@allowed parameter values forwarding

[ikkentim]

Is your feature request related to a problem? Please describe.
When creating a parameter, we can use @allowed(['a', 'b']) to specify allowed values.

Ideally, when a parameter is used in a resource or module where its parameter is also decorated with @allowed I would like to avoid repeating the list of allowed values, especially when the list is extensive.

@allowed(['Standard_RAGRS', 'Standard_LRS', 'Standard_GRS', 'Standard_RAGRS', 'Standard_ZRS', 'Premium_LRS']) // I'm probably missing a few
param sku string

resource storageAccount 'Microsoft.Storage/storageAccounts@2023-01-01' = {
  name: 'name'
  sku: {
    name: sku
  }
  // ...
}

Describe the solution you'd like
An implicit or explicit way to copy the allowed values of a certain property.

Possible syntax:

@allowed(allowedOf(storageAccount.sku.name))
param sku string

resource storageAccount 'Microsoft.Storage/storageAccounts@2023-01-01' = {
  name: 'name'
  sku: {
    name: sku
  }
  // ...
}

This would allow the @allowed decorator to dynamically inherit the allowed values from the resource or module property, reducing redundancy and improving maintainability.

[jeskew]

@allowed() will only support literal values, but you can use type syntax to make this work (and a type statement if you want to reuse it in multiple places):

param sku resourceInput<'Microsoft.Storage/storageAccounts@2023-01-01'>.sku.name

resource storageAccount 'Microsoft.Storage/storageAccounts@2023-01-01' = {
  name: 'name'
  sku: {
    name: sku
  }
  // ...
}