Terraform destroy calls CustomizeDiff though documentation suggests it shouldn't be

[prashantv]

SDK version

v2.24.1

Relevant provider source code

https://github.com/prashantv/terraform-customizediff-on-destroy-repro

Terraform Configuration Files

Config doesn't matter, as it seems to always happen. However, the above repo does contain a repro with config.

Debug Output

https://gist.github.com/prashantv/5e00eb5e6dc9215c280d7cb30a68cf26

Expected Behavior

CustomizeDiff shouldn't be called, as documented in the SDK docs.

// * Destroy: No runs (standard diff logic is skipped on destroy diffs)

If it is called, there should be some way for the provider to know that this is a destroy call.

Actual Behavior

CustomizeDiff is called.

Steps to Reproduce

See https://github.com/prashantv/terraform-customizediff-on-destroy-repro

[prashantv]

It looks like the CustomizeDiff is called due to the refresh step (which TF internally does using plan).

Using terraform destroy -refresh=false doesn't cause CustomizeDiff to be called.

However, as a provider developer, we can't tell users to avoid refresh (and shouldn't since there's a benefit to the refresh). Ideally the plugin SDK is responsible for handling this, as there doesn't seem to be a clear way to identify that a CustomizeDiff is happening as part of a destroy step.