[libcxx-commits] [libcxx] [libc++] Externally instantiate std::vformat_to (PR #71009)

[Louis Dionne via libcxx-commits]

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@@ -397,19 +397,31 @@ requires(output_iterator<_OutIt, const _CharT&>) _LIBCPP_HIDE_FROM_ABI _OutIt
 // https://reviews.llvm.org/D110499#inline-1180704
 // TODO FMT Evaluate whether we want to file a Clang bug report regarding this.
 template <output_iterator<const char&> _OutIt>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _OutIt
+_LIBCPP_ALWAYS_INLINE _OutIt
 vformat_to(_OutIt __out_it, string_view __fmt, format_args __args) {
   return _VSTD::__vformat_to(_VSTD::move(__out_it), __fmt, __args);
 }
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
 template <output_iterator<const wchar_t&> _OutIt>
-_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _OutIt
+_LIBCPP_ALWAYS_INLINE _OutIt
 vformat_to(_OutIt __out_it, wstring_view __fmt, wformat_args __args) {
   return _VSTD::__vformat_to(_VSTD::move(__out_it), __fmt, __args);
 }
 #endif
 
+#ifndef _LIBCPP_AVAILABILITY_HAS_NO_FORMAT_EXPLICIT_INSTANTIATIONS
+
+extern template _LIBCPP_EXPORTED_FROM_ABI back_insert_iterator<string>
+    vformat_to<back_insert_iterator<string>>(back_insert_iterator<string>, string_view, format_args);
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+extern template _LIBCPP_EXPORTED_FROM_ABI back_insert_iterator<wstring>
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ldionne wrote:

Could you check how much of an increase it is to instantiate for `char` + `wchar_t` vs for just `char`? If it is double the cost, we could consider only instantiating for `char` since it should be by far the most common.

https://github.com/llvm/llvm-project/pull/71009