bundlerEnv: ensure dependencies always included

Suppose I have a Gemfile like this:

    source "https://rubygems.org"
    gem "actioncable"
    gem "websocket-driver", group: :test

The gemset.nix generated by Bundix 2.4.1 will set ActionCable's groups
to [ "default" ], and websocket-driver's to [ "test" ]. This means that
the generated bundlerEnv wouldn't include websocket-driver unless the
test group was included, even though it's required by the default group.

This is arguably a bug in Bundix (websocket-driver's groups should
probably be [ "default" "test" ] or just [ "default" ]), but there's no
reason bundlerEnv should omit dependencies even given such an input --
it won't necessarily come from Bundix, and it would be good for
bundlerEnv to do the right thing.

To fix this, filterGemset is now a recursive function, that adds
dependencies of gems in the group to the filtered gemset until it
stabilises on the gems that match the required groups, and all of their
recursive dependencies.

lib/attrsets.nix

@@ -94,6 +94,15 @@ rec {
   attrValues = builtins.attrValues or (attrs: attrVals (attrNames attrs) attrs);
 
 
+  /* Given a set of attribute names, return the set of the corresponding
+     attributes from the given set.
+
+     Example:
+       getAttrs [ "a" "b" ] { a = 1; b = 2; c = 3; }
+       => { a = 1; b = 2; }
+  */
+  getAttrs = names: attrs: genAttrs names (name: attrs.${name});
+
   /* Collect each attribute named `attr' from a list of attribute
      sets.  Sets that don't contain the named attribute are ignored.
 

lib/default.nix

@@ -61,10 +61,10 @@ let
       boolToString mergeAttrs flip mapNullable inNixShell min max
       importJSON warn info nixpkgsVersion version mod compare
       splitByAndCompare functionArgs setFunctionArgs isFunction;
-    inherit (fixedPoints) fix fix' extends composeExtensions
+    inherit (fixedPoints) fix fix' converge extends composeExtensions
       makeExtensible makeExtensibleWithCustomName;
     inherit (attrsets) attrByPath hasAttrByPath setAttrByPath
-      getAttrFromPath attrVals attrValues catAttrs filterAttrs
+      getAttrFromPath attrVals attrValues getAttrs catAttrs filterAttrs
       filterAttrsRecursive foldAttrs collect nameValuePair mapAttrs
       mapAttrs' mapAttrsToList mapAttrsRecursive mapAttrsRecursiveCond
       genAttrs isDerivation toDerivation optionalAttrs

lib/fixed-points.nix

@@ -24,6 +24,16 @@ rec {
   # for a concrete example.
   fix' = f: let x = f x // { __unfix__ = f; }; in x;
 
+  # Return the fixpoint that `f` converges to when called recursively, starting
+  # with the input `x`.
+  #
+  #     nix-repl> converge (x: x / 2) 16
+  #     0
+  converge = f: x:
+    if (f x) == x
+    then x
+    else converge f (f x);
+
   # Modify the contents of an explicitly recursive attribute set in a way that
   # honors `self`-references. This is accomplished with a function
   #

pkgs/development/ruby-modules/bundled-common/functions.nix

@@ -1,5 +1,9 @@
 { lib, gemConfig, ... }:
-rec {
+
+let
+  inherit (lib) attrValues concatMap converge filterAttrs getAttrs;
+
+in rec {
   bundlerFiles = {
     gemfile ? null
   , lockfile ? null
@@ -22,7 +26,19 @@ rec {
     else gemset;
   };
 
-  filterGemset = {ruby, groups,...}: gemset: lib.filterAttrs (name: attrs: platformMatches ruby attrs && groupMatches groups attrs) gemset;
+  filterGemset = { ruby, groups, ... }: gemset:
+    let
+      platformGems = filterAttrs (_: platformMatches ruby) gemset;
+      directlyMatchingGems = filterAttrs (_: groupMatches groups) platformGems;
+
+      expandDependencies = gems:
+        let
+          depNames = concatMap (gem: gem.dependencies or []) (attrValues gems);
+          deps = getAttrs depNames platformGems;
+        in
+          gems // deps;
+    in
+      converge expandDependencies directlyMatchingGems;
 
   platformMatches = {rubyEngine, version, ...}: attrs: (
   !(attrs ? "platforms") ||