contrib/merge-kernel

#!/bin/bash
#
# Copyright 2018 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
#
# Script to merge upstream tags into chromeos.
# The command creates a new branch with merge results.
# If necessary, it also pushes the tag into the remote
# repository and creates a branch pointing to it.

readonly notify_to="chromeos-kernel@google.com"
readonly notify_cc="chromium-os-reviews@chromium.org"

# Valid tag pattern.
PATTERN="^v[2-9](\.[0-9]+)+$"
PATTERN_RC="^v[2-9](\.[0-9]+)+-rc$"
GLOB="v[2-9].*[0-9]"
NUMBER="^[1-9][0-9]*$"

if git help push | grep -q push-option; then
    git_skip_validation="-o skip-validation"
fi

# Initial parameter values.
changeid="" # Get Change-Id from CL or generate new Change-Id.
bug=""      # Get Bug-Id from CL or provide on on command line.
tag=""      # Tag to merge; must be provided on command line.
force=0     # Do not override Change-Id / Bug-Id.
prepare=0   # Do not prepare for upload.
upload=0    # Do not upload into Gerrit.
do_dryrun=0 # If 1, don't push anything upstream, don't send email.
notify=0    # Do not send notification e-mail.
deadline=3  # Feedback deadline (in days, default 3).
changes=()  # List of uncommitted CLs to be applied prior to merge.
patches=()  # List of patches to apply before committing merge.
reverts=()  # List of patches to revert as part of merge, after merge
prereverts=() # List of patches to revert as part of merge, prior to merge
dependency="" # No dependency
Subject=""  # default subject
namespace="" # default namespace

# derived parameters
skip_merge=0    # Skip actual merge and upload.
                # Will be set if tag has already been merged and force is true.

readonly tmpfile=$(mktemp)

trap 'rm -f "${tmpfile}"' EXIT
trap 'exit 2' SIGHUP SIGINT SIGQUIT SIGTERM

error() {
  printf '%b: error: %b\n' "${0##*/}" "$*" >&2
}

die() {
  error "$@"
  exit 1
}

usage() {
  cat <<-EOF
Usage: ${0##*/} [options] tag

Parameters:
  tag           Tag, branch, or SHA to merge. Must be either a valid stable
                branch release tag, a valid branch name, or a valid SHA.

Options:
  -b bug-id[,bug-id] ...
                Bug-id or list of bug IDs. Must be valid buganizer
                bug ID. Mandatory unless the merge branch already exists
                locally or in Gerrit.
  -c change-id  Change-Id as used by Gerrit. Optional.
  -d deadline   Feedback deadline in days (default: ${deadline})
  -f            Force. Override existing Change-Id and bug number.
  -h            Display help text and exit.
  -l change-id  Apply patch extracted from CL:change-id prior to merge.
                May be repeated multiple times.
  -n            Send notification e-mail to ${notify_to}.
  -N namespace  Namespace (branch prefix) to use
                Default 'stable-merge/linux' or 'merge', depending on context
  -q dependency Add dependency (Cq-Depend: <dependency>)
  -p            Prepare for upload into Gerrit. Implied if -u is specified.
  -r            Name of branch to base merge on. Determined from stable
                release tag or from target branch name if not provided.
                Must be existing local branch. Will be pushed into gerrit
                as part of the merge process if not already available in
                gerrit, and has to follow gerrit commit rules.
  -P sha        Revert patch <sha> as part of merge, pre-merge
                May be repeated multiple times.
  -R sha        Revert patch <sha> as part of merge, post-merge
                May be repeated multiple times.
  -s            Simulate, or dry-run. Don't actually push anything into
                gerrit, and don't send e-mails.
  -S subject    Replace default subject line with provided string
  -t            Target branch name. The branch must exist in the Chrome OS
                repository.
  -u            Upload merge into Gerrit.
  -x patchfile  Patch to apply before committing merge. Patch will be applied
                with "patch -p 1 < patchfile". May be repeated several times.
EOF

  if [[ $# -gt 0 ]]; then
    echo
    die "$@"
  fi
  exit 0
}

# Find and report remote.
find_remote() {
  local url="$1"
  local remote

  for remote in $(git remote 2>/dev/null); do
    rurl=$(git remote get-url "${remote}")
    # ignore trailing '/' when comparing repositories
    if [[ "${rurl%/}" == "${url%/}" ]]; then
      echo "${remote}"
      break
    fi
  done
}

