Auto merge of #86644 - Stupremee:replace-fakedefids-with-itemid, r=jyn514

rustdoc: Replace `FakeDefId` with new `ItemId` type

Follow up from #84707

`@Manishearth` [suggested](#84707 (comment)) that there should be a new `ItemId` type that can distinguish between auto traits, normal ids, and blanket impls instead of using `FakeDefId`s.

This type is introduced by this PR.

There are still some `FIXME`s left, because I was unsure what the best solution for them would be.

Especially the naming in general now is a bit weird right now and needs to be cleaned up. Now there are no "fake" ids so the `is_fake` method on `Item` does not really make sense and maybe the methods on `ItemId` should be renamed too?

Also, we need to represent the new item ids in the JSON backend somehow.

Author: bors

src/librustdoc/clean/auto_trait.rs

@@ -113,7 +113,7 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
             name: None,
             attrs: Default::default(),
             visibility: Inherited,
-            def_id: FakeDefId::new_fake(item_def_id.krate),
+            def_id: ItemId::Auto { trait_: trait_def_id, for_: item_def_id },
             kind: box ImplItem(Impl {
                 span: Span::dummy(),
                 unsafety: hir::Unsafety::Normal,

src/librustdoc/clean/blanket_impl.rs

@@ -96,7 +96,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                     name: None,
                     attrs: Default::default(),
                     visibility: Inherited,
-                    def_id: FakeDefId::new_fake(item_def_id.krate),
+                    def_id: ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
                     kind: box ImplItem(Impl {
                         span: self.cx.tcx.def_span(impl_def_id).clean(self.cx),
                         unsafety: hir::Unsafety::Normal,

src/librustdoc/clean/inline.rs

@@ -15,7 +15,7 @@ use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Symbol};
 
 use crate::clean::{
-    self, utils, Attributes, AttributesExt, FakeDefId, GetDefId, NestedAttributesExt, Type,
+    self, utils, Attributes, AttributesExt, GetDefId, ItemId, NestedAttributesExt, Type,
 };
 use crate::core::DocContext;
 use crate::formats::item_type::ItemType;
@@ -483,10 +483,11 @@ fn build_module(
             }
             if let Res::PrimTy(p) = item.res {
                 // Primitive types can't be inlined so generate an import instead.
+                let prim_ty = clean::PrimitiveType::from(p);
                 items.push(clean::Item {
                     name: None,
                     attrs: box clean::Attributes::default(),
-                    def_id: FakeDefId::new_fake(did.krate),
+                    def_id: ItemId::Primitive(prim_ty, did.krate),
                     visibility: clean::Public,
                     kind: box clean::ImportItem(clean::Import::new_simple(
                         item.ident.name,
@@ -495,7 +496,7 @@ fn build_module(
                                 global: false,
                                 res: item.res,
                                 segments: vec![clean::PathSegment {
-                                    name: clean::PrimitiveType::from(p).as_sym(),
+                                    name: prim_ty.as_sym(),
                                     args: clean::GenericArgs::AngleBracketed {
                                         args: Vec::new(),
                                         bindings: Vec::new(),

src/librustdoc/clean/types.rs

@@ -1,4 +1,4 @@
-use std::cell::{Cell, RefCell};
+use std::cell::RefCell;
 use std::default::Default;
 use std::hash::{Hash, Hasher};
 use std::iter::FromIterator;
@@ -48,73 +48,68 @@ use self::ItemKind::*;
 use self::SelfTy::*;
 use self::Type::*;
 
-crate type FakeDefIdSet = FxHashSet<FakeDefId>;
+crate type ItemIdSet = FxHashSet<ItemId>;
 
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Copy)]
-crate enum FakeDefId {
-    Real(DefId),
-    Fake(DefIndex, CrateNum),
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Copy)]
+crate enum ItemId {
+    /// A "normal" item that uses a [`DefId`] for identification.
+    DefId(DefId),
+    /// Identifier that is used for auto traits.
+    Auto { trait_: DefId, for_: DefId },
+    /// Identifier that is used for blanket implementations.
+    Blanket { impl_id: DefId, for_: DefId },
+    /// Identifier for primitive types.
+    Primitive(PrimitiveType, CrateNum),
 }
 
-impl FakeDefId {
-    #[cfg(parallel_compiler)]
-    crate fn new_fake(crate: CrateNum) -> Self {
-        unimplemented!("")
-    }
-
-    #[cfg(not(parallel_compiler))]
-    crate fn new_fake(krate: CrateNum) -> Self {
-        thread_local!(static FAKE_DEF_ID_COUNTER: Cell<usize> = Cell::new(0));
-        let id = FAKE_DEF_ID_COUNTER.with(|id| {
-            let tmp = id.get();
-            id.set(tmp + 1);
-            tmp
-        });
-        Self::Fake(DefIndex::from(id), krate)
-    }
-
+impl ItemId {
     #[inline]
     crate fn is_local(self) -> bool {
         match self {
-            FakeDefId::Real(id) => id.is_local(),
-            FakeDefId::Fake(_, krate) => krate == LOCAL_CRATE,
+            ItemId::Auto { for_: id, .. }
+            | ItemId::Blanket { for_: id, .. }
+            | ItemId::DefId(id) => id.is_local(),
+            ItemId::Primitive(_, krate) => krate == LOCAL_CRATE,
         }
     }
 
     #[inline]
     #[track_caller]
-    crate fn expect_real(self) -> rustc_hir::def_id::DefId {
-        self.as_real().unwrap_or_else(|| panic!("FakeDefId::expect_real: `{:?}` isn't real", self))
+    crate fn expect_def_id(self) -> DefId {
+        self.as_def_id()
+            .unwrap_or_else(|| panic!("ItemId::expect_def_id: `{:?}` isn't a DefId", self))
     }
 
