Reduce tracing output of memo

src/function/maybe_changed_after.rs

@@ -72,6 +72,7 @@ where
         tracing::debug!(
             "{database_key_index:?}: maybe_changed_after_cold, successful claim, \
                 revision = {revision:?}, old_memo = {old_memo:#?}",
+            old_memo = old_memo.tracing_debug()
         );
 
         // Check if the inputs are still valid and we can just compare `changed_at`.
@@ -105,7 +106,10 @@ where
         let verified_at = memo.verified_at.load();
         let revision_now = zalsa.current_revision();
 
-        tracing::debug!("{database_key_index:?}: shallow_verify_memo(memo = {memo:#?})",);
+        tracing::debug!(
+            "{database_key_index:?}: shallow_verify_memo(memo = {memo:#?})",
+            memo = memo.tracing_debug()
+        );
 
         if verified_at == revision_now {
             // Already verified.
@@ -140,7 +144,10 @@ where
         let zalsa = db.zalsa();
         let database_key_index = active_query.database_key_index;
 
-        tracing::debug!("{database_key_index:?}: deep_verify_memo(old_memo = {old_memo:#?})",);
+        tracing::debug!(
+            "{database_key_index:?}: deep_verify_memo(old_memo = {old_memo:#?})",
+            old_memo = old_memo.tracing_debug()
+        );
 
         if self.shallow_verify_memo(db, zalsa, database_key_index, old_memo) {
             return true;

src/function/memo.rs

@@ -1,3 +1,4 @@
+use std::fmt::Formatter;
 use std::sync::Arc;
 
 use arc_swap::{ArcSwap, Guard};
@@ -168,4 +169,29 @@ impl<V> Memo<V> {
             output.mark_validated_output(db, database_key_index);
         }
     }
+
+    pub(super) fn tracing_debug(&self) -> impl std::fmt::Debug + '_ {
+        struct TracingDebug<'a, T> {
+            memo: &'a Memo<T>,
+        }
+
+        impl<T> std::fmt::Debug for TracingDebug<'_, T> {
+            fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+                f.debug_struct("Memo")
+                    .field(
+                        "value",
+                        if self.memo.value.is_some() {
+                            &"Some(<value>)"
+                        } else {
+                            &"None"
+                        },
+                    )
+                    .field("verified_at", &self.memo.verified_at)
+                    .field("revisions", &self.memo.revisions)
+                    .finish()
+            }
+        }
+
+        TracingDebug { memo: self }
+    }
 }

src/function/specify.rs

@@ -81,7 +81,11 @@ where
             revisions,
         };
 
-        tracing::debug!("specify: about to add memo {:#?} for key {:?}", memo, key);
+        tracing::debug!(
+            "specify: about to add memo {:#?} for key {:?}",
+            memo.tracing_debug(),
+            key
+        );
         self.insert_memo(db, key, memo);
 
         // Record that the current query *specified* a value for this cell.