How to get width and height of widget after it's been drawn in awesome?

So this is the scenario: Let's say I have a textbox that I want to place exactly at the right-hand side of the screen, but STILL letting the textbox retain its own dimensions. In other words, I want to just specify the font, let the textbox pick the right dimensions and then place it at the edge of the screen. It'd be really easy if I knew the dimensions, since then I can do

local awful = require("awful")
local wibox = require("wibox")

local text_widget = wibox.widget({
    widget = wibox.widget.textbox,
    font = "Roboto Medium 15",
    text = "hello world",
})

local rightmost_place = wibox.widget({
    layout = wibox.layout.manual,
    {
        text_widget,
        point = {
            y = 0, 
            -- You can't actually do the `text_widget.geometry.width`
            x = awful.screen.focused().geometry.width
                - text_widget.geometry.width
        },
        -- We're not setting these so the textbox
        -- will get its size automatically
        -- forced_width = 
        -- forced_height = 
    },
})

So this way, whenever I were to type something in, the textbox will get bigger, but it would automatically reposition itself according to the x coordinate.

Also, this is not just about textboxes. I've had the same problem with other widgets, so my question is: is there some way to let the widgets get the dimensions that they prefer, but still get their geometry to reposition them where you'd like?

Solution

The issue is that widgets can be placed in multiple location (with multiple size) at the same time. This is useful for some case like the textclock to have a single instance (with a single timer) for all screens. This makes getting the size a bit tricky. If you don't plan to use the widget in multiple location, you can cheat and add the width/height properties.

-- in the declarative syntax, add an `id`
id = `id_of_the_widget_with_size`,

-- Get the widget (somewhere outside of the declarative section)
local w = rightmost_place:get_children_by_id("id_of_the_widget_with_size")[1]
w._real_draw = w.draw
w.draw = function(self, context, cr, width, height)
    self.width, self.height = width, height
    w._real_draw(self, context, cr, width, height)
end

Now, in theory, the widget will have a width and height property.