X rebuild: tests: Don't compute keyCover in trackSet

63s -> 61s

wcfs/internal/xbtree/δbtail_test.go

@@ -333,17 +333,26 @@ func (rbs RBucketSet) coverage() string {
 
 // trackSet returns what should be ΔBtail.trackSet coverage for specified tracked key set.
 func (rbs RBucketSet) trackSet(tracked SetKey) PPTreeSubSet {
-	trackSet, _ := rbs.trackSetWithCov(tracked)
+	// nil = don't compute keyCover
+	// (trackSet is called from inside hot inner loop of rebuild test)
+	trackSet := rbs._trackSetWithCov(tracked, nil)
 	return trackSet
 }
 
 // trackSetWithCov returns what should be ΔBtail.trackSet and its key coverage for specified tracked key set.
 func (rbs RBucketSet) trackSetWithCov(tracked SetKey) (trackSet PPTreeSubSet, keyCover *RangedKeySet) {
-	trackSet = PPTreeSubSet{}
 	keyCover = &RangedKeySet{}
+	trackSet = rbs._trackSetWithCov(tracked, keyCover)
+	return trackSet, keyCover
+}
+
+func (rbs RBucketSet) _trackSetWithCov(tracked SetKey, outKeyCover *RangedKeySet) (trackSet PPTreeSubSet) {
+	trackSet = PPTreeSubSet{}
 	for k := range tracked {
 		kb := rbs.Get(k)
-		keyCover.AddRange(KeyRange{kb.lo, kb.hi_})
+		if outKeyCover != nil {
+			outKeyCover.AddRange(KeyRange{kb.lo, kb.hi_})
+		}
 		// trackSet explicitly records only regular buckets.
 		// embedded buckets all have oid=zodb.InvalidOid and would lead to z
 		newNode := false
@@ -384,7 +393,7 @@ func (rbs RBucketSet) trackSetWithCov(tracked SetKey) (trackSet PPTreeSubSet, ke
 			p = p.parent
 		}
 	}
-	return trackSet, keyCover
+	return trackSet
 }