Introduce the usage of Module user-displayable exceptions to handle module errors (part 2)

[matks]

Questions	Answers
Branch?	1.7.6.x
Description?	Allow hooked modules to throw a ModuleErrorException or ModuleErrorInterface to display error messages to end-user
Type?	improvement
Category?	BO
BC breaks?	no
Deprecations?	no
Fixed ticket?	Fixes #13490 last issue: "How to handle errors happening inside module (translation + display to user)"
How to test?	See below

How to test

Attached is a demonstration module.
module_for_pr_hook_error.zip

If you install it and test this PR,

• on Add form, if you save you'll see an error message "An unexpected error occurred. [RuntimeException code 0]"
• on Edit form, if you save you'll see an error message "This is a nice display message"

PR notes

Background

This PR solves 2 issues:

• How to display error messages from a module hooked on a Add/Edit form process (see Issues when creating new module for PS 1.7.6 #13490)
• It also handles the usecase "module does throw an uncatched exception". In the Core, we do not catch the generic \Exception because we consider our duty to handle all exception paths and make sure we display the right error message for each, however we cannot guarantee Modules will do the same. So we catch \Exception in order to avoid the "blank page" behavior.

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This change is 

[jolelievre]

I'm wondering is it ok to have an empty interface? I don't mind it's just I wasn't sure it was possible

I had thought of a single getErrorMessage method which would allow to "customize" the exception message a bit (the simplest implementation being to simply return the exception message). This would allow to separate the exception message and the error message which might be different:

• exception message => technical message with (potentially) sensitive info (db infos, path infos, ...)
• error message => user message more "feature oriented" and safe to display

Besides by using ModuleErrorInterface you restrict its use to module only, maybe we could call it FlashErrorInterface which would allow us to use it with core exceptions as well this could simplify our internal getErrorMessages methods (yet it doesn't make this PR more complicated), wdyt?

[eternoendless]

Ideally it should extend Throwable, then it wouldn't be empty. But it's not possible. It's just a marker interface so that you have more flexibility to create your own exceptions in this specific case.

From a DX standpoint, it's easier to use the exception message. Regarding FlashErrorInterface it could be integrated in the core later and be made a parent to this one.

[eternoendless]

Ideally it should extend Throwable, then it wouldn't be empty. But it's not possible. It's just a marker interface so that you have more flexibility to create your own exceptions in this specific case.

From a DX standpoint, it's easier to use the exception message. Regarding FlashErrorInterface it could be integrated in the core later and be made a parent to this one.

[jolelievre]

Ok let's do that for now then :)

[jolelievre]

Thanks @matks

[matks]

I fixed the empty demo module, QA can proceed 🚀

[matks]

Thank you for review and QA 🎉