syntax_data: {"ast_node_type":"other","tokens":[{"end":70,"kind":"keyword","start":0,"text":"mir_opt_level:"}]}
source_snippet:     mir_opt_level: Option<usize> = (None, parse_opt_number, [TRACKED],
context_before:     #[rustc_lint_opt_deny_field_access("use `Session::mir_opt_level` instead of this field")]
context_after:         "MIR optimization level (0-4; default: 1 in non optimized builds and 2 in optimized builds)"),