Introducing macro: PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES

Author: rwgk

include/pybind11/attr.h

@@ -518,26 +518,26 @@ template <typename... Args> struct process_attributes {
     static void init(const Args&... args, function_record *r) {
         PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(r);
         PYBIND11_WORKAROUND_INCORRECT_ALL_GCC_UNUSED_BUT_SET_PARAMETER(r);
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0) ... };
-        silence_unused_warnings(unused);
+        PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES(
+            {0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0)...});
     }
     static void init(const Args&... args, type_record *r) {
         PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(r);
         PYBIND11_WORKAROUND_INCORRECT_ALL_GCC_UNUSED_BUT_SET_PARAMETER(r);
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0) ... };
-        silence_unused_warnings(unused);
+        PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES(
+            {0, (process_attribute<typename std::decay<Args>::type>::init(args, r), 0)...});
     }
     static void precall(function_call &call) {
         PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call);
-        // int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::precall(call), 0) ... };
-        // silence_unused_warnings(unused);
-        (int []) { 0, (process_attribute<typename std::decay<Args>::type>::precall(call), 0) ... };
+        PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES(
+            {0, (process_attribute<typename std::decay<Args>::type>::precall(call), 0)...});
     }
     static void postcall(function_call &call, handle fn_ret) {
         PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call, fn_ret);
         PYBIND11_WORKAROUND_INCORRECT_ALL_GCC_UNUSED_BUT_SET_PARAMETER(fn_ret);
-        int unused[] = { 0, (process_attribute<typename std::decay<Args>::type>::postcall(call, fn_ret), 0) ... };
-        silence_unused_warnings(unused);
+        PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES(
+            {0,
+             (process_attribute<typename std::decay<Args>::type>::postcall(call, fn_ret), 0)...});
     }
 };
 

include/pybind11/cast.h

@@ -1237,8 +1237,8 @@ class unpacking_collector {
         // Tuples aren't (easily) resizable so a list is needed for collection,
         // but the actual function call strictly requires a tuple.
         auto args_list = list();
-        int unused[] = { 0, (process(args_list, std::forward<Ts>(values)), 0)... };
-        silence_unused_warnings(unused);
+        PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES(
+            {0, (process(args_list, std::forward<Ts>(values)), 0)...});
 
         m_args = std::move(args_list);
     }

include/pybind11/detail/common.h

@@ -955,6 +955,17 @@ inline void silence_unused_warnings(Args &&...) {}
 #    define PYBIND11_WORKAROUND_INCORRECT_OLD_GCC_UNUSED_BUT_SET_PARAMETER(...)
 #endif
 
+// MSVC error C4576: a parenthesized type followed by an initializer list is a
+//                   non-standard explicit type conversion syntax
+// clang: expression result unused [-Wunused-value]
+#if defined(_MSC_VER) || defined(__clang__) // All versions (as of July 2021).
+#    define PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES(...)                              \
+        int dummy[] = __VA_ARGS__;                                                                \
+        detail::silence_unused_warnings(dummy)
+#else
+#    define PYBIND11_INT_ARRAY_WORKING_AROUND_MSVC_CLANG_ISSUES(...) (int[]) __VA_ARGS__
+#endif
+
 #if defined(_MSC_VER) // All versions (as of July 2021).
 
 // warning C4127: Conditional expression is constant