Add a git hook script that can be manually setup to run some checks on every push

Right now it just catches arcanist noisy tags, and include a script to
automatically clean these.

Follow up on http://lists.llvm.org/pipermail/llvm-dev/2019-December/137848.html

Differential Revision: https://reviews.llvm.org/D80978

llvm/docs/GettingStarted.rst

@@ -528,6 +528,17 @@ that include merges, so the `git rebase` step above is required.
 
 Please ask for help if you're having trouble with your particular git workflow.
 
+Git pre-push hook
+^^^^^^^^^^^^^^^^^
+
+We include an optional pre-push hook that run some sanity checks on the revisions
+you are about to push and ask confirmation if you push multiple commits at once.
+You can set it up (on Unix systems) by running from the repository root:
+
+.. code-block:: console
+
+  % ln -sf ../../llvm/utils/git/pre-push.py .git/hooks/pre-push
+
 Bisecting commits
 ^^^^^^^^^^^^^^^^^
 

llvm/docs/Phabricator.rst

@@ -183,6 +183,13 @@ that you close the review manually. In the web UI, under "Leap Into Action" put
 the git revision number in the Comment, set the Action to "Close Revision" and
 click Submit.  Note the review must have been Accepted first.
 
+Arcanist also adds extra tags that are mostly noise in the commit message, for
+this reason avoid using `arc land` and push commits to master directly with git
+after removing tags other than "Reviewed by" and "Differential Revision".
+You can run `llvm/utils/git/arcfilter.sh` to clean the commit message of the
+current "HEAD" commit automatically. You can also setup a git hook to catch this
+for you (see `Getting Started <GettingStarted.html#git-pre-push-hook>`).
+
 
 Committing someone's change from Phabricator
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -217,12 +224,6 @@ the following:
   ninja check-$whatever # Rerun the appropriate tests if needed.
   git push https://github.com/llvm/llvm-project.git HEAD:master
 
-Or
-
-::
-
-  arc land D<Revision>
-
 
 Abandoning a change
 -------------------

llvm/utils/git/arcfilter.sh

+#!/bin/sh
+
+# Remove the phabricator tags from the commit at HEAD
+git log -1 --pretty=%B | \
+  sed  's/^Summary://'  | \
+  awk '/Reviewers:|Subscribers:/{p=1} /Reviewed By:|Differential Revision:/{p=0} !p && !/^Summary:$/ {sub(/^Summary: /,"");print}' | \
+  git commit --amend --date=now -F -

