ct: Backport the snippets feature

* See #22

ct/datasource_ct_config.go

@@ -2,13 +2,15 @@ package ct
 
 import (
 	"encoding/json"
-	"errors"
+	"fmt"
 	"strconv"
 
 	"github.com/hashicorp/terraform/helper/hashcode"
 	"github.com/hashicorp/terraform/helper/schema"
 
 	ct "github.com/coreos/container-linux-config-transpiler/config"
+	ignition "github.com/coreos/ignition/config/v2_0"
+	ignitionTypesV2_0 "github.com/coreos/ignition/config/v2_0/types"
 )
 
 func dataSourceCTConfig() *schema.Resource {
@@ -26,6 +28,14 @@ func dataSourceCTConfig() *schema.Resource {
 				Default:  "",
 				ForceNew: true,
 			},
+			"snippets": &schema.Schema{
+				Type: schema.TypeList,
+				Elem: &schema.Schema{
+					Type: schema.TypeString,
+				},
+				Optional: true,
+				ForceNew: true,
+			},
 			"pretty_print": &schema.Schema{
 				Type:     schema.TypeBool,
 				Optional: true,
@@ -52,27 +62,50 @@ func dataSourceCTConfigRead(d *schema.ResourceData, meta interface{}) error {
 }
 
 func renderCTConfig(d *schema.ResourceData) (string, error) {
-	config := d.Get("content").(string)
+	// unchecked assertions seem to be the norm in Terraform :S
+	content := d.Get("content").(string)
 	platform := d.Get("platform").(string)
+	snippetsIface := d.Get("snippets").([]interface{})
 	pretty := d.Get("pretty_print").(bool)
 
-	// parse bytes int a Container Linux Config
-	cfg, rpt := ct.Parse([]byte(config))
-	if rpt.IsFatal() {
-		return "", errors.New(rpt.String())
+	snippets := make([]string, len(snippetsIface))
+	for i := range snippetsIface {
+		snippets[i] = snippetsIface[i].(string)
 	}
 
-	// convert Container Linux Config to an Ignition Config
-	ignition, rpt := ct.ConvertAs2_0(cfg, platform)
-	if rpt.IsFatal() {
-		return "", errors.New(rpt.String())
+	ign, err := clcToIgnition([]byte(content), platform)
+	if err != nil {
+		return "", err
+	}
+
+	for _, content := range snippets {
+		ignext, err := clcToIgnition([]byte(content), platform)
+		if err != nil {
+			return "", err
+		}
+		ign = ignition.Append(ign, ignext)
 	}
 
 	if pretty {
-		ignitionJSON, err := json.MarshalIndent(&ignition, "", "  ")
+		ignitionJSON, err := json.MarshalIndent(ign, "", "  ")
 		return string(ignitionJSON), err
 	}
 
-	ignitionJSON, err := json.Marshal(&ignition)
+	ignitionJSON, err := json.Marshal(ign)
 	return string(ignitionJSON), err
 }
+
+// Parse Container Linux config and convert to Ignition v2.0.0 format.
+func clcToIgnition(data []byte, platform string) (ignitionTypesV2_0.Config, error) {
+	// parse bytes into a Container Linux Config
+	clc, report := ct.Parse([]byte(data))
+	if report.IsFatal() {
+		return ignitionTypesV2_0.Config{}, fmt.Errorf("error parsing Container Linux Config: %v", report.String())
+	}
+	// convert Container Linux Config to an Ignition Config
+	ign, report := ct.ConvertAs2_0(clc, platform)
+	if report.IsFatal() {
+		return ignitionTypesV2_0.Config{}, fmt.Errorf("error converting to Ignition: %v", report.String())
+	}
+	return ign, nil
+}

ct/datasource_ct_config_test.go

@@ -108,6 +108,57 @@ const ec2Expected = `{
   "passwd": {}
 }`
 
+const snippetsResource = `
+data "ct_config" "combine" {
+	pretty_print = true
+	content = <<EOT
+---
+storage:
+  filesystems:
+    - name: "rootfs"
+      mount:
+        device: "/dev/disk/by-label/ROOT"
+        format: "ext4"
+EOT
+	snippets = [
+<<EOT
+---
+systemd:
+  units:
+    - name: docker.service
+      enable: true
+EOT
+	]
+}
+`
+const snippetsExpected = `{
+  "ignition": {
+    "version": "2.0.0",
+    "config": {}
+  },
+  "storage": {
+    "filesystems": [
+      {
+        "name": "rootfs",
+        "mount": {
+          "device": "/dev/disk/by-label/ROOT",
+          "format": "ext4"
+        }
+      }
+    ]
+  },
+  "systemd": {
+    "units": [
+      {
+        "name": "docker.service",
+        "enable": true
+      }
+    ]
+  },
+  "networkd": {},
+  "passwd": {}
+}`
+
 func TestRender(t *testing.T) {
 	r.UnitTest(t, r.TestCase{
 		Providers: testProviders,
@@ -124,6 +175,12 @@ func TestRender(t *testing.T) {
 					r.TestCheckResourceAttr("data.ct_config.ec2", "rendered", ec2Expected),
 				),
 			},
+			r.TestStep{
+				Config: snippetsResource,
+				Check: r.ComposeTestCheckFunc(
+					r.TestCheckResourceAttr("data.ct_config.combine", "rendered", snippetsExpected),
+				),
+			},
 		},
 	})
 }