From: Jonathan Wakely <jwakely@redhat.com>
Date: Tue, 28 Sep 2021 11:35:29 +0000 (+0100)
Subject: libstdc++: Improve std::forward static assert message
X-Git-Tag: basepoints/gcc-13~4382
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a11052d98db2f2a61841f0c5ee84de4ca1b3e296;p=thirdparty%2Fgcc.git

libstdc++: Improve std::forward static assert message

The previous message told you something was wrong, but not why it
happened or why it's bad. This changes it to explain that the function
is being misused.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/move.h (forward(remove_reference_t<T>&&)):
	Improve text of static_assert.
	* testsuite/20_util/forward/c_neg.cc: Adjust dg-error.
	* testsuite/20_util/forward/f_neg.cc: Likewise.
---

diff --git a/libstdc++-v3/include/bits/move.h b/libstdc++-v3/include/bits/move.h
index 3abbb37ceebb..2dd7ed9e4f91 100644
--- a/libstdc++-v3/include/bits/move.h
+++ b/libstdc++-v3/include/bits/move.h
@@ -88,8 +88,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr _Tp&&
     forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
     {
-      static_assert(!std::is_lvalue_reference<_Tp>::value, "template argument"
-		    " substituting _Tp must not be an lvalue reference type");
+      static_assert(!std::is_lvalue_reference<_Tp>::value,
+	  "std::forward must not be used to convert an rvalue to an lvalue");
       return static_cast<_Tp&&>(__t);
     }
 
diff --git a/libstdc++-v3/testsuite/20_util/forward/c_neg.cc b/libstdc++-v3/testsuite/20_util/forward/c_neg.cc
index dc7ec51bde62..3875792866e3 100644
--- a/libstdc++-v3/testsuite/20_util/forward/c_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/forward/c_neg.cc
@@ -17,7 +17,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-error "must not be an lvalue reference" "" { target *-*-* } 0 }
+// { dg-error "convert an rvalue to an lvalue" "" { target *-*-* } 0 }
 
 #include <list>
 
diff --git a/libstdc++-v3/testsuite/20_util/forward/f_neg.cc b/libstdc++-v3/testsuite/20_util/forward/f_neg.cc
index 4ccd7264c651..51ccaf29c1a2 100644
--- a/libstdc++-v3/testsuite/20_util/forward/f_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/forward/f_neg.cc
@@ -17,7 +17,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-error "must not be an lvalue reference" "" { target *-*-* } 0 }
+// { dg-error "convert an rvalue to an lvalue" "" { target *-*-* } 0 }
 
 #include <utility>