trie/bintrie: fix debug_executionWitness for binary tree (#33739)

The `Witness` method was not implemented for the binary tree, which
caused `debug_excutionWitness` to panic. This PR fixes that.

Note that the `TransitionTrie` version isn't implemented, and that's on
purpose: more thought must be given to what should go in the global
witness.

Author: gballet

trie/bintrie/trie.go

@@ -424,5 +424,5 @@ func (t *BinaryTrie) PrefetchStorage(addr common.Address, keys [][]byte) error {
 
 // Witness returns a set containing all trie nodes that have been accessed.
 func (t *BinaryTrie) Witness() map[string][]byte {
-	panic("not implemented")
+	return t.tracer.Values()
 }

trie/bintrie/trie_test.go

@@ -22,6 +22,7 @@ import (
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/trie"
 )
 
 var (
@@ -195,3 +196,29 @@ func TestMerkleizeMultipleEntries(t *testing.T) {
 		t.Fatalf("invalid root, expected=%x, got = %x", expected, got)
 	}
 }
+
+func TestBinaryTrieWitness(t *testing.T) {
+	tracer := trie.NewPrevalueTracer()
+
+	tr := &BinaryTrie{
+		root:   NewBinaryNode(),
+		tracer: tracer,
+	}
+	if w := tr.Witness(); len(w) != 0 {
+		t.Fatal("expected empty witness for fresh trie")
+	}
+
+	tracer.Put([]byte("path1"), []byte("blob1"))
+	tracer.Put([]byte("path2"), []byte("blob2"))
+
+	witness := tr.Witness()
+	if len(witness) != 2 {
+		t.Fatalf("expected 2 witness entries, got %d", len(witness))
+	}
+	if !bytes.Equal(witness[string([]byte("path1"))], []byte("blob1")) {
+		t.Fatal("unexpected witness value for path1")
+	}
+	if !bytes.Equal(witness[string([]byte("path2"))], []byte("blob2")) {
+		t.Fatal("unexpected witness value for path2")
+	}
+}