# Find remote. If there is no remote pointing to the referenced
# kernel repository, create one.
find_create_remote() {
  local url="$1"
  local default="$2"
  local result

  result="$(find_remote "${url}")"
  if [[ -z "${result}" ]]; then
    git remote add "${default}" "${url}"
    result="${default}"
  fi

  echo "${result}"
}

# Find and report CrOS remote.
# This is useful if the command runs on a checked out
# tree with several remotes.
find_chromeos() {
  local url="https://chromium.googlesource.com/chromiumos/third_party/kernel"

  find_remote "${url}"
}

# Find stable remote. If there is no remote pointing to the stable
# kernel repository, create one.
find_stable() {
  local url="git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git"

  find_create_remote "${url}" "stable"
}

# Find stable remote. If there is no remote pointing to the stable
# kernel repository, create one.
find_stable_rc() {
  local url="git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git"

  find_create_remote "${url}" "stable-rc"
}

do_getparams() {
  local bugs="" # List of bugs
  local nbug="" # Numerical part of bug #, for validation.
  local _bug
  local option
  local vtag

  while getopts "b:c:d:fhl:N:nP:pq:r:R:st:uS:x:" option; do
    case ${option} in
      b) bugs="${OPTARG}" ;;
      c) changeid="Change-Id: ${OPTARG}" ;;
      d) deadline="${OPTARG}"
         if ! [[ "${deadline}" =~ ${NUMBER} ]]; then
           die "Deadline must be numeric value > 0 (${deadline})"
         fi
         ;;
      f) force=1 ;;
      l) changes+=("${OPTARG}") ;;
      n) notify=1 ;;
      N) namespace="${OPTARG}" ;;
      p) prepare=1 ;;
      q) dependency="${OPTARG}" ;;
      r) rbranch="${OPTARG}" ;;
      P) prereverts+=("${OPTARG}") ;;
      R) reverts+=("${OPTARG}") ;;
      t) tbranch="${OPTARG}" ;;
      s) do_dryrun=1 ;;
      S) Subject="${OPTARG}" ;;
      u) upload=1 prepare=1 ;;
      x) patches+=("${OPTARG}") ;;
      h|?|*) usage ;;
    esac
  done
  shift $((OPTIND - 1))
  tag=$1
  if [[ -z "${tag}" ]]; then
    usage "tag parameter is mandatory"
  fi
  vtag=$(echo "${tag}" | grep -E "${PATTERN}")
  if [[ "${tag}" != "${vtag}" ]]; then
    # Not a stable release tag, meaning we can not get it from a stable release.
    # Maybe it is a stable release candidate.
    vtag=$(echo "${tag}" | grep -E "${PATTERN_RC}")
    if [[ "${tag}" != "${vtag}" ]]; then
      # Make sure that the reference exists and bail out if not.
      if ! git rev-parse --verify "${tag}" >/dev/null 2>&1; then
        die "Unknown reference '${tag}'."
      fi
    else
      die "${tag} references a stable release candidate. Not supported yet."
    fi
  fi
  if [[ -n "${rbranch}" ]]; then
    if ! git rev-parse --verify "${rbranch}" >/dev/null 2>&1; then
      die "No such branch: ${rbranch}."
    fi
  fi

  if [[ -n "${bugs}" ]]; then
    for _bug in ${bugs//,/ }; do
      if [[ "${_bug}" == b:* ]]; then          # buganizer
        nbug="${_bug##b:}"
      elif [[ "${_bug}" == b/* ]]; then        # buganizer, alternative
        nbug="${_bug##b/}"
      else                                     # crbug etc are not allowed.
        die "Invalid bug ID '${_bug}'."
      fi
      if [[ ! "${nbug}" =~ ${NUMBER} ]]; then
          die "Invalid bug ID '${_bug}'."
      fi
    done
    bug="BUG=${bugs}"
  fi
  dependency="${dependency:+Cq-Depend: ${dependency}}"
}

