feat: add defaultInherit for automatic release template inheritance (#2600)

* feat: add defaultInherit for automatic release template inheritance

Add a top-level defaultInherit field to helmfile.yaml that automatically
applies template inheritance to all releases without requiring explicit
inherit on each release.

The field accepts a single template name as a string or a list of
template names. Releases that already explicitly inherit from the same
template are not duplicated.

Fixes #2599

Signed-off-by: yxxhero <aiopsclub@163.com>

* style: fix gci formatting in app_template_test.go

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: correct relative chart path in integration test

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: use absolute chart path in bad-helmfile test

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: use clean chart path in bad-helmfile test

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: use dir variable for chart path

Signed-off-by: yxxhero <aiopsclub@163.com>

* test: fix flaky defaultInherit integration assertions

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/d0884e8e-8b1b-456d-8250-dec1566b8a37

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* test: tighten defaultInherit integration assertions

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/d0884e8e-8b1b-456d-8250-dec1566b8a37

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* test: harden release block parsing in issue-2599 case

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/d0884e8e-8b1b-456d-8250-dec1566b8a37

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* test: make issue-2599 assertions format-tolerant

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/d0884e8e-8b1b-456d-8250-dec1566b8a37

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* test: fix section extraction and regex matching in issue-2599 case

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/d0884e8e-8b1b-456d-8250-dec1566b8a37

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* fix: sanitize defaultInherit values and dedupe applied templates

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/85a8e815-3701-4b48-a28d-6bb2d50a3b40

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* chore: address validation feedback on defaultInherit fixes

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/85a8e815-3701-4b48-a28d-6bb2d50a3b40

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* fix: sanitize releaseInherit entries in applyDefaultInherit; add cleanup trap and quote vars in integration test

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/1fbf62d5-7ce2-42e5-898b-30151c0c1ef9

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* refactor: combine releaseInherit loops in applyDefaultInherit to avoid double TrimSpace; clarify test comment

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/1fbf62d5-7ce2-42e5-898b-30151c0c1ef9

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* test: align default inherit tests with yaml wrapper and assertions

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/3ea9b8e4-633f-43c4-899f-e063ec576486

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* test: address review feedback on defaultInherit tests

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/3ea9b8e4-633f-43c4-899f-e063ec576486

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* test: fix issue-2599 integration script helmfile invocation

Agent-Logs-Url: https://github.com/helmfile/helmfile/sessions/9452bb65-7086-459f-b5ae-0b00c1e021eb

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

---------

Signed-off-by: yxxhero <aiopsclub@163.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

docs/configuration.md

@@ -21,6 +21,7 @@ A `helmfile.yaml` has these top-level sections:
 | `values` | Default values available in templates |
 | `commonLabels` | Labels applied to all releases |
 | `templates` | Reusable release templates |
+| `defaultInherit` | Default template(s) for all releases to inherit |
 | `hooks` | Global lifecycle hooks |
 | `apiVersions` / `kubeVersion` | Kubernetes version capabilities |
 

docs/writing-helmfile.md

@@ -159,6 +159,48 @@ See [issue helmfile/helmfile#435](https://github.com/helmfile/helmfile/issues/43
 
 You might also find [issue roboll/helmfile#428](https://github.com/roboll/helmfile/issues/428) useful for more context on how we originally designed the release template and what it's supposed to solve.
 
+### Default Template Inheritance
+
+When all releases share the same template, specifying `inherit` on each one becomes repetitive. Use `defaultInherit` to apply a template to all releases automatically:
+
+```yaml
+templates:
+  default:
+    namespace: kube-system
+    missingFileHandler: Warn
+    values:
+    - config/{{`{{ .Release.Name }}`}}/values.yaml
+
+defaultInherit: default
+
+releases:
+- name: heapster
+  chart: stable/heapster
+  version: 0.3.2
+  # inherits from "default" automatically
+- name: kubernetes-dashboard
+  chart: stable/kubernetes-dashboard
+  version: 0.10.0
+  inherit:
+  - template: default
+    except:
+    - values
+```
+
+`defaultInherit` accepts a single template name or a list:
+
+```yaml
+# Single template
+defaultInherit: default
+
+# Multiple templates (merged in order)
+defaultInherit:
+  - ns-template
+  - defaults
+```
+
+If a release already inherits from the same template explicitly, the default is not duplicated. Use `except` in the release's `inherit` to exclude specific fields when needed.
+
 ## Layering Release Values
 
 Please note, that it is not possible to layer `values` sections. If `values` is defined in the release and in the release template, only the `values` defined in the release will be considered. The same applies to `secrets` and `set`.