syntax_data: {"ast_node_type":"other","tokens":[{"end":77,"kind":"keyword","start":0,"text":"dcx.emit_err(MutationOfLayoutConstrainedFieldRequiresUnsafe"}]}
source_snippet:                 dcx.emit_err(MutationOfLayoutConstrainedFieldRequiresUnsafe {
context_before:             MutationOfLayoutConstrainedField => {
context_after:                     span,