cmake: make the ExternalProject test work

By micromanaging the project dependency and its inclusion into the test
project. It feels like an awkward construct, but perhaps better than
nothing.

It's also fragile because it's a static build with no assistance from
the external project (curl in this case). Mitigated in test by disabling
all dependencies and some features.

Since there is no special core cmake logic to be tested here, in CI
the test is tested really. To keep CI jobs at minimum, only add 3 of
them, taking 42s in total. (All 6 would take 270s.)

Follow-up to e2a23d5d0d #17203

Closes #18208

.github/workflows/distcheck.yml

@@ -301,6 +301,9 @@ jobs:
         with:
           persist-credentials: false
 
+      - name: 'via ExternalProject'
+        if: ${{ !contains(matrix.image, 'linux') }}
+        run: ./tests/cmake/test.sh ExternalProject ${TESTOPTS}
       - name: 'via FetchContent'
         run: ./tests/cmake/test.sh FetchContent ${TESTOPTS} -DCURL_USE_OPENSSL=ON
       - name: 'via add_subdirectory'
@@ -308,6 +311,20 @@ jobs:
       - name: 'via find_package'
         run: ./tests/cmake/test.sh find_package ${TESTOPTS} -DCURL_USE_OPENSSL=ON
 
+      - name: 'via ExternalProject (old cmake)'
+        if: ${{ contains(matrix.image, 'linux') }}
+        run: |
+          export TEST_CMAKE_CONSUMER; TEST_CMAKE_CONSUMER="$(cat ~/old-cmake-path.txt)"
+          if [[ "${MATRIX_IMAGE}" = *'macos'* ]]; then
+            export CFLAGS='-arch arm64'
+            export TEST_CMAKE_FLAGS='-DCURL_USE_LIBPSL=OFF'  # auto-detection does not work with old-cmake
+          fi
+          if [[ "${MATRIX_IMAGE}" = *'windows'* ]]; then
+            export TEST_CMAKE_GENERATOR='MSYS Makefiles'
+            export TEST_CMAKE_FLAGS='-DCMAKE_C_COMPILER=x86_64-w64-mingw32-gcc -DOPENSSL_ROOT_DIR=C:/msys64/mingw64'
+          fi
+          ./tests/cmake/test.sh ExternalProject ${TESTOPTS}
+
       - name: 'via add_subdirectory OpenSSL (old cmake)'
         run: |
           export TEST_CMAKE_CONSUMER; TEST_CMAKE_CONSUMER="$(cat ~/old-cmake-path.txt)"

tests/cmake/CMakeLists.txt

@@ -31,20 +31,7 @@ option(TEST_INTEGRATION_MODE "Integration mode" "find_package")
 
 message(STATUS "TEST_INTEGRATION_MODE: ${TEST_INTEGRATION_MODE}")
 
-if(TEST_INTEGRATION_MODE STREQUAL "FetchContent" AND CMAKE_VERSION VERSION_LESS 3.14)
-  message(FATAL_ERROR "This test requires CMake 3.14 or upper")
-endif()
-
-if(TEST_INTEGRATION_MODE STREQUAL "ExternalProject")  # Broken
-  include(ExternalProject)
-  ExternalProject_Add(libssh2
-    URL "${FROM_ARCHIVE}" URL_HASH "SHA256=${FROM_HASH}"
-    INSTALL_COMMAND ""
-    DOWNLOAD_EXTRACT_TIMESTAMP ON)
-endif()
-
-if(TEST_INTEGRATION_MODE STREQUAL "find_package" OR
-   TEST_INTEGRATION_MODE STREQUAL "ExternalProject")
+if(TEST_INTEGRATION_MODE STREQUAL "find_package")
   find_package(CURL REQUIRED CONFIG)
   find_package(CURL REQUIRED CONFIG)  # Double-inclusion test
   foreach(_result_var IN ITEMS
@@ -75,6 +62,9 @@ elseif(TEST_INTEGRATION_MODE STREQUAL "add_subdirectory")
   set(BUILD_STATIC_LIBS ON CACHE BOOL "")
   add_subdirectory(curl)
 elseif(TEST_INTEGRATION_MODE STREQUAL "FetchContent")
+  if(CMAKE_VERSION VERSION_LESS 3.14)
+    message(FATAL_ERROR "This test requires CMake 3.14 or upper")
+  endif()
   include(FetchContent)
   option(FROM_GIT_REPO "Git URL" "https://github.com/curl/curl.git")
   option(FROM_GIT_TAG "Git tag" "master")
@@ -85,17 +75,48 @@ elseif(TEST_INTEGRATION_MODE STREQUAL "FetchContent")
   set(BUILD_SHARED_LIBS ON CACHE BOOL "")
   set(BUILD_STATIC_LIBS ON CACHE BOOL "")
   FetchContent_MakeAvailable(curl)  # Requires CMake 3.14
+elseif(TEST_INTEGRATION_MODE STREQUAL "ExternalProject")
+  include(ExternalProject)
+  set(_curl_install_dir "${CMAKE_BINARY_DIR}/curl-external-install")
+  set(_curl_libcurl_static_lib "${_curl_install_dir}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}curl${CMAKE_STATIC_LIBRARY_SUFFIX}")
+  string(REPLACE " " ";" CURL_TEST_OPTS "${CURL_TEST_OPTS}")
+  if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.24)
+    set(_download_extract_timestamp "DOWNLOAD_EXTRACT_TIMESTAMP" "ON")
+  endif()
+  ExternalProject_Add(curl-external
+    URL "${FROM_ARCHIVE}" URL_HASH "SHA256=${FROM_HASH}"
+    ${_download_extract_timestamp}
+    PREFIX "${CMAKE_BINARY_DIR}/curl-external"
+    CMAKE_ARGS "-DCMAKE_INSTALL_PREFIX=${_curl_install_dir}" -DBUILD_SHARED_LIBS=OFF -DCURL_USE_LIBPSL=OFF -DCURL_USE_PKGCONFIG=OFF
+      -DCURL_ENABLE_SSL=OFF -DCURL_ENABLE_SSL=OFF -DCURL_DISABLE_LDAP=ON -DCURL_USE_LIBSSH2=OFF -DUSE_NGHTTP2=OFF
+      -DCURL_BROTLI=OFF -DCURL_ZLIB=OFF -DCURL_ZSTD=OFF -DUSE_LIBIDN2=OFF -DENABLE_IPV6=OFF
+      ${CURL_TEST_OPTS}
+    BUILD_BYPRODUCTS "${_curl_libcurl_static_lib}")
+
+  add_executable(test-consumer-static-fetch "test.c")
+  add_dependencies(test-consumer-static-fetch curl-external)
+  if(WIN32)
+    target_compile_definitions(test-consumer-static-fetch PRIVATE "CURL_STATICLIB")
+    list(APPEND _curl_libcurl_static_lib "ws2_32" "bcrypt")
+  endif()
+  target_include_directories(test-consumer-static-fetch PRIVATE "${_curl_install_dir}/include")
+  target_link_libraries(test-consumer-static-fetch PRIVATE "${_curl_libcurl_static_lib}")
 endif()
 
