buildRubyGem: Provide manpages for Ruby gems (#49334)

pkgs/development/ruby-modules/bundler-app/default.nix

@@ -24,6 +24,7 @@
 , gemset ? null
 , preferLocalBuild ? false
 , allowSubstitutes ? false
+, installManpages ? true
 , meta ? {}
 , postBuild ? ""
 , gemConfig ? null
@@ -36,7 +37,7 @@ let
   // { inherit preferLocalBuild allowSubstitutes; }; # pass the defaults
 in
    runCommand basicEnv.name cmdArgs ''
-    mkdir -p $out/bin;
+    mkdir -p $out/bin
     ${(lib.concatMapStrings (x: "ln -s '${basicEnv}/bin/${x}' $out/bin/${x};\n") exes)}
     ${(lib.concatMapStrings (s: "makeWrapper $out/bin/$(basename ${s}) $srcdir/${s} " +
             "--set BUNDLE_GEMFILE ${basicEnv.confFiles}/Gemfile "+
@@ -45,5 +46,13 @@ in
             "--set GEM_HOME ${basicEnv}/${ruby.gemPath} "+
             "--set GEM_PATH ${basicEnv}/${ruby.gemPath} "+
             "--run \"cd $srcdir\";\n") scripts)}
+
+    ${lib.optionalString installManpages ''
+    for section in {1..9}; do
+      mandir="$out/share/man/man$section"
+      find -L ${basicEnv}/${ruby.gemPath}/gems/${basicEnv.name} \( -wholename "*/man/*.$section" -o -wholename "*/man/man$section/*.$section" \) -print -execdir mkdir -p $mandir \; -execdir cp '{}' $mandir \;
+    done
+    ''}
+
     ${postBuild}
   ''

pkgs/development/ruby-modules/gem/default.nix

@@ -44,6 +44,7 @@ lib.makeOverridable (
 # git checkout).
 # If you need to apply patches, make sure to set `dontBuild = false`;
 , dontBuild ? true
+, dontInstallManpages ? false
 , propagatedBuildInputs ? []
 , propagatedUserEnvPkgs ? []
 , buildFlags ? []
@@ -206,6 +207,14 @@ stdenv.mkDerivation ((builtins.removeAttrs attrs ["source"]) // {
     ruby ${./gem-post-build.rb} "$spec"
     ''}
 
+    ${lib.optionalString (!dontInstallManpages) ''
+    for section in {1..9}; do
+      mandir="$out/share/man/man$section"
+      find $out/lib \( -wholename "*/man/*.$section" -o -wholename "*/man/man$section/*.$section" \) \
+        -execdir mkdir -p $mandir \; -execdir cp '{}' $mandir \;
+    done
+    ''}
+
     runHook postInstall
   '';