Adding upstream version 1.69.0+dfsg1.upstream/1.69.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

5 files changed, 498 insertions, 440 deletions

diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 143d8f2f1..b1e59b0a4 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -11,7 +11,7 @@ use rustc_data_structures::sync::{Lock, LockGuard, Lrc, OnceCell};
 use rustc_data_structures::unhash::UnhashMap;
 use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
 use rustc_expand::proc_macro::{AttrProcMacro, BangProcMacro, DeriveProcMacro};
-use rustc_hir::def::{CtorKind, DefKind, Res};
+use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap, Res};
 use rustc_hir::def_id::{CrateNum, DefId, DefIndex, CRATE_DEF_INDEX, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathData, DefPathHash};
 use rustc_hir::diagnostic_items::DiagnosticItems;
@@ -654,7 +654,7 @@ impl<'a, 'tcx, T> Decodable<DecodeContext<'a, 'tcx>> for LazyValue<T> {
 impl<'a, 'tcx, T> Decodable<DecodeContext<'a, 'tcx>> for LazyArray<T> {
     fn decode(decoder: &mut DecodeContext<'a, 'tcx>) -> Self {
         let len = decoder.read_usize();
-        if len == 0 { LazyArray::empty() } else { decoder.read_lazy_array(len) }
+        if len == 0 { LazyArray::default() } else { decoder.read_lazy_array(len) }
     }
 }
 
@@ -864,7 +864,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .tables
                 .children
                 .get(self, index)
-                .unwrap_or_else(LazyArray::empty)
+                .expect("fields are not encoded for a variant")
                 .decode(self)
                 .map(|index| ty::FieldDef {
                     did: self.local_def_id(index),
@@ -896,7 +896,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .tables
                 .children
                 .get(self, item_id)
-                .unwrap_or_else(LazyArray::empty)
+                .expect("variants are not encoded for an enum")
                 .decode(self)
                 .filter_map(|index| {
                     let kind = self.def_kind(index);
@@ -910,7 +910,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             std::iter::once(self.get_variant(&kind, item_id, did)).collect()
         };
 
-        tcx.alloc_adt_def(did, adt_kind, variants, repr)
+        tcx.mk_adt_def(did, adt_kind, variants, repr)
     }
 
     fn get_generics(self, item_id: DefIndex, sess: &Session) -> ty::Generics {
@@ -985,7 +985,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         let vis = self.get_visibility(id);
         let span = self.get_span(id, sess);
         let macro_rules = match kind {
-            DefKind::Macro(..) => self.root.tables.macro_rules.get(self, id).is_some(),
+            DefKind::Macro(..) => self.root.tables.is_macro_rules.get(self, id),
             _ => false,
         };
 
@@ -1045,7 +1045,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .tables
             .fn_arg_names
             .get(self, id)
-            .unwrap_or_else(LazyArray::empty)
+            .expect("argument names not encoded for a function")
             .decode((self, sess))
             .nth(0)
             .map_or(false, |ident| ident.name == kw::SelfLower)
@@ -1060,7 +1060,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .tables
             .children
             .get(self, id)
-            .unwrap_or_else(LazyArray::empty)
+            .expect("associated items not encoded for an item")
             .decode((self, sess))
             .map(move |child_index| self.local_def_id(child_index))
     }
@@ -1068,13 +1068,12 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     fn get_associated_item(self, id: DefIndex, sess: &'a Session) -> ty::AssocItem {
         let name = self.item_name(id);
 
-        let kind = match self.def_kind(id) {
-            DefKind::AssocConst => ty::AssocKind::Const,
-            DefKind::AssocFn => ty::AssocKind::Fn,
-            DefKind::AssocTy => ty::AssocKind::Type,
+        let (kind, has_self) = match self.def_kind(id) {
+            DefKind::AssocConst => (ty::AssocKind::Const, false),
+            DefKind::AssocFn => (ty::AssocKind::Fn, self.get_fn_has_self_parameter(id, sess)),
+            DefKind::AssocTy => (ty::AssocKind::Type, false),
             _ => bug!("cannot get associated-item of `{:?}`", self.def_key(id)),
         };
-        let has_self = self.get_fn_has_self_parameter(id, sess);
         let container = self.root.tables.assoc_container.get(self, id).unwrap();
 
         ty::AssocItem {
@@ -1131,7 +1130,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .tables
             .children
             .get(self, id)
-            .unwrap_or_else(LazyArray::empty)
+            .expect("fields not encoded for a struct")
             .decode(self)
             .map(move |index| respan(self.get_span(index, sess), self.item_name(index)))
     }
@@ -1144,7 +1143,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .tables
             .children
             .get(self, id)
-            .unwrap_or_else(LazyArray::empty)
+            .expect("fields not encoded for a struct")
             .decode(self)
             .map(move |field_index| self.get_visibility(field_index))
     }
@@ -1159,52 +1158,23 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .tables
                 .inherent_impls
                 .get(self, id)
-                .unwrap_or_else(LazyArray::empty)
                 .decode(self)
                 .map(|index| self.local_def_id(index)),
         )
     }
 
-    /// Decodes all inherent impls in the crate (for rustdoc).
-    fn get_inherent_impls(self) -> impl Iterator<Item = (DefId, DefId)> + 'a {
-        (0..self.root.tables.inherent_impls.size()).flat_map(move |i| {
-            let ty_index = DefIndex::from_usize(i);
-            let ty_def_id = self.local_def_id(ty_index);
-            self.root
-                .tables
-                .inherent_impls
-                .get(self, ty_index)
-                .unwrap_or_else(LazyArray::empty)
-                .decode(self)
-                .map(move |impl_index| (ty_def_id, self.local_def_id(impl_index)))
-        })
-    }
-
     /// Decodes all traits in the crate (for rustdoc and rustc diagnostics).
     fn get_traits(self) -> impl Iterator<Item = DefId> + 'a {
         self.root.traits.decode(self).map(move |index| self.local_def_id(index))
     }
 
     /// Decodes all trait impls in the crate (for rustdoc).
-    fn get_trait_impls(self) -> impl Iterator<Item = (DefId, DefId, Option<SimplifiedType>)> + 'a {
-        self.cdata.trait_impls.iter().flat_map(move |(&(trait_cnum_raw, trait_index), impls)| {
-            let trait_def_id = DefId {
-                krate: self.cnum_map[CrateNum::from_u32(trait_cnum_raw)],
-                index: trait_index,
-            };
-            impls.decode(self).map(move |(impl_index, simplified_self_ty)| {
-                (trait_def_id, self.local_def_id(impl_index), simplified_self_ty)
-            })
+    fn get_trait_impls(self) -> impl Iterator<Item = DefId> + 'a {
+        self.cdata.trait_impls.values().flat_map(move |impls| {
+            impls.decode(self).map(move |(impl_index, _)| self.local_def_id(impl_index))
         })
     }
 
-    fn get_all_incoherent_impls(self) -> impl Iterator<Item = DefId> + 'a {
-        self.cdata
-            .incoherent_impls
-            .values()
-            .flat_map(move |impls| impls.decode(self).map(move |idx| self.local_def_id(idx)))
-    }
-
     fn get_incoherent_impls(self, tcx: TyCtxt<'tcx>, simp: SimplifiedType) -> &'tcx [DefId] {
         if let Some(impls) = self.cdata.incoherent_impls.get(&simp) {
             tcx.arena.alloc_from_iter(impls.decode(self).map(|idx| self.local_def_id(idx)))
@@ -1283,7 +1253,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     fn get_macro(self, id: DefIndex, sess: &Session) -> ast::MacroDef {
         match self.def_kind(id) {
             DefKind::Macro(_) => {
-                let macro_rules = self.root.tables.macro_rules.get(self, id).is_some();
+                let macro_rules = self.root.tables.is_macro_rules.get(self, id);
                 let body =
                     self.root.tables.macro_definition.get(self, id).unwrap().decode((self, sess));
                 ast::MacroDef { macro_rules, body: ast::ptr::P(body) }
@@ -1322,7 +1292,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     ) -> DefPathHash {
         *def_path_hashes
             .entry(index)
-            .or_insert_with(|| self.root.tables.def_path_hashes.get(self, index).unwrap())
+            .or_insert_with(|| self.root.tables.def_path_hashes.get(self, index))
     }
 
     #[inline]
@@ -1594,12 +1564,30 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             })
     }
 
-    fn get_may_have_doc_links(self, index: DefIndex) -> bool {
-        self.root.tables.may_have_doc_links.get(self, index).is_some()
+    fn get_attr_flags(self, index: DefIndex) -> AttrFlags {
+        self.root.tables.attr_flags.get(self, index)
     }
 
     fn get_is_intrinsic(self, index: DefIndex) -> bool {
-        self.root.tables.is_intrinsic.get(self, index).is_some()
+        self.root.tables.is_intrinsic.get(self, index)
+    }
+
+    fn get_doc_link_resolutions(self, index: DefIndex) -> DocLinkResMap {
+        self.root
+            .tables
+            .doc_link_resolutions
+            .get(self, index)
+            .expect("no resolutions for a doc link")
+            .decode(self)
+    }
+
+    fn get_doc_link_traits_in_scope(self, index: DefIndex) -> impl Iterator<Item = DefId> + 'a {
+        self.root
+            .tables
+            .doc_link_traits_in_scope
+            .get(self, index)
+            .expect("no traits in scope for a doc link")
+            .decode(self)
     }
 }
 
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 6fd5bd52a..83a0e833e 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -1,6 +1,8 @@
 use crate::creader::{CStore, LoadedMacro};
 use crate::foreign_modules;
 use crate::native_libs;
+use crate::rmeta::table::IsDefault;
+use crate::rmeta::AttrFlags;
 
 use rustc_ast as ast;
 use rustc_attr::Deprecation;
@@ -87,6 +89,14 @@ macro_rules! provide_one {
             }
         }
     };
+    ($tcx:ident, $def_id:ident, $other:ident, $cdata:ident, $name:ident => { table_defaulted_array }) => {
+        provide_one! {
+            $tcx, $def_id, $other, $cdata, $name => {
+                let lazy = $cdata.root.tables.$name.get($cdata, $def_id.index);
+                if lazy.is_default() { &[] } else { $tcx.arena.alloc_from_iter(lazy.decode(($cdata, $tcx))) }
+            }
+        }
+    };
     ($tcx:ident, $def_id:ident, $other:ident, $cdata:ident, $name:ident => { table_direct }) => {
         provide_one! {
             $tcx, $def_id, $other, $cdata, $name => {
@@ -104,7 +114,7 @@ macro_rules! provide_one {
         fn $name<'tcx>(
             $tcx: TyCtxt<'tcx>,
             def_id_arg: ty::query::query_keys::$name<'tcx>,
-        ) -> ty::query::query_values::$name<'tcx> {
+        ) -> ty::query::query_provided::$name<'tcx> {
             let _prof_timer =
                 $tcx.prof.generic_activity(concat!("metadata_decode_entry_", stringify!($name)));
 
