Android: Add support for unified headers

The unified headers are preferred as of NDK r15, so use them by default
if available and provide an option to use the deprecated headers.

Inspired-by: Florent Castelli <florent.castelli@gmail.com>
Fixes: #16584

8 files changed, 72 insertions, 16 deletions

diff --git a/Help/manual/cmake-toolchains.7.rst b/Help/manual/cmake-toolchains.7.rst
index 64abe9a..8554e87 100644
--- a/Help/manual/cmake-toolchains.7.rst
+++ b/Help/manual/cmake-toolchains.7.rst
@@ -385,6 +385,11 @@ Configure use of an Android NDK with the following variables:
   If not specified, a default for this variable will be chosen
   as specified :ref:`above <Cross Compiling for Android>`.
 
+:variable:`CMAKE_ANDROID_NDK_DEPRECATED_HEADERS`
+  Set to a true value to use the deprecated per-api-level headers
+  instead of the unified headers.  If not specified, the default will
+  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.
diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index 6ee4257..1a2726d 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -255,6 +255,7 @@ Variables that Control the Build
    /variable/CMAKE_ANDROID_NATIVE_LIB_DEPENDENCIES
    /variable/CMAKE_ANDROID_NATIVE_LIB_DIRECTORIES
    /variable/CMAKE_ANDROID_NDK
+   /variable/CMAKE_ANDROID_NDK_DEPRECATED_HEADERS
    /variable/CMAKE_ANDROID_NDK_TOOLCHAIN_HOST_TAG
    /variable/CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION
    /variable/CMAKE_ANDROID_PROCESS_MAX
diff --git a/Help/release/3.9.rst b/Help/release/3.9.rst
index 65bcd2e..333ba9e 100644
--- a/Help/release/3.9.rst
+++ b/Help/release/3.9.rst
@@ -62,6 +62,11 @@ Commands
 Variables
 ---------
 
+* A :variable:`CMAKE_ANDROID_NDK_DEPRECATED_HEADERS` variable was added
+  for use when :ref:`Cross Compiling for Android with the NDK` to request
+  use of the deprecated headers even when unified headers are available.
+  The default is now to use unified headers if available.
+
 * A :variable:`CMAKE_AUTOMOC_DEPEND_FILTERS` variable was introduced to
   allow :variable:`CMAKE_AUTOMOC` to extract additional dependency file names
   for ``moc`` from the contents of source files.
diff --git a/Help/variable/CMAKE_ANDROID_NDK_DEPRECATED_HEADERS.rst b/Help/variable/CMAKE_ANDROID_NDK_DEPRECATED_HEADERS.rst
new file mode 100644
index 0000000..8ea1257
--- /dev/null
+++ b/Help/variable/CMAKE_ANDROID_NDK_DEPRECATED_HEADERS.rst
@@ -0,0 +1,9 @@
+CMAKE_ANDROID_NDK_DEPRECATED_HEADERS
+------------------------------------
+
+When :ref:`Cross Compiling for Android with the NDK`, this variable
+may be set to specify whether to use the deprecated per-api-level
+headers instead of the unified headers.
+
+If not specified, the default will be *false* if using a NDK version
+that provides the unified headers and *true* otherwise.
diff --git a/Modules/Platform/Android-Common.cmake b/Modules/Platform/Android-Common.cmake
index 78938dc..ac72676 100644
--- a/Modules/Platform/Android-Common.cmake
+++ b/Modules/Platform/Android-Common.cmake
@@ -161,6 +161,9 @@ macro(__android_compiler_common lang)
   # tied to a specific API version.
   if(CMAKE_ANDROID_NDK)
     list(APPEND CMAKE_${lang}_STANDARD_INCLUDE_DIRECTORIES "${CMAKE_SYSROOT}/usr/include")
+    if(NOT CMAKE_ANDROID_NDK_DEPRECATED_HEADERS)
+      list(APPEND CMAKE_${lang}_STANDARD_INCLUDE_DIRECTORIES "${CMAKE_SYSROOT}/usr/include/${CMAKE_ANDROID_ARCH_HEADER_TRIPLE}")
+    endif()
     list(REMOVE_ITEM CMAKE_${lang}_IMPLICIT_INCLUDE_DIRECTORIES "/usr/include")
   endif()
 endmacro()
diff --git a/Modules/Platform/Android-Determine.cmake b/Modules/Platform/Android-Determine.cmake
index 076be85..add1dc1 100644
--- a/Modules/Platform/Android-Determine.cmake
+++ b/Modules/Platform/Android-Determine.cmake
@@ -197,22 +197,30 @@ endif()
 
