Make PackedFingerprint's Fingerprint private

compiler/rustc_data_structures/src/fingerprint.rs

@@ -170,9 +170,12 @@ impl FingerprintDecoder for opaque::Decoder<'_> {
 // `DepNode`s. As of this writing, the size of a `DepNode` decreases by ~30%
 // (from 24 bytes to 17) by using the packed representation here, which
 // noticeably decreases total memory usage when compiling large crates.
+//
+// The wrapped `Fingerprint` is private to reduce the chance of a client
+// invoking undefined behavior by taking a reference to the packed field.
 #[cfg_attr(any(target_arch = "x86", target_arch = "x86_64"), repr(packed))]
 #[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Copy, Hash)]
-pub struct PackedFingerprint(pub Fingerprint);
+pub struct PackedFingerprint(Fingerprint);
 
 impl std::fmt::Display for PackedFingerprint {
     #[inline]
@@ -198,3 +201,17 @@ impl<D: rustc_serialize::Decoder> Decodable<D> for PackedFingerprint {
         Fingerprint::decode(d).map(|f| PackedFingerprint(f))
     }
 }
+
+impl From<Fingerprint> for PackedFingerprint {
+    #[inline]
+    fn from(f: Fingerprint) -> PackedFingerprint {
+        PackedFingerprint(f)
+    }
+}
+
+impl From<PackedFingerprint> for Fingerprint {
+    #[inline]
+    fn from(f: PackedFingerprint) -> Fingerprint {
+        f.0
+    }
+}

compiler/rustc_middle/src/dep_graph/dep_node.rs

@@ -61,7 +61,7 @@ use crate::traits::query::{
 use crate::ty::subst::{GenericArg, SubstsRef};
 use crate::ty::{self, ParamEnvAnd, Ty, TyCtxt};
 
-use rustc_data_structures::fingerprint::{Fingerprint, PackedFingerprint};
+use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX};
 use rustc_hir::definitions::DefPathHash;
 use rustc_hir::HirId;
@@ -236,7 +236,7 @@ macro_rules! define_dep_nodes {
                 debug_assert!(kind.can_reconstruct_query_key() && kind.has_params());
                 DepNode {
                     kind,
-                    hash: PackedFingerprint(def_path_hash.0),
+                    hash: def_path_hash.0.into(),
                 }
             }
 
@@ -252,7 +252,7 @@ macro_rules! define_dep_nodes {
             /// has been removed.
             fn extract_def_id(&self, tcx: TyCtxt<'tcx>) -> Option<DefId> {
                 if self.kind.can_reconstruct_query_key() {
-                    let def_path_hash = DefPathHash(self.hash.0);
+                    let def_path_hash = DefPathHash(self.hash.into());
                     tcx.def_path_hash_to_def_id.as_ref()?.get(&def_path_hash).cloned()
                 } else {
                     None

compiler/rustc_query_system/src/dep_graph/dep_node.rs

@@ -62,7 +62,7 @@ impl<K: DepKind> DepNode<K> {
     /// does not require any parameters.
     pub fn new_no_params(kind: K) -> DepNode<K> {
         debug_assert!(!kind.has_params());
-        DepNode { kind, hash: PackedFingerprint(Fingerprint::ZERO) }
+        DepNode { kind, hash: Fingerprint::ZERO.into() }
     }
 
     pub fn construct<Ctxt, Key>(tcx: Ctxt, kind: K, arg: &Key) -> DepNode<K>
@@ -71,7 +71,7 @@ impl<K: DepKind> DepNode<K> {
         Key: DepNodeParams<Ctxt>,
     {
         let hash = arg.to_fingerprint(tcx);
-        let dep_node = DepNode { kind, hash: PackedFingerprint(hash) };
+        let dep_node = DepNode { kind, hash: hash.into() };
 
         #[cfg(debug_assertions)]
         {

compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -1,4 +1,4 @@
-use rustc_data_structures::fingerprint::{Fingerprint, PackedFingerprint};
+use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::profiling::QueryInvocationId;
 use rustc_data_structures::sharded::{self, Sharded};
@@ -976,7 +976,7 @@ impl<K: DepKind> CurrentDepGraph<K> {
             // Fingerprint::combine() is faster than sending Fingerprint
             // through the StableHasher (at least as long as StableHasher
             // is so slow).
-            hash: PackedFingerprint(self.anon_id_seed.combine(hasher.finish())),
+            hash: self.anon_id_seed.combine(hasher.finish()).into(),
         };
 
         self.intern_node(target_dep_node, task_deps.reads, Fingerprint::ZERO)