Changing filter plugin settings before they are saved

Question

(This is for D8, although parts of this filter settings API were already in D7.)

As far as I understand, a filter plugin exposes its settings solely with FilterBase::settingsForm() - the central architecture then automatically stores the submitted form values and loads them when creating the plugin instance, so that a filter plugin can find them in $this->settings.

I'd like to reorganize and clean up the submitted form values before they're stored, but I'm not sure where to intercept the form. Should I attach a #validate or a #submit? If the latter, how do I ensure that my #submit runs before FilterFormatInterface::submitForm()?

Answer 1

It looks like your only options right now are relying on generic form API features, like #process and #value_callback. FilterFormatFormBase doesn't call into the plugins for validate/submit, like we do for example for block plugins.

Answer 2

My new approach reverses the situation. Apparently I can't alter the structure of the values after the form is built - but I can change how the form is presented.

So instead of building the form in the user-friendly structure A and then failing to convert the values to developer-friendly structure B, I'll build a form as B and use a #theme hook to render it as A.