Required TF properties with a DefaultFunc should be optional in Pulumi

[thomas11]

When a property is defined like this in TF:

	"metadata_host": {
		Type:        pluginsdk.TypeString,
		Required:    true,
		DefaultFunc: pluginsdk.EnvDefaultFunc("ARM_METADATA_HOSTNAME", ""),
		Description: "The Hostname which should be used for the Azure Metadata Service.",
	},

Then the bridge will mark it as required in Pulumi, due to Required: true. However, since there is also a DefaultFunc, things work differently in Terraform: theDefaultFunc's return value will be used if the user doesn't specify a value, and the function itself returns a default from its second argument. So a value is guaranteed, even if it's the empty string.

Therefore, Pulumi should probably mark this property as optional.

See pulumi/pulumi-azuread#362 for the full original issue.

[t0yv0]

Thanks for filing this @thomas11 ! This an interesting feature, note also that rolling this out may cause breaking changes to the generated SDKs because of how some languages project optional vs required. So we perhaps need to flag this.

[iwahbe]

We generally consider it "non-breaking" to convert properties from required to optional, even though it breaks in some languages.

[VenelinMartinov]

Hit this again in pulumi/pulumi-okta#820

[VenelinMartinov]

Example from #1978 : Vault Provider Args token should not be mandatory pulumi/pulumi-vault#509

[VenelinMartinov]

@t0yv0 raised some concerns about backwards compatibility recently. I had a look at what the different languages do and it seems that all languages should be fine making this change:

Csharp changes the Arg class type to be optional:

       [Input("authServerId", required: true)]
        public Input<string> AuthServerId { get; set; } = null!;

becomes

        [Input("authServerId")]
        public Input<string>? AuthServerId { get; set; }

Go changes the input type from the StringInput interface to the StringPointerInput interface but both of these are satisfied by pulumi.String which is what users use:

AuthServerId pulumi.StringInput

becomes

AuthServerId pulumi.StringPtrInput

Java seems fine:

    @Import(name="authServerId", required=true)
    private Output<String> authServerId;

becomes

    @Import(name="authServerId")
    private @Nullable Output<String> authServerId;

Typescript is fine:

    authServerId: pulumi.Input<string>;

becomes

    authServerId?: pulumi.Input<string>;

Python seems fine too:

    def __init__(__self__, *,
                 auth_server_id: pulumi.Input[builtins.str],

becomes

    def __init__(__self__, *,
                 auth_server_id: Optional[pulumi.Input[builtins.str]] = None,

YAML is fine too.

[VenelinMartinov]

There's also no resources in AWS affected by this.

[t0yv0]

Go changes the input type from the StringInput interface to the StringPointerInput interface but both of these are satisfied by pulumi.String which is what users use:

Interesting find, the argument is incomplete because the user may not be just using pulumi.String but it does seem that this pattern in general is supported via:

https://github.com/pulumi/pulumi/blob/0c54b3f325f42e3c62ad5c2a8ad5197577f2c401/tests/integration/construct_component_output_values/testcomponent-go/pulumiTypes.go#L53

// BarPtrInput is an input type that accepts BarArgs, BarPtr and BarPtrOutput values.
// You can construct a concrete instance of `BarPtrInput` via:

So the monomorphized types representing Output<*X> can be passed into slots of type Input<X> it seems:

func Test_Compat(t *testing.T) {
	var x BarOutput
	var y BarPtrInput
	y = x
	panic(y)
}