syntax_data: {"ast_node_type":"other","tokens":[{"end":93,"kind":"keyword","start":0,"text":"MutationOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed"}]}
source_snippet:                     MutationOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
context_before:                 dcx.emit_err(
context_after:                         span,