                        match mt.mutbl {
+                            hir::Mutability::Not => hir::ImplicitSelfKind::RefImm,
+                            hir::Mutability::Mut => hir::ImplicitSelfKind::RefMut,
+                        }
+                    }
                     _ => hir::ImplicitSelfKind::None,
                 }
             }),

compiler/rustc_ast_lowering/src/lifetime_collector.rs

@@ -95,7 +95,7 @@ impl<'ast> Visitor<'ast> for LifetimeCollectVisitor<'ast> {
                 visit::walk_ty(self, t);
                 self.current_binders.pop();
             }
-            TyKind::Ref(None, _) => {
+            TyKind::Ref(None, _) | TyKind::PinnedRef(None, _) => {
                 self.record_elided_anchor(t.id, t.span);
                 visit::walk_ty(self, t);
             }

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -546,6 +546,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(mut_ref, "mutable by-reference bindings are experimental");
     gate_all!(global_registration, "global registration is experimental");
     gate_all!(return_type_notation, "return type notation is experimental");
+    gate_all!(pin_ergonomics, "pinned reference syntax is experimental");
 
     if !visitor.features.never_patterns {
         if let Some(spans) = spans.get(&sym::never_patterns) {

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1163,6 +1163,12 @@ impl<'a> State<'a> {
                 self.print_opt_lifetime(lifetime);
                 self.print_mt(mt, false);
             }
+            ast::TyKind::PinnedRef(lifetime, mt) => {
+                self.word("&");
+                self.print_opt_lifetime(lifetime);
+                self.word("pin ");
+                self.print_mt(mt, true);
+            }
             ast::TyKind::Never => {
                 self.word("!");
             }

compiler/rustc_hir/src/hir.rs

@@ -1,10 +1,9 @@
 use std::fmt;
 
-use rustc_ast as ast;
 use rustc_ast::util::parser::ExprPrecedence;
 use rustc_ast::{
-    Attribute, FloatTy, InlineAsmOptions, InlineAsmTemplatePiece, IntTy, Label, LitKind,
-    TraitObjectSyntax, UintTy,
+    self as ast, Attribute, FloatTy, InlineAsmOptions, InlineAsmTemplatePiece, IntTy, Label,
+    LitKind, TraitObjectSyntax, UintTy,
 };
 pub use rustc_ast::{
     BinOp, BinOpKind, BindingMode, BorrowKind, ByRef, CaptureBy, ImplPolarity, IsAuto, Movability,

