How to add a transformer?

[nickclassdojo]

Based on reading the docs, I assumed that I would be able to add a transformer and pass this to the generation via some CLI option to change the output of the generated code (https://heyapi.vercel.app/openapi-ts/transformers.html). The docs don't explain how to add one, just how to add an existing internal one for dates. Is this something that's possible? My use case would be something along the lines of wrapping the return of a service function in some Result type.

[mrlubos]

@nickclassdojo can you provide your config and an example code you're looking to generate/use?

[nickclassdojo]

The config looks like this:

export default defineConfig({
  client: "@hey-api/client-axios",
  input: <REDACTED_URL_TO_OPENAPI>,
  output: "src/openapi",
  useOptions: true,
  exportCore: true,
  debug: true,
});

Which generates the functions as expected. As an example, I would like to transform a function that is generated in the service from this:

export const deleteApiUserById = <ThrowOnError extends boolean = false>(options: Options<DeleteApiUserByIdData, ThrowOnError>) => { return (options?.client ?? client).delete<DeleteApiUserByIdResponse, DeleteApiUserByIdError, ThrowOnError>({
    ...options,
    url: '/api/teacher/{id}'
}); };

to something that is wrapped using neverthrow:

import { err, ok } from "neverthrow";
//...rest of service
export const deleteApiUserById = <ThrowOnError extends boolean = false>(
  options: Options<DeleteApiTeacherByIdData, ThrowOnError>,
) => {
  try {
    return ok(
      (options?.client ?? client).delete<DeleteApiUserByIdResponse, DeleteApiUserByIdError, ThrowOnError>({
        ...options,
        url: "/api/teacher/{id}",
      }),
    );
  } catch (e) {
    err<never, DeleteApiTeacherByIdError>(e);
  }
};

Looking in the config, I don't see any options to add a transformer at all. Does something exist

[mrlubos]

Not like this. Do you have a proposal how this could be achieved through configuration? Also, what is the intent behind using neverthrow? Does the function still throw even if you use throwOnError: false?

[nickclassdojo]

Don't have a full proposal, but I would imagine it would be adding a single configuration options for a function that maps the output

Maybe something like:

export default defineConfig({
  client: "@hey-api/client-axios",
  input: <REDACTED_URL_TO_OPENAPI>,
  output: "src/openapi",
  useOptions: true,
  exportCore: true,
  debug: true,
  transform: {
    /**
     * type OutputTransFormer<TOutput, TData, TError, TThrow extends boolean = false> = (
        data: RequestResult<TData, TError, TThrow>,
        ) => TOutput;

     */
    mapOutput: (result: RequestResult ) => {
        result.data !== null ? ok(data) : err(result.data.err)
    }
 }

Then in the generation, you could just wrap the output in config.transform?.mapOutput(output) potentially without needing to dig into the code generation really

[mrclrchtr]

@mrlubos I have a similar question that goes in a slightly different direction, but also fits the title quite well:

I would like to define a transformer for a custom format and this should be applied when a string has this format:

e.g.

export class LocalTime {
  hour: number;
  minute: number;

  constructor(hour: number, minute: number) {
    this.hour = hour;
    this.minute = minute;
  }
}

      time:
          type: string
          format: time

then I would like to be able to parse this string into LocalTime.

Maybe, I could create my own plugin for this?

If this doesn't fit here, I'll open a separate topic or issue.

[mrlubos]

You could certainly create your own plugins and hack around it, but that's probably not the best solution, even if it's currently the only available one.

Please open an issue for this feature, I'll have to think about it. We'll need to add an option to define custom transformers in the transformer plugin (difficulty: easy) and the types plugin will need to support the custom transform too (difficulty: unknown)

[j-ibarra]

@mrlubos can you check this #2281

[mrlubos]

Hey, merged it! Thanks for contributing to Hey API!