[gcc r11-1238] libstdc++: Fix istream::ignore discarding too many chars (PR 94749)

[gcc r11-1238] libstdc++: Fix istream::ignore discarding too many chars (PR 94749)

[Jonathan Wakely]

https://gcc.gnu.org/g:b32eea9c0c25a03e77170675abc4e4bcab6d2b3b

commit r11-1238-gb32eea9c0c25a03e77170675abc4e4bcab6d2b3b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jun 11 18:41:37 2020 +0100

    libstdc++: Fix istream::ignore discarding too many chars (PR 94749)
    
    The current code assumes that if the next character in the stream is
    equal to the delimiter then we stopped because we saw that delimiter,
    and so discards it.  But in the testcase for the PR we stop because we
    reached the maximum number of characters, and it's coincidence that the
    next character equals the delimiter. We should not discard the next
    character in that case.
    
    The fix is to check that we haven't discarded __n characters already,
    instead of checking whether the next character equals __delim. Because
    we've already checked for EOF, if we haven't discarded __n yet then we
    know we stopped because we saw the delimiter. On the other hand, if the
    next character is the delimiter we don't know if that's why we stopped.
    
            PR libstdc++/94749
            * include/bits/istream.tcc (basic_istream::ignore(streamsize, CharT)):
            Only discard an extra character if we didn't already reach the
            maximum number.
            * src/c++98/istream.cc (istream::ignore(streamsiz, char))
            (wistream::ignore(streamsize, wchar_t)): Likewise.
            * testsuite/27_io/basic_istream/ignore/char/94749.cc: New test.
            * testsuite/27_io/basic_istream/ignore/wchar_t/94749.cc: New test.

Diff:
---
 libstdc++-v3/include/bits/istream.tcc              |  6 +-
 libstdc++-v3/src/c++98/istream.cc                  | 12 ++--
 .../27_io/basic_istream/ignore/char/94749.cc       | 76 ++++++++++++++++++++++
 .../27_io/basic_istream/ignore/wchar_t/94749.cc    | 76 ++++++++++++++++++++++
 4 files changed, 158 insertions(+), 12 deletions(-)

diff --git a/libstdc++-v3/include/bits/istream.tcc b/libstdc++-v3/include/bits/istream.tcc
index c82da56b9f9..d36374c707f 100644
--- a/libstdc++-v3/include/bits/istream.tcc
+++ b/libstdc++-v3/include/bits/istream.tcc
@@ -601,11 +601,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
               if (traits_type::eq_int_type(__c, __eof))
                 __err |= ios_base::eofbit;
-	      else if (traits_type::eq_int_type(__c, __delim))
+	      else if (_M_gcount < __n) // implies __c == __delim
 		{
-		  if (_M_gcount
-		      < __gnu_cxx::__numeric_traits<streamsize>::__max)
-		    ++_M_gcount;
+		  ++_M_gcount;
 		  __sb->sbumpc();
 		}
             }
diff --git a/libstdc++-v3/src/c++98/istream.cc b/libstdc++-v3/src/c++98/istream.cc
index 79d829e23b4..d6fee1a0d66 100644
--- a/libstdc++-v3/src/c++98/istream.cc
+++ b/libstdc++-v3/src/c++98/istream.cc
@@ -171,11 +171,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 	      if (traits_type::eq_int_type(__c, __eof))
 		__err |= ios_base::eofbit;
-	      else if (traits_type::eq_int_type(__c, __delim))
+	      else if (_M_gcount < __n) // implies __c == __delim
 		{
-		  if (_M_gcount
-		      < __gnu_cxx::__numeric_traits<streamsize>::__max)
-		    ++_M_gcount;
+		  ++_M_gcount;
 		  __sb->sbumpc();
 		}
 	    }
@@ -413,11 +411,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 	      if (traits_type::eq_int_type(__c, __eof))
 		__err |= ios_base::eofbit;
-	      else if (traits_type::eq_int_type(__c, __delim))
+	      else if (_M_gcount < __n) // implies __c == __delim
 		{
-		  if (_M_gcount
-		      < __gnu_cxx::__numeric_traits<streamsize>::__max)
-		    ++_M_gcount;
+		  ++_M_gcount;
 		  __sb->sbumpc();
 		}
 	    }
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/ignore/char/94749.cc b/libstdc++-v3/testsuite/27_io/basic_istream/ignore/char/94749.cc
new file mode 100644
index 00000000000..03b5286b00e
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/ignore/char/94749.cc
@@ -0,0 +1,76 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run }
+
+// PR libstdc++/94749
+// basic_istream::ignore(n, c) discards n+1 if next character is equal to c.
+
+#include <sstream>
+#include <testsuite_hooks.h>
+
+typedef char C;
+
+void
+test01()
+{
+  std::basic_istringstream<C> s(" +   -");
+  s.ignore(1, '+');
+  VERIFY( s.get() == '+' );
+  s.ignore(3, '-');
+  VERIFY( s.get() == '-' );
+}
+
+void
+test02()
+{
+  std::basic_istringstream<C> s(".+...-");
+  s.ignore(1, '+');
+  VERIFY( s.get() == '+' );
+  s.ignore(3, '-');
+  VERIFY( s.get() == '-' );
+}
+
+void
+test03()
+{
+  std::basic_istringstream<C, __gnu_cxx::char_traits<C> > s(" +   -");
+  s.ignore(1, '+');
+  VERIFY( s.get() == '+' );
+  s.ignore(3, '-');
+  VERIFY( s.get() == '-' );
+}
+
+void
+test04()
+{
+  std::basic_istringstream<C, __gnu_cxx::char_traits<C> > s(".+...-");
+  s.ignore(1, '+');
+  VERIFY( s.get() == '+' );
+  s.ignore(3, '-');
+  VERIFY( s.get() == '-' );
+}
+
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+}
diff --git a/libstdc++-v3/testsuite/27_io/basic_istream/ignore/wchar_t/94749.cc b/libstdc++-v3/testsuite/27_io/basic_istream/ignore/wchar_t/94749.cc
new file mode 100644
index 00000000000..e5ec4e7d697
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_istream/ignore/wchar_t/94749.cc
@@ -0,0 +1,76 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run }
+
+// PR libstdc++/94749
+// basic_istream::ignore(n, c) discards n+1 if next character is equal to c.
+
+#include <sstream>
+#include <testsuite_hooks.h>
+
+typedef wchar_t C;
+
+void
+test01()
+{
+  std::basic_istringstream<C> s(L" +   -");
+  s.ignore(1, L'+');
+  VERIFY( s.get() == L'+' );
+  s.ignore(3, L'-');
+  VERIFY( s.get() == L'-' );
+}
+
+void
+test02()
+{
+  std::basic_istringstream<C> s(L".+...-");
+  s.ignore(1, L'+');
+  VERIFY( s.get() == L'+' );
+  s.ignore(3, L'-');
+  VERIFY( s.get() == L'-' );
+}
+
+void
+test03()
+{
+  std::basic_istringstream<C, __gnu_cxx::char_traits<C> > s(L" +   -");
+  s.ignore(1, L'+');
+  VERIFY( s.get() == L'+' );
+  s.ignore(3, L'-');
+  VERIFY( s.get() == L'-' );
+}
+
+void
+test04()
+{
+  std::basic_istringstream<C, __gnu_cxx::char_traits<C> > s(L".+...-");
+  s.ignore(1, L'+');
+  VERIFY( s.get() == L'+' );
+  s.ignore(3, L'-');
+  VERIFY( s.get() == L'-' );
+}
+
+
+int
+main()
+{
+  // test01();
+  // test02();
+  test03();
+  test04();
+}