[3.12] gh-107249: Implement Py_UNUSED() for MSVC (GH-107250) (#127907)

gh-107249: Implement Py_UNUSED() for MSVC (GH-107250) Fix warnings C4100 in Py_UNUSED() when Python is built with "cl /W4". Example with this function included by Python.h: static inline unsigned int PyUnicode_IS_READY(PyObject* Py_UNUSED(op)) { return 1; } Without this change, building a C program with "cl /W4" which just includes Python.h emits the warning: Include\cpython/unicodeobject.h(199): warning C4100: '_unused_op': unreferenced formal parameter This change fix this warning. (cherry picked from commit 6a43cce) Co-authored-by: Victor Stinner <[email protected]>
python · Dec 13, 2024 · f3a689f · f3a689f
1 parent b184f48
commit f3a689f
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diff --git a/Include/pymacro.h b/Include/pymacro.h
@@ -118,6 +118,15 @@
  */
 #if defined(__GNUC__) || defined(__clang__)
 #  define Py_UNUSED(name) _unused_ ## name __attribute__((unused))
+#elif defined(_MSC_VER)
+   // Disable warning C4100: unreferenced formal parameter,
+   // declare the parameter,
+   // restore old compiler warnings.
+#  define Py_UNUSED(name) \
+        __pragma(warning(push)) \
+        __pragma(warning(suppress: 4100)) \
+        _unused_ ## name \
+        __pragma(warning(pop))
 #else
 #  define Py_UNUSED(name) _unused_ ## name
 #endif

diff --git a/Misc/NEWS.d/next/C API/2023-07-25-17-23-08.gh-issue-107249.xqk2ke.rst b/Misc/NEWS.d/next/C API/2023-07-25-17-23-08.gh-issue-107249.xqk2ke.rst
@@ -0,0 +1,2 @@
+Implement the :c:macro:`Py_UNUSED` macro for Windows MSVC compiler. Patch by
+Victor Stinner.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Implement the :c:macro:`Py_UNUSED` macro for Windows MSVC compiler. Patch by
		Victor Stinner.