[committed] libstdc++: Implement LWG 415 for std::ws

[committed] libstdc++: Implement LWG 415 for std::ws

[Jonathan Wakely]

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For C++11 std::ws changed to be an unformatted input function, meaning
it constructs a sentry and sets badbit on exceptions.

libstdc++-v3/ChangeLog:

	* doc/xml/manual/intro.xml: Document LWG 415 change.
	* doc/html/manual/bugs.html: Regenerate.
	* include/bits/istream.tcc (ws): Create sentry and catch
	exceptions.
	* testsuite/27_io/basic_istream/ws/char/lwg415.cc: New test.
	* testsuite/27_io/basic_istream/ws/wchar_t/lwg415.cc: New test.

Tested powerpc64le-linux. Committed to trunk.


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commit e5c422b7d8af6f42f8ab230133210742b7ac5661
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Jun 25 21:33:02 2021

    libstdc++: Implement LWG 415 for std::ws
    
    For C++11 std::ws changed to be an unformatted input function, meaning
    it constructs a sentry and sets badbit on exceptions.
    
    libstdc++-v3/ChangeLog:
    
            * doc/xml/manual/intro.xml: Document LWG 415 change.
            * doc/html/manual/bugs.html: Regenerate.
            * include/bits/istream.tcc (ws): Create sentry and catch
            exceptions.
            * testsuite/27_io/basic_istream/ws/char/lwg415.cc: New test.
            * testsuite/27_io/basic_istream/ws/wchar_t/lwg415.cc: New test.

diff --git a/libstdc++-v3/doc/xml/manual/intro.xml b/libstdc++-v3/doc/xml/manual/intro.xml
index 45762caa711..86ed6964b6a 100644
--- a/libstdc++-v3/doc/xml/manual/intro.xml
+++ b/libstdc++-v3/doc/xml/manual/intro.xml
@@ -634,6 +634,13 @@ requirements of the license of GCC.
     <listitem><para>Have <code>open</code> clear the error flags.
     </para></listitem></varlistentry>
 
+    <varlistentry xml:id="manual.bugs.dr415"><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="&DR;#415">415</link>:
+	<emphasis>Behavior of std::ws</emphasis>
+    </term>
+    <listitem><para>Change it to be an unformatted input function
+      (i.e. construct a sentry and catch exceptions).
+    </para></listitem></varlistentry>
+
     <varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-closed.html#431">431</link>:
 	<emphasis>Swapping containers with unequal allocators</emphasis>
     </term>
diff --git a/libstdc++-v3/include/bits/istream.tcc b/libstdc++-v3/include/bits/istream.tcc
index 1b046bec937..2a153c2e140 100644
--- a/libstdc++-v3/include/bits/istream.tcc
+++ b/libstdc++-v3/include/bits/istream.tcc
@@ -1057,17 +1057,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef typename __istream_type::int_type		__int_type;
       typedef ctype<_CharT>				__ctype_type;
 
-      const __ctype_type& __ct = use_facet<__ctype_type>(__in.getloc());
-      const __int_type __eof = _Traits::eof();
-      __streambuf_type* __sb = __in.rdbuf();
-      __int_type __c = __sb->sgetc();
+      // _GLIBCXX_RESOLVE_LIB_DEFECTS
+      // 451. behavior of std::ws
+      typename __istream_type::sentry __cerb(__in, true);
+      if (__cerb)
+	{
+	  ios_base::iostate __err = ios_base::goodbit;
+	  __try
+	    {
+	      const __ctype_type& __ct = use_facet<__ctype_type>(__in.getloc());
+	      const __int_type __eof = _Traits::eof();
+	      __streambuf_type* __sb = __in.rdbuf();
+	      __int_type __c = __sb->sgetc();
 
-      while (!_Traits::eq_int_type(__c, __eof)
-	     && __ct.is(ctype_base::space, _Traits::to_char_type(__c)))
-	__c = __sb->snextc();
-
-       if (_Traits::eq_int_type(__c, __eof))
-	 __in.setstate(ios_base::eofbit);
+	      while (true)
+		{
+		  if (_Traits::eq_int_type(__c, __eof))
+		    {
+		      __err = ios_base::eofbit;
+		      break;
+		    }
+		  if (!__ct.is(ctype_base::space, _Traits::to_char_type(__c)))
+		    break;
+		  __c = __sb->snextc();
+		}
+	    }
+	  __catch (const __cxxabiv1::__forced_unwind&)
+	    {
+	      __in._M_setstate(ios_base::badbit);
+	      __throw_exception_again;
+	    }
+	  __catch (...)
+	    {
+	      __in._M_setstate(ios_base::badbit);
+	    }
+	  if (__err)
+	    __in.setstate(__err);
+	}
       return __in;
     }
 
