file.yaml

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

#@ if/end data.values.configFileContents.defaultHttpVersions:
default-http-versions: #@ data.values.configFileContents.defaultHttpVersions

schema.yaml

#@ def default_conns():
- foo: 2
  bar: 1
#@ end

#@data/values-schema
---
configFileContents:
  #@schema/default default_conns()
  defaultHttpVersions:
  - foo: 1
    bar: 2

values.yaml

#@data/values
---
configFileContents:
  defaultHttpVersions:
    - foo: 4
    - bar: 2