when clearing blocks, also clear the tree nodes if safe (#729)

* when clearing blocks, also clear the tree nodes if safe

* if in range, its not in bitfield

Author: mafintosh

lib/bitfield.js

@@ -400,6 +400,30 @@ module.exports = class Bitfield {
     return this.findLast(false, position)
   }
 
+  hasSet (start, length) {
+    const end = start + length
+
+    let j = start & (BITS_PER_SEGMENT - 1)
+    let i = (start - j) / BITS_PER_SEGMENT
+
+    while (i < this._segments.maxLength) {
+      const s = this._segments.get(i)
+
+      let index = -1
+
+      if (s) index = s.findFirst(true, j)
+
+      if (index !== -1) return (i * BITS_PER_SEGMENT + index) < end
+
+      j = 0
+      i++
+
+      if (i * BITS_PER_SEGMENT >= end) return false
+    }
+
+    return false
+  }
+
   count (start, length, val) {
     let j = start & (BITS_PER_PAGE - 1)
     let i = (start - j) / BITS_PER_PAGE

lib/session-state.js

@@ -476,6 +476,22 @@ module.exports = class SessionState {
     try {
       const tx = this.createWriteBatch()
 
+      const ite = flat.iterator(start * 2)
+      while (!isRootIndex(ite.index, this.roots)) {
+        const a = ite.index
+        const b = ite.sibling()
+        ite.parent()
+
+        const [left, right] = flat.spans(b)
+        const s = left / 2
+        const e = (right / 2) + 1
+        const has = (s <= start && e <= end) ? false : this.core.bitfield.hasSet(s, e - s)
+        if (has) break
+
+        tx.deleteTreeNode(a)
+        tx.deleteTreeNode(b)
+      }
+
       if (this.isDefault()) {
         await storeBitfieldRange(this.storage, tx, start, end, false)
         if (start < this.core.header.hints.contiguousLength) {
@@ -1134,3 +1150,11 @@ function getCoreHead (storage) {
   b.tryFlush()
   return p
 }
+
+function isRootIndex (index, roots) {
+  for (const node of roots) {
+    if (node.index === index) return true
+  }
+
+  return false
+}