compiler/rustc_parse/src/parser/ty.rs

@@ -4,7 +4,8 @@ use rustc_ast::util::case::Case;
 use rustc_ast::{
     self as ast, BareFnTy, BoundAsyncness, BoundConstness, BoundPolarity, DUMMY_NODE_ID, FnRetTy,
     GenericBound, GenericBounds, GenericParam, Generics, Lifetime, MacCall, MutTy, Mutability,
-    PolyTraitRef, PreciseCapturingArg, TraitBoundModifiers, TraitObjectSyntax, Ty, TyKind,
+    Pinnedness, PolyTraitRef, PreciseCapturingArg, TraitBoundModifiers, TraitObjectSyntax, Ty,
+    TyKind,
 };
 use rustc_errors::{Applicability, PResult};
 use rustc_span::symbol::{Ident, kw, sym};
@@ -487,7 +488,10 @@ impl<'a> Parser<'a> {
     fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
         let and_span = self.prev_token.span;
         let mut opt_lifetime = self.check_lifetime().then(|| self.expect_lifetime());
-        let mut mutbl = self.parse_mutability();
+        let (pinned, mut mutbl) = match self.parse_pin_and_mut() {
+            Some(pin_mut) => pin_mut,
+            None => (Pinnedness::Not, self.parse_mutability()),
+        };
         if self.token.is_lifetime() && mutbl == Mutability::Mut && opt_lifetime.is_none() {
             // A lifetime is invalid here: it would be part of a bare trait bound, which requires
             // it to be followed by a plus, but we disallow plus in the pointee type.
@@ -523,7 +527,35 @@ impl<'a> Parser<'a> {
             self.bump_with((dyn_tok, dyn_tok_sp));
         }
         let ty = self.parse_ty_no_plus()?;
-        Ok(TyKind::Ref(opt_lifetime, MutTy { ty, mutbl }))
+        Ok(match pinned {
+            Pinnedness::Not => TyKind::Ref(opt_lifetime, MutTy { ty, mutbl }),
+            Pinnedness::Pinned => TyKind::PinnedRef(opt_lifetime, MutTy { ty, mutbl }),
+        })
+    }
+
+    /// Parses `pin` and `mut` annotations on references.
+    ///
+    /// It must be either `pin const` or `pin mut`.
+    pub(crate) fn parse_pin_and_mut(&mut self) -> Option<(Pinnedness, Mutability)> {
+        if self.token.is_ident_named(sym::pin) {
+            let result = self.look_ahead(1, |token| {
+                if token.is_keyword(kw::Const) {
+                    Some((Pinnedness::Pinned, Mutability::Not))
+                } else if token.is_keyword(kw::Mut) {
+                    Some((Pinnedness::Pinned, Mutability::Mut))
+                } else {
+                    None
+                }
+            });
+            if result.is_some() {
+                self.psess.gated_spans.gate(sym::pin_ergonomics, self.token.span);
+                self.bump();
+                self.bump();
+            }
+            result
+        } else {
+            None
+        }
     }
 
     // Parses the `typeof(EXPR)`.

compiler/rustc_passes/src/hir_stats.rs

@@ -579,6 +579,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
             Array,
             Ptr,
             Ref,
+            PinnedRef,
             BareFn,
             Never,
             Tup,

compiler/rustc_resolve/src/late.rs

@@ -779,7 +779,7 @@ impl<'ra: 'ast, 'ast, 'tcx> Visitor<'ast> for LateResolutionVisitor<'_, 'ast, 'r
         let prev = self.diag_metadata.current_trait_object;
         let prev_ty = self.diag_metadata.current_type_path;
         match &ty.kind {
-            TyKind::Ref(None, _) => {
+            TyKind::Ref(None, _) | TyKind::PinnedRef(None, _) => {
                 // Elided lifetime in reference: we resolve as if there was some lifetime `'_` with
                 // NodeId `ty.id`.
                 // This span will be used in case of elision failure.
@@ -2326,7 +2326,7 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         impl<'ra> Visitor<'ra> for FindReferenceVisitor<'_, '_, '_> {
             fn visit_ty(&mut self, ty: &'ra Ty) {
                 trace!("FindReferenceVisitor considering ty={:?}", ty);
-                if let TyKind::Ref(lt, _) = ty.kind {
+                if let TyKind::Ref(lt, _) | TyKind::PinnedRef(lt, _) = ty.kind {
                     // See if anything inside the &thing contains Self
                     let mut visitor =
                         SelfVisitor { r: self.r, impl_self: self.impl_self, self_found: false };

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -3482,7 +3482,7 @@ struct LifetimeFinder<'ast> {
 
 impl<'ast> Visitor<'ast> for LifetimeFinder<'ast> {
     fn visit_ty(&mut self, t: &'ast Ty) {
-        if let TyKind::Ref(_, mut_ty) = &t.kind {
+        if let TyKind::Ref(_, mut_ty) | TyKind::PinnedRef(_, mut_ty) = &t.kind {
             self.seen.push(t);
             if t.span.lo() == self.lifetime.lo() {
                 self.found = Some(&mut_ty.ty);

