nixos, lib: implement relatedPackages option

This allows one to specify "related packages" in NixOS that get rendered into
the configuration.nix(5) man page. The interface philosophy is pretty much
stolen from TeX bibliography.

3 files changed, 30 insertions, 6 deletions

diff --git a/lib/options.nix b/lib/options.nix
index 769d3cc5572..ab1201c718a 100644
--- a/lib/options.nix
+++ b/lib/options.nix
@@ -14,6 +14,7 @@ rec {
     , defaultText ? null # Textual representation of the default, for in the manual.
     , example ? null # Example value used in the manual.
     , description ? null # String describing the option.
+    , relatedPackages ? null # Related packages used in the manual.
     , type ? null # Option type, providing type-checking and value merging.
     , apply ? null # Function that converts the option value to something else.
     , internal ? null # Whether the option is for NixOS developers only.
@@ -76,7 +77,6 @@ rec {
   getValues = map (x: x.value);
   getFiles = map (x: x.file);
 
-
   # Generate documentation template from the list of option declaration like
   # the set generated with filterOptionSets.
   optionAttrSetToDocList = optionAttrSetToDocList' [];
@@ -93,9 +93,10 @@ rec {
           readOnly = opt.readOnly or false;
           type = opt.type.description or null;
         }
-        // (if opt ? example then { example = scrubOptionValue opt.example; } else {})
-        // (if opt ? default then { default = scrubOptionValue opt.default; } else {})
-        // (if opt ? defaultText then { default = opt.defaultText; } else {});
+        // optionalAttrs (opt ? example) { example = scrubOptionValue opt.example; }
+        // optionalAttrs (opt ? default) { default = scrubOptionValue opt.default; }
+        // optionalAttrs (opt ? defaultText) { default = opt.defaultText; }
+        // optionalAttrs (opt ? relatedPackages && opt.relatedPackages != null) { inherit (opt) relatedPackages; };
 
         subOptions =
           let ss = opt.type.getSubOptions opt.loc;
diff --git a/nixos/doc/manual/default.nix b/nixos/doc/manual/default.nix
index 9a96f201a39..95363c2458f 100644
--- a/nixos/doc/manual/default.nix
+++ b/nixos/doc/manual/default.nix
@@ -15,13 +15,27 @@ let
     else if builtins.isFunction x then "<function>"
     else x;
 
-  # Clean up declaration sites to not refer to the NixOS source tree.
+  # Generate DocBook documentation for a list of packages
+  genRelatedPackages = packages:
+    let
+      unpack = p: if lib.isString p then { name = p; } else p;
+      describe = { name, package ? pkgs.${name}, comment ? "" }:
+          "<listitem>"
+        + "<para><option>pkgs.${name}</option> (${package.name}): ${package.meta.description or "???"}.</para>"
+        + lib.optionalString (comment != "") "\n<para>${comment}</para>"
+        # Lots of `longDescription's break DocBook, so we just wrap them into <programlisting>
+        + lib.optionalString (package.meta ? longDescription) "\n<programlisting>${package.meta.longDescription}</programlisting>"
+        + "</listitem>";
+    in "<itemizedlist>${lib.concatStringsSep "\n" (map (p: describe (unpack p)) packages)}</itemizedlist>";
+
   optionsList' = lib.flip map optionsList (opt: opt // {
+    # Clean up declaration sites to not refer to the NixOS source tree.
     declarations = map stripAnyPrefixes opt.declarations;
   }
   // lib.optionalAttrs (opt ? example) { example = substFunction opt.example; }
   // lib.optionalAttrs (opt ? default) { default = substFunction opt.default; }
-  // lib.optionalAttrs (opt ? type) { type = substFunction opt.type; });
+  // lib.optionalAttrs (opt ? type) { type = substFunction opt.type; }
+  // lib.optionalAttrs (opt ? relatedPackages) { relatedPackages = genRelatedPackages opt.relatedPackages; });
 
   # We need to strip references to /nix/store/* from options,
   # including any `extraSources` if some modules came from elsewhere,
diff --git a/nixos/doc/manual/options-to-docbook.xsl b/nixos/doc/manual/options-to-docbook.xsl
index 5387546b598..7b45b233ab2 100644
--- a/nixos/doc/manual/options-to-docbook.xsl
+++ b/nixos/doc/manual/options-to-docbook.xsl
@@ -70,6 +70,15 @@
                 </para>
               </xsl:if>
 
+              <xsl:if test="attr[@name = 'relatedPackages']">
+                <para>
+                  <emphasis>Related packages:</emphasis>
+                  <xsl:text> </xsl:text>
+                  <xsl:value-of disable-output-escaping="yes"
+                                select="attr[@name = 'relatedPackages']/string/@value" />
+                </para>
+              </xsl:if>
+
               <xsl:if test="count(attr[@name = 'declarations']/list/*) != 0">
                 <para>
                   <emphasis>Declared by:</emphasis>