[libc++] Add C++20 stringstream::view()

Reviewed By: #libc, philnik, Mordante

Spies: Mordante, philnik, libcxx-commits

Differential Revision: https://reviews.llvm.org/D148641

7 files changed, 287 insertions, 1 deletions

diff --git a/libcxx/docs/Status/Cxx20.rst b/libcxx/docs/Status/Cxx20.rst
index 11cd7c40bf51..e0ffdc6585d0 100644
--- a/libcxx/docs/Status/Cxx20.rst
+++ b/libcxx/docs/Status/Cxx20.rst
@@ -49,6 +49,7 @@ Paper Status
    .. [#note-P0883.1] P0883: shared_ptr and floating-point changes weren't applied as they themselves aren't implemented yet.
    .. [#note-P0883.2] P0883: ``ATOMIC_FLAG_INIT`` was marked deprecated in version 14.0, but was undeprecated with the implementation of LWG3659 in version 15.0.
    .. [#note-P2231] P2231: Optional is complete. The changes to variant haven't been implemented yet.
+   .. [#note-P0408] P0408: Only `view()` members implemented.
 
 .. _issues-status-cxx20:
 
diff --git a/libcxx/docs/Status/Cxx20Papers.csv b/libcxx/docs/Status/Cxx20Papers.csv
index 6b01966b6989..62951f56da83 100644
--- a/libcxx/docs/Status/Cxx20Papers.csv
+++ b/libcxx/docs/Status/Cxx20Papers.csv
@@ -99,7 +99,7 @@
 "`P1464R1 <https://wg21.link/P1464R1>`__","LWG","Mandating the Standard Library: Clause 22 - Iterators library","Kona","|Complete|","9.0"
 "","","","","","",""
 "`P0325R4 <https://wg21.link/P0325R4>`__","LWG","to_array from LFTS with updates","Cologne","|Complete|","10.0"
-"`P0408R7 <https://wg21.link/P0408R7>`__","LWG","Efficient Access to basic_stringbuf's Buffer","Cologne","",""
+"`P0408R7 <https://wg21.link/P0408R7>`__","LWG","Efficient Access to basic_stringbuf's Buffer","Cologne","|In Progress| [#note-P0408]_",""
 "`P0466R5 <https://wg21.link/P0466R5>`__","LWG","Layout-compatibility and Pointer-interconvertibility Traits","Cologne","",""
 "`P0553R4 <https://wg21.link/P0553R4>`__","LWG","Bit operations","Cologne","|Complete|","9.0"
 "`P0631R8 <https://wg21.link/P0631R8>`__","LWG","Math Constants","Cologne","|Complete|","11.0"
diff --git a/libcxx/include/sstream b/libcxx/include/sstream
index 6af2cb8fa87f..6dd581e30cb4 100644
--- a/libcxx/include/sstream
+++ b/libcxx/include/sstream
@@ -41,6 +41,7 @@ public:
     // [stringbuf.members] Member functions:
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& s);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 
 protected:
     // [stringbuf.virtuals] Overridden virtual functions:
@@ -92,6 +93,7 @@ public:
     basic_stringbuf<char_type, traits_type, allocator_type>* rdbuf() const;
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& s);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 };
 
 template <class charT, class traits, class Allocator>
@@ -132,6 +134,7 @@ public:
     basic_stringbuf<char_type, traits_type, allocator_type>* rdbuf() const;
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& s);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 };
 
 template <class charT, class traits, class Allocator>
@@ -172,6 +175,7 @@ public:
     basic_stringbuf<char_type, traits_type, allocator_type>* rdbuf() const;
     basic_string<char_type, traits_type, allocator_type> str() const;
     void str(const basic_string<char_type, traits_type, allocator_type>& str);
+    basic_string_view<char_type, traits_type> view() const noexcept; // C++20
 };
 
 template <class charT, class traits, class Allocator>
@@ -253,6 +257,10 @@ public:
     // [stringbuf.members] Member functions:
     string_type str() const;
     void str(const string_type& __s);
+#if _LIBCPP_STD_VER >= 20
+    _LIBCPP_HIDE_FROM_ABI
+    basic_string_view<char_type, traits_type> view() const noexcept;
+#endif
 
 protected:
     // [stringbuf.virtuals] Overridden virtual functions:
@@ -447,6 +455,9 @@ template <class _CharT, class _Traits, class _Allocator>
 basic_string<_CharT, _Traits, _Allocator>
 basic_stringbuf<_CharT, _Traits, _Allocator>::str() const
 {
+#if _LIBCPP_STD_VER >= 20
+    return string_type(view(), __str_.get_allocator());
+#else // _LIBCPP_STD_VER >= 20
     if (__mode_ & ios_base::out)
     {
         if (__hm_ < this->pptr())
@@ -456,6 +467,7 @@ basic_stringbuf<_CharT, _Traits, _Allocator>::str() const
     else if (__mode_ & ios_base::in)
         return string_type(this->eback(), this->egptr(), __str_.get_allocator());
     return string_type(__str_.get_allocator());
+#endif // _LIBCPP_STD_VER >= 20
 }
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -491,6 +503,20 @@ basic_stringbuf<_CharT, _Traits, _Allocator>::str(const string_type& __s)
     }
 }
 