     #[inline]
-    crate fn as_real(self) -> Option<DefId> {
+    crate fn as_def_id(self) -> Option<DefId> {
         match self {
-            FakeDefId::Real(id) => Some(id),
-            FakeDefId::Fake(_, _) => None,
+            ItemId::DefId(id) => Some(id),
+            _ => None,
         }
     }
 
     #[inline]
     crate fn krate(self) -> CrateNum {
         match self {
-            FakeDefId::Real(id) => id.krate,
-            FakeDefId::Fake(_, krate) => krate,
+            ItemId::Auto { for_: id, .. }
+            | ItemId::Blanket { for_: id, .. }
+            | ItemId::DefId(id) => id.krate,
+            ItemId::Primitive(_, krate) => krate,
         }
     }
 
     #[inline]
     crate fn index(self) -> Option<DefIndex> {
         match self {
-            FakeDefId::Real(id) => Some(id.index),
-            FakeDefId::Fake(_, _) => None,
+            ItemId::DefId(id) => Some(id.index),
+            _ => None,
         }
     }
 }
 
-impl From<DefId> for FakeDefId {
+impl From<DefId> for ItemId {
     fn from(id: DefId) -> Self {
-        Self::Real(id)
+        Self::DefId(id)
     }
 }
 
@@ -338,14 +333,14 @@ crate struct Item {
     /// Information about this item that is specific to what kind of item it is.
     /// E.g., struct vs enum vs function.
     crate kind: Box<ItemKind>,
-    crate def_id: FakeDefId,
+    crate def_id: ItemId,
 
     crate cfg: Option<Arc<Cfg>>,
 }
 
 // `Item` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-rustc_data_structures::static_assert_size!(Item, 48);
+rustc_data_structures::static_assert_size!(Item, 56);
 
 crate fn rustc_span(def_id: DefId, tcx: TyCtxt<'_>) -> Span {
     Span::from_rustc_span(def_id.as_local().map_or_else(
@@ -359,19 +354,19 @@ crate fn rustc_span(def_id: DefId, tcx: TyCtxt<'_>) -> Span {
 
 impl Item {
     crate fn stability<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Option<&'tcx Stability> {
-        if self.is_fake() { None } else { tcx.lookup_stability(self.def_id.expect_real()) }
+        self.def_id.as_def_id().and_then(|did| tcx.lookup_stability(did))
     }
 
     crate fn const_stability<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Option<&'tcx ConstStability> {
-        if self.is_fake() { None } else { tcx.lookup_const_stability(self.def_id.expect_real()) }
+        self.def_id.as_def_id().and_then(|did| tcx.lookup_const_stability(did))
     }
 
     crate fn deprecation(&self, tcx: TyCtxt<'_>) -> Option<Deprecation> {
-        if self.is_fake() { None } else { tcx.lookup_deprecation(self.def_id.expect_real()) }
+        self.def_id.as_def_id().and_then(|did| tcx.lookup_deprecation(did))
     }
 
     crate fn inner_docs(&self, tcx: TyCtxt<'_>) -> bool {
-        if self.is_fake() { false } else { tcx.get_attrs(self.def_id.expect_real()).inner_docs() }
+        self.def_id.as_def_id().map(|did| tcx.get_attrs(did).inner_docs()).unwrap_or(false)
     }
 
     crate fn span(&self, tcx: TyCtxt<'_>) -> Span {
@@ -383,10 +378,8 @@ impl Item {
             kind
         {
             *span
-        } else if self.is_fake() {
-            Span::dummy()
         } else {
-            rustc_span(self.def_id.expect_real(), tcx)
+            self.def_id.as_def_id().map(|did| rustc_span(did, tcx)).unwrap_or_else(|| Span::dummy())
         }
     }
 
@@ -551,7 +544,7 @@ impl Item {
     }
 
     crate fn is_crate(&self) -> bool {
-        self.is_mod() && self.def_id.as_real().map_or(false, |did| did.index == CRATE_DEF_INDEX)
+        self.is_mod() && self.def_id.as_def_id().map_or(false, |did| did.index == CRATE_DEF_INDEX)
     }
     crate fn is_mod(&self) -> bool {
         self.type_() == ItemType::Module
@@ -662,10 +655,6 @@ impl Item {
             _ => false,
         }
     }
-
-    crate fn is_fake(&self) -> bool {
-        matches!(self.def_id, FakeDefId::Fake(_, _))
-    }
 }
 
 #[derive(Clone, Debug)]

src/librustdoc/core.rs

@@ -30,7 +30,7 @@ use std::mem;
 use std::rc::Rc;
 
 use crate::clean::inline::build_external_trait;
-use crate::clean::{self, FakeDefId, TraitWithExtraInfo};
+use crate::clean::{self, ItemId, TraitWithExtraInfo};
 use crate::config::{Options as RustdocOptions, OutputFormat, RenderOptions};
 use crate::formats::cache::Cache;
 use crate::passes::{self, Condition::*, ConditionalPass};
@@ -78,7 +78,7 @@ crate struct DocContext<'tcx> {
     /// This same cache is used throughout rustdoc, including in [`crate::html::render`].
     crate cache: Cache,
     /// Used by [`clean::inline`] to tell if an item has already been inlined.
-    crate inlined: FxHashSet<FakeDefId>,
+    crate inlined: FxHashSet<ItemId>,
     /// Used by `calculate_doc_coverage`.
     crate output_format: OutputFormat,
 }
@@ -128,12 +128,13 @@ impl<'tcx> DocContext<'tcx> {
 
     /// Like `hir().local_def_id_to_hir_id()`, but skips calling it on fake DefIds.
     /// (This avoids a slice-index-out-of-bounds panic.)
-    crate fn as_local_hir_id(tcx: TyCtxt<'_>, def_id: FakeDefId) -> Option<HirId> {
+    crate fn as_local_hir_id(tcx: TyCtxt<'_>, def_id: ItemId) -> Option<HirId> {
         match def_id {
-            FakeDefId::Real(real_id) => {
+            ItemId::DefId(real_id) => {
                 real_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
             }
-            FakeDefId::Fake(_, _) => None,
+            // FIXME: Can this be `Some` for `Auto` or `Blanket`?
+            _ => None,
         }
     }
 }

src/librustdoc/formats/cache.rs

@@ -8,7 +8,7 @@ use rustc_middle::middle::privacy::AccessLevels;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::symbol::sym;
 
