Create a from-source Nix package for oils-for-nix

mypy-0.780.nix

@@ -0,0 +1,40 @@
+{
+  lib,
+  fetchFromGitHub,
+  python3,
+}:
+
+python3.pkgs.buildPythonPackage rec {
+  pname = "mypy";
+  # This is the version oils-for-unix uses for mycpp Python-to-C++ translation
+  version = "0.780";
+
+  src = fetchFromGitHub {
+    owner = "python";
+    repo = "mypy";
+    rev = "v${version}";
+    # Fetch submodules to include typeshed (required for type stubs)
+    fetchSubmodules = true;
+    hash = "sha256-czwCx6ZjCu3CrVmbI6NbstzWM0GvuPTWJiiUhXSznu4=";
+  };
+
+  # Do not use mypyc to compile.
+  # Rather, build interpreted so mycpp can extend its classes.
+  preBuild = ''
+    export MYPY_USE_MYPYC=0
+  '';
+
+  # Skip tests to speed up build
+  doCheck = false;
+
+  dependencies = with python3.pkgs; [
+    mypy-extensions
+    typing-extensions
+    typed-ast
+  ];
+
+  # Ensure we're not pulling in a compiled version
+  pythonImportsCheck = [ "mypy" ];
+
+  meta.license = lib.licenses.mit;
+}