CON-1508: Decorator based arguments validation approach

[PavelLoparev]

Arguments decorator-based validation approach:

1. IsNotEmpty argument decorator "registers" validation in the target object (just an array of strings like <methodName>:<parameterIndex>:<validatorName>)
2. Validation method decorator reads all registered validations and executes them.

This scheme with 2 decorators instead of just one argument decorator is only needed because argument level decorator can't access actual argument value (it's weird)

Usage example:

export class MyClass {
    @Validate
    async myMethod(@IsNotEmpty test: string): Promise<void> {
        ...
    }
}

As I get it I can't use class-validator lib because it's only for class property validations, not method arguments.

[PavelLoparev]

@dimitrystd it's just an example of how it can be used (SUBM api class is in private sdk)

[dimitrystd]

Looks interesting. Just two concerns:

• It only works with simple types. If we pass an object of Parameters class then we can't validate it. Or need to write more code.
  Using ! and strict compilation can give us similar results.
• We implement just another validation package.

[PavelLoparev]

We would need to refactor here and there to support strictNullChecks mode.

[PavelLoparev]

Registers validation for argument (it's not possible to get value of the argument in an argument decorator which is weird)

[PavelLoparev]

Actual validation logic

[PavelLoparev]

Walk through registered validations and execute them

[PavelLoparev]

We decided to move this approach directly to the class-validator lib (typestack/class-validator#2432). If it will be accepted there we will get back to this ticket.