COMP: ExternalProject.cmake - Ported GIT_TAG from CMake-trunk

GIT_TAG allows to specify a commit id, branch name or tag that should
be checked out after the git repository is cloned.

Code specific to gitclone and gitupdate step has been factored out into
two functions: _ep_write_gitclone_script and _ep_write_gitupdate_script

CMake/ExternalProject.cmake

@@ -18,9 +18,10 @@
 #    [SVN_REVISION rev]          # Revision to checkout from Subversion repo
 #    [SVN_USERNAME john ]        # Username to use for Subversion checkout and update
 #    [SVN_PASSWORD doe ]         # Password to use for Subversion checkout and update
+#    [GIT_REPOSITORY url]        # URL of GIT repo
+#    [GIT_TAG tag]               # Git branch name, commit id or tag
 #    [URL /.../src.tgz]          # Full path or URL of source
 #    [TIMEOUT seconds]           # Time allowed for file download operations
-#    [GIT_REPOSITORY url]        # URL of GIT repo
 #   #--Update/Patch step----------
 #    [UPDATE_COMMAND cmd...]     # Source work-tree update command
 #    [PATCH_COMMAND cmd...]      # Command to patch downloaded source
@@ -205,6 +206,92 @@ define_property(DIRECTORY PROPERTY "EP_PREFIX" INHERITED
   "ExternalProject module."
   )
 
+function(_ep_write_gitclone_script script_filename source_dir git_EXECUTABLE git_repository git_tag src_name work_dir)
+  file(WRITE ${script_filename}
+"execute_process(
+  COMMAND \${CMAKE_COMMAND} -E remove_directory \"${source_dir}\"
+  RESULT_VARIABLE error_code
+  )
+if(error_code)
+  message(FATAL_ERROR \"Failed to remove directory: '${source_dir}'\")
+endif()
+
+execute_process(
+  COMMAND \"${git_EXECUTABLE}\" clone \"${git_repository}\" \"${src_name}\"
+  WORKING_DIRECTORY \"${work_dir}\"
+  RESULT_VARIABLE error_code
+  )
+if(error_code)
+  message(FATAL_ERROR \"Failed to clone repository: '${git_repository}'\")
+endif()
+
+if(NOT \"${git_tag}\" STREQUAL \"\")
+  execute_process(
+    COMMAND \"${git_EXECUTABLE}\" checkout ${git_tag}
+    WORKING_DIRECTORY \"${work_dir}/${src_name}\"
+    RESULT_VARIABLE error_code
+    ERROR_QUIET
+    )
+  if(error_code)
+    message(FATAL_ERROR \"Failed to checkout tag: '${git_tag}'\")
+  endif()
+endif()
+"
+)
+endfunction(_ep_write_gitclone_script)
+
+#
+# Since patch may have been applied: git reset --hard HEAD
+# Switch back to master: git checkout master
+# Pull in changes: git pull 
+# If a tag is specified, attempt to checkout: git checkout TAG
+# If patch_cmd is specified, attempt to re-apply the patches
+function(_ep_write_gitupdate_script script_filename source_dir git_EXECUTABLE git_repository git_tag src_name work_dir patch_cmd)
+  file(WRITE ${script_filename}
+"execute_process(
+  COMMAND \"${git_EXECUTABLE}\" reset --hard HEAD
+  WORKING_DIRECTORY \"${work_dir}\"
+  RESULT_VARIABLE error_code
+  )
+execute_process(
+  COMMAND \"${git_EXECUTABLE}\" checkout master
+  WORKING_DIRECTORY \"${work_dir}\"
+  RESULT_VARIABLE error_code
+  )
+if(error_code)
+  message(FATAL_ERROR \"Failed to checkout master - repository: ${git_repository}\")
+endif()
+execute_process(
+  COMMAND \"${git_EXECUTABLE}\" pull
+  WORKING_DIRECTORY \"${work_dir}\"
+  RESULT_VARIABLE error_code
+  )
+if(error_code)
+  message(FATAL_ERROR \"Failed to pull - repository: ${git_repository}\")
+endif()
+if(NOT \"${git_tag}\" STREQUAL \"\")
+  execute_process(
+    COMMAND \"${git_EXECUTABLE}\" checkout ${git_tag}
+    WORKING_DIRECTORY \"${work_dir}\"
+    RESULT_VARIABLE error_code
+    ERROR_QUIET
+    )
+  if(error_code)
+    message(FATAL_ERROR \"Failed to checkout tag ${git_tag} - repository: ${git_repository}\")
+  endif()
+endif()
+if(NOT \"${patch_cmd}\" STREQUAL \"\")
+  execute_process(
+    COMMAND \"${patch_cmd}\"
+    WORKING_DIRECTORY \"${work_dir}\"
+    RESULT_VARIABLE error_code
+    )
+  if(error_code)
+    message(FATAL_ERROR \"Failed to apply patch for ${name}\")
+  endif()
+endif()
+")
+endfunction(_ep_write_gitupdate_script)
 
 function(_ep_write_downloadfile_script script_filename remote local timeout)
   if(timeout)
@@ -684,22 +771,16 @@ function(_ep_add_download_command name)
     list(APPEND depends ${stamp_dir}/${name}-svninfo.txt)
   elseif(git_repository)
     #find_package(Git)
-    find_program(Git_EXECUTABLE git
-      PATHS
-        "C:/Program Files/Git/bin"
-        "C:/Program Files (x86)/Git/bin"
-      DOC "git command line client")
-    mark_as_advanced(Git_EXECUTABLE)
-    if(NOT Git_EXECUTABLE)
-      message(FATAL_ERROR "error: could not find git to clone ${name} - Make sure Git_EXECUTABLE is set properly")
+    find_program(git_EXECUTABLE NAMES git.cmd git eg.cmd eg DOC "git command line client")
+    if(NOT git_EXECUTABLE)
+      message(FATAL_ERROR "error: could not find git for clone of ${name} - Make sure git_EXECUTABLE is set properly")
     endif()
 
