Add error strings to exceptions

qutebrowser/app.py

@@ -409,7 +409,7 @@ class QuteBrowser(QApplication):
             Always raises Exception.
 
         """
-        raise Exception
+        raise Exception("Forced crash")
 
     @pyqtSlot()
     def shutdown(self, do_quit=True):

qutebrowser/commands/template.py

@@ -74,7 +74,8 @@ class Command(QObject):
                 (self.nargs == '?' and len(args) > 1) or
                 (self.nargs == '+' and len(args) < 1)):
             # for nargs == '*', anything is okay
-            raise ArgumentCountError
+            raise ArgumentCountError("{} args expected, but got {}".format(
+                self.nargs, len(args)))
 
     def run(self, args=None, count=None):
         """Run the command.

qutebrowser/commands/utils.py

@@ -160,12 +160,12 @@ class CommandParser(QObject):
         """
         parts = text.strip().split(maxsplit=1)
         if not parts:
-            raise NoSuchCommandError
+            raise NoSuchCommandError("No command given")
         cmdstr = parts[0]
         try:
             cmd = cmd_dict[cmdstr]
         except KeyError:
-            raise NoSuchCommandError(cmdstr)
+            raise NoSuchCommandError("Command {} not found.".format(cmdstr))
 
         if len(parts) == 1:
             args = []

qutebrowser/models/completion.py

@@ -362,7 +362,7 @@ class CompletionItem():
         elif role == Qt.UserRole:
             return self._marks
         else:
-            raise ValueError
+            raise ValueError("Invalid role {}".format(role))
 
     def setdata(self, column, value, role=Qt.DisplayRole):
         """Set the data for column/role to value.
@@ -381,7 +381,7 @@ class CompletionItem():
         elif role == Qt.UserRole:
             self._marks = value
         else:
-            raise ValueError
+            raise ValueError("Invalid role {}".format(role))
 
     def column_count(self):
         """Get the column count in the item.

qutebrowser/utils/about.py

@@ -52,7 +52,7 @@ def handle(url):
 
     """
     if not is_about_url(url):
-        raise ValueError
+        raise ValueError("URL {} is not an about URL".format(url))
     handler = getattr(AboutHandlers, _transform_url(url))
     return handler()
 

qutebrowser/utils/url.py

@@ -54,8 +54,10 @@ def _get_search_url(txt):
                                      fallback=None)
         term = txt
         logging.debug('engine: default, term "{}"'.format(txt))
-    if template is None or not term:
+    if template is None:
-        raise ValueError
+        raise ValueError("Search template is None")
+    if not term:
+        raise ValueError("No search term given")
     return QUrl.fromUserInput(template.format(urllib.parse.quote(term)))