cppgc: mirror: Add copybara and migration scripts

The CL add two files:
1) copy.bara.sky - source file for copybara that needs to migrate cppgc
from v8 repo to GitHub;
2) export_to_github.sh - top level bash script that runs copybara and
generates CMake files if needed.

Bug: v8:10724
Change-Id: I6a5f0ed1d007533914d578203a37fab2c3e9774a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2320651Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69123}

tools/cppgc/copy.bara.sky

+# Copyright 2020 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+INTERESTING_PATHS = [
+    'AUTHORS',
+    'CODE_OF_CONDUCT.md',
+    'LICENSE',
+    'samples/cppgc/**',
+    'src/base/**',
+    'src/heap/base/**',
+    'src/heap/cppgc/**',
+    'include/cppgc/**',
+    'include/v8config.h',
+    'include/v8-platform.h',
+    'testing/**',
+    'test/unittests/heap/cppgc/**',
+]
+
+origin_url = 'https://chromium.googlesource.com/v8/v8.git'
+# TODO(v8:10724): Add GitHub destination url.
+destination_url = 'TODO'
+
+# This workflow syncs cppgc source inside V8's googlesource repo with GitHub.
+core.workflow(
+    name='default',
+    origin=git.origin(
+        url=origin_url,
+        ref='master',
+    ),
+    destination=git.destination(url=destination_url, ),
+    origin_files=glob(INTERESTING_PATHS,
+                      exclude=['samples/cppgc/cppgc-for-v8-embedders.cc']),
+    destination_files=glob(['**'], exclude=['CMakeLists.txt', 'cmake/**']),
+    mode='SQUASH',
+    authoring=authoring.pass_thru('V8 Team <v8-dev@googlegroups.com>'),
+    transformations=[
+        metadata.squash_notes(prefix='Export of V8 changes from ' +
+                              origin_url + '\n\nList of included changes:\n\n')
+    ]
+)

tools/cppgc/export_to_github.sh

+#!/bin/sh
+#
+# Copyright 2020 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+source_dir=$(cd "$(dirname "$0")"; pwd -P)
+
+copybara_exe=copybara
+copybara_file="$source_dir/copy.bara.sky"
+init_history=''
+
+for arg in "$@"; do
+  case $arg in
+    --copybara-exe=*)
+      copybara_exe="${arg#*=}"
+      shift
+      ;;
+    --copybara-file=*)
+      copybara_file="${arg#*=}"
+      shift
+      ;;
+    --init-history)
+      init_history='--init-history --force'
+      shift
+      ;;
+    *)
+      echo -e "Usage:$arg"
+      echo -e "    export_to_github.sh [--copybara-exe=<path-to-copybara>]\n" \
+              "                       [--copybara-file=<path-to-copy.bara.sky>]"
+      exit 1
+  esac
+done
+
+v8_origin="https://chromium.googlesource.com/v8/v8.git"
+v8_ref="master"
+
+NOCOLOR="\033[0m"
+RED="\033[0;31m"
+GREEN="\033[0;32m"
+BLUE="\033[0;34m"
+
+function fail {
+  echo -e "${RED}${1}${NOCOLOR}" > /dev/stderr
+  exit 1
+}
+
+function success {
+  echo -e "${BLUE}${1}${NOCOLOR}" > /dev/stderr
+  exit 0
+}
+
+function message {
+  echo -e "${GREEN}${1}${NOCOLOR}" > /dev/stderr
+}
+
+function cleanup {
+  if [ -d "$git_temp_dir" ]; then
+    rm -rf $git_temp_dir
+  fi
+}
+
+trap "exit 1" HUP INT PIPE QUIT TERM
+trap cleanup EXIT
+
+[ ! -x $copybara_exe ] && fail "$copybara_exe doesn't exist or was not found in PATH!"
+[ ! -f $copybara_file ] && fail "Input $copybara_file doesn't exist!"
+
+git_temp_dir=$(mktemp -d)
+if [[ ! "$git_temp_dir" || ! -d "$git_temp_dir" ]]; then
+  fail "Failed to create temporary dir"
+fi
+
+if [[ $init_history ]]; then
+  read -p "--init-history is only supposed to be used on the first export of \
+cppgc. Is this what is really intended? (y/N)" answer
+  if [ "$answer" != "y" ]; then
+    exit 0
+  fi
+fi
+
+message "Running copybara..."
+$copybara_exe $init_history $copybara_file --dry-run --git-destination-path $git_temp_dir
+result=$?
+if [ "$result" -eq 4 ]; then
+  success "Nothing needs to be done, exiting..."
+elif [ "$result" -ne 0 ]; then
+  fail "Failed to run copybara"
+fi
+
+cd $git_temp_dir
+
+main_gn="BUILD.gn"
+test_gn="test/unittests/BUILD.gn"
+gen_cmake="tools/cppgc/gen_cmake.py"
+
+message "Checking out BUILD.gn files..."
+git remote add v8_origin "$v8_origin"
+git fetch --depth=1 v8_origin $v8_ref
+git checkout v8_origin/master -- "$main_gn" "$test_gn" "$gen_cmake" \
+  || fail "Failed to checkout BUILD.gn from V8 origin"
+
+message "Generating CMakeLists.txt..."
+cmakelists="$git_temp_dir/CMakeLists.txt"
+$gen_cmake --out=$cmakelists --main-gn=$main_gn --test-gn=$test_gn \
+  || fail "CMakeLists.txt generation has failed!"
+
+git rm -f $main_gn $test_gn $gen_cmake > /dev/null
+
+if git status -s | grep -q $(basename $cmakelists); then
+  message "CMakeLists.txt needs to be changed"
+  git add $cmakelists
+  git commit --amend --no-edit > /dev/null
+else
+  message "No changes in CMakeLists.txt need to be done"
+fi
+
+message "Pushing changes to GitHub..."
+git push copybara_remote master
+
+success "CppGC GitHub mirror was successfully updated"