libiio: disable Python for static builds

libiio's Python bindings use ctypes to load the shared library, which
obviously can't work with a static build. This has recently started
causing eval errors because the package uses
stdenv.hostPlatform.extensions.sharedLibrary, which isn't available when
building a static library.

This patch adds a flag to disable the Python bindings, and automatically
disables them for static builds.

Note that even with this patch, static libiio doesn't build successfully
by default. You have to disable avahi and manually disable libxml2 with
custom CMake flags.

pkgs/development/libraries/libiio/default.nix

@@ -4,7 +4,7 @@
 , flex
 , bison
 , libxml2
-, python
+, pythonSupport ? !stdenv.hostPlatform.hasSharedLibraries, python
 , libusb1
 , avahiSupport ? true, avahi
 , libaio
@@ -19,7 +19,8 @@ stdenv.mkDerivation rec {
   pname = "libiio";
   version = "0.24";
 
-  outputs = [ "out" "lib" "dev" "python" ];
+  outputs = [ "out" "lib" "dev" ]
+    ++ lib.optional pythonSupport "python";
 
   src = fetchFromGitHub {
     owner = "analogdevicesinc";
@@ -37,8 +38,9 @@ stdenv.mkDerivation rec {
     flex
     bison
     pkg-config
+  ] ++ lib.optionals pythonSupport ([
     python
-  ] ++ lib.optional python.isPy3k python.pkgs.setuptools;
+  ] ++ lib.optional python.isPy3k python.pkgs.setuptools);
 
   buildInputs = [
     libxml2
@@ -49,25 +51,26 @@ stdenv.mkDerivation rec {
 
   cmakeFlags = [
     "-DUDEV_RULES_INSTALL_DIR=${placeholder "out"}/lib/udev/rules.d"
-    "-DPython_EXECUTABLE=${python.pythonForBuild.interpreter}"
-    "-DPYTHON_BINDINGS=on"
     # osx framework is disabled,
     # the linux-like directory structure is used for proper output splitting
     "-DOSX_PACKAGE=off"
     "-DOSX_FRAMEWORK=off"
+  ] ++ lib.optionals pythonSupport [
+    "-DPython_EXECUTABLE=${python.pythonForBuild.interpreter}"
+    "-DPYTHON_BINDINGS=on"
   ] ++ lib.optionals (!avahiSupport) [
     "-DHAVE_DNS_SD=OFF"
   ];
 
   postPatch = ''
-    # Hardcode path to the shared library into the bindings.
-    sed "s#@libiio@#$lib/lib/libiio${stdenv.hostPlatform.extensions.sharedLibrary}#g" ${./hardcode-library-path.patch} | patch -p1
-
     substituteInPlace libiio.rules.cmakein \
       --replace /bin/sh ${runtimeShell}
+  '' + lib.optionalString pythonSupport ''
+    # Hardcode path to the shared library into the bindings.
+    sed "s#@libiio@#$lib/lib/libiio${stdenv.hostPlatform.extensions.sharedLibrary}#g" ${./hardcode-library-path.patch} | patch -p1
   '';
 
-  postInstall = ''
+  postInstall = lib.optionalString pythonSupport ''
     # Move Python bindings into a separate output.
     moveToOutput ${python.sitePackages} "$python"
   '';

pkgs/top-level/python-packages.nix

@@ -5882,7 +5882,10 @@ self: super: with self; {
     inherit (pkgs.config) cudaSupport;
   };
 
-  libiio = (toPythonModule (pkgs.libiio.override { inherit python; })).python;
+  libiio = (toPythonModule (pkgs.libiio.override {
+    pythonSupport = true;
+    inherit python;
+  })).python;
 
   libkeepass = callPackage ../development/python-modules/libkeepass { };