gh-77532: Minor tweaks to allow compiling with PlatformToolset=ClangCL on Windows (GH-101352)

To use this, ensure that clang support was selected in Visual Studio Installer, then set the PlatformToolset environment variable to "ClangCL" and build as normal from the command line.
It remains unsupported, but at least is possible now for experimentation.

Include/cpython/pytime.h

@@ -53,6 +53,10 @@ functions and constants
 extern "C" {
 #endif
 
+#ifdef __clang__
+struct timeval;
+#endif
+
 /* _PyTime_t: Python timestamp with subsecond precision. It can be used to
    store a duration, and so indirectly a date (related to another date, like
    UNIX epoch). */

Include/internal/pycore_tracemalloc.h

@@ -36,11 +36,13 @@ struct _PyTraceMalloc_Config {
 
 /* Pack the frame_t structure to reduce the memory footprint on 64-bit
    architectures: 12 bytes instead of 16. */
+#if defined(_MSC_VER)
+#pragma pack(push, 4)
+#endif
+
 struct
 #ifdef __GNUC__
 __attribute__((packed))
-#elif defined(_MSC_VER)
-#pragma pack(push, 4)
 #endif
 tracemalloc_frame {
     /* filename cannot be NULL: "<unknown>" is used if the Python frame

Misc/NEWS.d/next/Build/2023-01-26-19-02-11.gh-issue-77532.cXD8bg.rst

@@ -0,0 +1 @@
+Minor fixes to allow building with ``PlatformToolset=ClangCL`` on Windows.

Modules/_decimal/libmpdec/mpdecimal.c

@@ -76,6 +76,12 @@
   #endif
 #endif
 
+/* ClangCL claims to support 128-bit int, but doesn't */
+#if defined(__SIZEOF_INT128__) && defined(__clang__) && defined(_MSC_VER)
+#undef __SIZEOF_INT128__
+#endif
+
+
 
 #define MPD_NEWTONDIV_CUTOFF 1024L
 

PC/launcher2.c

@@ -465,10 +465,14 @@ dumpSearchInfo(SearchInfo *search)
         return;
     }
 
-#define DEBUGNAME(s) L"SearchInfo." ## s
-#define DEBUG(s) debug(DEBUGNAME(#s) L": %s\n", (search->s) ? (search->s) : L"(null)")
-#define DEBUG_2(s, sl) _debugStringAndLength((search->s), (search->sl), DEBUGNAME(#s))
-#define DEBUG_BOOL(s) debug(DEBUGNAME(#s) L": %s\n", (search->s) ? L"True" : L"False")
+#ifdef __clang__
+#define DEBUGNAME(s) L # s
+#else
+#define DEBUGNAME(s) # s
+#endif
+#define DEBUG(s) debug(L"SearchInfo." DEBUGNAME(s) L": %s\n", (search->s) ? (search->s) : L"(null)")
+#define DEBUG_2(s, sl) _debugStringAndLength((search->s), (search->sl), L"SearchInfo." DEBUGNAME(s))
+#define DEBUG_BOOL(s) debug(L"SearchInfo." DEBUGNAME(s) L": %s\n", (search->s) ? L"True" : L"False")
     DEBUG(originalCmdLine);
     DEBUG(restOfCmdLine);
     DEBUG(executablePath);

PC/pyconfig.h

@@ -76,30 +76,26 @@ WIN32 is still required for the locale module.
 /* Compiler specific defines */
 
 /* ------------------------------------------------------------------------*/
-/* Microsoft C defines _MSC_VER */
+/* Microsoft C defines _MSC_VER, as does clang-cl.exe */
 #ifdef _MSC_VER
 
 /* We want COMPILER to expand to a string containing _MSC_VER's *value*.
  * This is horridly tricky, because the stringization operator only works
  * on macro arguments, and doesn't evaluate macros passed *as* arguments.
- * Attempts simpler than the following appear doomed to produce "_MSC_VER"
- * literally in the string.
  */
 #define _Py_PASTE_VERSION(SUFFIX) \
         ("[MSC v." _Py_STRINGIZE(_MSC_VER) " " SUFFIX "]")
 /* e.g., this produces, after compile-time string catenation,
- *      ("[MSC v.1200 32 bit (Intel)]")
+ *      ("[MSC v.1900 64 bit (Intel)]")
  *
  * _Py_STRINGIZE(_MSC_VER) expands to
- * _Py_STRINGIZE1((_MSC_VER)) expands to
- * _Py_STRINGIZE2(_MSC_VER) but as this call is the result of token-pasting
- *      it's scanned again for macros and so further expands to (under MSVC 6)
- * _Py_STRINGIZE2(1200) which then expands to
- * "1200"
+ * _Py_STRINGIZE1(_MSC_VER) and this second macro call is scanned
+ *      again for macros and so further expands to
+ * _Py_STRINGIZE1(1900) which then expands to
+ * "1900"
  */
-#define _Py_STRINGIZE(X) _Py_STRINGIZE1((X))
-#define _Py_STRINGIZE1(X) _Py_STRINGIZE2 ## X
-#define _Py_STRINGIZE2(X) #X
+#define _Py_STRINGIZE(X) _Py_STRINGIZE1(X)
+#define _Py_STRINGIZE1(X) #X
 
