FetchContent: Invoke steps directly and avoid a separate sub-build

The cost of setting up and executing a separate sub-build to do the
download, update and patch steps required for FetchContent population
can be significant with some platforms and CMake generators. Avoid the
sub-build altogether by invoking the step scripts directly.

Previously, if no generator was set (e.g. population was being done in
script mode), a generator needed to be available on the default PATH.
Since we no longer use a sub-build, this restriction is also now gone.

Fixes: #21703

1 files changed, 17 insertions, 114 deletions

diff --git a/Modules/FetchContent.cmake b/Modules/FetchContent.cmake
index 8adef47778..6a4cf38884 100644
--- a/Modules/FetchContent.cmake
+++ b/Modules/FetchContent.cmake
@@ -849,8 +849,6 @@ function(__FetchContent_directPopulate contentName)
       SUBBUILD_DIR
       SOURCE_DIR
       BINARY_DIR
-      # We need special processing if DOWNLOAD_NO_EXTRACT is true
-      DOWNLOAD_NO_EXTRACT
       # Prevent the following from being passed through
       CONFIGURE_COMMAND
       BUILD_COMMAND
@@ -894,123 +892,28 @@ function(__FetchContent_directPopulate contentName)
   set(${contentName}_SOURCE_DIR "${ARG_SOURCE_DIR}" PARENT_SCOPE)
   set(${contentName}_BINARY_DIR "${ARG_BINARY_DIR}" PARENT_SCOPE)
 
-  # The unparsed arguments may contain spaces, so build up ARG_EXTRA
-  # in such a way that it correctly substitutes into the generated
-  # CMakeLists.txt file with each argument quoted.
-  unset(ARG_EXTRA)
-  foreach(arg IN LISTS ARG_UNPARSED_ARGUMENTS)
-    set(ARG_EXTRA "${ARG_EXTRA} \"${arg}\"")
-  endforeach()
-
-  if(ARG_DOWNLOAD_NO_EXTRACT)
-    set(ARG_EXTRA "${ARG_EXTRA} DOWNLOAD_NO_EXTRACT YES")
-    set(__FETCHCONTENT_COPY_FILE
-"
-ExternalProject_Get_Property(${contentName}-populate DOWNLOADED_FILE)
-get_filename_component(dlFileName \"\${DOWNLOADED_FILE}\" NAME)
-
-ExternalProject_Add_Step(${contentName}-populate copyfile
-  COMMAND    \"${CMAKE_COMMAND}\" -E copy_if_different
-             \"<DOWNLOADED_FILE>\" \"${ARG_SOURCE_DIR}\"
-  DEPENDEES  patch
-  DEPENDERS  configure
-  BYPRODUCTS \"${ARG_SOURCE_DIR}/\${dlFileName}\"
-  COMMENT    \"Copying file to SOURCE_DIR\"
-)
-")
+  if(ARG_QUIET)
+    set(quiet TRUE)
   else()
-    unset(__FETCHCONTENT_COPY_FILE)
-  endif()
-
-  # Hide output if requested, but save it to a variable in case there's an
-  # error so we can show the output upon failure. When not quiet, don't
-  # capture the output to a variable because the user may want to see the
-  # output as it happens (e.g. progress during long downloads). Combine both
-  # stdout and stderr in the one capture variable so the output stays in order.
-  if (ARG_QUIET)
-    set(outputOptions
-        OUTPUT_VARIABLE capturedOutput
-        ERROR_VARIABLE  capturedOutput
-    )
-  else()
-    set(capturedOutput)
-    set(outputOptions)
+    set(quiet FALSE)
     message(STATUS "Populating ${contentName}")
   endif()
 
