Allow query system to recover a HirId.

compiler/rustc_middle/src/dep_graph/dep_node.rs

@@ -62,7 +62,7 @@ use crate::ty::TyCtxt;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_hir::definitions::DefPathHash;
-use rustc_hir::HirId;
+use rustc_hir::{HirId, ItemLocalId};
 use rustc_query_system::dep_graph::FingerprintStyle;
 use rustc_span::symbol::Symbol;
 use std::hash::Hash;
@@ -289,7 +289,7 @@ impl DepNodeExt for DepNode {
         let kind = dep_kind_from_label_string(label)?;
 
         match kind.fingerprint_style(tcx) {
-            FingerprintStyle::Opaque => Err(()),
+            FingerprintStyle::Opaque | FingerprintStyle::HirId => Err(()),
             FingerprintStyle::Unit => Ok(DepNode::new_no_params(tcx, kind)),
             FingerprintStyle::DefPathHash => {
                 Ok(DepNode::from_def_path_hash(tcx, def_path_hash, kind))
@@ -417,7 +417,7 @@ impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for (DefId, DefId) {
 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
     #[inline(always)]
     fn fingerprint_style() -> FingerprintStyle {
-        FingerprintStyle::Opaque
+        FingerprintStyle::HirId
     }
 
     // We actually would not need to specialize the implementation of this
@@ -426,10 +426,36 @@ impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
     #[inline(always)]
     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
         let HirId { owner, local_id } = *self;
-
         let def_path_hash = tcx.def_path_hash(owner.to_def_id());
-        let local_id = Fingerprint::from_smaller_hash(local_id.as_u32().into());
+        Fingerprint::new(
+            // `owner` is local, so is completely defined by the local hash
+            def_path_hash.local_hash(),
+            local_id.as_u32().into(),
+        )
+    }
 
-        def_path_hash.0.combine(local_id)
+    #[inline(always)]
+    fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
+        let HirId { owner, local_id } = *self;
+        format!("{}.{}", tcx.def_path_str(owner.to_def_id()), local_id.as_u32())
+    }
+
+    #[inline(always)]
+    fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
+        if dep_node.kind.fingerprint_style(tcx) == FingerprintStyle::HirId {
+            let (local_hash, local_id) = Fingerprint::from(dep_node.hash).as_value();
+            let def_path_hash = DefPathHash::new(tcx.sess.local_stable_crate_id(), local_hash);
+            let owner = tcx
+                .def_path_hash_to_def_id(def_path_hash, &mut || {
+                    panic!("Failed to extract HirId: {:?} {}", dep_node.kind, dep_node.hash)
+                })
+                .expect_local();
+            let local_id = local_id
+                .try_into()
+                .unwrap_or_else(|_| panic!("local id should be u32, found {:?}", local_id));
+            Some(HirId { owner, local_id: ItemLocalId::from_u32(local_id) })
+        } else {
+            None
+        }
     }
 }

compiler/rustc_query_system/src/dep_graph/mod.rs

@@ -67,6 +67,8 @@ impl<T: DepContext> HasDepContext for T {
 pub enum FingerprintStyle {
     /// The fingerprint is actually a DefPathHash.
     DefPathHash,
+    /// The fingerprint is actually a HirId.
+    HirId,
     /// Query key was `()` or equivalent, so fingerprint is just zero.
     Unit,
     /// Some opaque hash.
@@ -77,7 +79,9 @@ impl FingerprintStyle {
     #[inline]
     pub fn reconstructible(self) -> bool {
         match self {
-            FingerprintStyle::DefPathHash | FingerprintStyle::Unit => true,
+            FingerprintStyle::DefPathHash | FingerprintStyle::Unit | FingerprintStyle::HirId => {
+                true
+            }
             FingerprintStyle::Opaque => false,
         }
     }