The helm charts use symlinks to utilise a central collection of templates that is used for every chart. The values.yaml is symlinked into the directory of each chart as default_values.yaml. Each chart has an overwrite_values.yaml file which specifies the values for that particular chart and overwrites the values from default_values.yaml.

Before the chart can be installed locally for testing or is built for publishing, the actual values.yaml for Helm needs to be created (paths are specified from root of repository):

cd helm/chart/
yq '. *= load("overwrite_values.yaml")' default_values.yaml > values.yaml

Furthermore, each chart has an environments directory which contains a values file with the name of the environment (e.g. production.yaml). These values are not bundled into the chart on construction but rather supplied when installing the chart.