luci-base: luci.js: tweak error handling

If the ui class is loaded, use its modalDialog facility to display runtime
errors, alternatively render them into the maincontent area.

Also prevent duplication of stack trace information and throw a low level
error on session expiration to allow higher layers to properly handle it.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

modules/luci-base/htdocs/luci-static/resources/luci.js

@@ -488,12 +488,22 @@
 			}
 
 			/* Append shortened & beautified stacktrace to message */
-			e.message += '\n' + stack.join('\n')
+			var trace = stack.join('\n')
 				.replace(/(.*?)@(.+):(\d+):(\d+)/g, '  at $1 ($2:$3:$4)');
 
+			if (e.message.indexOf(trace) == -1)
+				e.message += '\n' + trace;
+
 			if (window.console && console.debug)
 				console.debug(e);
 
+			if (this.ui)
+				this.ui.showModal(_('Runtime error'),
+					E('pre', { 'class': 'alert-message error' }, e));
+			else
+				L.dom.content(document.querySelector('#maincontent'),
+					E('pre', { 'class': 'alert-message error' }, e));
+
 			throw e;
 		},
 
@@ -610,7 +620,7 @@
 						}, _('To login…')))
 				]);
 
-				L.error('AuthenticationError', 'Session expired');
+				throw 'Session expired';
 			});
 
 			originalCBIInit();