Android: Use unified toolchain in NDK r19+

The NDK build system now uses only a single toolchain in

    <ndk>/toolchains/llvm/prebuilt/<host>

Its compilers are always `bin/{clang,clang++}` and its binutils are
always `bin/<triple>-*`.  It is a standalone toolchain:

* The Anrdoid API level is specified at the end of `--target=`.
* The standard library may be specified via `-stdlib=`.
* No need to pass system includes or libraries explicitly.
* No need to pass `--sysroot` or `-gcc-toolchain`.

Teach CMake to recognize NDK versions that have a unified
toolchain with its own sysroot and use the above approach.

Fixes: #18739

6 files changed, 82 insertions, 3 deletions

diff --git a/Modules/Platform/Android-Clang.cmake b/Modules/Platform/Android-Clang.cmake
index 9ed1e01..847178f 100644
--- a/Modules/Platform/Android-Clang.cmake
+++ b/Modules/Platform/Android-Clang.cmake
@@ -40,6 +40,9 @@ macro(__android_compiler_clang lang)
   endif()
   if(NOT CMAKE_${lang}_COMPILER_TARGET)
     set(CMAKE_${lang}_COMPILER_TARGET "${_ANDROID_ABI_CLANG_TARGET}")
+    if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
+      string(APPEND CMAKE_${lang}_COMPILER_TARGET "${CMAKE_SYSTEM_VERSION}")
+    endif()
     list(APPEND CMAKE_${lang}_COMPILER_PREDEFINES_COMMAND "--target=${CMAKE_${lang}_COMPILER_TARGET}")
   endif()
 endmacro()
diff --git a/Modules/Platform/Android-Common.cmake b/Modules/Platform/Android-Common.cmake
index fb9ebd0..1affcd0 100644
--- a/Modules/Platform/Android-Common.cmake
+++ b/Modules/Platform/Android-Common.cmake
@@ -47,7 +47,41 @@ if(CMAKE_ANDROID_NDK)
 endif()
 
 if(CMAKE_ANDROID_STL_TYPE)
-  if(CMAKE_ANDROID_NDK)
+  if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
+    if(CMAKE_ANDROID_STL_TYPE STREQUAL "system")
+      set(_ANDROID_STL_EXCEPTIONS 0)
+      set(_ANDROID_STL_RTTI 0)
+      macro(__android_stl lang)
+        string(APPEND CMAKE_${lang}_FLAGS_INIT " -stdlib=libstdc++")
+      endmacro()
+    elseif(CMAKE_ANDROID_STL_TYPE STREQUAL "c++_static")
+      set(_ANDROID_STL_EXCEPTIONS 1)
+      set(_ANDROID_STL_RTTI 1)
+      macro(__android_stl lang)
+        string(APPEND CMAKE_${lang}_FLAGS_INIT " -stdlib=libc++")
+        string(APPEND CMAKE_${lang}_STANDARD_LIBRARIES " -static-libstdc++")
+      endmacro()
+    elseif(CMAKE_ANDROID_STL_TYPE STREQUAL "c++_shared")
+      set(_ANDROID_STL_EXCEPTIONS 1)
+      set(_ANDROID_STL_RTTI 1)
+      macro(__android_stl lang)
+        string(APPEND CMAKE_${lang}_FLAGS_INIT " -stdlib=libc++")
+      endmacro()
+    elseif(CMAKE_ANDROID_STL_TYPE STREQUAL "none")
+      set(_ANDROID_STL_RTTI 0)
+      set(_ANDROID_STL_EXCEPTIONS 0)
+      macro(__android_stl lang)
+        # FIXME: Add a way to add project-wide language-specific compile-only flags.
+        set(CMAKE_CXX_COMPILE_OBJECT
+          "<CMAKE_CXX_COMPILER>  <DEFINES> <INCLUDES> <FLAGS> -o <OBJECT> -c <SOURCE> -nostdinc++")
+        string(APPEND CMAKE_${lang}_STANDARD_LIBRARIES " -nostdlib++")
+      endmacro()
+    else()
+      message(FATAL_ERROR
+        "Android: STL '${CMAKE_ANDROID_STL_TYPE}' not supported by this NDK."
+        )
+    endif()
+  elseif(CMAKE_ANDROID_NDK)
 
     macro(__android_stl_inc lang dir req)
       if(EXISTS "${dir}")
@@ -152,6 +186,10 @@ macro(__android_compiler_common lang)
     __android_stl(CXX)
   endif()
 
+  if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
+    string(APPEND CMAKE_${lang}_STANDARD_LIBRARIES " -latomic -lm")
+  endif()
+
   # <ndk>/build/core/definitions.mk appends the sysroot's include directory
   # explicitly at the end of the command-line include path so that it
   # precedes the toolchain's builtin include directories.  This is
@@ -161,7 +199,7 @@ macro(__android_compiler_common lang)
   #
   # Do not do this for a standalone toolchain because it is already
   # tied to a specific API version.
-  if(CMAKE_ANDROID_NDK)
+  if(CMAKE_ANDROID_NDK AND NOT CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
     if(CMAKE_SYSROOT_COMPILE)
       set(_cmake_sysroot_compile "${CMAKE_SYSROOT_COMPILE}")
     else()
diff --git a/Modules/Platform/Android-Determine.cmake b/Modules/Platform/Android-Determine.cmake
index 56ed328..e7c1b48 100644
--- a/Modules/Platform/Android-Determine.cmake
+++ b/Modules/Platform/Android-Determine.cmake
@@ -221,8 +221,15 @@ if(CMAKE_ANDROID_NDK)
   else()
     message(FATAL_ERROR "Android: Builds hosted on '${CMAKE_HOST_SYSTEM_NAME}' not supported.")
   endif()
+
+  # Look for a unified toolchain/sysroot provided with the NDK.
+  set(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED "${CMAKE_ANDROID_NDK}/toolchains/llvm/prebuilt/${CMAKE_ANDROID_NDK_TOOLCHAIN_HOST_TAG}")
+  if(NOT IS_DIRECTORY "${CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED}/sysroot")
+    set(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED "")
+  endif()
 else()
   set(CMAKE_ANDROID_NDK_TOOLCHAIN_HOST_TAG "")
+  set(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED "")
 endif()
 
