Add field representing types

Cargo.lock

@@ -3431,6 +3431,7 @@ dependencies = [
  "rustc_macros",
  "rustc_serialize",
  "rustc_span",
+ "serde",
  "tracing",
 ]
 
@@ -4298,6 +4299,7 @@ dependencies = [
  "rustc_target",
  "rustc_thread_pool",
  "rustc_type_ir",
+ "serde",
  "smallvec",
  "thin-vec",
  "tracing",

compiler/rustc_abi/Cargo.toml

@@ -15,6 +15,7 @@ rustc_index = { path = "../rustc_index", default-features = false }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }
 rustc_span = { path = "../rustc_span", optional = true }
+serde = { version = "1.0.125", features = ["derive"] }
 tracing = "0.1"
 # tidy-alphabetical-end
 

compiler/rustc_abi/src/layout/ty.rs

@@ -33,7 +33,7 @@ rustc_index::newtype_index! {
     /// `b` is `FieldIdx(1)` in `VariantIdx(0)`,
     /// `d` is `FieldIdx(1)` in `VariantIdx(1)`, and
     /// `f` is `FieldIdx(1)` in `VariantIdx(0)`.
-    #[derive(HashStable_Generic)]
+    #[derive(HashStable_Generic, serde::Serialize)]
     #[encodable]
     #[orderable]
     pub struct FieldIdx {}
@@ -57,7 +57,7 @@ rustc_index::newtype_index! {
     ///
     /// `struct`s, `tuples`, and `unions`s are considered to have a single variant
     /// with variant index zero, aka [`FIRST_VARIANT`].
-    #[derive(HashStable_Generic)]
+    #[derive(HashStable_Generic, serde::Serialize)]
     #[encodable]
     #[orderable]
     pub struct VariantIdx {

compiler/rustc_ast/src/ast.rs

@@ -2557,6 +2557,11 @@ pub enum TyKind {
     /// Pattern types like `pattern_type!(u32 is 1..=)`, which is the same as `NonZero<u32>`,
     /// just as part of the type system.
     Pat(Box<Ty>, Box<TyPat>),
+    /// A `field_of` expression (e.g., `builtin # field_of(Struct, field)`).
+    ///
+    /// Usually not written directly in user code but indirectly via the macro
+    /// `core::field::field_of!(...)`.
+    FieldOf(Box<Ty>, Vec<Ident>),
     /// Sometimes we need a dummy value when no error has occurred.
     Dummy,
     /// Placeholder for a kind that has failed to be defined.

compiler/rustc_ast/src/util/classify.rs

@@ -298,6 +298,7 @@ fn type_trailing_braced_mac_call(mut ty: &ast::Ty) -> Option<&ast::MacCall> {
             | ast::TyKind::ImplicitSelf
             | ast::TyKind::CVarArgs
             | ast::TyKind::Pat(..)
+            | ast::TyKind::FieldOf(..)
             | ast::TyKind::Dummy
             | ast::TyKind::Err(..) => break None,
         }

compiler/rustc_ast_lowering/src/lib.rs

@@ -1499,6 +1499,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             TyKind::Pat(ty, pat) => {
                 hir::TyKind::Pat(self.lower_ty_alloc(ty, itctx), self.lower_ty_pat(pat, ty.span))
             }
+            TyKind::FieldOf(ty, fields) => match self.lower_ty_field_path(fields, ty.span) {
+                Ok(field_path) => hir::TyKind::FieldOf(self.lower_ty_alloc(ty, itctx), field_path),
+                Err(err) => hir::TyKind::Err(err),
+            },
             TyKind::MacCall(_) => {
                 span_bug!(t.span, "`TyKind::MacCall` should have been expanded by now")
             }

compiler/rustc_ast_lowering/src/pat.rs

@@ -7,7 +7,7 @@ use rustc_hir::definitions::DefPathData;
 use rustc_hir::{self as hir, LangItem, Target};
 use rustc_middle::span_bug;
 use rustc_span::source_map::{Spanned, respan};
-use rustc_span::{DesugaringKind, Ident, Span};
+use rustc_span::{DesugaringKind, ErrorGuaranteed, Ident, Span};
 
 use super::errors::{
     ArbitraryExpressionInPattern, ExtraDoubleDot, MisplacedDoubleDot, SubTupleBinding,
@@ -478,6 +478,33 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         hir::TyPat { hir_id: pat_hir_id, kind: node, span: self.lower_span(pattern.span) }
     }
 
