Merge branch 'dev' into sorting-remove-IsSortedAndUnique

vms/proposervm/tree/tree.go

@@ -12,6 +12,23 @@ import (
 	"github.com/ava-labs/avalanchego/snow/consensus/snowman"
 )
 
+// Tree handles the propagation of block acceptance and rejection to inner
+// blocks.
+//
+// The Tree is needed because:
+// 1. The consensus engine guarantees that for each verified block, either
+// Accept() or Reject() are eventually called, and they are called only once.
+// The proposervm must maintain these invariants for the wrapped VM.
+// 2. A given inner block may be wrapped into multiple different proposervm
+// blocks (e.g. same inner block generated by two validators).
+//
+// The Tree prevents Accept() and Reject() from being called multiple times on
+// the same inner block by:
+// 1. tracking inner blocks in a tree-like structure, to be able to easily spot
+// siblings
+// 2. rejecting an inner block only when one of the siblings is accepted.
+// Rejection of a proposervm block does not imply its inner block rejection
+// (it may be held by a different proposervm block).
 type Tree interface {
 	// Add places the block in the tree
 	Add(snowman.Block)

vms/proposervm/tree/tree_test.go

@@ -45,6 +45,9 @@ func TestAcceptSingleBlock(t *testing.T) {
 
 	require.NoError(tr.Accept(context.Background(), block))
 	require.Equal(choices.Accepted, block.Status())
+
+	_, contains = tr.Get(block)
+	require.False(contains)
 }
 
 func TestAcceptBlockConflict(t *testing.T) {
@@ -68,18 +71,26 @@ func TestAcceptBlockConflict(t *testing.T) {
 
 	tr := New()
 
+	// add conflicting blocks
 	tr.Add(blockToAccept)
-	tr.Add(blockToReject)
-
 	_, contains := tr.Get(blockToAccept)
 	require.True(contains)
 
+	tr.Add(blockToReject)
 	_, contains = tr.Get(blockToReject)
 	require.True(contains)
 
+	// accept one of them
 	require.NoError(tr.Accept(context.Background(), blockToAccept))
+
+	// check their statuses and that they are removed from the tree
 	require.Equal(choices.Accepted, blockToAccept.Status())
+	_, contains = tr.Get(blockToAccept)
+	require.False(contains)
+
 	require.Equal(choices.Rejected, blockToReject.Status())
+	_, contains = tr.Get(blockToReject)
+	require.False(contains)
 }
 
 func TestAcceptChainConflict(t *testing.T) {
@@ -111,21 +122,32 @@ func TestAcceptChainConflict(t *testing.T) {
 
 	tr := New()
 
+	// add conflicting blocks.
 	tr.Add(blockToAccept)
-	tr.Add(blockToReject)
-	tr.Add(blockToRejectChild)
-
 	_, contains := tr.Get(blockToAccept)
 	require.True(contains)
 
+	tr.Add(blockToReject)
 	_, contains = tr.Get(blockToReject)
 	require.True(contains)
 
+	tr.Add(blockToRejectChild)
 	_, contains = tr.Get(blockToRejectChild)
 	require.True(contains)
 
+	// accept one of them
 	require.NoError(tr.Accept(context.Background(), blockToAccept))
+
+	// check their statuses and whether they are removed from tree
 	require.Equal(choices.Accepted, blockToAccept.Status())
+	_, contains = tr.Get(blockToAccept)
+	require.False(contains)
+
 	require.Equal(choices.Rejected, blockToReject.Status())
+	_, contains = tr.Get(blockToReject)
+	require.False(contains)
+
 	require.Equal(choices.Rejected, blockToRejectChild.Status())
+	_, contains = tr.Get(blockToRejectChild)
+	require.False(contains)
 }