Implement pin-project in pattern matching for &pin mut|const T

compiler/rustc_ast/src/ast.rs

@@ -790,14 +790,14 @@ pub struct PatField {
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 #[derive(Encodable, Decodable, HashStable_Generic, Walkable)]
 pub enum ByRef {
-    Yes(Mutability),
+    Yes(Pinnedness, Mutability),
     No,
 }
 
 impl ByRef {
     #[must_use]
     pub fn cap_ref_mutability(mut self, mutbl: Mutability) -> Self {
-        if let ByRef::Yes(old_mutbl) = &mut self {
+        if let ByRef::Yes(_, old_mutbl) = &mut self {
             *old_mutbl = cmp::min(*old_mutbl, mutbl);
         }
         self
@@ -815,20 +815,33 @@ pub struct BindingMode(pub ByRef, pub Mutability);
 
 impl BindingMode {
     pub const NONE: Self = Self(ByRef::No, Mutability::Not);
-    pub const REF: Self = Self(ByRef::Yes(Mutability::Not), Mutability::Not);
+    pub const REF: Self = Self(ByRef::Yes(Pinnedness::Not, Mutability::Not), Mutability::Not);
+    pub const REF_PIN: Self =
+        Self(ByRef::Yes(Pinnedness::Pinned, Mutability::Not), Mutability::Not);
     pub const MUT: Self = Self(ByRef::No, Mutability::Mut);
-    pub const REF_MUT: Self = Self(ByRef::Yes(Mutability::Mut), Mutability::Not);
-    pub const MUT_REF: Self = Self(ByRef::Yes(Mutability::Not), Mutability::Mut);
-    pub const MUT_REF_MUT: Self = Self(ByRef::Yes(Mutability::Mut), Mutability::Mut);
+    pub const REF_MUT: Self = Self(ByRef::Yes(Pinnedness::Not, Mutability::Mut), Mutability::Not);
+    pub const REF_PIN_MUT: Self =
+        Self(ByRef::Yes(Pinnedness::Pinned, Mutability::Mut), Mutability::Not);
+    pub const MUT_REF: Self = Self(ByRef::Yes(Pinnedness::Not, Mutability::Not), Mutability::Mut);
+    pub const MUT_REF_PIN: Self =
+        Self(ByRef::Yes(Pinnedness::Pinned, Mutability::Not), Mutability::Mut);
+    pub const MUT_REF_MUT: Self =
+        Self(ByRef::Yes(Pinnedness::Not, Mutability::Mut), Mutability::Mut);
+    pub const MUT_REF_PIN_MUT: Self =
+        Self(ByRef::Yes(Pinnedness::Pinned, Mutability::Mut), Mutability::Mut);
 
     pub fn prefix_str(self) -> &'static str {
         match self {
             Self::NONE => "",
             Self::REF => "ref ",
+            Self::REF_PIN => "ref pin const ",
             Self::MUT => "mut ",
             Self::REF_MUT => "ref mut ",
+            Self::REF_PIN_MUT => "ref pin mut ",
             Self::MUT_REF => "mut ref ",
+            Self::MUT_REF_PIN => "mut ref pin ",
             Self::MUT_REF_MUT => "mut ref mut ",
+            Self::MUT_REF_PIN_MUT => "mut ref pin mut ",
         }
     }
 }

compiler/rustc_ast/src/visit.rs

@@ -368,6 +368,7 @@ macro_rules! common_visitor_and_walkers {
             crate::tokenstream::TokenStream,
             Movability,
             Mutability,
+            Pinnedness,
             Result<(), rustc_span::ErrorGuaranteed>,
             rustc_data_structures::fx::FxHashMap<Symbol, usize>,
             rustc_span::ErrorGuaranteed,

compiler/rustc_ast_ir/src/lib.rs

@@ -311,3 +311,10 @@ pub enum Pinnedness {
     Not,
     Pinned,
 }
+
+impl Pinnedness {
+    /// Return `true` if self is pinned
+    pub fn is_pinned(self) -> bool {
+        matches!(self, Self::Pinned)
+    }
+}

