python-module.cc

#include <Python.h>

#include "internal/eval.hh"
#include "internal/ptr.hh"

#include <nix/config.h>

#include <eval.hh>
#include <globals.hh>
#include <shared.hh>

namespace pythonnix {

#define _public_ __attribute__((visibility("default")))

PyObject *NixError = nullptr;

static PyMethodDef NixMethods[] = {{"eval", (PyCFunction)eval,
                                    METH_VARARGS | METH_KEYWORDS,
                                    "Eval nix expression"},
                                   {NULL, NULL, 0, NULL}};

static struct PyModuleDef nixmodule = {
    PyModuleDef_HEAD_INIT, "nix", "Nix expression bindings",
    -1, /* size of per-interpreter state of the module,
           or -1 if the module keeps state in global variables. */
    NixMethods};

extern "C" _public_ PyObject *PyInit_nix(void) {
  // By default, Nix sets the build-hook to be "$(readlink /proc/self/exe) __build-remote", expecting the current binary to be Nix itself.
  // But when we call the Nix library from Python this isn't the case, the current binary is Python then
  // So we need to change this default, pointing it to the Nix binary instead
  nix::settings.buildHook = nix::settings.nixBinDir + "/nix";
  // And by setting buildHook before calling initNix, we can override the defaults without overriding the user-provided options from the config files
  nix::initNix();
  nix::initGC();

  PyObjPtr m(PyModule_Create(&nixmodule));

  if (!m) {
    return nullptr;
  }

  NixError = PyErr_NewExceptionWithDoc(
      "nix.NixError",                             /* char *name */
      "Base exception class for the nix module.", /* char *doc */
      NULL,                                       /* PyObject *base */
      NULL                                        /* PyObject *dict */
  );

  if (!NixError) {
    return nullptr;
  }

  if (PyModule_AddObject(m.get(), "NixError", NixError) == -1) {
    return nullptr;
  }

  return m.release();
}
} // namespace pythonnix