From 9e50a890853333f5d9eb36305763d7ab00886825 Mon Sep 17 00:00:00 2001
From: Chris Peterson <cpeterson@mozilla.com>
Date: Wed, 16 Nov 2022 00:54:27 +0000
Subject: [PATCH] Bug 1800293 - mfbt: Don't use std::is_literal_type when
compiling as C++20. r=glandium
`std::is_literal_type` was deprecated in C++17 and removed in C++20. Continue using it when compiling as C++17 to retain what benefits it does provide for generic code.
> The `is_literal` type trait offers negligible value to generic code, as what is really needed is the ability to know that a specific construction would produce constant initialization. The core term of a literal type having at least one constexpr constructor is too weak to be used meaningfully.
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0174r2.html
https://en.cppreference.com/w/cpp/types/is_literal_type
Differential Revision: https://phabricator.services.mozilla.com/D161952
---
mfbt/tests/TestResult.cpp | 2 ++
mfbt/tests/TestTypedEnum.cpp | 4 ++--
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/mfbt/tests/TestResult.cpp b/mfbt/tests/TestResult.cpp
index b66d3b608ed2c..20680e41c832c 100644
--- a/mfbt/tests/TestResult.cpp
+++ b/mfbt/tests/TestResult.cpp
@@ -98,11 +98,13 @@ static_assert(sizeof(Foo32) >= sizeof(uintptr_t) ||
sizeof(Result<Foo16, Foo32>) <= sizeof(uintptr_t),
"Result with small types should be pointer-sized");
+#if __cplusplus < 202002L
static_assert(std::is_literal_type_v<Result<int*, Failed>>);
static_assert(std::is_literal_type_v<Result<Ok, Failed>>);
static_assert(std::is_literal_type_v<Result<Ok, Foo8>>);
static_assert(std::is_literal_type_v<Result<Foo8, Foo16>>);
static_assert(!std::is_literal_type_v<Result<Ok, UniquePtr<int>>>);
+#endif
static constexpr GenericErrorResult<Failed> Fail() { return Err(Failed{}); }
diff --git a/mfbt/tests/TestTypedEnum.cpp b/mfbt/tests/TestTypedEnum.cpp
index 814d3485ce416..cddbb39e0b75f 100644
--- a/mfbt/tests/TestTypedEnum.cpp
+++ b/mfbt/tests/TestTypedEnum.cpp
@@ -11,10 +11,10 @@
#include <type_traits>
// A rough feature check for is_literal_type. Not very carefully checked.
-// Feel free to amend as needed.
+// Feel free to amend as needed. is_literal_type was removed in C++20.
// We leave ANDROID out because it's using stlport which doesn't have
// std::is_literal_type.
-#if __cplusplus >= 201103L && !defined(ANDROID)
+#if __cplusplus >= 201103L && __cplusplus < 202002L && !defined(ANDROID)
# if defined(__clang__)
/*
* Per Clang documentation, "Note that marketing version numbers should not
--
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