ExternalProject: Allow passing config flags to git clone

Add a `GIT_CONFIG` parameter that allows to specify `--config` flags
that are passed to the git clone command.  This can be used to specify
for example `core.autocrlf=true`.  The `--config` parameter is supported
since Git 1.7.7.

Help/release/dev/ExternalProject-GIT_CONFIG.rst

@@ -0,0 +1,5 @@
+ExternalProject-GIT_CONFIG
+--------------------------
+
+* The :module:`ExternalProject` module gained a ``GIT_CONFIG`` option
+  to pass ``--config`` options to Git when cloning repositories.

Modules/ExternalProject.cmake

@@ -73,6 +73,10 @@ Create custom targets to build projects in external trees
     does not output anything which can make the build appear to have stalled.
     This option forces Git to output progress information during the clone step
     so that forward progress is indicated.
+  ``GIT_CONFIG <option>...``
+    Tell Git to clone with ``--config <option>``.  Use additional configuration
+    parameters when cloning the project (``key=value`` as expected by ``git
+    config``).
   ``HG_REPOSITORY <url>``
     URL of mercurial repo
   ``HG_TAG <tag>``
@@ -514,7 +518,7 @@ define_property(DIRECTORY PROPERTY "EP_UPDATE_DISCONNECTED" INHERITED
   "ExternalProject module."
   )
 
-function(_ep_write_gitclone_script script_filename source_dir git_EXECUTABLE git_repository git_tag git_remote_name git_submodules git_shallow git_progress src_name work_dir gitclone_infofile gitclone_stampfile tls_verify)
+function(_ep_write_gitclone_script script_filename source_dir git_EXECUTABLE git_repository git_tag git_remote_name git_submodules git_shallow git_progress git_config src_name work_dir gitclone_infofile gitclone_stampfile tls_verify)
   if(NOT GIT_VERSION_STRING VERSION_LESS 1.7.10)
     set(git_clone_shallow_options "--depth 1 --no-single-branch")
   else()
@@ -565,6 +569,11 @@ if(git_progress)
   list(APPEND git_clone_options --progress)
 endif()
 
+set(git_config \"${git_config}\")
+foreach(config IN LISTS git_config)
+  list(APPEND git_clone_options --config \${config})
+endforeach()
+
 # try the clone 3 times incase there is an odd git clone issue
 set(error_code 1)
 set(number_of_tries 0)
@@ -1812,6 +1821,7 @@ function(_ep_add_download_command name)
     endif()
     get_property(git_shallow TARGET ${name} PROPERTY _EP_GIT_SHALLOW)
     get_property(git_progress TARGET ${name} PROPERTY _EP_GIT_PROGRESS)
+    get_property(git_config TARGET ${name} PROPERTY _EP_GIT_CONFIG)
 
     # For the download step, and the git clone operation, only the repository
     # should be recorded in a configured RepositoryInfo file. If the repo
@@ -1836,7 +1846,7 @@ function(_ep_add_download_command name)
     # The script will delete the source directory and then call git clone.
     #
     _ep_write_gitclone_script(${tmp_dir}/${name}-gitclone.cmake ${source_dir}
-      ${GIT_EXECUTABLE} ${git_repository} ${git_tag} ${git_remote_name} "${git_submodules}" "${git_shallow}" "${git_progress}" ${src_name} ${work_dir}
+      ${GIT_EXECUTABLE} ${git_repository} ${git_tag} ${git_remote_name} "${git_submodules}" "${git_shallow}" "${git_progress}" "${git_config}" ${src_name} ${work_dir}
       ${stamp_dir}/${name}-gitinfo.txt ${stamp_dir}/${name}-gitclone-lastrun.txt "${tls_verify}"
       )
     set(comment "Performing download step (git clone) for '${name}'")

Tests/ExternalProject/CMakeLists.txt

@@ -363,6 +363,23 @@ if(do_git_tests)
   )
   set_property(TARGET ${proj} PROPERTY FOLDER "GIT")
 
+  # Live git / master (no GIT_TAG), but git config flags
+  #
+  # The `git clone --config` parameter has been introduced in Git 1.7.7
+  if(NOT git_version VERSION_LESS 1.7.7)
+    set(proj TutorialStep1-GIT-config)
+    ExternalProject_Add(${proj}
+      GIT_REPOSITORY "${local_git_repo}"
+      GIT_CONFIG core.eol=lf core.autocrlf=input
+      CMAKE_GENERATOR "${CMAKE_GENERATOR}"
+      CMAKE_ARGS -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR>
+      INSTALL_COMMAND ""
+      DEPENDS "SetupLocalGITRepository"
+      LOG_UPDATE 1
+    )
+    set_property(TARGET ${proj} PROPERTY FOLDER "GIT")
+  endif()
+
   # git by explicit branch/tag with empty submodule list
   #
   set(proj TutorialStep1-GIT-bytag-withsubmodules)