 # https://developer.android.com/ndk/guides/abis.html
 
-set(_ANDROID_ABI_arm64-v8a_PROC   "aarch64")
-set(_ANDROID_ABI_arm64-v8a_ARCH   "arm64")
-set(_ANDROID_ABI_armeabi-v7a_PROC "armv7-a")
-set(_ANDROID_ABI_armeabi-v7a_ARCH "arm")
-set(_ANDROID_ABI_armeabi-v6_PROC  "armv6")
-set(_ANDROID_ABI_armeabi-v6_ARCH  "arm")
-set(_ANDROID_ABI_armeabi_PROC     "armv5te")
-set(_ANDROID_ABI_armeabi_ARCH     "arm")
-set(_ANDROID_ABI_mips_PROC        "mips")
-set(_ANDROID_ABI_mips_ARCH        "mips")
-set(_ANDROID_ABI_mips64_PROC      "mips64")
-set(_ANDROID_ABI_mips64_ARCH      "mips64")
-set(_ANDROID_ABI_x86_PROC         "i686")
-set(_ANDROID_ABI_x86_ARCH         "x86")
-set(_ANDROID_ABI_x86_64_PROC      "x86_64")
-set(_ANDROID_ABI_x86_64_ARCH      "x86_64")
+set(_ANDROID_ABI_arm64-v8a_PROC     "aarch64")
+set(_ANDROID_ABI_arm64-v8a_ARCH     "arm64")
+set(_ANDROID_ABI_arm64-v8a_HEADER   "aarch64-linux-android")
+set(_ANDROID_ABI_armeabi-v7a_PROC   "armv7-a")
+set(_ANDROID_ABI_armeabi-v7a_ARCH   "arm")
+set(_ANDROID_ABI_armeabi-v7a_HEADER "arm-linux-androideabi")
+set(_ANDROID_ABI_armeabi-v6_PROC    "armv6")
+set(_ANDROID_ABI_armeabi-v6_ARCH    "arm")
+set(_ANDROID_ABI_armeabi-v6_HEADER  "arm-linux-androideabi")
+set(_ANDROID_ABI_armeabi_PROC       "armv5te")
+set(_ANDROID_ABI_armeabi_ARCH       "arm")
+set(_ANDROID_ABI_armeabi_HEADER     "arm-linux-androideabi")
+set(_ANDROID_ABI_mips_PROC          "mips")
+set(_ANDROID_ABI_mips_ARCH          "mips")
+set(_ANDROID_ABI_mips_HEADER        "mipsel-linux-android")
+set(_ANDROID_ABI_mips64_PROC        "mips64")
+set(_ANDROID_ABI_mips64_ARCH        "mips64")
+set(_ANDROID_ABI_mips64_HEADER      "mips64el-linux-android")
+set(_ANDROID_ABI_x86_PROC           "i686")
+set(_ANDROID_ABI_x86_ARCH           "x86")
+set(_ANDROID_ABI_x86_HEADER         "i686-linux-android")
+set(_ANDROID_ABI_x86_64_PROC        "x86_64")
+set(_ANDROID_ABI_x86_64_ARCH        "x86_64")
+set(_ANDROID_ABI_x86_64_HEADER      "x86_64-linux-android")
 
 set(_ANDROID_PROC_aarch64_ARCH_ABI "arm64-v8a")
 set(_ANDROID_PROC_armv7-a_ARCH_ABI "armeabi-v7a")
@@ -264,6 +272,7 @@ if(_ANDROID_SYSROOT_ARCH AND NOT "x${_ANDROID_SYSROOT_ARCH}" STREQUAL "x${CMAKE_
     "does not match architecture '${CMAKE_ANDROID_ARCH}' for the ABI '${CMAKE_ANDROID_ARCH_ABI}'."
     )
 endif()
+set(CMAKE_ANDROID_ARCH_HEADER_TRIPLE "${_ANDROID_ABI_${CMAKE_ANDROID_ARCH_ABI}_HEADER}")
 
