chore: Grants migration guide

MIGRATION_GUIDE.md

@@ -1,9 +1,170 @@
 # Migration guide
 
-This document is meant to help you migrate your Terraform config to new newest version. In migration guides we will only 
-describe deprecations or breaking changes and help you to change your configuration to keep the same (or similar) behaviour
+This document is meant to help you migrate your Terraform config to the new newest version. In migration guides, we will only 
+describe deprecations or breaking changes and help you to change your configuration to keep the same (or similar) behavior
 across different versions.
 
+## vX.XX.X -> v0.85.0
+
+### Migration from old grant resources to new ones
+
+In recent changes, we introduced new grant resources intended to replace old grant solutions. Here's some of the useful
+information that may help during the migration of the grant resources. Here's an example of the `snowflake_database_grant` to `snowflake_grant_privileges_to_account_role` migration.
+The migration can be done in two ways. Either you can remove old grant resources and replace them with new ones or perform
+more complicated migration, but without revoking any grant (no downtime migration). We'll focus on the second one as the first approach
+is pretty straight forward. As an example we'll take `snowflake_database_grant` that grants one privilege to two roles:
+
+```terraform
+resource "snowflake_database_grant" "old_resource" {
+  depends_on = [ snowflake_database.test, snowflake_role.a, snowflake_role.b ]
+  database_name = snowflake_database.test.name
+  privilege = "USAGE"
+  roles = [ snowflake_role.a.name, snowflake_role.b.name ]
+}
+```
+
+#### 1. terraform list
+
+Run `terraform state list` to search the grants you're looking for (for larger configurations it's best to filter the results), 
+for example, `terraform state list | grep "snowflake_database_grant"`.
+
+#### 2. terraform rm
+
+Now choose which one you would to migrate next and remove it from the state with `terraform state rm <resource_address>`. 
+In our example, `terraform state rm snowflake_database_grant.old_resource`. After running the command, you can remove the resource from the configuration 
+(removing the state will "detach" it from the resource block, so after removing it, the Terraform won't try to revoke USAGE from our roles).
+
+#### 3. Two options from here
+
+At this point, we have several options for creating new grant resources that will replace the old ones.
+We will cover three options:
+- Configuration + Terraform CLI
+- Configuration + import block
+- Generating the configuration with import block and `terraform plan -generate-config-out`
+
+#### 3.1.1. Write a new grant resource that will be an equivalent of the older one
+
+```terraform
+resource "snowflake_grant_privileges_to_account_role" "new_resource" {
+  depends_on = [snowflake_database.test, snowflake_role.a, snowflake_role.b]
+  for_each   = toset([snowflake_role.a.name, snowflake_role.b.name])
+  privileges = ["USAGE"]
+  role_name  = each.key
+  on_account_object {
+    object_type = "DATABASE"
+    object_name = snowflake_database.test.name
+  }
+}
+```
+
+#### 3.1.2. terraform import
+
+Write the `terraform import` command with the ID so that the resource will be able to parse and fill the state correctly.
+You can find import syntax in the documentation for a given resource, [here](https://registry.terraform.io/providers/Snowflake-Labs/snowflake/latest/docs/resources/grant_privileges_to_account_role#import)
+is the one for `snowflake_grant_privileges_to_account_role`. In our case, the command will look like this:
+```shell 
+terraform import 'snowflake_grant_privileges_to_account_role.new_resource["role_a_name"]' 'role_a_name|USAGE|false|false|OnAccountObject|DATABASE|database_name'
+terraform import 'snowflake_grant_privileges_to_account_role.new_resource["role_b_name"]' 'role_b_name|USAGE|false|false|OnAccountObject|DATABASE|database_name'
+```
+
+[Hashicorp documentation reference on import command](https://developer.hashicorp.com/terraform/cli/commands/import)
+
+#### 3.2.1 Write import block with new resource
+
+This is similar to the first approach, but here we don't have to worry about importing each `for_each`
+entry one by one. In the `locals` block, we're defining a map of resource name to ID. Then, we have 
+to write a new resource similar to the first approach. In the end, we have to define an import block
