7 files changed, 78 insertions, 6 deletions
diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 50817dd0a80..8e1cb6a514f 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -756,6 +756,13 @@ impl<'hir> Map<'hir> {
         }
     }
 
+    pub fn expect_field(self, id: HirId) -> &'hir FieldDef<'hir> {
+        match self.tcx.hir_node(id) {
+            Node::Field(field) => field,
+            _ => bug!("expected field, found {}", self.node_to_string(id)),
+        }
+    }
+
     pub fn expect_foreign_item(self, id: OwnerId) -> &'hir ForeignItem<'hir> {
         match self.tcx.hir_owner_node(id) {
             OwnerNode::ForeignItem(item) => item,
diff --git a/compiler/rustc_middle/src/query/erase.rs b/compiler/rustc_middle/src/query/erase.rs
index a272a51f327..7039749b1b7 100644
--- a/compiler/rustc_middle/src/query/erase.rs
+++ b/compiler/rustc_middle/src/query/erase.rs
@@ -238,6 +238,7 @@ trivial! {
     Option<rustc_span::def_id::DefId>,
     Option<rustc_span::def_id::LocalDefId>,
     Option<rustc_span::Span>,
+    Option<rustc_target::abi::FieldIdx>,
     Option<rustc_target::spec::PanicStrategy>,
     Option<usize>,
     Result<(), rustc_errors::ErrorGuaranteed>,
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 938fba0ed09..e9f61a54270 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -2217,6 +2217,10 @@ rustc_queries! {
         desc { "whether the item should be made inlinable across crates" }
         separate_provide_extern
     }
+
+    query find_field((def_id, ident): (DefId, rustc_span::symbol::Ident)) -> Option<rustc_target::abi::FieldIdx> {
+        desc { |tcx| "find the index of maybe nested field `{ident}` in `{}`", tcx.def_path_str(def_id) }
+    }
 }
 
 rustc_query_append! { define_callbacks! }
diff --git a/compiler/rustc_middle/src/ty/adt.rs b/compiler/rustc_middle/src/ty/adt.rs
index 685c3e87dac..d07a53ee679 100644
--- a/compiler/rustc_middle/src/ty/adt.rs
+++ b/compiler/rustc_middle/src/ty/adt.rs
@@ -50,6 +50,8 @@ bitflags! {
         const IS_VARIANT_LIST_NON_EXHAUSTIVE = 1 << 8;
         /// Indicates whether the type is `UnsafeCell`.
         const IS_UNSAFE_CELL              = 1 << 9;
+        /// Indicates whether the type is anonymous.
+        const IS_ANONYMOUS                = 1 << 10;
     }
 }
 rustc_data_structures::external_bitflags_debug! { AdtFlags }
@@ -233,8 +235,12 @@ impl AdtDefData {
         kind: AdtKind,
         variants: IndexVec<VariantIdx, VariantDef>,
         repr: ReprOptions,
+        is_anonymous: bool,
     ) -> Self {
-        debug!("AdtDef::new({:?}, {:?}, {:?}, {:?})", did, kind, variants, repr);
+        debug!(
+            "AdtDef::new({:?}, {:?}, {:?}, {:?}, {:?})",
+            did, kind, variants, repr, is_anonymous
+        );
         let mut flags = AdtFlags::NO_ADT_FLAGS;
 
         if kind == AdtKind::Enum && tcx.has_attr(did, sym::non_exhaustive) {
@@ -267,6 +273,9 @@ impl AdtDefData {
         if Some(did) == tcx.lang_items().unsafe_cell_type() {
             flags |= AdtFlags::IS_UNSAFE_CELL;
         }
+        if is_anonymous {
+            flags |= AdtFlags::IS_ANONYMOUS;
+        }
 
         AdtDefData { did, variants, flags, repr }
     }
@@ -365,6 +374,12 @@ impl<'tcx> AdtDef<'tcx> {
         self.flags().contains(AdtFlags::IS_MANUALLY_DROP)
     }
 
+    /// Returns `true` if this is an anonymous adt
+    #[inline]
+    pub fn is_anonymous(self) -> bool {
+        self.flags().contains(AdtFlags::IS_ANONYMOUS)
+    }
+
     /// Returns `true` if this type has a destructor.
     pub fn has_dtor(self, tcx: TyCtxt<'tcx>) -> bool {
         self.destructor(tcx).is_some()
@@ -386,7 +401,7 @@ impl<'tcx> AdtDef<'tcx> {
     }
 
     /// Returns an iterator over all fields contained
-    /// by this ADT.
+    /// by this ADT (nested unnamed fields are not expanded).
     #[inline]
     pub fn all_fields(self) -> impl Iterator<Item = &'tcx FieldDef> + Clone {
         self.variants().iter().flat_map(|v| v.fields.iter())
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index b747f0a4fb6..9a0eea6592f 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -715,8 +715,16 @@ impl<'tcx> TyCtxt<'tcx> {
         kind: AdtKind,
         variants: IndexVec<VariantIdx, ty::VariantDef>,
         repr: ReprOptions,
+        is_anonymous: bool,
     ) -> ty::AdtDef<'tcx> {
-        self.mk_adt_def_from_data(ty::AdtDefData::new(self, did, kind, variants, repr))
+        self.mk_adt_def_from_data(ty::AdtDefData::new(
+            self,
+            did,
+            kind,
+            variants,
+            repr,
+            is_anonymous,
+        ))
     }
 
