pystark windows compilation fix

Author: Jose Fernandez

.vscode/settings.json

@@ -0,0 +1,4 @@
+{
+    "python-envs.defaultEnvManager": "ms-python.python:conda",
+    "python-envs.defaultPackageManager": "ms-python.python:conda"
+}

pystark/cpp/CMakeLists.txt

@@ -29,6 +29,21 @@ FetchContent_Declare(
     GIT_SHALLOW    TRUE
 )
 
+# nanobind caches NB_SUFFIX (the .pyd/.so extension tag) in CMakeCache.txt.
+# When the active Python interpreter changes (e.g. cp312 → cp311) the cached
+# value becomes stale because nanobind uses "set(... CACHE INTERNAL)" without
+# FORCE, so it never overwrites an existing entry.  We query the interpreter
+# here and force-write the cache entry so that the generated library always
+# carries the correct tag regardless of previous configure runs.
+execute_process(
+    COMMAND "${Python_EXECUTABLE}" "-c"
+        "import sysconfig; print(sysconfig.get_config_var('EXT_SUFFIX'))"
+    OUTPUT_VARIABLE _pystark_ext_suffix
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+)
+set(NB_SUFFIX  "${_pystark_ext_suffix}" CACHE INTERNAL "" FORCE)
+set(NB_SUFFIX_S "${_pystark_ext_suffix}" CACHE INTERNAL "" FORCE)
+
 FetchContent_MakeAvailable(nanobind)
 
 # Source files

pystark/cpp/nanobind_stark_include_all.h

@@ -18,6 +18,14 @@ using namespace nb::literals;
 
 #include <cstring>
 
+// ssize_t is a POSIX type not provided by MSVC's standard headers.
+// Python's headers define Py_ssize_t; make ssize_t an alias so that nanobind's
+// ndarray.h (template <ssize_t... Is> struct shape) and our own templates
+// compile cleanly on Windows.
+#if defined(_MSC_VER) && !defined(ssize_t)
+using ssize_t = Py_ssize_t;
+#endif
+
 
 // Type shortcuts
 #include <stark>