Exception "Can't support 'refAlias' type." is thrown when using Exclude<Type, ExcludedUnion> with Typescript >= 4.2.2

[ggrossetie]

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Expected Behavior

The following definition:

export type Severity = 'critical' | 'high' | 'medium' | 'low';

export type SecuritySeverity = Exclude<Severity, 'low'>;

should produce the following Tsoa.ReferenceType with Typescript >= 4.2.2:

{
  "dataType": "refAlias",
  "refName": "SecuritySeverity",
  "type": {
    "dataType": "refAlias",
    "description": "Exclude from T those types that are assignable to U",
    "refName": "Exclude_Severity.low_",
    "type": {
      "dataType": "union",
      "types": [
        {
          "dataType": "enum",
          "enums": [
            "critical"
          ]
        },
        {
          "dataType": "enum",
          "enums": [
            "high"
          ]
        },
        {
          "dataType": "enum",
          "enums": [
            "medium"
          ]
        }
      ]
    },
    "validators": {}
  },
  "validators": {}
}

Current Behavior

With Typescript 4.2.2, I get the following Tsoa.ReferenceType:

{
  "dataType": "refAlias",
  "description": "Exclude from T those types that are assignable to U",
  "refName": "Exclude_Severity.low_",
  "type": {
    "dataType": "refObject",
    "refName": "SecuritySeverity"
  },
  "validators": {}
}

Since I'm using this type in a Query parameter:

@Route('/test')
export class TestController {
  @Get('/issues')
  public async getSecurityIssues(@Query('type') securitySeverity: SecuritySeverity): Promise<void> {
    return Promise.resolve();
  }
}

I get the following exception:

Generate swagger error.
 Error: @Query('type') Can't support 'refAlias' type. 
 in 'TestController.getSecurityIssues'

The reason is that refObject is not a supported data type.

Possible Solution

I think the root cause is that the latest versions of Typescript now return an aliasSymbol:

https://github.com/lukeautry/tsoa/blob/ea976ee5cac9edba0a2fbc9eb8d2729c4237f491/packages/cli/src/metadataGeneration/typeResolver.ts#L206

With Typescript 4.1.2, the aliasSymbol is undefined and as a result we don't step into this if:

https://github.com/lukeautry/tsoa/blob/ea976ee5cac9edba0a2fbc9eb8d2729c4237f491/packages/cli/src/metadataGeneration/typeResolver.ts#L208-L226

Having said that, I'm not familiar enough with Typescript internals nor with this code base to suggest a fix, sorry 😞

Steps to Reproduce

Here's a sample project that reproduces this issue: https://github.com/Mogztter/bug-tsoa-ts43-ref-alias If you follow the instructions in the README you should be able to reproduce this issue.

You should also be able to confirm that this issue cannot be reproduced with Typescript 4.1.

Context (Environment)

Version of the library: 3.14.1 Version of NodeJS: 14.15.4

I'm not using yarn but I don't think it matters in this case 😃

[github-actions[bot]]

Hello there Mogztter 👋

Thank you for opening your very first issue in this project.

We will try to get back to you as soon as we can.👀

[Lleios]

Same issue with tsoa 4.0.0-rc.1 (Typescript 4.1 and more recent versions)

[Toltar]

I have the same issue here

[WoH]

I'm curious how this behaves now, TS 4.8 treats this differently apparently

[Craigfis]

Hitting this also with TS4.8.

[KennyLindahl]

Getting the same symptom, can't do this for example:

const hello = {
  test: 'whatever'
}

type test = {
  key: typeof hello.test
}

---

EDIT:

However this seems to work:

const hello = {
  test: 'whatever'
}

type test = {
  key: typeof hello["test"]
}