hgext/show.py

revlog: introduce an experimental flag to slice chunks reads when too sparse

Delta chains can become quite sparse if there is a lot of unrelated data between
relevant pieces. Right now, revlog always reads all the necessary data for the
delta chain in one single read. This can lead to a lot of unrelated data to be
read (see issue5482 for more details).
One can use the `experimental.maxdeltachainspan` option with a large value
(or -1) to easily produce a very sparse delta chain.

This change introduces the ability to slice the chunks retrieval into  multiple
reads, skipping large sections of unrelated data. Preliminary testing shows
interesting results. For example the peak memory consumption to read a manifest
on a large repository is reduced from 600MB to 250MB (200MB without
maxdeltachainspan). However, the slicing itself and the multiple reads can have
an negative impact on performance. This is why the new feature is hidden behind
an experimental flag.

Future changesets will add various parameters to control the slicing heuristics.
We hope to experiment a wide variety of repositories during 4.4 and hopefully
turn the feature on by default in 4.5.
As a first try, the algorithm itself is prone to deep changes. However, we wish
to define APIs and have a baseline to work on.

# show.py - Extension implementing `hg show`
#
# Copyright 2017 Gregory Szorc <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

"""unified command to show various repository information (EXPERIMENTAL)

This extension provides the :hg:`show` command, which provides a central
command for displaying commonly-accessed repository data and views of that
data.

The following config options can influence operation.

``commands``
------------

``show.aliasprefix``
   List of strings that will register aliases for views. e.g. ``s`` will
   effectively set config options ``alias.s<view> = show <view>`` for all
   views. i.e. `hg swork` would execute `hg show work`.

   Aliases that would conflict with existing registrations will not be
   performed.
"""

from __future__ import absolute_import

from mercurial.i18n import _
from mercurial.node import nullrev
from mercurial import (
    cmdutil,
    commands,
    destutil,
    error,
    formatter,
    graphmod,
    phases,
    pycompat,
    registrar,
    revset,
    revsetlang,
)

# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
# be specifying the version(s) of Mercurial they are tested with, or
# leave the attribute unspecified.
testedwith = 'ships-with-hg-core'

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

configtable = {}
configitem = registrar.configitem(configtable)
configitem('commands', 'show.aliasprefix',
    default=list,
)

revsetpredicate = registrar.revsetpredicate()

class showcmdfunc(registrar._funcregistrarbase):
    """Register a function to be invoked for an `hg show <thing>`."""

    # Used by _formatdoc().
    _docformat = '%s -- %s'

    def _extrasetup(self, name, func, fmtopic=None, csettopic=None):
        """Called with decorator arguments to register a show view.

        ``name`` is the sub-command name.

        ``func`` is the function being decorated.

        ``fmtopic`` is the topic in the style that will be rendered for
        this view.

        ``csettopic`` is the topic in the style to be used for a changeset
        printer.

        If ``fmtopic`` is specified, the view function will receive a
        formatter instance. If ``csettopic`` is specified, the view
        function will receive a changeset printer.
        """
        func._fmtopic = fmtopic
        func._csettopic = csettopic

showview = showcmdfunc()

@command('show', [
    # TODO: Switch this template flag to use cmdutil.formatteropts if
    # 'hg show' becomes stable before --template/-T is stable. For now,
    # we are putting it here without the '(EXPERIMENTAL)' flag because it
    # is an important part of the 'hg show' user experience and the entire
    # 'hg show' experience is experimental.
    ('T', 'template', '', ('display with template'), _('TEMPLATE')),
    ], _('VIEW'))
def show(ui, repo, view=None, template=None):
    """show various repository information

    A requested view of repository data is displayed.

    If no view is requested, the list of available views is shown and the
    command aborts.

    .. note::

       There are no backwards compatibility guarantees for the output of this
       command. Output may change in any future Mercurial release.

       Consumers wanting stable command output should specify a template via
       ``-T/--template``.

