code: function groupByLineNumber(acc, node) {
              for (let i = node.loc.start.line; i <= node.loc.end.line; ++i) {
                  ensureArrayAndPush(acc, i, node);
              }
              return acc;
          }
docs: A reducer to group an AST node by line number, both start and end.
  
  @param {Object} acc the accumulator
  @param {ASTNode} node the AST node in question
  @returns {Object} the modified accumulator
  @private