ExternalProject: factor out gitupdate step to separate file

The refactoring exposed that the original implementation
was referring to an undefined variable src_name, which was
previously only used in error messages. This has been fixed
as part of the refactoring work.

Fixes: #20336

Modules/ExternalProject-gitupdate.cmake.in

@@ -0,0 +1,165 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file Copyright.txt or https://cmake.org/licensing for details.
+
+cmake_minimum_required(VERSION 3.5)
+
+execute_process(
+  COMMAND "@git_EXECUTABLE@" rev-list --max-count=1 HEAD
+  WORKING_DIRECTORY "@work_dir@"
+  RESULT_VARIABLE error_code
+  OUTPUT_VARIABLE head_sha
+  OUTPUT_STRIP_TRAILING_WHITESPACE
+  )
+if(error_code)
+  message(FATAL_ERROR "Failed to get the hash for HEAD")
+endif()
+
+execute_process(
+  COMMAND "@git_EXECUTABLE@" show-ref "@git_tag@"
+  WORKING_DIRECTORY "@work_dir@"
+  OUTPUT_VARIABLE show_ref_output
+  )
+# If a remote ref is asked for, which can possibly move around,
+# we must always do a fetch and checkout.
+if("${show_ref_output}" MATCHES "remotes")
+  set(is_remote_ref 1)
+else()
+  set(is_remote_ref 0)
+endif()
+
+# Tag is in the form <remote>/<tag> (i.e. origin/master) we must strip
+# the remote from the tag.
+if("${show_ref_output}" MATCHES "refs/remotes/@git_tag@")
+  string(REGEX MATCH "^([^/]+)/(.+)$" _unused "@git_tag@")
+  set(git_remote "${CMAKE_MATCH_1}")
+  set(git_tag "${CMAKE_MATCH_2}")
+else()
+  set(git_remote "@git_remote_name@")
+  set(git_tag "@git_tag@")
+endif()
+
+# This will fail if the tag does not exist (it probably has not been fetched
+# yet).
+execute_process(
+  COMMAND "@git_EXECUTABLE@" rev-list --max-count=1 "${git_tag}"
+  WORKING_DIRECTORY "@work_dir@"
+  RESULT_VARIABLE error_code
+  OUTPUT_VARIABLE tag_sha
+  OUTPUT_STRIP_TRAILING_WHITESPACE
+  )
+
+# Is the hash checkout out that we want?
+if(error_code OR is_remote_ref OR NOT ("${tag_sha}" STREQUAL "${head_sha}"))
+  execute_process(
+    COMMAND "@git_EXECUTABLE@" fetch
+    WORKING_DIRECTORY "@work_dir@"
+    RESULT_VARIABLE error_code
+    )
+  if(error_code)
+    message(FATAL_ERROR "Failed to fetch repository '@git_repository@'")
+  endif()
+
+  if(is_remote_ref)
+    # Check if stash is needed
+    execute_process(
+      COMMAND "@git_EXECUTABLE@" status --porcelain
+      WORKING_DIRECTORY "@work_dir@"
+      RESULT_VARIABLE error_code
+      OUTPUT_VARIABLE repo_status
+      )
+    if(error_code)
+      message(FATAL_ERROR "Failed to get the status")
+    endif()
+    string(LENGTH "${repo_status}" need_stash)
+
+    # If not in clean state, stash changes in order to be able to be able to
+    # perform git pull --rebase
+    if(need_stash)
+      execute_process(
+        COMMAND "@git_EXECUTABLE@" stash save @git_stash_save_options@
+        WORKING_DIRECTORY "@work_dir@"
+        RESULT_VARIABLE error_code
+        )
+      if(error_code)
+        message(FATAL_ERROR "Failed to stash changes")
+      endif()
+    endif()
+
+    # Pull changes from the remote branch
+    execute_process(
+      COMMAND "@git_EXECUTABLE@" rebase "${git_remote}/${git_tag}"
+      WORKING_DIRECTORY "@work_dir@"
+      RESULT_VARIABLE error_code
+      )
+    if(error_code)
+      # Rebase failed: Restore previous state.
+      execute_process(
+        COMMAND "@git_EXECUTABLE@" rebase --abort
+        WORKING_DIRECTORY "@work_dir@"
+      )
+      if(need_stash)
+        execute_process(
+          COMMAND "@git_EXECUTABLE@" stash pop --index --quiet
+          WORKING_DIRECTORY "@work_dir@"
+          )
+      endif()
+      message(FATAL_ERROR "\nFailed to rebase in: '@work_dir@'."
+                          "\nYou will have to resolve the conflicts manually")
+    endif()
+
+    if(need_stash)
+      execute_process(
+        COMMAND "@git_EXECUTABLE@" stash pop --index --quiet
+        WORKING_DIRECTORY "@work_dir@"
+        RESULT_VARIABLE error_code
+        )
+      if(error_code)
+        # Stash pop --index failed: Try again dropping the index
+        execute_process(
+          COMMAND "@git_EXECUTABLE@" reset --hard --quiet
+          WORKING_DIRECTORY "@work_dir@"
+          RESULT_VARIABLE error_code
+          )
+        execute_process(
+          COMMAND "@git_EXECUTABLE@" stash pop --quiet
+          WORKING_DIRECTORY "@work_dir@"
+          RESULT_VARIABLE error_code
+          )
+        if(error_code)
+          # Stash pop failed: Restore previous state.
+          execute_process(
+            COMMAND "@git_EXECUTABLE@" reset --hard --quiet ${head_sha}
+            WORKING_DIRECTORY "@work_dir@"
+          )
+          execute_process(
+            COMMAND "@git_EXECUTABLE@" stash pop --index --quiet
+            WORKING_DIRECTORY "@work_dir@"
+          )
+          message(FATAL_ERROR "\nFailed to unstash changes in: '@work_dir@'."
+                              "\nYou will have to resolve the conflicts manually")
+        endif()
+      endif()
+    endif()
+  else()
+    execute_process(
+      COMMAND "@git_EXECUTABLE@" checkout "${git_tag}"
+      WORKING_DIRECTORY "@work_dir@"
+      RESULT_VARIABLE error_code
+      )
+    if(error_code)
+      message(FATAL_ERROR "Failed to checkout tag: '${git_tag}'")
+    endif()
+  endif()
+
+  set(init_submodules "@init_submodules@")
+  if(init_submodules)
+    execute_process(
+      COMMAND "@git_EXECUTABLE@" submodule update @git_submodules_recurse@ --init @git_submodules@
+      WORKING_DIRECTORY "@work_dir@"
+      RESULT_VARIABLE error_code
+      )
+  endif()
+  if(error_code)
+    message(FATAL_ERROR "Failed to update submodules in: '@work_dir@'")
+  endif()
+endif()