@@ -120,7 +130,13 @@ macro_rules! provide_one {
                 $tcx.ensure().crate_hash($def_id.krate);
             }
 
-            let $cdata = CStore::from_tcx($tcx).get_crate_data($def_id.krate);
+            let cdata = rustc_data_structures::sync::MappedReadGuard::map(CStore::from_tcx($tcx), |c| {
+                c.get_crate_data($def_id.krate).cdata
+            });
+            let $cdata = crate::creader::CrateMetadataRef {
+                cdata: &cdata,
+                cstore: &CStore::from_tcx($tcx),
+            };
 
             $compute
         }
@@ -186,10 +202,10 @@ impl IntoArgs for (CrateNum, SimplifiedType) {
 }
 
 provide! { tcx, def_id, other, cdata,
-    explicit_item_bounds => { table }
+    explicit_item_bounds => { table_defaulted_array }
     explicit_predicates_of => { table }
     generics_of => { table }
-    inferred_outlives_of => { table }
+    inferred_outlives_of => { table_defaulted_array }
     super_predicates_of => { table }
     type_of => { table }
     variances_of => { table }
@@ -201,6 +217,7 @@ provide! { tcx, def_id, other, cdata,
     thir_abstract_const => { table }
     optimized_mir => { table }
     mir_for_ctfe => { table }
+    mir_generator_witnesses => { table }
     promoted_mir => { table }
     def_span => { table }
     def_ident_span => { table }
@@ -225,12 +242,7 @@ provide! { tcx, def_id, other, cdata,
     deduced_param_attrs => { table }
     is_type_alias_impl_trait => {
         debug_assert_eq!(tcx.def_kind(def_id), DefKind::OpaqueTy);
-        cdata
-            .root
-            .tables
-            .is_type_alias_impl_trait
-            .get(cdata, def_id.index)
-            .is_some()
+        cdata.root.tables.is_type_alias_impl_trait.get(cdata, def_id.index)
     }
     collect_return_position_impl_trait_in_trait_tys => {
         Ok(cdata
@@ -242,6 +254,8 @@ provide! { tcx, def_id, other, cdata,
             .process_decoded(tcx, || panic!("{def_id:?} does not have trait_impl_trait_tys")))
      }
 
+    associated_items_for_impl_trait_in_trait => { table_defaulted_array }
+
     visibility => { cdata.get_visibility(def_id.index) }
     adt_def => { cdata.get_adt_def(def_id.index, tcx) }
     adt_destructor => {
@@ -298,6 +312,7 @@ provide! { tcx, def_id, other, cdata,
     extra_filename => { cdata.root.extra_filename.clone() }
 
     traits_in_crate => { tcx.arena.alloc_from_iter(cdata.get_traits()) }
+    trait_impls_in_crate => { tcx.arena.alloc_from_iter(cdata.get_trait_impls()) }
     implementations_of_trait => { cdata.get_implementations_of_trait(tcx, other) }
     crate_incoherent_impls => { cdata.get_incoherent_impls(tcx, other) }
 
@@ -338,6 +353,11 @@ provide! { tcx, def_id, other, cdata,
     crate_extern_paths => { cdata.source().paths().cloned().collect() }
     expn_that_defined => { cdata.get_expn_that_defined(def_id.index, tcx.sess) }
     generator_diagnostic_data => { cdata.get_generator_diagnostic_data(tcx, def_id.index) }
+    is_doc_hidden => { cdata.get_attr_flags(def_id.index).contains(AttrFlags::IS_DOC_HIDDEN) }
+    doc_link_resolutions => { tcx.arena.alloc(cdata.get_doc_link_resolutions(def_id.index)) }
+    doc_link_traits_in_scope => {
+        tcx.arena.alloc_from_iter(cdata.get_doc_link_traits_in_scope(def_id.index))
+    }
 }
 
 pub(in crate::rmeta) fn provide(providers: &mut Providers) {
@@ -425,7 +445,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
                         return;
                     }
 
-                    if ty::util::is_doc_hidden(tcx, parent) {
+                    if tcx.is_doc_hidden(parent) {
                         fallback_map.push((def_id, parent));
                         return;
                     }
@@ -597,42 +617,6 @@ impl CStore {
     ) -> Span {
         self.get_crate_data(cnum).get_proc_macro_quoted_span(id, sess)
     }
-
-    /// Decodes all trait impls in the crate (for rustdoc).
-    pub fn trait_impls_in_crate_untracked(
-        &self,
-        cnum: CrateNum,
-    ) -> impl Iterator<Item = (DefId, DefId, Option<SimplifiedType>)> + '_ {
-        self.get_crate_data(cnum).get_trait_impls()
-    }
-
-    /// Decodes all inherent impls in the crate (for rustdoc).
-    pub fn inherent_impls_in_crate_untracked(
-        &self,
-        cnum: CrateNum,
-    ) -> impl Iterator<Item = (DefId, DefId)> + '_ {
-        self.get_crate_data(cnum).get_inherent_impls()
-    }
-
-    /// Decodes all incoherent inherent impls in the crate (for rustdoc).
-    pub fn incoherent_impls_in_crate_untracked(
-        &self,
-        cnum: CrateNum,
-    ) -> impl Iterator<Item = DefId> + '_ {
-        self.get_crate_data(cnum).get_all_incoherent_impls()
-    }
-
-    pub fn associated_item_def_ids_untracked<'a>(
-        &'a self,
-        def_id: DefId,
-        sess: &'a Session,
-    ) -> impl Iterator<Item = DefId> + 'a {
-        self.get_crate_data(def_id.krate).get_associated_item_def_ids(def_id.index, sess)
-    }
-
-    pub fn may_have_doc_links_untracked(&self, def_id: DefId) -> bool {
-        self.get_crate_data(def_id.krate).get_may_have_doc_links(def_id.index)
-    }
 }
 
 impl CrateStore for CStore {
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 8f7a61b72..3ab01f780 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -38,7 +38,6 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{
     self, DebuggerVisualizerFile, ExternalSource, FileName, SourceFile, Span, SyntaxContext,
 };
-use rustc_target::abi::VariantIdx;
 use std::borrow::Borrow;
 use std::collections::hash_map::Entry;
 use std::hash::Hash;
@@ -76,13 +75,13 @@ pub(super) struct EncodeContext<'a, 'tcx> {
     symbol_table: FxHashMap<Symbol, usize>,
 }
 
-/// If the current crate is a proc-macro, returns early with `LazyArray::empty()`.
+/// If the current crate is a proc-macro, returns early with `LazyArray::default()`.
 /// This is useful for skipping the encoding of things that aren't needed
 /// for proc-macro crates.
 macro_rules! empty_proc_macro {
     ($self:ident) => {
         if $self.is_proc_macro {
-            return LazyArray::empty();
+            return LazyArray::default();
         }
     };
 }
@@ -365,25 +364,35 @@ impl<'a, 'tcx> TyEncoder for EncodeContext<'a, 'tcx> {
     }
 }
 
-// Shorthand for `$self.$tables.$table.set($def_id.index, $self.lazy_value($value))`, which would
+// Shorthand for `$self.$tables.$table.set_some($def_id.index, $self.lazy_value($value))`, which would
 // normally need extra variables to avoid errors about multiple mutable borrows.
 macro_rules! record {
     ($self:ident.$tables:ident.$table:ident[$def_id:expr] <- $value:expr) => {{
         {
             let value = $value;
             let lazy = $self.lazy(value);
-            $self.$tables.$table.set($def_id.index, lazy);
+            $self.$tables.$table.set_some($def_id.index, lazy);
         }
     }};
 }
 
-// Shorthand for `$self.$tables.$table.set($def_id.index, $self.lazy_value($value))`, which would
+// Shorthand for `$self.$tables.$table.set_some($def_id.index, $self.lazy_value($value))`, which would
 // normally need extra variables to avoid errors about multiple mutable borrows.
 macro_rules! record_array {
     ($self:ident.$tables:ident.$table:ident[$def_id:expr] <- $value:expr) => {{
         {
             let value = $value;
             let lazy = $self.lazy_array(value);
+            $self.$tables.$table.set_some($def_id.index, lazy);
+        }
+    }};
+}
+
+macro_rules! record_defaulted_array {
+    ($self:ident.$tables:ident.$table:ident[$def_id:expr] <- $value:expr) => {{
+        {
+            let value = $value;
+            let lazy = $self.lazy_array(value);
             $self.$tables.$table.set($def_id.index, lazy);
         }
     }};
@@ -467,13 +476,13 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             {
                 let def_key = self.lazy(table.def_key(def_index));
                 let def_path_hash = table.def_path_hash(def_index);
-                self.tables.def_keys.set(def_index, def_key);
+                self.tables.def_keys.set_some(def_index, def_key);
                 self.tables.def_path_hashes.set(def_index, def_path_hash);
             }
         } else {
             for (def_index, def_key, def_path_hash) in table.enumerated_keys_and_path_hashes() {
                 let def_key = self.lazy(def_key);
-                self.tables.def_keys.set(def_index, def_key);
+                self.tables.def_keys.set_some(def_index, def_key);
                 self.tables.def_path_hashes.set(def_index, *def_path_hash);
             }
         }
@@ -483,7 +492,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         self.lazy(DefPathHashMapRef::BorrowedFromTcx(self.tcx.def_path_hash_to_def_index_map()))
     }
 
-    fn encode_source_map(&mut self) -> LazyTable<u32, LazyValue<rustc_span::SourceFile>> {
+    fn encode_source_map(&mut self) -> LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>> {
         let source_map = self.tcx.sess.source_map();
         let all_source_files = source_map.files();
 
@@ -548,7 +557,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
             let on_disk_index: u32 =
                 on_disk_index.try_into().expect("cannot export more than U32_MAX files");
-            adapted.set(on_disk_index, self.lazy(source_file));
+            adapted.set_some(on_disk_index, self.lazy(source_file));
         }
 
         adapted.encode(&mut self.opaque)
@@ -760,36 +769,50 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     }
 }
 
