syntax_data: {"ast_node_type":"other","tokens":[{"end":26,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // during testing.
context_before:         // RUSTC_FORCE_RUSTC_VERSION is used to inject rustc version information
context_after:         if let Some(val) = std::env::var_os("RUSTC_FORCE_RUSTC_VERSION") {