Fix the Cython version check in meson.build

Author: oscarbenjamin

.github/workflows/buildwheel.yml

@@ -103,8 +103,8 @@ jobs:
           python --version --version
           which python
           python -c "import sysconfig; print(sysconfig.get_config_var('Py_GIL_DISABLED'))"
-          python -c "import sys; print(sys._is_gil_enabled())"
-          python -c "import sys; import flint; print(sys._is_gil_enabled())"
+          python -c "import sys; print(getattr(sys, '_is_gil_enabled', lambda: True)())"
+          python -c "import sys; import flint; print(getattr(sys, '_is_gil_enabled', lambda: True)())"
 
       - run: python -m flint.test --verbose
 

meson.build

@@ -83,10 +83,15 @@ add_project_arguments(
     language : 'cython'
 )
 
-# Enable free-threading if Cython is new enough:
+# Enable free-threading if Cython is new enough. The check should be
+# >= 3.1.0a1 but meson gets confused by the a1 alpha release suffix.
+# so we go with >= 3.1 (which will be correct once 3.1 is released).
 cy = meson.get_compiler('cython')
-if cy.version().version_compare('>=3.1.0a1')
-    add_project_arguments('-Xfreethreading_compatible=true', language : 'cython')
+if cy.version().version_compare('>=3.1')
+  message('Enabling freethreading')
+  add_project_arguments('-Xfreethreading_compatible=true', language : 'cython')
+else
+  message('Disabling freethreading')
 endif
 
 if get_option('coverage')