[1/2] libstdc++: Implement LWG 3391 changes to move/counted_iterator::base

Message ID 20210505202312.1609984-1-ppalka@redhat.com
State New
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  • [1/2] libstdc++: Implement LWG 3391 changes to move/counted_iterator::base
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Commit Message

Marek Polacek via Gcc-patches May 5, 2021, 8:23 p.m.
Tested on x86_64-pc-linux-gnu, does this look OK for trunk/10/11?

libstdc++-v3/ChangeLog:

	* include/bits/stl_iterator.h (move_iterator::base): Make the
	const& overload return a const reference and remove its
	constraint as per LWG 3391.  Make unconditionally noexcept.
	(counted_iterator::base): Likewise.
	* testsuite/24_iterators/move_iterator/lwg3391.cc: New test.
	* testsuite/24_iterators/move_iterator/move_only.cc: Adjust
	has_member_base concept to decay-copy the result of base().
---
 libstdc++-v3/include/bits/stl_iterator.h      | 13 ++-----
 .../24_iterators/move_iterator/lwg3391.cc     | 37 +++++++++++++++++++
 .../24_iterators/move_iterator/move_only.cc   |  8 +++-
 3 files changed, 48 insertions(+), 10 deletions(-)
 create mode 100644 libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc

-- 
2.31.1.442.g7e39198978

Comments

Marek Polacek via Gcc-patches May 6, 2021, 10:27 a.m. | #1
On 05/05/21 16:23 -0400, Patrick Palka via Libstdc++ wrote:
>Tested on x86_64-pc-linux-gnu, does this look OK for trunk/10/11?


Yes, thanks.

>libstdc++-v3/ChangeLog:

>

>	* include/bits/stl_iterator.h (move_iterator::base): Make the

>	const& overload return a const reference and remove its

>	constraint as per LWG 3391.  Make unconditionally noexcept.

>	(counted_iterator::base): Likewise.

>	* testsuite/24_iterators/move_iterator/lwg3391.cc: New test.

>	* testsuite/24_iterators/move_iterator/move_only.cc: Adjust

>	has_member_base concept to decay-copy the result of base().

>---

> libstdc++-v3/include/bits/stl_iterator.h      | 13 ++-----

> .../24_iterators/move_iterator/lwg3391.cc     | 37 +++++++++++++++++++

> .../24_iterators/move_iterator/move_only.cc   |  8 +++-

> 3 files changed, 48 insertions(+), 10 deletions(-)

> create mode 100644 libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc

>

>diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h

>index 049f83cff90..2409cd71f86 100644

>--- a/libstdc++-v3/include/bits/stl_iterator.h

>+++ b/libstdc++-v3/include/bits/stl_iterator.h

>@@ -1409,11 +1409,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION

>       base() const

>       { return _M_current; }

> #else

>-      constexpr iterator_type

>-      base() const &

>-#if __cpp_lib_concepts

>-	requires copy_constructible<iterator_type>

>-#endif

>+      constexpr const iterator_type&

>+      base() const & noexcept

>       { return _M_current; }

>

>       constexpr iterator_type

>@@ -2141,10 +2138,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION

> 	  return *this;

> 	}

>

>-      constexpr _It

>-      base() const &

>-      noexcept(is_nothrow_copy_constructible_v<_It>)

>-      requires copy_constructible<_It>

>+      constexpr const _It&

>+      base() const & noexcept

>       { return _M_current; }

>

>       constexpr _It

>diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc

>new file mode 100644

>index 00000000000..18e015777cd

>--- /dev/null

>+++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc

>@@ -0,0 +1,37 @@

>+// Copyright (C) 2021 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/>.

>+

>+// { dg-options "-std=gnu++2a" }

>+// { dg-do compile { target c++2a } }

>+

>+// Verify LWG 3391 changes.

>+

>+#include <iterator>

>+#include <ranges>

>+

>+#include <testsuite_iterators.h>

>+

>+using __gnu_test::test_range;

>+using __gnu_test::input_iterator_wrapper_nocopy;

>+

>+void

>+test01()

>+{

>+  extern test_range<int, input_iterator_wrapper_nocopy> rx;

>+  auto v = rx | std::views::take(5);

>+  std::ranges::begin(v) != std::ranges::end(v);

>+}

>diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc

>index 639adfab0e2..5537dfbf3cd 100644

>--- a/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc

>+++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc

>@@ -43,7 +43,13 @@ template<> struct std::iterator_traits<move_only_iterator>

> static_assert(std::input_iterator<move_only_iterator>);

>

> template<typename T>

>-  concept has_member_base = requires (T t) { std::forward<T>(t).base(); };

>+  concept has_member_base = requires (T t) {

>+    // LWG 3391 made the const& overload of move_iterator::base()

>+    // unconstrained and return a const reference.  So rather than checking

>+    // whether base() is valid (which is now trivially true in an unevaluated

>+    // context), the below now checks whether decay-copying base() is valid.

>+    [](auto){}(std::forward<T>(t).base());

>+  };

>

> using move_only_move_iterator = std::move_iterator<move_only_iterator>;

>

>-- 

>2.31.1.442.g7e39198978

>

Patch

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 049f83cff90..2409cd71f86 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1409,11 +1409,8 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       base() const
       { return _M_current; }
 #else
-      constexpr iterator_type
-      base() const &
-#if __cpp_lib_concepts
-	requires copy_constructible<iterator_type>
-#endif
+      constexpr const iterator_type&
+      base() const & noexcept
       { return _M_current; }
 
       constexpr iterator_type
@@ -2141,10 +2138,8 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  return *this;
 	}
 
-      constexpr _It
-      base() const &
-      noexcept(is_nothrow_copy_constructible_v<_It>)
-      requires copy_constructible<_It>
+      constexpr const _It&
+      base() const & noexcept
       { return _M_current; }
 
       constexpr _It
diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc
new file mode 100644
index 00000000000..18e015777cd
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/lwg3391.cc
@@ -0,0 +1,37 @@ 
+// Copyright (C) 2021 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+// Verify LWG 3391 changes.
+
+#include <iterator>
+#include <ranges>
+
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_range;
+using __gnu_test::input_iterator_wrapper_nocopy;
+
+void
+test01()
+{
+  extern test_range<int, input_iterator_wrapper_nocopy> rx;
+  auto v = rx | std::views::take(5);
+  std::ranges::begin(v) != std::ranges::end(v);
+}
diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc
index 639adfab0e2..5537dfbf3cd 100644
--- a/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc
+++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/move_only.cc
@@ -43,7 +43,13 @@  template<> struct std::iterator_traits<move_only_iterator>
 static_assert(std::input_iterator<move_only_iterator>);
 
 template<typename T>
-  concept has_member_base = requires (T t) { std::forward<T>(t).base(); };
+  concept has_member_base = requires (T t) {
+    // LWG 3391 made the const& overload of move_iterator::base()
+    // unconstrained and return a const reference.  So rather than checking
+    // whether base() is valid (which is now trivially true in an unevaluated
+    // context), the below now checks whether decay-copying base() is valid.
+    [](auto){}(std::forward<T>(t).base());
+  };
 
 using move_only_move_iterator = std::move_iterator<move_only_iterator>;