Add tabs.min_width setting

Controls min width in pixels of non pinned tabs

Closes #3690

qutebrowser/config/configdata.yml

@@ -1406,6 +1406,16 @@ tabs.width:
   desc: "Width (in pixels or as percentage of the window) of the tab bar if
     it's vertical."
 
+tabs.min_width:
+  default: -1
+  type:
+    name: Int
+    minval: -1
+  desc: >-
+    Minimum width (in pixels) of tabs (-1 to use text contents for min width).
+
+    This setting only applies when tabs are horizontal.
+
 tabs.width.indicator:
   renamed: tabs.indicator.width
 

qutebrowser/mainwindow/tabwidget.py

@@ -358,7 +358,8 @@ class TabBar(QTabBar):
         # Clear _minimum_tab_size_hint_helper cache when appropriate
         if option in ["tabs.indicator.padding",
                       "tabs.padding",
-                      "tabs.indicator.width"]:
+                      "tabs.indicator.width",
+                      "tabs.min_width"]:
             self._minimum_tab_size_hint_helper.cache_clear()
 
     def _on_show_switching_delay_changed(self):
@@ -495,13 +496,13 @@ class TabBar(QTabBar):
             # Never consider ellipsis an option for pinned tabs
             ellipsis = False
         return self._minimum_tab_size_hint_helper(self.tabText(index),
-                                                  icon_width,
-                                                  ellipsis)
+                                                  icon_width, ellipsis,
+                                                  pinned)
 
     @functools.lru_cache(maxsize=2**9)
     def _minimum_tab_size_hint_helper(self, tab_text: str,
                                       icon_width: int,
-                                      ellipsis: bool) -> QSize:
+                                      ellipsis: bool, pinned: bool) -> QSize:
         """Helper function to cache tab results.
 
         Config values accessed in here should be added to _on_config_changed to
@@ -526,6 +527,9 @@ class TabBar(QTabBar):
         height = self.fontMetrics().height() + padding_v
         width = (text_width + icon_width +
                  padding_h + indicator_width)
+        min_width = config.val.tabs.min_width
+        if not pinned and not self.vertical and min_width > 0:
+            width = max(min_width, width)
         return QSize(width, height)
 
     def _pinned_statistics(self) -> (int, int):