Build: Stop using precompiled headers (PCH)

This had very bad interactions with ccache, often leading to rebuilds
with 100% cache misses, etc. Ali says it wasn't that big of a speedup
in the end anyway, so let's not bother with it.

We can always bring it back in the future if it seems like a good idea.

CMakeLists.txt

@@ -26,7 +26,6 @@ option(ENABLE_ALL_THE_DEBUG_MACROS "Enable all debug macros to validate they sti
 option(ENABLE_COMPILETIME_FORMAT_CHECK "Enable compiletime format string checks" ON)
 option(ENABLE_PCI_IDS_DOWNLOAD "Enable download of the pci.ids database at build time" ON)
 option(BUILD_LAGOM "Build parts of the system targeting the host OS for fuzzing/testing" OFF)
-option(PRECOMPILE_COMMON_HEADERS "Precompile some common headers to speedup compilation" OFF)
 option(ENABLE_KERNEL_LTO "Build the kernel with link-time optimization" OFF)
 
 add_custom_target(run

Kernel/CMakeLists.txt

@@ -383,7 +383,6 @@ endif()
 target_link_libraries(Kernel kernel_heap gcc stdc++)
 add_dependencies(Kernel boot kernel_heap)
 install(TARGETS Kernel RUNTIME DESTINATION boot)
-serenity_add_ak_precompiled_headers_to_target(Kernel)
 
 add_custom_command(
     TARGET Kernel

Meta/CMake/precompile-headers.cmake

@@ -1,9 +0,0 @@
-function(serenity_add_precompiled_header_to_target target header)
-    if (PRECOMPILE_COMMON_HEADERS AND COMMAND target_precompile_headers)
-        target_precompile_headers(${target} PRIVATE ${header})
-    endif ()
-endfunction()
-
-function(serenity_add_ak_precompiled_headers_to_target target)
-    serenity_add_precompiled_header_to_target(${target} ${CMAKE_SOURCE_DIR}/Meta/Precompile/AK.h)
-endfunction()

Meta/CMake/utils.cmake

@@ -1,5 +1,3 @@
-include(${CMAKE_SOURCE_DIR}/Meta/CMake/precompile-headers.cmake)
-
 function(serenity_install_headers target_name)
     file(GLOB_RECURSE headers RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} "*.h")
     foreach(header ${headers})
@@ -32,7 +30,6 @@ function(serenity_lib target_name fs_name)
     add_library(${target_name} SHARED ${SOURCES} ${GENERATED_SOURCES})
     install(TARGETS ${target_name} DESTINATION usr/lib)
     set_target_properties(${target_name} PROPERTIES OUTPUT_NAME ${fs_name})
-    serenity_add_ak_precompiled_headers_to_target(${target_name})
     serenity_generated_sources(${target_name})
 endfunction()
 
@@ -69,7 +66,6 @@ endfunction()
 function(serenity_bin target_name)
     add_executable(${target_name} ${SOURCES})
     install(TARGETS ${target_name} RUNTIME DESTINATION bin)
-    serenity_add_ak_precompiled_headers_to_target(${target_name})
     serenity_generated_sources(${target_name})
 endfunction()
 

Meta/Precompile/AK.h

@@ -1,28 +0,0 @@
-/*
- * Copyright (c) 2021, Ali Mohammad Pur <ali.mpfard@gmail.com>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#pragma once
-
-#include <AK/Assertions.h>
-#include <AK/Badge.h>
-#include <AK/ByteBuffer.h>
-#include <AK/Format.h>
-#include <AK/Forward.h>
-#include <AK/Function.h>
-#include <AK/HashMap.h>
-#include <AK/JsonObject.h>
-#include <AK/LexicalPath.h>
-#include <AK/Optional.h>
-#include <AK/OwnPtr.h>
-#include <AK/RefCounted.h>
-#include <AK/RefPtr.h>
-#include <AK/StdLibExtras.h>
-#include <AK/String.h>
-#include <AK/StringBuilder.h>
-#include <AK/StringView.h>
-#include <AK/Types.h>
-#include <AK/URL.h>
-#include <AK/Vector.h>

Userland/Libraries/LibJS/CMakeLists.txt

@@ -93,6 +93,3 @@ set(SOURCES
 
 serenity_lib(LibJS js)
 target_link_libraries(LibJS LibM LibCore LibCrypto LibRegex LibSyntax)
-
-serenity_add_precompiled_header_to_target(LibJS ${CMAKE_CURRENT_SOURCE_DIR}/Heap/Heap.h)
-serenity_add_precompiled_header_to_target(LibJS ${CMAKE_CURRENT_SOURCE_DIR}/Runtime/GlobalObject.h)