Add CI builds for free-threaded Python versions (#150)

Add missing error-checking in PyLong export tests.

Author: ngoldbaum

.github/workflows/build.yml

@@ -27,9 +27,11 @@ jobs:
           - "3.11"
           - "3.12"
           - "3.13"
+          - "3.13t"
           # CPython 3.14 final is scheduled for October 2025:
           # https://peps.python.org/pep-0719/
           - "3.14"
+          - "3.14t"
 
           # PyPy versions:
           # - https://github.com/actions/setup-python/blob/main/docs/advanced-usage.md
@@ -68,6 +70,8 @@ jobs:
             python: "3.12"
           - os: windows-latest
             python: "3.13"
+          - os: windows-latest
+            python: "3.13t"
 
           # macOS
           # Python 3.9 is the oldest version available on macOS/arm64.
@@ -81,6 +85,8 @@ jobs:
             python: "3.12"
           - os: macos-latest
             python: "3.13"
+          - os: macos-latest
+            python: "3.13t"
 
           # Ubuntu: test deadsnakes Python versions which are not supported by
           # GHA python-versions.

tests/test_pythoncapi_compat_cext.c

@@ -1432,29 +1432,48 @@ test_long_api(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
     PyLongWriter *writer;
     static PyLongExport long_export;
 
-    writer = PyLongWriter_Create(1, 1, (void**)&digits);
+    writer = PyLongWriter_Create(1, 1, (void **)&digits);
+    if (writer == NULL) {
+        return NULL;
+    }
     PyLongWriter_Discard(writer);
 
-    writer = PyLongWriter_Create(1, 1, (void**)&digits);
+    writer = PyLongWriter_Create(1, 1, (void **)&digits);
+    if (writer == NULL) {
+        return NULL;
+    }
     digits[0] = 123;
     obj = PyLongWriter_Finish(writer);
+    if (obj == NULL) {
+        return NULL;
+    }
 
     check_int(obj, -123);
-    PyLong_Export(obj, &long_export);
+    if (PyLong_Export(obj, &long_export) < 0) {
+        return NULL;
+    }
     assert(long_export.value == -123);
     assert(long_export.digits == NULL);
     PyLong_FreeExport(&long_export);
     Py_DECREF(obj);
 
-    writer = PyLongWriter_Create(0, 5, (void**)&digits);
+    writer = PyLongWriter_Create(0, 5, (void **)&digits);
+    if (writer == NULL) {
+        return NULL;
+    }
     digits[0] = 1;
     digits[1] = 0;
     digits[2] = 0;
     digits[3] = 0;
     digits[4] = 1;
     obj = PyLongWriter_Finish(writer);
+    if (obj == NULL) {
+        return NULL;
+    }
 
-    PyLong_Export(obj, &long_export);
+    if (PyLong_Export(obj, &long_export) < 0) {
+        return NULL;
+    }
     assert(long_export.value == 0);
     digits = (digit*)long_export.digits;
     assert(digits[0] == 1);