+struct AnalyzeAttrState {
+    is_exported: bool,
+    is_doc_hidden: bool,
+}
+
 /// Returns whether an attribute needs to be recorded in metadata, that is, if it's usable and
 /// useful in downstream crates. Local-only attributes are an obvious example, but some
 /// rustdoc-specific attributes can equally be of use while documenting the current crate only.
 ///
 /// Removing these superfluous attributes speeds up compilation by making the metadata smaller.
 ///
-/// Note: the `is_def_id_public` parameter is used to cache whether the given `DefId` has a public
+/// Note: the `is_exported` parameter is used to cache whether the given `DefId` has a public
 /// visibility: this is a piece of data that can be computed once per defid, and not once per
 /// attribute. Some attributes would only be usable downstream if they are public.
 #[inline]
-fn should_encode_attr(
-    tcx: TyCtxt<'_>,
-    attr: &Attribute,
-    def_id: LocalDefId,
-    is_def_id_public: &mut Option<bool>,
-) -> bool {
+fn analyze_attr(attr: &Attribute, state: &mut AnalyzeAttrState) -> bool {
+    let mut should_encode = false;
     if rustc_feature::is_builtin_only_local(attr.name_or_empty()) {
         // Attributes marked local-only don't need to be encoded for downstream crates.
-        false
     } else if attr.doc_str().is_some() {
-        // We keep all public doc comments because they might be "imported" into downstream crates
-        // if they use `#[doc(inline)]` to copy an item's documentation into their own.
-        *is_def_id_public.get_or_insert_with(|| tcx.effective_visibilities(()).is_exported(def_id))
+        // We keep all doc comments reachable to rustdoc because they might be "imported" into
+        // downstream crates if they use `#[doc(inline)]` to copy an item's documentation into
+        // their own.
+        if state.is_exported {
+            should_encode = true;
+        }
     } else if attr.has_name(sym::doc) {
-        // If this is a `doc` attribute, and it's marked `inline` (as in `#[doc(inline)]`), we can
-        // remove it. It won't be inlinable in downstream crates.
-        attr.meta_item_list().map(|l| l.iter().any(|l| !l.has_name(sym::inline))).unwrap_or(false)
+        // If this is a `doc` attribute that doesn't have anything except maybe `inline` (as in
+        // `#[doc(inline)]`), then we can remove it. It won't be inlinable in downstream crates.
+        if let Some(item_list) = attr.meta_item_list() {
+            for item in item_list {
+                if !item.has_name(sym::inline) {
+                    should_encode = true;
+                    if item.has_name(sym::hidden) {
+                        state.is_doc_hidden = true;
+                        break;
+                    }
+                }
+            }
+        }
     } else {
-        true
+        should_encode = true;
     }
+    should_encode
 }
 
 fn should_encode_visibility(def_kind: DefKind) -> bool {
@@ -815,7 +838,7 @@ fn should_encode_visibility(def_kind: DefKind) -> bool {
         | DefKind::ForeignMod
         | DefKind::OpaqueTy
         | DefKind::ImplTraitPlaceholder
-        | DefKind::Impl
+        | DefKind::Impl { .. }
         | DefKind::Field => true,
         DefKind::TyParam
         | DefKind::ConstParam
@@ -850,7 +873,7 @@ fn should_encode_stability(def_kind: DefKind) -> bool {
         | DefKind::ImplTraitPlaceholder
         | DefKind::Enum
         | DefKind::Union
-        | DefKind::Impl
+        | DefKind::Impl { .. }
         | DefKind::Trait
         | DefKind::TraitAlias
         | DefKind::Macro(..)
@@ -928,7 +951,7 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
         | DefKind::Const
         | DefKind::ForeignMod
         | DefKind::TyAlias
-        | DefKind::Impl
+        | DefKind::Impl { .. }
         | DefKind::Trait
         | DefKind::TraitAlias
         | DefKind::Macro(..)
@@ -965,7 +988,7 @@ fn should_encode_generics(def_kind: DefKind) -> bool {
         | DefKind::InlineConst
         | DefKind::OpaqueTy
         | DefKind::ImplTraitPlaceholder
-        | DefKind::Impl
+        | DefKind::Impl { .. }
         | DefKind::Field
         | DefKind::TyParam
         | DefKind::Closure
@@ -995,7 +1018,7 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
         | DefKind::TyAlias
         | DefKind::OpaqueTy
         | DefKind::ForeignTy
-        | DefKind::Impl
+        | DefKind::Impl { .. }
         | DefKind::AssocFn
         | DefKind::AssocConst
         | DefKind::Closure
@@ -1058,7 +1081,7 @@ fn should_encode_const(def_kind: DefKind) -> bool {
         | DefKind::OpaqueTy
         | DefKind::ImplTraitPlaceholder
         | DefKind::ForeignTy
-        | DefKind::Impl
+        | DefKind::Impl { .. }
         | DefKind::AssocFn
         | DefKind::Closure
         | DefKind::Generator
@@ -1078,49 +1101,40 @@ fn should_encode_const(def_kind: DefKind) -> bool {
     }
 }
 
-fn should_encode_trait_impl_trait_tys(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-    if tcx.def_kind(def_id) != DefKind::AssocFn {
-        return false;
-    }
-
-    let Some(item) = tcx.opt_associated_item(def_id) else { return false; };
-    if item.container != ty::AssocItemContainer::ImplContainer {
-        return false;
+// We only encode impl trait in trait when using `lower-impl-trait-in-trait-to-assoc-ty` unstable
+// option.
+fn should_encode_fn_impl_trait_in_trait<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
+    if tcx.sess.opts.unstable_opts.lower_impl_trait_in_trait_to_assoc_ty
+        && let Some(assoc_item) = tcx.opt_associated_item(def_id)
+        && assoc_item.container == ty::AssocItemContainer::TraitContainer
+        && assoc_item.kind == ty::AssocKind::Fn
+    {
+        true
+    } else {
+        false
     }
-
-    let Some(trait_item_def_id) = item.trait_item_def_id else { return false; };
-
-    // FIXME(RPITIT): This does a somewhat manual walk through the signature
-    // of the trait fn to look for any RPITITs, but that's kinda doing a lot
-    // of work. We can probably remove this when we refactor RPITITs to be
-    // associated types.
-    tcx.fn_sig(trait_item_def_id).skip_binder().output().walk().any(|arg| {
-        if let ty::GenericArgKind::Type(ty) = arg.unpack()
-            && let ty::Alias(ty::Projection, data) = ty.kind()
-            && tcx.def_kind(data.def_id) == DefKind::ImplTraitPlaceholder
-        {
-            true
-        } else {
-            false
-        }
-    })
 }
 
 impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     fn encode_attrs(&mut self, def_id: LocalDefId) {
         let tcx = self.tcx;
-        let mut is_public: Option<bool> = None;
-
-        let mut attrs = tcx
-            .hir()
-            .attrs(tcx.hir().local_def_id_to_hir_id(def_id))
+        let mut state = AnalyzeAttrState {
+            is_exported: tcx.effective_visibilities(()).is_exported(def_id),
+            is_doc_hidden: false,
+        };
+        let attr_iter = tcx
+            .opt_local_def_id_to_hir_id(def_id)
+            .map_or(Default::default(), |hir_id| tcx.hir().attrs(hir_id))
             .iter()
-            .filter(move |attr| should_encode_attr(tcx, attr, def_id, &mut is_public));
+            .filter(|attr| analyze_attr(attr, &mut state));
+
+        record_array!(self.tables.attributes[def_id.to_def_id()] <- attr_iter);
 
-        record_array!(self.tables.attributes[def_id.to_def_id()] <- attrs.clone());
-        if attrs.any(|attr| attr.may_have_doc_links()) {
-            self.tables.may_have_doc_links.set(def_id.local_def_index, ());
+        let mut attr_flags = AttrFlags::empty();
+        if state.is_doc_hidden {
+            attr_flags |= AttrFlags::IS_DOC_HIDDEN;
         }
+        self.tables.attr_flags.set(def_id.local_def_index, attr_flags);
     }
 
     fn encode_def_ids(&mut self) {
@@ -1132,7 +1146,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             let def_id = local_id.to_def_id();
             let def_kind = tcx.opt_def_kind(local_id);
             let Some(def_kind) = def_kind else { continue };
-            self.tables.opt_def_kind.set(def_id.index, def_kind);
+            self.tables.opt_def_kind.set_some(def_id.index, def_kind);
             let def_span = tcx.def_span(local_id);
             record!(self.tables.def_span[def_id] <- def_span);
             self.encode_attrs(local_id);
@@ -1163,9 +1177,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 record!(self.tables.generics_of[def_id] <- g);
                 record!(self.tables.explicit_predicates_of[def_id] <- self.tcx.explicit_predicates_of(def_id));
                 let inferred_outlives = self.tcx.inferred_outlives_of(def_id);
-                if !inferred_outlives.is_empty() {
-                    record_array!(self.tables.inferred_outlives_of[def_id] <- inferred_outlives);
-                }
+                record_defaulted_array!(self.tables.inferred_outlives_of[def_id] <- inferred_outlives);
             }
             if should_encode_type(tcx, local_id, def_kind) {
                 record!(self.tables.type_of[def_id] <- self.tcx.type_of(def_id));
@@ -1178,70 +1190,85 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 record!(self.tables.super_predicates_of[def_id] <- self.tcx.super_predicates_of(def_id));
             }
             if let DefKind::Enum | DefKind::Struct | DefKind::Union = def_kind {
-                let params_in_repr = self.tcx.params_in_repr(def_id);
-                record!(self.tables.params_in_repr[def_id] <- params_in_repr);
+                self.encode_info_for_adt(def_id);
             }
-            if should_encode_trait_impl_trait_tys(tcx, def_id)
+            if tcx.impl_method_has_trait_impl_trait_tys(def_id)
                 && let Ok(table) = self.tcx.collect_return_position_impl_trait_in_trait_tys(def_id)
             {
                 record!(self.tables.trait_impl_trait_tys[def_id] <- table);
             }
+            if should_encode_fn_impl_trait_in_trait(tcx, def_id) {
+                let table = tcx.associated_items_for_impl_trait_in_trait(def_id);
+                record_defaulted_array!(self.tables.associated_items_for_impl_trait_in_trait[def_id] <- table);
+            }
         }
+
         let inherent_impls = tcx.with_stable_hashing_context(|hcx| {
             tcx.crate_inherent_impls(()).inherent_impls.to_sorted(&hcx, true)
         });
-
-        for (def_id, implementations) in inherent_impls {
-            if implementations.is_empty() {
-                continue;
-            }
-            record_array!(self.tables.inherent_impls[def_id.to_def_id()] <- implementations.iter().map(|&def_id| {
+        for (def_id, impls) in inherent_impls {
+            record_defaulted_array!(self.tables.inherent_impls[def_id.to_def_id()] <- impls.iter().map(|def_id| {
                 assert!(def_id.is_local());
                 def_id.index
             }));
         }
+
+        for (def_id, res_map) in &tcx.resolutions(()).doc_link_resolutions {
+            record!(self.tables.doc_link_resolutions[def_id.to_def_id()] <- res_map);
+        }
+
+        for (def_id, traits) in &tcx.resolutions(()).doc_link_traits_in_scope {
+            record_array!(self.tables.doc_link_traits_in_scope[def_id.to_def_id()] <- traits);
+        }
     }
 