-    # TODO  [GIT_REVISION revision]        # Revision to checkout from GIT repo
-    #get_property(git_revision TARGET ${name} PROPERTY _EP_GIT_REVISION)
+    get_property(git_tag TARGET ${name} PROPERTY _EP_GIT_TAG)
 
     set(repository ${git_repository})
     set(module)
-    set(tag ${git_revision})
+    set(tag ${git_tag})
     configure_file(
       "${CMAKE_ROOT}/Modules/RepositoryInfo.txt.in"
       "${stamp_dir}/${name}-gitinfo.txt"
@@ -707,26 +788,16 @@ function(_ep_add_download_command name)
       )
 
     get_filename_component(src_name "${source_dir}" NAME)
-    get_filename_component(work_dir "${source_dir}/../" REALPATH)
+    get_filename_component(work_dir "${source_dir}" PATH)
 
-    # Since Git doesn't allow to clone if the repository exists,
-    # let's create a cmake script that will be invoked as a download command.
-    # That script will delete the source directory and call the appropriate git clone command
-    file(WRITE ${tmp_dir}/${name}-gitclone.cmake "
-execute_process(
-  COMMAND \"${CMAKE_COMMAND}\" -E remove_directory \"${source_dir}\"
-  RESULT_VARIABLE error_code
-  )
-execute_process(
-  COMMAND \"${Git_EXECUTABLE}\" clone \"${git_repository}\" \"${src_name}\"
-  WORKING_DIRECTORY \"${work_dir}\"
-  RESULT_VARIABLE error_code
-  )
-if(error_code)
-  message(FATAL_ERROR \"Failed to clone repository: ${git_repository}\")
-endif()
-")    
-    set(comment "Performing download step (GIT clone) for '${name}'")
+    # Since git clone doesn't succeed if the non-empty source_dir exists,
+    # create a cmake script to invoke as download command.
+    # 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}" ${src_name} ${work_dir})
+	  
+    set(comment "Performing download step (git clone) for '${name}'")
     set(cmd ${CMAKE_COMMAND} -P ${tmp_dir}/${name}-gitclone.cmake)
     list(APPEND depends ${stamp_dir}/${name}-gitinfo.txt)
   elseif(url)
@@ -790,12 +861,7 @@ function(_ep_add_update_command name)
   get_property(git_repository TARGET ${name} PROPERTY _EP_GIT_REPOSITORY)
   
   # Patch
-  get_property(patch_cmd_set TARGET ${name} PROPERTY _EP_PATCH_COMMAND SET)
   get_property(patch_cmd TARGET ${name} PROPERTY _EP_PATCH_COMMAND)
-  set(patch_work_dir)
-  if(patch_cmd_set)
-    set(patch_work_dir ${source_dir})
-  endif()
 
   set(work_dir)
   set(comment)
@@ -824,40 +890,19 @@ function(_ep_add_update_command name)
     set(cmd ${Subversion_SVN_EXECUTABLE} up ${svn_revision} --username=${svn_username} --password=${svn_password})
     set(always 1)
   elseif(git_repository)
-    if(NOT Git_EXECUTABLE)
+    if(NOT git_EXECUTABLE)
       message(FATAL_ERROR "error: could not find git for pull of ${name}")
     endif()
     set(work_dir ${source_dir})
-
+    get_filename_component(src_name "${source_dir}" NAME)
+    
+    get_property(git_tag TARGET ${name} PROPERTY _EP_GIT_TAG)
+    
     # The following script will allow to reset, pull and re-apply patches
-    file(WRITE ${tmp_dir}/${name}-gitupdate.cmake "
-execute_process(
-  COMMAND \"${Git_EXECUTABLE}\" reset --hard HEAD
-  WORKING_DIRECTORY \"${work_dir}\"
-  RESULT_VARIABLE error_code
-  )
-execute_process(
-  COMMAND \"${Git_EXECUTABLE}\" pull
-  WORKING_DIRECTORY \"${work_dir}\"
-  RESULT_VARIABLE error_code
-  )
-if(error_code)
-  message(FATAL_ERROR \"Failed to pull - repository: ${git_repository}\")
-endif()
-if(${patch_cmd_set})
-  execute_process(
-    COMMAND \"${patch_cmd}\"
-    WORKING_DIRECTORY \"${patch_work_dir}\"
-    RESULT_VARIABLE error_code
-    )
-  if(error_code)
-    message(FATAL_ERROR \"Failed to apply patch for ${name}\")
-  endif()
-endif()
-")
+    _ep_write_gitupdate_script(${tmp_dir}/${name}-gitupdate.cmake ${source_dir} ${git_EXECUTABLE} 
+    ${git_repository} "${git_tag}" ${src_name} ${work_dir} "${patch_cmd}")
 
-    set(comment "Performing update step (GIT pull) for '${name}'")
-    #get_property(git_revision TARGET ${name} PROPERTY _EP_GIT_REVISION)
+    set(comment "Performing update step (git pull) for '${name}'")
     set(cmd ${CMAKE_COMMAND} -P ${tmp_dir}/${name}-gitupdate.cmake)
     set(always 1)
   endif()
@@ -1066,4 +1111,4 @@ function(ExternalProject_Add name)
   # on install.
   #
   _ep_add_test_command(${name})
-endfunction(ExternalProject_Add)
+endfunction(ExternalProject_Add)