+    pub(crate) fn lower_ty_field_path(
+        &mut self,
+        fields: &[Ident],
+        ty_span: Span,
+    ) -> Result<&'hir hir::TyFieldPath, ErrorGuaranteed> {
+        Ok(self.arena.alloc(self.lower_ty_field_path_mut(fields, ty_span)?))
+    }
+
+    fn lower_ty_field_path_mut(
+        &mut self,
+        fields: &[Ident],
+        ty_span: Span,
+    ) -> Result<hir::TyFieldPath, ErrorGuaranteed> {
+        match fields.len() {
+            0 => span_bug!(ty_span, "expected at least one field ident parsed in `field_of!`"),
+            1 => Ok(hir::TyFieldPath { variant: None, field: self.lower_ident(fields[0]) }),
+            2 => Ok(hir::TyFieldPath {
+                variant: Some(self.lower_ident(fields[0])),
+                field: self.lower_ident(fields[1]),
+            }),
+            _ => Err(self.dcx().span_err(
+                fields.iter().map(|f| f.span).collect::<Vec<_>>(),
+                "`field_of!` only supports a single field or a variant with a field",
+            )),
+        }
+    }
+
     /// Lowers the range end of an exclusive range (`2..5`) to an inclusive range 2..=(5 - 1).
     /// This way the type system doesn't have to handle the distinction between inclusive/exclusive ranges.
     fn lower_excluded_range_end(&mut self, e: &AnonConst) -> &'hir hir::ConstArg<'hir> {

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1377,6 +1377,25 @@ impl<'a> State<'a> {
                 self.word(" is ");
                 self.print_ty_pat(pat);
             }
+            ast::TyKind::FieldOf(ty, fields) => {
+                self.word("builtin # field_of");
+                self.popen();
+                let ib = self.ibox(0);
+                self.print_type(ty);
+                self.word(",");
+                self.space();
+
+                if let Some((&first, rest)) = fields.split_first() {
+                    self.print_ident(first);
+
+                    for &field in rest {
+                        self.word(".");
+                        self.print_ident(field);
+                    }
+                }
+                self.end(ib);
+                self.pclose();
+            }
         }
         self.end(ib);
     }

compiler/rustc_borrowck/src/lib.rs

@@ -1875,6 +1875,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     | ty::Str
                     | ty::Array(_, _)
                     | ty::Pat(_, _)
+                    | ty::FRT(..)
                     | ty::Slice(_)
                     | ty::FnDef(_, _)
                     | ty::FnPtr(..)
@@ -1919,6 +1920,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     | ty::Str
                     | ty::Array(_, _)
                     | ty::Pat(_, _)
+                    | ty::FRT(..)
                     | ty::Slice(_)
                     | ty::RawPtr(_, _)
                     | ty::Ref(_, _, _)

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -216,6 +216,8 @@ fn push_debuginfo_type_name<'tcx>(
                 write!(output, "{:?}", t).unwrap();
             }
         }
+        // FIXME(FRTs): implement debuginfo for field representing types
+        ty::FRT(..) => todo!(),
         ty::Slice(inner_type) => {
             if cpp_like_debuginfo {
                 output.push_str("slice2$<");

compiler/rustc_const_eval/src/const_eval/type_info.rs

@@ -122,6 +122,7 @@ impl<'tcx> InterpCx<'tcx, CompileTimeMachine<'tcx>> {
                             variant
                         }
                         ty::Adt(_, _)
+                        | ty::FRT(_, _)
                         | ty::Foreign(_)
                         | ty::Pat(_, _)
                         | ty::Slice(_)

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -90,7 +90,7 @@ fn const_to_valtree_inner<'tcx>(
     }
 
     match ty.kind() {
-        ty::FnDef(..) => {
+        ty::FnDef(..) | ty::FRT(..) => {
             *num_nodes += 1;
             Ok(ty::ValTree::zst(tcx))
         }
@@ -273,7 +273,7 @@ pub fn valtree_to_const_value<'tcx>(
     // create inner `MPlace`s which are filled recursively.
     // FIXME: Does this need an example?
     match *cv.ty.kind() {
-        ty::FnDef(..) => {
+        ty::FnDef(..) | ty::FRT(..) => {
             assert!(cv.valtree.is_zst());
             mir::ConstValue::ZeroSized
         }

