Are glimmer components currently supported in routes?
I’m guessing that the answer is “no” for Discourse, but would be pleased to learn otherwise.
Yes you can use .gjs files for route templates in Discourse right now. In fact, we just converted a whole load of them today in core! Check out https://github.com/discourse/discourse/tree/main/app/assets/javascripts/discourse/app/templates for examples.
“someone” is Discourse - we sponsored the development of ember-route-template, and it’s in our GitHub organisation 
We’re not on the latest Ember 6.x yet, but we use that addon to enable the functionality.
Oh beautiful! Thanks for the quick reply!
Haha, I didn’t even see it was in the Discourse github. Good point. 
Adding a new route to the app I found to be very non-obvious. I will document here for others.
I wanted to add a /print route at the root.
The final code that worked for me was as follows. county-fence is my plugin name, so replace that with your own.
assets/javascripts/discourse/routes/county-fence-route-map.js.es6
export default function() {
this.route('print', { path: '/print' });
}
assets/javascripts/discourse/routes/print.js
import Route from "@ember/routing/route";
export default class PrintRoute extends Route {
model() {
return { message: "This is a custom print page!" };
}
}
assets/javascripts/discourse/templates/print.gjs
import RouteTemplate from "ember-route-template";
import ...;
export default RouteTemplate(
<template>
...
</template>
)
plugin.rb
after_initialize do
require_relative "app/controllers/print_controller"
end
app/controllers/print_controller.rb
# frozen_string_literal: true
# HTTP Status codes: https://github.com/discourse/discourse/blob/main/lib/discourse.rb
class ::CountyFence::PrintController < ::ApplicationController
requires_plugin CountyFence::PLUGIN_NAME
def save_print
end
def list_prints
render json: { name: "donut", description: "delicious!" }
end
def get_print
end
end
Discourse::Application.routes.append do
post "/print" => "county_fence/print#save_print"
get "/print" => "county_fence/print#list_prints"
get "/print/:id" => "county_fence/print#get_print"
end
Is there a way I can get a blank page without the layout, navbars, or any CSS of the site? I want to use the Glimmer component, but none of the website styles are helpful in terms of producing a print page.
If its just styling for an actually printed page, and you don’t mind the navbar and extra stuff when viewing the page, you can use @media print CSS selector to change the styling when printing. Discourse already hides a lot of things during print (discourse/app/assets/stylesheets/common/printer-friendly.scss at main · discourse/discourse · GitHub). You can preview the page using print media simulation mode in firefox’s inspect mode. There should be an equivalent feature in chrome’s inspect mode.
If you need a complete blank canvas to work with, not just in the print mode but also in normal web browsing, you can use a bit of CSS trickery.
Suppose your glimmer component has a root div with id="print-component__root", we can let CSS check for its existence with a :has() selector (or just add/remove a class to body from the glimmer component lifecycle), and selectively apply styling.
body:has(#print-component__root) {
header,
.avatar,
.sidebar-wrapper,
... {
all: unset !important; // all: unset might be a bit too aggressive
display: none !important;
}
}
#print-component__root {
// normal styling
}
There might be a better, cleaner way that would actually remove the DOM elements, but the CSS is a good workaround to reset everything.
My SCSS isn’t loading. Any ideas? I set up my files per the chat plugin in core.
I have in plugins.rb:
register_asset "stylesheets/common/index.scss"
In assets/stylesheets/common/index.scss:
@import "common";
In assets/stylesheets/common/common.scss:
body:has(#print-root) {
header,
.avatar,
.sidebar-wrapper {
all: unset; // all: unset might be a bit too aggressive
display: none !important;
}
}
Just to make sure the issue is with loading the SCSS and not an issue with style rule I gave you, try adding a style without the :has() selector. Something like:
.sidebar-wrapper {
outline: 5px solid red;
}
I would also try restarting your rails server. I’ve had issues in the past where adding/removing register_asset calls would require me to do a full docker container reboot.
:has() selector.index.scss to verify it’s not the @import statementd/rake assets:clobber tmp:clear and d/rails sNothing so far is getting it to load.
Most other files cause an auto-reload in the browser. This one isn’t doing that. So I think that register_asset may be where the problem lies. I think register asset automatically looks in the assets folder? All of the examples I’m looking at indicate this is the case.
d/rails c and DiscoursePluginRegistry.stylesheets reveals:
"county-fence"=>#<Set: {"/src/plugins/county-fence/assets/stylesheets/common/index.scss"}>
So something is happening. ^^
I found in the d/rails s logs: No such file or directory @ rb_sysopen - /src/app/assets/stylesheets/plugin-cf.scss.
So even though the plugin is symlinked into the /plugins folder as county-fence, and my plugin is explicitly named county-fence in plugins.rb, some code is reading the underlying directory name plugin-cf and making assumptions about what the compiled CSS name for my plugin is.
Is this a bug or a feature? 
I think the moral of this story is do not under any circumstances name your plugin directory anything except the matching name of your plugin. A symlink named correctly is not sufficient.
EDIT: also register_asset "stylesheets/common/index.scss", plugin: "county-fence" is a workaround that forces the plugin name to be set correctly.