bisect-merges

#!/usr/bin/env python

import json
import optparse
import os
import subprocess
import sys


def gitdir():
    """Return the path to the current git repo's .git directory."""
    proc = subprocess.Popen(["git", "rev-parse", "--git-dir"],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    stdout, stderr = proc.communicate()

    if proc.returncode:
        raise RuntimeError("rev-parse --git-dir returned nonzero (%d):\n%s" % (proc.returncode, stderr))

    return stdout.strip()


def revparse(rev):
    """Resolves a shaish into a sha via git-rev-parse."""
    if not rev:
        raise ValueError("revparse() needs a valid shaish to parse.")

    proc = subprocess.Popen(["git", "rev-parse", "--verify", "--quiet", rev],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    stdout, stderr = proc.communicate()

    if proc.returncode:
        raise RuntimeError("rev-parse %s returned nonzero (%d):\n%s" % (rev, proc.returncode, stderr))

    return stdout.strip()


def namerev(rev):
    """Resolves a shaish into a name via git-name-rev."""
    if not rev:
        raise ValueError("namerev() needs a valid shaish to parse.")

    proc = subprocess.Popen(["git", "name-rev", "--name-only", rev],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    stdout, stderr = proc.communicate()

    if proc.returncode:
        raise RuntimeError("name-rev %s returned nonzero (%d):\n%s" % (rev, proc.returncode, stderr))

    return stdout.strip()


def revlist(start, end, *args):
    """Returns a list of revisions in start..end (as git-rev-list yields).

    Any extra arguments are passed to the git subprocess as arguments."""
    if not start:
        raise ValueError("revlist() needs a valid start shaish.")

    if not end:
        end = 'HEAD'

    proc = subprocess.Popen(["git", "rev-list"] + list(args) + ["%s..%s" % (start,end)],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    stdout, stderr = proc.communicate()

    if proc.returncode:
        raise RuntimeError("rev-list returned nonzero (%d):\n%s" % (proc.returncode, stderr))

    return stdout.strip().split("\n")


def checkout(rev, *args):
    """Check out a specified shaish in the current git repository.

    Any extra arguments are passed to the git subprocess as arguments."""
    if not rev:
        raise ValueError("checkout() needs a valid shaish to check out.")

    proc = subprocess.Popen(["git", "checkout"] + list(args) + [rev],
        stderr=subprocess.PIPE)
    stdout, stderr = proc.communicate()

    if proc.returncode:
        raise RuntimeError("rev-list returned nonzero (%d):\n%s" % (proc.returncode, stderr))


def write_shalist(git_dir, revisions):
    """Write a list of SHAs to the appropriate file."""

    shalist_path = os.path.join(git_dir, 'BISECT_MERGES_SHALIST')
    shalist_file = open(shalist_path, 'w')
    shalist_file.writelines("%s\n" % r for r in revisions)
    shalist_file.close()


def read_shalist(git_dir):
    """Read in a list of SHAs from the appropriate file."""

    shalist_path = os.path.join(git_dir, 'BISECT_MERGES_SHALIST')

    if not os.path.exists(shalist_path):
        print >> sys.stderr, "There does not seem to be a bisection in progress."
        sys.exit(1)

    shalist_file = open(shalist_path)
    revisions = [line.strip() for line in shalist_file]
    shalist_file.close()
    return revisions


def write_metadata(git_dir, metadata):
    """Write metadata out to the appropriate file."""

    metadata_path = os.path.join(git_dir, 'BISECT_MERGES_INFO')
    metadata_file = open(metadata_path, 'w')
    json.dump(metadata, metadata_file)
    metadata_file.close()


def read_metadata(git_dir):
    """Read metadata out of the appropriate file."""

    metadata_path = os.path.join(git_dir, 'BISECT_MERGES_INFO')

    if not os.path.exists(metadata_path):
        print >> sys.stderr, "There does not seem to be a bisection in progress."
        sys.exit(1)

    metadata_file = open(metadata_path)
    metadata = json.load(metadata_file)
    metadata_file.close()
    return metadata


def bisect_start(opts, args):
    """Starts a bisection.

