Delay a bug when overwriting fed value.

Author: cjgillot

compiler/rustc_middle/src/query/plumbing.rs

@@ -533,12 +533,20 @@ macro_rules! define_feedable {
                             let (value_hash, old_hash): (Fingerprint, Fingerprint) = tcx.with_stable_hashing_context(|mut hcx|
                                 (hasher(&mut hcx, &value), hasher(&mut hcx, &old))
                             );
-                            assert_eq!(
-                                old_hash, value_hash,
-                                "Trying to feed an already recorded value for query {} key={key:?}:\nold value: {old:?}\nnew value: {value:?}",
-                                stringify!($name),
-                            )
+                            if old_hash != value_hash {
+                                // We have an inconsistency. This can happen if one of the two
+                                // results is tainted by errors. In this case, delay a bug to
+                                // ensure compilation is doomed, and keep the `old` value.
+                                tcx.sess.delay_span_bug(DUMMY_SP, format!(
+                                    "Trying to feed an already recorded value for query {} key={key:?}:\n\
+                                    old value: {old:?}\nnew value: {value:?}",
+                                    stringify!($name),
+                                ));
+                            }
                         } else {
+                            // The query is `no_hash`, so we have no way to perform a sanity check.
+                            // If feeding the same value multiple times needs to be supported,
+                            // the query should not be marked `no_hash`.
                             bug!(
                                 "Trying to feed an already recorded value for query {} key={key:?}:\nold value: {old:?}\nnew value: {value:?}",
                                 stringify!($name),

compiler/rustc_query_system/src/query/plumbing.rs

@@ -433,16 +433,22 @@ where
                 (hasher(&mut hcx, &cached_result), hasher(&mut hcx, &result))
             });
             let formatter = query.format_value();
-            debug_assert_eq!(
-                old_hash,
-                new_hash,
-                "Computed query value for {:?}({:?}) is inconsistent with fed value,\n\
-                computed={:#?}\nfed={:#?}",
-                query.dep_kind(),
-                key,
-                formatter(&result),
-                formatter(&cached_result),
-            );
+            if old_hash != new_hash {
+                // We have an inconsistency. This can happen if one of the two
+                // results is tainted by errors. In this case, delay a bug to
+                // ensure compilation is doomed.
+                qcx.dep_context().sess().delay_span_bug(
+                    DUMMY_SP,
+                    format!(
+                        "Computed query value for {:?}({:?}) is inconsistent with fed value,\n\
+                        computed={:#?}\nfed={:#?}",
+                        query.dep_kind(),
+                        key,
+                        formatter(&result),
+                        formatter(&cached_result),
+                    ),
+                );
+            }
         }
     }
     job_owner.complete(cache, result, dep_node_index);

tests/incremental/const-generic-type-cycle.rs

@@ -3,6 +3,7 @@
 //
 // compile-flags: -Zincremental-ignore-spans
 // revisions: cpass cfail
+// error-pattern: cycle detected when computing type of `Bar::N`
 
 #![feature(trait_alias)]
 #![crate_type="lib"]