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -12,7 +12,7 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::interpret::{CTFE_ALLOC_SALT, read_target_uint, write_target_uint};
 use rustc_middle::mir::{self, BinOp, ConstValue, NonDivergingIntrinsic};
 use rustc_middle::ty::layout::TyAndLayout;
-use rustc_middle::ty::{FloatTy, PolyExistentialPredicate, Ty, TyCtxt};
+use rustc_middle::ty::{FieldIdData, FloatTy, PolyExistentialPredicate, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug, ty};
 use rustc_span::{Symbol, sym};
 use rustc_trait_selection::traits::{Obligation, ObligationCause, ObligationCtxt};
@@ -222,6 +222,33 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
                 self.write_scalar(Scalar::from_target_usize(offset, self), dest)?;
             }
+            sym::field_offset => {
+                let frt_ty = instance.args.type_at(0);
+
+                let (ty, field) = match frt_ty.kind() {
+                    &ty::FRT(ty, field) => (ty, field),
+                    ty::Alias(..) | ty::Param(..) | ty::Placeholder(..) | ty::Infer(..) => {
+                        // This can happen in code which is generic over the field type.
+                        throw_inval!(TooGeneric)
+                    }
+                    _ => {
+                        span_bug!(self.cur_span(), "expected field representing type, got {frt_ty}")
+                    }
+                };
+                let FieldIdData::Resolved { variant, field } = &*field.0 else {
+                    span_bug!(
+                        self.cur_span(),
+                        "expected resolved field representing type, got `field_of!({ty}, {field:?})`"
+                    )
+                };
+                let layout = self.layout_of(ty)?;
+                let cx = ty::layout::LayoutCx::new(*self.tcx, self.typing_env);
+
+                let layout = layout.for_variant(&cx, *variant);
+                let offset = layout.fields.offset(field.index()).bytes();
+
+                self.write_scalar(Scalar::from_target_usize(offset, self), dest)?;
+            }
             sym::vtable_for => {
                 let tp_ty = instance.args.type_at(0);
                 let result_ty = instance.args.type_at(1);
@@ -300,6 +327,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                     | ty::UnsafeBinder(_)
                     | ty::Never
                     | ty::Tuple(_)
+                    | ty::FRT(..)
                     | ty::Error(_) => ConstValue::from_target_usize(0u64, &tcx),
                 };
                 let val = self.const_val_to_op(val, dest.layout.ty, Some(dest.layout))?;

compiler/rustc_const_eval/src/interpret/stack.rs

@@ -507,6 +507,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 | ty::Closure(..)
                 | ty::CoroutineClosure(..)
                 | ty::Never
+                | ty::FRT(..)
                 | ty::Error(_) => true,
 
                 ty::Str | ty::Slice(_) | ty::Dynamic(_, _) | ty::Foreign(..) => false,

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -785,6 +785,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
             | ty::Dynamic(..)
             | ty::Closure(..)
             | ty::Pat(..)
+            | ty::FRT(..)
             | ty::CoroutineClosure(..)
             | ty::Coroutine(..) => interp_ok(false),
             // Some types only occur during typechecking, they have no layout.

compiler/rustc_const_eval/src/util/type_name.rs

@@ -34,6 +34,7 @@ impl<'tcx> Printer<'tcx> for TypeNamePrinter<'tcx> {
             | ty::Float(_)
             | ty::Str
             | ty::Pat(_, _)
+            | ty::FRT(..)
             | ty::Array(_, _)
             | ty::Slice(_)
             | ty::RawPtr(_, _)

compiler/rustc_feature/src/unstable.rs

@@ -488,6 +488,8 @@ declare_features! (
     (unstable, ffi_const, "1.45.0", Some(58328)),
     /// Allows the use of `#[ffi_pure]` on foreign functions.
     (unstable, ffi_pure, "1.45.0", Some(58329)),
+    /// Experimental field projections.
+    (incomplete, field_projections, "CURRENT_RUSTC_VERSION", Some(145383)),
     /// Controlling the behavior of fmt::Debug
     (unstable, fmt_debug, "1.82.0", Some(129709)),
     /// Allows using `#[align(...)]` on function items

