Pulumi-inexpressible values after MaxItemsOne flattening under ConfigModeAttr

[VenelinMartinov]

What happened?

Combining MaxItemsOne with ConfigModeAttr yields inexpressible values in pulumi land because of MaxItemsOne flattening.

Azure classic is a provider which uses ConfigModeAttr quite a bit so might be a good place to look for examples of real world usage.

Example

schema:

"f0": {
	Optional:   true,
	Type:       schema.TypeList,
	MaxItems:   1,
	ConfigMode: schema.SchemaConfigModeAttr,
	Elem: &schema.Resource{
		Schema: map[string]*schema.Schema{
			"x": {Optional: true, Type: schema.TypeString},
		},
	},
}

in terraform we can pass:

resource "crossprovider_testres" "example" {
  f0 = []
}

but on pulumi side we can either not specify it, pass x=nil or x=non-nil.

These map to nil, nil, and non-nil respectively but none of them map to [].

Output of pulumi about

.

Additional context

No response

Contributing

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[t0yv0]

Yes, somewhat of a known unfortunate issue, thanks for documenting this. This would benefit from fully worked examples and impact. For an attribute of this type:

TF has 5 unknown, nil, [], [{"foo": "bar"}] states.

Pulumi has 4 unknown, nil, {"foo": "bar"} states.

We cannot turnaround or map 1:1, but we can decide whether Pulumi nil should map to nil or to [], how does it map currently, and what are the trade-offs.