# Validate environment and repository.
# We need a couple of commands, the repository must be
# a CrOS kernel repository, and it must be clean.
do_validate() {
  local gerrit
  local chromeos
  local jq

  gerrit=$(which gerrit)
  if [[ -z "${gerrit}" ]]; then
    die "gerrit is required. Get from chromite or run from chroot."
  fi
  jq=$(which jq)
  if [[ -z ${jq} ]]; then
    die "jq is required. Install (apt-get install jq) or run from chroot."
  fi
  chromeos=$(find_chromeos)
  if [[ -z ${chromeos} ]]; then
    die "$(pwd) is not a Chromium OS kernel repository."
  fi
  if [[ -n "$(git status -s)" ]]; then
    die "Requires clean repository."
  fi
  if [[ -n "${tbranch}" ]]; then
    if ! git rev-parse --verify "${chromeos}/${tbranch}" >/dev/null 2>&1; then
      die "No such branch: ${chromeos}/${tbranch}."
    fi
  fi
}

# Validate provided Change-IDs.
do_validate_changeids() {
  local cl
  local ref

  for cl in "${changes[@]}"; do
    ref=$(gerrit --json search "change:${cl}" \
          | jq ".[].currentPatchSet.ref")
    if [[ -z "${ref}" ]]; then
      die "No such Change-Id: ${cl}."
    fi
  done
}

# Initialize global variables, plus some more validation.
do_setup() {
  readonly stable=$(find_stable)
  readonly stable_rc=$(find_stable_rc)
  local vtag
  local dvtag

  # If a stable release tag is provided, we need to update stable
  # at this point to get the tag if it is not already available.
  vtag=$(echo "${tag}" | grep -E "${PATTERN}")
  if [[ "${tag}" == "${vtag}" ]]; then
    if ! git rev-parse --verify "${tag}" >/dev/null 2>&1; then
      if ! git fetch "${stable}" > /dev/null 2>&1; then
        die "Failed to update stable release."
      fi
      if ! git rev-parse --verify "${tag}" >/dev/null 2>&1; then
        die "Reference ${tag} not available."
      fi
    fi
  else
    # This might be a stable release candidate.
    vtag=$(echo "${tag}" | grep -E "${PATTERN_RC}")
    if [[ "${tag}" == "${vtag}" ]]; then
      git fetch "${stable_rc}" > /dev/null 2>&1
      # The stable release tag is "vX.Y.Z-rc". Stable release candidate
      # branches are named "remote/linux-X.Y.y".
      # Extract 'X' and 'Y', create the remote branch name,
      # clone/update the remote branch, and set a matching tag
      # on top of it.

      die "Stable release candidates are not yet supported."
    fi
  fi

  readonly ctag=$(git describe --match "${GLOB}" --abbrev=0 "${tag}" \
                     2>/dev/null | cut -f1,2 -d. | sed -e 's/v//')
  readonly dtag=$(git describe --tags "${tag}")

  # While we accept any valid reference as <tag>, we want it to be based
  # on an existing release tag.
  dbtag=${dtag%%-*}
  dvtag=$(git describe --tags --abbrev=0 "${dtag}")
  if [[ "${dbtag}" != "${dvtag}" ]]; then
    die "${tag} (${dtag}) is not based on an existing release tag."
  fi

  readonly chromeos=$(find_chromeos)
  if [[ -z "${chromeos}" ]]; then
    die "Chromium OS kernel repository not found."
  fi

  # cbranch: Chromeos branch name
  # mcbranch: local copy (baseline)
  # ocbranch: remote (target) branch
  #
  # Note: This assumes that the target repository is ${chromeos},
  # even if a remote branch has been specified. It might make sense
  # to make this configurable.
  if [[ -n "${tbranch}" ]]; then
    readonly cbranch="${tbranch}"
  else
    readonly cbranch="chromeos-${ctag}"
  fi
  if [[ -n "${rbranch}" ]]; then
    readonly ocbranch="${rbranch}"
  else
    readonly ocbranch="${chromeos}/${cbranch}"
  fi

  readonly mcbranch="merge/${cbranch}"

  # Topic to use.
  readonly topic="merge-${dtag}"

  if ! git rev-parse --verify "${ocbranch}" >/dev/null 2>&1; then
    usage "Invalid tag '${tag}': No such branch: '${ocbranch}'"
  fi

  # mbranch: Local branch used to execute the merge.
  readonly mbranch="${mcbranch}-${dtag}"

  # Determine namespace to use if not provided
  if [[ -z "${namespace}" ]]; then
    if [[ "${tag}" == "${vtag}" ]]; then
      namespace="stable-merge/linux"
    else
      namespace="merge"
    fi
  fi

