`layoutComponentImprovements` feature flag not working in dev bundles

[sissbruecker]

Description

When using a dev bundle, either the default one or a custom one, then the layoutComponentImprovements feature flag does not work in that the styles that it should define are not added to the page.

Looks like the logic here doesn't work for some reason:

web-components/packages/vertical-layout/src/styles/vaadin-vertical-layout-core-styles.js

Lines 34 to 50 in 7619a45

	// Layout improvements are part of a feature for Flow users where children that have been configured to use full size
	// using `HasSize.setSizeFull()` and others, get additional styles so that they effectively take the remaining space in
	// the layout, rather than explicitly use 100% width/height. The respective data attributes are set by Flow's `HasSize`
	// class.
	const enableLayoutImprovements = window.Vaadin.featureFlags.layoutComponentImprovements;
	const layoutImprovementStyles = css`
	::slotted([data-height-full]) {
	flex: 1;
	}
	::slotted(vaadin-horizontal-layout[data-height-full]),
	::slotted(vaadin-vertical-layout[data-height-full]) {
	min-height: 0;
	}
	`;
	export const verticalLayoutStyles = enableLayoutImprovements ? [baseStyles, layoutImprovementStyles] : [baseStyles];

It does work in production bundles, and when using vaadin.frontend.hotdeploy=true.

Expected outcome

The styles for the feature should be defined, regardless whether you use a dev bundle or not.

Minimal reproducible example

Example project: project.zip

Steps to reproduce

1. Start the project
2. Verify that the style rule above is not applied to the nested layout
3. Enable vaadin.frontend.hotdeploy in application properties, restart
4. Verify that the style rule above is now applied to the nested layout

Environment

Vaadin version(s): 24.8

Browsers

No response

[sissbruecker]

The feature flags aren't yet loaded / defined in the browser when the style module is evaluated, but are at some later point. Looks like a Flow issue, this seems to be related: vaadin/flow#20991

[rolfsmeds]

As vaadin/flow#20991 has been fixed, is this a related but separate issue?

[sissbruecker]

Not sure, but vaadin/flow#20991 was fixed before discovering this. So whatever it did isn't effective for this specific feature flag.