Sanity check computed value for feeable queries.

compiler/rustc_macros/src/query.rs

@@ -359,6 +359,15 @@ macro_rules! passthrough {
         });
 
         if modifiers.feedable.is_some() {
+            assert!(modifiers.anon.is_none(), "Query {name} cannot be both `feedable` and `anon`.");
+            assert!(
+                modifiers.eval_always.is_none(),
+                "Query {name} cannot be both `feedable` and `eval_always`."
+            );
+            assert!(
+                modifiers.no_hash.is_none(),
+                "Query {name} cannot be both `feedable` and `no_hash`."
+            );
             feedable_queries.extend(quote! {
                 #(#doc_comments)*
                 [#attribute_stream] fn #name(#arg) #result,

compiler/rustc_query_impl/src/plumbing.rs

@@ -252,6 +252,18 @@ macro_rules! depth_limit {
     };
 }
 
+macro_rules! feedable {
+    ([]) => {{
+        false
+    }};
+    ([(feedable) $($rest:tt)*]) => {{
+        true
+    }};
+    ([$other:tt $($modifiers:tt)*]) => {
+        feedable!([$($modifiers)*])
+    };
+}
+
 macro_rules! hash_result {
     ([]) => {{
         Some(dep_graph::hash_result)
@@ -491,6 +503,7 @@ fn make_vtable(tcx: QueryCtxt<'tcx>, key: &Self::Key) ->
                     anon: is_anon!([$($modifiers)*]),
                     eval_always: is_eval_always!([$($modifiers)*]),
                     depth_limit: depth_limit!([$($modifiers)*]),
+                    feedable: feedable!([$($modifiers)*]),
                     dep_kind: dep_graph::DepKind::$name,
                     hash_result: hash_result!([$($modifiers)*]),
                     handle_cycle_error: handle_cycle_error!([$($modifiers)*]),

compiler/rustc_query_system/src/query/config.rs

@@ -15,8 +15,8 @@ pub trait QueryConfig<Qcx: QueryContext> {
     const NAME: &'static str;
 
     type Key: Eq + Hash + Clone + Debug;
-    type Value;
-    type Stored: Clone;
+    type Value: Debug;
+    type Stored: Debug + Clone + std::borrow::Borrow<Self::Value>;
 
     type Cache: QueryCache<Key = Self::Key, Stored = Self::Stored, Value = Self::Value>;
 
@@ -45,6 +45,7 @@ pub struct QueryVTable<Qcx: QueryContext, K, V> {
     pub dep_kind: Qcx::DepKind,
     pub eval_always: bool,
     pub depth_limit: bool,
+    pub feedable: bool,
 
     pub compute: fn(Qcx::DepContext, K) -> V,
     pub hash_result: Option<fn(&mut StableHashingContext<'_>, &V) -> Fingerprint>,

compiler/rustc_query_system/src/query/plumbing.rs

@@ -20,6 +20,7 @@
 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed, FatalError};
 use rustc_session::Session;
 use rustc_span::{Span, DUMMY_SP};
+use std::borrow::Borrow;
 use std::cell::Cell;
 use std::collections::hash_map::Entry;
 use std::fmt::Debug;
@@ -370,11 +371,26 @@ fn try_execute_query<Qcx, C>(
     C: QueryCache,
     C::Key: Clone + DepNodeParams<Qcx::DepContext>,
     C::Value: Value<Qcx::DepContext>,
+    C::Stored: Debug + std::borrow::Borrow<C::Value>,
     Qcx: QueryContext,
 {
     match JobOwner::<'_, C::Key>::try_start(&qcx, state, span, key.clone()) {
         TryGetJob::NotYetStarted(job) => {
-            let (result, dep_node_index) = execute_job(qcx, key, dep_node, query, job.id);
+            let (result, dep_node_index) = execute_job(qcx, key.clone(), dep_node, query, job.id);
+            if query.feedable {
+                // We may have put a value inside the cache from inside the execution.
+                // Verify that it has the same hash as what we have now, to ensure consistency.
+                let _ = cache.lookup(&key, |cached_result, _| {
+                    let hasher = query.hash_result.expect("feedable forbids no_hash");
+                    let old_hash = qcx.dep_context().with_stable_hashing_context(|mut hcx| hasher(&mut hcx, cached_result.borrow()));
+                    let new_hash = qcx.dep_context().with_stable_hashing_context(|mut hcx| hasher(&mut hcx, &result));
+                    debug_assert_eq!(
+                        old_hash, new_hash,
+                        "Computed query value for {:?}({:?}) is inconsistent with fed value,\ncomputed={:#?}\nfed={:#?}",
+                        query.dep_kind, key, result, cached_result,
+                    );
+                });
+            }
             let result = job.complete(cache, result, dep_node_index);
             (result, Some(dep_node_index))
         }