+#if _LIBCPP_STD_VER >= 20
+template <class _CharT, class _Traits, class _Allocator>
+_LIBCPP_HIDE_FROM_ABI basic_string_view<_CharT, _Traits>
+basic_stringbuf<_CharT, _Traits, _Allocator>::view() const noexcept {
+    if (__mode_ & ios_base::out) {
+        if (__hm_ < this->pptr())
+            __hm_ = this->pptr();
+        return basic_string_view<_CharT, _Traits>(this->pbase(), __hm_);
+    } else if (__mode_ & ios_base::in)
+        return basic_string_view<_CharT, _Traits>(this->eback(), this->egptr());
+    return basic_string_view<_CharT, _Traits>();
+}
+#endif // _LIBCPP_STD_VER >= 20
+
 template <class _CharT, class _Traits, class _Allocator>
 typename basic_stringbuf<_CharT, _Traits, _Allocator>::int_type
 basic_stringbuf<_CharT, _Traits, _Allocator>::underflow()
@@ -694,6 +720,12 @@ public:
     void str(const string_type& __s) {
         __sb_.str(__s);
     }
+#if _LIBCPP_STD_VER >= 20
+    _LIBCPP_HIDE_FROM_ABI
+    basic_string_view<char_type, traits_type> view() const noexcept {
+        return __sb_.view();
+    }
+#endif
 };
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -775,6 +807,12 @@ public:
     void str(const string_type& __s) {
         __sb_.str(__s);
     }
+#if _LIBCPP_STD_VER >= 20
+    _LIBCPP_HIDE_FROM_ABI
+    basic_string_view<char_type, traits_type> view() const noexcept {
+        return __sb_.view();
+    }
+#endif
 };
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -855,6 +893,12 @@ public:
     void str(const string_type& __s) {
         __sb_.str(__s);
     }
+#if _LIBCPP_STD_VER >= 20
+    _LIBCPP_HIDE_FROM_ABI
+    basic_string_view<char_type, traits_type> view() const noexcept {
+        return __sb_.view();
+    }
+#endif
 };
 