-use crate::clean::{self, FakeDefId, GetDefId};
+use crate::clean::{self, GetDefId, ItemId};
 use crate::fold::DocFolder;
 use crate::formats::item_type::ItemType;
 use crate::formats::Impl;
@@ -122,7 +122,7 @@ crate struct Cache {
     /// All intra-doc links resolved so far.
     ///
     /// Links are indexed by the DefId of the item they document.
-    crate intra_doc_links: BTreeMap<FakeDefId, Vec<clean::ItemLink>>,
+    crate intra_doc_links: FxHashMap<ItemId, Vec<clean::ItemLink>>,
 }
 
 /// This struct is used to wrap the `cache` and `tcx` in order to run `DocFolder`.
@@ -215,7 +215,7 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
         // Propagate a trait method's documentation to all implementors of the
         // trait.
         if let clean::TraitItem(ref t) = *item.kind {
-            self.cache.traits.entry(item.def_id.expect_real()).or_insert_with(|| {
+            self.cache.traits.entry(item.def_id.expect_def_id()).or_insert_with(|| {
                 clean::TraitWithExtraInfo {
                     trait_: t.clone(),
                     is_notable: item.attrs.has_doc_flag(sym::notable_trait),
@@ -348,11 +348,11 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
                     // `public_items` map, so we can skip inserting into the
                     // paths map if there was already an entry present and we're
                     // not a public item.
-                    if !self.cache.paths.contains_key(&item.def_id.expect_real())
-                        || self.cache.access_levels.is_public(item.def_id.expect_real())
+                    if !self.cache.paths.contains_key(&item.def_id.expect_def_id())
+                        || self.cache.access_levels.is_public(item.def_id.expect_def_id())
                     {
                         self.cache.paths.insert(
-                            item.def_id.expect_real(),
+                            item.def_id.expect_def_id(),
                             (self.cache.stack.clone(), item.type_()),
                         );
                     }
@@ -361,7 +361,7 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
             clean::PrimitiveItem(..) => {
                 self.cache
                     .paths
-                    .insert(item.def_id.expect_real(), (self.cache.stack.clone(), item.type_()));
+                    .insert(item.def_id.expect_def_id(), (self.cache.stack.clone(), item.type_()));
             }
 
             clean::ExternCrateItem { .. }
@@ -391,7 +391,7 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
             | clean::StructItem(..)
             | clean::UnionItem(..)
             | clean::VariantItem(..) => {
-                self.cache.parent_stack.push(item.def_id.expect_real());
+                self.cache.parent_stack.push(item.def_id.expect_def_id());
                 self.cache.parent_is_trait_impl = false;
                 true
             }

src/librustdoc/html/format.rs

@@ -19,7 +19,7 @@ use rustc_span::def_id::CRATE_DEF_INDEX;
 use rustc_target::spec::abi::Abi;
 
 use crate::clean::{
-    self, utils::find_nearest_parent_module, ExternalCrate, FakeDefId, GetDefId, PrimitiveType,
+    self, utils::find_nearest_parent_module, ExternalCrate, GetDefId, ItemId, PrimitiveType,
 };
 use crate::formats::item_type::ItemType;
 use crate::html::escape::Escape;
@@ -1181,7 +1181,7 @@ impl clean::FnDecl {
 impl clean::Visibility {
     crate fn print_with_space<'a, 'tcx: 'a>(
         self,
-        item_did: FakeDefId,
+        item_did: ItemId,
         cx: &'a Context<'tcx>,
     ) -> impl fmt::Display + 'a + Captures<'tcx> {
         let to_print = match self {
@@ -1191,7 +1191,7 @@ impl clean::Visibility {
                 // FIXME(camelid): This may not work correctly if `item_did` is a module.
                 //                 However, rustdoc currently never displays a module's
                 //                 visibility, so it shouldn't matter.
-                let parent_module = find_nearest_parent_module(cx.tcx(), item_did.expect_real());
+                let parent_module = find_nearest_parent_module(cx.tcx(), item_did.expect_def_id());
 
                 if vis_did.index == CRATE_DEF_INDEX {
                     "pub(crate) ".to_owned()

src/librustdoc/html/render/context.rs

@@ -230,7 +230,7 @@ impl<'tcx> Context<'tcx> {
                 &self.shared.style_files,
             )
         } else {
-            if let Some(&(ref names, ty)) = self.cache.paths.get(&it.def_id.expect_real()) {
+            if let Some(&(ref names, ty)) = self.cache.paths.get(&it.def_id.expect_def_id()) {
                 let mut path = String::new();
                 for name in &names[..names.len() - 1] {
                     path.push_str(name);

src/librustdoc/html/render/mod.rs

@@ -53,7 +53,7 @@ use rustc_span::symbol::{kw, sym, Symbol};
 use serde::ser::SerializeSeq;
 use serde::{Serialize, Serializer};
 
-use crate::clean::{self, FakeDefId, GetDefId, RenderedLink, SelfTy};
+use crate::clean::{self, GetDefId, ItemId, RenderedLink, SelfTy};
 use crate::docfs::PathError;
 use crate::error::Error;
 use crate::formats::cache::Cache;
@@ -735,7 +735,7 @@ fn naive_assoc_href(it: &clean::Item, link: AssocItemLink<'_>, cx: &Context<'_>)
         AssocItemLink::Anchor(Some(ref id)) => format!("#{}", id),
         AssocItemLink::Anchor(None) => anchor,
         AssocItemLink::GotoSource(did, _) => {
-            href(did.expect_real(), cx).map(|p| format!("{}{}", p.0, anchor)).unwrap_or(anchor)
+            href(did.expect_def_id(), cx).map(|p| format!("{}{}", p.0, anchor)).unwrap_or(anchor)
         }
     }
 }
@@ -867,7 +867,7 @@ fn render_assoc_item(
                     ItemType::TyMethod
                 };
 
