rustc_metadata: Encode doc(hidden) flag to metadata

To retrieve these flags rustdoc currently has to mass decode full attributes for items in the whole crate tree, so it's better to pre-compute it in advance.

This is especially for short-term performance of rust-lang#107054 because resolver cannot use memoization of query results yet.

Cargo.lock

@@ -4326,6 +4326,7 @@ dependencies = [
 name = "rustc_metadata"
 version = "0.0.0"
 dependencies = [
+ "bitflags",
  "libloading",
  "odht",
  "rustc_ast",

compiler/rustc_metadata/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 [lib]
 
 [dependencies]
+bitflags = "1.2.1"
 libloading = "0.7.1"
 odht = { version = "0.3.1", features = ["nightly"] }
 snap = "1"

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1594,8 +1594,8 @@ 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).unwrap_or(AttrFlags::empty())
     }
 
     fn get_is_intrinsic(self, index: DefIndex) -> bool {

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -1,6 +1,7 @@
 use crate::creader::{CStore, LoadedMacro};
 use crate::foreign_modules;
 use crate::native_libs;
+use crate::rmeta::AttrFlags;
 
 use rustc_ast as ast;
 use rustc_attr::Deprecation;
@@ -338,6 +339,7 @@ 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) }
 }
 
 pub(in crate::rmeta) fn provide(providers: &mut Providers) {
@@ -425,7 +427,7 @@ 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;
                     }
@@ -631,7 +633,9 @@ impl CStore {
     }
 
     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)
+        self.get_crate_data(def_id.krate)
+            .get_attr_flags(def_id.index)
+            .contains(AttrFlags::MAY_HAVE_DOC_LINKS)
     }
 }
 

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1111,15 +1111,26 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         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 hir_attrs = tcx.hir().attrs(tcx.hir().local_def_id_to_hir_id(def_id));
+        let mut attrs = hir_attrs
             .iter()
             .filter(move |attr| should_encode_attr(tcx, attr, def_id, &mut is_public));
 
         record_array!(self.tables.attributes[def_id.to_def_id()] <- attrs.clone());
+        let mut attr_flags = AttrFlags::empty();
         if attrs.any(|attr| attr.may_have_doc_links()) {
-            self.tables.may_have_doc_links.set(def_id.local_def_index, ());
+            attr_flags |= AttrFlags::MAY_HAVE_DOC_LINKS;
+        }
+        if hir_attrs
+            .iter()
+            .filter(|attr| attr.has_name(sym::doc))
+            .filter_map(|attr| attr.meta_item_list())
+            .any(|items| items.iter().any(|item| item.has_name(sym::hidden)))
+        {
+            attr_flags |= AttrFlags::IS_DOC_HIDDEN;
+        }
+        if !attr_flags.is_empty() {
+            self.tables.attr_flags.set(def_id.local_def_index, attr_flags);
         }
     }
 

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -395,7 +395,7 @@ define_tables! {
     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, ()>,
+    attr_flags: Table<DefIndex, AttrFlags>,
     variant_data: Table<DefIndex, LazyValue<VariantData>>,
     assoc_container: Table<DefIndex, ty::AssocItemContainer>,
     // Slot is full when macro is macro_rules.
@@ -418,6 +418,13 @@ struct VariantData {
     is_non_exhaustive: bool,
 }
 
+bitflags::bitflags! {
+    pub struct AttrFlags: u8 {
+        const MAY_HAVE_DOC_LINKS = 1 << 0;
+        const IS_DOC_HIDDEN      = 1 << 1;
+    }
+}
+
 // Tags used for encoding Spans:
 const TAG_VALID_SPAN_LOCAL: u8 = 0;
 const TAG_VALID_SPAN_FOREIGN: u8 = 1;
@@ -440,4 +447,5 @@ trivially_parameterized_over_tcx! {
     IncoherentImpls,
     CrateRoot,
     CrateDep,
+    AttrFlags,
 }

compiler/rustc_metadata/src/rmeta/table.rs

@@ -199,6 +199,20 @@ impl FixedSizeEncoding for Option<RawDefId> {
     }
 }
 
+impl FixedSizeEncoding for Option<AttrFlags> {
+    type ByteArray = [u8; 1];
+
+    #[inline]
+    fn from_bytes(b: &[u8; 1]) -> Self {
+        (b[0] != 0).then(|| AttrFlags::from_bits_truncate(b[0]))
+    }
+
+    #[inline]
+    fn write_to_bytes(self, b: &mut [u8; 1]) {
+        b[0] = self.map_or(0, |flags| flags.bits())
+    }
+}
+
 impl FixedSizeEncoding for Option<()> {
     type ByteArray = [u8; 1];
 

compiler/rustc_middle/src/query/mod.rs

@@ -1157,6 +1157,7 @@ rustc_queries! {
     /// Determines whether an item is annotated with `doc(hidden)`.
     query is_doc_hidden(def_id: DefId) -> bool {
         desc { |tcx| "checking whether `{}` is `doc(hidden)`", tcx.def_path_str(def_id) }
+        separate_provide_extern
     }
 
     /// Determines whether an item is annotated with `doc(notable_trait)`.

compiler/rustc_middle/src/ty/util.rs

@@ -1310,7 +1310,8 @@ pub fn reveal_opaque_types_in_bounds<'tcx>(
 }
 
 /// Determines whether an item is annotated with `doc(hidden)`.
-pub fn is_doc_hidden(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+fn is_doc_hidden(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+    assert!(def_id.is_local());
     tcx.get_attrs(def_id, sym::doc)
         .filter_map(|attr| attr.meta_item_list())
         .any(|items| items.iter().any(|item| item.has_name(sym::hidden)))

src/librustdoc/clean/types.rs

@@ -2498,14 +2498,7 @@ impl Import {
     }
 
     pub(crate) fn imported_item_is_doc_hidden(&self, tcx: TyCtxt<'_>) -> bool {
-        match self.source.did {
-            Some(did) => tcx
-                .get_attrs(did, sym::doc)
-                .filter_map(ast::Attribute::meta_item_list)
-                .flatten()
-                .has_word(sym::hidden),
-            None => false,
-        }
+        self.source.did.map_or(false, |did| tcx.is_doc_hidden(did))
     }
 }