feat: disallow condition depending on the containing property

[barmac]

Closes #125

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Note that this requires the validator to accept $data property. The monaco editor handles this correctly, and in ajv you need to pass $data: true to the constructor.

[barmac]

The dropdown choices condition is still missing here.

[barmac]

Choices#condition is there. The solution works in the ajv validator with $data: true, but does not highlight problems in Monaco (cf. #125 (comment)). However, the main goal of protection against invalid templates is achieved.

[nikku]

I'm not sold on whether baking this into the JSON schema validator is a good thing, especially as it adds quite some complexity to it.

Good thing is that we $comment on what is happening why. What would be the alternative, and did you consider it? I guess programmatic validation?

[barmac]

I'm not sold on whether baking this into the JSON schema validator is a good thing, especially as it adds quite some complexity to it.

Good thing is that we $comment on what is happening why. What would be the alternative, and did you consider it? I guess programmatic validation?

The alternative would be to implement the solution directly in https://github.com/bpmn-io/element-templates-validator. Let's consider the pros and cons of each option.

JSON schema:
(+) will be picked up automatically by the tools if they accept $data format
(+) is close to the specification of templates
(+) provides JSON path in the error that can be picked up by the tools
(-) is more difficult to understand if you know JS but not JSON schema

JS validator:
(+) easier to understand for JavaScript devs
(-) away from the rest of templates specification (schema)
(-) will never be picked up automatically by JSON schema tools

Also notice that the actual implementation is only in these two files:

• error messages: https://github.com/camunda/element-templates-json-schema/pull/128/files#diff-28cd73e9ca9485c1e9bce98c303bb880ea1a7e96dbad5e1f5216e9f87a084c24
• condition: https://github.com/camunda/element-templates-json-schema/pull/128/files#diff-ee6be2266742098acb7feb7e3d946c44fc93a48369bc849d010a4dbd6d04def2

The rest is refactoring via 34db754

[nikku]

I subscribe to the pros and cons, thanks for outlining them here.

[nikku]

Looks good to me.