`<LinkTo>` without `@route` param but with `@query` breaks when navigating to error route

[buschtoens]

While working on ember-engines/ember-engines#642 to make ember-engines compatible with Ember Octane, I noticed that #17772 appears to have broken an edge case for <LinkTo> without a @route argument, but with a @query argument.

I made a reproduction here: https://codesandbox.io/s/p32ozvvz0x

If no explicit @route is passed it will be set to (or remain) UNDEFINED:

ember.js/packages/@ember/-internals/glimmer/lib/components/link-to.ts

Lines 895 to 900 in 2cc3573

	// 3. If there is a `route`, it is now at index 0.
	if (params.length === 0) {
	this.set('route', UNDEFINED);
	} else {
	this.set('route', params.shift());
	}

In this case _route returns the currently active route:

ember.js/packages/@ember/-internals/glimmer/lib/components/link-to.ts

Lines 490 to 493 in 2cc3573

	_route: computed('route', '_currentRoute', function computeLinkToComponentRoute(this: any) {
	let { route } = this;
	return route === UNDEFINED ? this._currentRoute : route;
	}),

This then breaks the href computed property in L791, if the router performs an intermediate transition to an error route:

ember.js/packages/@ember/-internals/glimmer/lib/components/link-to.ts

Lines 749 to 804 in 2cc3573

	/**
	Sets the element's `href` attribute to the url for
	the `LinkComponent`'s targeted route.
	If the `LinkComponent`'s `tagName` is changed to a value other
	than `a`, this property will be ignored.
	@property href
	@private
	*/
	href: computed(
	'_currentRouterState',
	'_route',
	'_models',
	'_query',
	'tagName',
	'loading',
	'loadingHref',
	function computeLinkToComponentHref(this: any) {
	if (this.tagName !== 'a') {
	return;
	}
	if (this.loading) {
	return this.loadingHref;
	}
	let { _route: route, _models: models, _query: query, _routing: routing } = this;
	if (DEBUG) {
	/*
	* Unfortunately, to get decent error messages, we need to do this.
	* In some future state we should be able to use a "feature flag"
	* which allows us to strip this without needing to call it twice.
	*
	* if (isDebugBuild()) {
	* // Do the useful debug thing, probably including try/catch.
	* } else {
	* // Do the performant thing.
	* }
	*/
	try {
	return routing.generateURL(route, models, query);
	} catch (e) {
	// tslint:disable-next-line:max-line-length
	assert(
	`You attempted to generate a link for the "${this.route}" route, but did not ` +
	`pass the models required for generating its dynamic segments. ` +
	e.message
	);
	}
	} else {
	return routing.generateURL(route, models, query);
	}
	}
	),

routing.generateURL(route, models, query) is called as:

routing.generateURL("blog.post.error", [], { lang: "Japanese" });

Which misses the error param:

Error: You must provide param `error` to `generate`.

This apparently used to work and while being a weird edge-case, I would still expect it to work.

[rwjblue]

Thank you for reporting!

[rwjblue]

Just to confirm, this is a bug in 3.10.0-beta series right?

[buschtoens]

Correct! AFAICT it's working in 3.9.