Fix lint:

Various lint fixes. The ones we will likely revisit later are:

* unused sibling arg in parent TabbedBrowser class
* seperate-but-similar UndoEntry implementations
* variables with two leading underscores in notree
* `_tree_tab_give()` implementation

qutebrowser/browser/commands.py:499:9: F841 local variable 'oldroot' is assigned to but never used

In `_tree_tab_give()` there is a check to see if a node being moved needs to
be re parented. That used to use `is not oldroot` and I changed it in
c2bc549605a3c to be `parent.uid in uid_map`, eg is this a child node of the
tree being moved. Now we don't need oldroot anymore but I forgot to clean it
up.

PS: not sure why that check is so complicated. Won't it only ever be false for
the top node being moved? So we can just say `if node !=
current_widget.node:`? I guess that's irrelevant if that's all going to be
re-written anyhow.

qutebrowser/mainwindow/treetabbedbrowser.py:83:1: D202 No blank lines allowed after function docstring

qutebrowser/mainwindow/treetabwidget.py:77:22: C419 Unnecessary list comprehension passed to all() prevents short-circuiting - rewrite as a generator.

qutebrowser/mainwindow/treetabwidget.py:78:13: C1804: "self.widget(idx).url().toString() == ''" can be simplified to "not self.widget(idx).url().toString()", if it is striclty a string, as an empty string is falsey (use-implicit-booleaness-not-comparison-to-string)

qutebrowser/mainwindow/treetabwidget.py:132:16: R5501: Consider using "elif" instead of "else" then "if" to remove one indentation level (else-if-used)

Ran out of energy at the double negative. Hope that's okay.

qutebrowser/mainwindow/treetabbedbrowser.py:131:35: W0613: Unused argument 'idx' (unused-argument)

Add an unused-argument ignore line because, while we aren't using index (tab
undo entries remember their parents instead of their index) I think we'll be
pulling this method up to the parent class later which does use it.

qutebrowser/mainwindow/treetabbedbrowser.py:198:4: W0237: Parameter 'idx' has been renamed to 'sibling' in overriding 'TreeTabbedBrowser.tabopen' method (arguments-renamed)

Urghgh, I have no idea why this would be like this. I looked through the
codebase both for `sibling` and `tabopen` and didn't see this being called
with positional arguments beyond the url. So seems safe to change it.

Probably some linter will be complaining that it still doesn't match the
signature of the parent...

qutebrowser/mainwindow/treetabbedbrowser.py:19:0: W0611: Unused log imported from qutebrowser.utils (unused-import)
qutebrowser/mainwindow/treetabbedbrowser.py:214:0: I0021: Useless suppression of 'arguments-differ' (useless-suppression)

And I guess this is the complaint about the arguments differing. But it says we
don't need the suppression anymore? We'll, I'll add it to the parent and see
what that does.

qutebrowser/misc/notree.py:60:4: C0103: Class constant name "PRE" doesn't conform to snake_case naming style (invalid-name)
qutebrowser/misc/notree.py:61:4: C0103: Class constant name "POST" doesn't conform to snake_case naming style (invalid-name)
qutebrowser/misc/notree.py:62:4: C0103: Class constant name "POST_R" doesn't conform to snake_case naming style (invalid-name)

I assume these are copied from anytree. Not a huge fan, why are the variables
names so much less readable than the values?

qutebrowser/misc/notree.py:221:16: R5501: Consider using "elif" instead of "else" then "if" to remove one indentation level (else-if-used)

qutebrowser/misc/notree.py:289:12: W0719: Raising too general exception: Exception (broad-exception-raised)

`promote()` is only called from one place in commands.py currently. So we are
essentially validating config, so this error "shouldn't happen". If this was
going to be called from more places we should probably make an enum in notree
and maybe generate the config from that? Or validate it against the config (in
a test?) or something.

qutebrowser/misc/notree.py:256:4: W0238: Unused private member `Node.__add_child(self, node: 'Node[T]')` (unused-private-member)
qutebrowser/misc/notree.py:260:4: W0238: Unused private member `Node.__disown(self, value: 'Node[T]')` (unused-private-member)
qutebrowser/misc/notree.py:190:12: W0238: Unused private member `Node.__modified` (unused-private-member)

I assume these are copied from anytree. The internet says variables with two
leading underscores are mangled by the interpreter to be
`__classname__variable` so that you don't have to worry about child and parent
classes fighting over variable names.

