[PATCH] PR libstdc++/81256 fix exception handling in basic_filebuf::close

[Jonathan Wakely]

As explained in the PR, we were incorrectly swallowing exceptions from
basic_filebuf::close(). They should propagate from that function, but
still be swallowed in the destructor.

	PR libstdc++/81256
	* include/bits/fstream.tcc (basic_filebuf::close): Do not swallow
	exceptions from _M_terminate_output().
	* include/std/fstream (basic_filebuf::~basic_filebuf): Swallow any
	exceptions from close().
	* testsuite/27_io/basic_filebuf/close/81256.cc: New.

Tested powerp64le-linux, committed to trunk.


-------------- next part --------------
commit adcfbaa7023dc8d2d5cfa0b6971a99d0ed33a1f5
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon May 14 17:13:05 2018 +0100

    PR libstdc++/81256 fix exception handling in basic_filebuf::close
    
            PR libstdc++/81256
            * include/bits/fstream.tcc (basic_filebuf::close): Do not swallow
            exceptions from _M_terminate_output().
            * include/std/fstream (basic_filebuf::~basic_filebuf): Swallow any
            exceptions from close().
            * testsuite/27_io/basic_filebuf/close/81256.cc: New.

diff --git a/libstdc++-v3/include/bits/fstream.tcc b/libstdc++-v3/include/bits/fstream.tcc
index f23ff7af4eb..08cf189ee06 100644
--- a/libstdc++-v3/include/bits/fstream.tcc
+++ b/libstdc++-v3/include/bits/fstream.tcc
@@ -239,13 +239,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    if (!_M_terminate_output())
 	      __testfail = true;
 	  }
-	__catch(__cxxabiv1::__forced_unwind&)
+	__catch(...)
 	  {
 	    _M_file.close();
 	    __throw_exception_again;
 	  }
-	__catch(...)
-	  { __testfail = true; }
       }
 
       if (!_M_file.close())
diff --git a/libstdc++-v3/include/std/fstream b/libstdc++-v3/include/std/fstream
index 3a5895d68b0..05661d9d58f 100644
--- a/libstdc++-v3/include/std/fstream
+++ b/libstdc++-v3/include/std/fstream
@@ -244,7 +244,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        */
       virtual
       ~basic_filebuf()
-      { this->close(); }
+      {
+	__try
+	  { this->close(); }
+	__catch(...)
+	  { }
+      }
 
 #if __cplusplus >= 201103L
       basic_filebuf& operator=(const basic_filebuf&) = delete;
diff --git a/libstdc++-v3/testsuite/27_io/basic_filebuf/close/81256.cc b/libstdc++-v3/testsuite/27_io/basic_filebuf/close/81256.cc
new file mode 100644
index 00000000000..aef7364526b
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_filebuf/close/81256.cc
@@ -0,0 +1,109 @@
+// Copyright (C) 2018 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 { target c++11 } }
+
+#include <fstream>
+#include <locale>
+#include <testsuite_hooks.h>
+
+struct E : std::runtime_error
+{
+  E() : runtime_error("") { }
+};
+
+struct Cvt : std::codecvt<wchar_t, char, std::mbstate_t>
+{
+  explicit Cvt(size_t refs) : codecvt(refs) { }
+
+  mutable int exceptions_thrown = 0;
+
+private:
+  int
+  do_encoding() const noexcept override
+  { return -1; }
+
+  bool
+  do_always_noconv() const noexcept override
+  { return false; }
+
+  result
+  do_unshift(state_type&, char*, char*, char*&) const override
+  {
+    ++exceptions_thrown;
+    throw E();
+  }
+};
+
+struct filebuf : std::basic_filebuf<wchar_t>
+{
+  explicit filebuf(Cvt* c)
+  {
+    std::locale loc(std::locale::classic(), c);
+    imbue(loc);
+  }
+};
+
+void
+test01()
+{
+  // This facet needs to still be valid when ~basic_filebuf runs:
+  Cvt conv{1};
+  {
+    filebuf fb(&conv);
+    fb.open("output.txt", std::wios::out);
+    fb.sputn(L"x", 1);
+
+    bool caught = false;
+    try
+    {
+      /* [filebuf.members] p7: If one of these calls throws an exception,
+       * the exception is caught and rethrown after closing the file.  */
+      fb.close();
+    }
+    catch (const E&)
+    {
+      caught = true;
+    }
+    VERIFY( conv.exceptions_thrown == 1 );
+    VERIFY( caught );
+  }
+  VERIFY( conv.exceptions_thrown == 1 );
+}
+
+void
+test02()
+{
+  // This facet needs to still be valid when ~basic_filebuf runs:
+  Cvt conv{1};
+  {
+    filebuf fb(&conv);
+    fb.open("output.txt", std::wios::out);
+    fb.sputn(L"x", 1);
+    /* [filebuf.cons] p5: If an exception occurs during the destruction
+     * of the object, including the call to close(), the exception is
+     * caught but not rethrown.  */
+  }
+  VERIFY( conv.exceptions_thrown == 1 );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}