[libc++] Fix link error with _LIBCPP_HIDE_FROM_ABI_PER_TU and std::string

Summary:
This is effectively a revert of r344616, which was a partial fix for
PR38964 (compilation of <string> with GCC in C++03 mode). However, that
configuration is explicitly not supported anymore and that partial fix
breaks compilation with Clang when per-TU insulation is provided.

PR42676
rdar://52899715

Reviewers: mclow.lists, EricWF

Subscribers: christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D64941

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@366567 91177308-0d34-0410-b5e6-96231b3b80d8

include/string

@@ -812,9 +812,7 @@ public:
     basic_string(basic_string&& __str, const allocator_type& __a);
 #endif  // _LIBCPP_CXX03_LANG
 
-#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
     template <class = typename enable_if<__is_allocator<_Allocator>::value, nullptr_t>::type>
-#endif
     _LIBCPP_INLINE_VISIBILITY
     basic_string(const _CharT* __s) {
       _LIBCPP_ASSERT(__s != nullptr, "basic_string(const char*) detected nullptr");
@@ -824,9 +822,7 @@ public:
 #   endif
     }
 
-#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
     template <class = typename enable_if<__is_allocator<_Allocator>::value, nullptr_t>::type>
-#endif
         _LIBCPP_INLINE_VISIBILITY
         basic_string(const _CharT* __s, const _Allocator& __a);
 
@@ -837,9 +833,7 @@ public:
     _LIBCPP_INLINE_VISIBILITY
     basic_string(size_type __n, _CharT __c);
 
-#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
     template <class = typename enable_if<__is_allocator<_Allocator>::value, nullptr_t>::type>
-#endif
         _LIBCPP_INLINE_VISIBILITY
         basic_string(size_type __n, _CharT __c, const _Allocator& __a);
 
@@ -1800,9 +1794,7 @@ basic_string<_CharT, _Traits, _Allocator>::__init(const value_type* __s, size_ty
 }
 
 template <class _CharT, class _Traits, class _Allocator>
-#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
 template <class>
-#endif
 basic_string<_CharT, _Traits, _Allocator>::basic_string(const _CharT* __s, const _Allocator& __a)
     : __r_(__second_tag(), __a)
 {
@@ -1939,9 +1931,7 @@ basic_string<_CharT, _Traits, _Allocator>::basic_string(size_type __n, _CharT __
 }
 
 template <class _CharT, class _Traits, class _Allocator>
-#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
 template <class>
-#endif
 basic_string<_CharT, _Traits, _Allocator>::basic_string(size_type __n, _CharT __c, const _Allocator& __a)
     : __r_(__second_tag(), __a)
 {

test/libcxx/strings/basic.string/PR42676.sh.cpp

@@ -0,0 +1,21 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// Regression test for PR42676.
+
+// RUN: %cxx %flags %s -o %t.exe %compile_flags -D_LIBCPP_HIDE_FROM_ABI_PER_TU
+// RUN: %t.exe
+
+#include <memory>
+#include <string>
+
+int main() {
+    std::string s1(10u, '-', std::allocator<char>()); (void)s1;
+    std::string s2("hello", std::allocator<char>()); (void)s2;
+    std::string s3("hello"); (void)s3;
+}