[opencv4:android] build failure (folder /include is empty or not present)

[pthom]

When building opencv4 for android, the compilation and "cmake install" steps succeed.
However, after this, vcpkg will complain that "The folder /include is empty or not present".

This seems to be due to the fact that opencv emits a non standard include folder hierarchy: see below.

Host Environment

• Host OS: Linux, ubuntu 18.04
• Target OS: Android armeabi-v7a
• Compiler: android-ndk / May 2020

To Reproduce

1. Cherry-pick a PR that fixes an issue for protobuf under android: [protobuf] Correct protobuf under android (Fix issue #8218) #11228

(I submitted this PR a few minutes ago)

2. Use this triplet file:

triplets/android-armeabi-v7a.cmake

set(VCPKG_TARGET_ARCHITECTURE arm)
set(VCPKG_CRT_LINKAGE static)
set(VCPKG_LIBRARY_LINKAGE dynamic)
set(VCPKG_CMAKE_SYSTEM_NAME Android)

set(ANDROID_NDK_HOME $ENV{ANDROID_NDK_HOME})
if ("${ANDROID_NDK_HOME}" MATCHES "^$")
  message(FATAL_ERROR 
    "Please set an env variable ANDROID_NDK_HOME pointing to your ndk-bundle folder. 
    For example: export ANDROID_NDK_HOME=/home/your-account/Android/Sdk/ndk-bundle")
endif()
set(VCPKG_CHAINLOAD_TOOLCHAIN_FILE ${ANDROID_NDK_HOME}/build/cmake/android.toolchain.cmake)

set(ANDROID_ABI armeabi-v7a)
# ANDROID_ABI can be : "armeabi-v7a" , "armeabi-v7a with NEON", "arm64-v8a", "x86" or "x86_64"

3. Download and install the android ndk-bundle

4. Set an env var to the ndk-bundle folder

export ANDROID_NDK_HOME=/home/your-account/Android/Sdk/ndk-bundle

5. Build the opencv4 package

./vcpkg install "opencv4[core]:android-armeabi-v7a"

Failure logs

-- Installing: .../vcpkg/packages/opencv4_android-armeabi-v7a/share/opencv4/copyright
-- Performing post-build validation
The folder /include is empty or not present. This indicates the library was not correctly installed.
The following files are placed in
.../vcpkg/packages/opencv4_android-armeabi-v7a:

    .../vcpkg/packages/opencv4_android-armeabi-v7a/README.android

Files cannot be present in those directories.

The following files are placed in
.../vcpkg/packages/opencv4_android-armeabi-v7a/debug:

    .../vcpkg/packages/opencv4_android-armeabi-v7a/debug/README.android

Files cannot be present in those directories.

Found 3 error(s). Please correct the portfile:
    ../vcpkg/ports/opencv4/portfile.cmake
-- Performing post-build validation done
Error: Building package opencv4:android-armeabi-v7a failed with: POST_BUILD_CHECKS_FAILED

-Cut and past the appropriate build messages from the console output.
-Please attach any additional failure logs mentioned in the console output.

Additional context

Please note that this issue can only be reproduced after applying a patch on protobuf package for android

[pthom]

I have a possible patch, like this:

diff --git a/ports/opencv4/portfile.cmake b/ports/opencv4/portfile.cmake
index 95c4c53dc..e918daa09 100644
--- a/ports/opencv4/portfile.cmake
+++ b/ports/opencv4/portfile.cmake
@@ -389,4 +389,11 @@ file(REMOVE ${CURRENT_PACKAGES_DIR}/debug/setup_vars_opencv4.cmd)
 file(REMOVE ${CURRENT_PACKAGES_DIR}/LICENSE)
 file(REMOVE ${CURRENT_PACKAGES_DIR}/debug/LICENSE)
 
+if(${VCPKG_CMAKE_SYSTEM_NAME} STREQUAL "Android")
+  file(RENAME ${CURRENT_PACKAGES_DIR}/sdk/native/jni/include ${CURRENT_PACKAGES_DIR}/include)
+  file(REMOVE_RECURSE ${CURRENT_PACKAGES_DIR}/sdk)
+  file(REMOVE_RECURSE ${CURRENT_PACKAGES_DIR}/README.android)
+  file(REMOVE_RECURSE ${CURRENT_PACKAGES_DIR}/debug/README.android)
+endif()
+
 file(INSTALL ${SOURCE_PATH}/LICENSE DESTINATION ${CURRENT_PACKAGES_DIR}/share/${PORT} RENAME copyright)

But I do not know if it makes sense: all it does is reorganize the package folder content after opencv installation. vcpkg seems to be happy after this and the installation succeeds.

Does my patch make sense ?

---

Remark: with my patch, there is a naming issue (which might be unrelated): the advice given by vcpkg for use in cmake list reads:

    find_package(abi-armeabi-v7a CONFIG REQUIRED)

instead of

    find_package(opencv4 CONFIG REQUIRED)

./vcpkg install "opencv4[core]:android-armeabi-v7a"
Computing installation plan...
The following packages will be built and installed:
    opencv4[core]:android-armeabi-v7a
Starting package 1/1: opencv4:android-armeabi-v7a
Building package opencv4[core]:android-armeabi-v7a...
-- Using cached /home/pascal/dvp/vcpkg/downloads/opencv-opencv-4.1.1.tar.gz
-- Using source at /home/pascal/dvp/vcpkg/buildtrees/opencv4/src/4.1.1-fb9e10326a
-- Configuring android-armeabi-v7a-dbg
-- Configuring android-armeabi-v7a-rel
-- Building android-armeabi-v7a-dbg
-- Building android-armeabi-v7a-rel
-- Installing: /home/pascal/dvp/vcpkg/packages/opencv4_android-armeabi-v7a/share/opencv4/copyright
-- Performing post-build validation
-- Performing post-build validation done
Building package opencv4[core]:android-armeabi-v7a... done
Installing package opencv4[core]:android-armeabi-v7a...
Installing package opencv4[core]:android-armeabi-v7a... done
Elapsed time for package opencv4:android-armeabi-v7a: 17.27 s

Total elapsed time: 17.27 s

The package opencv4:android-armeabi-v7a provides CMake targets:

    find_package(abi-armeabi-v7a CONFIG REQUIRED)
    # Note: 9 target(s) were omitted.
    target_link_libraries(main PRIVATE opencv_ml opencv_core opencv_flann opencv_photo)

[pthom]

I'm closing this issue, since there is an ongoing port of opencv4.3 in which I explained some possible adaptations here: #11130 (comment)