 /* MSVC defines _WINxx to differentiate the windows platform types
 
@@ -122,13 +118,16 @@ WIN32 is still required for the locale module.
  */
 #ifdef MS_WIN64
 #if defined(_M_X64) || defined(_M_AMD64)
-#if defined(__INTEL_COMPILER)
+#if defined(__clang__)
+#define COMPILER ("[Clang " __clang_version__ "] 64 bit (AMD64) with MSC v." _Py_STRINGIZE(_MSC_VER) " CRT]")
+#define PY_SUPPORT_TIER 0
+#elif defined(__INTEL_COMPILER)
 #define COMPILER ("[ICC v." _Py_STRINGIZE(__INTEL_COMPILER) " 64 bit (amd64) with MSC v." _Py_STRINGIZE(_MSC_VER) " CRT]")
 #define PY_SUPPORT_TIER 0
 #else
 #define COMPILER _Py_PASTE_VERSION("64 bit (AMD64)")
 #define PY_SUPPORT_TIER 1
-#endif /* __INTEL_COMPILER */
+#endif /* __clang__ */
 #define PYD_PLATFORM_TAG "win_amd64"
 #elif defined(_M_ARM64)
 #define COMPILER _Py_PASTE_VERSION("64 bit (ARM64)")
@@ -181,13 +180,16 @@ typedef _W64 int Py_ssize_t;
 
 #if defined(MS_WIN32) && !defined(MS_WIN64)
 #if defined(_M_IX86)
-#if defined(__INTEL_COMPILER)
+#if defined(__clang__)
+#define COMPILER ("[Clang " __clang_version__ "] 32 bit (Intel) with MSC v." _Py_STRINGIZE(_MSC_VER) " CRT]")
+#define PY_SUPPORT_TIER 0
+#elif defined(__INTEL_COMPILER)
 #define COMPILER ("[ICC v." _Py_STRINGIZE(__INTEL_COMPILER) " 32 bit (Intel) with MSC v." _Py_STRINGIZE(_MSC_VER) " CRT]")
 #define PY_SUPPORT_TIER 0
 #else
 #define COMPILER _Py_PASTE_VERSION("32 bit (Intel)")
 #define PY_SUPPORT_TIER 1
-#endif /* __INTEL_COMPILER */
+#endif /* __clang__ */
 #define PYD_PLATFORM_TAG "win32"
 #elif defined(_M_ARM)
 #define COMPILER _Py_PASTE_VERSION("32 bit (ARM)")

PCbuild/pyproject.props

@@ -25,7 +25,8 @@
     <_DebugPreprocessorDefinition>NDEBUG;</_DebugPreprocessorDefinition>
     <_DebugPreprocessorDefinition Condition="$(Configuration) == 'Debug'">_DEBUG;</_DebugPreprocessorDefinition>
     <_PlatformPreprocessorDefinition>_WIN32;</_PlatformPreprocessorDefinition>
-    <_PlatformPreprocessorDefinition Condition="$(Platform) == 'x64'">_WIN64;_M_X64;</_PlatformPreprocessorDefinition>
+    <_PlatformPreprocessorDefinition Condition="$(Platform) == 'x64'">_WIN64;</_PlatformPreprocessorDefinition>
+    <_PlatformPreprocessorDefinition Condition="$(Platform) == 'x64' and $(PlatformToolset) != 'ClangCL'">_M_X64;$(_PlatformPreprocessorDefinition)</_PlatformPreprocessorDefinition>
     <_Py3NamePreprocessorDefinition>PY3_DLLNAME=L"$(Py3DllName)";</_Py3NamePreprocessorDefinition>
   </PropertyGroup>
   <ItemDefinitionGroup>
@@ -45,8 +46,10 @@
       <SuppressStartupBanner>true</SuppressStartupBanner>
       <WholeProgramOptimization>true</WholeProgramOptimization>
       <ControlFlowGuard Condition="$(EnableControlFlowGuard) != ''">$(EnableControlFlowGuard)</ControlFlowGuard>
-      <AdditionalOptions>/utf-8 %(AdditionalOptions)</AdditionalOptions>
       <MultiProcessorCompilation>true</MultiProcessorCompilation>
+      <AdditionalOptions>/utf-8 %(AdditionalOptions)</AdditionalOptions>
+      <AdditionalOptions Condition="$(PlatformToolset) == 'ClangCL'">-Wno-deprecated-non-prototype -Wno-unused-label -Wno-pointer-sign -Wno-incompatible-pointer-types-discards-qualifiers -Wno-unused-function %(AdditionalOptions)</AdditionalOptions>
+      <AdditionalOptions Condition="$(Configuration) != 'Debug' and $(PlatformToolset) == 'ClangCL'">-flto %(AdditionalOptions)</AdditionalOptions>
     </ClCompile>
     <ClCompile Condition="$(Configuration) == 'Debug'">
       <InlineFunctionExpansion>OnlyExplicitInline</InlineFunctionExpansion>