We don't have any examples of this pattern in the codebase currently and this
Node class seems designed for composition, not inheritance. So I think I would
prefer to change them to have a single underscore. That seems like something
that people might want to discuss though, so for now silence pylint as it's
presumably comparing some mangled vs unmangled name (eg if I rename them it's
happy).

qutebrowser/misc/notree.py:68:0: I0021: Useless suppression of 'invalid-name' (useless-suppression)

5 files changed, 45 insertions, 37 deletions

diff --git a/qutebrowser/browser/commands.py b/qutebrowser/browser/commands.py
index d7212d6ce..6784f0c1d 100644
--- a/qutebrowser/browser/commands.py
+++ b/qutebrowser/browser/commands.py
@@ -496,7 +496,6 @@ class CommandDispatcher:
 
         # second pass: copy tree structure over
         newroot = tabbed_browser.widget.tree_root
-        oldroot = self._tabbed_browser.widget.tree_root
         for node in traversed:
             if node.parent.uid in uid_map:
                 uid = uid_map[node.uid]
diff --git a/qutebrowser/mainwindow/tabbedbrowser.py b/qutebrowser/mainwindow/tabbedbrowser.py
index 89b43285d..c07b9e1ad 100644
--- a/qutebrowser/mainwindow/tabbedbrowser.py
+++ b/qutebrowser/mainwindow/tabbedbrowser.py
@@ -616,6 +616,7 @@ class TabbedBrowser(QWidget):
             background: bool = None,
             related: bool = True,
             idx: int = None,
+            sibling: bool = False,  # pylint: disable=unused-argument
     ) -> browsertab.AbstractTab:
         """Open a new tab with a given URL.
 
diff --git a/qutebrowser/mainwindow/treetabbedbrowser.py b/qutebrowser/mainwindow/treetabbedbrowser.py
index 5e2f796f1..75a3c55f8 100644
--- a/qutebrowser/mainwindow/treetabbedbrowser.py
+++ b/qutebrowser/mainwindow/treetabbedbrowser.py
@@ -16,7 +16,6 @@ from qutebrowser.mainwindow.tabbedbrowser import TabbedBrowser
 from qutebrowser.mainwindow.treetabwidget import TreeTabWidget
 from qutebrowser.browser import browsertab
 from qutebrowser.misc import notree
-from qutebrowser.utils import log
 
 
 @dataclasses.dataclass
@@ -81,7 +80,6 @@ class TreeTabbedBrowser(TabbedBrowser):
 
     def _remove_tab(self, tab, *, add_undo=True, new_undo=True, crashed=False):
         """Handle children positioning after a tab is removed."""
-
         if not tab.url().isEmpty() and tab.url().isValid() and add_undo:
             idx = self.widget.indexOf(tab)
             self._add_undo_entry(tab, idx, new_undo)
@@ -128,7 +126,12 @@ class TreeTabbedBrowser(TabbedBrowser):
 
         self.widget.tree_tab_update()
 
-    def _add_undo_entry(self, tab, idx, new_undo):
+    def _add_undo_entry(
+        self,
+        tab,
+        idx,  # pylint: disable=unused-argument
+        new_undo,
+    ):
         """Save undo entry with tree information.
 
         This function was removed in tabbedbrowser, but it is still useful here because
@@ -199,8 +202,8 @@ class TreeTabbedBrowser(TabbedBrowser):
             self, url: QUrl = None,
             background: bool = None,
             related: bool = True,
-            sibling: bool = False,
             idx: int = None,
+            sibling: bool = False,
     ) -> browsertab.AbstractTab:
         """Open a new tab with a given url.
 
@@ -211,7 +214,6 @@ class TreeTabbedBrowser(TabbedBrowser):
                      focused tab.  Follows `tabs.new_position.tree.sibling`.
 
