Auto merge of #139751 - frank-king:feature/pin-project, r=Nadrieril,traviscross

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

This PR implements part of #130494. It supports pin-project in pattern matching for `&pin mut|const T`.

~Pin-projection by field access (i.e. `&pin mut|const place.field`) is not fully supported yet since pinned-borrow is not ready (#135731).~

CC `@traviscross`

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -789,14 +789,14 @@ 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
@@ -814,20 +814,33 @@ 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

@@ -1712,10 +1712,15 @@ 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_v2;
 pub(crate) mod proc_macro_attrs;
 pub(crate) mod prototype;
 pub(crate) mod repr;

compiler/rustc_attr_parsing/src/attributes/pin_v2.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 PinV2Parser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for PinV2Parser {
+    const PATH: &[Symbol] = &[sym::pin_v2];
+    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::PinV2;
+}

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_v2::PinV2Parser;
 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<PinV2Parser>>,
         Single<WithoutArgs<PointeeParser>>,
         Single<WithoutArgs<ProcMacroAttributeParser>>,
         Single<WithoutArgs<ProcMacroParser>>,

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -1188,7 +1188,7 @@ 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

@@ -2584,6 +2584,16 @@ 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

@@ -893,6 +893,15 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::No, loop_match, experimental!(loop_match)
     ),
 
+    // The `#[pin_v2]` attribute is part of the `pin_ergonomics` experiment
+    // that allows structurally pinning, tracked in:
+    //
+    // - https://github.com/rust-lang/rust/issues/130494
+    gated!(
+        pin_v2, Normal, template!(Word), ErrorFollowing,
+        EncodeCrossCrate::Yes, pin_ergonomics, experimental!(pin_v2),
+    ),
+
     // ==========================================================================
     // Internal attributes: Stability, deprecation, and unsafe:
     // ==========================================================================