Document ConnectBlock connectTrace postconditions

Author: TheBlueMatt

src/validation.cpp

@@ -2164,6 +2164,10 @@ struct ConnectTrace {
 /**
  * Connect a new block to chainActive. pblock is either NULL or a pointer to a CBlock
  * corresponding to pindexNew, to bypass loading it again from disk.
+ *
+ * The block is always added to connectTrace (either after loading from disk or by copying
+ * pblock) - if that is not intended, care must be taken to remove the last entry in
+ * blocksConnected in case of failure.
  */
 bool static ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace)
 {