[libc++] Fix modules build - Rework __refstring definition

[EricWF]

Summary

__libcpp_refstring currently has two different definitions. First there is the complete definition in <__refstring> but there is also a second in <stdexcept>. The historical reason for this split is because both libc++ and libc++abi need to see the inline definitions of __libcpp_refstrings methods, but the <stdexcept> header doesn't. However this is an ODR violation and breaks the modules build.

This patch fixes the issue by creating a single class definition in <stdexcept> and changing <__refstring> to contain only the inline method definitions. This way both libcxx/src/stdexcept.cpp and libcxxabi/src/stdexcept.cpp see the same declaration in <stdexcept> and definitions in <__refstring>

include/__refstring

 //===------------------------ __refstring ---------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___REFSTRING
 #define _LIBCPP___REFSTRING
 
 #include <__config>
+#include <stdexcept>
 #include <cstddef>
 #include <cstring>
 #ifdef __APPLE__
 #include <dlfcn.h>
 #include <mach-o/dyld.h>
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-class _LIBCPP_HIDDEN __libcpp_refstring
-{
-private:
-    const char* str_;
-
-    typedef int count_t;
+namespace __refstring_imp { namespace {
 
-    struct _Rep_base
-    {
-        std::size_t len;
-        std::size_t cap;
-        count_t     count;
-    };
+struct _Rep_base {
 
-    static
-    _Rep_base*
-    rep_from_data(const char *data_) _NOEXCEPT
-    {
-        char *data = const_cast<char *>(data_);
-        return reinterpret_cast<_Rep_base *>(data - sizeof(_Rep_base));
-    }
-    static
-    char *
-    data_from_rep(_Rep_base *rep) _NOEXCEPT
-    {
-        char *data = reinterpret_cast<char *>(rep);
-        return data + sizeof(*rep);
-    }
+inline _Rep_base* rep_from_data(const char *data_) noexcept {
+
+inline char * data_from_rep(_Rep_base *rep) noexcept {
 
-#ifdef __APPLE__
-    static
-    const char*
-    compute_gcc_empty_string_storage() _NOEXCEPT
-    {
-        void* handle = dlopen("/usr/lib/libstdc++.6.dylib", RTLD_NOLOAD);
-        if (handle == nullptr)
-            return nullptr;
-        void* sym = dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE");
-        if (sym == nullptr)
-            return nullptr;
-        return data_from_rep(reinterpret_cast<_Rep_base *>(sym));
-    }
+#if defined(__APPLE__)
+inline
+const char* compute_gcc_empty_string_storage() _NOEXCEPT
 
-    static
-    const char*
-    get_gcc_empty_string_storage() _NOEXCEPT
-    {
-        static const char* p = compute_gcc_empty_string_storage();
-        return p;
-    }
-
-    bool
-    uses_refcount() const
-    {
-        return str_ != get_gcc_empty_string_storage();
-    }
-#else
-    bool
-    uses_refcount() const
-    {
-        return true;
-    }
+inline
 #endif
 
-public:
-    explicit __libcpp_refstring(const char* msg) {
-        std::size_t len = strlen(msg);
-        _Rep_base* rep = static_cast<_Rep_base *>(::operator new(sizeof(*rep) + len + 1));
-        rep->len = len;
-        rep->cap = len;
-        rep->count = 0;
-        char *data = data_from_rep(rep);
-        std::memcpy(data, msg, len + 1);
-        str_ = data;
-    }
+}} // namespace __refstring_imp
+
+using namespace __refstring_imp;
+
+inline
+__libcpp_refstring::__libcpp_refstring(const char* msg) {
+    __imp_ = data;
 
-    __libcpp_refstring(const __libcpp_refstring& s) _NOEXCEPT : str_(s.str_)
-    {
-        if (uses_refcount())
-            __sync_add_and_fetch(&rep_from_data(str_)->count, 1);
-    }
+inline
+__libcpp_refstring::__libcpp_refstring(const __libcpp_refstring &s) _NOEXCEPT
+    : __imp_(s.__imp_)
+    if (__uses_refcount())
+        __sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
 