-                href(did.expect_real(), cx)
+                href(did.expect_def_id(), cx)
                     .map(|p| format!("{}#{}.{}", p.0, ty, name))
                     .unwrap_or_else(|| format!("#{}.{}", ty, name))
             }
@@ -987,7 +987,7 @@ fn render_attributes_in_code(w: &mut Buffer, it: &clean::Item) {
 #[derive(Copy, Clone)]
 enum AssocItemLink<'a> {
     Anchor(Option<&'a str>),
-    GotoSource(FakeDefId, &'a FxHashSet<Symbol>),
+    GotoSource(ItemId, &'a FxHashSet<Symbol>),
 }
 
 impl<'a> AssocItemLink<'a> {
@@ -1819,7 +1819,7 @@ fn small_url_encode(s: String) -> String {
 }
 
 fn sidebar_assoc_items(cx: &Context<'_>, out: &mut Buffer, it: &clean::Item) {
-    let did = it.def_id.expect_real();
+    let did = it.def_id.expect_def_id();
     if let Some(v) = cx.cache.impls.get(&did) {
         let mut used_links = FxHashSet::default();
         let cache = cx.cache();
@@ -2109,7 +2109,7 @@ fn sidebar_trait(cx: &Context<'_>, buf: &mut Buffer, it: &clean::Item, t: &clean
         "</div>",
     );
 
-    if let Some(implementors) = cx.cache.implementors.get(&it.def_id.expect_real()) {
+    if let Some(implementors) = cx.cache.implementors.get(&it.def_id.expect_def_id()) {
         let cache = cx.cache();
         let mut res = implementors
             .iter()

src/librustdoc/html/render/print_item.rs

@@ -289,15 +289,15 @@ fn item_module(w: &mut Buffer, cx: &Context<'_>, item: &clean::Item, items: &[cl
                         w,
                         "<div class=\"item-left\"><code>{}extern crate {} as {};",
                         myitem.visibility.print_with_space(myitem.def_id, cx),
-                        anchor(myitem.def_id.expect_real(), &*src.as_str(), cx),
+                        anchor(myitem.def_id.expect_def_id(), &*src.as_str(), cx),
                         myitem.name.as_ref().unwrap(),
                     ),
                     None => write!(
                         w,
                         "<div class=\"item-left\"><code>{}extern crate {};",
                         myitem.visibility.print_with_space(myitem.def_id, cx),
                         anchor(
-                            myitem.def_id.expect_real(),
+                            myitem.def_id.expect_def_id(),
                             &*myitem.name.as_ref().unwrap().as_str(),
                             cx
                         ),
@@ -669,9 +669,9 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
     }
 
     // If there are methods directly on this trait object, render them here.
-    render_assoc_items(w, cx, it, it.def_id.expect_real(), AssocItemRender::All);
+    render_assoc_items(w, cx, it, it.def_id.expect_def_id(), AssocItemRender::All);
 
-    if let Some(implementors) = cx.cache.implementors.get(&it.def_id.expect_real()) {
+    if let Some(implementors) = cx.cache.implementors.get(&it.def_id.expect_def_id()) {
         // The DefId is for the first Type found with that name. The bool is
         // if any Types with the same name but different DefId have been found.
         let mut implementor_dups: FxHashMap<Symbol, (DefId, bool)> = FxHashMap::default();
@@ -787,7 +787,7 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
         path = if it.def_id.is_local() {
             cx.current.join("/")
         } else {
-            let (ref path, _) = cx.cache.external_paths[&it.def_id.expect_real()];
+            let (ref path, _) = cx.cache.external_paths[&it.def_id.expect_def_id()];
             path[..path.len() - 1].join("/")
         },
         ty = it.type_(),
@@ -813,7 +813,7 @@ fn item_trait_alias(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clea
     // won't be visible anywhere in the docs. It would be nice to also show
     // associated items from the aliased type (see discussion in #32077), but
     // we need #14072 to make sense of the generics.
-    render_assoc_items(w, cx, it, it.def_id.expect_real(), AssocItemRender::All)
+    render_assoc_items(w, cx, it, it.def_id.expect_def_id(), AssocItemRender::All)
 }
 
 fn item_opaque_ty(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::OpaqueTy) {
@@ -834,7 +834,7 @@ fn item_opaque_ty(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean:
     // won't be visible anywhere in the docs. It would be nice to also show
     // associated items from the aliased type (see discussion in #32077), but
     // we need #14072 to make sense of the generics.
-    render_assoc_items(w, cx, it, it.def_id.expect_real(), AssocItemRender::All)
+    render_assoc_items(w, cx, it, it.def_id.expect_def_id(), AssocItemRender::All)
 }
 
 fn item_typedef(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Typedef) {
@@ -851,7 +851,7 @@ fn item_typedef(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::T
 
     document(w, cx, it, None);
 
-    let def_id = it.def_id.expect_real();
+    let def_id = it.def_id.expect_def_id();
     // Render any items associated directly to this alias, as otherwise they
     // won't be visible anywhere in the docs. It would be nice to also show
     // associated items from the aliased type (see discussion in #32077), but
@@ -903,7 +903,7 @@ fn item_union(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::Uni
             document(w, cx, field, Some(it));
         }
     }
-    let def_id = it.def_id.expect_real();
+    let def_id = it.def_id.expect_def_id();
     render_assoc_items(w, cx, it, def_id, AssocItemRender::All);
     document_type_layout(w, cx, def_id);
 }
@@ -1041,7 +1041,7 @@ fn item_enum(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, e: &clean::Enum
             }
         }
     }
-    let def_id = it.def_id.expect_real();
+    let def_id = it.def_id.expect_def_id();
     render_assoc_items(w, cx, it, def_id, AssocItemRender::All);
     document_type_layout(w, cx, def_id);
 }
@@ -1093,7 +1093,7 @@ fn item_proc_macro(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, m: &clean
 
