awful.tag: Delete a screen's tag on removal

Any clients with these tags end up somewhere random (the first tag on the first
remaining screen). This certainly can be improved in the future, but at least
this is a start.

Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/awful/tag.lua

@@ -1352,11 +1352,35 @@ capi.tag.add_signal("property::urgent")
 
 capi.tag.add_signal("property::urgent_count")
 capi.tag.add_signal("property::volatile")
+capi.tag.add_signal("removal-pending")
 
 capi.screen.add_signal("tag::history::update")
 
 capi.screen.connect_signal("tag::history::update", tag.history.update)
 
+capi.screen.connect_signal("removed", function(s)
+    -- First give other code a chance to clean up
+    for _, t in pairs(s.tags) do
+        t:emit_signal("removal-pending")
+    end
+    -- Then force all clients left to go somewhere random
+    local fallback = nil
+    for other_screen in capi.screen do
+        if #other_screen.tags > 0 then
+            fallback = other_screen.tags[1]
+            break
+        end
+    end
+    for _, t in pairs(s.tags) do
+        t:delete(fallback, true)
+    end
+    -- If any tag survived until now, forcefully get rid of it
+    for _, t in pairs(s.tags) do
+        t.activated = false
+        data.tags[t] = nil
+    end
+end)
+
 function tag.mt:__call(...)
     return tag.new(...)
 end

tests/examples/shims/screen.lua

@@ -100,6 +100,8 @@ end
 screen._add_screen {width=320, height=240}
 
 screen.add_signal("property::workarea")
+screen.add_signal("added")
+screen.add_signal("removed")
 
 return screen