     /// Allocates a read-only byte or string literal for `mir::interpret`.
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index c9137f374a2..e73b9836174 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1130,6 +1130,8 @@ bitflags! {
         /// Indicates whether this variant was obtained as part of recovering from
         /// a syntactic error. May be incomplete or bogus.
         const IS_RECOVERED = 1 << 1;
+        /// Indicates whether this variant has unnamed fields.
+        const HAS_UNNAMED_FIELDS = 1 << 2;
     }
 }
 rustc_data_structures::external_bitflags_debug! { VariantFlags }
@@ -1143,7 +1145,7 @@ pub struct VariantDef {
     /// `DefId` that identifies the variant's constructor.
     /// If this variant is a struct variant, then this is `None`.
     pub ctor: Option<(CtorKind, DefId)>,
-    /// Variant or struct name.
+    /// Variant or struct name, maybe empty for anonymous adt (struct or union).
     pub name: Symbol,
     /// Discriminant of this variant.
     pub discr: VariantDiscr,
@@ -1180,11 +1182,12 @@ impl VariantDef {
         parent_did: DefId,
         recovered: bool,
         is_field_list_non_exhaustive: bool,
+        has_unnamed_fields: bool,
     ) -> Self {
         debug!(
             "VariantDef::new(name = {:?}, variant_did = {:?}, ctor = {:?}, discr = {:?},
-             fields = {:?}, adt_kind = {:?}, parent_did = {:?})",
-            name, variant_did, ctor, discr, fields, adt_kind, parent_did,
+             fields = {:?}, adt_kind = {:?}, parent_did = {:?}, has_unnamed_fields = {:?})",
+            name, variant_did, ctor, discr, fields, adt_kind, parent_did, has_unnamed_fields,
         );
 
         let mut flags = VariantFlags::NO_VARIANT_FLAGS;
@@ -1196,6 +1199,10 @@ impl VariantDef {
             flags |= VariantFlags::IS_RECOVERED;
         }
 
+        if has_unnamed_fields {
+            flags |= VariantFlags::HAS_UNNAMED_FIELDS;
+        }
+
         VariantDef { def_id: variant_did.unwrap_or(parent_did), ctor, name, discr, fields, flags }
     }
 
@@ -1211,6 +1218,12 @@ impl VariantDef {
         self.flags.intersects(VariantFlags::IS_RECOVERED)
     }
 
+    /// Does this variant contains unnamed fields
+    #[inline]
+    pub fn has_unnamed_fields(&self) -> bool {
+        self.flags.intersects(VariantFlags::HAS_UNNAMED_FIELDS)
+    }
+
     /// Computes the `Ident` of this variant by looking up the `Span`
     pub fn ident(&self, tcx: TyCtxt<'_>) -> Ident {
         Ident::new(self.name, tcx.def_ident_span(self.def_id).unwrap())
@@ -1374,6 +1387,11 @@ impl<'tcx> FieldDef {
     pub fn ident(&self, tcx: TyCtxt<'_>) -> Ident {
         Ident::new(self.name, tcx.def_ident_span(self.did).unwrap())
     }
+
+    /// Returns whether the field is unnamed
+    pub fn is_unnamed(&self) -> bool {
+        self.name == rustc_span::symbol::kw::Underscore
+    }
 }
 
 #[derive(Debug, PartialEq, Eq)]
diff --git a/compiler/rustc_middle/src/ty/typeck_results.rs b/compiler/rustc_middle/src/ty/typeck_results.rs
index ad41a674dd8..be91474b988 100644
--- a/compiler/rustc_middle/src/ty/typeck_results.rs
+++ b/compiler/rustc_middle/src/ty/typeck_results.rs
@@ -44,6 +44,12 @@ pub struct TypeckResults<'tcx> {
     /// belongs, but it may not exist if it's a tuple field (`tuple.0`).
     field_indices: ItemLocalMap<FieldIdx>,
 
+    /// Resolved types and indices for the nested fields' accesses of `obj.field` (expanded
+    /// to `obj._(1)._(2).field` in THIR). This map only stores the intermediate type
+    /// of `obj._(1)` and index of `_(1)._(2)`, and the type of `_(1)._(2)`, and the index of
+    /// `_(2).field`.
+    nested_fields: ItemLocalMap<Vec<(Ty<'tcx>, FieldIdx)>>,
+
     /// Stores the types for various nodes in the AST. Note that this table
     /// is not guaranteed to be populated outside inference. See
     /// typeck::check::fn_ctxt for details.
@@ -214,6 +220,7 @@ impl<'tcx> TypeckResults<'tcx> {
             hir_owner,
             type_dependent_defs: Default::default(),
             field_indices: Default::default(),
+            nested_fields: Default::default(),
             user_provided_types: Default::default(),
             user_provided_sigs: Default::default(),
             node_types: Default::default(),
@@ -285,6 +292,18 @@ impl<'tcx> TypeckResults<'tcx> {
         self.field_indices().get(id).cloned()
     }
 
+    pub fn nested_fields(&self) -> LocalTableInContext<'_, Vec<(Ty<'tcx>, FieldIdx)>> {
+        LocalTableInContext { hir_owner: self.hir_owner, data: &self.nested_fields }
+    }
+
+    pub fn nested_fields_mut(&mut self) -> LocalTableInContextMut<'_, Vec<(Ty<'tcx>, FieldIdx)>> {
+        LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.nested_fields }
+    }
+
+    pub fn nested_field_tys_and_indices(&self, id: hir::HirId) -> &[(Ty<'tcx>, FieldIdx)] {
+        self.nested_fields().get(id).map_or(&[], Vec::as_slice)
+    }
+
     pub fn user_provided_types(&self) -> LocalTableInContext<'_, CanonicalUserType<'tcx>> {
         LocalTableInContext { hir_owner: self.hir_owner, data: &self.user_provided_types }
     }