Support default value for any type

[LittleWat]

Describe the problem/challenge you have

I want set the default value for any type but I can't.

Here is the example.

• schema.yaml

#@data/values-schema
---
test:
  #@schema/type any=True
  optional_config:
    param1: "a"
    param2: "b"

• template.yaml

#@ load("@ytt:data", "data")

conf: #@ data.values.test.optional_config

• value.yaml

#@data/values
---
test:
  optional_config:
    param3: "c"

$  ytt -f value.yaml -f schema.yaml -f template.yaml
ytt: Error: Overlaying data values (in following order: value.yaml):
  Document on line value.yaml:2:
    Map item (key 'test') on line value.yaml:3:
      Map item (key 'optional_config') on line value.yaml:4:
        Map item (key 'param3') on line value.yaml:5:
          Expected number of matched nodes to be 1, but was 0

Describe the solution you'd like

In the example, the expected output is:

conf:
    param1: a
    param2: b
    param3: c

I hope this is supported 🙏

Or I would be glad if you could share the workarounds for this 🙇‍♂️

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[LittleWat]

I found the workaround for this. It was necessary to write the Starlark code, though.

• schema.yaml

#@data/values-schema
---
test:
  #@schema/type any=True
  optional_config: null

_default_optional_config:
  param1: a
  param2: b

• template.yaml

#@ load("@ytt:data", "data")
#@ load("@ytt:struct", "struct")

#@ def combine_with_default(user_config, default_config):
#@  result = struct.decode(default_config)
#@  if user_config:
#@      result.update(struct.decode(user_config))
#@  end
#@  return result
#@ end

conf: #@ combine_with_default(data.values.test.optional_config, data.values._default_optional_config)

• value.yaml

#@data/values
---
test:
  optional_config:
    param1: "aaa"
    param3: "c"
    parma4:
      param4_4: "ddd"

and here is the execution result:

$  ytt -f schema.yaml -f template.yaml -f value.yaml
conf:
  param1: aaa
  param2: b
  param3: c
  parma4:
    param4_4: ddd

[prembhaskal]

@LittleWat What you are trying to achieve can be easily done using an overlay

• template.yml

#@ load("@ytt:data", "data")

conf: #@ data.values.test.optional_config

• default-schema.yml

#@data/values-schema
---
test:
  #@schema/type any=True
  optional_config:
    param1: a
    param2: b

• val.yml

#@ load("@ytt:overlay", "overlay")

#@overlay/match by=overlay.all
---
conf:
  #@overlay/match missing_ok=True
    param3: c

[prembhaskal]

you can even overlay data values instead of overlaying final results using below variant of val.yml

• val.yml (overlay data-values)

#@ load("@ytt:overlay", "overlay")
#@data/values

#@overlay/match by=overlay.all
---
test:
  optional_config:
  #@overlay/match missing_ok=True
    param3: c
    

[prembhaskal]

Also feel free to use / explore carvel channel on kubernetes slack. A question similar to yours is here - https://kubernetes.slack.com/archives/CH8KCCKA5/p1675159628085549

[LittleWat]

@prembhaskal Hi, thank you for your quick replies!

I see! #@overlay function can be used here. However, in our use-case, we want to let our customers configure just #@data/values file to abstract(simplify) the k8s configuration. It would be necessary to let our customers understand the logic behind it when using the #@overlay function, which is not so ideal. But it might be necessary. Thanks anyway!!

[prembhaskal]

hmm understood, so you want to hide the complexity of overlay from end user, but still allow them to pass in the extra configurations.
I think we can do that by making overlay to read from another data values file. something like below (a pseudo code btw)

#@ load("@ytt:overlay", "overlay")
#@load("@ytt:data", "data")
#@data/values

#@overlay/match by=overlay.all
---
test:
  optional_config:
  #@overlay/match missing_ok=True
    #@ data.other_optional_config

I can give it a try later today.