-    fn encode_enum_variant_info(&mut self, def: ty::AdtDef<'tcx>, index: VariantIdx) {
+    #[instrument(level = "trace", skip(self))]
+    fn encode_info_for_adt(&mut self, def_id: DefId) {
         let tcx = self.tcx;
-        let variant = &def.variant(index);
-        let def_id = variant.def_id;
-        debug!("EncodeContext::encode_enum_variant_info({:?})", def_id);
-
-        let data = VariantData {
-            discr: variant.discr,
-            ctor: variant.ctor.map(|(kind, def_id)| (kind, def_id.index)),
-            is_non_exhaustive: variant.is_field_list_non_exhaustive(),
-        };
+        let adt_def = tcx.adt_def(def_id);
+        record!(self.tables.repr_options[def_id] <- adt_def.repr());
+
+        let params_in_repr = self.tcx.params_in_repr(def_id);
+        record!(self.tables.params_in_repr[def_id] <- params_in_repr);
 
-        record!(self.tables.variant_data[def_id] <- data);
-        self.tables.constness.set(def_id.index, hir::Constness::Const);
-        record_array!(self.tables.children[def_id] <- variant.fields.iter().map(|f| {
-            assert!(f.did.is_local());
-            f.did.index
-        }));
-        if let Some((CtorKind::Fn, ctor_def_id)) = variant.ctor {
-            // FIXME(eddyb) encode signature only in `encode_enum_variant_ctor`.
-            record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(ctor_def_id));
+        if adt_def.is_enum() {
+            record_array!(self.tables.children[def_id] <- iter::from_generator(||
+                for variant in tcx.adt_def(def_id).variants() {
+                    yield variant.def_id.index;
+                    // Encode constructors which take a separate slot in value namespace.
+                    if let Some(ctor_def_id) = variant.ctor_def_id() {
+                        yield ctor_def_id.index;
+                    }
+                }
+            ));
+        } else {
+            // For non-enum, there is only one variant, and its def_id is the adt's.
+            debug_assert_eq!(adt_def.variants().len(), 1);
+            debug_assert_eq!(adt_def.non_enum_variant().def_id, def_id);
+            // Therefore, the loop over variants will encode its fields as the adt's children.
         }
-    }
 
-    fn encode_enum_variant_ctor(&mut self, def: ty::AdtDef<'tcx>, index: VariantIdx) {
-        let variant = &def.variant(index);
-        let Some((ctor_kind, def_id)) = variant.ctor else { return };
-        debug!("EncodeContext::encode_enum_variant_ctor({:?})", def_id);
+        for variant in adt_def.variants().iter() {
+            let data = VariantData {
+                discr: variant.discr,
+                ctor: variant.ctor.map(|(kind, def_id)| (kind, def_id.index)),
+                is_non_exhaustive: variant.is_field_list_non_exhaustive(),
+            };
+            record!(self.tables.variant_data[variant.def_id] <- data);
 
-        // FIXME(eddyb) encode only the `CtorKind` for constructors.
-        let data = VariantData {
-            discr: variant.discr,
-            ctor: Some((ctor_kind, def_id.index)),
-            is_non_exhaustive: variant.is_field_list_non_exhaustive(),
-        };
+            self.tables.constness.set_some(variant.def_id.index, hir::Constness::Const);
+            record_array!(self.tables.children[variant.def_id] <- variant.fields.iter().map(|f| {
+                assert!(f.did.is_local());
+                f.did.index
+            }));
 
-        record!(self.tables.variant_data[def_id] <- data);
-        self.tables.constness.set(def_id.index, hir::Constness::Const);
-        if ctor_kind == CtorKind::Fn {
-            record!(self.tables.fn_sig[def_id] <- self.tcx.fn_sig(def_id));
+            if let Some((CtorKind::Fn, ctor_def_id)) = variant.ctor {
+                self.tables.constness.set_some(ctor_def_id.index, hir::Constness::Const);
+                let fn_sig = tcx.fn_sig(ctor_def_id);
+                record!(self.tables.fn_sig[ctor_def_id] <- fn_sig);
+                // FIXME only encode signature for ctor_def_id
+                record!(self.tables.fn_sig[variant.def_id] <- fn_sig);
+            }
         }
     }
 
@@ -1275,8 +1302,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                         hir::ItemKind::Struct(ref vdata, _) => {
                             yield item_id.owner_id.def_id.local_def_index;
                             // Encode constructors which take a separate slot in value namespace.
-                            if let Some(ctor_hir_id) = vdata.ctor_hir_id() {
-                                yield tcx.hir().local_def_id(ctor_hir_id).local_def_index;
+                            if let Some(ctor_def_id) = vdata.ctor_def_id() {
+                                yield ctor_def_id.local_def_index;
                             }
                         }
                         _ if tcx.def_key(item_id.owner_id.to_def_id()).get_opt_name().is_some() => {
@@ -1294,31 +1321,10 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         }
     }
 
-    fn encode_struct_ctor(&mut self, adt_def: ty::AdtDef<'tcx>) {
-        let variant = adt_def.non_enum_variant();
-        let Some((ctor_kind, def_id)) = variant.ctor else { return };
-        debug!("EncodeContext::encode_struct_ctor({:?})", def_id);
-
-        let data = VariantData {
-            discr: variant.discr,
-            ctor: Some((ctor_kind, def_id.index)),
-            is_non_exhaustive: variant.is_field_list_non_exhaustive(),
-        };
-
-        record!(self.tables.repr_options[def_id] <- adt_def.repr());
-        record!(self.tables.variant_data[def_id] <- data);
-        self.tables.constness.set(def_id.index, hir::Constness::Const);
-        if ctor_kind == CtorKind::Fn {
-            record!(self.tables.fn_sig[def_id] <- self.tcx.fn_sig(def_id));
-        }
-    }
-
     fn encode_explicit_item_bounds(&mut self, def_id: DefId) {
         debug!("EncodeContext::encode_explicit_item_bounds({:?})", def_id);
         let bounds = self.tcx.explicit_item_bounds(def_id);
-        if !bounds.is_empty() {
-            record_array!(self.tables.explicit_item_bounds[def_id] <- bounds);
-        }
+        record_defaulted_array!(self.tables.explicit_item_bounds[def_id] <- bounds);
     }
 
     fn encode_info_for_trait_item(&mut self, def_id: DefId) {
@@ -1326,16 +1332,16 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         let tcx = self.tcx;
 
         let impl_defaultness = tcx.impl_defaultness(def_id.expect_local());
-        self.tables.impl_defaultness.set(def_id.index, impl_defaultness);
+        self.tables.impl_defaultness.set_some(def_id.index, impl_defaultness);
         let trait_item = tcx.associated_item(def_id);
-        self.tables.assoc_container.set(def_id.index, trait_item.container);
+        self.tables.assoc_container.set_some(def_id.index, trait_item.container);
 
         match trait_item.kind {
             ty::AssocKind::Const => {}
             ty::AssocKind::Fn => {
                 record_array!(self.tables.fn_arg_names[def_id] <- tcx.fn_arg_names(def_id));
-                self.tables.asyncness.set(def_id.index, tcx.asyncness(def_id));
-                self.tables.constness.set(def_id.index, hir::Constness::NotConst);
+                self.tables.asyncness.set_some(def_id.index, tcx.asyncness(def_id));
+                self.tables.constness.set_some(def_id.index, hir::Constness::NotConst);
             }
             ty::AssocKind::Type => {
                 self.encode_explicit_item_bounds(def_id);
@@ -1351,14 +1357,14 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         let tcx = self.tcx;
 
         let ast_item = self.tcx.hir().expect_impl_item(def_id.expect_local());
-        self.tables.impl_defaultness.set(def_id.index, ast_item.defaultness);
+        self.tables.impl_defaultness.set_some(def_id.index, ast_item.defaultness);
         let impl_item = self.tcx.associated_item(def_id);
-        self.tables.assoc_container.set(def_id.index, impl_item.container);
+        self.tables.assoc_container.set_some(def_id.index, impl_item.container);
 
         match impl_item.kind {
             ty::AssocKind::Fn => {
                 let hir::ImplItemKind::Fn(ref sig, body) = ast_item.kind else { bug!() };
-                self.tables.asyncness.set(def_id.index, sig.header.asyncness);
+                self.tables.asyncness.set_some(def_id.index, sig.header.asyncness);
                 record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));
                 // Can be inside `impl const Trait`, so using sig.header.constness is not reliable
                 let constness = if self.tcx.is_const_fn_raw(def_id) {
@@ -1366,18 +1372,16 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 } else {
                     hir::Constness::NotConst
                 };
-                self.tables.constness.set(def_id.index, constness);
+                self.tables.constness.set_some(def_id.index, constness);
             }
             ty::AssocKind::Const | ty::AssocKind::Type => {}
         }
         if let Some(trait_item_def_id) = impl_item.trait_item_def_id {
-            self.tables.trait_item_def_id.set(def_id.index, trait_item_def_id.into());
+            self.tables.trait_item_def_id.set_some(def_id.index, trait_item_def_id.into());
         }
         if impl_item.kind == ty::AssocKind::Fn {
             record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
-            if tcx.is_intrinsic(def_id) {
-                self.tables.is_intrinsic.set(def_id.index, ());
-            }
+            self.tables.is_intrinsic.set(def_id.index, tcx.is_intrinsic(def_id));
         }
     }
 
