Merge bitcoin#8665: Assert all the things!

4d51e9b Assert ConnectBlock block and pIndex are the same block (NicolasDorier)
972714c pow: GetNextWorkRequired never called with NULL pindexLast (Daniel Cousens)
cc44c8f ContextualCheckBlockHeader should never have pindexPrev to NULL (NicolasDorier)

Tree-SHA512: 7cc568bf9417267c335f21ec3d1505b26e56e5b3d5f4d3dbb555279489800aaa65a3bcd7bc376e274dd102912aec16ddbb18de2e2060b2667b41eb979cd9321e

src/pow.cpp

@@ -146,12 +146,9 @@ unsigned int static DarkGravityWave(const CBlockIndex* pindexLast, const CBlockH
 
 unsigned int GetNextWorkRequiredBTC(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
 {
+    assert(pindexLast != NULL);
     unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact();
 
-    // Genesis block
-    if (pindexLast == NULL)
-        return nProofOfWorkLimit;
-
     // Only change once per interval
     if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0)
     {

src/validation.cpp

@@ -1896,7 +1896,10 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
                   CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck = false)
 {
     AssertLockHeld(cs_main);
-
+    assert(pindex);
+    // pindex->phashBlock can be null if called by CreateNewBlock/TestBlockValidity
+    assert((pindex->phashBlock == NULL) ||
+           (*pindex->phashBlock == block.GetHash()));
     int64_t nTimeStart = GetTimeMicros();
 
     // Check it again in case a previous version let a bad block in
@@ -3321,7 +3324,8 @@ static bool CheckIndexAgainstCheckpoint(const CBlockIndex* pindexPrev, CValidati
 
 bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, const Consensus::Params& consensusParams, const CBlockIndex* pindexPrev, int64_t nAdjustedTime)
 {
-    const int nHeight = pindexPrev == NULL ? 0 : pindexPrev->nHeight + 1;
+    assert(pindexPrev != NULL);
+    const int nHeight = pindexPrev->nHeight + 1;
     // Check proof of work
     if(Params().NetworkIDString() == CBaseChainParams::MAIN && nHeight <= 68589){
         // architecture issues with DGW v1 and v2)