-  if(CMAKE_GENERATOR)
-    set(subCMakeOpts "-G${CMAKE_GENERATOR}")
-    if(CMAKE_GENERATOR_PLATFORM)
-      list(APPEND subCMakeOpts "-A${CMAKE_GENERATOR_PLATFORM}")
-    endif()
-    if(CMAKE_GENERATOR_TOOLSET)
-      list(APPEND subCMakeOpts "-T${CMAKE_GENERATOR_TOOLSET}")
-    endif()
-
-    if(CMAKE_MAKE_PROGRAM)
-      list(APPEND subCMakeOpts "-DCMAKE_MAKE_PROGRAM:FILEPATH=${CMAKE_MAKE_PROGRAM}")
-    endif()
-
-  else()
-    # Likely we've been invoked via CMake's script mode where no
-    # generator is set (and hence CMAKE_MAKE_PROGRAM could not be
-    # trusted even if provided). We will have to rely on being
-    # able to find the default generator and build tool.
-    unset(subCMakeOpts)
-  endif()
-
-  if(DEFINED CMAKE_EP_GIT_REMOTE_UPDATE_STRATEGY)
-    list(APPEND subCMakeOpts
-      "-DCMAKE_EP_GIT_REMOTE_UPDATE_STRATEGY=${CMAKE_EP_GIT_REMOTE_UPDATE_STRATEGY}")
-  endif()
-
-  # Avoid using if(... IN_LIST ...) so we don't have to alter policy settings
-  set(__FETCHCONTENT_CACHED_INFO "")
-  list(FIND ARG_UNPARSED_ARGUMENTS GIT_REPOSITORY indexResult)
-  if(indexResult GREATER_EQUAL 0)
-    find_package(Git QUIET)
-    set(__FETCHCONTENT_CACHED_INFO
-"# Pass through things we've already detected in the main project to avoid
-# paying the cost of redetecting them again in ExternalProject_Add()
-set(GIT_EXECUTABLE [==[${GIT_EXECUTABLE}]==])
-set(GIT_VERSION_STRING [==[${GIT_VERSION_STRING}]==])
-set_property(GLOBAL PROPERTY _CMAKE_FindGit_GIT_EXECUTABLE_VERSION
-  [==[${GIT_EXECUTABLE};${GIT_VERSION_STRING}]==]
-)
-")
-  endif()
-
-  # Create and build a separate CMake project to carry out the population.
-  # If we've already previously done these steps, they will not cause
-  # anything to be updated, so extra rebuilds of the project won't occur.
-  # Make sure to pass through CMAKE_MAKE_PROGRAM in case the main project
-  # has this set to something not findable on the PATH.
-  configure_file("${CMAKE_CURRENT_FUNCTION_LIST_DIR}/FetchContent/CMakeLists.cmake.in"
-                 "${ARG_SUBBUILD_DIR}/CMakeLists.txt")
-  execute_process(
-    COMMAND ${CMAKE_COMMAND} ${subCMakeOpts} .
-    RESULT_VARIABLE result
-    ${outputOptions}
-    WORKING_DIRECTORY "${ARG_SUBBUILD_DIR}"
-  )
-  if(result)
-    if(capturedOutput)
-      message("${capturedOutput}")
-    endif()
-    message(FATAL_ERROR "CMake step for ${contentName} failed: ${result}")
-  endif()
-  execute_process(
-    COMMAND ${CMAKE_COMMAND} --build .
-    RESULT_VARIABLE result
-    ${outputOptions}
-    WORKING_DIRECTORY "${ARG_SUBBUILD_DIR}"
+  include(ExternalProject)
+  set(argsQuoted)
+  foreach(__item IN LISTS ARG_UNPARSED_ARGUMENTS)
+    string(APPEND argsQuoted " [==[${__item}]==]")
+  endforeach()
+  cmake_language(EVAL CODE "
+    _ep_do_preconfigure_steps_now(${contentName}
+      ${argsQuoted}
+      QUIET                   ${quiet}
+      SOURCE_DIR              [==[${ARG_SOURCE_DIR}]==]
+      BINARY_DIR              [==[${ARG_BINARY_DIR}]==]
+      USES_TERMINAL_DOWNLOAD  YES
+      USES_TERMINAL_UPDATE    YES
+    )"
   )
-  if(result)
-    if(capturedOutput)
-      message("${capturedOutput}")
-    endif()
-    message(FATAL_ERROR "Build step for ${contentName} failed: ${result}")
-  endif()
 
 endfunction()