Make def_path_hash_to_def_id a hook

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

@@ -650,14 +650,18 @@ impl CrateStore for CStore {
     fn def_path_hash(&self, def: DefId) -> DefPathHash {
         self.get_crate_data(def.krate).def_path_hash(def.index)
     }
-
-    fn def_path_hash_to_def_id(&self, cnum: CrateNum, hash: DefPathHash) -> DefId {
-        let def_index = self.get_crate_data(cnum).def_path_hash_to_def_index(hash);
-        DefId { krate: cnum, index: def_index }
-    }
 }
 
 fn provide_cstore_hooks(providers: &mut Providers) {
+    providers.hooks.def_path_hash_to_def_id_extern = |tcx, hash, stable_crate_id| {
+        // If this is a DefPathHash from an upstream crate, let the CrateStore map
+        // it to a DefId.
+        let cstore = CStore::from_tcx(tcx.tcx);
+        let cnum = cstore.stable_crate_id_to_crate_num(stable_crate_id);
+        let def_index = cstore.get_crate_data(cnum).def_path_hash_to_def_index(hash);
+        DefId { krate: cnum, index: def_index }
+    };
+
     providers.hooks.expn_hash_to_expn_id = |tcx, cnum, index_guess, hash| {
         let cstore = CStore::from_tcx(tcx.tcx);
         cstore.get_crate_data(cnum).expn_hash_to_expn_id(tcx.sess, index_guess, hash)

compiler/rustc_middle/src/hooks/mod.rs

@@ -6,6 +6,8 @@
 use crate::mir;
 use crate::query::TyCtxtAt;
 use crate::ty::{Ty, TyCtxt};
+use rustc_hir::def_id::{DefId, DefPathHash};
+use rustc_session::StableCrateId;
 use rustc_span::def_id::{CrateNum, LocalDefId};
 use rustc_span::{ExpnHash, ExpnId, DUMMY_SP};
 
@@ -94,4 +96,10 @@ declare_hooks! {
         index_guess: u32,
         hash: ExpnHash
     ) -> ExpnId;
+
+    /// Converts a `DefPathHash` to its corresponding `DefId` in the current compilation
+    /// session, if it still exists. This is used during incremental compilation to
+    /// turn a deserialized `DefPathHash` into its current `DefId`.
+    /// Will fetch a DefId from a DefPathHash for a foreign crate.
+    hook def_path_hash_to_def_id_extern(hash: DefPathHash, stable_crate_id: StableCrateId) -> DefId;
 }

compiler/rustc_middle/src/ty/context.rs

@@ -1073,11 +1073,7 @@ impl<'tcx> TyCtxt<'tcx> {
         if stable_crate_id == self.stable_crate_id(LOCAL_CRATE) {
             self.untracked.definitions.read().local_def_path_hash_to_def_id(hash, err).to_def_id()
         } else {
-            // If this is a DefPathHash from an upstream crate, let the CrateStore map
-            // it to a DefId.
-            let cstore = &*self.cstore_untracked();
-            let cnum = cstore.stable_crate_id_to_crate_num(stable_crate_id);
-            cstore.def_path_hash_to_def_id(cnum, hash)
+            self.def_path_hash_to_def_id_extern(hash, stable_crate_id)
         }
     }
 

compiler/rustc_session/src/cstore.rs

@@ -218,9 +218,6 @@ pub trait CrateStore: std::fmt::Debug {
     fn crate_name(&self, cnum: CrateNum) -> Symbol;
     fn stable_crate_id(&self, cnum: CrateNum) -> StableCrateId;
     fn stable_crate_id_to_crate_num(&self, stable_crate_id: StableCrateId) -> CrateNum;
-
-    /// Fetch a DefId from a DefPathHash for a foreign crate.
-    fn def_path_hash_to_def_id(&self, cnum: CrateNum, hash: DefPathHash) -> DefId;
 }
 
 pub type CrateStoreDyn = dyn CrateStore + sync::DynSync + sync::DynSend;