 fn item_primitive(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item) {
     document(w, cx, it, None);
-    render_assoc_items(w, cx, it, it.def_id.expect_real(), AssocItemRender::All)
+    render_assoc_items(w, cx, it, it.def_id.expect_def_id(), AssocItemRender::All)
 }
 
 fn item_constant(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, c: &clean::Constant) {
@@ -1182,7 +1182,7 @@ fn item_struct(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, s: &clean::St
             }
         }
     }
-    let def_id = it.def_id.expect_real();
+    let def_id = it.def_id.expect_def_id();
     render_assoc_items(w, cx, it, def_id, AssocItemRender::All);
     document_type_layout(w, cx, def_id);
 }
@@ -1213,7 +1213,7 @@ fn item_foreign_type(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item) {
 
     document(w, cx, it, None);
 
-    render_assoc_items(w, cx, it, it.def_id.expect_real(), AssocItemRender::All)
+    render_assoc_items(w, cx, it, it.def_id.expect_def_id(), AssocItemRender::All)
 }
 
 fn item_keyword(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item) {

src/librustdoc/json/conversions.rs

@@ -5,17 +5,18 @@
 #![allow(rustc::default_hash_types)]
 
 use std::convert::From;
+use std::fmt;
 
 use rustc_ast::ast;
-use rustc_hir::def::CtorKind;
+use rustc_hir::{def::CtorKind, def_id::DefId};
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::CRATE_DEF_INDEX;
 use rustc_span::Pos;
 
 use rustdoc_json_types::*;
 
 use crate::clean::utils::print_const_expr;
-use crate::clean::{self, FakeDefId};
+use crate::clean::{self, ItemId};
 use crate::formats::item_type::ItemType;
 use crate::json::JsonRenderer;
 use std::collections::HashSet;
@@ -30,7 +31,7 @@ impl JsonRenderer<'_> {
             .into_iter()
             .flatten()
             .filter_map(|clean::ItemLink { link, did, .. }| {
-                did.map(|did| (link.clone(), from_def_id(did.into())))
+                did.map(|did| (link.clone(), from_item_id(did.into())))
             })
             .collect();
         let docs = item.attrs.collapsed_doc_value();
@@ -47,7 +48,7 @@ impl JsonRenderer<'_> {
             _ => from_clean_item(item, self.tcx),
         };
         Some(Item {
-            id: from_def_id(def_id),
+            id: from_item_id(def_id),
             crate_id: def_id.krate().as_u32(),
             name: name.map(|sym| sym.to_string()),
             span: self.convert_span(span),
@@ -86,7 +87,7 @@ impl JsonRenderer<'_> {
             Inherited => Visibility::Default,
             Restricted(did) if did.index == CRATE_DEF_INDEX => Visibility::Crate,
             Restricted(did) => Visibility::Restricted {
-                parent: from_def_id(did.into()),
+                parent: from_item_id(did.into()),
                 path: self.tcx.def_path(did).to_string_no_crate_verbose(),
             },
         }
@@ -170,12 +171,24 @@ impl FromWithTcx<clean::TypeBindingKind> for TypeBindingKind {
     }
 }
 
-crate fn from_def_id(did: FakeDefId) -> Id {
+crate fn from_item_id(did: ItemId) -> Id {
+    struct DisplayDefId(DefId);
+
+    impl fmt::Display for DisplayDefId {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(f, "{}:{}", self.0.krate.as_u32(), u32::from(self.0.index))
+        }
+    }
+
     match did {
-        FakeDefId::Real(did) => Id(format!("{}:{}", did.krate.as_u32(), u32::from(did.index))),
-        // We need to differentiate real and fake ids, because the indices might overlap for fake
-        // and real DefId's, which would cause two different Id's treated as they were the same.
-        FakeDefId::Fake(idx, krate) => Id(format!("F{}:{}", krate.as_u32(), u32::from(idx))),
+        ItemId::DefId(did) => Id(format!("{}", DisplayDefId(did))),
+        ItemId::Blanket { for_, impl_id } => {
+            Id(format!("b:{}-{}", DisplayDefId(impl_id), DisplayDefId(for_)))
+        }
+        ItemId::Auto { for_, trait_ } => {
+            Id(format!("a:{}-{}", DisplayDefId(trait_), DisplayDefId(for_)))
+        }
+        ItemId::Primitive(ty, krate) => Id(format!("p:{}:{}", krate.as_u32(), ty.as_sym())),
     }
 }
 
@@ -375,7 +388,7 @@ impl FromWithTcx<clean::Type> for Type {
         match ty {
             ResolvedPath { path, did, is_generic: _ } => Type::ResolvedPath {
                 name: path.whole_name(),
-                id: from_def_id(did.into()),
+                id: from_item_id(did.into()),
                 args: path.segments.last().map(|args| Box::new(args.clone().args.into_tcx(tcx))),
                 param_names: Vec::new(),
             },
@@ -387,7 +400,7 @@ impl FromWithTcx<clean::Type> for Type {
 
                 Type::ResolvedPath {
                     name: path.whole_name(),
-                    id: from_def_id(id.into()),
+                    id: from_item_id(id.into()),
                     args: path
                         .segments
                         .last()
@@ -568,13 +581,13 @@ impl FromWithTcx<clean::Import> for Import {
             Simple(s) => Import {
                 source: import.source.path.whole_name(),
                 name: s.to_string(),
-                id: import.source.did.map(FakeDefId::from).map(from_def_id),
+                id: import.source.did.map(ItemId::from).map(from_item_id),
                 glob: false,
             },
             Glob => Import {
                 source: import.source.path.whole_name(),
                 name: import.source.path.last_name().to_string(),
-                id: import.source.did.map(FakeDefId::from).map(from_def_id),
+                id: import.source.did.map(ItemId::from).map(from_item_id),
                 glob: true,
             },
         }
@@ -668,5 +681,5 @@ impl FromWithTcx<ItemType> for ItemKind {
 }
 
 fn ids(items: impl IntoIterator<Item = clean::Item>) -> Vec<Id> {
-    items.into_iter().filter(|x| !x.is_stripped()).map(|i| from_def_id(i.def_id)).collect()
+    items.into_iter().filter(|x| !x.is_stripped()).map(|i| from_item_id(i.def_id)).collect()
 }

src/librustdoc/json/mod.rs

@@ -25,7 +25,7 @@ use crate::error::Error;
 use crate::formats::cache::Cache;
 use crate::formats::FormatRenderer;
 use crate::html::render::cache::ExternalLocation;
-use crate::json::conversions::{from_def_id, IntoWithTcx};
+use crate::json::conversions::{from_item_id, IntoWithTcx};
 