+which will import defined IDs to a specified resource.
+
+```terraform
+locals {
+  migrations = {
+    "${snowflake_role.a.name}" = "\"${snowflake_role.a.name}\"|false|false|USAGE|OnAccountObject|DATABASE|\"${snowflake_database.test.name}\""
+    "${snowflake_role.b.name}" = "\"${snowflake_role.b.name}\"|false|false|USAGE|OnAccountObject|DATABASE|\"${snowflake_database.test.name}\""
+  }
+}
+
+resource "snowflake_grant_privileges_to_account_role" "new_resource" {
+  depends_on = [snowflake_database.test, snowflake_role.a, snowflake_role.b]
+  for_each   = local.migrations
+  privileges = ["USAGE"]
+  account_role_name  = "\"${each.key}\""
+  on_account_object {
+    object_type = "DATABASE"
+    object_name = "\"${snowflake_database.test.name}\""
+  }
+}
+
+import {
+  to = snowflake_grant_privileges_to_account_role.new_resource[each.key]
+  id = each.value
+  for_each = local.migrations
+}
+```
+
+[Hashicorp documentation reference on import block](https://developer.hashicorp.com/terraform/language/import)
+
+#### 3.2.2 Run terraform plan and apply
+
+After running `terraform plan` you'll see if resources can be imported without any change. If that's the case
+and nothing has to be adjusted, then we can perform `terraform apply` to import the state into our new grant resources.
+
+#### 3.3.1. Write import block
+
+Unfortunately, `for_each` cannot be used when generating with import blocks, so we have to define them one by one.
+For simplicity, we'll define just one import block (the second one would look the same, only with a different role).
+
+```terraform
+import {
+  to = snowflake_grant_privileges_to_account_role.new_resource_role_a
+  id = "\"${snowflake_role.a.name}\"|false|false|USAGE|OnAccountObject|DATABASE|\"${snowflake_database.test.name}\""
+}
+```
+[Hashicorp documentation reference on import block](https://developer.hashicorp.com/terraform/language/import)
+
+#### 3.3.2. terraform plan -generate-config-out
+
+After specifying the import block run the `terraform plan -generate-config-out=generated.tf` command,
+which will scan your configuration files search for import blocks, and put the generated configurations inside the `generated.tf` file.
+
+```terraform
+# __generated__ by Terraform
+# Please review these resources and move them into your main configuration files.
+
+# __generated__ by Terraform
+resource "snowflake_grant_privileges_to_account_role" "new_resource_role_a" {
+  account_role_name    = "\"test_role_321123123\""
+  all_privileges       = false
+  always_apply         = false
+  always_apply_trigger = null
+  on_account           = false
+  privileges           = ["USAGE"]
+  with_grant_option    = false
+  on_account_object {
+    object_name = "\"test_database_1231321\""
+    object_type = "DATABASE"
+  }
+}
+```
+
+#### 3.3.3. terraform plan and apply
+
+After running `terraform plan` you'll see if there are any changes we have to do before applying our generated configuration.
+If no errors are appearing you can run `terraform apply` to import state into generated configurations. 
+
+#### 3.3.4. Thoughts on configuration generation
+
+Config generation may be a good solution for a few reasons, but it also comes with limitations:
+- Manual review/fixing
+    - Half of the values could be removed because they're the same as the default values
+- No `for_each` capabilities
+    - You cannot specify `for_each` in the import block like in the second approach which promotes incremental migration
+    - Generated configurations can't use `for_each` which results in much more configuration code
+- No resource reference
+    - As you can see `account_role_name` and `object_name` are plain values, but the values most likely should be referenced by other resources' names.
+
+[Hashicorp documentation reference on generating configuration limitations](https://developer.hashicorp.com/terraform/language/import/generating-configuration)
+
 ## v0.84.0 ➞ v0.85.0
 
 ### snowflake_notification_integration resource changes

pkg/resources/testdata/TestAcc_GrantPrivilegesToShare/OnDatabase/test.tf

@@ -1,11 +1,12 @@
-resource "snowflake_database" "test" {
-  name = var.database
-}
-
 resource "snowflake_share" "test" {
   name = var.to_share
 }
 
+resource "snowflake_database" "test" {
+  depends_on = [snowflake_share.test]
+  name = var.database
+}
+
 resource "snowflake_grant_privileges_to_share" "test" {
   to_share    = snowflake_share.test.name
   privileges  = var.privileges