internal/keyspan: refactor interleaving iterator

This commit refactors the interleaving iterator with a goal of simplifying its
logic, but also to support a future mode in which the interleaving iterator may
interleave end boundaries during iteration.

The logic to interleave span bounds and point keys is disentangled from the
logic to determine when to yield a key-value pair to the caller. This also
allows the yielding logic to be shared among forward and reverse iteration.

compaction.go

@@ -1244,7 +1244,7 @@ func (c *compaction) newInputIter(
 			if rangeKeyIter := f.newRangeKeyIter(nil); rangeKeyIter != nil {
 				mi := &keyspan.MergingIter{}
 				mi.Init(c.cmp, rangeKeyCompactionTransform(c.equal, snapshots, c.elideRangeKey), new(keyspan.MergingBuffers), rangeKeyIter)
-				c.rangeKeyInterleaving.Init(c.comparer, iter, mi, nil /* hooks */, nil /* lowerBound */, nil /* upperBound */)
+				c.rangeKeyInterleaving.Init(c.comparer, iter, mi, keyspan.InterleavingIterOpts{})
 				iter = &c.rangeKeyInterleaving
 			}
 			return iter, nil
@@ -1271,7 +1271,7 @@ func (c *compaction) newInputIter(
 		if len(rangeKeyIters) > 0 {
 			mi := &keyspan.MergingIter{}
 			mi.Init(c.cmp, rangeKeyCompactionTransform(c.equal, snapshots, c.elideRangeKey), new(keyspan.MergingBuffers), rangeKeyIters...)
-			c.rangeKeyInterleaving.Init(c.comparer, iter, mi, nil /* hooks */, nil /* lowerBound */, nil /* upperBound */)
+			c.rangeKeyInterleaving.Init(c.comparer, iter, mi, keyspan.InterleavingIterOpts{})
 			iter = &c.rangeKeyInterleaving
 		}
 		return iter, nil
@@ -1557,7 +1557,7 @@ func (c *compaction) newInputIter(
 		mi.Init(c.cmp, rangeKeyCompactionTransform(c.equal, snapshots, c.elideRangeKey), new(keyspan.MergingBuffers), rangeKeyIters...)
 		di := &keyspan.DefragmentingIter{}
 		di.Init(c.comparer, mi, keyspan.DefragmentInternal, keyspan.StaticDefragmentReducer, new(keyspan.DefragmentingBuffers))
-		c.rangeKeyInterleaving.Init(c.comparer, pointKeyIter, di, nil /* hooks */, nil /* lowerBound */, nil /* upperBound */)
+		c.rangeKeyInterleaving.Init(c.comparer, pointKeyIter, di, keyspan.InterleavingIterOpts{})
 		return &c.rangeKeyInterleaving, nil
 	}
 

compaction_iter_test.go

@@ -109,7 +109,7 @@ func TestCompactionIter(t *testing.T) {
 			base.DefaultComparer,
 			fi,
 			keyspan.NewIter(base.DefaultComparer.Compare, rangeKeys),
-			nil, nil, nil)
+			keyspan.InterleavingIterOpts{})
 		iter := newInvalidatingIter(interleavingIter)
 		iter.ignoreKind(InternalKeyKindRangeDelete)
 		if merge == nil {

db.go

@@ -1168,7 +1168,11 @@ func finishInitializingIter(ctx context.Context, buf *iterAlloc) *Iterator {
 			// dbi already had an initialized range key iterator, in case the point
 			// iterator changed or the range key masking suffix changed.
 			dbi.rangeKey.iiter.Init(&dbi.comparer, dbi.iter, dbi.rangeKey.rangeKeyIter,
-				&dbi.rangeKeyMasking, dbi.opts.LowerBound, dbi.opts.UpperBound)
+				keyspan.InterleavingIterOpts{
+					Mask:       &dbi.rangeKeyMasking,
+					LowerBound: dbi.opts.LowerBound,
+					UpperBound: dbi.opts.UpperBound,
+				})
 			dbi.iter = &dbi.rangeKey.iiter
 		}
 	} else {
@@ -1314,7 +1318,10 @@ func finishInitializingInternalIter(buf *iterAlloc, i *scanInternalIterator) *sc
 	// iterator that interleaves range keys pulled from
 	// i.rangeKey.rangeKeyIter.
 	i.rangeKey.iiter.Init(i.comparer, i.iter, i.rangeKey.rangeKeyIter,
-		nil /* mask */, i.opts.LowerBound, i.opts.UpperBound)
+		keyspan.InterleavingIterOpts{
+			LowerBound: i.opts.LowerBound,
+			UpperBound: i.opts.UpperBound,
+		})
 	i.iter = &i.rangeKey.iiter
 
 	return i

external_iterator.go

@@ -319,8 +319,12 @@ func finishInitializingExternal(ctx context.Context, it *Iterator) {
 			}
 		}
 		if it.rangeKey != nil {
-			it.rangeKey.iiter.Init(&it.comparer, it.iter, it.rangeKey.rangeKeyIter, &it.rangeKeyMasking,
-				it.opts.LowerBound, it.opts.UpperBound)
+			it.rangeKey.iiter.Init(&it.comparer, it.iter, it.rangeKey.rangeKeyIter,
+				keyspan.InterleavingIterOpts{
+					Mask:       &it.rangeKeyMasking,
+					LowerBound: it.opts.LowerBound,
+					UpperBound: it.opts.UpperBound,
+				})
 			it.iter = &it.rangeKey.iiter
 		}
 	}