 #[derive(Clone)]
 crate struct JsonRenderer<'tcx> {
@@ -53,7 +53,7 @@ impl JsonRenderer<'tcx> {
                     .map(|i| {
                         let item = &i.impl_item;
                         self.item(item.clone()).unwrap();
-                        from_def_id(item.def_id)
+                        from_item_id(item.def_id)
                     })
                     .collect()
             })
@@ -71,7 +71,7 @@ impl JsonRenderer<'tcx> {
                         let item = &i.impl_item;
                         if item.def_id.is_local() {
                             self.item(item.clone()).unwrap();
-                            Some(from_def_id(item.def_id))
+                            Some(from_item_id(item.def_id))
                         } else {
                             None
                         }
@@ -91,9 +91,9 @@ impl JsonRenderer<'tcx> {
                     let trait_item = &trait_item.trait_;
                     trait_item.items.clone().into_iter().for_each(|i| self.item(i).unwrap());
                     Some((
-                        from_def_id(id.into()),
+                        from_item_id(id.into()),
                         types::Item {
-                            id: from_def_id(id.into()),
+                            id: from_item_id(id.into()),
                             crate_id: id.krate.as_u32(),
                             name: self
                                 .cache
@@ -164,13 +164,13 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
         let id = item.def_id;
         if let Some(mut new_item) = self.convert_item(item) {
             if let types::ItemEnum::Trait(ref mut t) = new_item.inner {
-                t.implementors = self.get_trait_implementors(id.expect_real())
+                t.implementors = self.get_trait_implementors(id.expect_def_id())
             } else if let types::ItemEnum::Struct(ref mut s) = new_item.inner {
-                s.impls = self.get_impls(id.expect_real())
+                s.impls = self.get_impls(id.expect_def_id())
             } else if let types::ItemEnum::Enum(ref mut e) = new_item.inner {
-                e.impls = self.get_impls(id.expect_real())
+                e.impls = self.get_impls(id.expect_def_id())
             }
-            let removed = self.index.borrow_mut().insert(from_def_id(id), new_item.clone());
+            let removed = self.index.borrow_mut().insert(from_item_id(id), new_item.clone());
 
             // FIXME(adotinthevoid): Currently, the index is duplicated. This is a sanity check
             // to make sure the items are unique. The main place this happens is when an item, is
@@ -207,7 +207,7 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
                 .chain(self.cache.external_paths.clone().into_iter())
                 .map(|(k, (path, kind))| {
                     (
-                        from_def_id(k.into()),
+                        from_item_id(k.into()),
                         types::ItemSummary {
                             crate_id: k.krate.as_u32(),
                             path,

src/librustdoc/passes/calculate_doc_coverage.rs

@@ -213,13 +213,13 @@ impl<'a, 'b> fold::DocFolder for CoverageCalculator<'a, 'b> {
 
                 let filename = i.span(self.ctx.tcx).filename(self.ctx.sess());
                 let has_doc_example = tests.found_tests != 0;
-                // The `expect_real()` should be okay because `local_def_id_to_hir_id`
+                // The `expect_def_id()` should be okay because `local_def_id_to_hir_id`
                 // would presumably panic if a fake `DefIndex` were passed.
                 let hir_id = self
                     .ctx
                     .tcx
                     .hir()
-                    .local_def_id_to_hir_id(i.def_id.expect_real().expect_local());
+                    .local_def_id_to_hir_id(i.def_id.expect_def_id().expect_local());
                 let (level, source) = self.ctx.tcx.lint_level_at_node(MISSING_DOCS, hir_id);
                 // `missing_docs` is allow-by-default, so don't treat this as ignoring the item
                 // unless the user had an explicit `allow`

src/librustdoc/passes/check_code_block_syntax.rs

@@ -53,7 +53,7 @@ impl<'a, 'tcx> SyntaxChecker<'a, 'tcx> {
             return;
         }
 
-        let local_id = match item.def_id.as_real().and_then(|x| x.as_local()) {
+        let local_id = match item.def_id.as_def_id().and_then(|x| x.as_local()) {
             Some(id) => id,
             // We don't need to check the syntax for other crates so returning
             // without doing anything should not be a problem.
@@ -137,7 +137,7 @@ impl<'a, 'tcx> DocFolder for SyntaxChecker<'a, 'tcx> {
             let sp = item.attr_span(self.cx.tcx);
             let extra = crate::html::markdown::ExtraInfo::new_did(
                 self.cx.tcx,
-                item.def_id.expect_real(),
+                item.def_id.expect_def_id(),
                 sp,
             );
             for code_block in markdown::rust_code_blocks(&dox, &extra) {

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -830,49 +830,48 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
     fn fold_item(&mut self, item: Item) -> Option<Item> {
         use rustc_middle::ty::DefIdTree;
 
-        let parent_node = if item.is_fake() {
-            None
-        } else {
-            find_nearest_parent_module(self.cx.tcx, item.def_id.expect_real())
-        };
-
+        let parent_node =
+            item.def_id.as_def_id().and_then(|did| find_nearest_parent_module(self.cx.tcx, did));
         if parent_node.is_some() {
             trace!("got parent node for {:?} {:?}, id {:?}", item.type_(), item.name, item.def_id);
         }
 
