Tsoa: undefined is not supported in model properties

[cedricboidin]

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Expected Behavior

I would like to use models that can have the undefined type:

import {Controller, Get, Route} from 'tsoa';

interface User {
  name: string | undefined;
}

@Route('user')
export class UserController extends Controller {
  @Get()
  public async getUser(): Promise<User> {
    return {name: undefined};
  }
}

Current Behavior

I get an error when trying to generate the spec:

yarn tsoa spec
yarn run v1.22.4
$ /Users/cedric/dev/kraaft-firebase/app-engine/node_modules/.bin/tsoa spec
There was a problem resolving type of 'User'.
Generate swagger error.
 Error: Unknown type: UndefinedKeyword
At: src/api/userController.ts:10:10.
This was caused by 'string | undefined'
    at new GenerateMetadataError (/Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/exceptions.js:22:28)
    at TypeResolver.resolve (/Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/typeResolver.js:308:19)
    at /Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/typeResolver.js:113:95
    at Array.map (<anonymous>)
    at TypeResolver.resolve (/Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/typeResolver.js:112:45)
    at TypeResolver.propertyFromSignature (/Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/typeResolver.js:761:143)
    at /Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/typeResolver.js:727:161
    at Array.map (<anonymous>)
    at TypeResolver.getModelProperties (/Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/typeResolver.js:727:124)
    at TypeResolver.getModelReference (/Users/cedric/dev/kraaft-firebase/app-engine/node_modules/tsoa/node_modules/@tsoa/cli/dist/metadataGeneration/typeResolver.js:552:31)

Possible Solution

The attribute could be treated as if it was optional.

Steps to Reproduce

1. create a controller like the one above
2. generate the spec: yarn tsoa spec

Context (Environment)

Version of the library: 3.4.0
Version of NodeJS: v10.21.0

• Confirm you were using yarn not npm: [x]

Detailed Description

Breaking change?

No

[silmood]

Same problem here ✋

Version of the library: 3.4.0
Version of NodeJS: v15.5.0

Checking TypeResolver.resolve method, there isn't a validation for ts.SyntaxKind.UndefinedKeyword so this throws the exception on line 288. I made a quick experiment adding a simple || in ts.SyntaxKind.NullKeyword case:

if (this.typeNode.kind === ts.SyntaxKind.NullKeyword 
    || this.typeNode.kind === ts.SyntaxKind.UndefinedKeyword) {

    var enumType = {
        dataType: 'enum',
        enums: [null],
    };

   return enumType;
 }

With this change ts.SyntaxKind.UndefinedKeyword is treated as null type and the error won't happen. However, this doesn't treat the field as optional and i don't think the solution would be as simple as that 😅. I hope this info can be helpful

[WoH]

OpenAPI 2/3 does not support an undefined type, only optional properties. We still want to distinguish between null and undefined, so modeling this in TS using

interface User {
  name?: string;
}

is the best way to represent this currently.
The proper way to solve this would be to add a Tsoa.UndefinedType, which marks the property as optional if it is a property type and handles the case where it is not, for example a route handler: public getStuff(): undefined.

[github-actions[bot]]

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[ljwagerfield]

@WoH would you be able to elaborate on what you mentioned?

The proper way to solve this would be to add a Tsoa.UndefinedType

Is this something we can do in our code, or is this a suggested change to TSOA that one could raise as a PR?

I'd really love undefined to be treated as an optional property: the convention in our codebase is to avoid ? to prevent refactoring errors where a new (optional) property is added to a type, but the developer forgets to set it in all places. By using | undefined the developer is forced to think about whether the property needs setting to undefined or some other value.

[WoH]

Is this something we can do in our code, or is this a suggested change to TSOA that one could raise as a PR?

The latter