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1711,10 +1711,15 @@ impl<'a> State<'a> {
                 if mutbl.is_mut() {
                     self.word_nbsp("mut");
                 }
-                if let ByRef::Yes(rmutbl) = by_ref {
+                if let ByRef::Yes(pinnedness, rmutbl) = by_ref {
                     self.word_nbsp("ref");
+                    if pinnedness.is_pinned() {
+                        self.word_nbsp("pin");
+                    }
                     if rmutbl.is_mut() {
                         self.word_nbsp("mut");
+                    } else if pinnedness.is_pinned() {
+                        self.word_nbsp("const");
                     }
                 }
                 self.print_ident(*ident);

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -48,6 +48,7 @@ pub(crate) mod must_use;
 pub(crate) mod no_implicit_prelude;
 pub(crate) mod non_exhaustive;
 pub(crate) mod path;
+pub(crate) mod pin_project;
 pub(crate) mod proc_macro_attrs;
 pub(crate) mod prototype;
 pub(crate) mod repr;

compiler/rustc_attr_parsing/src/attributes/pin_project.rs

@@ -0,0 +1,21 @@
+use rustc_hir::Target;
+use rustc_hir::attrs::AttributeKind;
+use rustc_span::{Span, Symbol, sym};
+
+use crate::attributes::{NoArgsAttributeParser, OnDuplicate};
+use crate::context::Stage;
+use crate::target_checking::AllowedTargets;
+use crate::target_checking::Policy::Allow;
+
+pub(crate) struct PinProjectParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for PinProjectParser {
+    const PATH: &[Symbol] = &[sym::pin_project];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Enum),
+        Allow(Target::Struct),
+        Allow(Target::Union),
+    ]);
+    const CREATE: fn(Span) -> AttributeKind = AttributeKind::PinProject;
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -47,6 +47,7 @@ use crate::attributes::must_use::MustUseParser;
 use crate::attributes::no_implicit_prelude::NoImplicitPreludeParser;
 use crate::attributes::non_exhaustive::NonExhaustiveParser;
 use crate::attributes::path::PathParser as PathAttributeParser;
+use crate::attributes::pin_project::PinProjectParser;
 use crate::attributes::proc_macro_attrs::{
     ProcMacroAttributeParser, ProcMacroDeriveParser, ProcMacroParser, RustcBuiltinMacroParser,
 };
@@ -233,6 +234,7 @@ attribute_parsers!(
         Single<WithoutArgs<NonExhaustiveParser>>,
         Single<WithoutArgs<ParenSugarParser>>,
         Single<WithoutArgs<PassByValueParser>>,
+        Single<WithoutArgs<PinProjectParser>>,
         Single<WithoutArgs<PointeeParser>>,
         Single<WithoutArgs<ProcMacroAttributeParser>>,
         Single<WithoutArgs<ProcMacroParser>>,

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -1190,7 +1190,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }
 
             LocalInfo::User(mir::BindingForm::Var(mir::VarBindingForm {
-                binding_mode: BindingMode(ByRef::Yes(_), _),
+                binding_mode: BindingMode(ByRef::Yes(..), _),
                 ..
             })) => {
                 let pattern_span: Span = local_decl.source_info.span;

compiler/rustc_borrowck/src/lib.rs

@@ -2604,6 +2604,16 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                             _ => bug!("Deref of unexpected type: {:?}", base_ty),
                         }
                     }
+                    // Check as the inner reference type if it is a field projection
+                    // from the `&pin` pattern
+                    ProjectionElem::Field(FieldIdx::ZERO, _)
+                        if let Some(adt) =
+                            place_base.ty(self.body(), self.infcx.tcx).ty.ty_adt_def()
+                            && adt.is_pin()
+                            && self.infcx.tcx.features().pin_ergonomics() =>
+                    {
+                        self.is_mutable(place_base, is_local_mutation_allowed)
+                    }
                     // All other projections are owned by their base path, so mutable if
                     // base path is mutable
                     ProjectionElem::Field(..)

compiler/rustc_feature/src/builtin_attrs.rs

@@ -888,6 +888,15 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::No, loop_match, experimental!(loop_match)
     ),
 
