[libc++] Inlines format_error for clang-cl DLL.

[Mordante]

Summary

This version is build without support for the experimental library but
the code still wants to link this function. Inlining the function solves
the issue.

[mstorsjo]

Not much opinion on the change itself, but one nitpick about a comment.

libcxx/include/__format/format_error.h

35

Nitpick, "Clang-cl", or "MSVC mode" or something like that, but not plain "Clang".

[Mordante]

libcxx/include/__format/format_error.h

35

Thanks for the comment! I'll fix it when landing the patch.

[ldionne]

LGTM but we should really look into fixing the experimental library on Windows/shared.

libcxx/CMakeLists.txt

target_compile_definitions(${target} PRIVATE
                                  _CRTBLD
                                  # Don't warn on the use of "deprecated"
                                  # "insecure" functions which are standards
                                  # specified.
                                  _CRT_SECURE_NO_WARNINGS
                                  # Use the ISO conforming behaviour for conversion
                                  # in printf, scanf.
                                  _CRT_STDIO_ISO_WIDE_SPECIFIERS)
+    # Clang-cl shared builds don't support the experimental library.
+    # To avoid linker errors the format_error destructor is inlined for the
+    # dylib. Users can never use format in this mode.
+    # TODO FMT Remove when format becomes mainline.
+    if (LIBCXX_ENABLE_SHARED)
+      target_compile_definitions(${target} PRIVATE
+                                 _LIBCPP_INLINE_FORMAT_ERROR_DTOR)
+    endif()
   endif()
 endfunction()
 
 # Configuration file flags =====================================================
 config_define(${LIBCXX_ABI_VERSION} _LIBCPP_ABI_VERSION)
 config_define(${LIBCXX_ABI_NAMESPACE} _LIBCPP_ABI_NAMESPACE)
 config_define_if(LIBCXX_ABI_FORCE_ITANIUM _LIBCPP_ABI_FORCE_ITANIUM)
 config_define_if(LIBCXX_ABI_FORCE_MICROSOFT _LIBCPP_ABI_FORCE_MICROSOFT)

libcxx/include/__format/format_error.h

 #if _LIBCPP_STD_VER > 17
 
 class _LIBCPP_EXCEPTION_ABI format_error : public runtime_error {
 public:
   _LIBCPP_HIDE_FROM_ABI explicit format_error(const string& __s)
       : runtime_error(__s) {}
   _LIBCPP_HIDE_FROM_ABI explicit format_error(const char* __s)
       : runtime_error(__s) {}
+  // TODO FMT Remove when format is no longer experimental.
+  // Avoids linker errors when building the Clang-cl Windows DLL which doesn't
+  // support the experimental library.
+#  ifndef _LIBCPP_INLINE_FORMAT_ERROR_DTOR
   ~format_error() noexcept override;
+#  else
+  ~format_error() noexcept  override {}
+#  endif
 };
 
 _LIBCPP_NORETURN inline _LIBCPP_HIDE_FROM_ABI void
 __throw_format_error(const char* __s) {
 #ifndef _LIBCPP_NO_EXCEPTIONS
   throw format_error(__s);
 #else
   (void)__s;

libcxx/src/format.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include <format>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+#ifndef _LIBCPP_INLINE_FORMAT_ERROR_DTOR
 format_error::~format_error() noexcept = default;
+#endif
 
 _LIBCPP_END_NAMESPACE_STD