Use !include and other YAML functions in scaffold templates

Two fields in the same scaffold template often need the exact same list of choices — a license picker and a region list are both really just "options sourced from some small reference table." Until now, that table had nowhere to live but inside scaffold.yaml itself, copied into every field that needed it. And a value as simple as the current git branch, an environment variable, or a random suffix had no path into a template at all, short of prompting the user for it by hand.

The Problem

Small pieces of reference data — license choices, region codes, a naming convention lookup — show up constantly in real scaffold templates, and they rarely stay confined to one field. A select field needs them as {label, value} options; a file elsewhere in the same template needs the raw table to look values up by key. Duplicating that table by hand, once per field that needs it, means every future edit has to find and update every copy — and a missed one quietly drifts out of sync with the rest. Beyond reference data, templates also commonly need small dynamic values — the user's git branch or commit SHA, an environment variable, a random suffix for a resource name — with no way to derive any of them automatically.

The Fix

scaffold.yaml now resolves a set of Atmos YAML functions — the same explicit-tag mechanism stack manifests already use — anywhere it currently accepts a literal value: options:, a type: computed field's value:, or a matrix: axis.

• !include/!include.raw pulls in a local or remote file, optionally reshaped with a YQ filter.
• !env reads an environment variable, !random generates a random number, and !cwd reads the current working directory.
• The !git.*/!repo-root family exposes the current git branch, commit SHA, repository name, and more.
• !literal preserves a value exactly as written, bypassing scaffold's own template evaluation — useful when a value legitimately contains {{ }} and shouldn't be treated as a template expression.

scaffold.yaml

spec:
  fields:
    - name: license
      type: select
      options: !include "./lib/licenses.yaml '. | to_entries | map({\"label\": .value.full_name, \"value\": .key})'"

    - name: license_lookup
      type: computed
      value: !include ./lib/licenses.yaml

    - name: branch
      type: computed
      value: !git.branch

A locally-included file that exists solely to be included is automatically excluded from generated output, the same way scaffold.yaml itself is. atmos scaffold validate resolves everything too, not just generate, so a missing file, a bad filter, or a malformed value is caught up front.

Not every YAML function is available here: anything that needs real stack, component, or backend context (!terraform.state, !store, !secret, and similar) is rejected with a clear error instead. A template's scaffold.yaml is often resolved just to show its name and description in atmos scaffold list or the interactive picker — before a user has chosen or generated anything — so only functions that are safe to run in that situation are supported.

The !exec function is excluded for a different reason: it needs no stack context at all, but scaffold.yaml is resolved for every template configured in atmos.yaml just to populate the list and picker, not only the one a user actually generates — so allowing shell execution there would let any configured template, including a shared or vendored one, run arbitrary code merely by being listed.

How to Use It

Add any of the functions above anywhere options:, a computed field's value: (see Computed Fields), or a matrix axis currently accepts a literal value. See the full examples/scaffolding-yaml-functions example, or the Loading External Data with !include and Other YAML Functions section of the atmos scaffold generate docs.

Get Involved

See the atmos scaffold generate docs for the full reference, or open an issue with feedback.