compiler/rustc_hir/src/hir.rs

@@ -1729,6 +1729,12 @@ impl<'hir> Block<'hir> {
     }
 }
 
+#[derive(Debug, Clone, Copy, HashStable_Generic)]
+pub struct TyFieldPath {
+    pub variant: Option<Ident>,
+    pub field: Ident,
+}
+
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub struct TyPat<'hir> {
     #[stable_hasher(ignore)]
@@ -3773,6 +3779,10 @@ pub enum TyKind<'hir, Unambig = ()> {
     Err(rustc_span::ErrorGuaranteed),
     /// Pattern types (`pattern_type!(u32 is 1..)`)
     Pat(&'hir Ty<'hir>, &'hir TyPat<'hir>),
+    /// Field representing type (`field_of!(Struct, field)`).
+    ///
+    /// The optional ident is the variant when an enum is passed `field_of!(Enum, Variant.field)`.
+    FieldOf(&'hir Ty<'hir>, &'hir TyFieldPath),
     /// `TyKind::Infer` means the type should be inferred instead of it having been
     /// specified. This can appear anywhere in a type.
     ///

compiler/rustc_hir/src/intravisit.rs

@@ -1047,6 +1047,13 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v, AmbigArg>) -
             try_visit!(visitor.visit_ty_unambig(ty));
             try_visit!(visitor.visit_pattern_type_pattern(pat));
         }
+        TyKind::FieldOf(ty, TyFieldPath { variant, field }) => {
+            try_visit!(visitor.visit_ty_unambig(ty));
+            if let Some(variant) = *variant {
+                try_visit!(visitor.visit_ident(variant));
+            }
+            try_visit!(visitor.visit_ident(*field));
+        }
     }
     V::Result::output()
 }

compiler/rustc_hir/src/lang_items.rs

@@ -448,6 +448,12 @@ language_item_table! {
     // Reborrowing related lang-items
     Reborrow,                sym::reborrow,            reborrow,                   Target::Trait,          GenericRequirement::Exact(0);
     CoerceShared,            sym::coerce_shared,       coerce_shared,              Target::Trait,          GenericRequirement::Exact(0);
+
+    // Field projection related lang-items
+    Field,                   sym::field,               field,                      Target::Trait,          GenericRequirement::Exact(0);
+    FieldBase,               sym::field_base,          field_base,                 Target::AssocTy,        GenericRequirement::Exact(0);
+    FieldType,               sym::field_type,          field_type,                 Target::AssocTy,        GenericRequirement::Exact(0);
+    FieldOffset,             sym::field_offset,        field_offset,               Target::AssocConst,     GenericRequirement::Exact(0);
 }
 
 /// The requirement imposed on the generics of a lang item

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -117,6 +117,7 @@ fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hi
         | sym::fabsf128
         | sym::fadd_algebraic
         | sym::fdiv_algebraic
+        | sym::field_offset
         | sym::floorf16
         | sym::floorf32
         | sym::floorf64
@@ -296,6 +297,7 @@ pub(crate) fn check_intrinsic_type(
             (1, 0, vec![Ty::new_imm_ptr(tcx, param(0))], tcx.types.usize)
         }
         sym::offset_of => (1, 0, vec![tcx.types.u32, tcx.types.u32], tcx.types.usize),
+        sym::field_offset => (1, 0, vec![], tcx.types.usize),
         sym::rustc_peek => (1, 0, vec![param(0)], param(0)),
         sym::caller_location => (0, 0, vec![], tcx.caller_location_ty()),
         sym::assert_inhabited | sym::assert_zero_valid | sym::assert_mem_uninitialized_valid => {

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -261,6 +261,17 @@ pub(super) fn check_item<'tcx>(
                         .with_span_label(sp, "auto trait")
                         .emit());
                 }
+                if is_auto && let rustc_hir::TyKind::FieldOf(..) = impl_.self_ty.kind {
+                    res = res.and(Err(tcx
+                        .dcx()
+                        .struct_span_err(
+                            item.span,
+                            "impls of auto traits for field representing types not supported",
+                        )
+                        .with_span_label(impl_.self_ty.span, "field representing type")
+                        .with_span_label(of_trait.trait_ref.path.span, "auto trait")
+                        .emit()));
+                }
                 match header.polarity {
                     ty::ImplPolarity::Positive => {
                         res = res.and(check_impl(tcx, item, impl_));