resource/aws_cloudwatch_event_target: Prevent potential panic and passthrough custom event_bus_name in v0 state upgrade

[bflad]

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Reference: #16069
Reference: #16075
Closes #16394

Release note for CHANGELOG:

resource/aws_cloudwatch_event_target: Prevent potential panic and prevent recreation after state upgrade with custom `event_bus_name` value

If a configuration was applied with version 3.14.0, the event_bus_name attribute could have a custom value and the state upgrader function would previously not pass it through.

Previous output from new unit test:

--- FAIL: TestResourceAwsCloudWatchEventTargetStateUpgradeV0EventBusName (0.00s)
    resource_aws_cloudwatch_event_target_migrate_test.go:66:

        expected:

        map[string]interface {}{"arn":"arn:aws:test:us-east-1:123456789012:test", "event_bus_name":"testbus", "rule":"testrule", "target_id":"testtargetid"}

        got:

        map[string]interface {}{"arn":"arn:aws:test:us-east-1:123456789012:test", "event_bus_name":"default", "rule":"testrule", "target_id":"testtargetid"}

Given this configuration:

terraform {
  required_providers {
    aws = "3.14.0"
  }
  required_version = "0.12.29"
}

provider "aws" {
  region = "us-east-2"
}

resource "aws_cloudwatch_event_bus" "test" {
  name = "16394-test"
}

resource "aws_cloudwatch_event_rule" "test" {
  event_bus_name = aws_cloudwatch_event_bus.test.name
  event_pattern = jsonencode({
    source = ["aws.ec2"]
  })
  name = "16394-test"
}

resource "aws_cloudwatch_event_target" "test" {
  arn            = aws_sns_topic.test.arn
  event_bus_name = aws_cloudwatch_event_bus.test.name
  rule           = aws_cloudwatch_event_rule.test.name
  target_id      = "16394-test"
}

resource "aws_sns_topic" "test" {
  name = "16394-test"
}

Output from console:

$ terraform init
...
$ terraform apply
...
Apply complete! Resources: 4 added, 0 changed, 0 destroyed.
# edit provider version to 3.18.0
$ terraform init
...
$ terraform apply
...
An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # aws_cloudwatch_event_target.test will be created
  + resource "aws_cloudwatch_event_target" "test" {
      + arn            = "arn:aws:sns:us-east-2:--OMITTED--:16394-test"
      + event_bus_name = "16394-test"
      + id             = (known after apply)
      + rule           = "16394-test"
      + target_id      = "16394-test"
    }

Plan: 1 to add, 0 to change, 0 to destroy.
# swap in built Terraform AWS Provider binary
$ terraform apply
...
Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Output from acceptance testing:

--- PASS: TestAccAWSCloudWatchEventTarget_basic (35.74s)
--- PASS: TestAccAWSCloudWatchEventTarget_batch (140.33s)
--- PASS: TestAccAWSCloudWatchEventTarget_disappears (17.51s)
--- PASS: TestAccAWSCloudWatchEventTarget_ecs (28.63s)
--- PASS: TestAccAWSCloudWatchEventTarget_ecsWithBlankTaskCount (31.25s)
--- PASS: TestAccAWSCloudWatchEventTarget_EventBusName (32.01s)
--- PASS: TestAccAWSCloudWatchEventTarget_full (59.07s)
--- PASS: TestAccAWSCloudWatchEventTarget_GeneratedTargetId (16.62s)
--- PASS: TestAccAWSCloudWatchEventTarget_input_transformer (47.34s)
--- PASS: TestAccAWSCloudWatchEventTarget_inputTransformerJsonString (38.99s)
--- PASS: TestAccAWSCloudWatchEventTarget_kinesis (59.09s)
--- PASS: TestAccAWSCloudWatchEventTarget_sqs (16.71s)
--- PASS: TestAccAWSCloudWatchEventTarget_ssmDocument (18.77s)

[anGie44]

Niiice, LGTM 👍

[ghost]

This has been released in version 3.20.0 of the Terraform AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template for triage. Thanks!

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!