commit 654f0c3862f7bae5bad07b4b451e10c9e9affa35
Author: Fujii Hironori <Hironori.Fujii@sony.com>
Date:   2025-03-18T12:35:31-07:00

    EnumTraits.h: error: no matching function for call to 'enumName' with Clang 20
    https://bugs.webkit.org/show_bug.cgi?id=289669
    
    Reviewed by Keith Miller.
    
    Clang 20 couldn't compile EnumTraits.h.
    
    > wtf/EnumTraits.h:212:33: note: candidate template ignored: invalid explicitly-specified argument for template parameter 'V'
    
    An invalid enum value can't be specifed to the template parameter `V`.
    
    > template<auto V> constexpr std::span<const char> enumName()
    
    The upstream Magic Enum C++ has a template variable `is_enum_constexpr_static_cast_valid<E, V>` to check a enum value is valid.
    <https://github.com/Neargye/magic_enum/blob/a413fcc9c46a020a746907136a384c227f3cd095/include/magic_enum/magic_enum.hpp#L624-L634>
    
    Imported the template variable.
    
    * Source/WTF/wtf/EnumTraits.h:
    (WTF::enumName):
    (WTF::makeEnumNames):
    
    Canonical link: https://commits.webkit.org/292321@main

diff --git Source/WTF/wtf/EnumTraits.h Source/WTF/wtf/EnumTraits.h
index 0d33e39a93dd..95e6318b6f1b 100644
--- Source/WTF/wtf/EnumTraits.h
+++ Source/WTF/wtf/EnumTraits.h
@@ -152,6 +152,16 @@ constexpr bool isZeroBasedContiguousEnum()
 #pragma clang diagnostic ignored "-Wenum-constexpr-conversion"
 #endif
 
+#if COMPILER(CLANG) && __clang_major__ >= 16
+template <typename E, auto V, typename = void>
+inline constexpr bool isEnumConstexprStaticCastValid = false;
+template <typename E, auto V>
+inline constexpr bool isEnumConstexprStaticCastValid<E, V, std::void_t<std::integral_constant<E, static_cast<E>(V)>>> = true;
+#else
+template <typename, auto>
+inline constexpr bool isEnumConstexprStaticCastValid = true;
+#endif
+
 template<typename E>
 constexpr std::span<const char> enumTypeNameImpl()
 {
@@ -215,6 +225,15 @@ constexpr std::span<const char> enumName()
     return result;
 }
 
+template<typename E, auto V>
+constexpr std::span<const char> enumName()
+{
+    if constexpr (isEnumConstexprStaticCastValid<E, V>)
+        return enumName<static_cast<E>(V)>();
+    else
+        return { };
+}
+
 template<typename E>
 constexpr std::underlying_type_t<E> enumNamesMin()
 {
@@ -264,7 +283,7 @@ constexpr auto makeEnumNames(std::index_sequence<Is...>)
 {
     constexpr auto min = enumNamesMin<E>();
     return std::array<std::span<const char>, sizeof...(Is)> {
-        enumName<static_cast<E>(static_cast<std::underlying_type_t<E>>(Is) + min)>()...
+        enumName<E, static_cast<std::underlying_type_t<E>>(Is) + min>()...
     };
 }