Add request::focus signal, with ewmh.focus being the default handler

This still does `client.focus = c` by default, but allows to customize
it.

This was initially suggested in #194, but by using `request::activate`
instead, which would not be the same.  Therefore a new signal is being
used instead.

Helped-by: Samir Benmendil <samir.benmendil@gmail.com>

lib/awful/client.lua

@@ -71,7 +71,7 @@ function client.jumpto(c, merge)
     end
 
     -- focus the client
-    capi.client.focus = c
+    c:emit_signal("request::focus", "client.jumpto")
     c:raise()
 end
 
@@ -213,7 +213,9 @@ function client.focus.history.previous()
         s = capi.mouse.screen
     end
     local c = client.focus.history.get(s, 1)
-    if c then capi.client.focus = c end
+    if c then
+        c:emit_signal("request::focus", "client.focus.history.previous")
+    end
 end
 
 --- Get visible clients from a screen.
@@ -303,7 +305,7 @@ function client.focus.bydirection(dir, c)
 
         -- If we found a client to focus, then do it.
         if target then
-            capi.client.focus = cltbl[target]
+            cltbl[target]:emit_signal("request::focus", "client.focus.bydirection")
         end
     end
 end
@@ -335,7 +337,7 @@ function client.focus.global_bydirection(dir, c)
             local target = util.get_rectangle_in_direction(dir, geomtbl, capi.screen[scr].geometry)
 
             if target then
-                capi.client.focus = cltbl[target]
+                cltbl[target]:emit_signal("request::focus", "client.focus.global_bydirection")
             end
         end
     end
@@ -348,7 +350,7 @@ end
 function client.focus.byidx(i, c)
     local target = client.next(i, c)
     if target then
-        capi.client.focus = target
+        target:emit_signal("request::focus", "client.focus.byidx")
     end
 end
 
@@ -403,7 +405,7 @@ function client.swap.global_bydirection(dir, c)
         end
 
         screen.focus(sel.screen)
-        capi.client.focus = sel
+        sel:emit_signal("request::focus", "client.swap.global_bydirection")
     end
 end
 

lib/awful/ewmh.lua

@@ -165,6 +165,14 @@ function ewmh.activate(c)
     end
 end
 
+--- Focus a window.
+--
+-- @client c The client.
+-- @tparam string context The context where this signal was used.
+function ewmh.focus(c, context)
+    client.focus = c
+end
+
 --- Tag a window with its requested tag
 --
 -- @client c A client to tag
@@ -185,6 +193,7 @@ function ewmh.urgent(c, urgent)
 end
 
 client.connect_signal("request::activate", ewmh.activate)
+client.connect_signal("request::focus", ewmh.focus)
 client.connect_signal("request::tag", ewmh.tag)
 client.connect_signal("request::urgent", ewmh.urgent)
 client.connect_signal("request::maximized_horizontal", maximized_horizontal)

lib/awful/layout/init.lua

@@ -178,7 +178,9 @@ local function arrange_on_tagged(c, tag)
     layout.arrange(tag.screen)
     if not capi.client.focus or not capi.client.focus:isvisible() then
         local c = client.focus.history.get(tag.screen, 0)
-        if c then capi.client.focus = c end
+        if c then
+            c:emit_signal("request::focus", "layout.arrange_on_tagged")
+        end
     end
 end
 local function arrange_tag(t)

lib/awful/menu.lua

@@ -476,7 +476,7 @@ function menu.clients(args, item_args)
                 if not c:isvisible() then
                     tags.viewmore(c:tags(), c.screen)
                 end
-                capi.client.focus = c
+                c:emit_signal("request::focus", "menu.clients")
                 c:raise()
             end,
             c.icon }

lib/awful/screen.lua

@@ -66,7 +66,9 @@ function screen.focus(_screen)
     capi.mouse.coords(pos, true)
 
     local c = client.focus.history.get(_screen, 0)
-    if c then capi.client.focus = c end
+    if c then
+        c:emit_signal("request::focus", "screen.focus")
+    end
 end
 
 --- Give the focus to a screen, and move pointer, by physical position relative to current screen.