Re: [RFC] clang-format: outline the git project's coding style

Hi all,

On Thu, 10 Aug 2017, Johannes Schindelin wrote:

FWIW I just set this up in my VSTS account, with the following build step (performed in one of the Hosted Linux agents, i.e. I do not even have to have a VM dedicated to the task):

-- snip --
die () {
    echo "$*" >&2
    exit 1
}

head=$(git rev-parse HEAD) || die "Could not determine HEAD"

test -n "$BUILD_SOURCEBRANCHNAME" || die "Need a source branch name to work with"

base=$(git merge-base origin/core/master HEAD) && count=$(git rev-list --count $base..) && test 0 -lt $count || die "Could not determine commits to clean up (count: $count)"

test -f .clang-format || git show origin/core/pu/.clang-format >.clang-format || die "Need a .clang-format"

sudo add-apt-repository 'deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial main' && sudo apt-get update && sudo apt-get --allow-unauthenticated -y install clang-format-6.0 || die "Could not install clang-format 6.0"

git filter-branch -f --tree-filter \
    'git diff HEAD^.. |
     clang-format-diff-6.0 -p 1 -i &&

     git update-index --refresh --ignore-submodules &&
     git diff-files --quiet --ignore-submodules ||
     git commit --amend -C HEAD' $base.. ||
die "Could not rewrite branch"

if test "$head" = "$(git rev-parse HEAD)"
then
    echo "No changes in $BUILD_SOURCEBRANCHNAME introduced by clang-format" >&2
else
    git push vsts +HEAD:refs/heads/clang-format/"$BUILD_SOURCEBRANCHNAME" ||
    die "Could not push clang-format/$BUILD_SOURCEBRANCHNAME"
    echo "Clean branch pushed as clang-format/$BUILD_SOURCEBRANCHNAME" >&2
    exit 123
fi
-- snap --

A couple of notes for the interested:

- you can easily set this up for yourself, as Visual Studio Team Services
  is free for small teams up to five people (including single developer
  "teams"): https://www.visualstudio.com/team-services/, and of course you
  can back it by your own git.git fork on GitHub, no need to host the code
  in VSTS.

  Disclaimer: I work closely with the developers behind Visual Studio Team
  Services, and I am a genuine fan, yet I understand if anybody thinks of
  this as advertising the service, so this will be the only time I mention
  this.

- the script assumes that there is a `core/master` tracking upstream Git's
  master branch, then reformats the commits in the current branch that are
  not also reachable from core/master.

- The push credentials to push the result at the end are of course not
  included in the script, they need to be provided separately.

- the exit code 123 when the branch needed to be rewritten indicates to
  any consumer that the build "failed". The reason is that I want to
  integrate this into a system where I open a PR in my own account, which
  triggers the build automatically contingent on the base branch being
  core/master, and if the build fails, the PR gets "blocked", providing a
  very easy way to see that there is still work to be done.

- for the moment, I do not push back to the original branch, even if I
  could. The reason is that already my first test produced a dubious
  result, see below.

I am reasonably happy with the way this build job works right now, especially given that I do not have to mess up any other setup I have just to get the bleeding edge version of Clang.

Now for the dubious result.

I took my most recent contribution, the lazyload one (which you can easily get yourself by fetching the lazyload-v2 tag from https://github.com/dscho/git), because it was pretty self-contained and small, only one patch. With the current .clang-format as per git.git's master (or for that matter, pu, as they are identical), the output `git show | clang-format-diff-6.0 -p 1` ends in this hunk:

-- snip --