Implement pattern matching for &pin mut|const T

Author: frank-king

compiler/rustc_ast/src/ast.rs

@@ -719,14 +719,14 @@ pub struct PatField {
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 #[derive(Encodable, Decodable, HashStable_Generic)]
 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
@@ -744,20 +744,33 @@ 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_ir/src/lib.rs

@@ -101,3 +101,10 @@ 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

@@ -1698,10 +1698,15 @@ 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_borrowck/src/diagnostics/mutability_errors.rs

@@ -1225,7 +1225,7 @@ 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

@@ -2530,6 +2530,16 @@ 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_hir/src/hir.rs

@@ -12,7 +12,7 @@ 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_attr_data_structures::AttributeKind;
 use rustc_data_structures::fingerprint::Fingerprint;

compiler/rustc_hir_analysis/src/check/region.rs

@@ -659,7 +659,7 @@ 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

@@ -1906,10 +1906,15 @@ 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/src/expr_use_visitor.rs

@@ -985,7 +985,7 @@ 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);
                         }
@@ -1003,7 +1003,7 @@ 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);
@@ -1255,22 +1255,34 @@ 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(_)) {
-                    // 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");
-                            Err(self
-                                .cx
-                                .report_bug(pat.span, "by-ref binding of non-derefable type"))
+                match bm.0 {
+                    hir::ByRef::Yes(pinnedness, _) => {
+                        let base_ty = if pinnedness.is_pinned() {
+                            base_ty.pinned_ty().ok_or_else(|| {
+                                debug!("By-pin-ref binding of non-`Pin` type");
+                                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");
+                                Err(self
+                                    .cx
+                                    .report_bug(pat.span, "by-ref binding of non-derefable type"))
+                            }
                         }
                     }
-                } else {
-                    Ok(base_ty)
+                    _ => Ok(base_ty),
                 }
             }
             _ => Ok(base_ty),
@@ -1696,6 +1708,16 @@ 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 => {
+                    let target_ty = match adjusts.peek() {
+                        Some(&&next_adjust) => next_adjust.source,
+                        // At the end of the deref chain, we get `pat`'s scrutinee.
+                        None => self.pat_ty_unadjusted(pat)?,
+                    };
+                    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.
@@ -1867,7 +1889,7 @@ 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` ...