 template <class _CharT, class _Traits, class _Allocator>
diff --git a/libcxx/test/std/input.output/string.streams/istringstream/istringstream.members/view.pass.cpp b/libcxx/test/std/input.output/string.streams/istringstream/istringstream.members/view.pass.cpp
new file mode 100644
index 000000000000..cdf7facd6de5
--- /dev/null
+++ b/libcxx/test/std/input.output/string.streams/istringstream/istringstream.members/view.pass.cpp
@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <sstream>
+
+// template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> >
+// class basic_istringstream
+
+// basic_string_view<charT, traits> view() const noexcept;
+
+#include <sstream>
+#include <cassert>
+#include <type_traits>
+
+#include "make_string.h"
+#include "test_macros.h"
+
+#define STR(S) MAKE_STRING(CharT, S)
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class CharT>
+struct my_char_traits : public std::char_traits<CharT> {};
+
+template <class CharT>
+static void test() {
+  std::basic_istringstream<CharT> ss(STR(" 123 456"));
+  static_assert(noexcept(ss.view()));
+  assert(ss.view() == SV(" 123 456"));
+  ss.str(STR(" 789"));
+  ss.clear();
+  assert(ss.view() == SV(" 789"));
+
+  const std::basic_istringstream<CharT> css(STR("abc"));
+  static_assert(noexcept(css.view()));
+  assert(css.view() == SV("abc"));
+
+  std::basic_istringstream<CharT, my_char_traits<CharT>> tss;
+  static_assert(std::is_same_v<decltype(tss.view()), std::basic_string_view<CharT, my_char_traits<CharT>>>);
+}
+
+int main(int, char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+  return 0;
+}
diff --git a/libcxx/test/std/input.output/string.streams/ostringstream/ostringstream.members/view.pass.cpp b/libcxx/test/std/input.output/string.streams/ostringstream/ostringstream.members/view.pass.cpp
new file mode 100644
index 000000000000..1dc691d0d11d
--- /dev/null
+++ b/libcxx/test/std/input.output/string.streams/ostringstream/ostringstream.members/view.pass.cpp
@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <sstream>
+
+// template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> >
+// class basic_ostringstream
+
+// basic_string_view<charT, traits> view() const noexcept;
+
+#include <sstream>
+#include <cassert>
+#include <type_traits>
+
+#include "make_string.h"
+#include "test_macros.h"
+
+#define STR(S) MAKE_STRING(CharT, S)
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class CharT>
+struct my_char_traits : public std::char_traits<CharT> {};
+
+template <class CharT>
+static void test() {
+  std::basic_ostringstream<CharT> ss(STR(" 123 456"));
+  static_assert(noexcept(ss.view()));
+  assert(ss.view() == SV(" 123 456"));
+  int i = 0;
+  ss << i;
+  assert(ss.view() == SV("0123 456"));
+  ss << 456;
+  assert(ss.view() == SV("0456 456"));
+  ss.str(STR(" 789"));
+  assert(ss.view() == SV(" 789"));
+  ss << SV("abc");
+  assert(ss.view() == SV("abc9"));
+
+  const std::basic_ostringstream<CharT> css(STR("abc"));
+  static_assert(noexcept(css.view()));
+  assert(css.view() == SV("abc"));
+
+  std::basic_ostringstream<CharT, my_char_traits<CharT>> tss;
+  static_assert(std::is_same_v<decltype(tss.view()), std::basic_string_view<CharT, my_char_traits<CharT>>>);
+}
+
+int main(int, char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+  return 0;
+}
diff --git a/libcxx/test/std/input.output/string.streams/stringbuf/stringbuf.members/view.pass.cpp b/libcxx/test/std/input.output/string.streams/stringbuf/stringbuf.members/view.pass.cpp
new file mode 100644
index 000000000000..4aa2e4ab2351
--- /dev/null
+++ b/libcxx/test/std/input.output/string.streams/stringbuf/stringbuf.members/view.pass.cpp
@@ -0,0 +1,59 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <sstream>
+
+// template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> >
+// class basic_stringbuf
+
+// basic_string_view<charT, traits> view() const noexcept;
+
+#include <sstream>
+#include <cassert>
+#include <type_traits>
+
+#include "make_string.h"
+#include "test_macros.h"
+
+#define STR(S) MAKE_STRING(CharT, S)
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class CharT>
+struct my_char_traits : public std::char_traits<CharT> {};
+
+template <class CharT>
+static void test() {
+  std::basic_stringbuf<CharT> buf(STR("testing"));
+  static_assert(noexcept(buf.view()));
+  assert(buf.view() == SV("testing"));
+  buf.str(STR("another test"));
+  assert(buf.view() == SV("another test"));
+
+  std::basic_stringbuf<CharT> robuf(STR("foo"), std::ios_base::in);
+  assert(robuf.view() == SV("foo"));
+
+  std::basic_stringbuf<CharT> nbuf(STR("not used"), 0);
+  assert(nbuf.view() == std::basic_string_view<CharT>());
+
+  const std::basic_stringbuf<CharT> cbuf(STR("abc"));
+  static_assert(noexcept(cbuf.view()));
+  assert(cbuf.view() == SV("abc"));
+
+  std::basic_stringbuf<CharT, my_char_traits<CharT>> tbuf;
+  static_assert(std::is_same_v<decltype(tbuf.view()), std::basic_string_view<CharT, my_char_traits<CharT>>>);
+}
+
+int main(int, char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+  return 0;
+}
diff --git a/libcxx/test/std/input.output/string.streams/stringstream.members/view.pass.cpp b/libcxx/test/std/input.output/string.streams/stringstream.members/view.pass.cpp
new file mode 100644
index 000000000000..f8f8a6567d7d
--- /dev/null
+++ b/libcxx/test/std/input.output/string.streams/stringstream.members/view.pass.cpp
@@ -0,0 +1,68 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <sstream>
+
+// template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> >
+// class basic_stringstream
+
+// basic_string_view<charT, traits> view() const noexcept;
+
+#include <sstream>
+#include <cassert>
+#include <type_traits>
+
+#include "make_string.h"
+#include "test_macros.h"
+
+#define STR(S) MAKE_STRING(CharT, S)
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class CharT>
+struct my_char_traits : public std::char_traits<CharT> {};
+
+template <class CharT>
+static void test() {
+  std::basic_stringstream<CharT> ss(STR(" 123 456 "));
+  static_assert(noexcept(ss.view()));
+  assert(ss.view() == SV(" 123 456 "));
+  int i = 0;
+  ss >> i;
+  assert(i == 123);
+  ss >> i;
+  assert(i == 456);
+  ss << i << ' ' << 123;
+  assert(ss.view() == SV("456 1236 "));
+  ss.str(STR("5466 89 "));
+  ss >> i;
+  assert(i == 5466);
+  ss >> i;
+  assert(i == 89);
+  ss << i << ' ' << 321;
+  assert(ss.view() == SV("89 3219 "));
+
+  const std::basic_stringstream<CharT> css(STR("abc"));
+  static_assert(noexcept(css.view()));
+  assert(css.view() == SV("abc"));
+
+  std::basic_stringstream<CharT, my_char_traits<CharT>> tss;
+  static_assert(std::is_same_v<decltype(tss.view()), std::basic_string_view<CharT, my_char_traits<CharT>>>);
+}
+
+int main(int, char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+  std::stringstream ss;
+  ss.write("\xd1", 1);
+  assert(ss.view().length() == 1);
+  return 0;
+}