DependsOn detection does not flow through existing resource definitions

[anthony-c-martin]

Repro:

var aksServicePrincipalObjectId = 'aksServicePrincipalObjectId'
var aksDefaultPoolSubnetName = 'asdf'
resource virtualNetwork 'Microsoft.Network/virtualNetworks@2020-08-01' = {
  name: 'asdfasdf'
}

resource userAssignedIdentities 'Microsoft.ManagedIdentity/userAssignedIdentities@2018-11-30' = {
  name: 'asdfsdf'
  location: 'West US'
}

resource aksDefaultPoolSubnet 'Microsoft.Network/virtualNetworks/subnets@2020-08-01' existing = {
  parent: virtualNetwork
  name: aksDefaultPoolSubnetName
}

resource roleAssignment 'Microsoft.Authorization/roleAssignments@2020-04-01-preview' = {
  name: guid(aksDefaultPoolSubnet.id, 'Network Contributor')
  scope: aksDefaultPoolSubnet
  properties: {
    principalId: aksServicePrincipalObjectId
    roleDefinitionId: '4d97b98b-1d4f-4787-a291-c67834d212e7'
  }
  dependsOn: [
    userAssignedIdentities
  ]
}

• roleAssignment contains a reference to aksDefaultPoolSubnet. Although this resource has been marked as existing, it in turn has a dependency on virtualNetwork. This dependency is being ignored when the template is generated, meaning that the roleAssignment resource does not contain a dependsOn statement.

Generated resource statement from the template output:

{
  "type": "Microsoft.Authorization/roleAssignments",
  "apiVersion": "2020-04-01-preview",
  "scope": "[format('Microsoft.Network/virtualNetworks/{0}/subnets/{1}', 'asdfasdf', variables('aksDefaultPoolSubnetName'))]",
  "name": "[guid(resourceId('Microsoft.Network/virtualNetworks/subnets', 'asdfasdf', variables('aksDefaultPoolSubnetName')), 'Network Contributor')]",
  "properties": {
    "principalId": "[variables('aksServicePrincipalObjectId')]",
    "roleDefinitionId": "4d97b98b-1d4f-4787-a291-c67834d212e7"
  },
  "dependsOn": [
    "[resourceId('Microsoft.ManagedIdentity/userAssignedIdentities', 'asdfsdf')]"
  ]
}

Bicep version: v0.3.135-g23fb6c0bc0