Bicep build generates Object instead of Array for resources when using user-defined functions

[galiacheng]

Bicep version

0.30.23

Describe the bug

I am using Bicep to develop and maintain the source code for the Azure WebLogic on AKS marketplace offer. The marketplace requires converting Bicep scripts to ARM templates, following this ARM structure, where the resources section must be an array.

However, when building with bicep build or az bicep build, I receive an object instead of an array for the resources section, leading to a Partner Center error: Package acceptance validation error: JsonSchemaValidationError The json file 'mainTemplate.json' is invalid for the provided schema. Line Number: '0', Error: 'Invalid type. Expected Array but got Object.'

I traced this issue to user-defined functions in the Bicep script. Without them, the resources section builds correctly as an array. You can view the built ARM template and error in this GitHub action.

To Reproduce

1. Bicep script without user defined function. Run az bicep build -f main.bicep to build the following content.

   param location string
   
   resource stg 'Microsoft.Storage/storageAccounts@2021-04-01' = {
   name: 'hellotest20241008001'
   location: location
   sku: {
     name: 'Standard_LRS'
   }
   kind: 'StorageV2'
   properties: {
     supportsHttpsTrafficOnly: true
   }
   }
   
   output storageEndpoint object = stg.properties.primaryEndpoints
   

   Got ARM template as following, type of resources is Array.

   {
     "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
     "contentVersion": "1.0.0.0",
     "metadata": {
       "_generator": {
         "name": "bicep",
         "version": "0.30.23.60470",
         "templateHash": "5107046056470376467"
       }
     },
     "parameters": {
       "location": {
         "type": "string"
       }
     },
     "resources": [
       {
         "type": "Microsoft.Storage/storageAccounts",
         "apiVersion": "2021-04-01",
         "name": "hellotest20241008001",
         "location": "[parameters('location')]",
         "sku": {
           "name": "Standard_LRS"
         },
         "kind": "StorageV2",
         "properties": {
           "supportsHttpsTrafficOnly": true
         }
       }
     ],
     "outputs": {
       "storageEndpoint": {
         "type": "object",
         "value": "[reference(resourceId('Microsoft.Storage/storageAccounts', 'hellotest20241008001'), '2021-04-01').primaryEndpoints]"
       }
     }
   }

2. Bicep script with user defined function. Run az bicep build -f main.bicep to build the following content.

   param location string
   
   var uniqueStorageName = abc(resourceGroup().id)
   
   func abc(resourceId string) string => string(resourceId)
   
   resource stg 'Microsoft.Storage/storageAccounts@2021-04-01' = {
     name: uniqueStorageName
     location: location
     sku: {
       name: 'Standard_LRS'
     }
     kind: 'StorageV2'
     properties: {
       supportsHttpsTrafficOnly: true
     }
   }
   
   output storageEndpoint object = stg.properties.primaryEndpoints

   Got ARM template as following, type of resources is Object.

   {
     "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
     "languageVersion": "2.0",
     "contentVersion": "1.0.0.0",
     "metadata": {
       "_generator": {
         "name": "bicep",
         "version": "0.30.23.60470",
         "templateHash": "8515690428638717928"
       }
     },
     "functions": [
       {
         "namespace": "__bicep",
         "members": {
           "abc": {
             "parameters": [
               {
                 "type": "string",
                 "name": "resourceId"
               }
             ],
             "output": {
               "type": "string",
               "value": "[string(parameters('resourceId'))]"
             }
           }
         }
       }
     ],
     "parameters": {
       "location": {
         "type": "string"
       }
     },
     "variables": {
       "uniqueStorageName": "[__bicep.abc(resourceGroup().id)]"
     },
     "resources": {
       "stg": {
         "type": "Microsoft.Storage/storageAccounts",
         "apiVersion": "2021-04-01",
         "name": "[variables('uniqueStorageName')]",
         "location": "[parameters('location')]",
         "sku": {
           "name": "Standard_LRS"
         },
         "kind": "StorageV2",
         "properties": {
           "supportsHttpsTrafficOnly": true
         }
       }
     },
     "outputs": {
       "storageEndpoint": {
         "type": "object",
         "value": "[reference('stg').primaryEndpoints]"
       }
     }
   }

Additional context

The expected outcome is that, in both cases, the resources section should be an array, consistent with the ARM template definition.

[anthony-c-martin]

The reason for this is that usage of user-defined functions depends on language version 2.0.

The change from array -> object is explained here.

[galiacheng]

Thanks for your prompt response, @anthony-c-martin. Could we clarify this in the documentation?

I would expect there to be documentation specifying which features trigger a language version 2.0 template, as the Java EE on Azure team uses Bicep extensively to build marketplace offers.

[anthony-c-martin]

Thanks for your prompt response, @anthony-c-martin. Could we clarify this in the documentation?

@stephaniezyen I see you started this under #14866. Please could we arrange for this to be moved to the official Microsoft docs?