[BUG] typescript-fetch openapi generator fails out-of-the-box

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What’s the actual output vs expected output?
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Description

I added this to my package.json: "@openapitools/openapi-generator-cli": "^2.3.10", and when I run this command: "generate:api": "(rm -rf src/api/gen || rmdir src/api/gen /s /q) && openapi-generator-cli generate -g typescript-fetch --additional-properties=supportsES6=true,typescriptThreePlus=true -i ../openapi/schema.yaml -o ./src/api/gen" I get the following error:

Failed to compile.

/##/runtime.ts
TypeScript error in /###/runtime.ts(152,3):
Type '((input: RequestInfo, init?: RequestInit | undefined) => Promise<Response>) | undefined' is not assignable to type '(input: RequestInfo, init?: RequestInit | undefined) => Promise<Response>'.
  Type 'undefined' is not assignable to type '(input: RequestInfo, init?: RequestInit | undefined) => Promise<Response>'.  TS2322

    150 | 
    151 |     get fetchApi(): FetchAPI {
  > 152 |               return this.configuration.fetchApi;
        |               ^
    153 |     }
    154 | 
    155 |     get middleware(): Middleware[] {

When I add “as FetchAPI” to line 152, everything works correctly. I have no idea where the problem is. Why does it generate code with this error?

openapi-generator version

2.3.10

OpenAPI declaration file content or url

N/A

Generation Details

N/A

Steps to reproduce

N/A

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/10164 https://github.com/OpenAPITools/openapi-generator/pull/10216 - supposedly it was fixed but it’s still an issue when using version 2.3.10

Suggest a fix

Not sure about the fix. I quickly worked around it by casting it “as FetchAPI” which is not a good solution:

    150 | 
    151 |     get fetchApi(): FetchAPI {
   152 |               return this.configuration.fetchApi as FetchAPI;
        |               
    153 |     }

[xsorifc28]

I am seeing the same issue with generator-cli v5.2.1

On v5.1.1 the generated code is (runtime.ts):

export class Configuration {
     ...
    get fetchApi(): FetchAPI {
        return this.configuration.fetchApi || window.fetch.bind(window);
    }
    ...
}

On v5.2.1 the generated code is (runtime.ts):

export class Configuration {
     ...
    get fetchApi(): FetchAPI {
        return this.configuration.fetchApi;
    }
    ...
}

Possibly related to changes from #10050?

[RonnyLark]

We have been using generated api for a few months and now are trying to move to TS strict mode. But it seems that the generated runtime.ts files have inherent strict-failing lines; for instance:

export class Configuration {
    ...

    protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
        const { url, init } = await this.createFetchParams(context, initOverrides);
        const response = await this.fetchApi(url, init);
        if (response.status >= 200 && response.status < 300) {
            return response;
        }
        throw new ResponseError(response, 'Response returned an error code');
    }

    ...
}

'response' is possibly 'undefined'.ts(18048)
Argument of type 'undefined' is not assignable to parameter of type 'Response'.ts(2345)

There are a total of 12 errors in each runtime.ts file failing the strictNullChecks strict clause. Run with version 6.2.0 and typescript-fetch.

I hope this thread is still being looked at.