Add HIP for outputting chart JSON schemas

hips/hip-9999.md

@@ -0,0 +1,85 @@
+---
+hip: "9999"
+title: "Output Helm Chart Schemas"
+authors: [ "Remco Haszing <remcohaszing@gmail.com>" ]
+created: "2021-07-14"
+type: "feature"
+status: "draft"
+---
+
+## Abstract
+
+Helm supports JSON schema validation to validate `values.yaml`.
+It would be nice if JSON schema validation is also possible by editors of `values.yaml` files.
+It would be nice if JSON schemas can be referenced by dependant Helm chart JSON schemas.
+Both will be possible if the JSON schemas are served on separate URLs.
+
+## Motivation
+
+For Helm users it would be nice if they can reference JSON schemas from a Helm chart.
+
+If a Helm chart depends on another Helm chart, its JSON schema can reference the original JSON schema like so:
+
+```json
+{
+ "properties": {
+ "my-chart": {
+ "$ref": "https://charts.example/my-chart-1.2.3.schema.json"
+ }
+ }
+}
+```
+
+If a user wants to enable JSON schema validation and completion for `values.yaml` when using [`yaml-language-server`](https://github.com/redhat-developer/yaml-language-server), this can be accomplished by a modeline:
+
+```yaml
+# yaml-language-server: $schema=https://charts.example/my-chart-1.2.3.schema.json
+```
+
+## Rationale
+
+By outputting the JSON schema next to the packaged Helm chart, Helm determines the standard output location.
+Chart publishers could copy their JSON schema manually, but this isn’t standardized in any way.
+If Helm determines the standard output location of such files, chart publishers are likely to use this.
+Helm already outputs an additional file for signed charts. This proposal is consistent with that behaviour.
+
+## Specification
+
+If a Helm chart containing a `values.schema.json` is built using `helm package`, Helm will output the contents of `values.schema.jsob` alongside of it.
+The file structure of the output will look like this:
+
+```
+├─ my-chart-1.2.3.json.schema
+├─ my-chart-1.2.3.tgz
+└─ my-chart-1.2.3.tgz.prov
+```
+
+## Backwards Compatibility
+
+Outputting an additional file is backwards compatible.
+If a chart published previously assumed a single output file, as was the case for unsigned charts, the JSON schema file is ignored.
+
+## Security implications
+
+This HIP has no security implications.
+
+## How to teach this
+
+The documentation should be updated to reflect this change.
+Users should be recommended to publish the JSON file as well, thus not treating the output directory as the output, not just the Helm chart package.
+
+## Reference Implementation
+
+## Rejected ideas
+
+N/A
+
+## Open issues
+
+https://github.com/helm/helm/issues/9920
+
+## References
+
+- [`yaml-language-server`](https://github.com/redhat-developer/yaml-language-server)
+- `yaml-language-server` [modeline](https://github.com/redhat-developer/yaml-language-server#using-inlined-schema)
+- [JSON schema $ref](https://json-schema.org/understanding-json-schema/structuring.html#ref)