code: function checkSpacingForFunction(node) {
              const firstToken = node && sourceCode.getFirstToken(node);
  
              if (firstToken &&
                  ((firstToken.type === "Keyword" && firstToken.value === "function") ||
                  firstToken.value === "async")
              ) {
                  checkSpacingBefore(firstToken);
              }
          }
docs: Reports `async` or `function` keywords of a given node if usage of
  spacing around those keywords is invalid.
  
  @param {ASTNode} node - A node to report.
  @returns {void}