  # obranch: chromeos branch used as reference.
  # May include local reverts from merge if necessary.
  # If necessary, a branch with this name will be created locally and
  # in the chromeos repository. It is necessary to perform the merge.
  readonly obranch="${namespace}/${dtag}"

  if [[ ${do_dryrun} -ne 0 ]]; then
    readonly dryrun="--dry-run"
  fi

  Subject="CHROMIUM: ${Subject:-Merge '${tag}' into ${cbranch}}"
}

have_version() {
  local tag
  local tot_tag
  local index
  local v1
  local v2
  local vtag

  tag=$1
  vtag=$(echo "${tag}" | grep -E "${PATTERN}")
  if [[ "${tag}" != "${vtag}" ]]; then
    # Not a release tag, can not evaluate.
    return 0
  fi

  tot_tag=$(git describe --match "v[2-9].*[0-9]" --abbrev=0 "${ocbranch}")

  index=1
  while true; do
    v1=$(echo "${tag}" | cut -f${index} -d. | sed -e 's/[^0-9]//g')
    v2=$(echo "${tot_tag}" | cut -f${index} -d. | sed -e 's/[^0-9]//g')
    # If both version numbers are empty, we reached the end of the
    # version number string, and the versions are equal.
    # Return true.
    if [[ -z "${v1}" && -z "${v2}" ]]; then
      return 1
    fi
    # Interpret empty minor version numbers as version 0.
    if [[ -z "${v1}" ]]; then
      v1=0
    fi
    if [[ -z "${v2}" ]]; then
      v2=0
    fi
    # If ToT version is larger than tag, return true.
    if [[ ${v2} -gt ${v1} ]]; then
      return 1
    fi
    # If tag version is targer than ToT, return false.
    if [[ ${v2} -lt ${v1} ]]; then
      return 0
    fi
    index=$((index + 1))
  done
}

# Remove double quotes from beginning and end of a string, and
# remove the escape character from double quotes within the string.
dequote() {
  local tmp="${1#\"}"    # beginning
  tmp="${tmp%\"}"        # end
  echo "${tmp//\\\"/\"}" # remove embedded escape characters
}

# Try to find the merge CL.
# Walk through all CLs tagged with the merge topic
# and try to find one with the expected subject line.
# If found, set merge_cl to the respective value for later use.
find_merge_cl() {
  local cls
  local cl
  local subject

  cls=($(gerrit --json search "hashtag:${topic}" \
                    | jq ".[].number" | sed -e 's/"//g'))

  for cl in "${cls[@]}"; do
    subject=$(dequote "$(gerrit --json search "change:${cl}" \
                         | jq ".[].subject")")
    if [[ "${subject}" == "${Subject}" ]]; then
      merge_cl="${cl}"
      break
    fi
  done
}

# Prepare for merge.
# - Update remotes.
# - Verify that tag exists.
# - Search for merge in gerrit. If it exists, validate bug ID and Change-Id.
# - Push tag and reference branch into CrOS repository if necessary.
do_prepare() {
  local vtag
  local obug
  local ochangeid
  local odependency
  local ref

  find_merge_cl

  printf "Updating ${chromeos}..."
  git fetch "${chromeos}" > /dev/null
  printf "\nUpdating ${mcbranch} ..."
  if git rev-parse --verify "${mcbranch}" >/dev/null 2>&1; then
    if ! git checkout "${mcbranch}" >/dev/null 2>&1; then
      die "Failed to check out '${mcbranch}'."
    fi
    git pull >/dev/null
  else
    if ! git checkout -b "${mcbranch}" "${ocbranch}"; then
      die "Failed to create '${mcbranch}' from '${ocbranch}'."
    fi
  fi
  echo

  # Abort if chromeos already includes the tag unless 'force' is set.
  if ! have_version "${dtag}"; then
    if [[ ${force} -eq 0 ]]; then
      die "Tag or reference '${tag}' already in '${ocbranch}'."
    fi
    echo "Warning: Tag '${tag}' already in '${ocbranch}'."
    echo "Will not merge/notify/prepare/upload."
    skip_merge=1
    prepare=0
    notify=0
    upload=0
  fi

  if [[ -n "${merge_cl}" ]]; then
    ref=$(dequote "$(gerrit --json search "change:${merge_cl}" \
                     | jq ".[].currentPatchSet.ref")")
  fi
  if [[ -n "${ref}" ]]; then
    if ! git fetch "${chromeos}" "${ref}" >/dev/null 2>&1; then
      die "Failed to fetch '${ref}' from '${chromeos}'."
    fi
    git show -s --format=%B FETCH_HEAD > "${tmpfile}"
  else
    # We may have a local merge branch.
    if git rev-parse --verify "${mbranch}" >/dev/null 2>&1; then
      local subject

