[GitHub Actions] Add prepare_git_repo script

build_tools/ci/githubactions/prepare_git_repo.cmake

@@ -0,0 +1,44 @@
+cmake_minimum_required(VERSION 3.3)
+cmake_policy(SET CMP0054 NEW)
+
+# [preparegitrepo.cmake]
+#
+# Copyright © 2018-2020 pastdue ( https://github.com/past-due/ ) and contributors
+# License: MIT License ( https://opensource.org/licenses/MIT )
+#
+
+# GitHub Actions: Repo prep
+macro(create_all_branches)
+
+	# Keep track of where Travis put us.
+	# We are on a detached head, and we need to be able to go back to it.
+	execute_process( COMMAND ${GIT_EXECUTABLE} rev-parse HEAD
+					 OUTPUT_VARIABLE build_head
+					 OUTPUT_STRIP_TRAILING_WHITESPACE )
+	execute_process(COMMAND ${CMAKE_COMMAND} -E echo "build_head: ${build_head}")
+
+	# "git fetch --prune"
+	execute_process(COMMAND ${GIT_EXECUTABLE} fetch --prune --progress)
+
+	# also fetch the tags
+	# "git fetch --tags"
+	execute_process(COMMAND ${GIT_EXECUTABLE} fetch --tags)
+
+	# checkout master to ensure that a local master branch exists
+	# "git checkout -qf master"
+	execute_process(COMMAND ${GIT_EXECUTABLE} checkout -qf master)
+
+	# finally, go back to where we were at the beginning
+	# "git checkout -qf ${build_head}"
+	execute_process(COMMAND ${GIT_EXECUTABLE} checkout -qf ${build_head})
+
+endmacro()
+
+find_package(Git REQUIRED)
+
+if(DEFINED ENV{GITHUB_ACTIONS} AND "$ENV{GITHUB_ACTIONS}" STREQUAL "true")
+	create_all_branches()
+	message( STATUS "Prepared GitHub Actions Git repo for autorevision" )
+else()
+	message( WARNING "GitHub Actions environment not detected" )
+endif()