Cleanup of file-scoped and globally-scoped warning suppression pragmas across pybind11 header files. (#3201)

* Removing all MSVC C4127 warning suppression pragmas.

* Removing MSVC /WX (WERROR). To get a full list of all warnings.

* Inserting PYBIND11_SILENCE_MSVC_C4127. Changing one runtime if to #if.

* Changing PYBIND11_SILENCE_MSVC_C4127 macro to use absolute namespace (for use outside pybind11 include directory).

* Restoring MSVC /WX (WERROR).

* Removing globally-scoped suppression for clang -Wunsequenced. Based on an experiment under PR #3202 it is obsolete and can simply be removed.

include/pybind11/detail/common.h

@@ -968,7 +968,7 @@ inline void silence_unused_warnings(Args &&...) {}
 // warning C4127: Conditional expression is constant
 constexpr inline bool silence_msvc_c4127(bool cond) { return cond; }
 
-#    define PYBIND11_SILENCE_MSVC_C4127(...) detail::silence_msvc_c4127(__VA_ARGS__)
+#    define PYBIND11_SILENCE_MSVC_C4127(...) ::pybind11::detail::silence_msvc_c4127(__VA_ARGS__)
 
 #else
 #    define PYBIND11_SILENCE_MSVC_C4127(...) __VA_ARGS__

include/pybind11/numpy.h

@@ -25,11 +25,6 @@
 #include <vector>
 #include <typeindex>
 
-#if defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
-
 /* This will be true on all flat address space platforms and allows us to reduce the
    whole npy_intp / ssize_t / Py_intptr_t business down to just ssize_t for all size
    and dimension types (e.g. shape, strides, indexing), instead of inflicting this
@@ -747,7 +742,7 @@ public:
      * and the caller must take care not to access invalid dimensions or dimension indices.
      */
     template <typename T, ssize_t Dims = -1> detail::unchecked_mutable_reference<T, Dims> mutable_unchecked() & {
-        if (Dims >= 0 && ndim() != Dims)
+        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims)
             throw std::domain_error("array has incorrect number of dimensions: " + std::to_string(ndim()) +
                     "; expected " + std::to_string(Dims));
         return detail::unchecked_mutable_reference<T, Dims>(mutable_data(), shape(), strides(), ndim());
@@ -761,7 +756,7 @@ public:
      * invalid dimensions or dimension indices.
      */
     template <typename T, ssize_t Dims = -1> detail::unchecked_reference<T, Dims> unchecked() const & {
-        if (Dims >= 0 && ndim() != Dims)
+        if (PYBIND11_SILENCE_MSVC_C4127(Dims >= 0) && ndim() != Dims)
             throw std::domain_error("array has incorrect number of dimensions: " + std::to_string(ndim()) +
                     "; expected " + std::to_string(Dims));
         return detail::unchecked_reference<T, Dims>(data(), shape(), strides(), ndim());
@@ -1708,7 +1703,3 @@ Helper vectorize(Return (Class::*f)(Args...) const) {
 }
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(_MSC_VER)
-#pragma warning(pop)
-#endif

include/pybind11/operators.h

@@ -11,13 +11,6 @@
 
 #include "pybind11.h"
 
-#if defined(__clang__) && !defined(__INTEL_COMPILER)
-#  pragma clang diagnostic ignored "-Wunsequenced" // multiple unsequenced modifications to 'self' (when using def(py::self OP Type()))
-#elif defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
-
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
 
@@ -58,7 +51,8 @@ template <op_id id, op_type ot, typename L, typename R> struct op_ {
         using op = op_impl<id, ot, Base, L_type, R_type>;
         cl.def(op::name(), &op::execute, is_operator(), extra...);
         #if PY_MAJOR_VERSION < 3
-        if (id == op_truediv || id == op_itruediv)
+        if (PYBIND11_SILENCE_MSVC_C4127(id == op_truediv) ||
+            PYBIND11_SILENCE_MSVC_C4127(id == op_itruediv))
             cl.def(id == op_itruediv ? "__idiv__" : ot == op_l ? "__div__" : "__rdiv__",
                     &op::execute, is_operator(), extra...);
         #endif
@@ -167,7 +161,3 @@ using detail::self;
 using detail::hash;
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(_MSC_VER)
-#  pragma warning(pop)
-#endif

include/pybind11/stl.h

@@ -19,11 +19,6 @@
 #include <deque>
 #include <valarray>
 
-#if defined(_MSC_VER)
-#pragma warning(push)
-#pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
-
 #ifdef __has_include
 // std::optional (but including it in c++14 mode isn't allowed)
 #  if defined(PYBIND11_CPP17) && __has_include(<optional>)
@@ -390,7 +385,3 @@ inline std::ostream &operator<<(std::ostream &os, const handle &obj) {
 }
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
-
-#if defined(_MSC_VER)
-#pragma warning(pop)
-#endif

tests/test_builtin_casters.cpp

@@ -10,11 +10,6 @@
 #include "pybind11_tests.h"
 #include <pybind11/complex.h>
 
-#if defined(_MSC_VER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#endif
-
 struct ConstRefCasted {
   int tag;
 };
@@ -73,7 +68,7 @@ TEST_SUBMODULE(builtin_casters, m) {
     std::wstring wstr;
     wstr.push_back(0x61); // a
     wstr.push_back(0x2e18); // ⸘
-    if (sizeof(wchar_t) == 2) { wstr.push_back(mathbfA16_1); wstr.push_back(mathbfA16_2); } // 𝐀, utf16
+    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2)) { wstr.push_back(mathbfA16_1); wstr.push_back(mathbfA16_2); } // 𝐀, utf16
     else { wstr.push_back((wchar_t) mathbfA32); } // 𝐀, utf32
     wstr.push_back(0x7a); // z
 
@@ -83,11 +78,12 @@ TEST_SUBMODULE(builtin_casters, m) {
     m.def("good_wchar_string", [=]() { return wstr; }); // a‽𝐀z
     m.def("bad_utf8_string", []()  { return std::string("abc\xd0" "def"); });
     m.def("bad_utf16_string", [=]() { return std::u16string({ b16, char16_t(0xd800), z16 }); });
+#if PY_MAJOR_VERSION >= 3
     // Under Python 2.7, invalid unicode UTF-32 characters don't appear to trigger UnicodeDecodeError
-    if (PY_MAJOR_VERSION >= 3)
     m.def("bad_utf32_string", [=]() { return std::u32string({ a32, char32_t(0xd800), z32 }); });
-    if (PY_MAJOR_VERSION >= 3 || sizeof(wchar_t) == 2)
+    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(wchar_t) == 2))
         m.def("bad_wchar_string", [=]() { return std::wstring({ wchar_t(0x61), wchar_t(0xd800) }); });
+#endif
     m.def("u8_Z", []() -> char { return 'Z'; });
     m.def("u8_eacute", []() -> char { return '\xe9'; });
     m.def("u16_ibang", [=]() -> char16_t { return ib16; });