bluez-headers: expose bluez header files

This escapes infinite recursion, because Python cannot depend on bluez
due to infinite recursion on multiple paths. But it only wants
bluetooth.h at build time, so this is sufficient.

In 5.84 the source path changes from lib/ to lib/bluetooth, which will
require an update to the install phase.

pkgs/by-name/bl/bluez-headers/package.nix

···
+{
+  lib,
+  stdenv,
+  fetchurl,
+}:
+
+# This package only provides the bluetooth headers from the bluez package
+# for consumption in Python, which cannot consume bluez.dev due to multiple
+# infinite recursion paths.
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "bluez-headers";
+  version = "5.83";
+
+  # This package has the source, because of the emulatorAvailable check in the
+  # bluez function args, that causes an infinite recursion with Python on cross
+  # builds.
+  src = fetchurl {
+    url = "mirror://kernel/linux/bluetooth/bluez-${finalAttrs.version}.tar.xz";
+    hash = "sha256-EIUi2QnSIFgTmb/sk9qrYgNVOc7vPdo+eZcHhcY70kw=";
+  };
+
+  dontConfigure = true;
+  dontBuild = true;
+
+  installPhase = ''
+    mkdir -p $out/include/bluetooth
+    cp -v lib/*.h "$out/include/bluetooth/"
+  '';
+
+  meta = {
+    homepage = "https://www.bluez.org/";
+    description = "Official Linux Bluetooth protocol stack";
+    changelog = "https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/ChangeLog?h=${finalAttrs.version}";
+    license = with lib.licenses; [
+      bsd2
+      gpl2Plus
+      lgpl21Plus
+      mit
+    ];
+    maintainers = with lib.maintainers; [ ];
+    platforms = lib.platforms.linux;
+  };
+})

pkgs/by-name/bl/bluez/package.nix

···
   stdenv,
   alsa-lib,
   autoreconfHook,
+  bluez-headers,
   dbus,
   docutils,
   ell,
···
 
 stdenv.mkDerivation (finalAttrs: {
   pname = "bluez";
-  version = "5.83";
-
-  src = fetchurl {
-    url = "mirror://kernel/linux/bluetooth/bluez-${finalAttrs.version}.tar.xz";
-    hash = "sha256-EIUi2QnSIFgTmb/sk9qrYgNVOc7vPdo+eZcHhcY70kw=";
-  };
+  inherit (bluez-headers) version src;
 
   patches = [
     (fetchurl {
···
     url = "https://git.kernel.org/pub/scm/bluetooth/bluez.git";
   };
 
-  meta = {
-    homepage = "https://www.bluez.org/";
-    description = "Official Linux Bluetooth protocol stack";
-    changelog = "https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/ChangeLog?h=${finalAttrs.version}";
-    license = with lib.licenses; [
-      bsd2
-      gpl2Plus
-      lgpl21Plus
-      mit
-    ];
+  meta = bluez-headers.meta // {
     mainProgram = "btinfo";
-    maintainers = with lib.maintainers; [ ];
-    platforms = lib.platforms.linux;
   };
 })