naughty: Improve the rendering of notifications with invalid markup.

Some case like `foo<b>bar` still fail, but at least `foo<<<>>>bar`
works.

Fix #3022

lib/naughty/widget/_markup.lua

@@ -0,0 +1,62 @@
+local beautiful = require("beautiful")
+
+local module = {}
+
+-- Since some escaping needs to be undone, we have to escape the escaped <>.
+local pre_escape = {["&lt;"] = "&zzlt;", ["&gt;"] = "&zzgt;"}
+
+local escape_pattern = "[<>&]"
+local escape_subs    = { ['<'] = "&lt;", ['>'] = "&gt;", ['&'] = "&amp;" }
+
+-- Also reverse escaping some allowed tags because people actually use them.
+local escape_undo = {['&lt;span '] = "<span "}
+
+for _, allowed in ipairs {'b', 'i', 'u', 'span'} do
+    escape_undo['&lt;' ..allowed..'&gt;'] = "<" ..allowed..">"
+    escape_undo['&lt;/'..allowed..'&gt;'] = "</"..allowed..">"
+end
+
+-- Best effort attempt to allow a subset of pango markup in the text while
+-- removing invalid content. If invalid content is present, nothing is
+-- displayed.
+local function escape_text(text)
+    -- Take care of the already escaped content.
+    for pattern, subs in pairs(pre_escape) do
+        text = text:gsub(pattern, subs)
+    end
+
+    -- Try to set the text while only interpreting <br>.
+    text = text:gsub("<br[ /]*>", "\n")
+
+    -- Since the title cannot contain markup, it must be escaped first so that
+    -- it is not interpreted by Pango later.
+    text = text:gsub(escape_pattern, escape_subs)
+
+    -- Restore a subset of markup tags.
+    for pattern, subs in pairs(escape_undo) do
+        text = text:gsub(pattern, subs)
+    end
+
+    -- Restore pre-escaped content.
+    for subs, pattern in pairs(pre_escape) do
+        text = text:gsub(pattern, subs)
+    end
+
+    return text
+end
+
+function module.set_markup(wdg, text, fg, font)
+    local ret = escape_text(text or "")
+    fg = fg or beautiful.notification_fg
+
+    wdg:set_font(font or beautiful.notification_font)
+
+    if fg then
+        ret = "<span color='" .. fg .. "'>" .. ret .. "</span>"
+    end
+
+    wdg:set_markup_silently(ret)
+    return ret
+end
+
+return module

lib/naughty/widget/message.lua

@@ -17,22 +17,10 @@
 local textbox = require("wibox.widget.textbox")
 local gtable  = require("gears.table")
 local beautiful = require("beautiful")
+local markup  = require("naughty.widget._markup").set_markup
 
 local message = {}
 
-local function markup(notif, wdg)
-    local ret = notif.message or ""
-    local fg = notif.fg or beautiful.notification_fg
-
-    wdg:set_font(notif.font or beautiful.notification_font)
-
-    if fg then
-        ret = "<span color='" .. fg .. "'>" .. ret .. "</span>"
-    end
-
-    return ret
-end
-
 --- The attached notification.
 -- @property notification
 -- @tparam naughty.notification notification
@@ -48,7 +36,7 @@ function message:set_notification(notif)
             self._private.message_changed_callback)
     end
 
-    self:set_markup(markup(notif, self))
+    markup(self, notif.message, notif.fg, notif.font)
 
     self._private.notification = notif
 
@@ -73,7 +61,12 @@ local function new(args)
     gtable.crush(tb, message, true)
 
     function tb._private.message_changed_callback()
-        tb:set_markup(markup(tb._private.notification, tb))
+        markup(
+            tb,
+            tb._private.notification.message,
+            tb._private.notification.fg,
+            tb._private.notification.font
+        )
     end
 
     if args.notification then

lib/naughty/widget/title.lua

@@ -17,22 +17,10 @@
 local textbox = require("wibox.widget.textbox")
 local gtable  = require("gears.table")
 local beautiful = require("beautiful")
+local markup  = require("naughty.widget._markup").set_markup
 
 local title = {}
 
-local function markup(notif, wdg)
-    local ret = "<b>"..(notif.title or "").."</b>"
-    local fg = notif.fg or beautiful.notification_fg
-
-    wdg:set_font(notif.font or beautiful.notification_font)
-
-    if fg then
-        ret = "<span color='" .. fg .. "'>" .. ret .. "</span>"
-    end
-
-    return ret
-end
-
 --- The attached notification.
 -- @property notification
 -- @tparam naughty.notification notification
@@ -48,7 +36,7 @@ function title:set_notification(notif)
             self._private.title_changed_callback)
     end
 
-    self:set_markup(markup(notif, self))
+    markup(self, notif.title, notif.fg, notif.font)
 
     self._private.notification = notif
     self._private.title_changed_callback()
@@ -74,7 +62,12 @@ local function new(args)
     gtable.crush(tb, title, true)
 
     function tb._private.title_changed_callback()
-        tb:set_markup(markup(tb._private.notification, tb))
+        markup(
+            tb,
+            tb._private.notification.title,
+            tb._private.notification.fg,
+            tb._private.notification.font
+        )
     end
 
     if args.notification then