    1. Verify that both start and end are valid shaish's.
    2. Grab the list of revisions in between them.
    3. Write out the list to .git/BISECT_MERGES_SHALIST
    4. Write out other metadata to .git/BISECT_MERGES_INFO
    5. Check out the middle revision.
    """

    git_dir = gitdir()
    metadata_path = os.path.join(git_dir, 'BISECT_MERGES_INFO')
    shalist_path = os.path.join(git_dir, 'BISECT_MERGES_SHALIST')
    if os.path.exists(shalist_path) or os.path.exists(metadata_path):
        print >> sys.stderr, "Aborting 'start': There appears to already be a bisection in process."
        sys.exit(1)

    current_branch = namerev('HEAD')

    start = revparse(args[1])
    if len(args) > 2:
        end = revparse(args[2])
    else:
        end = revparse('HEAD')

    revisions = revlist(start, end, '--first-parent')

    print "Bisecting %d revisions." % len(revisions)

    write_shalist(git_dir, revisions)
    write_metadata(git_dir, {'previous_checkout': current_branch})

    checkout(revisions[len(revisions) // 2])

    if not opts.quiet:
        print "Checked out first candidate. Use '%s good' or '%s bad' to mark appropriately after testing." % (sys.argv[0], sys.argv[0])
        print "(You can also use '%s abort' to stop bisecting and return to where you where before.)" % sys.argv[0]


def bisect_abort(opts, args):
    """Abort the current bisection and go back to where we were before."""

    git_dir = gitdir()
    metadata = read_metadata(git_dir)

    metadata_path = os.path.join(git_dir, 'BISECT_MERGES_INFO')
    shalist_path = os.path.join(git_dir, 'BISECT_MERGES_SHALIST')
    if os.path.exists(shalist_path):
        os.unlink(shalist_path)
    os.unlink(metadata_path)

    print "Aborting bisection, checking out previous (%s) ..." % metadata['previous_checkout']

    checkout(metadata['previous_checkout'])


def bisect_mark(opts, args):
    """Mark the current revision as either good or bad and continue the bisection."""

    git_dir = gitdir()
    revisions = read_shalist(git_dir)

    head = revparse('HEAD')
    index = revisions.index(head)
    if args[0] == 'good':
        # Good revision means we want to pare off this rev and everything before it
        # in time (after it in the list)
        revisions = revisions[:index]
    else:
        # Bad revision means we want to pare off everything after this rev in time
        # (before it in the list)
        revisions = revisions[index:]

    if len(revisions) > 1:
        print "%d revisions left to bisect." % len(revisions)

        write_shalist(git_dir, revisions)
        checkout(revisions[len(revisions) // 2])

        if not opts.quiet:
            print "Checked next first candidate. Use '%s good' or '%s bad' to mark appropriately after testing." % (sys.argv[0], sys.argv[0])
            print "(You can also use '%s abort' to stop bisecting and return to where you where before.)" % sys.argv[0]
    else:
        earliest_bad = revisions[0]
        if head != earliest_bad:
            checkout(earliest_bad)
        print "Done bisecting. Earliest bad revision (%s) has been checked out." % earliest_bad[:7]

        shalist_path = os.path.join(git_dir, 'BISECT_MERGES_SHALIST')
        if os.path.exists(shalist_path):
            os.unlink(shalist_path)

        metadata_path = os.path.join(git_dir, 'BISECT_MERGES_INFO')
        if os.path.exists(metadata_path):
            os.unlink(metadata_path)

def main():
    usage = "Usage: %prog [options] [start <known-good> [<known-bad>] | good | bad | abort]"
    parser = optparse.OptionParser(usage)

    parser.add_option("-q", "--quiet", dest="quiet", default=False, action="store_true",
        help="Provide fewer instructions and/or detail.")

    options, arguments = parser.parse_args()

    if not arguments:
        parser.error("You must specify one of: start, good, bad, abort.")

    if arguments[0] == "start":
        if len(arguments) < 2:
            parser.error("Action 'start' must be followed by a known-good shaish.")
        bisect_start(options, arguments)
    elif arguments[0] in ("good", "bad"):
        bisect_mark(options, arguments)
    elif arguments[0] == "abort":
        bisect_abort(options, arguments)
    else:
        parser.error("Unrecognized action '%s' - must be one of: start, good, bad, abort)." % arguments[0])

if __name__ == "__main__":
    main()

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