client: Simplify screen selection decision tree.

This commit remove the `awful.tag` "manage" hook. The relevant
code has been moved to ewmh.lua request::tag handler. The handler
is called either by a volontary screen change or by a forced one.

It also require the awful.rules to be executed. This is done by
default and the user would have to explicitly disable that
behavior. From now on, disabling the rules require the user to
handle tag selection.

Fixes #1028 #1052

lib/awful/ewmh.lua

@@ -122,20 +122,41 @@ function ewmh.activate(c, context, hints) -- luacheck: no unused args
     end
 end
 
+-- Get tags that are on the same screen as the client. This should _almost_
+-- always return the same content as c:tags().
+local function get_valid_tags(c, s)
+    local tags, new_tags = c:tags(), {}
+
+    for _, t in ipairs(tags) do
+        if screen[s] == t.screen then
+            table.insert(new_tags, t)
+        end
+    end
+
+    return new_tags
+end
+
 --- Tag a window with its requested tag.
 --
 -- It is the default signal handler for `request::tag` on a `client`.
 --
 -- @signalhandler awful.ewmh.tag
 -- @client c A client to tag
--- @tag[opt] t A tag to use. If omitted, then the client is made sticky.
+-- @tparam[opt] tag|boolean t A tag to use. If true, then the client is made sticky.
 -- @tparam[opt={}] table hints Extra information
 function ewmh.tag(c, t, hints) --luacheck: no unused
     -- There is nothing to do
-    if not t and #c:tags() > 0 then return end
+    if not t and #get_valid_tags(c, c.screen) > 0 then return end
 
     if not t then
+        if c.transient_for then
+            c.screen = c.transient_for.screen
+            if not c.sticky then
+                c:tags(c.transient_for:tags())
+            end
+        else
             c:to_selected_tags()
+        end
     elseif type(t) == "boolean" and t then
         c.sticky = true
     else

lib/awful/tag.lua

@@ -12,6 +12,7 @@ local util = require("awful.util")
 local ascreen = require("awful.screen")
 local beautiful = require("beautiful")
 local object = require("gears.object")
+local timer = require("gears.timer")
 local pairs = pairs
 local ipairs = ipairs
 local table = table
@@ -1277,21 +1278,25 @@ function tag.attached_connect_signal(screen, ...)
 end
 
 -- Register standard signals.
-capi.client.connect_signal("manage", function(c)
-    -- If we are not managing this application at startup,
-    -- move it to the screen where the mouse is.
-    -- We only do it for "normal" windows (i.e. no dock, etc).
-    if not awesome.startup and c.type ~= "desktop" and c.type ~= "dock" then
-        if c.transient_for then
-            c.screen = c.transient_for.screen
-            if not c.sticky then
-                c:tags(c.transient_for:tags())
-            end
-        else
-            c.screen = ascreen.focused()
+capi.client.connect_signal("property::screen", function(c)
+    -- First, the delayed timer is necessary to avoid a race condition with
+    -- awful.rules. It is also messing up the tags before the user have a chance
+    -- to set them manually.
+    timer.delayed_call(function()
+        local tags, new_tags = c:tags(), {}
+
+        for _, t in ipairs(tags) do
+            if t.screen == c.screen then
+                table.insert(new_tags, t)
             end
         end
-    c:connect_signal("property::screen", function() c:to_selected_tags() end)
+
+        if #new_tags == 0 then
+            c:emit_signal("request::tag", nil, {reason="screen"})
+        elseif #new_tags < #tags then
+            c:tags(new_tags)
+        end
+    end)
 end)
 
 -- Keep track of the number of urgent clients.