Marked preview as Computed: true

[melinath]

Partially resolved hashicorp/terraform-provider-google#8251.

I think the issue is that "preview" is optional; if it wasn't provided, it would be tracked as nil by the provider and "false" by the state. When the user goes to make a plan, terraform detects that "preview" will be updated from false -> null, which changes the hash of the object (which looks like a delete/recreate.) Changing to Computed fixes this by setting the provider's value from the API as well as the state.

There is a separate issue where changes are still erroneously detected if a match uses expr instead of config - I'm having some trouble figuring out the best solution in that case but wanted to get the first part out there at least :-)

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

compute: fixed overly-aggressive detection of changes to google_compute_security_policy rules

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 1 insertion(+))
Terraform Beta: Diff ( 1 file changed, 1 insertion(+))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=171151"

[modular-magician]

Oops! It looks like you're using an unknown release-note type in your changelog entries:

• REPLACEME

Please only use the types listed in https://github.com/GoogleCloudPlatform/magic-modules/blob/master/.ci/RELEASE_NOTES_GUIDE.md.

[melinath]

/gcbrun

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 1 insertion(+))
Terraform Beta: Diff ( 2 files changed, 2 insertions(+), 1 deletion(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=171235"

[ScottSuarez]

your analysis makes sense to me! :)

[ScottSuarez]

gonna add @slevenick for a quick second pass. I don't know if it would be better to have a diff suppress? I think this is fine

[slevenick]

Quick sanity check, can a user go from setting preview = true to preview = false and have the value actually update? Optional+Computed has some issues in these cases, but I might be thinking of objects rather than primitive values like booleans

[melinath]

I don't seem to have any problems doing that in local testing.