Params CompareExpression `.thenElse` does not support `RegExp` as value, therefore disallows the use of RegExp values for CORS options

[sceee]

Related issues

#1787
#1406
#1903

Actually I am trying to do this #1903 (comment) - however it turned out that #1903 unfortunately does not support setting regex CORS options directly from the .env files.

[REQUIRED] Version info

node: v24.18.0

firebase-functions: v7.3.0

firebase-tools: v15.23.0

firebase-admin: v13.10.0

[REQUIRED] Test case

const environmentVariable_Some = defineBoolean('SOME')
const environmentVariable_Staging = defineBoolean('IS_STAGING')

const corsOptionsLocal = [/^http:\/\/localhost:808[0|1]$/]
const corsOptionsStaging = [/^https:\/\/(staging|otherstaging)\.example\.com$/]
const corsOptionsProduction = [/^https:\/\/(some|other)\.example\.com$/]

const corsOptions = environmentVariable_Some
  .equals(true)
  .thenElse(corsOptionsLocal, environmentVariable_Staging.equals(true).thenElse(corsOptionsStaging, corsOptionsProduction))

export const myFn = onCall(
  {
    cors: corsOptions
  },
  async () => {
    ...
  }

[REQUIRED] Steps to reproduce

1. Run npx tsc

[REQUIRED] Expected behavior

I can set dynamic (RegExp-based) allowed CORS hosts dynamically depending on the environment.
The onCall cors option allows the following types:

(property) HttpsOptions.cors?: string | boolean | RegExp | Expression<string> | Expression<string[]> | (string | RegExp)[] | undefined

...so it should also be possible to create a Expression<RegExp> using the .equals(xx).thenElse(...) CompareExpression helper.

[REQUIRED] Actual behavior

Argument of type 'RegExp[]' is not assignable to parameter of type 'string | number | boolean | string[] | Expression<string | number | boolean | string[]>'.
  Type 'RegExp[]' is not assignable to type 'string[]'.
    Type 'RegExp' is not assignable to type 'string'.

Were you able to successfully deploy your functions?

No

[IzaakGough]

Hi @sceee, thanks for raising this! We will review this as soon as possible.

[IzaakGough]

I reproduced this with the snippet above. Afaik RegExp has never been supported as an Expression/thenElse value here, so this is more of a feature request than a bug/regression.
Happy to look into this though! - it should be a fairly small change