syntax_data: {"ast_node_type":"variable","tokens":[{"end":60,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let join_block = this.cfg.start_new_block();
context_before:                 // blocks, so make both of them meet up in a new block.
context_after:                 this.cfg.goto(then_blk, source_info, join_block);