[committed,v2] libstdc++: Fix std::codecvt<wchar_t, char, mbstate_t> for empty dest [PR37475]

diff --git a/libstdc++-v3/config/locale/gnu/codecvt_members.cc b/libstdc++-v3/config/locale/gnu/codecvt_members.cc
index 034713d236e..794f25a5f35 100644
--- a/libstdc++-v3/config/locale/gnu/codecvt_members.cc
+++ b/libstdc++-v3/config/locale/gnu/codecvt_members.cc
@@ -37,8 +37,23 @@  namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
-  // Specializations.
 #ifdef _GLIBCXX_USE_WCHAR_T
+namespace
+{
+  // RAII type for changing and restoring the current thread's locale.
+  struct Guard
+  {
+#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
+    explicit Guard(__c_locale loc) : old(__uselocale(loc)) { }
+    ~Guard() { __uselocale(old); }
+#else
+    explicit Guard(__c_locale) { }
+#endif
+    __c_locale old;
+  };
+}
+
+  // Specializations.
   codecvt_base::result
   codecvt<wchar_t, char, mbstate_t>::
   do_out(state_type& __state, const intern_type* __from,
@@ -46,22 +61,21 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	 extern_type* __to, extern_type* __to_end,
 	 extern_type*& __to_next) const
   {
-    result __ret = ok;
     state_type __tmp_state(__state);
-
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __c_locale __old = __uselocale(_M_c_locale_codecvt);
-#endif
+    Guard g(_M_c_locale_codecvt);
 
     // wcsnrtombs is *very* fast but stops if encounters NUL characters:
     // in case we fall back to wcrtomb and then continue, in a loop.
     // NB: wcsnrtombs is a GNU extension
-    for (__from_next = __from, __to_next = __to;
-	 __from_next < __from_end && __to_next < __to_end
-	 && __ret == ok;)
+    __from_next = __from;
+    __to_next = __to;
+    while (__from_next < __from_end)
       {
-	const intern_type* __from_chunk_end = wmemchr(__from_next, L'\0',
-						      __from_end - __from_next);
+	if (__to_next >= __to_end)
+	  return partial;
+
+	const intern_type* __from_chunk_end
+	  = wmemchr(__from_next, L'\0', __from_end - __from_next);
 	if (!__from_chunk_end)
 	  __from_chunk_end = __from_end;
 
@@ -77,12 +91,12 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    for (; __from < __from_next; ++__from)
 	      __to_next += wcrtomb(__to_next, *__from, &__tmp_state);
 	    __state = __tmp_state;
-	    __ret = error;
+	    return error;
 	  }
 	else if (__from_next && __from_next < __from_chunk_end)
 	  {
 	    __to_next += __conv;
-	    __ret = partial;
+	    return partial;
 	  }
 	else
 	  {
@@ -90,13 +104,13 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    __to_next += __conv;
 	  }
 
-	if (__from_next < __from_end && __ret == ok)
+	if (__from_next < __from_end)
 	  {
 	    extern_type __buf[MB_LEN_MAX];
 	    __tmp_state = __state;
 	    const size_t __conv2 = wcrtomb(__buf, *__from_next, &__tmp_state);
 	    if (__conv2 > static_cast<size_t>(__to_end - __to_next))
-	      __ret = partial;
+	      return partial;
 	    else
 	      {
 		memcpy(__to_next, __buf, __conv2);
@@ -107,11 +121,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  }
       }
 
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __uselocale(__old);
-#endif
-
-    return __ret;
+    return ok;
   }
 
   codecvt_base::result
@@ -121,24 +131,22 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	intern_type* __to, intern_type* __to_end,
 	intern_type*& __to_next) const
   {
-    result __ret = ok;
     state_type __tmp_state(__state);
-
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __c_locale __old = __uselocale(_M_c_locale_codecvt);
-#endif
+    Guard g(_M_c_locale_codecvt);
 
