Android: Root searches within the NDK for unified toolchains

Set `CMAKE_FIND_ROOT_PATH_MODE_*` appropriately.

1 files changed, 38 insertions, 0 deletions

diff --git a/Modules/Platform/Android.cmake b/Modules/Platform/Android.cmake
index 8ffa1b2..17d056a 100644
--- a/Modules/Platform/Android.cmake
+++ b/Modules/Platform/Android.cmake
@@ -22,3 +22,41 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "")
 if(CMAKE_VS_PLATFORM_NAME STREQUAL "Tegra-Android")
   set(CMAKE_LINK_LIBRARY_FLAG "")
 endif()
+
+# Commonly used Android toolchain files that pre-date CMake upstream support
+# set CMAKE_SYSTEM_VERSION to 1.  Avoid interfering with them.
+if(CMAKE_SYSTEM_VERSION EQUAL 1)
+  return()
+endif()
+
+if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
+  # Tell CMake not to search host sysroots for headers/libraries.
+  # CMAKE_FIND_ROOT_PATH must be non-empty for CMAKE_FIND_ROOT_PATH_MODE_* == ONLY
+  # to be meaningful.  The actual path  used here is fairly meaningless since CMake
+  # doesn't handle the NDK sysroot layout (per-arch and per-verion subdirectories for
+  # libraries), so find_library is handled separately by CMAKE_SYSTEM_LIBRARY_PATH.
+  # https://github.com/android-ndk/ndk/issues/890
+  if(NOT CMAKE_FIND_ROOT_PATH)
+    list(APPEND CMAKE_FIND_ROOT_PATH "${CMAKE_ANDROID_NDK}")
+  endif()
+
+  # Allow users to override these values in case they want more strict behaviors.
+  # For example, they may want to prevent the NDK's libz from being picked up so
+  # they can use their own.
+  # https://github.com/android-ndk/ndk/issues/517
+  if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_PROGRAM)
+    set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+  endif()
+
+  if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_LIBRARY)
+    set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+  endif()
+
+  if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_INCLUDE)
+    set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+  endif()
+
+  if(NOT DEFINED CMAKE_FIND_ROOT_PATH_MODE_PACKAGE)
+    set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+  endif()
+endif()