schematics: add prompt for migration

[spike-rabbit]

The ng-add script should prompt the user whether a migration to siemens package should be run.

We should prompt whether we run the migrations or not.
So either:

• Just install dependencies
• or install dependencies and run migrations

[spliffone]

@spike-rabbit Why do we want to prompt? Usually when ever we find in the package.json the previous element dependency we should always migrate. Why do we want to diverge from our documented migration strategy?

[spike-rabbit]

It's easier for developer. When updating element, one usually hopefully first bumps the deps and adds the Siemens packages.
Then doing a first commit I guess.
Afterwards you adjust to the breaking changes. Next commit.
Then we can do the full migration of the optional parts which causes a lot of changes.

[spliffone]

Yes it will, but we shouldn't provide different migration paths since this would force use to handle two cases for the breaking changes:

1. migrating @simpl related components (we have one global export)
2. migrating @siemens related components (we have dedicated packages)

My main point, we can't enforce the order in which programs migrate so I honestly suggest to stick to one migration path which will update everything at ones.

[spike-rabbit]

Ahh, I should have clarified this more.

I just meant we should prompt whether we run the migrations or not.
So either:

• Just install dependencies
• or install dependencies and run migrations. The order of migrations I would not allow to be changed, for the exact same reasons you mentioned

[spliffone]

Actually Angular only provide static prompts and I am a bit uncertain how to provide a conditional prompt. The angular cli has a function askConfirmation but they didn't export it.

I guess bothering each and every user with the question "Would you like to migrate from @simpl to @siemens ?" can be come a pain. So I would prefer we leave it like it is.

[spike-rabbit]

I think having a static question is the nicer approach.

We are abusing the ng-add a little. Usually this is just used to install dependencies and maybe modify some config files.
But running a full migration is for sure not in the scope.

So we should in general recommend all apps to use the ng add @siemens/element-ng stuff when updating.
But give them the option to opt out the immediate migration. No one will run this frequently so an additional prompt is ok.