Move the fingerprint_style special case into DepKindVTable creation

compiler/rustc_query_impl/src/plumbing.rs

@@ -24,7 +24,7 @@ use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::print::with_reduced_queries;
 use rustc_middle::ty::tls::{self, ImplicitCtxt};
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_query_system::dep_graph::{DepNodeParams, HasDepContext};
+use rustc_query_system::dep_graph::{DepNodeParams, FingerprintStyle, HasDepContext};
 use rustc_query_system::ich::StableHashingContext;
 use rustc_query_system::query::{
     QueryCache, QueryContext, QueryDispatcher, QueryJobId, QueryMap, QuerySideEffect,
@@ -519,7 +519,11 @@ pub(crate) fn make_dep_kind_vtable_for_query<'tcx, Q>(
 where
     Q: QueryDispatcherUnerased<'tcx>,
 {
-    let fingerprint_style = <Q::Dispatcher as QueryDispatcher>::Key::fingerprint_style();
+    let fingerprint_style = if is_anon {
+        FingerprintStyle::Opaque
+    } else {
+        <Q::Dispatcher as QueryDispatcher>::Key::fingerprint_style()
+    };
 
     if is_anon || !fingerprint_style.reconstructible() {
         return DepKindVTable {

compiler/rustc_query_system/src/dep_graph/dep_node.rs

@@ -237,8 +237,9 @@ pub struct DepKindVTable<Tcx: DepContext> {
     /// cached within one compiler invocation.
     pub is_eval_always: bool,
 
-    /// Whether the query key can be recovered from the hashed fingerprint.
-    /// See [DepNodeParams] trait for the behaviour of each key type.
+    /// Indicates whether and how the query key can be recovered from its hashed fingerprint.
+    ///
+    /// The [`DepNodeParams`] trait determines the fingerprint style for each key type.
     pub fingerprint_style: FingerprintStyle,
 
     /// The red/green evaluation system will try to mark a specific DepNode in the

compiler/rustc_query_system/src/dep_graph/mod.rs

@@ -39,11 +39,7 @@ pub trait DepContext: Copy {
 
     #[inline(always)]
     fn fingerprint_style(self, kind: DepKind) -> FingerprintStyle {
-        let vtable = self.dep_kind_vtable(kind);
-        if vtable.is_anon {
-            return FingerprintStyle::Opaque;
-        }
-        vtable.fingerprint_style
+        self.dep_kind_vtable(kind).fingerprint_style
     }
 
     #[inline(always)]
@@ -148,6 +144,9 @@ impl<T: HasDepContext, Q: Copy> HasDepContext for (T, Q) {
 }
 
 /// Describes the contents of the fingerprint generated by a given query.
+///
+/// This is mainly for determining whether and how we can reconstruct a key
+/// from the fingerprint.
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
 pub enum FingerprintStyle {
     /// The fingerprint is actually a DefPathHash.
@@ -156,7 +155,7 @@ pub enum FingerprintStyle {
     HirId,
     /// Query key was `()` or equivalent, so fingerprint is just zero.
     Unit,
-    /// Some opaque hash.
+    /// The fingerprint is an opaque hash, and a key cannot be reconstructed from it.
     Opaque,
 }