dont erase a trail msg redundantly

lib/index.js

@@ -55,12 +55,12 @@ function initGC(peer, config) {
     const done = multicb({ pluck: 1 })
 
     /**
-     * @param {string} explanation
+     * @param {string} errExplanation
      */
-    function makeRecCB(explanation) {
+    function makeRecCB(errExplanation) {
       const cb = done()
       return (/**@type {Error=}*/ err) => {
-        if (err) debug('%s: %s', explanation, flattenCauseChain(err))
+        if (err) debug('%s: %s', errExplanation, flattenCauseChain(err))
         cb()
       }
     }
@@ -70,13 +70,18 @@ function initGC(peer, config) {
       if (!rec.msg) continue
       const { id: msgID, msg } = rec
       const [purpose, details] = peer.goals.getMsgPurpose(msgID, msg)
-      if (purpose === 'goal') continue // don't cleanup
-      if (purpose === 'none') {
+      switch (purpose) {
+        case 'goal': {
+          continue // don't cleanup
+        }
+        case 'none': {
           const recCB = makeRecCB('Failed to delete msg when cleaning up')
           debug('Deleting msg %s with purpose=none', msgID)
           peer.db.del(msgID, recCB)
           waiting = true
-      } else if (purpose === 'ghost') {
+          continue
+        }
+        case 'ghost': {
           const { tangleID, span } = details
           const recCB = makeRecCB('Failed to delete ghost msg when cleaning up')
           // TODO: Could one msg be a ghostable in MANY tangles? Or just one?
@@ -86,13 +91,20 @@ function initGC(peer, config) {
             peer.db.del(msgID, recCB)
           })
           waiting = true
-      } else if (purpose === 'trail') {
+          continue
+        }
+        case 'trail': {
+          if (!msg.data) continue // it's already erased
           const recCB = makeRecCB('Failed to erase trail msg when cleaning up')
           debug('Erasing msg %s with purpose=trail', msgID)
           peer.db.erase(msgID, recCB)
           waiting = true
-      } else {
+          continue
+        }
+        default: {
           cb(new Error('Unreachable'))
+          return
+        }
       }
     }
 

test/feed-holes.test.js

@@ -52,7 +52,16 @@ test('Feed holes', async (t) => {
   alice.goals.set(postFeedID, 'newest-4')
   assert('alice set a goal for newest-4 of post feed')
 
+  // Mock db.erase so we can inspect how many times it was called
+  const prevErase = alice.db.erase
+  const calledErase = []
+  alice.db.erase = (msgID, cb) => {
+    calledErase.push(msgID)
+    prevErase(msgID, cb)
+  }
+
   await p(alice.gc.forceImmediately)()
+  assert.deepEqual(calledErase, [posts[2]], 'erased A2')
 
   assert.deepEqual(
     getTexts([...alice.db.msgs()]),
@@ -60,5 +69,8 @@ test('Feed holes', async (t) => {
     'alice has only the end of the feed'
   )
 
+  await p(alice.gc.forceImmediately)()
+  assert.deepEqual(calledErase, [posts[2]], 'no double erasing')
+
   await p(alice.close)(true)
 })