buildPythonPackage: use a separate file to fire off setup.py

pkgs/development/python-modules/generic/default.nix

@@ -50,7 +50,7 @@ then throw "${name} not supported for interpreter ${python.executable}"
 else
 
 let
-  setuppy = "import setuptools, tokenize;__file__='setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\\r\\n', '\\n'), __file__, 'exec'))";
+  setuppy = ./run_setup.py;
 in
 python.stdenv.mkDerivation (builtins.removeAttrs attrs ["disabled"] // {
   inherit doCheck;
@@ -75,18 +75,19 @@ python.stdenv.mkDerivation (builtins.removeAttrs attrs ["disabled"] // {
     runHook postConfigure
   '';
 
-  checkPhase = attrs.checkPhase or ''
-    runHook preCheck
-    ${python.interpreter} -c "${setuppy}" test
-    runHook postCheck
-  '';
-
   buildPhase = attrs.buildPhase or ''
     runHook preBuild
-    ${python.interpreter} -c "${setuppy}" bdist_wheel
+    cp ${setuppy} nix_run_setup.py
+    ${python.interpreter} nix_run_setup.py build_ext ${lib.concatStringsSep " " setupPyBuildFlags} bdist_wheel
     runHook postBuild
   '';
 
+  checkPhase = attrs.checkPhase or ''
+    runHook preCheck
+    ${python.interpreter} nix_run_setup.py test
+    runHook postCheck
+  '';
+
   installPhase = attrs.installPhase or ''
     runHook preInstall
 

pkgs/development/python-modules/generic/run_setup.py

@@ -0,0 +1,6 @@
+import setuptools
+import tokenize
+
+__file__='setup.py';
+
+exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\\r\\n', '\\n'), __file__, 'exec'))