syntax_data: {"ast_node_type":"other","tokens":[{"end":76,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // a MIR body for the def kind, and some MIR passes (like promotion)
context_before:         // Note that we also support `SyntheticCoroutineBody` since we create
context_after:         // may require doing analysis using its typing env.