@@ -1398,6 +1402,10 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             debug!("EntryBuilder::encode_mir({:?})", def_id);
             if encode_opt {
                 record!(self.tables.optimized_mir[def_id.to_def_id()] <- tcx.optimized_mir(def_id));
+
+                if tcx.sess.opts.unstable_opts.drop_tracking_mir && let DefKind::Generator = self.tcx.def_kind(def_id) {
+                    record!(self.tables.mir_generator_witnesses[def_id.to_def_id()] <- tcx.mir_generator_witnesses(def_id));
+                }
             }
             if encode_const {
                 record!(self.tables.mir_for_ctfe[def_id.to_def_id()] <- tcx.mir_for_ctfe(def_id));
@@ -1502,14 +1510,12 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
         match item.kind {
             hir::ItemKind::Fn(ref sig, .., body) => {
-                self.tables.asyncness.set(def_id.index, sig.header.asyncness);
+                self.tables.asyncness.set_some(def_id.index, sig.header.asyncness);
                 record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));
-                self.tables.constness.set(def_id.index, sig.header.constness);
+                self.tables.constness.set_some(def_id.index, sig.header.constness);
             }
             hir::ItemKind::Macro(ref macro_def, _) => {
-                if macro_def.macro_rules {
-                    self.tables.macro_rules.set(def_id.index, ());
-                }
+                self.tables.is_macro_rules.set(def_id.index, macro_def.macro_rules);
                 record!(self.tables.macro_definition[def_id] <- &*macro_def.body);
             }
             hir::ItemKind::Mod(ref m) => {
@@ -1517,47 +1523,21 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             }
             hir::ItemKind::OpaqueTy(ref opaque) => {
                 self.encode_explicit_item_bounds(def_id);
-                if matches!(opaque.origin, hir::OpaqueTyOrigin::TyAlias) {
-                    self.tables.is_type_alias_impl_trait.set(def_id.index, ());
-                }
-            }
-            hir::ItemKind::Enum(..) => {
-                let adt_def = self.tcx.adt_def(def_id);
-                record!(self.tables.repr_options[def_id] <- adt_def.repr());
-            }
-            hir::ItemKind::Struct(..) => {
-                let adt_def = self.tcx.adt_def(def_id);
-                record!(self.tables.repr_options[def_id] <- adt_def.repr());
-                self.tables.constness.set(def_id.index, hir::Constness::Const);
-
-                let variant = adt_def.non_enum_variant();
-                record!(self.tables.variant_data[def_id] <- VariantData {
-                    discr: variant.discr,
-                    ctor: variant.ctor.map(|(kind, def_id)| (kind, def_id.index)),
-                    is_non_exhaustive: variant.is_field_list_non_exhaustive(),
-                });
-            }
-            hir::ItemKind::Union(..) => {
-                let adt_def = self.tcx.adt_def(def_id);
-                record!(self.tables.repr_options[def_id] <- adt_def.repr());
-
-                let variant = adt_def.non_enum_variant();
-                record!(self.tables.variant_data[def_id] <- VariantData {
-                    discr: variant.discr,
-                    ctor: variant.ctor.map(|(kind, def_id)| (kind, def_id.index)),
-                    is_non_exhaustive: variant.is_field_list_non_exhaustive(),
-                });
+                self.tables
+                    .is_type_alias_impl_trait
+                    .set(def_id.index, matches!(opaque.origin, hir::OpaqueTyOrigin::TyAlias));
             }
             hir::ItemKind::Impl(hir::Impl { defaultness, constness, .. }) => {
-                self.tables.impl_defaultness.set(def_id.index, *defaultness);
-                self.tables.constness.set(def_id.index, *constness);
+                self.tables.impl_defaultness.set_some(def_id.index, *defaultness);
+                self.tables.constness.set_some(def_id.index, *constness);
 
-                let trait_ref = self.tcx.impl_trait_ref(def_id).map(ty::EarlyBinder::skip_binder);
+                let trait_ref = self.tcx.impl_trait_ref(def_id);
                 if let Some(trait_ref) = trait_ref {
+                    let trait_ref = trait_ref.skip_binder();
                     let trait_def = self.tcx.trait_def(trait_ref.def_id);
                     if let Ok(mut an) = trait_def.ancestors(self.tcx, def_id) {
                         if let Some(specialization_graph::Node::Impl(parent)) = an.nth(1) {
-                            self.tables.impl_parent.set(def_id.index, parent.into());
+                            self.tables.impl_parent.set_some(def_id.index, parent.into());
                         }
                     }
 
@@ -1571,7 +1551,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 }
 
                 let polarity = self.tcx.impl_polarity(def_id);
-                self.tables.impl_polarity.set(def_id.index, polarity);
+                self.tables.impl_polarity.set_some(def_id.index, polarity);
             }
             hir::ItemKind::Trait(..) => {
                 let trait_def = self.tcx.trait_def(def_id);
@@ -1586,31 +1566,15 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             }
             hir::ItemKind::Static(..)
             | hir::ItemKind::Const(..)
+            | hir::ItemKind::Enum(..)
+            | hir::ItemKind::Struct(..)
+            | hir::ItemKind::Union(..)
             | hir::ItemKind::ForeignMod { .. }
             | hir::ItemKind::GlobalAsm(..)
             | hir::ItemKind::TyAlias(..) => {}
         };
         // FIXME(eddyb) there should be a nicer way to do this.
         match item.kind {
-            hir::ItemKind::Enum(..) => {
-                record_array!(self.tables.children[def_id] <- iter::from_generator(||
-                    for variant in tcx.adt_def(def_id).variants() {
-                        yield variant.def_id.index;
-                        // Encode constructors which take a separate slot in value namespace.
-                        if let Some(ctor_def_id) = variant.ctor_def_id() {
-                            yield ctor_def_id.index;
-                        }
-                    }
-                ))
-            }
-            hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) => {
-                record_array!(self.tables.children[def_id] <-
-                    self.tcx.adt_def(def_id).non_enum_variant().fields.iter().map(|f| {
-                        assert!(f.did.is_local());
-                        f.did.index
-                    })
-                )
-            }
             hir::ItemKind::Impl { .. } | hir::ItemKind::Trait(..) => {
                 let associated_item_def_ids = self.tcx.associated_item_def_ids(def_id);
                 record_array!(self.tables.children[def_id] <-
@@ -1624,9 +1588,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         }
         if let hir::ItemKind::Fn(..) = item.kind {
             record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
-            if tcx.is_intrinsic(def_id) {
-                self.tables.is_intrinsic.set(def_id.index, ());
-            }
+            self.tables.is_intrinsic.set(def_id.index, tcx.is_intrinsic(def_id));
         }
         if let hir::ItemKind::Impl { .. } = item.kind {
             if let Some(trait_ref) = self.tcx.impl_trait_ref(def_id) {
@@ -1638,17 +1600,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         // so it's easier to do that here then to wait until we would encounter
         // normally in the visitor walk.
         match item.kind {
-            hir::ItemKind::Enum(..) => {
-                let def = self.tcx.adt_def(item.owner_id.to_def_id());
-                for (i, _) in def.variants().iter_enumerated() {
-                    self.encode_enum_variant_info(def, i);
-                    self.encode_enum_variant_ctor(def, i);
-                }
-            }
-            hir::ItemKind::Struct(..) => {
-                let def = self.tcx.adt_def(item.owner_id.to_def_id());
-                self.encode_struct_ctor(def);
-            }
             hir::ItemKind::Impl { .. } => {
                 for &trait_item_def_id in
                     self.tcx.associated_item_def_ids(item.owner_id.to_def_id()).iter()
@@ -1670,7 +1621,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     #[instrument(level = "debug", skip(self))]
     fn encode_info_for_closure(&mut self, def_id: LocalDefId) {
         // NOTE(eddyb) `tcx.type_of(def_id)` isn't used because it's fully generic,
-        // including on the signature, which is inferred in `typeck.
+        // including on the signature, which is inferred in `typeck`.
         let typeck_result: &'tcx ty::TypeckResults<'tcx> = self.tcx.typeck(def_id);
         let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
         let ty = typeck_result.node_type(hir_id);
@@ -1684,8 +1635,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
             ty::Closure(_, substs) => {
                 let constness = self.tcx.constness(def_id.to_def_id());
-                self.tables.constness.set(def_id.to_def_id().index, constness);
-                record!(self.tables.fn_sig[def_id.to_def_id()] <- substs.as_closure().sig());
+                self.tables.constness.set_some(def_id.to_def_id().index, constness);
+                record!(self.tables.fn_sig[def_id.to_def_id()] <- ty::EarlyBinder(substs.as_closure().sig()));
             }
 
             _ => bug!("closure that is neither generator nor closure"),
@@ -1712,12 +1663,12 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         self.hygiene_ctxt.encode(
             &mut (&mut *self, &mut syntax_contexts, &mut expn_data_table, &mut expn_hash_table),
             |(this, syntax_contexts, _, _), index, ctxt_data| {
-                syntax_contexts.set(index, this.lazy(ctxt_data));
+                syntax_contexts.set_some(index, this.lazy(ctxt_data));
             },
             |(this, _, expn_data_table, expn_hash_table), index, expn_data, hash| {
                 if let Some(index) = index.as_local() {
-                    expn_data_table.set(index.as_raw(), this.lazy(expn_data));
-                    expn_hash_table.set(index.as_raw(), this.lazy(hash));
+                    expn_data_table.set_some(index.as_raw(), this.lazy(expn_data));
+                    expn_hash_table.set_some(index.as_raw(), this.lazy(hash));
                 }
             },
         );
@@ -1742,10 +1693,10 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             let spans = self.tcx.sess.parse_sess.proc_macro_quoted_spans();
             for (i, span) in spans.into_iter().enumerate() {
                 let span = self.lazy(span);
-                self.tables.proc_macro_quoted_spans.set(i, span);
+                self.tables.proc_macro_quoted_spans.set_some(i, span);
             }
 
