[no-release-notes] track join memos for external use (#2917)

Author: max-hoffman

sql/analyzer/indexed_joins.go

@@ -216,6 +216,9 @@ func replanJoin(ctx *sql.Context, n *plan.JoinNode, a *Analyzer, scope *plan.Sco
 	if a.Verbose && a.Debug {
 		a.Log(m.String())
 	}
+	if scope != nil {
+		scope.JoinTrees = append(scope.JoinTrees, m.String())
+	}
 
 	return m.BestRootPlan(ctx)
 }

sql/plan/scope.go

@@ -43,6 +43,7 @@ type Scope struct {
 	inJoin        bool
 	inLateralJoin bool
 	joinSiblings  []sql.Node
+	JoinTrees     []string
 }
 
 func (s *Scope) SetJoin(b bool) {