[PATCH] libstdc++: Fix std::ranges::iota is not included in numeric [PR108760]

["Michael Levine (BLOOMBERG/ 919 3RD A)" <mlevine55@bloomberg.net>]

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This patch fixes GCC Bug 108760:  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108760

Before this patch, using std::ranges::iota required including <algorithm> when it should have been sufficient to only include <numeric>.

When the patch is applied, the following code will compile:  https://godbolt.org/z/33EPeqd1b

I added a test case for this change as well.

I built my local version of gcc using the following configuration:  $ ../gcc/configure --disable-bootstrap --prefix="$(pwd)/_pfx/" --enable-languages=c,c++,lto

and I tested my changes by running:  $ make check-c++ -jN -k

I ran this on the following OS:

Virtualization: wsl
Operating System: Ubuntu 20.04.6 LTS
Kernel: Linux 5.15.146.1-microsoft-standard-WSL2
Architecture: x86-64



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From bd04070c281572ed7a3b48e3d33543e25b8c8afe Mon Sep 17 00:00:00 2001
From: Michael Levine <mlevine55@bloomberg.net>
Date: Fri, 23 Feb 2024 14:13:13 -0500
Subject: [PATCH 1/2] Fix the bug

Signed-off-by: Michael Levine <mlevine55@bloomberg.net>
---
 libstdc++-v3/include/bits/ranges_algo.h | 52 ----------------------
 libstdc++-v3/include/bits/stl_numeric.h | 57 ++++++++++++++++++++++++-
 2 files changed, 56 insertions(+), 53 deletions(-)

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index 62faff173bd..d258be0b93f 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -3521,58 +3521,6 @@ namespace ranges
 
 #endif // __glibcxx_ranges_contains
 
-#if __glibcxx_ranges_iota >= 202202L // C++ >= 23
-
-  template<typename _Out, typename _Tp>
-    struct out_value_result
-    {
-      [[no_unique_address]] _Out out;
-      [[no_unique_address]] _Tp value;
-
-      template<typename _Out2, typename _Tp2>
-	requires convertible_to<const _Out&, _Out2>
-	  && convertible_to<const _Tp&, _Tp2>
-	constexpr
-	operator out_value_result<_Out2, _Tp2>() const &
-	{ return {out, value}; }
-
-      template<typename _Out2, typename _Tp2>
-	requires convertible_to<_Out, _Out2>
-	  && convertible_to<_Tp, _Tp2>
-	constexpr
-	operator out_value_result<_Out2, _Tp2>() &&
-	{ return {std::move(out), std::move(value)}; }
-    };
-
-  template<typename _Out, typename _Tp>
-    using iota_result = out_value_result<_Out, _Tp>;
-
-  struct __iota_fn
-  {
-    template<input_or_output_iterator _Out, sentinel_for<_Out> _Sent, weakly_incrementable _Tp>
-      requires indirectly_writable<_Out, const _Tp&>
-      constexpr iota_result<_Out, _Tp>
-      operator()(_Out __first, _Sent __last, _Tp __value) const
-      {
-	while (__first != __last)
-	  {
-	    *__first = static_cast<const _Tp&>(__value);
-	    ++__first;
-	    ++__value;
-	  }
-	return {std::move(__first), std::move(__value)};
-      }
-
-    template<weakly_incrementable _Tp, output_range<const _Tp&> _Range>
-      constexpr iota_result<borrowed_iterator_t<_Range>, _Tp>
-      operator()(_Range&& __r, _Tp __value) const
-      { return (*this)(ranges::begin(__r), ranges::end(__r), std::move(__value)); }
-  };
-
-  inline constexpr __iota_fn iota{};
-
-#endif // __glibcxx_ranges_iota
-
 #if __glibcxx_ranges_find_last >= 202207L // C++ >= 23
 
   struct __find_last_fn
diff --git a/libstdc++-v3/include/bits/stl_numeric.h b/libstdc++-v3/include/bits/stl_numeric.h
index fe911154ab7..1b06c26dc02 100644
--- a/libstdc++-v3/include/bits/stl_numeric.h
+++ b/libstdc++-v3/include/bits/stl_numeric.h
@@ -59,7 +59,7 @@
 #include <bits/concept_check.h>
 #include <debug/debug.h>
 #include <bits/move.h> // For _GLIBCXX_MOVE
-
+#include <bits/ranges_base.h> // For _Range as used by std::ranges::iota
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -102,6 +102,61 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 #endif
 