-            self.tables.opt_def_kind.set(LOCAL_CRATE.as_def_id().index, DefKind::Mod);
+            self.tables.opt_def_kind.set_some(LOCAL_CRATE.as_def_id().index, DefKind::Mod);
             record!(self.tables.def_span[LOCAL_CRATE.as_def_id()] <- tcx.def_span(LOCAL_CRATE.as_def_id()));
             self.encode_attrs(LOCAL_CRATE.as_def_id().expect_local());
             let vis = tcx.local_visibility(CRATE_DEF_ID).map_id(|def_id| def_id.local_def_index);
@@ -1754,6 +1705,12 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 record!(self.tables.lookup_stability[LOCAL_CRATE.as_def_id()] <- stability);
             }
             self.encode_deprecation(LOCAL_CRATE.as_def_id());
+            if let Some(res_map) = tcx.resolutions(()).doc_link_resolutions.get(&CRATE_DEF_ID) {
+                record!(self.tables.doc_link_resolutions[LOCAL_CRATE.as_def_id()] <- res_map);
+            }
+            if let Some(traits) = tcx.resolutions(()).doc_link_traits_in_scope.get(&CRATE_DEF_ID) {
+                record_array!(self.tables.doc_link_traits_in_scope[LOCAL_CRATE.as_def_id()] <- traits);
+            }
 
             // Normally, this information is encoded when we walk the items
             // defined in this crate. However, we skip doing that for proc-macro crates,
@@ -1787,8 +1744,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 def_key.disambiguated_data.data = DefPathData::MacroNs(name);
 
                 let def_id = id.to_def_id();
-                self.tables.opt_def_kind.set(def_id.index, DefKind::Macro(macro_kind));
-                self.tables.proc_macro.set(def_id.index, macro_kind);
+                self.tables.opt_def_kind.set_some(def_id.index, DefKind::Macro(macro_kind));
+                self.tables.proc_macro.set_some(def_id.index, macro_kind);
                 self.encode_attrs(id);
                 record!(self.tables.def_keys[def_id] <- def_key);
                 record!(self.tables.def_ident_span[def_id] <- span);
@@ -1894,7 +1851,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             FxHashMap::default();
 
         for id in tcx.hir().items() {
-            if matches!(tcx.def_kind(id.owner_id), DefKind::Impl) {
+            if matches!(tcx.def_kind(id.owner_id), DefKind::Impl { .. }) {
                 if let Some(trait_ref) = tcx.impl_trait_ref(id.owner_id) {
                     let trait_ref = trait_ref.subst_identity();
 
@@ -2003,7 +1960,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 Linkage::Static => Some(LinkagePreference::RequireStatic),
             }));
         }
-        LazyArray::empty()
+        LazyArray::default()
     }
 
     fn encode_info_for_foreign_item(&mut self, def_id: DefId, nitem: &hir::ForeignItem<'_>) {
@@ -2013,22 +1970,20 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
         match nitem.kind {
             hir::ForeignItemKind::Fn(_, ref names, _) => {
-                self.tables.asyncness.set(def_id.index, hir::IsAsync::NotAsync);
+                self.tables.asyncness.set_some(def_id.index, hir::IsAsync::NotAsync);
                 record_array!(self.tables.fn_arg_names[def_id] <- *names);
                 let constness = if self.tcx.is_const_fn_raw(def_id) {
                     hir::Constness::Const
                 } else {
                     hir::Constness::NotConst
                 };
-                self.tables.constness.set(def_id.index, constness);
+                self.tables.constness.set_some(def_id.index, constness);
                 record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
             }
             hir::ForeignItemKind::Static(..) | hir::ForeignItemKind::Type => {}
         }
         if let hir::ForeignItemKind::Fn(..) = nitem.kind {
-            if tcx.is_intrinsic(def_id) {
-                self.tables.is_intrinsic.set(def_id.index, ());
-            }
+            self.tables.is_intrinsic.set(def_id.index, tcx.is_intrinsic(def_id));
         }
     }
 }
@@ -2266,6 +2221,18 @@ fn encode_metadata_impl(tcx: TyCtxt<'_>, path: &Path) {
 
 pub fn provide(providers: &mut Providers) {
     *providers = Providers {
+        doc_link_resolutions: |tcx, def_id| {
+            tcx.resolutions(())
+                .doc_link_resolutions
+                .get(&def_id.expect_local())
+                .expect("no resolutions for a doc link")
+        },
+        doc_link_traits_in_scope: |tcx, def_id| {
+            tcx.resolutions(())
+                .doc_link_traits_in_scope
+                .get(&def_id.expect_local())
+                .expect("no traits in scope for a doc link")
+        },
         traits_in_crate: |tcx, cnum| {
             assert_eq!(cnum, LOCAL_CRATE);
 
@@ -2280,6 +2247,22 @@ pub fn provide(providers: &mut Providers) {
             traits.sort_by_cached_key(|&def_id| tcx.def_path_hash(def_id));
             tcx.arena.alloc_slice(&traits)
         },
+        trait_impls_in_crate: |tcx, cnum| {
+            assert_eq!(cnum, LOCAL_CRATE);
+
+            let mut trait_impls = Vec::new();
+            for id in tcx.hir().items() {
+                if matches!(tcx.def_kind(id.owner_id), DefKind::Impl { .. })
+                    && tcx.impl_trait_ref(id.owner_id).is_some()
+                {
+                    trait_impls.push(id.owner_id.to_def_id())
+                }
+            }
+
+            // Bring everything into deterministic order.
+            trait_impls.sort_by_cached_key(|&def_id| tcx.def_path_hash(def_id));
+            tcx.arena.alloc_slice(&trait_impls)
+        },
 
         ..*providers
     }
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index 5066dbbb9..a7ec2d790 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -9,7 +9,7 @@ use rustc_attr as attr;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::MetadataRef;
 use rustc_hir as hir;
-use rustc_hir::def::{CtorKind, DefKind};
+use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap};
 use rustc_hir::def_id::{CrateNum, DefId, DefIndex, DefPathHash, StableCrateId};
 use rustc_hir::definitions::DefKey;
 use rustc_hir::lang_items::LangItem;
@@ -18,7 +18,7 @@ use rustc_index::vec::IndexVec;
 use rustc_middle::metadata::ModChild;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
-use rustc_middle::middle::resolve_lifetime::ObjectLifetimeDefault;
+use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
 use rustc_middle::mir;
 use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::query::Providers;
@@ -115,14 +115,16 @@ impl<T: ParameterizedOverTcx> ParameterizedOverTcx for LazyArray<T> {
     type Value<'tcx> = LazyArray<T::Value<'tcx>>;
 }
 
+impl<T> Default for LazyArray<T> {
+    fn default() -> LazyArray<T> {
+        LazyArray::from_position_and_num_elems(NonZeroUsize::new(1).unwrap(), 0)
+    }
+}
+
 impl<T> LazyArray<T> {
     fn from_position_and_num_elems(position: NonZeroUsize, num_elems: usize) -> LazyArray<T> {
         LazyArray { position, num_elems, _marker: PhantomData }
     }
-
-    fn empty() -> LazyArray<T> {
-        LazyArray::from_position_and_num_elems(NonZeroUsize::new(1).unwrap(), 0)
-    }
 }
 
 /// A list of lazily-decoded values, with the added capability of random access.
@@ -185,9 +187,9 @@ enum LazyState {
     Previous(NonZeroUsize),
 }
 
-type SyntaxContextTable = LazyTable<u32, LazyValue<SyntaxContextData>>;
-type ExpnDataTable = LazyTable<ExpnIndex, LazyValue<ExpnData>>;
-type ExpnHashTable = LazyTable<ExpnIndex, LazyValue<ExpnHash>>;
+type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextData>>>;
+type ExpnDataTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnData>>>;
+type ExpnHashTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnHash>>>;
 
 #[derive(MetadataEncodable, MetadataDecodable)]
 pub(crate) struct ProcMacroData {
@@ -253,7 +255,7 @@ pub(crate) struct CrateRoot {
 
     def_path_hash_map: LazyValue<DefPathHashMapRef<'static>>,
 
-    source_map: LazyTable<u32, LazyValue<rustc_span::SourceFile>>,
+    source_map: LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>>,
 
     compiler_builtins: bool,
     needs_allocator: bool,
@@ -315,21 +317,27 @@ pub(crate) struct IncoherentImpls {
 
 /// Define `LazyTables` and `TableBuilders` at the same time.
 macro_rules! define_tables {
-    ($($name:ident: Table<$IDX:ty, $T:ty>),+ $(,)?) => {
+    (
+        - defaulted: $($name1:ident: Table<$IDX1:ty, $T1:ty>,)+
+        - optional: $($name2:ident: Table<$IDX2:ty, $T2:ty>,)+
+    ) => {
         #[derive(MetadataEncodable, MetadataDecodable)]
         pub(crate) struct LazyTables {
-            $($name: LazyTable<$IDX, $T>),+
+            $($name1: LazyTable<$IDX1, $T1>,)+
+            $($name2: LazyTable<$IDX2, Option<$T2>>,)+
         }
 
         #[derive(Default)]
         struct TableBuilders {
-            $($name: TableBuilder<$IDX, $T>),+
+            $($name1: TableBuilder<$IDX1, $T1>,)+
+            $($name2: TableBuilder<$IDX2, Option<$T2>>,)+
         }
 
         impl TableBuilders {
             fn encode(&self, buf: &mut FileEncoder) -> LazyTables {
                 LazyTables {
-                    $($name: self.$name.encode(buf)),+
+                    $($name1: self.$name1.encode(buf),)+
+                    $($name2: self.$name2.encode(buf),)+
                 }
             }
         }
@@ -337,9 +345,20 @@ macro_rules! define_tables {
 }
 
