Incorectly typed error interceptor of fetch-client

[zumm]

Description

Type states response argument is always defined, but in fact it isn't:

      // client.gen.ts
      for (const fn of interceptors.error.fns) {
        if (fn) {
          finalError = (await fn(error, undefined as any, request, opts)) as unknown;
        }
      }

Reproducible example or configuration

No response

OpenAPI specification (optional)

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System information (optional)

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[thomasboyt]

This would be great to fix and correctly document, because it's actually a handy feature: response isn't present when the error is from a request failure, in which case error is one of the handful of Error subclasses that fetch can throw.

However, if response is present, you can then assume the error is the response body from the response.

This is also a bug in the result type from this client, I believe, where response is similarly not present if the request failed.

[mrlubos]

@thomasboyt @zumm does this preview resolve the issues you're experiencing? #3750 (comment)