This commit improves the file system configuration step's error handling
by performing validation only when the next button is clicked. This
allows an invalid state to temporarily exist while the user is modifying
the mountpoints without bothersome error messages needlessly appearing.
Broadly speaking there were two options for the implementation: (1)
delay the validation, performing validation only upon clicking the next
button -or- (2) perform validation immediately as normal but hide error
messages until the next button is clicked. Option (1) proved to be
untenable - Data Driven Forms does provide `pauseValidation()` and
`resumeValidation()` functions from React Final Form which theoretically
would make this option possible... However, we need to call
`resumeValidation()` in the next button's click handler and then
immediately make a decision based on the validation results either to
remain on the step and display the errors or move to the next step.
When we tried implmenting this we found that `resumeValidation()` does
not immediately peform validation - validation only resumes after
exiting the handler. Therefore, this approach was not considered and
option (2) was used.
In order to gain control over the behavior of the next button, custom
buttons are implemented for this step. Sharing state between the custom
buttons and the form was a challenge. With pure React it would have been
as simple as moving the relevant state to the parent component, but that
was not possible due to Data Driven Forms. Instead, state is shared
using the form state. A new property,
`'file-system-config-show-errors'`, in the form state is used to
determine whether or not error messages should be displayed.
In order to cause a re-render upon a change in
`'file-system-config-show-errors'`, the file system configuration
component is wrapped in a `<FormSpy>` component.
Rely on the index matching instead. During a drag, if onDragOver is
fired the index the item will be dragged to (the target index) will be
set. If the target index doesn't match the source index, the new
tempItemOrder is made and the new target index is set.
Initially this index is null, so even if the target index is the
same as the current index, the tempItemOrder and target index will be
set once.
By not shorting this event based on the visual layout, the drag state
gets initialized correctly every time.
Fixes#679
