[NOD-1129] Fix NewBlockTemplate creating incesous blocks (#870)

* [NOD-1129] Implement TestIncestousNewBlockTemplate.

* [NOD-1129] Add some debug logs to TestIncestousNewBlockTemplate.

* [NOD-1129] Fix merge errors.

* [NOD-1129] Narrow down on the failure.

* [NOD-1129] Fix bad initial value for child.interval in reachabilityTreeNode.addChild.

* [NOD-1129] Rewrite the test to be specific to reachability.

domain/blockdag/reachability.go

@@ -268,6 +268,12 @@ func (rtn *reachabilityTreeNode) addChild(child *reachabilityTreeNode, reindexRo
 	rtn.children = append(rtn.children, child)
 	child.parent = rtn
 
+	// Temporarily set the child's interval to be empty, at
+	// the start of rtn's remaining interval. This is done
+	// so that child-of-rtn checks (e.g.
+	// findAncestorAmongChildren) will not fail for rtn.
+	child.interval = newReachabilityInterval(remaining.start, remaining.start-1)
+
 	// Handle rtn not being a descendant of the reindex root.
 	// Note that we check rtn here instead of child because
 	// at this point we don't yet know child's interval.

domain/blockdag/reachability_test.go

@@ -1047,3 +1047,37 @@ func TestReindexIntervalsEarlierThanReindexRoot(t *testing.T) {
 		}
 	}
 }
+
+func TestTipsAfterReindexIntervalsEarlierThanReindexRoot(t *testing.T) {
+	// Create a new database and DAG instance to run tests against.
+	dag, teardownFunc, err := DAGSetup("TestTipsAfterReindexIntervalsEarlierThanReindexRoot", true, Config{
+		DAGParams: &dagconfig.SimnetParams,
+	})
+	if err != nil {
+		t.Fatalf("Failed to setup DAG instance: %v", err)
+	}
+	defer teardownFunc()
+
+	// Set the reindex window to a low number to make this test run fast
+	originalReachabilityReindexWindow := reachabilityReindexWindow
+	reachabilityReindexWindow = 10
+	defer func() {
+		reachabilityReindexWindow = originalReachabilityReindexWindow
+	}()
+
+	// Add a chain of reachabilityReindexWindow + 1 blocks above the genesis.
+	// This will set the reindex root to the child of genesis
+	chainTipHash := dag.Params.GenesisHash
+	for i := uint64(0); i < reachabilityReindexWindow+1; i++ {
+		block := PrepareAndProcessBlockForTest(t, dag, []*daghash.Hash{chainTipHash}, nil)
+		chainTipHash = block.BlockHash()
+	}
+
+	// Add another block above the genesis block. This will trigger an
+	// earlier-than-reindex-root reindex
+	sideBlock := PrepareAndProcessBlockForTest(t, dag, []*daghash.Hash{dag.Params.GenesisHash}, nil)
+
+	// Add a block whose parents are the chain tip and the side block.
+	// We expect this not to fail
+	PrepareAndProcessBlockForTest(t, dag, []*daghash.Hash{chainTipHash, sideBlock.BlockHash()}, nil)
+}

network/rpc/handle_get_block_template.go

@@ -13,7 +13,6 @@ import (
 
 	"github.com/kaspanet/kaspad/domain/blockdag"
 	"github.com/kaspanet/kaspad/domain/mining"
-	"github.com/kaspanet/kaspad/domain/txscript"
 	"github.com/kaspanet/kaspad/network/domainmessage"
 	"github.com/kaspanet/kaspad/network/rpc/model"
 	"github.com/kaspanet/kaspad/util"
@@ -72,18 +71,6 @@ func newGbtWorkState() *gbtWorkState {
 	}
 }
 
-// builderScript is a convenience function which is used for hard-coded scripts
-// built with the script builder. Any errors are converted to a panic since it
-// is only, and must only, be used with hard-coded, and therefore, known good,
-// scripts.
-func builderScript(builder *txscript.ScriptBuilder) []byte {
-	script, err := builder.Script()
-	if err != nil {
-		panic(err)
-	}
-	return script
-}
-
 // handleGetBlockTemplate implements the getBlockTemplate command.
 func handleGetBlockTemplate(s *Server, cmd interface{}, closeChan <-chan struct{}) (interface{}, error) {
 	c := cmd.(*model.GetBlockTemplateCmd)