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

Help/manual/cmake-toolchains.7.rst

@@ -399,8 +399,10 @@ Configure use of an Android NDK with the following variables:
   be false unless using a NDK that does not provide unified headers.
 
 :variable:`CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION`
-  Set to the version of the NDK toolchain to be selected as the compiler.
-  If not specified, the default will be the latest available GCC toolchain.
+  On NDK r19 or above, this variable must be unset or set to ``clang``.
+  On NDK r18 or below, set this to the version of the NDK toolchain to
+  be selected as the compiler.  If not specified, the default will be
+  the latest available GCC toolchain.
 
 :variable:`CMAKE_ANDROID_STL_TYPE`
   Set to specify which C++ standard library to use.  If not specified,

Help/variable/CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION.rst

@@ -3,7 +3,11 @@ CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION
 
 When :ref:`Cross Compiling for Android with the NDK`, this variable
 may be set to specify the version of the toolchain to be used
-as the compiler.  The variable must be set to one of these forms:
+as the compiler.
+
+On NDK r19 or above, this variable must be unset or set to ``clang``.
+
+On NDK r18 or below, this variable must be set to one of these forms:
 
 * ``<major>.<minor>``: GCC of specified version
 * ``clang<major>.<minor>``: Clang of specified version

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()

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()

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()
 

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}")

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:
 #

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()
 

Tests/RunCMake/Android/ndk-arm64-v8a-stdout.txt

@@ -1,2 +1,2 @@
 -- Android: Targeting API '[0-9]+' with architecture 'arm64', ABI 'arm64-v8a', and processor 'aarch64'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')

Tests/RunCMake/Android/ndk-armeabi-arm-stdout.txt

@@ -1,3 +1,3 @@
 -- Android: Targeting API '[0-9]+' with architecture 'arm', ABI 'armeabi', and processor 'armv5te'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')
 .*-- CMAKE_ANDROID_ARM_MODE=1

Tests/RunCMake/Android/ndk-armeabi-v7a-neon-stdout.txt

@@ -1,3 +1,3 @@
 -- Android: Targeting API '[0-9]+' with architecture 'arm', ABI 'armeabi-v7a', and processor 'armv7-a'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')
 .*-- CMAKE_ANDROID_ARM_NEON=1

Tests/RunCMake/Android/ndk-armeabi-v7a-stdout.txt

@@ -1,3 +1,3 @@
 -- Android: Targeting API '[0-9]+' with architecture 'arm', ABI 'armeabi-v7a', and processor 'armv7-a'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')
 .*-- CMAKE_ANDROID_ARM_NEON=0

Tests/RunCMake/Android/ndk-badver-stderr.txt

@@ -1,11 +1,12 @@
 ^CMake Error at .*/Modules/Platform/Android/Determine-Compiler-NDK.cmake:[0-9]+ \(message\):
-  Android: The CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION value 'badver' is not one
+  Android: The CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION value 'badver' is not(
+  supported by this NDK.  It must be 'clang' or not set at all\.| one
   of the allowed forms:
 
     <major>.<minor>       = GCC of specified version
     clang<major>.<minor>  = Clang of specified version
     clang                 = Clang of most recent available version
-
+)
 Call Stack \(most recent call first\):
 .*
   ndk-badver.cmake:1 \(enable_language\)

Tests/RunCMake/Android/ndk-badvernum-stderr.txt

@@ -1,4 +1,6 @@
-^CMake Error at .*/Modules/Platform/Android/Determine-Compiler-NDK.cmake:[0-9]+ \(message\):
+^CMake Error at .*/Modules/Platform/Android/Determine-Compiler-NDK.cmake:[0-9]+ \(message\):(
+  Android: The CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION value '1.0' is not
+  supported by this NDK.  It must be 'clang' or not set at all.|
   Android: No toolchain for ABI 'armeabi(-v7a)?' found in the NDK:
 
     .*
@@ -6,7 +8,7 @@
   of the version specified by CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION:
 
     1\.0
-
+)
 Call Stack \(most recent call first\):
 .*
   ndk-badvernum.cmake:1 \(enable_language\)

Tests/RunCMake/Android/ndk-mips-stdout.txt

@@ -1,2 +1,2 @@
 -- Android: Targeting API '[0-9]+' with architecture 'mips', ABI 'mips', and processor 'mips'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')

Tests/RunCMake/Android/ndk-mips64-stdout.txt

@@ -1,2 +1,2 @@
 -- Android: Targeting API '[0-9]+' with architecture 'mips64', ABI 'mips64', and processor 'mips64'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')

Tests/RunCMake/Android/ndk-x86-stdout.txt

@@ -1,2 +1,2 @@
 -- Android: Targeting API '[0-9]+' with architecture 'x86', ABI 'x86', and processor 'i686'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')

Tests/RunCMake/Android/ndk-x86_64-stdout.txt

@@ -1,2 +1,2 @@
 -- Android: Targeting API '[0-9]+' with architecture 'x86_64', ABI 'x86_64', and processor 'x86_64'
--- Android: Selected (Clang toolchain '[^']+' with )?GCC toolchain '[^']+'
+-- Android: Selected (unified Clang toolchain|(Clang toolchain '[^']+' with )?GCC toolchain '[^']+')