There's a bug here: https://github.com/openapi-contrib/openapi3-generator/blob/0.13.0/lib/generator.js#L144-L147

    Promise.all(
      _.map(files, (operation, operation_name) => generateOperationFile(config, operation, operation_name))
    ).then(resolve).catch(reject);
    resolve();

The outer promise here is being resolved before the Promise.all has a chance to finish, and if there's a rejection, it is ignored. I was running this tool from a docker container and only 75% of the expected files were being generated. I tracked it down to errors on that line not being handled properly..... With the resolve removed, I get the error back properly:

Error: EMFILE: too many open files, open '/api-docs/templates/my-template/$$path$$.js'

Why I'm getting that in docker and not locally is still a mystery to me... but this routine seems inefficient. As as test I logged out the name of the file that was being read here: https://github.com/openapi-contrib/openapi3-generator/blob/0.13.0/lib/generator.js#L96-L97

const generateOperationFile = (config, operation, operation_name) => new Promise((resolve, reject) => {
  console.log(path.join(config.root, config.file_name))
  fs.readFile(path.join(config.root, config.file_name), 'utf8', (err, data) => {

And I get the same file logged out a couple thousands times.... Because it's a Promise.all I imagine node will try to load all of them at the same time, and I'm guessing in my particular case, there's not enough file descriptors available and it blows up.... Further, I logged out the file path that it writes in this routine, and it's writing out the same file multiple times.... Seems like the data structure being passed generated / passed in there could do with a Sets instead to avoid duplicates?