WIP: Addressed some comments

Author: Zingam

libcxx/include/span

@@ -233,7 +233,8 @@ public:
   _LIBCPP_HIDE_FROM_ABI constexpr explicit span(std::initializer_list<value_type> __il)
     requires is_const_v<element_type>
       : __data_{__il.begin()} {
-    _LIBCPP_ASSERT_INTERNAL(_Extent == __il.size(), "Size mismatch in span's constructor _Extent != __il.size().");
+    _LIBCPP_ASSERT_VALID_INPUT_RANGE(
+        _Extent == __il.size(), "Size mismatch in span's constructor _Extent != __il.size().");
   }
 #  endif
 

libcxx/test/std/containers/views/views.span/span.cons/initializer_list.pass.cpp

@@ -17,6 +17,7 @@
 #include <span>
 #include <type_traits>
 
+#include "test_convertible.h"
 #include "test_macros.h"
 
 #if TEST_STD_VER >= 26
@@ -31,6 +32,8 @@ static_assert(!ConstElementType<std::span<int>>);
 static_assert(ConstElementType<std::span<const int, 94>>);
 static_assert(!ConstElementType<std::span<int, 94>>);
 
+// Constructor constraings
+
 template <typename I, typename T, std::size_t... N>
 concept HasInitializerListCtr = requires(I il) { std::span<T, N...>{il}; };
 
@@ -39,6 +42,15 @@ static_assert(!HasInitializerListCtr<std::initializer_list<int>, int>);
 static_assert(HasInitializerListCtr<std::initializer_list<const int>, const int, 94>);
 static_assert(!HasInitializerListCtr<std::initializer_list<int>, int, 94>);
 
+// Constructor conditionally explicit
+
+static_assert(!test_convertible<std::span<const int, 28>, std::initializer_list<int>>(),
+              "This constructor must be explicit");
+static_assert(std::is_constructible_v<std::span<const int, 28>, std::initializer_list<int>>);
+static_assert(test_convertible<std::span<const int>, std::initializer_list<int>>(),
+              "This constructor must not be explicit");
+static_assert(std::is_constructible_v<std::span<const int>, std::initializer_list<int>>);
+
 #endif
 
 struct Sink {

libcxx/test/std/containers/views/views.span/span.cons/iterator_len.verify.cpp

@@ -34,12 +34,7 @@ void test() {
   std::span<int> sp = {0, 0};
   // expected-error@+1 {{no matching constructor for initialization of 'std::span<int, 2>'}}
   std::span<int, 2> sp2 = {0, 0};
-#if TEST_STD_VER >= 26
-  // No error in C++26
-  std::span<const int> csp = {0, 0};
-  // expected-error@+1 {{chosen constructor is explicit in copy-initialization}}
-  std::span<const int, 2> csp2 = {0, 0};
-#else
+#if TEST_STD_VER < 26
   // expected-error@+1 {{no matching constructor for initialization of 'std::span<const int>'}}
   std::span<const int> csp = {0, 0};
   // expected-error@+1 {{no matching constructor for initialization of 'std::span<const int, 2>'}}