 # https://developer.android.com/ndk/guides/abis.html
@@ -370,6 +377,7 @@ if(CMAKE_ANDROID_NDK)
     "set(CMAKE_ANDROID_ARCH_TRIPLE \"${CMAKE_ANDROID_ARCH_TRIPLE}\")\n"
     "set(CMAKE_ANDROID_NDK_DEPRECATED_HEADERS \"${CMAKE_ANDROID_NDK_DEPRECATED_HEADERS}\")\n"
     "set(CMAKE_ANDROID_NDK_TOOLCHAIN_HOST_TAG \"${CMAKE_ANDROID_NDK_TOOLCHAIN_HOST_TAG}\")\n"
+    "set(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED \"${CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED}\")\n"
     )
 endif()
 
diff --git a/Modules/Platform/Android-Initialize.cmake b/Modules/Platform/Android-Initialize.cmake
index 1dcb939..a5d2820 100644
--- a/Modules/Platform/Android-Initialize.cmake
+++ b/Modules/Platform/Android-Initialize.cmake
@@ -19,6 +19,11 @@ endif()
 
 set(CMAKE_BUILD_TYPE_INIT Debug)
 
+# Skip sysroot selection if the NDK has a unified toolchain.
+if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
+  return()
+endif()
+
 if(NOT CMAKE_SYSROOT)
   if(CMAKE_ANDROID_NDK)
     set(CMAKE_SYSROOT "${CMAKE_ANDROID_NDK}/platforms/android-${CMAKE_SYSTEM_VERSION}/arch-${CMAKE_ANDROID_ARCH}")
diff --git a/Modules/Platform/Android/Determine-Compiler-NDK.cmake b/Modules/Platform/Android/Determine-Compiler-NDK.cmake
index e5a7390..e009c10 100644
--- a/Modules/Platform/Android/Determine-Compiler-NDK.cmake
+++ b/Modules/Platform/Android/Determine-Compiler-NDK.cmake
@@ -1,6 +1,31 @@
 # Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
 # file Copyright.txt or https://cmake.org/licensing for details.
 
+# In Android NDK r19 and above there is a single clang toolchain.
+if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
+  if(CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION AND NOT CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION STREQUAL "clang")
+    message(FATAL_ERROR
+      "Android: The CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION value '${CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION}' "
+      "is not supported by this NDK.  It must be 'clang' or not set at all."
+      )
+  endif()
+  message(STATUS "Android: Selected unified Clang toolchain")
+  set(_ANDROID_TOOL_NDK_TOOLCHAIN_VERSION "clang")
+  set(_ANDROID_TOOL_C_COMPILER "${CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED}/bin/clang${_ANDROID_HOST_EXT}")
+  set(_ANDROID_TOOL_C_TOOLCHAIN_MACHINE "${CMAKE_ANDROID_ARCH_TRIPLE}")
+  set(_ANDROID_TOOL_C_TOOLCHAIN_VERSION "")
+  set(_ANDROID_TOOL_C_COMPILER_EXTERNAL_TOOLCHAIN "")
+  set(_ANDROID_TOOL_C_TOOLCHAIN_PREFIX "${CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED}/bin/${CMAKE_ANDROID_ARCH_TRIPLE}-")
+  set(_ANDROID_TOOL_C_TOOLCHAIN_SUFFIX "${_ANDROID_HOST_EXT}")
+  set(_ANDROID_TOOL_CXX_COMPILER "${CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED}/bin/clang++${_ANDROID_HOST_EXT}")
+  set(_ANDROID_TOOL_CXX_TOOLCHAIN_MACHINE "${CMAKE_ANDROID_ARCH_TRIPLE}")
+  set(_ANDROID_TOOL_CXX_TOOLCHAIN_VERSION "")
+  set(_ANDROID_TOOL_CXX_COMPILER_EXTERNAL_TOOLCHAIN "")
+  set(_ANDROID_TOOL_CXX_TOOLCHAIN_PREFIX "${CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED}/bin/${CMAKE_ANDROID_ARCH_TRIPLE}-")
+  set(_ANDROID_TOOL_CXX_TOOLCHAIN_SUFFIX "${_ANDROID_HOST_EXT}")
+  return()
+endif()
+
 # In Android NDK releases there is build system toolchain selection logic in
 # these files:
 #
diff --git a/Modules/Platform/Android/abi-common.cmake b/Modules/Platform/Android/abi-common.cmake
index 6bce3c7..b01ef61 100644
--- a/Modules/Platform/Android/abi-common.cmake
+++ b/Modules/Platform/Android/abi-common.cmake
@@ -3,7 +3,7 @@ string(APPEND _ANDROID_ABI_INIT_CFLAGS
   " -no-canonical-prefixes"
   )
 
-if(CMAKE_ANDROID_NDK AND NOT CMAKE_ANDROID_NDK_DEPRECATED_HEADERS)
+if(CMAKE_ANDROID_NDK AND NOT CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED AND NOT CMAKE_ANDROID_NDK_DEPRECATED_HEADERS)
   string(APPEND _ANDROID_ABI_INIT_CFLAGS " -D__ANDROID_API__=${CMAKE_SYSTEM_VERSION}")
 endif()