 # Select a processor.
 if(NOT CMAKE_SYSTEM_PROCESSOR)
@@ -275,6 +284,16 @@ if(NOT _ANDROID_ABI_${CMAKE_ANDROID_ARCH_ABI}_PROC STREQUAL CMAKE_SYSTEM_PROCESS
   message(FATAL_ERROR "Android: The specified CMAKE_ANDROID_ARCH_ABI='${CMAKE_ANDROID_ARCH_ABI}' and CMAKE_SYSTEM_PROCESSOR='${CMAKE_SYSTEM_PROCESSOR}' is not a valid combination.")
 endif()
 
+if(CMAKE_ANDROID_NDK AND NOT DEFINED CMAKE_ANDROID_NDK_DEPRECATED_HEADERS)
+  if(IS_DIRECTORY "${CMAKE_ANDROID_NDK}/sysroot/usr/include/${CMAKE_ANDROID_ARCH_HEADER_TRIPLE}")
+    # Unified headers exist so we use them by default.
+    set(CMAKE_ANDROID_NDK_DEPRECATED_HEADERS 0)
+  else()
+    # Unified headers do not exist so use the deprecated headers.
+    set(CMAKE_ANDROID_NDK_DEPRECATED_HEADERS 1)
+  endif()
+endif()
+
 # Save the Android-specific information in CMakeSystem.cmake.
 set(CMAKE_SYSTEM_CUSTOM_CODE "
 set(CMAKE_ANDROID_NDK \"${CMAKE_ANDROID_NDK}\")
@@ -283,6 +302,13 @@ set(CMAKE_ANDROID_ARCH \"${CMAKE_ANDROID_ARCH}\")
 set(CMAKE_ANDROID_ARCH_ABI \"${CMAKE_ANDROID_ARCH_ABI}\")
 ")
 
+if(CMAKE_ANDROID_NDK)
+  string(APPEND CMAKE_SYSTEM_CUSTOM_CODE
+    "set(CMAKE_ANDROID_ARCH_HEADER_TRIPLE \"${CMAKE_ANDROID_ARCH_HEADER_TRIPLE}\")\n"
+    "set(CMAKE_ANDROID_NDK_DEPRECATED_HEADERS \"${CMAKE_ANDROID_NDK_DEPRECATED_HEADERS}\")\n"
+    )
+endif()
+
 # Select an ARM variant.
 if(CMAKE_ANDROID_ARCH_ABI MATCHES "^armeabi")
   if(CMAKE_ANDROID_ARM_MODE)
diff --git a/Modules/Platform/Android-Initialize.cmake b/Modules/Platform/Android-Initialize.cmake
index a327223..a434f90 100644
--- a/Modules/Platform/Android-Initialize.cmake
+++ b/Modules/Platform/Android-Initialize.cmake
@@ -20,6 +20,9 @@ endif()
 if(NOT CMAKE_SYSROOT)
   if(CMAKE_ANDROID_NDK)
     set(CMAKE_SYSROOT "${CMAKE_ANDROID_NDK}/platforms/android-${CMAKE_SYSTEM_VERSION}/arch-${CMAKE_ANDROID_ARCH}")
+    if(NOT CMAKE_ANDROID_NDK_DEPRECATED_HEADERS)
+      set(CMAKE_SYSROOT_COMPILE "${CMAKE_ANDROID_NDK}/sysroot")
+    endif()
   elseif(CMAKE_ANDROID_STANDALONE_TOOLCHAIN)
     set(CMAKE_SYSROOT "${CMAKE_ANDROID_STANDALONE_TOOLCHAIN}/sysroot")
   endif()
diff --git a/Modules/Platform/Android/abi-common.cmake b/Modules/Platform/Android/abi-common.cmake
index 3b0eb01..10fb897 100644
--- a/Modules/Platform/Android/abi-common.cmake
+++ b/Modules/Platform/Android/abi-common.cmake
@@ -3,6 +3,10 @@ string(APPEND _ANDROID_ABI_INIT_CFLAGS
   " -no-canonical-prefixes"
   )
 
+if(CMAKE_ANDROID_NDK AND NOT CMAKE_ANDROID_NDK_DEPRECATED_HEADERS)
+  string(APPEND _ANDROID_ABI_INIT_CFLAGS " -D__ANDROID_API__=${CMAKE_SYSTEM_VERSION}")
+endif()
+
 if(NOT DEFINED CMAKE_POSITION_INDEPENDENT_CODE
     AND NOT CMAKE_SYSTEM_VERSION VERSION_LESS 16)
   set(CMAKE_POSITION_INDEPENDENT_CODE ON)