planner: fix potential panic when generating hints in statement summary (pingcap#46312) (pingcap#46393)

close pingcap#46311

Author: ti-chi-bot

planner/core/logical_plan_builder.go

@@ -410,8 +410,7 @@ func (b *PlanBuilder) buildResultSetNode(ctx context.Context, node ast.ResultSet
 			}
 		}
 		// `TableName` is not a select block, so we do not need to handle it.
-		if !isTableName && b.ctx.GetSessionVars().PlannerSelectBlockAsName.Load() != nil {
-			plannerSelectBlockAsName := *(b.ctx.GetSessionVars().PlannerSelectBlockAsName.Load())
+		if plannerSelectBlockAsName := *(b.ctx.GetSessionVars().PlannerSelectBlockAsName.Load()); len(plannerSelectBlockAsName) > 0 && !isTableName {
 			plannerSelectBlockAsName[p.SelectBlockOffset()] = ast.HintTable{DBName: p.OutputNames()[0].DBName, TableName: p.OutputNames()[0].TblName}
 		}
 		// Duplicate column name in one table is not allowed.

planner/core/planbuilder.go

@@ -756,7 +756,7 @@ func NewPlanBuilder(opts ...PlanBuilderOpt) *PlanBuilder {
 func (b *PlanBuilder) Init(sctx sessionctx.Context, is infoschema.InfoSchema, processor *hint.BlockHintProcessor) (*PlanBuilder, []ast.HintTable) {
 	savedBlockNames := sctx.GetSessionVars().PlannerSelectBlockAsName.Load()
 	if processor == nil {
-		sctx.GetSessionVars().PlannerSelectBlockAsName.Store(nil)
+		sctx.GetSessionVars().PlannerSelectBlockAsName.Store(&[]ast.HintTable{})
 	} else {
 		newPlannerSelectBlockAsName := make([]ast.HintTable, processor.MaxSelectStmtOffset()+1)
 		sctx.GetSessionVars().PlannerSelectBlockAsName.Store(&newPlannerSelectBlockAsName)