         // find item's parent to resolve `Self` in item's docs below
         debug!("looking for the `Self` type");
-        let self_id = if item.is_fake() {
-            None
-        // Checking if the item is a field in an enum variant
-        } else if (matches!(self.cx.tcx.def_kind(item.def_id.expect_real()), DefKind::Field)
-            && matches!(
-                self.cx.tcx.def_kind(self.cx.tcx.parent(item.def_id.expect_real()).unwrap()),
-                DefKind::Variant
-            ))
-        {
-            self.cx
-                .tcx
-                .parent(item.def_id.expect_real())
-                .and_then(|item_id| self.cx.tcx.parent(item_id))
-        } else if matches!(
-            self.cx.tcx.def_kind(item.def_id.expect_real()),
-            DefKind::AssocConst
-                | DefKind::AssocFn
-                | DefKind::AssocTy
-                | DefKind::Variant
-                | DefKind::Field
-        ) {
-            self.cx.tcx.parent(item.def_id.expect_real())
-        // HACK(jynelson): `clean` marks associated types as `TypedefItem`, not as `AssocTypeItem`.
-        // Fixing this breaks `fn render_deref_methods`.
-        // As a workaround, see if the parent of the item is an `impl`; if so this must be an associated item,
-        // regardless of what rustdoc wants to call it.
-        } else if let Some(parent) = self.cx.tcx.parent(item.def_id.expect_real()) {
-            let parent_kind = self.cx.tcx.def_kind(parent);
-            Some(if parent_kind == DefKind::Impl { parent } else { item.def_id.expect_real() })
-        } else {
-            Some(item.def_id.expect_real())
+        let self_id = match item.def_id.as_def_id() {
+            None => None,
+            Some(did)
+                if (matches!(self.cx.tcx.def_kind(did), DefKind::Field)
+                    && matches!(
+                        self.cx.tcx.def_kind(self.cx.tcx.parent(did).unwrap()),
+                        DefKind::Variant
+                    )) =>
+            {
+                self.cx.tcx.parent(did).and_then(|item_id| self.cx.tcx.parent(item_id))
+            }
+            Some(did)
+                if matches!(
+                    self.cx.tcx.def_kind(did),
+                    DefKind::AssocConst
+                        | DefKind::AssocFn
+                        | DefKind::AssocTy
+                        | DefKind::Variant
+                        | DefKind::Field
+                ) =>
+            {
+                self.cx.tcx.parent(did)
+            }
+            Some(did) => match self.cx.tcx.parent(did) {
+                // HACK(jynelson): `clean` marks associated types as `TypedefItem`, not as `AssocTypeItem`.
+                // Fixing this breaks `fn render_deref_methods`.
+                // As a workaround, see if the parent of the item is an `impl`; if so this must be an associated item,
+                // regardless of what rustdoc wants to call it.
+                Some(parent) => {
+                    let parent_kind = self.cx.tcx.def_kind(parent);
+                    Some(if parent_kind == DefKind::Impl { parent } else { did })
+                }
+                None => Some(did),
+            },
         };
 
         // FIXME(jynelson): this shouldn't go through stringification, rustdoc should just use the DefId directly
@@ -897,7 +896,7 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
         let inner_docs = item.inner_docs(self.cx.tcx);
 
         if item.is_mod() && inner_docs {
-            self.mod_ids.push(item.def_id.expect_real());
+            self.mod_ids.push(item.def_id.expect_def_id());
         }
 
         // We want to resolve in the lexical scope of the documentation.
@@ -924,7 +923,7 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
 
         Some(if item.is_mod() {
             if !inner_docs {
-                self.mod_ids.push(item.def_id.expect_real());
+                self.mod_ids.push(item.def_id.expect_def_id());
             }
 
             let ret = self.fold_item_recur(item);
@@ -1235,10 +1234,10 @@ impl LinkCollector<'_, '_> {
             // item can be non-local e.g. when using #[doc(primitive = "pointer")]
             if let Some((src_id, dst_id)) = id
                 .as_local()
-                // The `expect_real()` should be okay because `local_def_id_to_hir_id`
+                // The `expect_def_id()` should be okay because `local_def_id_to_hir_id`
                 // would presumably panic if a fake `DefIndex` were passed.
                 .and_then(|dst_id| {
-                    item.def_id.expect_real().as_local().map(|src_id| (src_id, dst_id))
+                    item.def_id.expect_def_id().as_local().map(|src_id| (src_id, dst_id))
                 })
             {
                 let hir_src = self.cx.tcx.hir().local_def_id_to_hir_id(src_id);

src/librustdoc/passes/collect_trait_impls.rs

@@ -136,10 +136,15 @@ impl<'a, 'tcx> DocFolder for SyntheticImplCollector<'a, 'tcx> {
     fn fold_item(&mut self, i: Item) -> Option<Item> {
         if i.is_struct() || i.is_enum() || i.is_union() {
             // FIXME(eddyb) is this `doc(hidden)` check needed?
-            if !self.cx.tcx.get_attrs(i.def_id.expect_real()).lists(sym::doc).has_word(sym::hidden)
+            if !self
+                .cx
+                .tcx
+                .get_attrs(i.def_id.expect_def_id())
+                .lists(sym::doc)
+                .has_word(sym::hidden)
             {
                 self.impls
-                    .extend(get_auto_trait_and_blanket_impls(self.cx, i.def_id.expect_real()));
+                    .extend(get_auto_trait_and_blanket_impls(self.cx, i.def_id.expect_def_id()));
             }
         }
 
@@ -149,7 +154,7 @@ impl<'a, 'tcx> DocFolder for SyntheticImplCollector<'a, 'tcx> {
 
