feat: add validation support in marker type

[MahmoudShakour]

fixes: #347

[fsommar]

Can you add a test for multiple validation markers, and a test for using quotes (e.g. self == "foobar")?

[fsommar]

I didn't realize it when writing my feature request, but the fact that each validation is a struct with at least rule and typically also message means that this syntax needs to be updated to support that too

[MahmoudShakour]

@fsommar
got it. i had that question in my mind but thought you want the default message to be displayed.
what do you think about this format ?

validation="rule:"self == oldSelf",message:"can't be changed"" 

[fsommar]

@MahmoudShakour nested quotes is going to be hard to parse for both humans and machines, I think. What about updating the right-hand side to support either strings, like today, or JSON objects? The JSON object suggestion would look something like this:

immutableFoo: |
  string |
  validation={
    "rule": "self == oldSelf",
    "message": "can't be changed"
  }

Another suggestion, where the index is arbitrary as long as it's unique (could be 0 and 1 also):

immutableBar: |
  integer
  validation[immutability].rule="self == oldSelf"
  validation[immutability].message="can't be changed"
  validation[positive].rule="self > 0 || self == -1"
  validation[positive].message="has to be positive or -1"

[a-hilaly]

Hi @MahmoudShakour - are you still working on this one?

[DhairyaMajmudar]

@a-hilaly If @MahmoudShakour is okay with it, I’d be happy to take this on since I have priorly worked with Markers logic in PR #424

[a-hilaly]

please go for it @DhairyaMajmudar - can you please make sure to add @MahmoudShakour as co-author or fork his branch so that we can preserve some of his work.

[DhairyaMajmudar]

Thank you, yeah sure will add him as commit co-author