From 2887692065c38ef6617f423feafc6b69dd0a0681 Mon Sep 17 00:00:00 2001
From: bjacob <benoitjacob@google.com>
Date: Fri, 22 Jan 2021 20:23:42 -0500
Subject: Allow late definitions of cpuinfo but only when ruy is a subdir.
 (#250)

---
 CMakeLists.txt | 42 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 55e3397..98d480d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,9 +18,13 @@ project(ruy CXX)
 cmake_minimum_required(VERSION 3.13)  # Copied from IREE
 set(CMAKE_CXX_STANDARD 14)
 
+
+
 if (PROJECT_NAME STREQUAL CMAKE_PROJECT_NAME)
+  set(RUY_IS_TOPLEVEL TRUE)
   set(RUY_MINIMAL_BUILD_DEFAULT_VALUE OFF)
 else()
+  set(RUY_IS_TOPLEVEL FALSE)
   set(RUY_MINIMAL_BUILD_DEFAULT_VALUE ON)
 endif()
 
@@ -36,14 +40,38 @@ include(cmake/ruy_cc_library.cmake)
 include(cmake/ruy_cc_binary.cmake)
 include(cmake/ruy_cc_test.cmake)
 
+# Skip cpuinfo if it was already generated, which can happen when ruy is
+# a subdirectory in a wider project that already uses cpuinfo.
 if (NOT TARGET cpuinfo)
-  # Disabling cpuinfo's tests and benchmarks to prevent a copy of its
-  # googletest dependency getting downloaded into a 'deps' directory in the
-  # source tree!
-  set(CPUINFO_BUILD_BENCHMARKS OFF CACHE BOOL "" FORCE)
-  set(CPUINFO_BUILD_UNIT_TESTS OFF CACHE BOOL "" FORCE)
-  set(CPUINFO_BUILD_MOCK_TESTS OFF CACHE BOOL "" FORCE)
-  add_subdirectory("third_party/cpuinfo" EXCLUDE_FROM_ALL)
+  # Test if the third_party/cpuinfo submodule was checked out before
+  # adding that subdirectory, so we can do more helpful things below in the
+  # else() block when it's not.
+  set(RUY_CPUINFO_CMAKELISTS_FILE "${CMAKE_CURRENT_SOURCE_DIR}/third_party/cpuinfo/CMakeLists.txt")
+  if (EXISTS "${RUY_CPUINFO_CMAKELISTS_FILE}")
+    # Disabling cpuinfo's tests and benchmarks to prevent a copy of its
+    # googletest dependency getting downloaded into a 'deps' directory in the
+    # source tree!
+    set(CPUINFO_BUILD_BENCHMARKS OFF CACHE BOOL "" FORCE)
+    set(CPUINFO_BUILD_UNIT_TESTS OFF CACHE BOOL "" FORCE)
+    set(CPUINFO_BUILD_MOCK_TESTS OFF CACHE BOOL "" FORCE)
+    add_subdirectory("third_party/cpuinfo" EXCLUDE_FROM_ALL)
+  else()
+    # third_party/cpuinfo is not checked out. That could be intentional when
+    # ruy is a subdirectory in a wider project that is already providing
+    # the cpuinfo target. Maybe that wider project's CMakeLists is ordered
+    # in such a way that cpuinfo gets generated after ruy. In that case,
+    # it's helpful that we continue silently. In the worst case if the cpuinfo
+    # target never gets defined, ruy will fail to compile.
+    # On the other hand, if ruy is the top-level project here (not part of a
+    # wider project) then nothing will define the cpuinfo target for us,
+    # so we will definitely fail to compile, so we may as well fail right here.
+    if (RUY_IS_TOPLEVEL)
+      message(FATAL_ERROR "This file does not exist:\n${RUY_CPUINFO_CMAKELISTS_FILE}\n"
+                    "That typically means that the git submodules of the ruy "
+                    "repository haven't been checked out. Try this in the ruy "
+                    "git directory:\n  git submodule update --init")
+    endif()
+  endif()
 endif()
 
 # googletest is only needed for tests. Projects embedding ruy as a subdirectory
-- 
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