    List of available views:
    """
    if ui.plain() and not template:
        hint = _('invoke with -T/--template to control output format')
        raise error.Abort(_('must specify a template in plain mode'), hint=hint)

    views = showview._table

    if not view:
        ui.pager('show')
        # TODO consider using formatter here so available views can be
        # rendered to custom format.
        ui.write(_('available views:\n'))
        ui.write('\n')

        for name, func in sorted(views.items()):
            ui.write(('%s\n') % func.__doc__)

        ui.write('\n')
        raise error.Abort(_('no view requested'),
                          hint=_('use "hg show VIEW" to choose a view'))

    # TODO use same logic as dispatch to perform prefix matching.
    if view not in views:
        raise error.Abort(_('unknown view: %s') % view,
                          hint=_('run "hg show" to see available views'))

    template = template or 'show'

    fn = views[view]
    ui.pager('show')

    if fn._fmtopic:
        fmtopic = 'show%s' % fn._fmtopic
        with ui.formatter(fmtopic, {'template': template}) as fm:
            return fn(ui, repo, fm)
    elif fn._csettopic:
        ref = 'show%s' % fn._csettopic
        spec = formatter.lookuptemplate(ui, ref, template)
        displayer = cmdutil.changeset_templater(ui, repo, spec, buffered=True)
        return fn(ui, repo, displayer)
    else:
        return fn(ui, repo)

@showview('bookmarks', fmtopic='bookmarks')
def showbookmarks(ui, repo, fm):
    """bookmarks and their associated changeset"""
    marks = repo._bookmarks
    if not len(marks):
        # This is a bit hacky. Ideally, templates would have a way to
        # specify an empty output, but we shouldn't corrupt JSON while
        # waiting for this functionality.
        if not isinstance(fm, formatter.jsonformatter):
            ui.write(_('(no bookmarks set)\n'))
        return

    revs = [repo[node].rev() for node in marks.values()]
    active = repo._activebookmark
    longestname = max(len(b) for b in marks)
    nodelen = longestshortest(repo, revs)

    for bm, node in sorted(marks.items()):
        fm.startitem()
        fm.context(ctx=repo[node])
        fm.write('bookmark', '%s', bm)
        fm.write('node', fm.hexfunc(node), fm.hexfunc(node))
        fm.data(active=bm == active,
                longestbookmarklen=longestname,
                nodelen=nodelen)

@showview('stack', csettopic='stack')
def showstack(ui, repo, displayer):
    """current line of work"""
    wdirctx = repo['.']
    if wdirctx.rev() == nullrev:
        raise error.Abort(_('stack view only available when there is a '
                            'working directory'))

    if wdirctx.phase() == phases.public:
        ui.write(_('(empty stack; working directory parent is a published '
                   'changeset)\n'))
        return

    # TODO extract "find stack" into a function to facilitate
    # customization and reuse.

    baserev = destutil.stackbase(ui, repo)
    basectx = None

    if baserev is None:
        baserev = wdirctx.rev()
        stackrevs = {wdirctx.rev()}
    else:
        stackrevs = set(repo.revs('%d::.', baserev))

    ctx = repo[baserev]
    if ctx.p1().rev() != nullrev:
        basectx = ctx.p1()

    # And relevant descendants.
    branchpointattip = False
    cl = repo.changelog

    for rev in cl.descendants([wdirctx.rev()]):
        ctx = repo[rev]

        # Will only happen if . is public.
        if ctx.phase() == phases.public:
            break

        stackrevs.add(ctx.rev())

        # ctx.children() within a function iterating on descandants
        # potentially has severe performance concerns because revlog.children()
        # iterates over all revisions after ctx's node. However, the number of
        # draft changesets should be a reasonably small number. So even if
        # this is quadratic, the perf impact should be minimal.
        if len(ctx.children()) > 1:
            branchpointattip = True
            break

    stackrevs = list(sorted(stackrevs, reverse=True))

