doc/lib-functions: remove warnings

Building the nixpkgs manual currently triggers a bunch of deprecation
warnings, because every attribute in `lib` is evaluated to see if it's
an attrset to generate locations for.

Instead, share the lib subsets to include in the documentation
between `lib-function-docs` and `lib-function-locations` so they can
coordinate.

Also generate the list of sections instead of duplicating it in
`library.xml`.

doc/doc-support/lib-function-docs.nix

@@ -1,30 +1,31 @@
-# Generates the documentation for library functions via nixdoc. To add
-# another library function file to this list, the include list in the
-# file `doc/functions/library.xml` must also be updated.
+# Generates the documentation for library functions via nixdoc.
 
-{ pkgs ? import ./.. {}, locationsXml }:
+{ pkgs, locationsXml, libsets }:
 
 with pkgs; stdenv.mkDerivation {
   name = "nixpkgs-lib-docs";
-  src = ./../../lib;
+  src = ../../lib;
 
   buildInputs = [ nixdoc ];
   installPhase = ''
     function docgen {
-      nixdoc -c "$1" -d "$2" -f "../lib/$1.nix"  > "$out/$1.xml"
+      nixdoc -c "$1" -d "$2" -f "$1.nix" > "$out/$1.xml"
+      echo "<xi:include href='$1.xml' />" >> "$out/index.xml"
     }
 
-    mkdir -p $out
-    ln -s ${locationsXml} $out/locations.xml
+    mkdir -p "$out"
 
-    docgen asserts 'Assert functions'
-    docgen attrsets 'Attribute-set functions'
-    docgen strings 'String manipulation functions'
-    docgen trivial 'Miscellaneous functions'
-    docgen lists 'List manipulation functions'
-    docgen debug 'Debugging functions'
-    docgen options 'NixOS / nixpkgs option handling'
-    docgen filesystem 'Filesystem functions'
-    docgen sources 'Source filtering functions'
+    cat > "$out/index.xml" << 'EOF'
+    <?xml version="1.0" encoding="utf-8"?>
+    <root xmlns:xi="http://www.w3.org/2001/XInclude">
+    EOF
+
+    ${lib.concatStrings (lib.mapAttrsToList (name: description: ''
+      docgen ${name} ${lib.escapeShellArg description}
+    '') libsets)}
+
+    echo "</root>" >> "$out/index.xml"
+
+    ln -s ${locationsXml} $out/locations.xml
   '';
 }