syntax_data: {"ast_node_type":"function","tokens":[{"end":63,"kind":"keyword","start":0,"text":"pub"}]}
source_snippet:     pub fn span_until_non_whitespace(&self, sp: Span) -> Span {
context_before:     /// If `sp` points to `"let mut x"`, then a span pointing at `"let "` will be returned.
context_after:         let mut whitespace_found = false;