llvm/utils/git/pre-push.py

+#!/usr/bin/env python3
+#
+# ======- pre-push - LLVM Git Help Integration ---------*- python -*--========#
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# ==------------------------------------------------------------------------==#
+
+"""
+pre-push git hook integration
+=============================
+
+This script is intended to be setup as a pre-push hook, from the root of the
+repo run:
+
+   ln -sf ../../llvm/utils/git/pre-push.py .git/hooks/pre-push
+
+From the git doc:
+
+  The pre-push hook runs during git push, after the remote refs have been
+  updated but before any objects have been transferred. It receives the name
+  and location of the remote as parameters, and a list of to-be-updated refs
+  through stdin. You can use it to validate a set of ref updates before a push
+  occurs (a non-zero exit code will abort the push).
+"""
+
+import argparse
+import collections
+import os
+import re
+import shutil
+import subprocess
+import sys
+import time
+import getpass
+from shlex import quote
+
+VERBOSE = False
+QUIET = False
+dev_null_fd = None
+z40 = '0000000000000000000000000000000000000000'
+
+
+def eprint(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+
+def log(*args, **kwargs):
+    if QUIET:
+        return
+    print(*args, **kwargs)
+
+
+def log_verbose(*args, **kwargs):
+    if not VERBOSE:
+        return
+    print(*args, **kwargs)
+
+
+def die(msg):
+    eprint(msg)
+    sys.exit(1)
+
+
+def ask_confirm(prompt):
+    while True:
+        query = input('%s (y/N): ' % (prompt))
+        if query.lower() not in ['y', 'n', '']:
+           print('Expect y or n!')
+           continue
+        return query.lower() == 'y'
+
+
+def get_dev_null():
+    """Lazily create a /dev/null fd for use in shell()"""
+    global dev_null_fd
+    if dev_null_fd is None:
+        dev_null_fd = open(os.devnull, 'w')
+    return dev_null_fd
+
+
+def shell(cmd, strip=True, cwd=None, stdin=None, die_on_failure=True,
+          ignore_errors=False, text=True, print_raw_stderr=False):
+    # Escape args when logging for easy repro.
+    quoted_cmd = [quote(arg) for arg in cmd]
+    cwd_msg = ''
+    if cwd:
+      cwd_msg = ' in %s' % cwd
+    log_verbose('Running%s: %s' % (cwd_msg, ' '.join(quoted_cmd)))
+
+    err_pipe = subprocess.PIPE
+    if ignore_errors:
+        # Silence errors if requested.
+        err_pipe = get_dev_null()
+
+    start = time.time()
+    p = subprocess.Popen(cmd, cwd=cwd, stdout=subprocess.PIPE, stderr=err_pipe,
+                         stdin=subprocess.PIPE,
+                         universal_newlines=text)
+    stdout, stderr = p.communicate(input=stdin)
+    elapsed = time.time() - start
+
+    log_verbose('Command took %0.1fs' % elapsed)
+
+    if p.returncode == 0 or ignore_errors:
+        if stderr and not ignore_errors:
+            if not print_raw_stderr:
+                eprint('`%s` printed to stderr:' % ' '.join(quoted_cmd))
+            eprint(stderr.rstrip())
+        if strip:
+            if text:
+                stdout = stdout.rstrip('\r\n')
+            else:
+                stdout = stdout.rstrip(b'\r\n')
+        if VERBOSE:
+            for l in stdout.splitlines():
+                log_verbose('STDOUT: %s' % l)
+        return stdout
+    err_msg = '`%s` returned %s' % (' '.join(quoted_cmd), p.returncode)
+    eprint(err_msg)
+    if stderr:
+        eprint(stderr.rstrip())
+    if die_on_failure:
+        sys.exit(2)
+    raise RuntimeError(err_msg)
+
+
+def git(*cmd, **kwargs):
+    return shell(['git'] + list(cmd), **kwargs)
+
+
+def get_revs_to_push(range):
+    commits = git('rev-list', range).splitlines()
+    # Reverse the order so we print the oldest commit first
+    commits.reverse()
+    return commits
+
+
+def handle_push(args, local_ref, local_sha, remote_ref, remote_sha):
+    '''Check a single push request (which can include multiple revisions)'''
+    log_verbose('Handle push, reproduce with '
+                '`echo %s %s %s %s | pre-push.py %s %s'
+                 % (local_ref, local_sha, remote_ref, remote_sha, args.remote,
+                    args.url))
+    # Handle request to delete
+    if local_sha == z40:
+        if not ask_confirm('Are you sure you want to delete "%s" on remote "%s"?' % (remote_ref, args.url)):
+            die("Aborting")
+        return
+
+    # Push a new branch
+    if remote_sha == z40:
+      if not ask_confirm('Are you sure you want to push a new branch/tag "%s" on remote "%s"?' % (remote_ref, args.url)):
+        die("Aborting")
+      range=local_sha
+      return
+    else:
+      # Update to existing branch, examine new commits
+      range='%s..%s' % (remote_sha, local_sha)
+      # Check that the remote commit exists, otherwise let git proceed
+      if "commit" not in git('cat-file','-t', remote_sha, ignore_errors=True):
+          return
+
+    revs = get_revs_to_push(range)
+    if not revs:
+        # This can happen if someone is force pushing an older revision to a branch
+        return
+
+    # Print the revision about to be pushed commits
+    print('Pushing to "%s" on remote "%s"' % (remote_ref, args.url))
+    for sha in revs:
+      print(' - ' + git('show', '--oneline', '--quiet', sha))
+
+    if len(revs) > 1:
+      if not ask_confirm('Are you sure you want to push %d commits?' % len(revs)):
+          die('Aborting')
+
+
+    for sha in revs:
+      msg = git('log', '--format=%B', '-n1', sha)
+      if 'Differential Revision' not in msg:
+          continue
+      for line in msg.splitlines():
+          for tag in ['Summary', 'Reviewers', 'Subscribers', 'Tags']:
+            if line.startswith(tag + ':'):
+              eprint('Please remove arcanist tags from the commit message (found "%s" tag in %s)' % (tag, sha[:12]))
+              if len(revs) == 1:
+                  eprint('Try running: llvm/utils/git/arcfilter.sh')
+              die('Aborting (force push by adding "--no-verify")')
+
+    return
+
+
+if __name__ == '__main__':
+    if not shutil.which('git'):
+        die('error: cannot find git command')
+
+    argv = sys.argv[1:]
+    p = argparse.ArgumentParser(
+        prog='pre-push', formatter_class=argparse.RawDescriptionHelpFormatter,
+        description=__doc__)
+    verbosity_group = p.add_mutually_exclusive_group()
+    verbosity_group.add_argument('-q', '--quiet', action='store_true',
+                                 help='print less information')
+    verbosity_group.add_argument('-v', '--verbose', action='store_true',
+                                 help='print more information')
+
+    p.add_argument('remote', type=str, help='Name of the remote')
+    p.add_argument('url', type=str, help='URL for the remote')
+
+    args = p.parse_args(argv)
+    VERBOSE = args.verbose
+    QUIET = args.quiet
+
+    lines = sys.stdin.readlines()
+    sys.stdin = open('/dev/tty', 'r')
+    for line in lines:
+      local_ref, local_sha, remote_ref, remote_sha = line.split()
+      handle_push(args, local_ref, local_sha, remote_ref, remote_sha)