Add a flag to optionally enable Github Markdown Formatting for diffs

[enochlo]

Heavily inspired from #1325 and looking at #1395. Thanks @raxod502-plaid for the base for the regex.

I added the ability to optionally enable Atlantis to do some Github markdown diff formatting, to enable color coded comments. Also added some tests using the original PR as reference for correctness. This has been pretty useful for me, and hopefully will be useful for the users asking for a bit more Github friendliness :)

This flag will turn comments into something like this:

New Atlantis Comment

Ran Plan for dir: `path/to/terraform` workspace: `default`

Show Output

Note: Objects have changed outside of Terraform

Terraform detected the following changes made outside of Terraform since the
last "terraform apply":

  # module.dev-roles.module.iam_assumable_roles_with_saml.aws_iam_role.role1[0] has been changed
! resource "aws_iam_role" "role1" {
        id                    = "User-Role1"
!       managed_policy_arns   = [
+           "arn:aws:iam::aws:policy/Policy1",
        ]
        name                  = "User-Role1"
+       tags                  = {
+           "Created-By" = "terraform"
+           "Owner"      = "owner@me.com"
        }
        # (8 unchanged attributes hidden)

        # (1 unchanged block hidden)
    }
  # module.dev-roles.module.iam_assumable_roles_with_saml.aws_iam_role.role2[0] has been changed
! resource "aws_iam_role" "role2" {
!       assume_role_policy    = jsonencode(
!           {
!               Statement = [
!                   {
!                       Principal = {
!                           Federated = [
-                               "arn:aws:iam::123456789000:saml-provider/Provider1",
                                "arn:aws:iam::123456789000:saml-provider/Provider2",
+                               "arn:aws:iam::123456789000:saml-provider/Provider1",
                            ]
                        }
                        # (4 unchanged elements hidden)
                    },
                ]
                # (1 unchanged element hidden)
            }
        )
        id                    = "User-Role2"
!       managed_policy_arns   = [
+           "arn:aws:iam::aws:policy/Policy2",
        ]
        name                  = "User-Role2"
+       tags                  = {
+           "Created-By" = "terraform"
+           "Owner"      = "owner@me.com"
        }
        # (7 unchanged attributes hidden)

        # (1 unchanged block hidden)
    }
  # module.dev-roles.module.iam_assumable_roles_with_saml.aws_iam_role.role3[0] has been changed
! resource "aws_iam_role" "admin" {
        id                    = "User-Role3"
!       managed_policy_arns   = [
+           "arn:aws:iam::aws:policy/Policy3",
        ]
        name                  = "User-Role3"
+       tags                  = {
+           "Created-By" = "terraform"
+           "Owner"      = "owner@me.com"
        }
        # (8 unchanged attributes hidden)

        # (1 unchanged block hidden)
    }

Unless you have made equivalent changes to your configuration, or ignored the
relevant attributes using ignore_changes, the following plan may include
actions to undo or respond to these changes.

─────────────────────────────────────────────────────────────────────────────

Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
! update in-place

Terraform will perform the following actions:

  # module.dev-roles.module.iam_assumable_roles_with_saml.aws_iam_role.role3[0] will be updated in-place
! resource "aws_iam_role" "admin" {
        id                    = "User-Role3"
        name                  = "User-Role3"
!       tags                  = {
-           "Created-By" = "terraform" -> null
-           "Owner"      = "owner@me.com" -> null
        }
!       tags_all              = {
!           "Created-By"  = "terraform" -> "terraformasdasd"
-           "Owner"       = "owner@me.com" -> null
+           "RandomTag"   = ";aslkdjlk"
            # (3 unchanged elements hidden)
        }
        # (8 unchanged attributes hidden)

        # (1 unchanged block hidden)
    }

  # module.dev-roles.module.iam_assumable_roles_with_saml.aws_iam_role.role1[0] will be updated in-place
! resource "aws_iam_role" "role1" {
        id                    = "User-Role1"
        name                  = "User-Role1"
!       tags                  = {
-           "Created-By" = "terraform" -> null
-           "Owner"      = "owner@me.com" -> null
        }
!       tags_all              = {
!           "Created-By"  = "terraform" -> "terraformasdasd"
-           "Owner"       = "owner@me.com" -> null
+           "RandomTag"   = ";aslkdjlk"
            # (3 unchanged elements hidden)
        }
        # (8 unchanged attributes hidden)

        # (1 unchanged block hidden)
    }

  # module.dev-roles.module.iam_assumable_roles_with_saml.aws_iam_role.role2[0] will be updated in-place
! resource "aws_iam_role" "role2" {
        id                    = "User-Role2"
        name                  = "User-Role2"
!       tags                  = {
-           "Created-By" = "terraform" -> null
-           "Owner"      = "owner@me.com" -> null
        }
!       tags_all              = {
!           "Created-By"  = "terraform" -> "terraformasdasd"
-           "Owner"       = "owner@me.com" -> null
+           "RandomTag"   = ";aslkdjlk"
            # (3 unchanged elements hidden)
        }
        # (8 unchanged attributes hidden)

        # (1 unchanged block hidden)
    }

Plan: 0 to add, 3 to change, 0 to destroy.

• ▶️ To apply this plan, comment:
  • atlantis apply -d path/to/terraform
• 🚮 To delete this plan click here
• 🔁 To plan this project again, comment:
  • atlantis plan -d path/to/terraform

Note: Objects have changed outside of Terraform
Plan: 0 to add, 3 to change, 0 to destroy.

---

• ⏩ To apply all unapplied plans from this pull request, comment:
  • atlantis apply
• 🚮 To delete all plans and locks for the PR, comment:
  • atlantis unlock

[nishkrishnan]

Nice job! Thanks for contributing!

[enochlo]

@nishkrishnan any next steps for me here to get this merged? :)

[nishkrishnan]

@nishkrishnan any next steps for me here to get this merged? :)

I'm just going to leave it open for a bit for other maintainers to look at and then I'll merge it in.

[jamengual]

looks good, thanks

[xavipanda]

oh this one is such a great feature!! im looking forward to see it released to enable it! thank you so much

[richstokes]

What is the flag / how do you enable this feature?

[raxod502-plaid]

https://github.com/runatlantis/atlantis/pull/1751/files#diff-55955da5052d3dd54dcfb2c3d21a3b1be77e9430d26ab6b145a1971992d05ea5