 define_tables! {
+- defaulted:
+    is_intrinsic: Table<DefIndex, bool>,
+    is_macro_rules: Table<DefIndex, bool>,
+    is_type_alias_impl_trait: Table<DefIndex, bool>,
+    attr_flags: Table<DefIndex, AttrFlags>,
+    def_path_hashes: Table<DefIndex, DefPathHash>,
+    explicit_item_bounds: Table<DefIndex, LazyArray<(ty::Predicate<'static>, Span)>>,
+    inferred_outlives_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
+    inherent_impls: Table<DefIndex, LazyArray<DefIndex>>,
+    associated_items_for_impl_trait_in_trait: Table<DefIndex, LazyArray<DefId>>,
+
+- optional:
     attributes: Table<DefIndex, LazyArray<ast::Attribute>>,
     children: Table<DefIndex, LazyArray<DefIndex>>,
-
     opt_def_kind: Table<DefIndex, DefKind>,
     visibility: Table<DefIndex, LazyValue<ty::Visibility<DefIndex>>>,
     def_span: Table<DefIndex, LazyValue<Span>>,
@@ -348,29 +367,25 @@ define_tables! {
     lookup_const_stability: Table<DefIndex, LazyValue<attr::ConstStability>>,
     lookup_default_body_stability: Table<DefIndex, LazyValue<attr::DefaultBodyStability>>,
     lookup_deprecation_entry: Table<DefIndex, LazyValue<attr::Deprecation>>,
-    // As an optimization, a missing entry indicates an empty `&[]`.
-    explicit_item_bounds: Table<DefIndex, LazyArray<(ty::Predicate<'static>, Span)>>,
     explicit_predicates_of: Table<DefIndex, LazyValue<ty::GenericPredicates<'static>>>,
     generics_of: Table<DefIndex, LazyValue<ty::Generics>>,
-    // As an optimization, a missing entry indicates an empty `&[]`.
-    inferred_outlives_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
     super_predicates_of: Table<DefIndex, LazyValue<ty::GenericPredicates<'static>>>,
-    type_of: Table<DefIndex, LazyValue<Ty<'static>>>,
+    type_of: Table<DefIndex, LazyValue<ty::EarlyBinder<Ty<'static>>>>,
     variances_of: Table<DefIndex, LazyArray<ty::Variance>>,
-    fn_sig: Table<DefIndex, LazyValue<ty::PolyFnSig<'static>>>,
+    fn_sig: Table<DefIndex, LazyValue<ty::EarlyBinder<ty::PolyFnSig<'static>>>>,
     codegen_fn_attrs: Table<DefIndex, LazyValue<CodegenFnAttrs>>,
     impl_trait_ref: Table<DefIndex, LazyValue<ty::EarlyBinder<ty::TraitRef<'static>>>>,
     const_param_default: Table<DefIndex, LazyValue<ty::EarlyBinder<rustc_middle::ty::Const<'static>>>>,
     object_lifetime_default: Table<DefIndex, LazyValue<ObjectLifetimeDefault>>,
     optimized_mir: Table<DefIndex, LazyValue<mir::Body<'static>>>,
     mir_for_ctfe: Table<DefIndex, LazyValue<mir::Body<'static>>>,
+    mir_generator_witnesses: Table<DefIndex, LazyValue<mir::GeneratorLayout<'static>>>,
     promoted_mir: Table<DefIndex, LazyValue<IndexVec<mir::Promoted, mir::Body<'static>>>>,
     // FIXME(compiler-errors): Why isn't this a LazyArray?
     thir_abstract_const: Table<DefIndex, LazyValue<ty::Const<'static>>>,
     impl_parent: Table<DefIndex, RawDefId>,
     impl_polarity: Table<DefIndex, ty::ImplPolarity>,
     constness: Table<DefIndex, hir::Constness>,
-    is_intrinsic: Table<DefIndex, ()>,
     impl_defaultness: Table<DefIndex, hir::Defaultness>,
     // FIXME(eddyb) perhaps compute this on the fly if cheap enough?
     coerce_unsized_info: Table<DefIndex, LazyValue<ty::adjustment::CoerceUnsizedInfo>>,
@@ -380,9 +395,7 @@ define_tables! {
     fn_arg_names: Table<DefIndex, LazyArray<Ident>>,
     generator_kind: Table<DefIndex, LazyValue<hir::GeneratorKind>>,
     trait_def: Table<DefIndex, LazyValue<ty::TraitDef>>,
-
     trait_item_def_id: Table<DefIndex, RawDefId>,
-    inherent_impls: Table<DefIndex, LazyArray<DefIndex>>,
     expn_that_defined: Table<DefIndex, LazyValue<ExpnId>>,
     unused_generic_params: Table<DefIndex, LazyValue<UnusedGenericParams>>,
     params_in_repr: Table<DefIndex, LazyValue<BitSet<u32>>>,
@@ -392,22 +405,17 @@ define_tables! {
     // `DefPathTable` up front, since we may only ever use a few
     // definitions from any given crate.
     def_keys: Table<DefIndex, LazyValue<DefKey>>,
-    def_path_hashes: Table<DefIndex, DefPathHash>,
     proc_macro_quoted_spans: Table<usize, LazyValue<Span>>,
     generator_diagnostic_data: Table<DefIndex, LazyValue<GeneratorDiagnosticData<'static>>>,
-    may_have_doc_links: Table<DefIndex, ()>,
     variant_data: Table<DefIndex, LazyValue<VariantData>>,
     assoc_container: Table<DefIndex, ty::AssocItemContainer>,
-    // Slot is full when macro is macro_rules.
-    macro_rules: Table<DefIndex, ()>,
     macro_definition: Table<DefIndex, LazyValue<ast::DelimArgs>>,
     proc_macro: Table<DefIndex, MacroKind>,
     module_reexports: Table<DefIndex, LazyArray<ModChild>>,
     deduced_param_attrs: Table<DefIndex, LazyArray<DeducedParamAttrs>>,
-    // Slot is full when opaque is TAIT.
-    is_type_alias_impl_trait: Table<DefIndex, ()>,
-
     trait_impl_trait_tys: Table<DefIndex, LazyValue<FxHashMap<DefId, Ty<'static>>>>,
+    doc_link_resolutions: Table<DefIndex, LazyValue<DocLinkResMap>>,
+    doc_link_traits_in_scope: Table<DefIndex, LazyArray<DefId>>,
 }
 
 #[derive(TyEncodable, TyDecodable)]
@@ -418,6 +426,13 @@ struct VariantData {
     is_non_exhaustive: bool,
 }
 
+bitflags::bitflags! {
+    #[derive(Default)]
+    pub struct AttrFlags: u8 {
+        const IS_DOC_HIDDEN = 1 << 0;
+    }
+}
+
 // Tags used for encoding Spans:
 const TAG_VALID_SPAN_LOCAL: u8 = 0;
 const TAG_VALID_SPAN_FOREIGN: u8 = 1;
@@ -440,4 +455,5 @@ trivially_parameterized_over_tcx! {
     IncoherentImpls,
     CrateRoot,
     CrateDep,
+    AttrFlags,
 }
diff --git a/compiler/rustc_metadata/src/rmeta/table.rs b/compiler/rustc_metadata/src/rmeta/table.rs
index 716655c7f..b89d48ec1 100644
--- a/compiler/rustc_metadata/src/rmeta/table.rs
+++ b/compiler/rustc_metadata/src/rmeta/table.rs
@@ -10,18 +10,61 @@ use rustc_span::hygiene::MacroKind;
 use std::marker::PhantomData;
 use std::num::NonZeroUsize;
 
+pub(super) trait IsDefault: Default {
+    fn is_default(&self) -> bool;
+}
+
+impl<T> IsDefault for Option<T> {
+    fn is_default(&self) -> bool {
+        self.is_none()
+    }
+}
+
+impl IsDefault for AttrFlags {
+    fn is_default(&self) -> bool {
+        self.is_empty()
+    }
+}
+
+impl IsDefault for bool {
+    fn is_default(&self) -> bool {
+        !self
+    }
+}
+
+impl IsDefault for u32 {
+    fn is_default(&self) -> bool {
+        *self == 0
+    }
+}
+
+impl<T> IsDefault for LazyArray<T> {
+    fn is_default(&self) -> bool {
+        self.num_elems == 0
+    }
+}
+
+impl IsDefault for DefPathHash {
+    fn is_default(&self) -> bool {
+        self.0 == Fingerprint::ZERO
+    }
+}
+
 /// Helper trait, for encoding to, and decoding from, a fixed number of bytes.
 /// Used mainly for Lazy positions and lengths.
 /// Unchecked invariant: `Self::default()` should encode as `[0; BYTE_LEN]`,
 /// but this has no impact on safety.
-pub(super) trait FixedSizeEncoding: Default {
+pub(super) trait FixedSizeEncoding: IsDefault {
     /// This should be `[u8; BYTE_LEN]`;
+    /// Cannot use an associated `const BYTE_LEN: usize` instead due to const eval limitations.
     type ByteArray;
 
     fn from_bytes(b: &Self::ByteArray) -> Self;
     fn write_to_bytes(self, b: &mut Self::ByteArray);
 }
 
+/// This implementation is not used generically, but for reading/writing
+/// concrete `u32` fields in `Lazy*` structures, which may be zero.
 impl FixedSizeEncoding for u32 {
     type ByteArray = [u8; 4];
 
@@ -57,7 +100,7 @@ macro_rules! fixed_size_enum {
             fn write_to_bytes(self, b: &mut [u8;1]) {
                 use $ty::*;
                 b[0] = match self {
-                    None => 0,
+                    None => unreachable!(),
                     $(Some($($pat)*) => 1 + ${index()},)*
                 }
             }
@@ -93,7 +136,8 @@ fixed_size_enum! {
         ( Field                                    )
         ( LifetimeParam                            )
         ( GlobalAsm                                )
-        ( Impl                                     )
+        ( Impl { of_trait: false }                 )
+        ( Impl { of_trait: true }                  )
         ( Closure                                  )
         ( Generator                                )
         ( Static(ast::Mutability::Not)             )
@@ -154,20 +198,18 @@ fixed_size_enum! {
 }
 
 // We directly encode `DefPathHash` because a `LazyValue` would incur a 25% cost.
-impl FixedSizeEncoding for Option<DefPathHash> {
+impl FixedSizeEncoding for DefPathHash {
     type ByteArray = [u8; 16];
 
     #[inline]
     fn from_bytes(b: &[u8; 16]) -> Self {
-        Some(DefPathHash(Fingerprint::from_le_bytes(*b)))
+        DefPathHash(Fingerprint::from_le_bytes(*b))
     }
 
     #[inline]
     fn write_to_bytes(self, b: &mut [u8; 16]) {
-        let Some(DefPathHash(fingerprint)) = self else {
-            panic!("Trying to encode absent DefPathHash.")
-        };
-        *b = fingerprint.to_le_bytes();
+        debug_assert!(!self.is_default());
+        *b = self.0.to_le_bytes();
     }
 }
 
@@ -178,17 +220,17 @@ impl FixedSizeEncoding for Option<RawDefId> {
     #[inline]
     fn from_bytes(b: &[u8; 8]) -> Self {
         let krate = u32::from_le_bytes(b[0..4].try_into().unwrap());
-        let index = u32::from_le_bytes(b[4..8].try_into().unwrap());
         if krate == 0 {
             return None;
         }
+        let index = u32::from_le_bytes(b[4..8].try_into().unwrap());
         Some(RawDefId { krate: krate - 1, index })
     }
 