     // mbsnrtowcs is *very* fast but stops if encounters NUL characters:
     // in case we store a L'\0' and then continue, in a loop.
     // NB: mbsnrtowcs is a GNU extension
-    for (__from_next = __from, __to_next = __to;
-	 __from_next < __from_end && __to_next < __to_end
-	 && __ret == ok;)
+    __from_next = __from;
+    __to_next = __to;
+    while (__from_next < __from_end)
       {
-	const extern_type* __from_chunk_end;
-	__from_chunk_end = static_cast<const extern_type*>(memchr(__from_next, '\0',
-								  __from_end
-								  - __from_next));
+	if (__to_next >= __to_end)
+	  return partial;
+
+	const extern_type* __from_chunk_end
+	  = static_cast<const extern_type*>(memchr(__from_next, '\0',
+						   __from_end - __from_next));
 	if (!__from_chunk_end)
 	  __from_chunk_end = __from_end;
 
@@ -161,13 +169,13 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	      }
 	    __from_next = __from;
 	    __state = __tmp_state;
-	    __ret = error;
+	    return error;
 	  }
 	else if (__from_next && __from_next < __from_chunk_end)
 	  {
 	    // It is unclear what to return in this case (see DR 382).
 	    __to_next += __conv;
-	    __ret = partial;
+	    return partial;
 	  }
 	else
 	  {
@@ -175,7 +183,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    __to_next += __conv;
 	  }
 
-	if (__from_next < __from_end && __ret == ok)
+	if (__from_next < __from_end)
 	  {
 	    if (__to_next < __to_end)
 	      {
@@ -185,48 +193,30 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		*__to_next++ = L'\0';
 	      }
 	    else
-	      __ret = partial;
+	      return partial;
 	  }
       }
 
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __uselocale(__old);
-#endif
-
-    return __ret;
+    return ok;
   }
 
   int
   codecvt<wchar_t, char, mbstate_t>::
   do_encoding() const throw()
   {
+    Guard g(_M_c_locale_codecvt);
     // XXX This implementation assumes that the encoding is
     // stateless and is either single-byte or variable-width.
-    int __ret = 0;
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __c_locale __old = __uselocale(_M_c_locale_codecvt);
-#endif
-    if (MB_CUR_MAX == 1)
-      __ret = 1;
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __uselocale(__old);
-#endif
-    return __ret;
+    return MB_CUR_MAX == 1;
   }
 
   int
   codecvt<wchar_t, char, mbstate_t>::
   do_max_length() const throw()
   {
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __c_locale __old = __uselocale(_M_c_locale_codecvt);
-#endif
+    Guard g(_M_c_locale_codecvt);
     // XXX Probably wrong for stateful encodings.
-    int __ret = MB_CUR_MAX;
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __uselocale(__old);
-#endif
-    return __ret;
+    return MB_CUR_MAX;
   }
 
   int
@@ -236,10 +226,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
   {
     int __ret = 0;
     state_type __tmp_state(__state);
-
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __c_locale __old = __uselocale(_M_c_locale_codecvt);
-#endif
+    Guard g(_M_c_locale_codecvt);
 
     // mbsnrtowcs is *very* fast but stops if encounters NUL characters:
     // in case we advance past it and then continue, in a loop.
@@ -295,10 +282,6 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  }
       }
 
