ExternalProject: Enable Make Job Server with Explicit Build Command

Introduces `BUILD_JOB_SERVER_AWARE` option to `ExternalProject_Add` and
`JOB_SERVER_AWARE` to `ExternalProject_Add_Step`. When using an explicit
`BUILD_COMMAND` or `COMMAND`, the generated commands won't use `$(MAKE)`
thus failing to connect to the outer make's job server. These new
options enable explicit job server integration.

Co-authored-by: Brad King <brad.king@kitware.com>

Fixes: #16273

6 files changed, 71 insertions, 1 deletions

diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 8562e2b..a4f6141 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -851,7 +851,7 @@ endif()
 if(CMake_TEST_RunCMake_ExternalProject_DOWNLOAD_SERVER_TIMEOUT)
   list(APPEND ExternalProject_ARGS -DDOWNLOAD_SERVER_TIMEOUT=${CMake_TEST_RunCMake_ExternalProject_DOWNLOAD_SERVER_TIMEOUT})
 endif()
-add_RunCMake_test(ExternalProject)
+add_RunCMake_test(ExternalProject -DDETECT_JOBSERVER=$<TARGET_FILE:detect_jobserver>)
 add_RunCMake_test(FetchContent)
 add_RunCMake_test(FetchContent_find_package)
 set(CTestCommandLine_ARGS -DPython_EXECUTABLE=${Python_EXECUTABLE})
diff --git a/Tests/RunCMake/ExternalProject/DetectJobServer.cmake b/Tests/RunCMake/ExternalProject/DetectJobServer.cmake
new file mode 100644
index 0000000..c6e1412
--- /dev/null
+++ b/Tests/RunCMake/ExternalProject/DetectJobServer.cmake
@@ -0,0 +1,16 @@
+include(ExternalProject)
+ExternalProject_Add(Foo
+  SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/Foo
+  BUILD_COMMAND ${DETECT_JOBSERVER} "ep.txt"
+  BUILD_JOB_SERVER_AWARE 1
+  INSTALL_COMMAND ""
+)
+
+# Add a second step to test JOB_SERVER_AWARE
+ExternalProject_Add_Step(Foo
+  second_step
+  COMMAND ${DETECT_JOBSERVER} "ep_second_step.txt"
+  DEPENDEES build
+  ALWAYS 1
+  JOB_SERVER_AWARE 1
+)
diff --git a/Tests/RunCMake/ExternalProject/Foo/CMakeLists.txt b/Tests/RunCMake/ExternalProject/Foo/CMakeLists.txt
new file mode 100644
index 0000000..b38b173
--- /dev/null
+++ b/Tests/RunCMake/ExternalProject/Foo/CMakeLists.txt
@@ -0,0 +1,4 @@
+cmake_minimum_required(VERSION 3.27)
+project(Foo NONE)
+
+add_custom_target(drive ALL COMMAND ${CMAKE_COMMAND} -E true)
diff --git a/Tests/RunCMake/ExternalProject/GNUMakeJobServerAware-check.cmake b/Tests/RunCMake/ExternalProject/GNUMakeJobServerAware-check.cmake
new file mode 100644
index 0000000..55a9f0d
--- /dev/null
+++ b/Tests/RunCMake/ExternalProject/GNUMakeJobServerAware-check.cmake
@@ -0,0 +1,16 @@
+set(BUILD_DIR "${RunCMake_BINARY_DIR}/GNUMakeJobServerAware-build")
+
+function(check target regex)
+  file(STRINGS ${BUILD_DIR}/${target} lines
+    REGEX ${regex}
+  )
+
+  list(LENGTH lines len)
+  if(len EQUAL 0)
+    message(FATAL_ERROR "Could not find matching lines '${regex}' in ${BUILD_DIR}/${target}")
+  endif()
+endfunction()
+
+check("/CMakeFiles/Foo.dir/build.make" [[\+cd (/d )?"?.*"? && "?.*"? --build "?.*"?]])
+check("/CMakeFiles/Foo.dir/build.make" [[\+cd (/d )?"?.*"? && "?.*"? -E touch "?.*"?]])
+check("/CMakeFiles/Foo.dir/build.make" [[\+"?.*"? -E true]])
diff --git a/Tests/RunCMake/ExternalProject/GNUMakeJobServerAware.cmake b/Tests/RunCMake/ExternalProject/GNUMakeJobServerAware.cmake
new file mode 100644
index 0000000..3f688ca
--- /dev/null
+++ b/Tests/RunCMake/ExternalProject/GNUMakeJobServerAware.cmake
@@ -0,0 +1,16 @@
+include(ExternalProject)
+ExternalProject_Add(Foo
+  SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/Foo
+  BUILD_COMMAND ${CMAKE_COMMAND} --build <BINARY_DIR>
+  BUILD_JOB_SERVER_AWARE 1
+  INSTALL_COMMAND ""
+)
+
+# Add a second step to test JOB_SERVER_AWARE
+ExternalProject_Add_Step(Foo
+  second_step
+  COMMAND ${CMAKE_COMMAND} -E true
+  DEPENDEES build
+  ALWAYS 1
+  JOB_SERVER_AWARE 1
+)
diff --git a/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake b/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake
index 4afdef8..ffaa46c 100644
--- a/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake
+++ b/Tests/RunCMake/ExternalProject/RunCMakeTest.cmake
@@ -144,6 +144,24 @@ function(__ep_test_with_build_with_server testName)
   run_cmake_command(${testName}-build ${CMAKE_COMMAND} --build .)
 endfunction()
 
+if(RunCMake_GENERATOR MATCHES "(MSYS|MinGW|Unix) Makefiles")
+  __ep_test_with_build(GNUMakeJobServerAware)
+endif()
+
+function(__ep_test_jobserver)
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/DetectJobServer-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+  run_cmake_with_options(DetectJobServer -DDETECT_JOBSERVER=${DETECT_JOBSERVER})
+  run_cmake_command(DetectJobServer-clean ${CMAKE_COMMAND} --build . --target clean)
+  run_cmake_command(DetectJobServer-build ${CMAKE_COMMAND} --build . -j4)
+endfunction()
+
+if(RunCMake_GENERATOR MATCHES "(MinGW|Unix) Makefiles")
+  __ep_test_jobserver()
+endif()
+
 __ep_test_with_build(MultiCommand)
 
 set(RunCMake_TEST_OUTPUT_MERGE 1)