From b42c6ea281add0d5ad3bd2bec52742353c718603 Mon Sep 17 00:00:00 2001
From: AnotherTest <ali.mpfard@gmail.com>
Date: Sat, 3 Oct 2020 16:26:09 +0330
Subject: [PATCH] LibIPC: Make IPC::encode() and ::decode() fail at compiletime
 when used

This would previously fail at runtime, and it would have zero indication
of what exactly went wrong.
Also adds `AK::DependentFalse<Ts...>', which is a...dependent false.
---
 AK/StdLibExtras.h          | 4 ++++
 Libraries/LibIPC/Decoder.h | 3 ++-
 Libraries/LibIPC/Encoder.h | 1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/AK/StdLibExtras.h b/AK/StdLibExtras.h
index c47066df4a..e8e02703ee 100644
--- a/AK/StdLibExtras.h
+++ b/AK/StdLibExtras.h
@@ -504,6 +504,9 @@ using CopyConst =
 template<typename... Ts>
 using Void = void;
 
+template<typename... _Ignored>
+inline constexpr auto DependentFalse = false;
+
 }
 
 using AK::AddConst;
@@ -512,6 +515,7 @@ using AK::ceil_div;
 using AK::clamp;
 using AK::Conditional;
 using AK::declval;
+using AK::DependentFalse;
 using AK::exchange;
 using AK::forward;
 using AK::is_trivial;
diff --git a/Libraries/LibIPC/Decoder.h b/Libraries/LibIPC/Decoder.h
index 1f366f5d3f..37c3d6a848 100644
--- a/Libraries/LibIPC/Decoder.h
+++ b/Libraries/LibIPC/Decoder.h
@@ -28,6 +28,7 @@
 
 #include <AK/Forward.h>
 #include <AK/NumericLimits.h>
+#include <AK/StdLibExtras.h>
 #include <AK/String.h>
 #include <LibIPC/Forward.h>
 #include <LibIPC/Message.h>
@@ -37,8 +38,8 @@ namespace IPC {
 template<typename T>
 inline bool decode(Decoder&, T&)
 {
+    static_assert(DependentFalse<T>, "Base IPC::decoder() instantiated");
     ASSERT_NOT_REACHED();
-    return false;
 }
 
 class Decoder {
diff --git a/Libraries/LibIPC/Encoder.h b/Libraries/LibIPC/Encoder.h
index da88d889ac..b5869c5a82 100644
--- a/Libraries/LibIPC/Encoder.h
+++ b/Libraries/LibIPC/Encoder.h
@@ -34,6 +34,7 @@ namespace IPC {
 template<typename T>
 bool encode(Encoder&, T&)
 {
+    static_assert(DependentFalse<T>, "Base IPC::encode() was instantiated");
     ASSERT_NOT_REACHED();
 }