Per-file template delimiters for scaffold templates

A Helm chart is full of {{ }} expressions, and so is a GitHub Actions workflow with its ${{ github.sha }}. Put either one in a scaffold template that also uses {{ }} for its own variables, and the generator tries to render the chart's and the workflow's expressions too. A template could pick one delimiter pair for every file it generates, so mixing a chart or a workflow with ordinary files meant escaping every Helm and Actions expression by hand.

The Problem

Scaffold templates render with {{ }} by default, and spec.delimiters can switch the whole template to a different pair. That works while every file in the template agrees on one pair. It breaks down as soon as a single template generates files that already contain {{ }} of their own:

• A Helm chart needs its {{ .Values.image }} expressions to reach the generated chart untouched, so Helm can render them later.
• A GitHub Actions workflow needs ${{ github.sha }} to stay literal for the same reason.
• The rest of the project, such as stack files and READMEs, still wants the convenient default.

Switching the whole template to [[ ]] fixes the chart but forces every other file to change syntax with it. Keeping {{ }} means escaping every Helm and Actions expression by hand.

Custom delimiters also had a second gap. When Atmos checked a generated file path for unrendered template markers, it always looked for {{ and }}, no matter which delimiters the template used. A path that legitimately contained a literal {{, such as one produced under a [[ ]] template, was rejected as if a variable had been left unrendered.

The Fix

An entry in spec.files can now carry its own delimiters, which override the template-wide pair for every file the entry matches. The pair covers everything Atmos renders for those files: their content, their paths, target, and any matrix axis written as a Go template expression. The when condition is a CEL expression, so it never uses delimiters.

Atmos picks a file's delimiters in this order:

1. The delimiters of the matching spec.files entry. When several entries match the same file, the last one wins, as it does for path and when.
2. spec.delimiters.
3. {{ and }}.

Path validation now follows the same pair, so a literal {{ or ${{ in a path is accepted under [[ ]] while a forgotten [[ .Config.name ]] is still caught. Both atmos scaffold generate and atmos init honor per-file delimiters, and so do --dry-run previews and --update merges. An update keeps your edits to a chart file while Helm's own expressions stay literal.

How to Use It

Declare the template-wide default once, then override it for the files that need something else:

scaffold.yaml

spec:
  delimiters: ["{{", "}}"]          # template-wide default (optional)
  files:
    - path: "charts/**"             # Helm templates use {{ }} themselves
      delimiters: ["[[", "]]"]
    - path: ".github/workflows/*.yml.tmpl"
      delimiters: ["<<", ">>"]      # keeps ${{ github.sha }} literal

A chart template can then mix both syntaxes. Atmos fills in the [[ ]] expression and leaves the Helm expression for Helm:

charts/app/templates/deployment.yaml

# atmos:template
name: [[ .Config.name ]]
image: "{{ .Values.image }}"

Each pair must be exactly two non-empty strings, and atmos scaffold validate rejects anything else. See Template Delimiters for the full rules, and the atmos scaffold generate reference for how delimiters combine with target and matrix.

Get Involved

Try it on a template that generates a chart or a workflow, and open an issue with feedback or edge cases you run into.