Schema Validation v2

[pivotaljohn]

(this is the next feature increment of #561)

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As a Configuration Author I want to declare what constitutes a valid Data Value right in my schema definition In a way that requires even less custom Starlark code from me ⭐ And I can write fewer annotations ⭐ because ytt can confidently infer for what have written. *So that**

• I can state those invariants in one central place and know they will be respected throughout the execution
• those who use my ytt library and violate one of those variants will receive a helpful error message
• and my overall maintenance effort/costs are less than before. ⭐

(⭐ = a desired improvement on top of the MVP.)

[proposal] [getting started]

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Backlog

• ⚠️ This track of work is still being elaborated; some scope is likely missing.⚠️
• loads of ideas for improvements can be mined from #707's synthesis

UX:

• [ ] Use custom violation messages
  • on @assert/validate, implement 3-tuple rules where the third tuple is the violation template; to @schema/validation, add 3-tuple tules.
  • note: this is critical to improve the DX around unit testing (detailed in a conversation on #741)
• [ ] disallow @schema/validation in non-schema documents.
• [ ] disallow @assert/validate in schema documents.

Fast Follow: other must-have OOTB rules

• [ ] matches=

Programmatic Validation of YAML

• [ ] Validate a YAML document that contains @assert/validate annotations
  • expose assert.is_valid() as a method in @ytt:assert module

Include Validations in Schema Inspect

• [ ] Include validations when exporting schema to OpenAPI v3 (subset: one-for-ones)
  • need: https://kubernetes.slack.com/archives/CH8KCCKA5/p1661186311752459?thread_ts=1661185491.294779&cid=CH8KCCKA5
• [ ] Include validations when exporting schema to OpenAPI v3 (subset: needing translation)

Authoring Conveniences:

• [ ] Set a default validation for descendent Data Values (@schema/validate-string-default)
• [ ] Infer @schema/nullable for all children implicated in a @schema/validation one_not_null=

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Resources

• Schema proposal: Part 7 — Validating Documents
• Schema Validation proposal
• Previous Epic: #561

Related Issues:

• 103 — originating issue

• 556 — requesting "required" use-case, explicitly.