[CI] Test C API demo (#6159)

* Fix CMake install config to use dependencies

* [CI] Test C API demo

* Explicitly cast num_feature, to avoid warning in Linux

.github/workflows/main.yml

@@ -35,6 +35,47 @@ jobs:
       run: |
         cd build
         ctest --extra-verbose
+  c-api-demo:
+    name: Test installing XGBoost lib + building the C API demo
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ["ubuntu-latest"]
+        python-version: ["3.8"]
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: 'true'
+    - name: Install system packages
+      run: |
+        sudo apt-get install -y --no-install-recommends ninja-build
+    - uses: conda-incubator/setup-miniconda@v1
+      with:
+        auto-update-conda: true
+        python-version: ${{ matrix.python-version }}
+    - name: Display Conda env
+      shell: bash -l {0}
+      run: |
+        conda info
+        conda list
+    - name: Build and install XGBoost
+      shell: bash -l {0}
+      run: |
+        mkdir build
+        cd build
+        cmake .. -DBUILD_STATIC_LIB=ON -DCMAKE_INSTALL_PREFIX=$CONDA_PREFIX -GNinja
+        ninja -v install
+    - name: Build and run C API demo
+      shell: bash -l {0}
+      run: |
+        cd demo/c-api/
+        mkdir build
+        cd build
+        cmake .. -GNinja -DCMAKE_PREFIX_PATH=$CONDA_PREFIX
+        ninja -v
+        cd ..
+        ./build/api-demo
   test-with-jvm:
     name: Test JVM on OS ${{ matrix.os }}
     runs-on: ${{ matrix.os }}

CMakeLists.txt

@@ -290,7 +290,7 @@ install(DIRECTORY ${xgboost_SOURCE_DIR}/include/xgboost
 #
 # https://github.com/dmlc/xgboost/issues/6085
 if (BUILD_STATIC_LIB)
-  set(INSTALL_TARGETS xgboost runxgboost objxgboost rabit)
+  set(INSTALL_TARGETS xgboost runxgboost objxgboost rabit dmlc)
 else (BUILD_STATIC_LIB)
   set(INSTALL_TARGETS xgboost runxgboost)
 endif (BUILD_STATIC_LIB)

cmake/xgboost-config.cmake.in

@@ -1,5 +1,24 @@
 @PACKAGE_INIT@
 
+include(CMakeFindDependencyMacro)
+
+set(USE_OPENMP @USE_OPENMP@)
+set(USE_CUDA @USE_CUDA@)
+set(USE_NCCL @USE_NCCL@)
+
+find_dependency(Threads)
+if(USE_OPENMP)
+  find_dependency(OpenMP)
+endif()
+if(USE_CUDA)
+  find_dependency(CUDA)
+endif()
+if(USE_NCCL)
+  find_dependency(Nccl)
+endif()
+
 if(NOT TARGET xgboost::xgboost)
   include(${CMAKE_CURRENT_LIST_DIR}/XGBoostTargets.cmake)
 endif()
+
+message(STATUS "Found XGBoost (found version \"${xgboost_VERSION}\")")

demo/c-api/CMakeLists.txt

@@ -1,4 +1,5 @@
-cmake_minimum_required(VERSION 3.12)
+cmake_minimum_required(VERSION 3.13)
+project(api-demo LANGUAGES C CXX VERSION 0.0.1)
 find_package(xgboost REQUIRED)
 add_executable(api-demo c-api-demo.c)
-target_link_libraries(api-demo xgboost::xgboost)
+target_link_libraries(api-demo PRIVATE xgboost::xgboost)

demo/c-api/c-api-demo.c

@@ -62,7 +62,7 @@ int main(int argc, char** argv) {
 
   bst_ulong num_feature = 0;
   safe_xgboost(XGBoosterGetNumFeature(booster, &num_feature));
-  printf("num_feature: %llu\n", num_feature);
+  printf("num_feature: %lu\n", (unsigned long)(num_feature));
 
   // predict
   bst_ulong out_len = 0;