+    // The `#[pin_project]` attribute is part of the `pin_ergonomics` experiment
+    // that allows structurally pinning, tracked in:
+    //
+    // - https://github.com/rust-lang/rust/issues/130494
+    gated!(
+        pin_project, Normal, template!(Word), ErrorFollowing,
+        EncodeCrossCrate::Yes, pin_ergonomics, experimental!(pin_project),
+    ),
+
     // ==========================================================================
     // Internal attributes: Stability, deprecation, and unsafe:
     // ==========================================================================

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -632,6 +632,9 @@ pub enum AttributeKind {
     /// Represents `#[pattern_complexity_limit]`
     PatternComplexityLimit { attr_span: Span, limit_span: Span, limit: Limit },
 
+    /// Represents `#[pin_project]`
+    PinProject(Span),
+
     /// Represents `#[pointee]`
     Pointee(Span),
 

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -77,6 +77,7 @@ impl AttributeKind {
             PassByValue(..) => Yes,
             Path(..) => No,
             PatternComplexityLimit { .. } => No,
+            PinProject(..) => Yes,
             Pointee(..) => No,
             ProcMacro(..) => No,
             ProcMacroAttribute(..) => No,

compiler/rustc_hir/src/hir.rs

@@ -13,7 +13,7 @@ use rustc_ast::{
 pub use rustc_ast::{
     AssignOp, AssignOpKind, AttrId, AttrStyle, BinOp, BinOpKind, BindingMode, BorrowKind,
     BoundConstness, BoundPolarity, ByRef, CaptureBy, DelimArgs, ImplPolarity, IsAuto,
-    MetaItemInner, MetaItemLit, Movability, Mutability, UnOp,
+    MetaItemInner, MetaItemLit, Movability, Mutability, Pinnedness, UnOp,
 };
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::sorted_map::SortedMap;

compiler/rustc_hir_analysis/src/check/region.rs

@@ -574,7 +574,7 @@ fn resolve_local<'tcx>(
         // & expression, and its lifetime would be extended to the end of the block (due
         // to a different rule, not the below code).
         match pat.kind {
-            PatKind::Binding(hir::BindingMode(hir::ByRef::Yes(_), _), ..) => true,
+            PatKind::Binding(hir::BindingMode(hir::ByRef::Yes(..), _), ..) => true,
 
             PatKind::Struct(_, field_pats, _) => field_pats.iter().any(|fp| is_binding_pat(fp.pat)),
 

compiler/rustc_hir_pretty/src/lib.rs

@@ -1924,10 +1924,15 @@ impl<'a> State<'a> {
                 if mutbl.is_mut() {
                     self.word_nbsp("mut");
                 }
-                if let ByRef::Yes(rmutbl) = by_ref {
+                if let ByRef::Yes(pinnedness, rmutbl) = by_ref {
                     self.word_nbsp("ref");
+                    if pinnedness.is_pinned() {
+                        self.word_nbsp("pin");
+                    }
                     if rmutbl.is_mut() {
                         self.word_nbsp("mut");
+                    } else if pinnedness.is_pinned() {
+                        self.word_nbsp("const");
                     }
                 }
                 self.print_ident(ident);

compiler/rustc_hir_typeck/messages.ftl

@@ -227,6 +227,10 @@ hir_typeck_pass_to_variadic_function = can't pass `{$ty}` to variadic function
     .suggestion = cast the value to `{$cast_ty}`
     .teach_help = certain types, like `{$ty}`, must be cast before passing them to a variadic function to match the implicit cast that a C compiler would perform as part of C's numeric promotion rules
 
+hir_typeck_project_on_non_pin_project_type = cannot project on type that is not `#[pin_project]`
+    .note = type defined here
+    .suggestion = add `#[pin_project]` here
+
 hir_typeck_ptr_cast_add_auto_to_object = cannot add {$traits_len ->
     [1] auto trait {$traits}
     *[other] auto traits {$traits}

compiler/rustc_hir_typeck/src/errors.rs

@@ -1156,3 +1156,14 @@ pub(crate) struct ConstContinueBadLabel {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_typeck_project_on_non_pin_project_type)]
+pub(crate) struct ProjectOnNonPinProjectType {
+    #[primary_span]
+    pub span: Span,
+    #[note]
+    pub def_span: Option<Span>,
+    #[suggestion(code = "#[pin_project]\n", applicability = "machine-applicable")]
+    pub sugg_span: Option<Span>,
+}

