docs/options: Add option reference generator

Evaluate custom module options through a synthetic system, stabilize configuration-dependent defaults for rendering, and commit the generated reference beside its updater.
2026-08-01 23:59:17 +01:00
parent 4084dfe64e
commit b44095f1ed
7 changed files with 472 additions and 9 deletions
@@ -0,0 +1,108 @@
+#!/usr/bin/env python3
+"""Render docs/reference/nixos-options.md from the `my.*` module options.
+
+Builds the `optionsDoc` flake output (a `nixosOptionsDoc` JSON dump of the custom
+`my.*` options) and renders it to a per-module table. The prose lives in the option
+descriptions in `nixos/modules/`; this file is generated.
+"""
+
+import json
+import re
+import subprocess
+import sys
+from pathlib import Path
+
+OPTIONS_DOC_ATTR = ".#nixfiles.config.nixos.optionsDoc"
+OUT = Path("docs/reference/nixos-options.md")
+HEADER = "| Option | Type | Default | Description |"
+SEP = "|---|---|---|---|"
+
+
+def collapse(text: str) -> str:
+    # Strip the flake's own /nix/store/<hash>-source/ prefix from rendered values so
+    # defaults like `./.keys/deploy.pub` are stable (the hash changes every time this
+    # generated file — part of the source tree — is rewritten).
+    text = re.sub(r"/nix/store/[a-z0-9]{32}-source/", "", text)
+    text = re.sub(
+        r'<link\s+xlink:href="([^"]+)">([\s\S]+?)</link>',
+        r"[\2](\1)",
+        text,
+    )
+    return re.sub(r"\s+", " ", text).strip().replace("|", "\\|")
+
+
+def render_default(entry: dict) -> str:
+    if "default" not in entry:
+        return "—"
+    d = entry["default"]
+    # A dict default is a `defaultText` / `literalExpression` (pre-rendered Nix in `text`);
+    # anything else is a literal value we JSON-encode.
+    if isinstance(d, dict):
+        text = d.get("text")
+        if text is None:
+            text = json.dumps(d.get("value"))
+    else:
+        text = json.dumps(d)
+    text = collapse(text)
+    return f"`{text}`" if text else "—"
+
+
+def build_options_json() -> dict:
+    # `optionsDoc` builds to a derivation containing share/doc/nixos/options.json; the last
+    # printed out-path is the derivation root.
+    out = subprocess.run(
+        ["nix", "build", "--no-link", "--print-out-paths", OPTIONS_DOC_ATTR],
+        capture_output=True,
+        text=True,
+        check=True,
+    ).stdout.strip().splitlines()[-1]
+    return json.loads((Path(out) / "share/doc/nixos/options.json").read_text())
+
+
+def main() -> int:
+    opts = build_options_json()
+
+    by_module: dict[str, list[tuple[str, dict]]] = {}
+    for key, entry in opts.items():
+        decls = entry.get("declarations") or []
+        # Only document options declared in this repo's modules. Some `my.*` options
+        # (e.g. `my.buildAs`, which aliases `options.system.build`) pull in sub-options
+        # declared in nixpkgs; their declaration paths don't exist here — skip them.
+        if not decls or not Path(decls[0]).exists():
+            continue
+        by_module.setdefault(decls[0], []).append((key, entry))
+
+    lines = [
+        "# NixOS module options (`my.*`)",
+        "",
+        "> **Generated** from the module option descriptions by `nix run .#update-docs-options`;",
+        "> CI keeps it current. The source of truth is the `mkOpt'` / `mkBoolOpt'` declarations in",
+        "> `nixos/modules/` — edit those, not this file. For what each module is *for*, see the",
+        "> [shared-modules overview](../architecture.md#shared-modules).",
+        "",
+    ]
+    for decl in sorted(by_module):
+        mod = Path(decl).stem
+        if decl != "(unknown)":
+            lines.append(f"## `{mod}` — [`{decl}`](../../{decl})")
+        else:
+            lines.append(f"## `{mod}`")
+        lines += ["", HEADER, SEP]
+        for key, entry in sorted(by_module[decl], key=lambda kv: kv[0]):
+            lines.append(
+                f"| `{key}` | {collapse(entry.get('type', ''))} | "
+                f"{render_default(entry)} | {collapse(entry.get('description', ''))} |"
+            )
+        lines.append("")
+
+    OUT.parent.mkdir(parents=True, exist_ok=True)
+    new = "\n".join(lines).rstrip() + "\n"
+    old = OUT.read_text() if OUT.exists() else ""
+    if new != old:
+        OUT.write_text(new)
+        print(f"updated {OUT}")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())