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/ws/char/lwg415.cc b/libstdc++-v3/testsuite/27_io/basic_istream/ws/char/lwg415.cc
new file mode 100644
index 00000000000..fe6980dff29
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/ws/char/lwg415.cc
@@ -0,0 +1,77 @@
+#include <istream>
+
+// C++11 27.7.2.4 Standard basic_istream manipulators [istream.manip]
+//
+// LWG 415. behavior of std::ws
+// std::ws is an unformatted input function.
+
+#include <istream>
+#include <testsuite_hooks.h>
+#include <testsuite_io.h>
+
+void
+test01()
+{
+  std::istream is(0);
+  VERIFY( is.rdstate() == std::ios_base::badbit );
+
+  is >> std::ws; // sentry should set failbit
+  VERIFY( is.rdstate() & std::ios_base::failbit );
+}
+
+void
+test02()
+{
+  __gnu_test::sync_streambuf buf;
+  std::istream is(&buf);
+
+  __gnu_test::sync_streambuf buf_tie;
+  std::ostream os_tie(&buf_tie);
+
+  // A sentry should be constructed so is.tie()->flush() should be called.
+  // The standard allows the flush to be deferred because the put area of
+  // is_tie is empty, but libstdc++ doesn't defer it.
+  is.tie(&os_tie);
+
+  is >> std::ws;
+
+  VERIFY( is.eof() );
+  VERIFY( !is.fail() );
+  VERIFY( ! buf.sync_called() );
+  VERIFY( buf_tie.sync_called() );
+}
+
+void
+test03()
+{
+  __gnu_test::fail_streambuf buf;
+  std::istream is(&buf);
+
+  char c;
+  is >> c >> std::ws;
+  VERIFY( is.rdstate() == std::ios_base::badbit );
+
+  is.clear();
+  is.exceptions(std::ios_base::badbit);
+
+  try
+  {
+    is >> std::ws;
+    VERIFY( false );
+  }
+  catch (const __gnu_test::underflow_error&)
+  {
+    VERIFY( is.rdstate() == std::ios_base::badbit );
+  }
+  catch (...)
+  {
+    VERIFY( false );
+  }
+}
+
+int main()
+{
+  test01();
+  test02();
+  test03();
+}
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/ws/wchar_t/lwg415.cc b/libstdc++-v3/testsuite/27_io/basic_istream/ws/wchar_t/lwg415.cc
new file mode 100644
index 00000000000..fd040098b40
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/ws/wchar_t/lwg415.cc
@@ -0,0 +1,77 @@
+#include <istream>
+
+// C++11 27.7.2.4 Standard basic_istream manipulators [istream.manip]
+//
+// LWG 415. behavior of std::ws
+// std::ws is an unformatted input function.
+
+#include <istream>
+#include <testsuite_hooks.h>
+#include <testsuite_io.h>
+
+void
+test01()
+{
+  std::wistream is(0);
+  VERIFY( is.rdstate() == std::ios_base::badbit );
+
+  is >> std::ws; // sentry should set failbit
+  VERIFY( is.rdstate() & std::ios_base::failbit );
+}
+
+void
+test02()
+{
+  __gnu_test::sync_wstreambuf buf;
+  std::wistream is(&buf);
+
+  __gnu_test::sync_wstreambuf buf_tie;
+  std::wostream os_tie(&buf_tie);
+
+  // A sentry should be constructed so is.tie()->flush() should be called.
+  // The standard allows the flush to be deferred because the put area of
+  // is_tie is empty, but libstdc++ doesn't defer it.
+  is.tie(&os_tie);
+
+  is >> std::ws;
+
+  VERIFY( is.eof() );
+  VERIFY( !is.fail() );
+  VERIFY( ! buf.sync_called() );
+  VERIFY( buf_tie.sync_called() );
+}
+
+void
+test03()
+{
+  __gnu_test::fail_wstreambuf buf;
+  std::wistream is(&buf);
+
+  wchar_t c;
+  is >> c >> std::ws;
+  VERIFY( is.rdstate() == std::ios_base::badbit );
+
+  is.clear();
+  is.exceptions(std::ios_base::badbit);
+
+  try
+  {
+    is >> std::ws;
+    VERIFY( false );
+  }
+  catch (const __gnu_test::underflow_error&)
+  {
+    VERIFY( is.rdstate() == std::ios_base::badbit );
+  }
+  catch (...)
+  {
+    VERIFY( false );
+  }
+}
+
+int main()
+{
+  test01();
+  test02();
+  test03();
+}