Rollup merge of #156403 - SpriteOvO:type-info-refactor-variant, r=oli-obk

Add `TypeId` methods `variants` `fields` `field` for `type_info`

Tracking issue rust-lang/rust#146922

- Adds `fn TypeId::variants` returns the number of variants, for struct and union and primitive types, it's always 1.
- Adds `fn TypeId::fields` returns the number of fields.
- Adds `fn TypeId::field` returns a field representing type `FieldId`.
- Adds a new type `FieldId`, which is a wrapper of `FieldRepresentingType`'s `TypeId`.

For methods `{fields,field}`, if indexing out of bounds, a compile-time error will be raised.

Regarding the removal of `Type` items, this will be done in a later PR in one go.

r? @oli-obk

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -2,7 +2,7 @@
 use std::hash::Hash;
 use std::{fmt, mem};
 
-use rustc_abi::{Align, FIRST_VARIANT, FieldIdx, Size};
+use rustc_abi::{Align, FIRST_VARIANT, FieldIdx, Size, VariantIdx};
 use rustc_ast::Mutability;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap, IndexEntry};
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -622,6 +622,75 @@ fn call_intrinsic(
                 ecx.write_discriminant(variant_index, dest)?;
             }
 
+            sym::type_id_fields => {
+                let ty = ecx.read_type_id(&args[0])?;
+                let variant_idx = ecx.read_target_usize(&args[1])? as usize;
+
+                let variants_num =
+                    ty.ty_adt_def().map(|adt_def| adt_def.variants().len()).unwrap_or(1);
+                if variant_idx >= variants_num {
+                    throw_ub!(BoundsCheckFailed {
+                        len: variants_num as u64,
+                        index: variant_idx as u64
+                    });
+                }
+
+                let fields_num = match ty.kind() {
+                    ty::Adt(adt_def, _) => {
+                        let variant_def = &adt_def.variants()[VariantIdx::from_usize(variant_idx)];
+                        variant_def.fields.len()
+                    }
+                    ty::Tuple(fields) => fields.len(),
+                    _ => 0, // Other types have no fields
+                };
+
+                ecx.write_scalar(Scalar::from_target_usize(fields_num as u64, ecx), dest)?;
+            }
+
+            sym::type_id_field_representing_type => {
+                let ty = ecx.read_type_id(&args[0])?;
+                let variant_idx = ecx.read_target_usize(&args[1])? as usize;
+                let field_idx = ecx.read_target_usize(&args[2])? as usize;
+
+                let variants_num =
+                    ty.ty_adt_def().map(|adt_def| adt_def.variants().len()).unwrap_or(1);
+                if variant_idx >= variants_num {
+                    throw_ub!(BoundsCheckFailed {
+                        len: variants_num as u64,
+                        index: variant_idx as u64
+                    });
+                }
+
+                let fields_num = match ty.kind() {
+                    ty::Adt(adt_def, _) => {
+                        let variant_def = &adt_def.variants()[VariantIdx::from_usize(variant_idx)];
+                        variant_def.fields.len()
+                    }
+                    ty::Tuple(fields) => fields.len(),
+                    _ => 0, // Other types have no fields
+                };
+                if field_idx >= fields_num {
+                    throw_ub!(BoundsCheckFailed {
+                        len: fields_num as u64,
+                        index: field_idx as u64
+                    });
+                }
+
+                let frt = Ty::new_field_representing_type(
+                    *ecx.tcx,
+                    ty,
+                    VariantIdx::from_usize(variant_idx),
+                    FieldIdx::from_usize(field_idx),
+                );
+                ecx.write_type_id(frt, dest)?;
+            }
+
+            sym::type_id_variants => {
+                let ty = ecx.read_type_id(&args[0])?;
+                let variants_num = ty.ty_adt_def().map(|def| def.variants().len()).unwrap_or(1);
+                ecx.write_scalar(Scalar::from_target_usize(variants_num as u64, ecx), dest)?;
+            }
+
             sym::field_offset => {
                 let frt_ty = instance.args.type_at(0);
                 ensure_monomorphic_enough(ecx.tcx.tcx, frt_ty)?;
@@ -643,6 +712,20 @@ fn call_intrinsic(
                 ecx.write_scalar(Scalar::from_target_usize(offset, ecx), dest)?;
             }
 
+            sym::field_representing_type_actual_type_id => {
+                let frt_ty = ecx.read_type_id(&args[0])?;
+
+                let field_ty = if let ty::Adt(def, args) = frt_ty.kind()
+                    && let Some(FieldInfo { ty, .. }) =
+                        def.field_representing_type_info(ecx.tcx.tcx, args)
+                {
+                    ecx.tcx.erase_and_anonymize_regions(ty)
+                } else {
+                    span_bug!(ecx.cur_span(), "expected field representing type, got {frt_ty}")
+                };
+                ecx.write_type_id(field_ty, dest)?;
+            }
+
             _ => {
                 // We haven't handled the intrinsic, let's see if we can use a fallback body.
                 if ecx.tcx.intrinsic(instance.def_id()).unwrap().must_be_overridden {

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -114,6 +114,7 @@ fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hi
         | sym::fadd_algebraic
         | sym::fdiv_algebraic
         | sym::field_offset
+        | sym::field_representing_type_actual_type_id
         | sym::floorf16
         | sym::floorf32
         | sym::floorf64
@@ -213,6 +214,9 @@ fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hi
         | sym::truncf128
         | sym::type_id
         | sym::type_id_eq
+        | sym::type_id_field_representing_type
+        | sym::type_id_fields
+        | sym::type_id_variants
         | sym::type_id_vtable
         | sym::type_name
         | sym::type_of
@@ -319,6 +323,11 @@ pub(crate) fn check_intrinsic_type(
         sym::type_name => (1, 0, vec![], Ty::new_static_str(tcx)),
         sym::type_id => (1, 0, vec![], type_id_ty()),
         sym::type_id_eq => (0, 0, vec![type_id_ty(), type_id_ty()], tcx.types.bool),
+        sym::type_id_field_representing_type => {
+            (0, 0, vec![type_id_ty(), tcx.types.usize, tcx.types.usize], type_id_ty())
+        }
+        sym::type_id_fields => (0, 0, vec![type_id_ty(), tcx.types.usize], tcx.types.usize),
+        sym::type_id_variants => (0, 0, vec![type_id_ty()], tcx.types.usize),
         sym::type_id_vtable => {
             let dyn_metadata = tcx.require_lang_item(LangItem::DynMetadata, span);
             let dyn_metadata_adt_ref = tcx.adt_def(dyn_metadata);
@@ -339,6 +348,7 @@ pub(crate) fn check_intrinsic_type(
             vec![type_id_ty()],
             tcx.type_of(tcx.lang_items().type_struct().unwrap()).no_bound_vars().unwrap(),
         ),
+        sym::field_representing_type_actual_type_id => (0, 0, vec![type_id_ty()], type_id_ty()),
         sym::offload => (
             3,
             0,

compiler/rustc_span/src/symbol.rs

@@ -948,6 +948,7 @@
         field_offset,
         field_projections,
         field_representing_type,
+        field_representing_type_actual_type_id,
         field_representing_type_raw,
         field_type,
         fields,
@@ -2098,6 +2099,9 @@
         type_changing_struct_update,
         type_id,
         type_id_eq,
+        type_id_field_representing_type,
+        type_id_fields,
+        type_id_variants,
         type_id_vtable,
         type_info,
         type_ir,