      # Make sure the branch actually includes the merge we are looking for.
      git show -s --format=%B "${mbranch}" > "${tmpfile}"
      subject="$(head -n 1 "${tmpfile}")"
      if [[ "${subject}" != "${Subject}" ]]; then
        rm -f "${tmpfile}"
        touch "${tmpfile}"
      fi
    else
      rm -f "${tmpfile}"
      touch "${tmpfile}"
    fi
  fi
  obug=$(grep "^BUG=" "${tmpfile}")
  if [[ -n "${bug}" && -n "${obug}" && "${bug}" != "${obug}" \
          && ${force} -eq 0 ]]; then
    die "Bug mismatch: '${bug}' <-> '${obug}'. Use -f to override."
  fi
  if [[ -z "${bug}" ]]; then
    bug="${obug}"
  fi
  if [[ -z "${bug}" ]]; then
    die "New merge: must specify bug ID."
  fi
  ochangeid=$(grep "^Change-Id:" "${tmpfile}")
  if [[ -n "${changeid}" && -n "${ochangeid}" \
          && "${changeid}" != "${ochangeid}" && ${force} -eq 0 ]]; then
    die "Change-Id mismatch: '${changeid}' <-> '${ochangeid}'. Use -f to override."
  fi
  if [[ -z "${changeid}" ]]; then
    changeid="${ochangeid}"
  fi

  odependency=$(grep "^Cq-Depend:" "${tmpfile}")
  if [[ -n "${dependency}" && -n "${odependency}" && \
        "${dependency}" != "${odependency}" && ${force} -eq 0 ]]; then
    die "Dependency mismatch: '${dependency}' <-> '${odependency}'. Use -f to override."
  fi
  if [[ -z "${dependency}" ]]; then
    dependency="${odependency}"
  fi

  # Check out local reference branch; create it if needed.
  # It will be retained since it may be needed to apply reverts
  # prior to executing the merge.
  # It is the responsibility of the user to remove it after it is
  # no longer needed.
  # Note: git rev-parse returns success if ${obranch} includes an
  # abbreviated SHA. It also returns success if a _remote_ branch
  # with the same name exists. So let's use show-ref instead.
  # if ! git rev-parse --verify --quiet "${obranch}"; then
  if ! git show-ref --verify --quiet "refs/heads/${obranch}"; then
    if ! git checkout -b "${obranch}" "${tag}"; then
      die "Failed to create '${obranch}' from '${tag}'."
    fi
  else
    if ! git checkout "${obranch}"; then
      die "Failed to check out '${obranch}'."
    fi
  fi

  if [[ ${prepare} -ne 0 ]]; then
    # Push reference branch as well as the tag into the CrOS repository.
    # Assume linear changes only; if the reference branch is reparented,
    # the user has to explicitly update or remove the remote branch.
    # Only push tag if it is a release tag; otherwise we neither want nor
    # need it in the CrOS repository.
    vtag=$(echo "${tag}" | grep -E "${PATTERN}")
    if [[ -n "${vtag}" ]]; then
      git push ${git_skip_validation} --no-verify ${dryrun} "${chromeos}" "refs/tags/${tag}"
    else
      echo "${tag} is not a release tag, not pushed"
    fi
    if ! git push ${git_skip_validation} --no-verify ${dryrun} "${chromeos}" "${obranch}"; then
      die "Failed to upload '${obranch}' into '${chromeos}'."
    fi
  fi
}

