nixos/manual: improve error message for invalid values in `relatedPackages'

As reported in NixOS discourse[1], tracking down invalid values in
`relatedPackages'[2] (i.e. list-items that don't exist in `pkgs`) is
fairly hard as the message "Invalid package attribute path `foobar'"
is quite unhelpful and the trace doesn't point to the source of the
problem either.

This patch improves the error message by mentioning that the issue is an
invalid `relatedPackages`-declaration in $optionName.

[1] https://discourse.nixos.org/t/invalid-package-attribute-path-nextcloud19/8403/9
[2] https://nixos.org/nixpkgs/manual/#sec-functions-library-options

1 files changed, 3 insertions, 3 deletions

diff --git a/nixos/lib/make-options-doc/default.nix b/nixos/lib/make-options-doc/default.nix
index 772b7d3add9..a1161621f0d 100644
--- a/nixos/lib/make-options-doc/default.nix
+++ b/nixos/lib/make-options-doc/default.nix
@@ -36,7 +36,7 @@ let
     // 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 ? relatedPackages && opt.relatedPackages != []) { relatedPackages = genRelatedPackages opt.relatedPackages; }
+    // lib.optionalAttrs (opt ? relatedPackages && opt.relatedPackages != []) { relatedPackages = genRelatedPackages opt.relatedPackages opt.name; }
    );
 
   # Generate DocBook documentation for a list of packages. This is
@@ -48,7 +48,7 @@ let
   # - a list:    that will be interpreted as an attribute path from `pkgs`,
   # - an attrset: that can specify `name`, `path`, `package`, `comment`
   #   (either of `name`, `path` is required, the rest are optional).
-  genRelatedPackages = packages:
+  genRelatedPackages = packages: optName:
     let
       unpack = p: if lib.isString p then { name = p; }
                   else if lib.isList p then { path = p; }
@@ -58,7 +58,7 @@ let
           title = args.title or null;
           name = args.name or (lib.concatStringsSep "." args.path);
           path = args.path or [ args.name ];
-          package = args.package or (lib.attrByPath path (throw "Invalid package attribute path `${toString path}'") pkgs);
+          package = args.package or (lib.attrByPath path (throw "Invalid package attribute path `${toString path}' found while evaluating `relatedPackages' of option `${optName}'") pkgs);
         in "<listitem>"
         + "<para><literal>${lib.optionalString (title != null) "${title} aka "}pkgs.${name} (${package.meta.name})</literal>"
         + lib.optionalString (!package.meta.available) " <emphasis>[UNAVAILABLE]</emphasis>"