Report Schema Error when Data Values Overlay Fails

[cari-lynn]

Why / Context

Previously, there was some work done to report a schema error for when an overlay fails to overlay a data value onto a schema document, but the work was moved to this issue. Because of this, we have some tests that do not pass and are being skipped. Currently, instead of a schema error, we see an overlay error message.

Narrative:
As a configuration author
I want see a helpful error message when my data values file does not conform to my schema
so that I can easily find where the offending items are in my document and fix it

---

🟢 Report a Schema Error when Overlaying fails

Given I have a schema
And a data value that is not in my schema
When I run ytt that includes that schema and data value
Then I see a error that my data value did not conform to my schema

#@schema/match data_values=True
---
db_conn:
  port: 0

#@ load("@ytt:overlay", "overlay")
#@data/values
---
db_conn:
  #@overlay/match by=overlay.subset({"key_doesnt_exist": True})
  new_key: i should not be here

#! template.yml
#@ load("@ytt:data", "data")
---
db_conn: #@ data.values.db_conn

Then the result of ytt -f schema.yml -f dv.yml -f template.yml --enable-experiment-schema is:

data_values.yml:4 | new_key: i should not be here
                  |
                  | UNEXPECTED KEY - the key of this item was not found in the schema's corresponding map:
                  |      found: new_key
                  |   expected: (a key defined in map) (by schema.yml:3)
                  |   (hint: declare data values in schema and override them in a data values document)```

[pivotaljohn]

With the rise of the "Plain YAML as Data Values" (#381) feature comes an approach to providing Data Values that is designed to not result in overlay errors.

When that method becomes the primary way to supply data values, this work becomes far less valuable.

For that reason, we've decided to at least defer this work until later: moved to #323 for this reason.

[pivotaljohn]

We've recently clarified further the criteria for each pipeline in our backlog.
The probability that this bug will become "won't fix" has increased to the point it shouldn't be considered "carvel accepted" any longer.

For these reasons, moving to "New Issues".