Review by @paddyforan: Add a resourceComputeSnapshotExists function

builtin/providers/google/resource_compute_snapshot.go

@@ -14,6 +14,7 @@ func resourceComputeSnapshot() *schema.Resource {
 		Create: resourceComputeSnapshotCreate,
 		Read:   resourceComputeSnapshotRead,
 		Delete: resourceComputeSnapshotDelete,
+		Exists: resourceComputeSnapshotExists,
 
 		Schema: map[string]*schema.Schema{
 			"name": &schema.Schema{
@@ -182,3 +183,26 @@ func resourceComputeSnapshotDelete(d *schema.ResourceData, meta interface{}) err
 	d.SetId("")
 	return nil
 }
+
+func resourceComputeSnapshotExists(d *schema.ResourceData, meta interface{}) (bool, error) {
+	config := meta.(*Config)
+
+	project, err := getProject(d, config)
+	if err != nil {
+		return false, err
+	}
+
+	_, err = config.clientCompute.Snapshots.Get(
+		project, d.Id()).Do()
+	if err != nil {
+		if gerr, ok := err.(*googleapi.Error); ok && gerr.Code == 404 {
+			log.Printf("[WARN] Removing Snapshot %q because it's gone", d.Get("name").(string))
+			// The resource doesn't exist anymore
+			d.SetId("")
+
+			return false, err
+		}
+		return true, err
+	}
+	return true, nil
+}