     #[inline]
     fn write_to_bytes(self, b: &mut [u8; 8]) {
         match self {
-            None => *b = [0; 8],
+            None => unreachable!(),
             Some(RawDefId { krate, index }) => {
                 // CrateNum is less than `CrateNum::MAX_AS_U32`.
                 debug_assert!(krate < u32::MAX);
@@ -199,17 +241,33 @@ impl FixedSizeEncoding for Option<RawDefId> {
     }
 }
 
-impl FixedSizeEncoding for Option<()> {
+impl FixedSizeEncoding for AttrFlags {
+    type ByteArray = [u8; 1];
+
+    #[inline]
+    fn from_bytes(b: &[u8; 1]) -> Self {
+        AttrFlags::from_bits_truncate(b[0])
+    }
+
+    #[inline]
+    fn write_to_bytes(self, b: &mut [u8; 1]) {
+        debug_assert!(!self.is_default());
+        b[0] = self.bits();
+    }
+}
+
+impl FixedSizeEncoding for bool {
     type ByteArray = [u8; 1];
 
     #[inline]
     fn from_bytes(b: &[u8; 1]) -> Self {
-        (b[0] != 0).then(|| ())
+        b[0] != 0
     }
 
     #[inline]
     fn write_to_bytes(self, b: &mut [u8; 1]) {
-        b[0] = self.is_some() as u8
+        debug_assert!(!self.is_default());
+        b[0] = self as u8
     }
 }
 
@@ -227,76 +285,115 @@ impl<T> FixedSizeEncoding for Option<LazyValue<T>> {
 
     #[inline]
     fn write_to_bytes(self, b: &mut [u8; 4]) {
-        let position = self.map_or(0, |lazy| lazy.position.get());
+        match self {
+            None => unreachable!(),
+            Some(lazy) => {
+                let position = lazy.position.get();
+                let position: u32 = position.try_into().unwrap();
+                position.write_to_bytes(b)
+            }
+        }
+    }
+}
+
+impl<T> LazyArray<T> {
+    #[inline]
+    fn write_to_bytes_impl(self, b: &mut [u8; 8]) {
+        let ([position_bytes, meta_bytes],[])= b.as_chunks_mut::<4>() else { panic!() };
+
+        let position = self.position.get();
         let position: u32 = position.try_into().unwrap();
-        position.write_to_bytes(b)
+        position.write_to_bytes(position_bytes);
+
+        let len = self.num_elems;
+        let len: u32 = len.try_into().unwrap();
+        len.write_to_bytes(meta_bytes);
+    }
+
+    fn from_bytes_impl(position_bytes: &[u8; 4], meta_bytes: &[u8; 4]) -> Option<LazyArray<T>> {
+        let position = NonZeroUsize::new(u32::from_bytes(position_bytes) as usize)?;
+        let len = u32::from_bytes(meta_bytes) as usize;
+        Some(LazyArray::from_position_and_num_elems(position, len))
     }
 }
 
-impl<T> FixedSizeEncoding for Option<LazyArray<T>> {
+impl<T> FixedSizeEncoding for LazyArray<T> {
     type ByteArray = [u8; 8];
 
     #[inline]
     fn from_bytes(b: &[u8; 8]) -> Self {
-        let ([ref position_bytes, ref meta_bytes],[])= b.as_chunks::<4>() else { panic!() };
-        let position = NonZeroUsize::new(u32::from_bytes(position_bytes) as usize)?;
-        let len = u32::from_bytes(meta_bytes) as usize;
-        Some(LazyArray::from_position_and_num_elems(position, len))
+        let ([position_bytes, meta_bytes],[])= b.as_chunks::<4>() else { panic!() };
+        if *meta_bytes == [0; 4] {
+            return Default::default();
+        }
+        LazyArray::from_bytes_impl(position_bytes, meta_bytes).unwrap()
     }
 
     #[inline]
     fn write_to_bytes(self, b: &mut [u8; 8]) {
-        let ([ref mut position_bytes, ref mut meta_bytes],[])= b.as_chunks_mut::<4>() else { panic!() };
+        assert!(!self.is_default());
+        self.write_to_bytes_impl(b)
+    }
+}
 
-        let position = self.map_or(0, |lazy| lazy.position.get());
-        let position: u32 = position.try_into().unwrap();
-        position.write_to_bytes(position_bytes);
+impl<T> FixedSizeEncoding for Option<LazyArray<T>> {
+    type ByteArray = [u8; 8];
 
-        let len = self.map_or(0, |lazy| lazy.num_elems);
-        let len: u32 = len.try_into().unwrap();
-        len.write_to_bytes(meta_bytes);
+    #[inline]
+    fn from_bytes(b: &[u8; 8]) -> Self {
+        let ([position_bytes, meta_bytes],[])= b.as_chunks::<4>() else { panic!() };
+        LazyArray::from_bytes_impl(position_bytes, meta_bytes)
+    }
+
+    #[inline]
+    fn write_to_bytes(self, b: &mut [u8; 8]) {
+        match self {
+            None => unreachable!(),
+            Some(lazy) => lazy.write_to_bytes_impl(b),
+        }
     }
 }
 
 /// Helper for constructing a table's serialization (also see `Table`).
-pub(super) struct TableBuilder<I: Idx, T>
-where
-    Option<T>: FixedSizeEncoding,
-{
-    blocks: IndexVec<I, <Option<T> as FixedSizeEncoding>::ByteArray>,
+pub(super) struct TableBuilder<I: Idx, T: FixedSizeEncoding> {
+    blocks: IndexVec<I, T::ByteArray>,
     _marker: PhantomData<T>,
 }
 
-impl<I: Idx, T> Default for TableBuilder<I, T>
-where
-    Option<T>: FixedSizeEncoding,
-{
+impl<I: Idx, T: FixedSizeEncoding> Default for TableBuilder<I, T> {
     fn default() -> Self {
         TableBuilder { blocks: Default::default(), _marker: PhantomData }
     }
 }
 
-impl<I: Idx, T> TableBuilder<I, T>
+impl<I: Idx, const N: usize, T> TableBuilder<I, Option<T>>
 where
-    Option<T>: FixedSizeEncoding,
+    Option<T>: FixedSizeEncoding<ByteArray = [u8; N]>,
 {
-    pub(crate) fn set<const N: usize>(&mut self, i: I, value: T)
-    where
-        Option<T>: FixedSizeEncoding<ByteArray = [u8; N]>,
-    {
-        // FIXME(eddyb) investigate more compact encodings for sparse tables.
-        // On the PR @michaelwoerister mentioned:
-        // > Space requirements could perhaps be optimized by using the HAMT `popcnt`
-        // > trick (i.e. divide things into buckets of 32 or 64 items and then
-        // > store bit-masks of which item in each bucket is actually serialized).
-        self.blocks.ensure_contains_elem(i, || [0; N]);
-        Some(value).write_to_bytes(&mut self.blocks[i]);
-    }
-
-    pub(crate) fn encode<const N: usize>(&self, buf: &mut FileEncoder) -> LazyTable<I, T>
-    where
-        Option<T>: FixedSizeEncoding<ByteArray = [u8; N]>,
-    {
+    pub(crate) fn set_some(&mut self, i: I, value: T) {
+        self.set(i, Some(value))
+    }
+}
+
+impl<I: Idx, const N: usize, T: FixedSizeEncoding<ByteArray = [u8; N]>> TableBuilder<I, T> {
+    /// Sets the table value if it is not default.
+    /// ATTENTION: For optimization default values are simply ignored by this function, because
+    /// right now metadata tables never need to reset non-default values to default. If such need
+    /// arises in the future then a new method (e.g. `clear` or `reset`) will need to be introduced
+    /// for doing that explicitly.
+    pub(crate) fn set(&mut self, i: I, value: T) {
+        if !value.is_default() {
+            // FIXME(eddyb) investigate more compact encodings for sparse tables.
+            // On the PR @michaelwoerister mentioned:
+            // > Space requirements could perhaps be optimized by using the HAMT `popcnt`
+            // > trick (i.e. divide things into buckets of 32 or 64 items and then
+            // > store bit-masks of which item in each bucket is actually serialized).
+            self.blocks.ensure_contains_elem(i, || [0; N]);
+            value.write_to_bytes(&mut self.blocks[i]);
+        }
+    }
+
+    pub(crate) fn encode(&self, buf: &mut FileEncoder) -> LazyTable<I, T> {
         let pos = buf.position();
         for block in &self.blocks {
             buf.emit_raw_bytes(block);
@@ -309,34 +406,24 @@ where
     }
 }
 
-impl<I: Idx, T: ParameterizedOverTcx> LazyTable<I, T>
+impl<I: Idx, const N: usize, T: FixedSizeEncoding<ByteArray = [u8; N]> + ParameterizedOverTcx>
+    LazyTable<I, T>
 where
-    Option<T>: FixedSizeEncoding,
+    for<'tcx> T::Value<'tcx>: FixedSizeEncoding<ByteArray = [u8; N]>,
 {
     /// Given the metadata, extract out the value at a particular index (if any).
     #[inline(never)]
-    pub(super) fn get<'a, 'tcx, M: Metadata<'a, 'tcx>, const N: usize>(
-        &self,
-        metadata: M,
-        i: I,
-    ) -> Option<T::Value<'tcx>>
-    where
-        Option<T::Value<'tcx>>: FixedSizeEncoding<ByteArray = [u8; N]>,
-    {
+    pub(super) fn get<'a, 'tcx, M: Metadata<'a, 'tcx>>(&self, metadata: M, i: I) -> T::Value<'tcx> {
         debug!("LazyTable::lookup: index={:?} len={:?}", i, self.encoded_size);
 
         let start = self.position.get();
         let bytes = &metadata.blob()[start..start + self.encoded_size];
         let (bytes, []) = bytes.as_chunks::<N>() else { panic!() };
-        let bytes = bytes.get(i.index())?;
-        FixedSizeEncoding::from_bytes(bytes)
+        bytes.get(i.index()).map_or_else(Default::default, FixedSizeEncoding::from_bytes)
     }
 
     /// Size of the table in entries, including possible gaps.
-    pub(super) fn size<const N: usize>(&self) -> usize
-    where
-        for<'tcx> Option<T::Value<'tcx>>: FixedSizeEncoding<ByteArray = [u8; N]>,
-    {
+    pub(super) fn size(&self) -> usize {
         self.encoded_size / N
     }
 }