-add_executable(test-consumer-static-ns "test.c")
-target_link_libraries(test-consumer-static-ns PRIVATE "CURL::libcurl_static")
+if(TEST_INTEGRATION_MODE STREQUAL "find_package" OR
+   TEST_INTEGRATION_MODE STREQUAL "add_subdirectory" OR
+   TEST_INTEGRATION_MODE STREQUAL "FetchContent")
 
-add_executable(test-consumer-shared-ns "test.c")
-target_link_libraries(test-consumer-shared-ns PRIVATE "CURL::libcurl_shared")
+  add_executable(test-consumer-static-ns "test.c")
+  target_link_libraries(test-consumer-static-ns PRIVATE "CURL::libcurl_static")
 
-# Alias for either shared or static library
-add_executable(test-consumer-selected-ns "test.c")
-target_link_libraries(test-consumer-selected-ns PRIVATE "CURL::libcurl")
+  add_executable(test-consumer-shared-ns "test.c")
+  target_link_libraries(test-consumer-shared-ns PRIVATE "CURL::libcurl_shared")
+
+  # Alias for either shared or static library
+  add_executable(test-consumer-selected-ns "test.c")
+  target_link_libraries(test-consumer-selected-ns PRIVATE "CURL::libcurl")
+endif()
 
 if(TEST_INTEGRATION_MODE STREQUAL "add_subdirectory" OR
    TEST_INTEGRATION_MODE STREQUAL "FetchContent")

tests/cmake/test.sh

@@ -41,20 +41,20 @@ runresults() {
   set -x
 }
 
-if [ "${mode}" = 'ExternalProject' ]; then  # Broken
+if [ "${mode}" = 'all' ] || [ "${mode}" = 'ExternalProject' ]; then
   (cd "${src}"; git archive --format=tar HEAD) | gzip > source.tar.gz
   src="${PWD}/source.tar.gz"
   sha="$(openssl dgst -sha256 "${src}" | grep -a -i -o -E '[0-9a-f]{64}$')"
   bldc='bld-externalproject'
   rm -rf "${bldc}"
   if [ -n "${cmake_consumer_modern:-}" ]; then  # 3.15+
-    "${cmake_consumer}" -B "${bldc}" -G "${gen}" ${cmake_opts} -DCMAKE_UNITY_BUILD=ON ${TEST_CMAKE_FLAGS:-} "$@" \
+    "${cmake_consumer}" -B "${bldc}" -G "${gen}" ${TEST_CMAKE_FLAGS:-} -DCURL_TEST_OPTS="${cmake_opts} -DCMAKE_UNITY_BUILD=ON $*" \
       -DTEST_INTEGRATION_MODE=ExternalProject \
       -DFROM_ARCHIVE="${src}" -DFROM_HASH="${sha}"
     "${cmake_consumer}" --build "${bldc}" --verbose
   else
     mkdir "${bldc}"; cd "${bldc}"
-    "${cmake_consumer}" .. -G "${gen}" ${cmake_opts} ${TEST_CMAKE_FLAGS:-} "$@" \
+    "${cmake_consumer}" .. -G "${gen}" ${TEST_CMAKE_FLAGS:-} -DCURL_TEST_OPTS="${cmake_opts} $*" \
       -DTEST_INTEGRATION_MODE=ExternalProject \
       -DFROM_ARCHIVE="${src}" -DFROM_HASH="${sha}"
     VERBOSE=1 "${cmake_consumer}" --build .