contrib/debugshell.py

commands: add debugdeltachain command

We have debug commands for displaying overall revlog statistics
(debugrevlog) and for dumping a revlog index (debugindex). As part
of investigating various aspects of revlog behavior and performance,
I found it important to have an understanding of how revlog
delta chains behave in practice.

This patch implements a "debugdeltachain" command. For each revision
in a revlog, it dumps information about the delta chain. Which delta
chain it is part of, length of the delta chain, distance since base
revision, info about base revision, size of the delta chain, etc. The
generic formatting facility is used, which means we can templatize
output and get machine readable output like JSON.

This command has already uncovered some weird history in
mozilla-central I didn't know about. So I think it's valuable.

# debugshell extension
"""a python shell with repo, changelog & manifest objects"""

import sys
import mercurial
import code
from mercurial import cmdutil

cmdtable = {}
command = cmdutil.command(cmdtable)

def pdb(ui, repo, msg, **opts):
    objects = {
        'mercurial': mercurial,
        'repo': repo,
        'cl': repo.changelog,
        'mf': repo.manifest,
    }

    code.interact(msg, local=objects)

def ipdb(ui, repo, msg, **opts):
    import IPython

    cl = repo.changelog
    mf = repo.manifest
    cl, mf # use variables to appease pyflakes

    IPython.embed()

@command('debugshell|dbsh', [])
def debugshell(ui, repo, **opts):
    bannermsg = "loaded repo : %s\n" \
                "using source: %s" % (repo.root,
                                      mercurial.__path__[0])

    pdbmap = {
        'pdb'  : 'code',
        'ipdb' : 'IPython'
    }

    debugger = ui.config("ui", "debugger")
    if not debugger:
        debugger = 'pdb'

    # if IPython doesn't exist, fallback to code.interact
    try:
        __import__(pdbmap[debugger])
    except ImportError:
        ui.warn("%s debugger specified but %s module was not found\n"
                % (debugger, pdbmap[debugger]))
        debugger = 'pdb'

    getattr(sys.modules[__name__], debugger)(ui, repo, bannermsg, **opts)