    # Find likely target heads for the current stack. These are likely
    # merge or rebase targets.
    if basectx:
        # TODO make this customizable?
        newheads = set(repo.revs('heads(%d::) - %ld - not public()',
                                 basectx.rev(), stackrevs))
    else:
        newheads = set()

    allrevs = set(stackrevs) | newheads | set([baserev])
    nodelen = longestshortest(repo, allrevs)

    try:
        cmdutil.findcmd('rebase', commands.table)
        haverebase = True
    except (error.AmbiguousCommand, error.UnknownCommand):
        haverebase = False

    # TODO use templating.
    # TODO consider using graphmod. But it may not be necessary given
    # our simplicity and the customizations required.
    # TODO use proper graph symbols from graphmod

    shortesttmpl = formatter.maketemplater(ui, '{shortest(node, %d)}' % nodelen)
    def shortest(ctx):
        return shortesttmpl.render({'ctx': ctx, 'node': ctx.hex()})

    # We write out new heads to aid in DAG awareness and to help with decision
    # making on how the stack should be reconciled with commits made since the
    # branch point.
    if newheads:
        # Calculate distance from base so we can render the count and so we can
        # sort display order by commit distance.
        revdistance = {}
        for head in newheads:
            # There is some redundancy in DAG traversal here and therefore
            # room to optimize.
            ancestors = cl.ancestors([head], stoprev=basectx.rev())
            revdistance[head] = len(list(ancestors))

        sourcectx = repo[stackrevs[-1]]

        sortedheads = sorted(newheads, key=lambda x: revdistance[x],
                             reverse=True)

        for i, rev in enumerate(sortedheads):
            ctx = repo[rev]

            if i:
                ui.write(': ')
            else:
                ui.write('  ')

            ui.write(('o  '))
            displayer.show(ctx, nodelen=nodelen)
            displayer.flush(ctx)
            ui.write('\n')

            if i:
                ui.write(':/')
            else:
                ui.write(' /')

            ui.write('    (')
            ui.write(_('%d commits ahead') % revdistance[rev],
                     label='stack.commitdistance')

            if haverebase:
                # TODO may be able to omit --source in some scenarios
                ui.write('; ')
                ui.write(('hg rebase --source %s --dest %s' % (
                         shortest(sourcectx), shortest(ctx))),
                         label='stack.rebasehint')

            ui.write(')\n')

        ui.write(':\n:    ')
        ui.write(_('(stack head)\n'), label='stack.label')

    if branchpointattip:
        ui.write(' \\ /  ')
        ui.write(_('(multiple children)\n'), label='stack.label')
        ui.write('  |\n')

    for rev in stackrevs:
        ctx = repo[rev]
        symbol = '@' if rev == wdirctx.rev() else 'o'

        if newheads:
            ui.write(': ')
        else:
            ui.write('  ')

        ui.write(symbol, '  ')
        displayer.show(ctx, nodelen=nodelen)
        displayer.flush(ctx)
        ui.write('\n')

    # TODO display histedit hint?

    if basectx:
        # Vertically and horizontally separate stack base from parent
        # to reinforce stack boundary.
        if newheads:
            ui.write(':/   ')
        else:
            ui.write(' /   ')

        ui.write(_('(stack base)'), '\n', label='stack.label')
        ui.write(('o  '))

        displayer.show(basectx, nodelen=nodelen)
        displayer.flush(basectx)
        ui.write('\n')

@revsetpredicate('_underway([commitage[, headage]])')
def underwayrevset(repo, subset, x):
    args = revset.getargsdict(x, 'underway', 'commitage headage')
    if 'commitage' not in args:
        args['commitage'] = None
    if 'headage' not in args:
        args['headage'] = None

    # We assume callers of this revset add a topographical sort on the
    # result. This means there is no benefit to making the revset lazy
    # since the topographical sort needs to consume all revs.
    #
    # With this in mind, we build up the set manually instead of constructing
    # a complex revset. This enables faster execution.

