Add attribute mv and replace commands

[minamijoyo]

Summary

This pull request adds attribute mv and attribute replace commands.

Why

When working on dependency upgrades, I often come across warnings such as "A is deprecated. Use B instead". The current functionality only allows removing the old attribute and appending a new one to the end, which changes the order of the attributes and loses valuable comments. It would be great if we could rename an attribute.

For example, Terraform v1.10 introduced DynamoDB-free S3-native state locking in the s3 backend, and the upcoming Terraform v1.11 will start deprecating the old dynamodb_table attribute and recommend using the new use_lockfile. hashicorp/terraform#36257
It's easy to rewrite a few files by hand, but it could be tedious if you have hundreds of backend configurations across many repositories.

What

This pull request adds attribute mv and attribute replace commands to help such an upgrade work.

Note: As for implementation, hclwrite's attribute name is currently a private variable with no API for renaming it. Therefore, a forked version of hclwrite is used to implement this feature. So, we need to wait for the upstream patch to be merged before we merge this implementation. The upstream patch can be found at hashicorp/hcl#506. (Edit: The upstream patch has been merged 🎉 )

Regarding the design, we have aligned the attribute mv command with block mv. It accepts from and to addresses so that it can be extended in the future, but we have not implemented moving an attribute across blocks yet.

$ hcledit attribute mv --help
Move attribute (Rename attribute key)

Arguments:
  FROM_ADDRESS     An old address of attribute.
  TO_ADDRESS       A new address of attribute.

Usage:
  hcledit attribute mv <FROM_ADDRESS> <TO_ADDRESS> [flags]

Flags:
  -h, --help   help for mv

Global Flags:
  -f, --file string   A path of input file (default "-")
  -u, --update        Update files in-place

In addition to the attribute mv command, this PR also adds a new attribute replace command. This command not only renames the key of an attribute but also sets the value of the attribute. This could be done by combining attribute mv and attribute set, but doing it with a single command would be more convenient. This is because in dependency upgrade scenarios, where attribute A is deprecated and use B instead, it is often the case that not only the name of the attribute changes but also its value.

$ hcledit attribute replace --help
Replace both the name and value of matched attribute at a given address

Arguments:
  ADDRESS          An address of attribute to be replaced.
  NAME             A new name (key) of attribute.
  VALUE            A new value of attribute.
                   The value is set literally, even if references or expressions.
                   Thus, if you want to set a string literal "bar", be sure to
                   escape double quotes so that they are not discarded by your shell.
                   e.g.) hcledit attribute replace aaa.bbb.ccc foo '"bar"'

Usage:
  hcledit attribute replace <ADDRESS> <NAME> <VALUE> [flags]

Flags:
  -h, --help   help for replace

Global Flags:
  -f, --file string   A path of input file (default "-")
  -u, --update        Update files in-place

Examples

$ cat tmp/attr.hcl
resource "foo" "bar" {
  attr1 = "val1"
  nested {
    attr2 = "val2"
  }
}

$ cat tmp/attr.hcl | hcledit attribute mv resource.foo.bar.nested.attr2 resource.foo.bar.nested.attr3
resource "foo" "bar" {
  attr1 = "val1"
  nested {
    attr3 = "val2"
  }
}

$ cat tmp/attr.hcl | hcledit attribute replace resource.foo.bar.nested.attr2 attr3 '"val3"'
resource "foo" "bar" {
  attr1 = "val1"
  nested {
    attr3 = "val3"
  }
}

An example of rewriting s3 backend dynamodb_table to use_lockfile in Terraform v1.11 upgrade:

$ cat tmp/s3lock/main.tf
terraform {
  backend "s3" {
    region         = "ap-northeast-1"
    bucket         = "my-s3lock-test"
    key            = "dir1/terraform.tfstate"
    dynamodb_table = "tflock"
    profile        = "foo"
  }
}

$ cat tmp/s3lock/main.tf | hcledit attribute replace terraform.backend.s3.dynamodb_table use_lockfile true
terraform {
  backend "s3" {
    region       = "ap-northeast-1"
    bucket       = "my-s3lock-test"
    key          = "dir1/terraform.tfstate"
    use_lockfile = true
    profile      = "foo"
  }
}

You can combine it with find, xargs, etc., and rewrite multiple files at once:

$ find . -name "*.tf" | xargs -I{} hcledit attribute replace terraform.backend.s3.dynamodb_table use_lockfile true -f {} -u

While my initial motivation was the above, I'm sure there are many more real-world use cases, not just this one.