extract vpn tunnel region/project from vpn gateway

google-beta/resource_compute_vpn_tunnel.go

@@ -326,6 +326,11 @@ func resourceComputeVpnTunnelCreate(d *schema.ResourceData, meta interface{}) er
 		obj["region"] = regionProp
 	}
 
+	obj, err = resourceComputeVpnTunnelEncoder(d, meta, obj)
+	if err != nil {
+		return err
+	}
+
 	url, err := replaceVars(d, config, "https://www.googleapis.com/compute/beta/projects/{{project}}/regions/{{region}}/vpnTunnels")
 	if err != nil {
 		return err
@@ -694,3 +699,18 @@ func expandComputeVpnTunnelRegion(v interface{}, d *schema.ResourceData, config
 	}
 	return f.RelativeLink(), nil
 }
+
+func resourceComputeVpnTunnelEncoder(d *schema.ResourceData, meta interface{}, obj map[string]interface{}) (map[string]interface{}, error) {
+	config := meta.(*Config)
+	f, err := parseRegionalFieldValue("targetVpnGateways", d.Get("target_vpn_gateway").(string), "project", "region", "zone", d, config, true)
+	if err != nil {
+		return nil, err
+	}
+	if _, ok := d.GetOk("project"); !ok {
+		d.Set("project", f.Project)
+	}
+	if _, ok := d.GetOk("region"); !ok {
+		d.Set("region", f.Region)
+	}
+	return obj, nil
+}

website/docs/r/compute_vpn_tunnel.html.markdown

@@ -171,7 +171,7 @@ The following arguments are supported:
 
 * `region` -
   (Optional)
-  The region where the tunnel is located.
+  The region where the tunnel is located. If unset, is set to the region of `target_vpn_gateway`.
 * `project` - (Optional) The ID of the project in which the resource belongs.
     If it is not provided, the provider project is used.