+namespace ranges
+{
+#if __glibcxx_ranges_iota >= 202202L // C++ >= 23
+
+  template<typename _Out, typename _Tp>
+    struct out_value_result
+    {
+      [[no_unique_address]] _Out out;
+      [[no_unique_address]] _Tp value;
+
+      template<typename _Out2, typename _Tp2>
+	requires convertible_to<const _Out&, _Out2>
+	  && convertible_to<const _Tp&, _Tp2>
+	constexpr
+	operator out_value_result<_Out2, _Tp2>() const &
+	{ return {out, value}; }
+
+      template<typename _Out2, typename _Tp2>
+	requires convertible_to<_Out, _Out2>
+	  && convertible_to<_Tp, _Tp2>
+	constexpr
+	operator out_value_result<_Out2, _Tp2>() &&
+	{ return {std::move(out), std::move(value)}; }
+    };
+
+  template<typename _Out, typename _Tp>
+    using iota_result = out_value_result<_Out, _Tp>;
+
+  struct __iota_fn
+  {
+    template<input_or_output_iterator _Out, sentinel_for<_Out> _Sent, weakly_incrementable _Tp>
+      requires indirectly_writable<_Out, const _Tp&>
+      constexpr iota_result<_Out, _Tp>
+      operator()(_Out __first, _Sent __last, _Tp __value) const
+      {
+	while (__first != __last)
+	  {
+	    *__first = static_cast<const _Tp&>(__value);
+	    ++__first;
+	    ++__value;
+	  }
+	return {std::move(__first), std::move(__value)};
+      }
+
+    template<weakly_incrementable _Tp, output_range<const _Tp&> _Range>
+      constexpr iota_result<borrowed_iterator_t<_Range>, _Tp>
+      operator()(_Range&& __r, _Tp __value) const
+      { return (*this)(ranges::begin(__r), ranges::end(__r), std::move(__value)); }
+  };
+
+  inline constexpr __iota_fn iota{};
+
+#endif // __glibcxx_ranges_iota
+}
+
 _GLIBCXX_END_NAMESPACE_VERSION
 
 _GLIBCXX_BEGIN_NAMESPACE_ALGO
-- 
2.25.1


From c52c8d79fb3c7dc9d2512d1635712ffcd3dea07c Mon Sep 17 00:00:00 2001
From: Michael Levine <mlevine55@bloomberg.net>
Date: Tue, 16 Apr 2024 16:45:37 -0400
Subject: [PATCH 2/2] Added a test to verify that the bug has been fixed

Signed-off-by: Michael Levine <mlevine55@bloomberg.net>
---
 .../testsuite/std/ranges/iota/108760.cc       | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 libstdc++-v3/testsuite/std/ranges/iota/108760.cc

diff --git a/libstdc++-v3/testsuite/std/ranges/iota/108760.cc b/libstdc++-v3/testsuite/std/ranges/iota/108760.cc
new file mode 100644
index 00000000000..4f71383687c
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/iota/108760.cc
@@ -0,0 +1,41 @@
+// Copyright (C) 2020-2024 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This 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 General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// Fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108760
+// { dg-do run { target c++23 } }
+
+#include <numeric>
+#include <testsuite_hooks.h>
+
+const int ARR_SIZE = 4;
+
+void
+test01()
+{
+    int expected_arr[ARR_SIZE] = {0, 1, 2, 3};
+    int input_arr[ARR_SIZE] = {0, 0, 0, 0};
+    std::ranges::iota(input_arr, 0);
+    for (int i = 0; i < ARR_SIZE; i++) {
+        VERIFY( input_arr[i] == expected_arr[i]);
+    }
+}
+
+int
+main()
+{
+    test01();
+}
-- 
2.25.1