From 00e724fb8a240cd7f5e510327263026f64ed7550 Mon Sep 17 00:00:00 2001
From: Christian Blichmann <cblichmann@google.com>
Date: Wed, 23 Sep 2020 06:42:34 -0700
Subject: [PATCH] CMake build improvements

- Try to fix Ninja needlessly rebuilding everything every time
  See https://stackoverflow.com/questions/47087237/cmake-and-ninja-rebuild-unnecessary-files/47100426#47100426
- Since SAPI requires CMake >= 3.12, remove custom `list_join`

PiperOrigin-RevId: 333281764
Change-Id: I334d67d7ee54d21824b19e60a7a7f1e43bb5a057
---
 CMakeLists.txt            | 21 ++++++++++++---------
 cmake/SapiBuildDefs.cmake |  4 ++--
 cmake/SapiUtil.cmake      | 10 ----------
 3 files changed, 14 insertions(+), 21 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7c993f4..20b732e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,6 +14,16 @@
 
 cmake_minimum_required(VERSION 3.12)
 
+# Fix Ninja generator output to not rebuild entire sub-trees needlessly.
+if(CMAKE_GENERATOR MATCHES "Ninja")
+  file(WRITE "${CMAKE_BINARY_DIR}/UserMakeRulesOverride.cmake"
+    "string(REPLACE \"-MD\" \"-MMD\" CMAKE_DEPFILE_FLAGS_C \"\${CMAKE_DEPFILE_FLAGS_C}\")\n"
+    "string(REPLACE \"-MD\" \"-MMD\" CMAKE_DEPFILE_FLAGS_CXX \"\${CMAKE_DEPFILE_FLAGS_CXX}\")\n"
+  )
+  set(CMAKE_USER_MAKE_RULES_OVERRIDE
+      "${CMAKE_BINARY_DIR}/UserMakeRulesOverride.cmake" CACHE INTERNAL "")
+endif()
+
 project(SandboxedAPI C CXX ASM)
 
 # SAPI-wide setting for the language level
@@ -31,15 +41,8 @@ include(SapiDeps)
 include(SapiUtil)
 include(SapiBuildDefs)
 
-# Fix Ninja generator output to not rebuild entire sub-trees needlessly.
-if(CMAKE_GENERATOR MATCHES "Ninja")
-  file(WRITE "${SAPI_BINARY_DIR}/UserMakeRulesOverride.cmake"
-    "STRING(REPLACE \"-MD\" \"-MMD\" CMAKE_DEPFILE_FLAGS_C \"\${CMAKE_DEPFILE_FLAGS_C}\")\n"
-    "STRING(REPLACE \"-MD\" \"-MMD\" CMAKE_DEPFILE_FLAGS_CXX \"\${CMAKE_DEPFILE_FLAGS_CXX}\")\n"
-  )
-  set(CMAKE_USER_MAKE_RULES_OVERRIDE
-      "${SAPI_BINARY_DIR}/UserMakeRulesOverride.cmake" CACHE INTERNAL "")
-endif()
+# Allow the header generator to auto-configure include paths
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
 if (SAPI_FORCE_COLOR_OUTPUT)
   if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")  # GCC
diff --git a/cmake/SapiBuildDefs.cmake b/cmake/SapiBuildDefs.cmake
index 62583ec..5b9ce28 100644
--- a/cmake/SapiBuildDefs.cmake
+++ b/cmake/SapiBuildDefs.cmake
@@ -123,7 +123,7 @@ function(add_sapi_library)
   endif()
 
   # Interface
-  list_join(_sapi_FUNCTIONS "," _sapi_funcs)
+  list(JOIN _sapi_FUNCTIONS "," _sapi_funcs)
   foreach(src IN LISTS _sapi_INPUTS)
     get_filename_component(src "${src}" ABSOLUTE)
     list(APPEND _sapi_full_inputs "${src}")
@@ -149,7 +149,7 @@ function(add_sapi_library)
     )
   else()
     set(_sapi_isystem "${_sapi_NAME}.isystem")
-    list_join(_sapi_full_inputs "," _sapi_full_inputs)
+    list(JOIN _sapi_full_inputs "," _sapi_full_inputs)
     add_custom_command(
       OUTPUT "${_sapi_gen_header}" "${_sapi_isystem}"
       COMMAND sh -c
diff --git a/cmake/SapiUtil.cmake b/cmake/SapiUtil.cmake
index 8773f59..f4e891f 100644
--- a/cmake/SapiUtil.cmake
+++ b/cmake/SapiUtil.cmake
@@ -35,16 +35,6 @@ function(create_directory_symlink SOURCE DESTINATION)
   endif()
 endfunction()
 
-# Implements list(JOIN ...) for CMake < 3.12.
-function(list_join LIST SEP OUTPUT)
-  foreach(item IN LISTS ${LIST})
-    set(_concat "${_concat}${SEP}${item}")
-  endforeach()
-  string(LENGTH "${SEP}" _len)
-  string(SUBSTRING "${_concat}" ${_len} -1 _concat)
-  set(${OUTPUT} "${_concat}" PARENT_SCOPE)
-endfunction()
-
 # Helper function that behaves just like Protobuf's protobuf_generate_cpp(),
 # except that it strips import paths. This is necessary, because CMake's
 # protobuf rules don't work well with imports across different directories.