Add the attribute from the request to at-least-one validator's error message

[ChihweiLHBird]

In the schema:

var resourceSchema = schema.Schema{
    Attributes: map[string]schema.Attribute{
        // ... many other attributes
        "attribute1": schema.Int64Attribute{
            Validators: []validator.Int64{
                int64validator.AtLeastOneOf(path.MatchRoot("attribute2")),
            },
            Optional:    true,
            Computed:    true,
        },
    },
}

Let's don't put both attributes in the Terraform config file.

Previous error message:

│ Error: Invalid Attribute Combination
│ 
│   with my_reource.my-resource-instance,
│   on main.tf line 22, in resource "my_reource" "my-resource-instance":
│   22: resource "my_reource" "my-resource-instance" {
│ 
│ At least one attribute out of [attribute2] must be specified

This message above is misleading because it actually requires one of attribute1 and attribute2, but attribute1 is not in the error message.

Now with the change in this PR:

│ Error: Invalid Attribute Combination
│ 
│   with my_reource.my-resource-instance,
│   on main.tf line 22, in resource "my_reource" "my-resource-instance":
│   22: resource "my_reource" "my-resource-instance" {
│ 
│ At least one attribute out of [attribute1,attribute2] must be specified

We can correctly inform the user what attributes are required.

[bendbennett]

Hi @ChihweiLHBird 👋

Thank you for this submission.

Could I ask that you add test coverage to verify the behaviour of this change? Perhaps a new test to confirm that both the attribute upon which the AtLeastOneOf validator is declared, and all of the attributes supplied in the path.Expression args appear in the diagnostic.

Could you also add a change log entry as described in the New Pull Request section of the doc on contributing?

Thanks again.

[ChihweiLHBird]

Hi @bendbennett, thanks for letting me know! I just added them.

[ChihweiLHBird]

Hi @bflad, thanks for the suggestion! I think this suggestion is fine, but one downside is that in the future, if any error message is changed in the validator, the tests will need to be adjusted accordingly. This is somehow against the design principle of SSOT and might lead to more effort of maintenance required in the future IMO. However, they are only few error messages, thus the impact is pretty minimum and I think it would be fine. If you think it's okay, I can proceed to this way.

[bendbennett]

@ChihweiLHBird thank you very much for your PR. This looks good to me.

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