syntax_data: {"ast_node_type":"variable","tokens":[{"end":91,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// If `sp` points to `"let mut x"`, then a span pointing at `"let "` will be returned.
context_before:     ///
context_after:     pub fn span_until_non_whitespace(&self, sp: Span) -> Span {