[libcxx-commits] [libcxx] [libc++][ranges] Implement LWG4053 and LWG4054 (PR #88612)

[A. Jiang via libcxx-commits]

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@@ -60,6 +60,14 @@ static_assert(!std::is_invocable_v<decltype(std::views::repeat), NonCopyable>);
 // Tp is move_constructible
 static_assert(std::is_invocable_v<decltype(std::views::repeat), MoveOnly>);
 
+// LWG4053: Unary call to std::views::repeat does not decay the argument
+using RPV = std::ranges::repeat_view<const char*>;
+
+static_assert(std::same_as<decltype(std::views::repeat("foo", std::unreachable_sentinel)), RPV>);  // OK
+static_assert(std::same_as<decltype(std::views::repeat(+"foo", std::unreachable_sentinel)), RPV>); // OK
+static_assert(std::same_as<decltype(std::views::repeat("foo")), RPV>);                             // OK since LWG4053
+static_assert(std::same_as<decltype(std::views::repeat(+"foo")), RPV>);                            // OK
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frederick-vs-ja wrote:

> Does the follow case also well-formed?
> 
> ```
> static_assert(std::same_as<decltype(std::ranges::repeat_view(std::ranges::repeat_view(1))), std::ranges::repeat_view<std::ranges::repeat_view<int>>>);
> ```

No. The copy deduction candidate is selected here, so the deduced type is `std::ranges::repeat_view<int>`.
This is an unavoidable divergence between `views::repeat` and CTAD for `repeat_view`, and user code should always use `views::repeat`.

https://github.com/llvm/llvm-project/pull/88612