doc/packages/treefmt: add option reference docs

Add a `treefmt.optionsDoc` passthru, which is included on the treefmt
section of the nixpkgs manual.

This generates reference docs for options declared in
`treefmt.evalConfig`.

doc/doc-support/package.nix

@@ -49,6 +49,7 @@ stdenvNoCC.mkDerivation (
     postPatch = ''
       ln -s ${optionsJSON}/share/doc/nixos/options.json ./config-options.json
       ln -s ${treefmt.functionsDoc.markdown} ./packages/treefmt-functions.section.md
+      ln -s ${treefmt.optionsDoc.optionsJSON}/share/doc/nixos/options.json ./treefmt-options.json
     '';
 
     buildPhase = ''

doc/packages/treefmt.section.md

@@ -3,10 +3,21 @@
 [treefmt](https://github.com/numtide/treefmt) streamlines the process of applying formatters to your project, making it a breeze with just one command line.
 
 The [`treefmt` package](https://search.nixos.org/packages?channel=unstable&show=treefmt)
-provides functions for configuring treefmt using the module system, which are [documented below](#sec-functions-library-treefmt).
+provides functions for configuring treefmt using the module system, which are [documented below](#sec-functions-library-treefmt), along with [their options](#sec-treefmt-options-reference).
 
 Alternatively, treefmt can be configured using [treefmt-nix](https://github.com/numtide/treefmt-nix).
 
 ```{=include=} sections auto-id-prefix=auto-generated-treefmt-functions
 treefmt-functions.section.md
 ```
+
+## Options Reference {#sec-treefmt-options-reference}
+
+The following attributes can be passed to [`withConfig`](#pkgs.treefmt.withConfig) or [`evalConfig`](#pkgs.treefmt.evalConfig):
+
+```{=include=} options
+id-prefix: opt-treefmt-
+list-id: configuration-variable-list
+source: ../treefmt-options.json
+```
+

doc/redirects.json

@@ -420,6 +420,9 @@
   "sec-tools-of-stdenv": [
     "index.html#sec-tools-of-stdenv"
   ],
+  "sec-treefmt-options-reference": [
+    "index.html#sec-treefmt-options-reference"
+  ],
   "ssec-cosmic-common-issues": [
     "index.html#ssec-cosmic-common-issues"
   ],