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -986,7 +986,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                     // of the pattern, as this just looks confusing, instead use the span
                     // of the discriminant.
                     match bm.0 {
-                        hir::ByRef::Yes(m) => {
+                        hir::ByRef::Yes(_, m) => {
                             let bk = ty::BorrowKind::from_mutbl(m);
                             self.delegate.borrow_mut().borrow(place, discr_place.hir_id, bk);
                         }
@@ -1004,7 +1004,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                     // Deref patterns on boxes don't borrow, so we ignore them here.
                     // HACK: this could be a fake pattern corresponding to a deref inserted by match
                     // ergonomics, in which case `pat.hir_id` will be the id of the subpattern.
-                    if let hir::ByRef::Yes(mutability) =
+                    if let hir::ByRef::Yes(_, mutability) =
                         self.cx.typeck_results().deref_pat_borrow_mode(place.place.ty(), subpattern)
                     {
                         let bk = ty::BorrowKind::from_mutbl(mutability);
@@ -1256,15 +1256,23 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                     .get(pat.hir_id)
                     .expect("missing binding mode");
 
-                if matches!(bm.0, hir::ByRef::Yes(_)) {
+                if let hir::ByRef::Yes(pinnedness, _) = bm.0 {
+                    let base_ty = if pinnedness.is_pinned() {
+                        base_ty.pinned_ty().ok_or_else(|| {
+                            debug!("By-pin-ref binding of non-`Pin` type: {base_ty:?}");
+                            self.cx.report_bug(pat.span, "by-pin-ref binding of non-`Pin` type")
+                        })?
+                    } else {
+                        base_ty
+                    };
                     // a bind-by-ref means that the base_ty will be the type of the ident itself,
                     // but what we want here is the type of the underlying value being borrowed.
                     // So peel off one-level, turning the &T into T.
                     match self.cx.structurally_resolve_type(pat.span, base_ty).builtin_deref(false)
                     {
                         Some(ty) => Ok(ty),
                         None => {
-                            debug!("By-ref binding of non-derefable type");
+                            debug!("By-ref binding of non-derefable type: {base_ty:?}");
                             Err(self
                                 .cx
                                 .report_bug(pat.span, "by-ref binding of non-derefable type"))
@@ -1706,6 +1714,18 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                     };
                     self.pat_deref_place(pat.hir_id, place_with_id, pat, target_ty)?
                 }
+                adjustment::PatAdjust::PinDeref => {
+                    debug!("`PinDeref` of non-pinned-reference type: {:?}", adjust.source);
+                    let target_ty = adjust.source.pinned_ty().ok_or_else(|| {
+                        self.cx.report_bug(
+                            self.cx.tcx().hir_span(pat.hir_id),
+                            "`PinDeref` of non-pinned-reference type",
+                        )
+                    })?;
+                    let kind = ProjectionKind::Field(FieldIdx::ZERO, FIRST_VARIANT);
+                    place_with_id = self.cat_projection(pat.hir_id, place_with_id, target_ty, kind);
+                    self.cat_deref(pat.hir_id, place_with_id)?
+                }
             };
         }
         drop(typeck_results); // explicitly release borrow of typeck results, just in case.
@@ -1877,7 +1897,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
             // Deref patterns on boxes are lowered using a built-in deref.
             hir::ByRef::No => self.cat_deref(hir_id, base_place),
             // For other types, we create a temporary to match on.
-            hir::ByRef::Yes(mutability) => {
+            hir::ByRef::Yes(_, mutability) => {
                 let re_erased = self.cx.tcx().lifetimes.re_erased;
                 let ty = Ty::new_ref(self.cx.tcx(), re_erased, target_ty, mutability);
                 // A deref pattern stores the result of `Deref::deref` or `DerefMut::deref_mut` ...