-    __libcpp_refstring& operator=(const __libcpp_refstring& s) _NOEXCEPT
-    {
-        bool adjust_old_count = uses_refcount();
-        struct _Rep_base *old_rep = rep_from_data(str_);
-        str_ = s.str_;
-        if (uses_refcount())
-            __sync_add_and_fetch(&rep_from_data(str_)->count, 1);
-        if (adjust_old_count)
-        {
-            if (__sync_add_and_fetch(&old_rep->count, count_t(-1)) < 0)
-            {
-                ::operator delete(old_rep);
-            }
-        }
-        return *this;
-    }
+inline
+__libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) _NOEXCEPT {
+    bool adjust_old_count = __uses_refcount();
+    struct _Rep_base *old_rep = rep_from_data(__imp_);
+    __imp_ = s.__imp_;
+    if (__uses_refcount())
+        __sync_add_and_fetch(&rep_from_data(__imp_)->count, 1);
 
-    ~__libcpp_refstring()
-    {
-        if (uses_refcount())
-        {
-            _Rep_base* rep = rep_from_data(str_);
-            if (__sync_add_and_fetch(&rep->count, count_t(-1)) < 0)
-            {
-                ::operator delete(rep);
-            }
-        }
-    }
+inline
+__libcpp_refstring::~__libcpp_refstring() {
+    if (__uses_refcount()) {
+        _Rep_base* rep = rep_from_data(__imp_);
+        if (__sync_add_and_fetch(&rep->count, count_t(-1)) < 0) {
 
-    const char* c_str() const _NOEXCEPT {return str_;}
-};
+inline
+bool __libcpp_refstring::__uses_refcount() const {
+#ifdef __APPLE__
+    return __imp_ != get_gcc_empty_string_storage();
+#else
+    return true;
+#endif
+}
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif //_LIBCPP___REFSTRING

include/stdexcept

 #ifdef _LIBCPP_NO_EXCEPTIONS
 #include <cstdlib>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
-#ifndef _LIBCPP___REFSTRING
 _LIBCPP_BEGIN_NAMESPACE_STD
-class _LIBCPP_HIDDEN __libcpp_refstring {
-#ifdef __clang__
-    const char *__imp_ __attribute__((__unused__)); // only clang emits a warning
-#else
-    const char *__imp_;
-#endif
+
+class _LIBCPP_HIDDEN __libcpp_refstring
+{
+    const char* __imp_;
+
+    bool __uses_refcount() const;
+public:
+    explicit __libcpp_refstring(const char* msg);
+    __libcpp_refstring(const __libcpp_refstring& s) _NOEXCEPT;
+    __libcpp_refstring& operator=(const __libcpp_refstring& s) _NOEXCEPT;
+    ~__libcpp_refstring();
+
+    const char* c_str() const _NOEXCEPT {return __imp_;}
 };
+
 _LIBCPP_END_NAMESPACE_STD
-#endif
 
 namespace std  // purposefully not using versioning namespace
 {
 
 class _LIBCPP_EXCEPTION_ABI logic_error
     : public exception
 {
 private:

src/stdexcept.cpp

 //===------------------------ stdexcept.cpp -------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
-#include "__refstring"
 #include "stdexcept"
 #include "new"
 #include "string"
 #include "system_error"
+#include "__refstring"
 
 /* For _LIBCPPABI_VERSION */
 #if defined(LIBCXX_BUILDING_LIBCXXABI) || defined(__APPLE__) || defined(LIBCXXRT)
 #include <cxxabi.h>
 #endif
 
 static_assert(sizeof(std::__libcpp_refstring) == sizeof(const char *), "");
 
+
 namespace std  // purposefully not using versioning namespace
 {
 
 logic_error::logic_error(const string& msg) : __imp_(msg.c_str())
 {
 }
 
 logic_error::logic_error(const char* msg) : __imp_(msg)