[libcxx-commits] [libcxx] WIP [libc++][ranges] Add `convertible_to` test case for `enumerate_view` iterator ctor test (PR #212044)

[Lucas Mellone via libcxx-commits]

https://github.com/lknknm updated https://github.com/llvm/llvm-project/pull/212044

>From a7ca704bbf976908f4c938f89d4ca63488a65cae Mon Sep 17 00:00:00 2001
From: Lucas Mellone <github.snugness349 at passinbox.com>
Date: Sat, 25 Jul 2026 19:28:15 +0200
Subject: [PATCH 1/3] add: static_assert for convertible_to

---
 .../range.enumerate/iterator/ctor.convert.pass.cpp               | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp b/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
index f441de92f6a60..083b01e178daa 100644
--- a/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
+++ b/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
@@ -43,6 +43,7 @@ constexpr void test() {
   };
 
   static_assert(std::is_convertible_v<EnumerateIterator, EnumerateConstIterator>);
+  static_assert(std::convertible_to<EnumerateIterator, EnumerateConstIterator>);
 
   std::array array{0, 84, 2, 3, 4};
   auto view = make_enumerate_view(array.begin(), array.end());

>From bb0f70c7a8bef2692d7ba738cc0d5890cc717a9d Mon Sep 17 00:00:00 2001
From: Lucas Mellone <github.snugness349 at passinbox.com>
Date: Mon, 27 Jul 2026 22:32:20 +0200
Subject: [PATCH 2/3] remove: is_convertinble_v line

---
 .../range.enumerate/iterator/ctor.convert.pass.cpp               | 1 -
 1 file changed, 1 deletion(-)

diff --git a/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp b/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
index 083b01e178daa..a53700b027b21 100644
--- a/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
+++ b/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
@@ -42,7 +42,6 @@ constexpr void test() {
     return EnumerateView(std::move(view));
   };
 
-  static_assert(std::is_convertible_v<EnumerateIterator, EnumerateConstIterator>);
   static_assert(std::convertible_to<EnumerateIterator, EnumerateConstIterator>);
 
   std::array array{0, 84, 2, 3, 4};

>From 1cddab5d71fb55ccce6b88b2e6193b58040d5635 Mon Sep 17 00:00:00 2001
From: Lucas Mellone <github.snugness349 at passinbox.com>
Date: Wed, 29 Jul 2026 23:49:54 +0200
Subject: [PATCH 3/3] port: underlying non-const to const not convertible test
 case form zip view

---
 .../iterator/ctor.convert.pass.cpp            | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp b/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
index a53700b027b21..eda1087d0b34a 100644
--- a/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
+++ b/libcxx/test/std/ranges/range.adaptors/range.enumerate/iterator/ctor.convert.pass.cpp
@@ -27,8 +27,17 @@
 
 #include "test_iterators.h"
 
+#include "../../range_adaptor_types.h"
 #include "../types.h"
 
+using ConstIterIncompatibleView =
+    BasicView<forward_iterator<int*>,
+              forward_iterator<int*>,
+              random_access_iterator<const int*>,
+              random_access_iterator<const int*>>;
+static_assert(!std::convertible_to<std::ranges::iterator_t<ConstIterIncompatibleView>,
+                                   std::ranges::iterator_t<const ConstIterIncompatibleView>>);
+
 template <class Iterator, class Sentinel = sentinel_wrapper<Iterator>>
 constexpr void test() {
   using View                   = MinimalView<Iterator, Sentinel>;
@@ -64,6 +73,17 @@ constexpr void test() {
     assert(index == 1);
     assert(value == 84);
   }
+  {
+    // underlying non-const to const not convertible
+    int buffer[3] = {1, 2, 3};
+    std::ranges::enumerate_view v(ConstIterIncompatibleView{buffer});
+    auto iter1 = v.begin();
+    auto iter2 = std::as_const(v).begin();
+
+    static_assert(!std::is_same_v<decltype(iter1), decltype(iter2)>);
+    static_assert(!std::constructible_from<decltype(iter1), decltype(iter2)>);
+    static_assert(!std::constructible_from<decltype(iter2), decltype(iter1)>);
+  }
 }
 
 constexpr bool tests() {