# Custom Jsonnet Compiler

This directory contains a custom Jsonnet compiler built with Go. It wraps the standard `go-jsonnet` library and adds a native function `helmTemplate` to support rendering Helm charts directly within Jsonnet.

## `helmTemplate` Native Function

The `helmTemplate` function allows you to render a Helm chart located on the filesystem.

### Signature

```jsonnet
native("helmTemplate")(name, chartPath, opts)
```

- `name`: The release name.
- `chartPath`: The path to the Helm chart directory (containing `Chart.yaml`). **Crucial:** This path must be relative to the directory containing the file that calls `helmTemplate`. When using Bazel external repositories, this often means navigating up to the execution root (e.g., `../../external/repo_name`).
- `opts`: A configuration object.
    - `calledFrom`: (Required) The path of the file calling the function. Usually `std.thisFile`. The compiler uses this to resolve relative paths.
    - `nameFormat`: (Optional) Format string for resource names.
    - `values`: (Optional) Values to pass to the Helm chart.
    - `includeCRDs`: (Optional) Boolean, default `true`.
    - `namespace`: (Optional) Namespace for the release.

### Usage Example

```jsonnet
local helm = std.native("helmTemplate");

helm("my-release", "../../external/my_chart_repo", {
  calledFrom: std.thisFile,
  namespace: "default",
  values: {
    replicaCount: 2,
  },
})
```

## Bazel Integration

This compiler is registered as a custom toolchain in `//tools/jsonnet_compiler:helm_jsonnet_toolchain` and used by `rules_jsonnet`.

### Imports and JPaths

When using `rules_jsonnet`, the `imports` attribute adds directories to the Jsonnet search path (`-J`).
- `imports = ["."]` adds the package directory.
- `deps` on `jsonnet_library` targets adds their roots to the search path.

When importing files from external repositories (like `tanka-util`), ensure the import path matches the structure within that repository. For example, if `tanka-util` library is at the root of the `@github_com_grafana_jsonnet_libs_tanka_util` repo, you can import it as `import "tanka-util/main.libsonnet"` provided the repo root is in the search path (which `deps` handles).