@schema/default Annotation

[pivotaljohn]

@schema/default

work is on ytt branch: schema-default
Explicitly sets the default value of the annotated node.

@schema/default value

• value (any except function) — the overriding default value.

Notes:

• value must be of the type of the annotated node.
• The type of a node is never inferred from the overriding default value.
• this annotation is the only way to set a non-empty default value for arrays.

Narrative:
As a configuration author
I want to explicitly set a default value for a data value
so that I can specify default values for arrays

---

🍏 Set the default value

Given a document, array item, or map item is annotated with @schema/default <value>
And the value is of the same type as the key below it
When I run ytt that includes that schema
Then that value shows up as the default for that array

Scenario 1: 🍏 Set the default value of an int

#! schema.yml
#@data/values-schema
---
#@schema/default 1
number: 0

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

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

---
output: 1

Scenario 2: 🍏 Set the default value of an array

#! schema.yml
#@data/values-schema
---
#@ def array_definition():
#@ return "this is the default value"
#@ end

#@schema/default [array_definition()]
the_array:
- this defines the type only

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

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

---
output: 
- this is the default value

Scenario 3: 🟥 Keyword argument(s) of incorrect format

Given a document, array item, or map item is annotated with @schema/default with any other keyword argument (kwarg) except a value of the same type that is defined inline for arrays or maps
When I run ytt that includes that schema
Then I see an error message which includes line numbers to help point to where the error is, alongside a helpful message that describes the problem and how to fix it (unknown kwarg, fix by removing or using the only currently supported on, any)

More examples in the original ytt schema doc

Notes:

• Documentation should be included as part of this issue

[cari-lynn]

Available in v0.38.0