    # Mutable changesets (non-public) are the most important changesets
    # to return. ``not public()`` will also pull in obsolete changesets if
    # there is a non-obsolete changeset with obsolete ancestors. This is
    # why we exclude obsolete changesets from this query.
    rs = 'not public() and not obsolete()'
    rsargs = []
    if args['commitage']:
        rs += ' and date(%s)'
        rsargs.append(revsetlang.getstring(args['commitage'],
                                           _('commitage requires a string')))

    mutable = repo.revs(rs, *rsargs)
    relevant = revset.baseset(mutable)

    # Add parents of mutable changesets to provide context.
    relevant += repo.revs('parents(%ld)', mutable)

    # We also pull in (public) heads if they a) aren't closing a branch
    # b) are recent.
    rs = 'head() and not closed()'
    rsargs = []
    if args['headage']:
        rs += ' and date(%s)'
        rsargs.append(revsetlang.getstring(args['headage'],
                                           _('headage requires a string')))

    relevant += repo.revs(rs, *rsargs)

    # Add working directory parent.
    wdirrev = repo['.'].rev()
    if wdirrev != nullrev:
        relevant += revset.baseset({wdirrev})

    return subset & relevant

@showview('work', csettopic='work')
def showwork(ui, repo, displayer):
    """changesets that aren't finished"""
    # TODO support date-based limiting when calling revset.
    revs = repo.revs('sort(_underway(), topo)')
    nodelen = longestshortest(repo, revs)

    revdag = graphmod.dagwalker(repo, revs)

    ui.setconfig('experimental', 'graphshorten', True)
    cmdutil.displaygraph(ui, repo, revdag, displayer, graphmod.asciiedges,
                         props={'nodelen': nodelen})

def extsetup(ui):
    # Alias `hg <prefix><view>` to `hg show <view>`.
    for prefix in ui.configlist('commands', 'show.aliasprefix'):
        for view in showview._table:
            name = '%s%s' % (prefix, view)

            choice, allcommands = cmdutil.findpossible(name, commands.table,
                                                       strict=True)

            # This alias is already a command name. Don't set it.
            if name in choice:
                continue

            # Same for aliases.
            if ui.config('alias', name):
                continue

            ui.setconfig('alias', name, 'show %s' % view, source='show')

def longestshortest(repo, revs, minlen=4):
    """Return the length of the longest shortest node to identify revisions.

    The result of this function can be used with the ``shortest()`` template
    function to ensure that a value is unique and unambiguous for a given
    set of nodes.

    The number of revisions in the repo is taken into account to prevent
    a numeric node prefix from conflicting with an integer revision number.
    If we fail to do this, a value of e.g. ``10023`` could mean either
    revision 10023 or node ``10023abc...``.
    """
    tmpl = formatter.maketemplater(repo.ui, '{shortest(node, %d)}' % minlen)
    lens = [minlen]
    for rev in revs:
        ctx = repo[rev]
        shortest = tmpl.render({'ctx': ctx, 'node': ctx.hex()})
        lens.append(len(shortest))

    return max(lens)

# Adjust the docstring of the show command so it shows all registered views.
# This is a bit hacky because it runs at the end of module load. When moved
# into core or when another extension wants to provide a view, we'll need
# to do this more robustly.
# TODO make this more robust.
def _updatedocstring():
    longest = max(map(len, showview._table.keys()))
    entries = []
    for key in sorted(showview._table.keys()):
        entries.append(pycompat.sysstr('    %s   %s' % (
            key.ljust(longest), showview._table[key]._origdoc)))

    cmdtable['show'][0].__doc__ = pycompat.sysstr('%s\n\n%s\n    ') % (
        cmdtable['show'][0].__doc__.rstrip(),
        pycompat.sysstr('\n\n').join(entries))

_updatedocstring()