add field representing types

Cargo.lock

@@ -4749,6 +4749,7 @@ dependencies = [
  "ena",
  "indexmap",
  "rustc-hash 2.1.1",
+ "rustc_abi",
  "rustc_ast_ir",
  "rustc_data_structures",
  "rustc_error_messages",

compiler/rustc_ast/src/ast.rs

@@ -2553,6 +2553,11 @@ 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>, Option<Ident>, 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

@@ -1497,6 +1497,13 @@ 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, variant, field) => hir::TyKind::FieldOf(
+                self.lower_ty_alloc(ty, itctx),
+                self.arena.alloc(hir::TyFieldPath {
+                    variant: variant.map(|variant| self.lower_ident(variant)),
+                    field: self.lower_ident(*field),
+                }),
+            ),
             TyKind::MacCall(_) => {
                 span_bug!(t.span, "`TyKind::MacCall` should have been expanded by now")
             }

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1377,6 +1377,23 @@ impl<'a> State<'a> {
                 self.word(" is ");
                 self.print_ty_pat(pat);
             }
+            ast::TyKind::FieldOf(ty, variant, field) => {
+                self.word("builtin # field_of");
+                self.popen();
+                let ib = self.ibox(0);
+                self.print_type(ty);
+                self.word(",");
+                self.space();
+
+                if let Some(variant) = variant {
+                    self.print_ident(*variant);
+                    self.word(".");
+                }
+                self.print_ident(*field);
+
+                self.end(ib);
+                self.pclose();
+            }
         }
         self.end(ib);
     }

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -13,7 +13,9 @@ 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, TypeVisitableExt};
+use rustc_middle::ty::{
+    FieldInfo, FloatTy, PolyExistentialPredicate, Ty, TyCtxt, TypeVisitableExt,
+};
 use rustc_middle::{bug, span_bug, ty};
 use rustc_span::{Symbol, sym};
 use rustc_trait_selection::traits::{Obligation, ObligationCause, ObligationCtxt};
@@ -227,6 +229,32 @@ 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, variant, field) = match frt_ty.kind() {
+                    ty::Adt(def, args)
+                        if let Some(FieldInfo { base, variant_idx, field_idx, .. }) =
+                            def.field_representing_type_info(tcx, args) =>
+                    {
+                        (base, variant_idx, field_idx)
+                    }
+                    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 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);

compiler/rustc_feature/src/unstable.rs

@@ -221,6 +221,8 @@ declare_features! (
     (internal, custom_mir, "1.65.0", None),
     /// Implementation details of externally implementable items
     (internal, eii_internals, "1.94.0", None),
+    /// Implementation details of field representing types.
+    (internal, field_representing_type_raw, "CURRENT_RUSTC_VERSION", None),
     /// Outputs useful `assert!` messages
     (unstable, generic_assert, "1.63.0", None),
     /// Allows using the #[rustc_intrinsic] attribute.
@@ -492,6 +494,8 @@ 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)),
     /// Allows marking trait functions as `final` to prevent overriding impls
     (unstable, final_associated_functions, "CURRENT_RUSTC_VERSION", Some(1)),
     /// Controlling the behavior of fmt::Debug

compiler/rustc_hir/src/hir.rs

@@ -1737,6 +1737,12 @@ 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)]
@@ -3800,6 +3806,10 @@ 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

@@ -435,6 +435,13 @@ 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 representing types.
+    FieldRepresentingType,   sym::field_representing_type, field_representing_type,    Target::Struct,         GenericRequirement::Exact(3);
+    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
@@ -297,6 +298,7 @@ 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/errors.rs

@@ -1446,6 +1446,15 @@ pub struct NoVariantNamed<'tcx> {
     pub ty: Ty<'tcx>,
 }
 
+#[derive(Diagnostic)]
+#[diag("no field `{$field}` on type `{$ty}`", code = E0609)]
+pub struct NoFieldOnType<'tcx> {
+    #[primary_span]
+    pub span: Span,
+    pub ty: Ty<'tcx>,
+    pub field: Ident,
+}
+
 // FIXME(fmease): Deduplicate:
 
 #[derive(Diagnostic)]