src/tools/clippy/clippy_utils/src/ast_utils.rs

@@ -753,6 +753,9 @@ pub fn eq_ty(l: &Ty, r: &Ty) -> bool {
         (Ref(ll, l), Ref(rl, r)) => {
             both(ll.as_ref(), rl.as_ref(), |l, r| eq_id(l.ident, r.ident)) && l.mutbl == r.mutbl && eq_ty(&l.ty, &r.ty)
         },
+        (PinnedRef(ll, l), PinnedRef(rl, r)) => {
+            both(ll.as_ref(), rl.as_ref(), |l, r| eq_id(l.ident, r.ident)) && l.mutbl == r.mutbl && eq_ty(&l.ty, &r.ty)
+        },
         (BareFn(l), BareFn(r)) => {
             l.safety == r.safety
                 && eq_ext(&l.ext, &r.ext)

src/tools/rustfmt/src/types.rs

@@ -827,7 +827,8 @@ impl Rewrite for ast::Ty {
 
                 rewrite_unary_prefix(context, prefix, &*mt.ty, shape)
             }
-            ast::TyKind::Ref(ref lifetime, ref mt) => {
+            ast::TyKind::Ref(ref lifetime, ref mt)
+            | ast::TyKind::PinnedRef(ref lifetime, ref mt) => {
                 let mut_str = format_mutability(mt.mutbl);
                 let mut_len = mut_str.len();
                 let mut result = String::with_capacity(128);
@@ -861,6 +862,13 @@ impl Rewrite for ast::Ty {
                     cmnt_lo = lifetime.ident.span.hi();
                 }
 
+                if let ast::TyKind::PinnedRef(..) = self.kind {
+                    result.push_str("pin ");
+                    if ast::Mutability::Not == mt.mutbl {
+                        result.push_str("const ");
+                    }
+                }
+
                 if ast::Mutability::Mut == mt.mutbl {
                     let mut_hi = context.snippet_provider.span_after(self.span(), "mut");
                     let before_mut_span = mk_sp(cmnt_lo, mut_hi - BytePos::from_usize(3));
@@ -1260,9 +1268,9 @@ pub(crate) fn can_be_overflowed_type(
 ) -> bool {
     match ty.kind {
         ast::TyKind::Tup(..) => context.use_block_indent() && len == 1,
-        ast::TyKind::Ref(_, ref mutty) | ast::TyKind::Ptr(ref mutty) => {
-            can_be_overflowed_type(context, &*mutty.ty, len)
-        }
+        ast::TyKind::Ref(_, ref mutty)
+        | ast::TyKind::PinnedRef(_, ref mutty)
+        | ast::TyKind::Ptr(ref mutty) => can_be_overflowed_type(context, &*mutty.ty, len),
         _ => false,
     }
 }

src/tools/rustfmt/tests/source/pin_sugar.rs

@@ -0,0 +1,10 @@
+// See #130494
+
+#![feature(pin_ergonomics)]
+#![allow(incomplete_features)]
+
+fn f(x: &pin  const i32) {}
+fn g<'a>(x: &  'a pin const  i32) {}
+fn h<'a>(x: &  'a pin  
+mut i32) {}
+fn i(x: &pin      mut  i32) {}

src/tools/rustfmt/tests/target/pin_sugar.rs

@@ -0,0 +1,9 @@
+// See #130494
+
+#![feature(pin_ergonomics)]
+#![allow(incomplete_features)]
+
+fn f(x: &pin const i32) {}
+fn g<'a>(x: &'a pin const i32) {}
+fn h<'a>(x: &'a pin mut i32) {}
+fn i(x: &pin mut i32) {}

tests/ui/async-await/pin-sugar-ambiguity.rs

@@ -0,0 +1,15 @@
+//@ check-pass
+#![feature(pin_ergonomics)]
+#![allow(dead_code, incomplete_features)]
+
+// Handle the case where there's ambiguity between pin as a contextual keyword and pin as a path.
+
+struct Foo;
+
+mod pin {
+    pub struct Foo;
+}
+
+fn main() {
+    let _x: &pin ::Foo = &pin::Foo;
+}