Remove dependency on setuptools for pythran -E

This should simplify the life of scipy maintainers, see #2228.

.github/workflows/no-setuptools.yml

@@ -0,0 +1,32 @@
+name: no-setuptools
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        python-version: [3.12]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Setup Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v4
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install scipy-openblas64
+    - name: Setup
+      run: |
+        python -m pip install .
+        python -m pip uninstall -y setuptools  # the goal of that check is to test codegen without setuptools
+    - name: Testing scipy
+      run: |
+        find pythran/tests/scipy/ -name '*.py' -exec pythran -E {} \;

pythran/toolchain.py

@@ -8,7 +8,6 @@
 from pythran.cxxgen import PythonModule, Include, Line, Statement
 from pythran.cxxgen import FunctionBody, FunctionDeclaration, Value, Block
 from pythran.cxxgen import ReturnStatement
-from pythran.dist import PythranExtension, PythranBuildExt
 from pythran.errors import PythranCompileError
 from pythran.middlend import refine, mark_unexported_functions
 from pythran.passmanager import PassManager
@@ -24,12 +23,6 @@
 
 import sysconfig
 
-try:
-    # `numpy.distutils is deprecated, may not be present, or broken
-    from numpy.distutils.core import setup
-except Exception:
-    from setuptools import setup
-
 from tempfile import mkdtemp, NamedTemporaryFile
 import gast as ast
 import importlib
@@ -335,6 +328,14 @@ def compile_cxxfile(module_name, cxxfile, output_binary=None, **kwargs):
     Raises PythranCompileError on failure
 
     '''
+    # local import so that we don't depend on setuptools for the code generation
+    # part
+    from pythran.dist import PythranExtension, PythranBuildExt
+    try:
+        # `numpy.distutils is deprecated, may not be present, or broken
+        from numpy.distutils.core import setup
+    except Exception:
+        from setuptools import setup
 
     builddir = mkdtemp()
     buildtmp = mkdtemp()