 #[derive(Default)]
 struct ItemCollector {
-    items: FxHashSet<FakeDefId>,
+    items: FxHashSet<ItemId>,
 }
 
 impl ItemCollector {
@@ -168,7 +173,7 @@ impl DocFolder for ItemCollector {
 
 struct BadImplStripper {
     prims: FxHashSet<PrimitiveType>,
-    items: FxHashSet<FakeDefId>,
+    items: FxHashSet<ItemId>,
 }
 
 impl BadImplStripper {
@@ -185,7 +190,7 @@ impl BadImplStripper {
         }
     }
 
-    fn keep_impl_with_def_id(&self, did: FakeDefId) -> bool {
+    fn keep_impl_with_def_id(&self, did: ItemId) -> bool {
         self.items.contains(&did)
     }
 }

src/librustdoc/passes/doc_test_lints.rs

@@ -53,7 +53,7 @@ impl crate::doctest::Tester for Tests {
 }
 
 crate fn should_have_doc_example(cx: &DocContext<'_>, item: &clean::Item) -> bool {
-    if !cx.cache.access_levels.is_public(item.def_id.expect_real())
+    if !cx.cache.access_levels.is_public(item.def_id.expect_def_id())
         || matches!(
             *item.kind,
             clean::StructFieldItem(_)
@@ -71,9 +71,9 @@ crate fn should_have_doc_example(cx: &DocContext<'_>, item: &clean::Item) -> boo
     {
         return false;
     }
-    // The `expect_real()` should be okay because `local_def_id_to_hir_id`
+    // The `expect_def_id()` should be okay because `local_def_id_to_hir_id`
     // would presumably panic if a fake `DefIndex` were passed.
-    let hir_id = cx.tcx.hir().local_def_id_to_hir_id(item.def_id.expect_real().expect_local());
+    let hir_id = cx.tcx.hir().local_def_id_to_hir_id(item.def_id.expect_def_id().expect_local());
     if cx.tcx.hir().attrs(hir_id).lists(sym::doc).has_word(sym::hidden)
         || inherits_doc_hidden(cx.tcx, hir_id)
     {
@@ -107,7 +107,8 @@ crate fn look_for_tests<'tcx>(cx: &DocContext<'tcx>, dox: &str, item: &Item) {
                 |lint| lint.build("missing code example in this documentation").emit(),
             );
         }
-    } else if tests.found_tests > 0 && !cx.cache.access_levels.is_public(item.def_id.expect_real())
+    } else if tests.found_tests > 0
+        && !cx.cache.access_levels.is_public(item.def_id.expect_def_id())
     {
         cx.tcx.struct_span_lint_hir(
             crate::lint::PRIVATE_DOC_TESTS,

src/librustdoc/passes/strip_hidden.rs

@@ -2,7 +2,7 @@ use rustc_span::symbol::sym;
 use std::mem;
 
 use crate::clean;
-use crate::clean::{FakeDefIdSet, Item, NestedAttributesExt};
+use crate::clean::{Item, ItemIdSet, NestedAttributesExt};
 use crate::core::DocContext;
 use crate::fold::{strip_item, DocFolder};
 use crate::passes::{ImplStripper, Pass};
@@ -15,7 +15,7 @@ crate const STRIP_HIDDEN: Pass = Pass {
 
 /// Strip items marked `#[doc(hidden)]`
 crate fn strip_hidden(krate: clean::Crate, _: &mut DocContext<'_>) -> clean::Crate {
-    let mut retained = FakeDefIdSet::default();
+    let mut retained = ItemIdSet::default();
 
     // strip all #[doc(hidden)] items
     let krate = {
@@ -29,7 +29,7 @@ crate fn strip_hidden(krate: clean::Crate, _: &mut DocContext<'_>) -> clean::Cra
 }
 
 struct Stripper<'a> {
-    retained: &'a mut FakeDefIdSet,
+    retained: &'a mut ItemIdSet,
     update_retained: bool,
 }
 

src/librustdoc/passes/strip_private.rs

@@ -1,4 +1,4 @@
-use crate::clean::{self, FakeDefIdSet};
+use crate::clean::{self, ItemIdSet};
 use crate::core::DocContext;
 use crate::fold::DocFolder;
 use crate::passes::{ImplStripper, ImportStripper, Pass, Stripper};
@@ -14,7 +14,7 @@ crate const STRIP_PRIVATE: Pass = Pass {
 /// crate, specified by the `xcrate` flag.
 crate fn strip_private(mut krate: clean::Crate, cx: &mut DocContext<'_>) -> clean::Crate {
     // This stripper collects all *retained* nodes.
-    let mut retained = FakeDefIdSet::default();
+    let mut retained = ItemIdSet::default();
 
     // strip all private items
     {

src/librustdoc/passes/stripper.rs

@@ -2,11 +2,11 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::middle::privacy::AccessLevels;
 use std::mem;
 
-use crate::clean::{self, FakeDefIdSet, GetDefId, Item};
+use crate::clean::{self, GetDefId, Item, ItemIdSet};
 use crate::fold::{strip_item, DocFolder};
 
 crate struct Stripper<'a> {
-    crate retained: &'a mut FakeDefIdSet,
+    crate retained: &'a mut ItemIdSet,
     crate access_levels: &'a AccessLevels<DefId>,
     crate update_retained: bool,
 }
@@ -42,7 +42,7 @@ impl<'a> DocFolder for Stripper<'a> {
             | clean::TraitAliasItem(..)
             | clean::ForeignTypeItem => {
                 if i.def_id.is_local() {
-                    if !self.access_levels.is_exported(i.def_id.expect_real()) {
+                    if !self.access_levels.is_exported(i.def_id.expect_def_id()) {
                         debug!("Stripper: stripping {:?} {:?}", i.type_(), i.name);
                         return None;
                     }
@@ -116,7 +116,7 @@ impl<'a> DocFolder for Stripper<'a> {
 
 /// This stripper discards all impls which reference stripped items
 crate struct ImplStripper<'a> {
-    crate retained: &'a FakeDefIdSet,
+    crate retained: &'a ItemIdSet,
 }
 
 impl<'a> DocFolder for ImplStripper<'a> {