libstdc++: Add remaining C++20 additions to <sstream> [P0408R7]

This adds the new overloads of basic_stringbuf::str, and the
corresponding overloads to basic_istringstream, basic_ostringstream and
basic_stringstream.

libstdc++-v3/ChangeLog:

	* config/abi/pre/gnu.ver (GLIBCXX_3.4.21): Tighten patterns.
	(GLIBCXX_3.4.29): Export new symbols.
	* include/bits/alloc_traits.h (__allocator_like): New concept.
	* include/std/sstream (basic_stringbuf::swap): Add exception
	specification.
	(basic_stringbuf::str() const): Add ref-qualifier. Use new
	_M_high_mark function.
	(basic_stringbuf::str(const SAlloc&) const): Define new function.
	(basic_stringbuf::str() &&): Likewise.
	(basic_stringbuf::str(const basic_string<C,T,SAlloc>&)):
	Likewise.
	(basic_stringbuf::str(basic_string<C,T,Alloc>&&)): Likewise.
	(basic_stringbuf::view() const): Use _M_high_mark.
	(basic_istringstream::str, basic_ostringstream::str)
	(basic_stringstream::str): Define new overloads.
	* src/c++20/sstream-inst.cc (basic_stringbuf::str)
	(basic_istringstream::str, basic_ostringstream::str)
	(basic_stringstream::str): Explicit instantiation definitions
	for new overloads.
	* testsuite/27_io/basic_istringstream/view/char/1.cc: Add more
	checks.
	* testsuite/27_io/basic_istringstream/view/wchar_t/1.cc:
	Likewise.
	* testsuite/27_io/basic_ostringstream/view/char/1.cc:
	Likewise.
	* testsuite/27_io/basic_ostringstream/view/wchar_t/1.cc:
	Likewise.
	* testsuite/27_io/basic_stringstream/view/char/1.cc:
	Likewise.
	* testsuite/27_io/basic_stringstream/view/wchar_t/1.cc:
	Likewise.
	* testsuite/27_io/basic_istringstream/str/char/2.cc: New test.
	* testsuite/27_io/basic_istringstream/str/wchar_t/2.cc: New test.
	* testsuite/27_io/basic_ostringstream/str/char/3.cc: New test.
	* testsuite/27_io/basic_ostringstream/str/wchar_t/3.cc: New test.
	* testsuite/27_io/basic_stringbuf/str/char/4.cc: New test.
	* testsuite/27_io/basic_stringbuf/str/wchar_t/4.cc: New test.
	* testsuite/27_io/basic_stringstream/str/char/5.cc: New test.
	* testsuite/27_io/basic_stringstream/str/wchar_t/5.cc.cc: New test.

1 files changed, 48 insertions, 0 deletions

diff --git a/libstdc++-v3/src/c++20/sstream-inst.cc b/libstdc++-v3/src/c++20/sstream-inst.cc
index 7d275de5cc2..9e157d1b1bf 100644
--- a/libstdc++-v3/src/c++20/sstream-inst.cc
+++ b/libstdc++-v3/src/c++20/sstream-inst.cc
@@ -46,29 +46,53 @@ template basic_stringbuf<char>::basic_stringbuf(basic_stringbuf&&,
 						__xfer_bufptrs&&);
 template basic_stringbuf<char>::allocator_type
 basic_stringbuf<char>::get_allocator() const noexcept;
+template string
+basic_stringbuf<char>::str() const &;
+template string
+basic_stringbuf<char>::str() &&;
 template string_view
 basic_stringbuf<char>::view() const noexcept;
+template void
+basic_stringbuf<char>::str(string&&);
 
 template basic_istringstream<char>::basic_istringstream(ios_base::openmode,
 							const allocator_type&);
 template basic_istringstream<char>::basic_istringstream(__string_type&&,
 							ios_base::openmode);
+template string
+basic_istringstream<char>::str() const &;
+template string
+basic_istringstream<char>::str() &&;
 template string_view
 basic_istringstream<char>::view() const noexcept;
+template void
+basic_istringstream<char>::str(string&&);
 
 template basic_ostringstream<char>::basic_ostringstream(ios_base::openmode,
 							const allocator_type&);
 template basic_ostringstream<char>::basic_ostringstream(__string_type&&,
 							ios_base::openmode);
+template string
+basic_ostringstream<char>::str() const &;
+template string
+basic_ostringstream<char>::str() &&;
 template string_view
 basic_ostringstream<char>::view() const noexcept;
+template void
+basic_ostringstream<char>::str(string&&);
 
 template basic_stringstream<char>::basic_stringstream(ios_base::openmode,
 						      const allocator_type&);
 template basic_stringstream<char>::basic_stringstream(__string_type&&,
 						      ios_base::openmode);
+template string
+basic_stringstream<char>::str() const &;
+template string
+basic_stringstream<char>::str() &&;
 template string_view
 basic_stringstream<char>::view() const noexcept;
+template void
+basic_stringstream<char>::str(string&&);
 
 #ifdef _GLIBCXX_USE_WCHAR_T
 template basic_stringbuf<wchar_t>::basic_stringbuf(const allocator_type&);
@@ -84,29 +108,53 @@ template basic_stringbuf<wchar_t>::basic_stringbuf(basic_stringbuf&&,
 template basic_stringbuf<wchar_t>::allocator_type
 basic_stringbuf<wchar_t>::get_allocator() const noexcept;
 
+template wstring
+basic_stringbuf<wchar_t>::str() const &;
+template wstring
+basic_stringbuf<wchar_t>::str() &&;
 template wstring_view
 basic_stringbuf<wchar_t>::view() const noexcept;
+template void
+basic_stringbuf<wchar_t>::str(wstring&&);
 
 template basic_istringstream<wchar_t>::basic_istringstream(ios_base::openmode,
 							   const allocator_type&);
 template basic_istringstream<wchar_t>::basic_istringstream(__string_type&&,
 							   ios_base::openmode);
+template wstring
+basic_istringstream<wchar_t>::str() const &;
+template wstring
+basic_istringstream<wchar_t>::str() &&;
 template wstring_view
 basic_istringstream<wchar_t>::view() const noexcept;
+template void
+basic_istringstream<wchar_t>::str(wstring&&);
 
 template basic_ostringstream<wchar_t>::basic_ostringstream(ios_base::openmode,
 							   const allocator_type&);
 template basic_ostringstream<wchar_t>::basic_ostringstream(__string_type&&,
 							   ios_base::openmode);
+template wstring
+basic_ostringstream<wchar_t>::str() const &;
+template wstring
+basic_ostringstream<wchar_t>::str() &&;
 template wstring_view
 basic_ostringstream<wchar_t>::view() const noexcept;
+template void
+basic_ostringstream<wchar_t>::str(wstring&&);
 
 template basic_stringstream<wchar_t>::basic_stringstream(ios_base::openmode,
 							 const allocator_type&);
 template basic_stringstream<wchar_t>::basic_stringstream(__string_type&&,
 							 ios_base::openmode);
+template wstring
+basic_stringstream<wchar_t>::str() const &;
+template wstring
+basic_stringstream<wchar_t>::str() &&;
 template wstring_view
 basic_stringstream<wchar_t>::view() const noexcept;
+template void
+basic_stringstream<wchar_t>::str(wstring&&);
 #endif
 
 _GLIBCXX_END_NAMESPACE_VERSION