         """
-        # pylint: disable=arguments-differ
         # we save this now because super.tabopen also resets the focus
         cur_tab = self.widget.currentWidget()
         tab = super().tabopen(url, background, related, idx)
diff --git a/qutebrowser/mainwindow/treetabwidget.py b/qutebrowser/mainwindow/treetabwidget.py
index 082b7a079..92e18ae77 100644
--- a/qutebrowser/mainwindow/treetabwidget.py
+++ b/qutebrowser/mainwindow/treetabwidget.py
@@ -75,7 +75,7 @@ class TreeTabWidget(TabWidget):
         # empty_urls here is a proxy for "there is a session being loaded into
         # this window"
         empty_urls = all(
-            [self.widget(idx).url().toString() == "" for idx in range(self.count())]
+            not self.widget(idx).url().toString() for idx in range(self.count())
         )
         if empty_urls and is_hidden:
             # All tabs will be added to the tab widget during session load
@@ -121,24 +121,25 @@ class TreeTabWidget(TabWidget):
         for node in self.tree_root.traverse():
             if node.value is None:
                 continue
-            if any(ancestor.collapsed for ancestor in node.path[:-1]):
-                if self.indexOf(node.value) != -1:
-                    # node should be hidden but is shown
-                    cur_tab = node.value
-                    idx = self.indexOf(cur_tab)
-                    if idx != -1:
-                        self.removeTab(idx)
-            else:
-                if self.indexOf(node.value) == -1:
-                    # node should be shown but is hidden
-                    parent = node.parent
-                    tab = node.value
-                    name = tab.title()
-                    icon = tab.icon()
-                    if node.parent is not None:
-                        parent_idx = self.indexOf(node.parent.value)
-                    self.insertTab(parent_idx + 1, tab, icon, name)
-                    tab.node.parent = parent  # insertTab resets node
+
+            should_be_hidden = any(ancestor.collapsed for ancestor in node.path[:-1])
+            is_shown = self.indexOf(node.value) != -1
+            if should_be_hidden and is_shown:
+                # node should be hidden but is shown
+                cur_tab = node.value
+                idx = self.indexOf(cur_tab)
+                if idx != -1:
+                    self.removeTab(idx)
+            elif not should_be_hidden and not is_shown:
+                # node should be shown but is hidden
+                parent = node.parent
+                tab = node.value
+                name = tab.title()
+                icon = tab.icon()
+                if node.parent is not None:
+                    parent_idx = self.indexOf(node.parent.value)
+                self.insertTab(parent_idx + 1, tab, icon, name)
+                tab.node.parent = parent  # insertTab resets node
 
     def tree_tab_update(self):
         """Update titles and positions."""
diff --git a/qutebrowser/misc/notree.py b/qutebrowser/misc/notree.py
index 297673bfb..e12a8bf3f 100644
--- a/qutebrowser/misc/notree.py
+++ b/qutebrowser/misc/notree.py
@@ -57,15 +57,15 @@ class TraverseOrder(enum.Enum):
         POST_R: post-order-reverse: like POST but rightmost nodes first.
     """
 
-    PRE = 'pre-order'
-    POST = 'post-order'
-    POST_R = 'post-order-reverse'
+    PRE = 'pre-order'  # pylint: disable=invalid-name
+    POST = 'post-order'  # pylint: disable=invalid-name
+    POST_R = 'post-order-reverse'  # pylint: disable=invalid-name
 
 
 uid_gen = itertools.count(0)
 
 # generic type of value held by Node
-T = TypeVar('T')  # pylint: disable=invalid-name
+T = TypeVar('T')
 
 
 class Node(Generic[T]):
@@ -187,7 +187,7 @@ class Node(Generic[T]):
     def __set_modified(self) -> None:
         """If self is modified, every ancestor is modified as well."""
         for node in self.path:
-            node.__modified = True  # pylint: disable=protected-access
+            node.__modified = True  # pylint: disable=protected-access,unused-private-member
 
     def render(self) -> List[Tuple[str, 'Node[T]']]:
         """Render a tree with ascii symbols.
@@ -217,11 +217,10 @@ class Node(Generic[T]):
                     result += [subtree[0]]
                 else:
                     result += subtree
+            elif child is self.children[-1]:
+                result.append((CORNER, child))
             else:
-                if child is self.children[-1]:
-                    result.append((CORNER, child))
-                else:
-                    result.append((INTERSECTION, child))
+                result.append((INTERSECTION, child))
         self.__modified = False
         self.__rendered = list(result)
         return list(result)
@@ -253,11 +252,17 @@ class Node(Generic[T]):
         if order in [TraverseOrder.POST, TraverseOrder.POST_R]:
             yield self
 
-    def __add_child(self, node: 'Node[T]') -> None:
+    def __add_child(  # pylint: disable=unused-private-member
+        self,
+        node: 'Node[T]',
+    ) -> None:
         if node not in self.__children:
             self.__children.append(node)
 
-    def __disown(self, value: 'Node[T]') -> None:
+    def __disown(  # pylint: disable=unused-private-member
+        self,
+        value: 'Node[T]',
+    ) -> None:
         self.__set_modified()
         if value in self.__children:
             self.__children.remove(value)
@@ -286,7 +291,7 @@ class Node(Generic[T]):
 
         """
         if to not in ['first', 'last', 'next', 'prev']:
-            raise Exception("Invalid value supplied for 'to': " + to)
+            raise ValueError("Invalid value supplied for 'to': " + to)
         position = {'first': 0, 'last': -1}.get(to, None)
         diff = {'next': 1, 'prev': 0}.get(to, 1)
         count = times