Have pythran generate freethreading compatible code

This is the default, and can be changed through
--config backend.freethreading_compatible=false
or the equivalent pythranrc entry.

Fix #2258

.github/workflows/freethreading.yml

@@ -0,0 +1,48 @@
+# Kept seperate from core.yml because it uses a quantsight-built python setup
+name: freethreading
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        python-version: ["3.13t"]
+        cpp-version: [g++-8, clang-7]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install native dependencies
+      run: |
+        sudo apt install ${{ matrix.cpp-version }}
+        sudo apt install libopenblas-dev  # for meson integration testing
+    - name: Setup Python ${{ matrix.python-version }}
+      uses: quansight-labs/setup-python@v5.3.1
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install scipy-openblas64
+        pip install pytest-xdist
+    - name: Setup
+      run: |
+        python -m pip install .
+        printf '[compiler]\nblas=scipy-openblas\n' > ~/.config/.pythranrc
+        printf 'cflags=-std=c++11 -Wall -Werror -Wno-unknown-pragmas -Wno-unused-local-typedefs -Wno-cpp -Wno-deprecated-declarations' >> ~/.config/.pythranrc
+        if test "${{ matrix.cpp-version }}" = "clang-7" ; then printf -- " -Wno-absolute-value -Wno-parentheses-equality\n" ; else printf "\n" ; fi >> ~/.config/.pythranrc
+    - name: Testing minimal CLI
+      run: |
+        pythran --version
+        pythran --help
+        pythran-config -vvv
+    - name: Testing sequential
+      run: |
+        export CC=`echo ${{ matrix.cpp-version }} | sed -e 's/g++/gcc/'`
+        export CXX=`echo ${{ matrix.cpp-version }} | sed -e 's/clang/clang++/'`
+        pytest pythran/tests/test_base.py -v -x

docs/MANUAL.rst

@@ -753,6 +753,13 @@ This controls some behavior of the C++ backend, so the default should be safe::
     # to the original python code
     annotate = false
 
+    # set to 'lineno' if you want to generate line number instead of python extract
+    annotation_kind = 'comment'
+
+    # make generated module compatible with freethreading, see
+    # https://py-free-threading.github.io/
+    freethreading_compatible = true
+
 
 F.A.Q.
 ------

pythran/cxxgen.py

@@ -28,6 +28,7 @@
 #
 
 from textwrap import dedent
+from pythran.config import cfg
 from pythran.tables import pythran_ward
 from pythran.spec import signatures_to_string
 from pythran.utils import quote_cxxstring
@@ -732,11 +733,16 @@ def __str__(self):
                                    theDoc);
 
                 {extraobjects}
+                {freethreading}
                 return theModule;
             }}
             '''.format(name=self.name,
                        import_umath="import_umath();" if self.ufuncs else "",
                        extraobjects='\n'.join(theextraobjects),
+                       freethreading="""
+                            #ifdef Py_GIL_DISABLED
+                                PyUnstable_Module_SetGIL(theModule, Py_MOD_GIL_NOT_USED);
+                            #endif""" if cfg.getboolean("backend", "freethreading_compatible") else "",
                        **self.metadata))
 
         body = (self.preamble +

pythran/pythran.cfg

@@ -54,3 +54,7 @@ annotate = false
 
 # set to 'lineno' if you want to generate line number instead of python extract
 annotation_kind = 'comment'
+
+# make generated module compatible with freethreading, see
+# https://py-free-threading.github.io/
+freethreading_compatible = true