From 63f03d5e15fbe61cdda83af7cc6128ba5c400527 Mon Sep 17 00:00:00 2001
From: Gabriel Ferreira <gabrielcarvfer@gmail.com>
Date: Fri, 3 Jun 2022 18:26:30 -0300
Subject: [PATCH] build: re-enable PCH with CCache

Includes:
 - disable PCH validation when using XCode
 - disable Clang's PCH timestamping
 - add ostream header to the PCH
---
 CMakeLists.txt                             | 12 ++++++------
 build-support/macros-and-definitions.cmake | 12 ++++++++++++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3c64fea45..ef32f33f7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,15 +4,15 @@
 cmake_minimum_required(VERSION 3.10..3.10)
 
 # Use ccache if available
-mark_as_advanced(CCACHE_FOUND)
+mark_as_advanced(CCACHE)
 find_program(CCACHE ccache)
 if(NOT ("${CCACHE}" STREQUAL "CCACHE-NOTFOUND"))
   set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
-  message(
-    STATUS "CCache is enabled. Precompiled headers are disabled by default."
-  )
-  set(NS3_PRECOMPILE_HEADERS OFF
-      CACHE BOOL "Precompile module headers to speed up compilation" FORCE
+  message(STATUS "CCache is enabled.")
+  execute_process(
+    COMMAND
+      ${CCACHE} --set-config
+      sloppiness=pch_defines,time_macros,include_file_mtime,include_file_ctime
   )
 endif()
 
diff --git a/build-support/macros-and-definitions.cmake b/build-support/macros-and-definitions.cmake
index d816aeb68..e43eda439 100644
--- a/build-support/macros-and-definitions.cmake
+++ b/build-support/macros-and-definitions.cmake
@@ -1236,6 +1236,17 @@ macro(process_options)
   endif()
 
   if(${PRECOMPILE_HEADERS_ENABLED})
+    if(CLANG)
+      # Clang adds a timestamp to the PCH, which prevents ccache from working
+      # correctly
+      # https://github.com/ccache/ccache/issues/539#issuecomment-664198545
+      add_definitions(-Xclang -fno-pch-timestamp)
+    endif()
+    if(${XCODE})
+      # XCode is weird and messes up with the PCH, requiring this flag
+      # https://github.com/ccache/ccache/issues/156
+      add_definitions(-Xclang -fno-validate-pch)
+    endif()
     set(precompiled_header_libraries
         <algorithm>
         <cstdlib>
@@ -1247,6 +1258,7 @@ macro(process_options)
         <list>
         <map>
         <math.h>
+        <ostream>
         <set>
         <sstream>
         <stdint.h>