Separate success/error callbacks

qutebrowser/browser/browsertab.py

@@ -667,13 +667,15 @@ class AbstractElements:
         [typing.Sequence['webelem.AbstractWebElement']], None]
     _SingleCallback = typing.Callable[
         [typing.Optional['webelem.AbstractWebElement']], None]
+    _ErrorCallback = typing.Callable[[Exception], None]
 
     def __init__(self, tab: 'AbstractTab') -> None:
         self._widget = None
         self._tab = tab
 
     def find_css(self, selector: str,
-                 callback: _MultiCallback, *,
+                 callback: _MultiCallback,
+                 error_callback: _ErrorCallback, *,
                  only_visible: bool = False) -> None:
         """Find all HTML elements matching a given selector async.
 

qutebrowser/browser/hints.py

@@ -597,13 +597,6 @@ class HintManager(QObject):
             log.hints.debug("In _start_cb without context!")
             return
 
-        if elems is None:
-            message.error("Unknown error while getting hint elements.")
-            return
-        elif isinstance(elems, webelem.Error):
-            message.error(str(elems))
-            return
-
         if not elems:
             message.error("No elements found.")
             return
@@ -747,8 +740,11 @@ class HintManager(QObject):
         except webelem.Error as e:
             raise cmdutils.CommandError(str(e))
 
-        self._context.tab.elements.find_css(selector, self._start_cb,
-                                            only_visible=True)
+        self._context.tab.elements.find_css(
+            selector,
+            callback=self._start_cb,
+            error_cb=lambda err: message.error(str(err)),
+            only_visible=True)
 
     def _get_hint_mode(self, mode):
         """Get the hinting mode to use based on a mode argument."""

qutebrowser/browser/navigate.py

@@ -116,13 +116,6 @@ def prevnext(*, browsertab, win_id, baseurl, prev=False,
         window: True to open in a new window, False for the current one.
     """
     def _prevnext_cb(elems):
-        if elems is None:
-            message.error("Unknown error while getting hint elements")
-            return
-        elif isinstance(elems, webelem.Error):
-            message.error(str(elems))
-            return
-
         elem = _find_prevnext(prev, elems)
         word = 'prev' if prev else 'forward'
 
@@ -155,4 +148,5 @@ def prevnext(*, browsertab, win_id, baseurl, prev=False,
     except webelem.Error as e:
         raise Error(str(e))
 
-    browsertab.elements.find_css(link_selector, _prevnext_cb)
+    browsertab.elements.find_css(link_selector, callback=_prevnext_cb,
+                                 error_cb=lambda err: message.error(str(err)))

qutebrowser/browser/webengine/webenginetab.py

@@ -591,19 +591,20 @@ class WebEngineElements(browsertab.AbstractElements):
 
     """QtWebEngine implemementations related to elements on the page."""
 
-    def _js_cb_multiple(self, callback, js_elems):
+    def _js_cb_multiple(self, callback, error_cb, js_elems):
         """Handle found elements coming from JS and call the real callback.
 
         Args:
             callback: The callback to call with the found elements.
-                      Called with None if there was an error.
+            error_cb: The callback to call in case of an error.
             js_elems: The elements serialized from javascript.
         """
         if js_elems is None:
-            callback(None)
+            error_cb(webelem.Error("Unknown error while getting "
+                                   "elements"))
             return
         elif not js_elems['success']:
-            callback(webelem.Error(js_elems['error']))
+            error_cb(webelem.Error(js_elems['error']))
             return
 
         elems = []
@@ -630,10 +631,11 @@ class WebEngineElements(browsertab.AbstractElements):
             elem = webengineelem.WebEngineElement(js_elem, tab=self._tab)
             callback(elem)
 
-    def find_css(self, selector, callback, *, only_visible=False):
+    def find_css(self, selector, callback, error_cb, *,
+                 only_visible=False):
         js_code = javascript.assemble('webelem', 'find_css', selector,
                                       only_visible)
-        js_cb = functools.partial(self._js_cb_multiple, callback)
+        js_cb = functools.partial(self._js_cb_multiple, callback, error_cb)
         self._tab.run_js_async(js_code, js_cb)
 
     def find_id(self, elem_id, callback):

qutebrowser/browser/webkit/webkittab.py

@@ -563,7 +563,8 @@ class WebKitElements(browsertab.AbstractElements):
 
     """QtWebKit implemementations related to elements on the page."""
 
-    def find_css(self, selector, callback, *, only_visible=False):
+    def find_css(self, selector, callback, error_cb, *, only_visible=False):
+        utils.unused(error_cb)
         mainframe = self._widget.page().mainFrame()
         if mainframe is None:
             raise browsertab.WebTabError("No frame focused!")
@@ -592,7 +593,8 @@ class WebKitElements(browsertab.AbstractElements):
         # Escape non-alphanumeric characters in the selector
         # https://www.w3.org/TR/CSS2/syndata.html#value-def-identifier
         elem_id = re.sub(r'[^a-zA-Z0-9_-]', r'\\\g<0>', elem_id)
-        self.find_css('#' + elem_id, find_id_cb)
+        self.find_css('#' + elem_id, find_id_cb,
+                      error_callback=lambda exc: None)
 
     def find_focused(self, callback):
         frame = self._widget.page().currentFrame()