Fix nil pointer dereference in ResourceData.HasChangeExcept

[w-leads]

ResourceData.HasChangeExcept and ResourceData. HasChangesExcept accesses .diff.Attributes which could be nil and cause nil pointer dereference error.
This PR fixes the issue by checking the value and if it's nil, then return false(meaning no changes)

[hashicorp-cla]

All committers have signed the CLA.

[bflad]

Hi @w-leads 👋 Thank you for submitting this. Is this change required to fix an issue or is it purely for code correctness? The change looks good and makes sense, just trying to confirm this detail first to see if there are potentially other related issues as well. Thank you!

[w-leads]

@bflad Thank you for the reply! This is just for fixing the error I encountered while developing a custom terraform provider. I quickly tried to search for a related issue or PR but could not find it.

[bflad]

Great to know, @w-leads, and sorry you ran into trouble. Would you happen to have time to file a bug report so we can capture some of the details of how this happened? We would love to create some test cases to prevent future regressions. If not, no worries. Appreciate the time and effort you have put into this already.

[bflad]

Thank you again.

[w-leads]

@bflad While checking the behavior to file a bug report, I noticed that probably I'm using the function in a wrong way..
I wanted to run an additional step in terraform plan when a specific set of fields have planned changes, and I tried to use ResourceData.HasChangeExcept() in ReadContext, but should the func be called only by UpdateContext?

[bflad]

Thank you for the followup, @w-leads 👍

but should the func be called only by UpdateContext?

You are correct, the ResourceData.HasChange* methods are generally only applicable during the Resource.Update* methods. If you would like to customize the terraform plan operation before those resource methods are called, the Resource.CustomizeDiff functionality is available (note that it uses a similar, but separate ResourceDiff type).

More information about plan customization can be found at https://www.terraform.io/docs/extend/resources/customizing-differences.html, with some additional helpers available in the https://pkg.go.dev/github.com/hashicorp/terraform-plugin-sdk/v2/helper/customdiff package.

[bflad]

Looks good to me 🚀

[w-leads]

Thank you very much for the information! Will look into the documents
Also thank you for the review and merging the PR!

[github-actions]

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