-#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
-    __uselocale(__old);
-#endif
-
     return __ret;
   }
 #endif
diff --git a/libstdc++-v3/testsuite/22_locale/codecvt/in/char/37475.cc b/libstdc++-v3/testsuite/22_locale/codecvt/in/char/37475.cc
new file mode 100644
index 00000000000..6184c3280cb
--- /dev/null
+++ b/libstdc++-v3/testsuite/22_locale/codecvt/in/char/37475.cc
@@ -0,0 +1,23 @@ 
+#include <locale>
+#include <testsuite_hooks.h>
+
+void
+test_pr37475()
+{
+  typedef std::codecvt<char, char, std::mbstate_t> test_type;
+  const test_type& cvt = std::use_facet<test_type>(std::locale::classic());
+  const char from = 'a';
+  const char* from_next;
+  char to = 0;
+  char* to_next;
+  std::mbstate_t st = std::mbstate_t();
+  std::codecvt_base::result res
+    = cvt.in(st, &from, &from+1, from_next, &to, &to, to_next);
+
+  VERIFY( res == std::codecvt_base::noconv );
+}
+
+int main()
+{
+  test_pr37475();
+}
diff --git a/libstdc++-v3/testsuite/22_locale/codecvt/in/wchar_t/37475.cc b/libstdc++-v3/testsuite/22_locale/codecvt/in/wchar_t/37475.cc
new file mode 100644
index 00000000000..a0e64847ea9
--- /dev/null
+++ b/libstdc++-v3/testsuite/22_locale/codecvt/in/wchar_t/37475.cc
@@ -0,0 +1,23 @@ 
+#include <locale>
+#include <testsuite_hooks.h>
+
+void
+test_pr37475()
+{
+  typedef std::codecvt<wchar_t, char, std::mbstate_t> test_type;
+  const test_type& cvt = std::use_facet<test_type>(std::locale::classic());
+  const char from = 'a';
+  const char* from_next;
+  wchar_t to = 0;
+  wchar_t* to_next;
+  std::mbstate_t st = std::mbstate_t();
+  std::codecvt_base::result res
+    = cvt.in(st, &from, &from+1, from_next, &to, &to, to_next);
+
+  VERIFY( res == std::codecvt_base::partial );
+}
+
+int main()
+{
+  test_pr37475();
+}
diff --git a/libstdc++-v3/testsuite/22_locale/codecvt/out/char/37475.cc b/libstdc++-v3/testsuite/22_locale/codecvt/out/char/37475.cc
new file mode 100644
index 00000000000..8736e4b7f3f
--- /dev/null
+++ b/libstdc++-v3/testsuite/22_locale/codecvt/out/char/37475.cc
@@ -0,0 +1,23 @@ 
+#include <locale>
+#include <assert.h>
+
+void
+test_pr37475()
+{
+  typedef std::codecvt<char, char, std::mbstate_t> test_type;
+  const test_type& cvt = std::use_facet<test_type>(std::locale::classic());
+  const char from = 'a';
+  const char* from_next;
+  char to;
+  char* to_next;
+  std::mbstate_t st = std::mbstate_t();
+  std::codecvt_base::result res
+    = cvt.out(st, &from, &from+1, from_next, &to, &to, to_next);
+
+  assert( res == std::codecvt_base::noconv );
+}
+
+int main()
+{
+  test_pr37475();
+}
diff --git a/libstdc++-v3/testsuite/22_locale/codecvt/out/wchar_t/37475.cc b/libstdc++-v3/testsuite/22_locale/codecvt/out/wchar_t/37475.cc
new file mode 100644
index 00000000000..2cd2edb7404
--- /dev/null
+++ b/libstdc++-v3/testsuite/22_locale/codecvt/out/wchar_t/37475.cc
@@ -0,0 +1,23 @@ 
+#include <locale>
+#include <assert.h>
+
+void
+test_pr37475()
+{
+  typedef std::codecvt<wchar_t, char, std::mbstate_t> test_type;
+  const test_type& cvt = std::use_facet<test_type>(std::locale::classic());
+  const wchar_t from = L'a';
+  const wchar_t* from_next;
+  char to;
+  char* to_next;
+  std::mbstate_t st = std::mbstate_t();
+  std::codecvt_base::result res
+    = cvt.out(st, &from, &from+1, from_next, &to, &to, to_next);
+
+  assert( res == std::codecvt_base::partial );
+}
+
+int main()
+{
+  test_pr37475();
+}