assert: Support types without operator== (int) [BZ #21972]

ChangeLog

@@ -1,3 +1,14 @@
+2017-08-21  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #21972]
+	* assert/assert.h (assert): Use static_cast (bool) for C++.
+	Use the ternary operator in the warning branch for GNU C.
+	* assert/Makefile (tests): Add tst-assert-c++, tst-assert-g++.
+	(CFLAGS-tst-assert-c++.o): Compile in C++11 mode.
+	(CFLAGS-tst-assert-g++.o): Compile in GnU C++11 mode.
+	(LDLIBS-tst-assert-c++, LDLIBS-tst-assert-g++): Link with libstdc++.
+	* assert/tst-assert-c++.cc, assert/tst-assert-g++.cc: New files.
+
 2017-08-21  H.J. Lu  <hongjiu.lu@intel.com>
 
 	[BZ #18822]

assert/Makefile

@@ -25,6 +25,15 @@ include ../Makeconfig
 headers	:= assert.h
 
 routines := assert assert-perr __assert
-tests := test-assert test-assert-perr
+tests := test-assert test-assert-perr tst-assert-c++ tst-assert-g++
 
 include ../Rules
+
+ifeq ($(have-cxx-thread_local),yes)
+CFLAGS-tst-assert-c++.o = -std=c++11
+LDLIBS-tst-assert-c++ = -lstdc++
+CFLAGS-tst-assert-g++.o = -std=gnu++11
+LDLIBS-tst-assert-g++ = -lstdc++
+else
+tests-unsupported += tst-assert-c++ tst-assert-g++
+endif

assert/assert.h

@@ -85,7 +85,12 @@ __END_DECLS
 /* When possible, define assert so that it does not add extra
    parentheses around EXPR.  Otherwise, those added parentheses would
    suppress warnings we'd expect to be detected by gcc's -Wparentheses.  */
-# if !defined __GNUC__ || defined __STRICT_ANSI__
+# if defined __cplusplus
+#  define assert(expr)							\
+     (static_cast <bool> (expr)						\
+      ? void (0)							\
+      : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
+# elif !defined __GNUC__ || defined __STRICT_ANSI__
 #  define assert(expr)							\
     ((expr)								\
      ? __ASSERT_VOID_CAST (0)						\
@@ -93,12 +98,11 @@ __END_DECLS
 # else
 /* The first occurrence of EXPR is not evaluated due to the sizeof,
    but will trigger any pedantic warnings masked by the __extension__
-   for the second occurrence.  The explicit comparison against zero is
-   required to support function pointers and bit fields in this
-   context, and to suppress the evaluation of variable length
-   arrays.  */
+   for the second occurrence.  The ternary operator is required to
+   support function pointers and bit fields in this context, and to
+   suppress the evaluation of variable length arrays.  */
 #  define assert(expr)							\
-  ((void) sizeof ((expr) == 0), __extension__ ({			\
+  ((void) sizeof ((expr) ? 1 : 0), __extension__ ({			\
       if (expr)								\
         ; /* empty */							\
       else								\

assert/tst-assert-c++.cc

@@ -0,0 +1,78 @@
+/* Tests for interactions between C++ and assert.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <assert.h>
+
+/* The C++ standard requires that if the assert argument is a constant
+   subexpression, then the assert itself is one, too.  */
+constexpr int
+check_constexpr ()
+{
+  return (assert (true), 1);
+}
+
+/* Objects of this class can be contextually converted to bool, but
+   cannot be compared to int.  */
+struct no_int
+{
+  no_int () = default;
+  no_int (const no_int &) = delete;
+
+  explicit operator bool () const
+  {
+    return true;
+  }
+
+  bool operator! () const; /* No definition.  */
+  template <class T> bool operator== (T) const; /* No definition.  */
+  template <class T> bool operator!= (T) const; /* No definition.  */
+};
+
+/* This class tests that operator== is not used by assert.  */
+struct bool_and_int
+{
+  bool_and_int () = default;
+  bool_and_int (const no_int &) = delete;
+
+  explicit operator bool () const
+  {
+    return true;
+  }
+
+  bool operator! () const; /* No definition.  */
+  template <class T> bool operator== (T) const; /* No definition.  */
+  template <class T> bool operator!= (T) const; /* No definition.  */
+};
+
+static int
+do_test ()
+{
+  {
+    no_int value;
+    assert (value);
+  }
+
+  {
+    bool_and_int value;
+    assert (value);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>

assert/tst-assert-g++.cc

@@ -0,0 +1,19 @@
+/* Tests for interactions between C++ and assert.  GNU C++11 version.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <tst-assert-c++.cc>