3 files changed, 27 insertions, 7 deletions
diff --git a/compiler/rustc_hir/src/definitions.rs b/compiler/rustc_hir/src/definitions.rs
index ed7afcc07b1..d813c887eee 100644
--- a/compiler/rustc_hir/src/definitions.rs
+++ b/compiler/rustc_hir/src/definitions.rs
@@ -101,7 +101,11 @@ impl DefPathTable {
 pub struct Definitions {
     table: DefPathTable,
 
-    // FIXME(eddyb) ideally all `LocalDefId`s would be HIR owners.
+    /// Only [`LocalDefId`]s for items and item-like are HIR owners.
+    /// The associated `HirId` has a `local_id` of `0`.
+    /// Generic parameters and closures are also assigned a `LocalDefId` but are not HIR owners.
+    /// Their `HirId`s are defined by their position while lowering the enclosing owner.
+    // FIXME(cjgillot) Some `LocalDefId`s from `use` items are dropped during lowering and lack a `HirId`.
     pub(super) def_id_to_hir_id: IndexVec<LocalDefId, Option<hir::HirId>>,
     /// The reverse mapping of `def_id_to_hir_id`.
     pub(super) hir_id_to_def_id: FxHashMap<hir::HirId, LocalDefId>,
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 64bd32b8ddc..69572807e7c 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -1203,7 +1203,7 @@ pub enum UnsafeSource {
     UserProvided,
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Encodable, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Hash, Debug)]
 pub struct BodyId {
     pub hir_id: HirId,
 }
@@ -1980,7 +1980,7 @@ pub struct FnSig<'hir> {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Encodable, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug)]
 pub struct TraitItemId {
     pub def_id: LocalDefId,
 }
@@ -2043,7 +2043,7 @@ pub enum TraitItemKind<'hir> {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Encodable, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug)]
 pub struct ImplItemId {
     pub def_id: LocalDefId,
 }
@@ -2644,7 +2644,7 @@ impl<'hir> VariantData<'hir> {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Encodable, Debug, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, Hash)]
 pub struct ItemId {
     pub def_id: LocalDefId,
 }
@@ -2883,7 +2883,7 @@ pub enum AssocItemKind {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Encodable, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug)]
 pub struct ForeignItemId {
     pub def_id: LocalDefId,
 }
diff --git a/compiler/rustc_hir/src/hir_id.rs b/compiler/rustc_hir/src/hir_id.rs
index 39552eb9f31..1482a96cae3 100644
--- a/compiler/rustc_hir/src/hir_id.rs
+++ b/compiler/rustc_hir/src/hir_id.rs
@@ -11,7 +11,7 @@ use std::fmt;
 /// the `local_id` part of the `HirId` changing, which is a very useful property in
 /// incremental compilation where we have to persist things through changes to
 /// the code base.
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 #[derive(Encodable, Decodable)]
 pub struct HirId {
     pub owner: LocalDefId,
@@ -32,6 +32,10 @@ impl HirId {
     pub fn make_owner(owner: LocalDefId) -> Self {
         Self { owner, local_id: ItemLocalId::from_u32(0) }
     }
+
+    pub fn index(self) -> (usize, usize) {
+        (rustc_index::vec::Idx::index(self.owner), rustc_index::vec::Idx::index(self.local_id))
+    }
 }
 
 impl fmt::Display for HirId {
@@ -40,6 +44,18 @@ impl fmt::Display for HirId {
     }
 }
 
+impl Ord for HirId {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        (self.index()).cmp(&(other.index()))
+    }
+}
+
+impl PartialOrd for HirId {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(&other))
+    }
+}
+
 rustc_data_structures::define_id_collections!(HirIdMap, HirIdSet, HirId);
 rustc_data_structures::define_id_collections!(ItemLocalMap, ItemLocalSet, ItemLocalId);