Consolidate ConflictsWith errors

[danawillow]

SDK version

v1.4.0

Use-cases

Have a single error message for two related ConflictsWith fields- see hashicorp/terraform-provider-google#5284.

Attempted Solutions

If two fields conflict with each other, we can get a single error message by only setting ConflictsWith on one of them, which works fine.

However, if three fields (A, B, and C) conflict with each other, we would have to set ConflictsWith on at least two of them in order to cover all cases (setting it only on A would mean that a user could set B and C together in their config), which means that a user could end up with two error messages.

Proposal

Consolidate error messages when possible. In the example in the related issue, instead of having both Error: "name_prefix": conflicts with name and Error: "name": conflicts with name_prefix, recognize that those two are the same and only return one of them. My guess is that we'd also want to do something similar to ExactlyOneOf and AtLeastOneOf.

References

hashicorp/terraform-provider-google#5284

[jsoref]

For my reference, this appears to be:

terraform-plugin-sdk/helper/schema/schema.go

Line 1459 in 97d4d4b

func validateConflictingAttributes(

[radeksimko]

I agree with you @danawillow that these error messages and UX here could be improved.

The new "rich diagnostic errors/warnings" that came with 0.12 gave us the ability to carry helpful context alongside each message, so we can show the relevant snippet of code and point to the relevant line.

With that in mind we would need to tune this to allow us pointing to more than a single line of code, i.e. all conflicting fields, or we would need to arbitrarily pick one, which may confuse the user more than the current (verbose) messaging.

So aggregating the message itself is easy, aggregating the context is possible, but not as easy and we can't quite separate the two from each other as that is how errors & warnings are represented in the plugin protocol since 0.12.