Fix perma-diff on instance templates.

google/resource_compute_instance_template.go

@@ -20,6 +20,7 @@ func resourceComputeInstanceTemplate() *schema.Resource {
 			State: schema.ImportStatePassthrough,
 		},
 		SchemaVersion: 1,
+		CustomizeDiff: resourceComputeInstanceTemplateCustomizeDiff,
 		MigrateState:  resourceComputeInstanceTemplateMigrateState,
 
 		// A compute instance template is more or less a subset of a compute
@@ -99,10 +100,9 @@ func resourceComputeInstanceTemplate() *schema.Resource {
 						},
 
 						"source_image": &schema.Schema{
-							Type:             schema.TypeString,
-							Optional:         true,
-							DiffSuppressFunc: compareSelfLinkRelativePaths,
-							ForceNew:         true,
+							Type:     schema.TypeString,
+							Optional: true,
+							Computed: true,
 						},
 
 						"interface": &schema.Schema{
@@ -420,6 +420,48 @@ func resourceComputeInstanceTemplate() *schema.Resource {
 	}
 }
 
+func resourceComputeInstanceTemplateCustomizeDiff(diff *schema.ResourceDiff, meta interface{}) error {
+	config := meta.(*Config)
+	project, err := getProjectFromDiff(diff, config)
+	if err != nil {
+		return err
+	}
+	numDisks := diff.Get("disk.#").(int)
+	for i := 0; i < numDisks; i++ {
+		key := fmt.Sprintf("disk.%d.source_image", i)
+		if diff.HasChange(key) {
+			old, new := diff.GetChange(key)
+			if old == "" || new == "" {
+				// no sense in resolving empty strings
+				err = diff.ForceNew(key)
+				if err != nil {
+					return err
+				}
+				continue
+			}
+			oldResolved, err := resolveImage(config, project, old.(string))
+			if err != nil {
+				return err
+			}
+			newResolved, err := resolveImage(config, project, new.(string))
+			if err != nil {
+				return err
+			}
+			if oldResolved != newResolved {
+				err = diff.ForceNew(key)
+				if err != nil {
+					return err
+				}
+			}
+			err = diff.Clear(key)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 func buildDisks(d *schema.ResourceData, config *Config) ([]*computeBeta.AttachedDisk, error) {
 	project, err := getProject(d, config)
 	if err != nil {

google/utils.go

@@ -64,6 +64,20 @@ func getProject(d TerraformResourceData, config *Config) (string, error) {
 	return getProjectFromSchema("project", d, config)
 }
 
+// getProjectFromDiff reads the "project" field from the given diff and falls
+// back to the provider's value if not given. If the provider's value is not
+// given, an error is returned.
+func getProjectFromDiff(d *schema.ResourceDiff, config *Config) (string, error) {
+	res, ok := d.GetOk("project")
+	if ok {
+		return res.(string), nil
+	}
+	if config.Project != "" {
+		return config.Project, nil
+	}
+	return "", fmt.Errorf("%s: required field is not set", "project")
+}
+
 func getProjectFromInstanceState(is *terraform.InstanceState, config *Config) (string, error) {
 	res, ok := is.Attributes["project"]
 

vendor/vendor.json

@@ -665,10 +665,10 @@
 			"versionExact": "v0.11.2"
 		},
 		{
-			"checksumSHA1": "JHxGzmxcIS8NyLX9pGhK5beIra4=",
+			"checksumSHA1": "OOwTGBTHcUmQTPBdyscTMkjApbI=",
 			"path": "github.com/hashicorp/terraform/helper/schema",
-			"revision": "41e50bd32a8825a84535e353c3674af8ce799161",
-			"revisionTime": "2018-04-10T16:50:42Z",
+			"revision": "35d82b055591e9d47a254e68754216d8849ba67a",
+			"revisionTime": "2018-09-26T21:21:28Z",
 			"version": "v0.11.2",
 			"versionExact": "v0.11.2"
 		},