WORKSPACE: use nix for python/go if available
This introduces Nix, the package manager, and nixpkgs, the package
collection, into hscloud's bazel build machinery.
There are two reasons behind this:
- on NixOS, it's painful or at least very difficult to run hscloud out
of the box. Especially with rules_go, that download a blob from the
Internet to get a Go toolchain, it just fails outright. This solves
this and allows hscloud to be used on NixOS.
- on non-NixOS platforms that still might have access to Nix this
allows to somewhat hermeticize the build. Notably, Python now comes
from nixpkgs, and is fabricobbled in a way that makes pip3_import
use Nix system dependencies for ncurses and libpq.
This has been tested to run ci_presubmit on NixOS 20.09pre and Gentoo
~amd64.
Change-Id: Ic16e4827cb52a05aea0df0eed84d80c5e9ae0e07
diff --git a/third_party/nix/BUILD b/third_party/nix/BUILD
new file mode 100644
index 0000000..c0821e6
--- /dev/null
+++ b/third_party/nix/BUILD
@@ -0,0 +1,21 @@
+load("@rules_python//python:defs.bzl", "py_runtime_pair")
+
+# Python3 toolchain definition that uses //third_party/nix:python.nix (via
+# external repository).
+
+py_runtime(
+ name = "py3_runtime",
+ interpreter = "@hscloud_nix_python3//:python3",
+ python_version = "PY3",
+)
+
+py_runtime_pair(
+ name = "py_runtime_pair",
+ py3_runtime = ":py3_runtime",
+)
+
+toolchain(
+ name = "py_toolchain",
+ toolchain = ":py_runtime_pair",
+ toolchain_type = "@rules_python//python:toolchain_type",
+)