Implement HashStable directly.

src/librustc/dep_graph/mod.rs

@@ -184,5 +184,3 @@ fn def_id_corresponds_to_hir_dep_node(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
     def_id.index == hir_id.owner.local_def_index
 }
-
-impl rustc_query_system::HashStableContext for StableHashingContext<'_> {}

src/librustc_query_system/dep_graph/dep_node.rs

@@ -46,7 +46,6 @@
 
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_macros::HashStable_Generic;
 
 use std::fmt;
 use std::hash::Hash;
@@ -127,7 +126,6 @@ impl<Ctxt: DepContext, T> DepNodeParams<Ctxt> for T
 /// the need to be mapped or unmapped. (This ensures we can serialize
 /// them even in the absence of a tcx.)
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
-#[derive(HashStable_Generic)]
 pub struct WorkProductId {
     hash: Fingerprint,
 }
@@ -144,3 +142,10 @@ pub fn from_fingerprint(fingerprint: Fingerprint) -> WorkProductId {
         WorkProductId { hash: fingerprint }
     }
 }
+
+impl<HCX> HashStable<HCX> for WorkProductId {
+    #[inline]
+    fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
+        self.hash.hash_stable(hcx, hasher)
+    }
+}

src/librustc_query_system/dep_graph/mod.rs

@@ -22,7 +22,7 @@
 
 pub trait DepContext: Copy {
     type DepKind: self::DepKind;
-    type StableHashingContext: crate::HashStableContext;
+    type StableHashingContext;
 
     /// Create a hashing context for hashing new results.
     fn create_stable_hashing_context(&self) -> Self::StableHashingContext;

src/librustc_query_system/lib.rs

@@ -15,5 +15,3 @@
 
 pub mod dep_graph;
 pub mod query;
-
-pub trait HashStableContext {}