PR libstdc++/88738 treat shared_ptr and unique_ptr more like plain old pointers

        PR libstdc++/88738
        Warn about unused comparisons of shared_ptr/unique_ptr
        * include/bits/c++config [_GLIBCXX_NODISCARD]: Define.
        * include/bits/shared_ptr.h: Use it for operator ==, !=,
        <, <=, >, >= for shared_ptr.
        * include/bits/unique_ptr.h: Likewise for unique_ptr.

From-SVN: r267964

3 files changed, 44 insertions, 36 deletions

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 9b2fabd7d76..97bb6db70b1 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -99,6 +99,14 @@
 # define _GLIBCXX_ABI_TAG_CXX11 __attribute ((__abi_tag__ ("cxx11")))
 #endif
 
+// Macro to warn about unused results.
+#if __cplusplus >= 201703L
+# define _GLIBCXX_NODISCARD [[__nodiscard__]]
+#else
+# define _GLIBCXX_NODISCARD
+#endif
+
+
 
 #if __cplusplus
 
diff --git a/libstdc++-v3/include/bits/shared_ptr.h b/libstdc++-v3/include/bits/shared_ptr.h
index 99009ab4f99..d504627d1a0 100644
--- a/libstdc++-v3/include/bits/shared_ptr.h
+++ b/libstdc++-v3/include/bits/shared_ptr.h
@@ -380,37 +380,37 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // 20.7.2.2.7 shared_ptr comparisons
   template<typename _Tp, typename _Up>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
     { return __a.get() == __b.get(); }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
     { return !__a; }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     { return !__a; }
 
   template<typename _Tp, typename _Up>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
     { return __a.get() != __b.get(); }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
     { return (bool)__a; }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     { return (bool)__a; }
 
   template<typename _Tp, typename _Up>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
     {
       using _Tp_elt = typename shared_ptr<_Tp>::element_type;
@@ -420,7 +420,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
     {
       using _Tp_elt = typename shared_ptr<_Tp>::element_type;
@@ -428,7 +428,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     {
       using _Tp_elt = typename shared_ptr<_Tp>::element_type;
@@ -436,47 +436,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, typename _Up>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
     { return !(__b < __a); }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
     { return !(nullptr < __a); }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     { return !(__a < nullptr); }
 
   template<typename _Tp, typename _Up>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
     { return (__b < __a); }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
     { return nullptr < __a; }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     { return __a < nullptr; }
 
   template<typename _Tp, typename _Up>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
     { return !(__a < __b); }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
     { return !(__a < nullptr); }
 
   template<typename _Tp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     { return !(nullptr < __a); }
 
diff --git a/libstdc++-v3/include/bits/unique_ptr.h b/libstdc++-v3/include/bits/unique_ptr.h
index c7eb02e86fd..61a3ef05460 100644
--- a/libstdc++-v3/include/bits/unique_ptr.h
+++ b/libstdc++-v3/include/bits/unique_ptr.h
@@ -707,41 +707,41 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _Tp, typename _Dp,
 	   typename _Up, typename _Ep>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator==(const unique_ptr<_Tp, _Dp>& __x,
 	       const unique_ptr<_Up, _Ep>& __y)
     { return __x.get() == __y.get(); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator==(const unique_ptr<_Tp, _Dp>& __x, nullptr_t) noexcept
     { return !__x; }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator==(nullptr_t, const unique_ptr<_Tp, _Dp>& __x) noexcept
     { return !__x; }
 
   template<typename _Tp, typename _Dp,
 	   typename _Up, typename _Ep>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator!=(const unique_ptr<_Tp, _Dp>& __x,
 	       const unique_ptr<_Up, _Ep>& __y)
     { return __x.get() != __y.get(); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator!=(const unique_ptr<_Tp, _Dp>& __x, nullptr_t) noexcept
     { return (bool)__x; }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator!=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x) noexcept
     { return (bool)__x; }
 
   template<typename _Tp, typename _Dp,
 	   typename _Up, typename _Ep>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<(const unique_ptr<_Tp, _Dp>& __x,
 	      const unique_ptr<_Up, _Ep>& __y)
     {
@@ -752,67 +752,67 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
     { return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(__x.get(),
 								 nullptr); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
     { return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(nullptr,
 								 __x.get()); }
 
   template<typename _Tp, typename _Dp,
 	   typename _Up, typename _Ep>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<=(const unique_ptr<_Tp, _Dp>& __x,
 	       const unique_ptr<_Up, _Ep>& __y)
     { return !(__y < __x); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<=(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
     { return !(nullptr < __x); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator<=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
     { return !(__x < nullptr); }
 
   template<typename _Tp, typename _Dp,
 	   typename _Up, typename _Ep>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>(const unique_ptr<_Tp, _Dp>& __x,
 	      const unique_ptr<_Up, _Ep>& __y)
     { return (__y < __x); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
     { return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(nullptr,
 								 __x.get()); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
     { return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(__x.get(),
 								 nullptr); }
 
   template<typename _Tp, typename _Dp,
 	   typename _Up, typename _Ep>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>=(const unique_ptr<_Tp, _Dp>& __x,
 	       const unique_ptr<_Up, _Ep>& __y)
     { return !(__x < __y); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>=(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
     { return !(__x < nullptr); }
 
   template<typename _Tp, typename _Dp>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     operator>=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
     { return !(nullptr < __x); }