gitismerge()
{
    local sha="$1"
    local msha

    msha=$(git rev-list -1 --merges "${sha}"~1.."${sha}")
    [[ -n "$msha" ]]
}

# Apply patches from gerrit CLs into merge branch.
do_apply_changes() {
  local cl
  local ref

  for cl in "${changes[@]}"; do
    echo "Applying CL:${cl}"
    ref=$(dequote "$(gerrit --json search "change:${cl}" \
                     | jq ".[].currentPatchSet.ref" | head -n1)")
    if [[ -z "${ref}" ]]; then
      die "Patch set for CL:${cl} not found."
    fi
    if ! git fetch "${chromeos}" "${ref}" >/dev/null 2>&1; then
      die "Failed to fetch CL:${cl}."
    fi
    if gitismerge FETCH_HEAD; then
      # git cherry-pick -m <parent> does not work since it pulls in
      # the merge as single commit. This messes up history and was
      # seen to result in obscure and avoidable conflicts.
      if ! git merge --no-edit FETCH_HEAD; then
        die "Failed to merge CL:${cl} into merge branch."
      fi
    else
      if ! git cherry-pick FETCH_HEAD; then
        die "Failed to cherry-pick CL:${cl} into merge branch."
      fi
    fi
  done
}

# Apply reverts from list of SHAs from merge branch prior to
# the actual merge
do_apply_reverts() {
  local revert

  for revert in $*; do
    echo "Reverting commit ${revert}"
    if ! git revert --no-commit "${revert}"; then
      die "Failed to revert commit ${revert} in merge branch."
    fi
  done
}

# Do the merge.
# - Create merge branch.
# - Merge.
# - Handle conflicts [abort if there are unhandled conflicts].
# - Create detailed merge commit log.
do_merge() {
  # xbranch: Name of branch to merge.
  # ref: Baseline reference for request-pull.
  local xbranch
  local ref
  local patch
  local file
  local files
  local revert

  git branch -D "${mbranch}" >/dev/null 2>&1
  if ! git checkout -b "${mbranch}" "${ocbranch}"; then
    die "Failed to create merge branch '${mbranch}'."
  fi

  if [[ ${prepare} -eq 0 ]]; then
    xbranch="${obranch}"
  else
    xbranch="${chromeos}/${obranch}"
  fi

  if [[ -n "${prereverts[@]}" ]]; then
    do_apply_reverts ${prereverts[@]}
  fi

  do_apply_changes
  ref=$(git rev-parse HEAD)

  # Do the merge.
  # Use --no-ff to ensure this is always handled as merge, even for linear
  # merges. Otherwise linear merges would succeed and move the branch HEAD
  # forward even though --no-commit is specified. This lets us add an
  # explicit merge commit log.
  conflicts=()
  if ! git merge --no-commit --no-ff "${xbranch}" > "${tmpfile}"; then
    files=$(git rerere status)
    if [[ -n "${files}" ]]; then
      error "Unresolved conflicts:"
      for file in ${files}; do
        echo "    ${file}"
      done
      die "Please resolve conflicts, commit changes, and then rerun the merge script.\nMake sure you have 'git rerere' enabled."
    fi
    echo "All conflicts resolved, continuing"
    conflicts=($(grep CONFLICT "${tmpfile}" \
                 | sed -e 's/.*Merge conflict in //'))
  fi

  # Note: The following is no longer needed in recent versions of git.
  # Keep it around since it does not hurt.
  if [[ ${#conflicts[@]} -gt 0 ]]; then
    git add ${conflicts[*]}
  fi

  for patch in "${patches[@]}"; do
    if ! patch -p 1 < "${patch}" >"${tmpfile}"; then
      die "Failed to apply patch ${patch}"
    fi
    if ! git add $(sed -e 's/.* //' "${tmpfile}"); then
      die "Failed to add patched files to git commit list"
    fi
  done

  if ! git commit -s --no-edit; then
    die "Failed to commit merge."
  fi

  if [[ -n "${reverts[@]}" ]]; then
    do_apply_reverts ${reverts[@]}
    if ! git commit --amend --no-edit; then
      die "Failed to commit merge after post-commit reverts."
    fi
  fi

  # Update commit message.

  ( echo "${Subject}"
    echo
    echo "Merge of ${tag} into ${cbranch}"
    echo
  ) > "${tmpfile}"

  # Add conflicts to description.
  if [[ ${#conflicts[@]} -gt 0 ]]; then
    (
      echo "Conflicts:"
      for conflict in "${conflicts[@]}"; do
        echo "    ${conflict}"
      done
      echo
    ) >> "${tmpfile}"
  fi

