command/format: Correctly quote diff object keys

[kmoe]

This is a port of #25443 to the new diff renderer.

Fixes #21749

When rendering a diff, we should quote object attribute names if the string representation is not a valid identifier. While this is not
strictly necessary, it makes the diff output more closely resemble the configuration language, which is less confusing.

This commit applies to both top-level schema attributes and any object value attributes. We use a simplistic "%q" Go format string to quote the strings, which is not strictly identical to HCL's quoting requirements,but is the pattern used elsewhere in HCL and Terraform.

[alisdair]

Thank you!

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[stevehipwell]

This PR seems to break the representation of map(type) where the keys have been provided as string to allow special characters.

      ~ tags                  = {
          + "\"test.io/foo\"" = "my"
          + "\"test.io/bar\"" = "test"
            # (8 unchanged elements hidden)
        }

[alisdair]

@stevehipwell Thanks for the note!

If those two keys in your example are strings containing escaped quotes, then this behaviour is correct. This patch is intended to make the diff output more closely represent the HCL representation of a value. Writing the already-quoted value "test.io/foo" as a string literal in HCL results in "\"test.io/foo\"".

If that behaviour is not what you're describing, I'm unable to reproduce the problem, so filing a separate issue would help us investigate.

[stevehipwell]

@alisdair sorry I forgot the input values, they were as follows and didn't have any escaped quotes. They were also passing through a variable typed as map(string) so there is no type confusion.

locals {
  tags = {
    "test.io/foo" = "my"
    "test.io/bar" = "test"
  }
}

You can replicate this behaviour by using the following simple object to set the tags on an AWS resource (or other resource accepting map(string)) and seeing how the diff is represented.

locals {
  tags = {
    foo           = "my"
    "bar"        = "test"
    "foo/bar" = "my-test"
  }
}

Based on this test we can see that map keys with characters that HCL doesn't support in keys are being treated differently to keys without special character and that it's not the wrapping of the key with " that causes the issue here. Please note that these aren't special string characters. To me this representation looks completely wrong and seems like the HCL implementation is leaking out into user space.

As map(string) is HCL syntax on top of the Go map[string]string and the no-quote pattern is syntax sugar which can be used when there aren't any special characters, but still results in a quoted value in the diff, I'm struggling to see why the diff now shows extra wrapping \" characters when a key has certain characters in it?

[alisdair]

@stevehipwell After some more poking around I found a reproduction. It seems like this only happens on update, and not on create, which is why I missed it before. Tracking in #30854, thanks for the report!

[github-actions]

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