Split buildPythonPackage into setup hooks

This commit splits the `buildPythonPackage` into multiple setup hooks.

Generally, Python packages are built from source to wheels using `setuptools`.
The wheels are then installed with `pip`. Tests were often called with
`python setup.py test` but this is less common nowadays. Most projects
now use a different entry point for running tests, typically `pytest`
or `nosetests`.

Since the wheel format was introduced more tools were built to generate these,
e.g. `flit`. Since PEP 517 is provisionally accepted, defining a build-system
independent format (`pyproject.toml`), `pip` can now use that format to
execute the correct build-system.

In the past I've added support for PEP 517 (`pyproject`) to the Python
builder, resulting in a now rather large builder. Furthermore, it was not possible
to reuse components elsewhere. Therefore, the builder is now split into multiple
setup hooks.

The `setuptoolsCheckHook` is included now by default but in time it should
be removed from `buildPythonPackage` to make it easier to use another hook
(curently one has to pass in `dontUseSetuptoolsCheck`).

pkgs/development/interpreters/python/hooks/default.nix

@@ -0,0 +1,95 @@
+# Hooks for building Python packages.
+{ python
+, callPackage
+, makeSetupHook
+}:
+
+let
+  pythonInterpreter = python.pythonForBuild.interpreter;
+  pythonSitePackages = python.sitePackages;
+  pythonCheckInterpreter = python.interpreter;
+  setuppy = ../run_setup.py;
+in rec {
+
+  flitBuildHook = callPackage ({ flit }:
+    makeSetupHook {
+      name = "flit-build-hook";
+      deps = [ flit ];
+      substitutions = {
+        inherit pythonInterpreter;
+      };
+    } ./flit-build-hook.sh) {};
+
+  pipBuildHook = callPackage ({ pip }:
+    makeSetupHook {
+      name = "pip-build-hook.sh";
+      deps = [ pip ];
+      substitutions = {
+        inherit pythonInterpreter pythonSitePackages;
+      };
+    } ./pip-build-hook.sh) {};
+
+  pipInstallHook = callPackage ({ pip }:
+    makeSetupHook {
+      name = "pip-install-hook";
+      deps = [ pip ];
+      substitutions = {
+        inherit pythonInterpreter pythonSitePackages;
+      };
+    } ./pip-install-hook.sh) {};
+
+  pytestCheckHook = callPackage ({ pytest }:
+    makeSetupHook {
+      name = "pytest-check-hook";
+      deps = [ pytest ];
+      substitutions = {
+        inherit pythonCheckInterpreter;
+      };
+    } ./pytest-check-hook.sh) {};
+
+  pythonCatchConflictsHook = callPackage ({ setuptools }:
+    makeSetupHook {
+      name = "python-catch-conflicts-hook";
+      deps = [ setuptools ];
+      substitutions = {
+        inherit pythonInterpreter;
+        catchConflicts=../catch_conflicts/catch_conflicts.py;
+      };
+    } ./python-catch-conflicts-hook.sh) {};
+
+  pythonImportsCheckHook = callPackage ({}:
+    makeSetupHook {
+      name = "python-imports-check-hook.sh";
+      substitutions = {
+        inherit pythonCheckInterpreter;
+      };
+    } ./python-imports-check-hook.sh) {};
+
+  pythonRemoveBinBytecodeHook = callPackage ({ }:
+    makeSetupHook {
+      name = "python-remove-bin-bytecode-hook";
+    } ./python-remove-bin-bytecode-hook.sh) {};
+
+  setuptoolsBuildHook = callPackage ({ setuptools, wheel }:
+    makeSetupHook {
+      name = "setuptools-setup-hook";
+      deps = [ setuptools wheel ];
+      substitutions = {
+        inherit pythonInterpreter pythonSitePackages setuppy;
+      };
+    } ./setuptools-build-hook.sh) {};
+
+  setuptoolsCheckHook = callPackage ({ setuptools }:
+    makeSetupHook {
+      name = "setuptools-check-hook";
+      deps = [ setuptools ];
+      substitutions = {
+        inherit pythonCheckInterpreter setuppy;
+      };
+    } ./setuptools-check-hook.sh) {};
+
+  wheelUnpackHook = callPackage ({ }:
+    makeSetupHook {
+      name = "wheel-unpack-hook.sh";
+    } ./wheel-unpack-hook.sh) {};
+}