job: import jobs from non-default namespace

Since the `nomad_job` resource does not have a `namespace` attribute,
it's currently impossible to import jobs from a non-default namespace.

This commit adds a new helper that imports jobs using the
`<job>@<namespace>` ID syntax. Since `@` is not a valid character for
namespaces, the last `@` character (if found) represents the separator.

nomad/helper/import.go

@@ -0,0 +1,22 @@
+package helper
+
+import (
+	"context"
+	"strings"
+
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+)
+
+// NamespacedImporterContext allows importing resources under a namespace where
+// the namespace is not passed as an attribute.
+func NamespacedImporterContext(_ context.Context, d *schema.ResourceData, a any) ([]*schema.ResourceData, error) {
+	namespacedID := d.Id()
+	sepIdx := strings.LastIndex(d.Id(), "@")
+	if sepIdx == -1 {
+		return []*schema.ResourceData{d}, nil
+	}
+
+	d.SetId(namespacedID[:sepIdx])
+	d.Set("namespace", namespacedID[sepIdx+1:])
+	return []*schema.ResourceData{d}, nil
+}

nomad/resource_job.go

@@ -20,6 +20,7 @@ import (
 	"github.com/hashicorp/nomad/jobspec2"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+	"github.com/hashicorp/terraform-provider-nomad/nomad/helper"
 )
 
 func resourceJob() *schema.Resource {
@@ -37,7 +38,7 @@ func resourceJob() *schema.Resource {
 		},
 
 		Importer: &schema.ResourceImporter{
-			StateContext: schema.ImportStatePassthroughContext,
+			StateContext: helper.NamespacedImporterContext,
 		},
 
 		Schema: map[string]*schema.Schema{

website/docs/r/job.html.markdown

@@ -297,6 +297,27 @@ options when [`detach`](#detach) is set to `false`:
 - `create` `(string: "5m")` - Timeout when registering a new job.
 - `update` `(string: "5m")` - Timeout when updating an existing job.
 
+## Importing Jobs
+
+You can use the ID format `<job ID>@<namespace>` to import jobs from a
+non-default namespace.
+
+```console
+$ terraform import nomad_job.example example@my-namespace
+nomad_job.example: Importing from ID "example@my-namespace"...
+nomad_job.example: Import prepared!
+  Prepared nomad_job for import
+nomad_job.example: Refreshing state... [id=example@my-namespace]
+
+Import successful!
+
+The resources that were imported are shown above. These resources are now in
+your Terraform state and will henceforth be managed by Terraform.
+```
+
+The `@<namespace>` component my be omitted if the job is registered in the
+`default` namespace.
+
 [tf_docs_timeouts]: https://www.terraform.io/docs/configuration/blocks/resources/syntax.html#operation-timeouts
 [tf_docs_templatefile]: https://www.terraform.io/docs/configuration/functions/templatefile.html
 [tf_docs_string_template]: https://www.terraform.io/language/expressions/strings#string-templates