Today, a setting can declare that its validity depends on the values of other
related settings. However, the validity of a setting is not always checked
against the correct values of its dependent settings because those settings'
correct values may not be available when the validator runs.
This commit separates the validation of a settings updates into two phases,
with separate methods on the `Setting.Validator` interface. In the first phase
the setting's validity is checked in isolation, and in the second phase it is
checked again against the values of its related settings. Most settings only
use the first phase, and only the few settings with dependencies make use of
the second phase.
This pull request replaces the jvm-example plugin (from the jvm/site plugins era) by two new plugins: a custom-settings that shows how to register and use custom settings (including secured settings) in a plugin, and rest-handler plugin that shows how to register a rest handler.
The two plugins now reside in the plugins/examples project. They can serve as sample plugins for users, a special attention has been put on documentation. The packaging tests have been adapted to use the custom-settings plugin.
Christophe Bismuth
Tanguy Leroux