  # Add reverts to description.
  if [[ -n "${prereverts[@]}${reverts[@]}" ]]; then
    (
      echo "The following patches have been reverted as part of the merge"
      echo "to remove code which is obsolete or no longer applicable."
      echo
      for revert in ${prereverts[@]} ${reverts[@]}; do
        echo "    $(git show --oneline --no-decorate -s ${revert})"
      done
      echo
    ) >> "${tmpfile}"
  fi

  if [[ -n "$(git log --oneline "${tag}..${obranch}")" ]]; then
    ( echo "Changes applied on top of '${tag}' prior to merge:"
      git log --oneline --no-decorate "${tag}..${obranch}" | \
                        sed -e 's/^/    /'
      echo
    ) >> "${tmpfile}"
  fi

  ( echo "Changelog:"
    git request-pull "${ref}" . | \
                        sed -n '/^--------------/,$p'

    echo

    echo "${bug}"
    echo "TEST=Build and test on various affected systems"
    echo
    if [[ -n "${dependency}" ]]; then
      echo "${dependency}"
    fi
    if [[ -n "${changeid}" ]]; then
      echo "${changeid}"
    fi
  ) >> "${tmpfile}"

  # Amend commit with the updated description.
  if ! git commit -s --amend -F "${tmpfile}"; then
    die "Failed to amend merge with commit log."
  fi
}

do_notify() {
  local cl
  local email_cc
  local cc_notify_cc
  local subject
  local message
  local lbug
  local tdeadline

  if [[ -z "${merge_cl}" ]]; then
    die "No merge CL, can not send notifications."
  fi

  gerrit --json search "change:${merge_cl}" > "${tmpfile}"

  cl=$(dequote "$(jq ".[].number" "${tmpfile}")")
  if [[ -z "${cl}" ]]; then
    die "Missing CL for topic '${topic}' (upload into gerrit first)."
  fi

  subject=$(dequote "$(jq ".[].subject" "${tmpfile}")")
  message=$(dequote "$(jq ".[].commitMessage" "${tmpfile}" \
                       | sed -e 's/\\n/\n/g')")
  email_cc=$(dequote "$(jq ".[].owner.email" "${tmpfile}")")
  if [[ -n "${email_cc}" ]]; then
    email_cc="-cc=${email_cc}"
  fi

  if [[ -n "${notify_cc}" ]]; then
    cc_notify_cc="--cc=${notify_cc}"
  fi

  if [[ "${bug##BUG=b:}" != "${bug}" ]]; then          # buganizer
    lbug="https://b.corp.google.com/${bug##BUG=b:}"
  elif [[ "${bug##BUG=chromium:}" != "${bug}" ]]; then # crbug
    lbug="https://crbug.com/${bug##BUG=chromium:}"
  else                                                 # unknown/invalid
    lbug="${bug##BUG=}"
  fi

  tdeadline=$(($(date +%s) + deadline * 86400))

  cat <<-EOF > "${tmpfile}"
Subject: Review request: "${subject}"

This is the start of the review cycle for the merge of stable release
${tag} into ${cbranch}. If anyone has issues or concerns
with this stable release being applied, please let me know.

Bug: ${lbug}
Code review: https://chromium-review.googlesource.com/#/q/${cl}

Responses should be made by $(date --date="@${tdeadline}").
Anything received after that time might be too late.

Commit message and changelog are as follows.

${message}
EOF

  if ! git send-email ${dryrun} --to="${notify_to}" "${cc_notify_cc}" "${email_cc}" \
          --8bit-encoding="UTF-8" \
          --suppress-cc=all "${tmpfile}"; then
    die "Failed to send notification e-mail to '${notify_to}'."
  fi
}

do_upload() {
  if [[ ${upload} -ne 0 ]]; then
    if ! git push --no-verify ${dryrun} "${chromeos}" "${mbranch}:refs/for/${cbranch}%t=${topic}"; then
      die "Failed to upload changes into '${chromeos}'."
    fi
  elif [[ ${prepare} -ne 0 ]]; then
    echo "Push into ${chromeos} using the following command:"
    echo "    git push --no-verify ${chromeos} ${mbranch}:refs/for/${cbranch}%t=${topic}"
  fi
}

main() {
  do_getparams "$@"
  do_validate
  do_validate_changeids
  do_setup
  do_prepare
  if [[ ${skip_merge} -eq 0 ]]; then
    do_merge
    do_upload
  fi
  if [[ ${notify} -ne 0 ]]; then
    find_merge_cl
    do_notify
  fi

  exit 0
}

main "$@"