From: Jonathan Wakely <jwakely@redhat.com>
Date: Fri, 8 Dec 2023 13:47:04 +0000 (+0000)
Subject: libstdc++: Fix resolution of LWG 4016 for std::ranges::to [PR112876]
X-Git-Tag: basepoints/gcc-15~3782
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a314edee2490259d7f7caec8eef77846bcdb608b;p=thirdparty%2Fgcc.git

libstdc++: Fix resolution of LWG 4016 for std::ranges::to [PR112876]

What I implemented in r14-6199-g45630fbcf7875b does not match what I
proposed for LWG 4016, and it imposes additional, unwanted requirements
on the emplace and insert member functions of the container being
populated.

libstdc++-v3/ChangeLog:

	PR libstdc++/112876
	* include/std/ranges (ranges::to): Do not try to use an iterator
	returned by the container's emplace or insert member functions.
	* testsuite/std/ranges/conv/1.cc (Cont4::emplace, Cont4::insert):
	Use the iterator parameter. Do not return an iterator.
---

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index fb9df3d3e79b..be8475c0cb1b 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -9300,14 +9300,10 @@ namespace __detail
 		    __c.emplace_back(*__it);
 		  else if constexpr (requires { __c.push_back(*__it); })
 		    __c.push_back(*__it);
+		  else if constexpr (requires { __c.emplace(__c.end(), *__it); })
+		    __c.emplace(__c.end(), *__it);
 		  else
-		    {
-		      auto __end = __c.end();
-		      if constexpr (requires { __c.emplace(__end, *__it); })
-			__end = __c.emplace(__end, *__it);
-		      else
-			__end = __c.insert(__end, *__it);
-		    }
+		    __c.insert(__c.end(), *__it);
 		  ++__it;
 		}
 	      return __c;
diff --git a/libstdc++-v3/testsuite/std/ranges/conv/1.cc b/libstdc++-v3/testsuite/std/ranges/conv/1.cc
index b5f861dedb30..6d6a708ab64c 100644
--- a/libstdc++-v3/testsuite/std/ranges/conv/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/conv/1.cc
@@ -236,19 +236,19 @@ struct Cont4
   template<typename T>
     requires (Kind <= Emplace)
     && requires(C& c, T&& t) { c.emplace(c.end(), std::forward<T>(t)); }
-    typename C::iterator
-    emplace(typename C::iterator, T&& t)
+    void
+    emplace(typename C::iterator pos, T&& t)
     {
       kind = Emplace;
-      return c.emplace(c.end(), std::forward<T>(t));
+      c.emplace(pos, std::forward<T>(t));
     }
 
   template<typename T>
-    typename C::iterator
-    insert(typename C::iterator, T&& t)
+    void
+    insert(typename C::iterator pos, T&& t)
     {
       kind = Insert;
-      return c.insert(c.end(), std::forward<T>(t));
+      c.insert(pos, std::forward<T>(t));
     }
 
   // Required to satisfy reservable-container