Track changes in parent theme

[TobiasSagmeister]

Describe your motivation

For Vaadin themes, there is a file called theme.json which has a property parent for the parent theme.
With this property it is possible to achieve inheritance of themes.

In dev mode, only the current theme, not the parent one, is tracked for changes.
Therefore the server has to be restarted on each change in the parent theme.

In our case the themes are located in own modules.

Describe the solution you'd like

The parent theme should be tracked for changes as well.
So no restart of the server is needed.

Describe alternatives you've considered

The default maven way in com.vaadin.base.devserver.ExternalDependencyWatcher is to consider only the maven parent and its child modules. In case there is a child module which has a dependency to another module with resources (e.g. the parent theme), it does not work.

There is an undocumented property called frontend.hotdeploy.dependencies.
It defines a comma-separated list of folders to monitor in com.vaadin.base.devserver.ExternalDependencyWatcher.
With this property it works for such use cases as kind of workaround.

Additional context

This feature request was discussed previously via Vaadin Expert Chat.

[Artur-]

The parent theme is tracked, provided you have a multi module project with the parent and the child theme. But you are saying that your setup is such that you build a jar of the parent theme, copy it somewhere and then you want hot deployment to work?

[TobiasSagmeister]

In com.vaadin.base.devserver.ExternalDependencyWatcher, the parent pom is evaluated for its child modules.
Only these directories are tracked for changes.
But in our case in one of this modules, there is the dependency to the parent theme, which is not considered.

[Artur-]

So what is the project layout like?

[TobiasSagmeister]

Our project structure is like this:

• Parent-Module
  • Parent-Theme-Module
  • Project-Module
    • Project-Server-Module
    • Project-Theme-Module
      • (Dependency to Parent-Theme-Module)

Meanwhile I found a solution for us with the mentioned property.
We load the paths to the resource directories from the class path and set them in the property.

[mshabarov]

A few thoughts for next steps:

1. This parameter is not documented, it makes sense to add it to documentation.
2. For Vite dev server mode and for bundle mode Flow has different implementations for theme changes monitoring, we have to know/test in which mode the above use case doesn't work.
3. Perhaps the direct parent theme is monitored, but not the all hierarchy of parent themes.

@TobiasSagmeister could you please share which mode do you use (Vite dev server or bundle) and what is the Vaadin version?

[TobiasSagmeister]

@mshabarov Sure, we use Vite-Server with Vaadin 24.4.6.