repair: determine what upgrade will do

This commit introduces code for determining what actions/improvements
an upgrade should perform.

The "upgradefindimprovements" function introduces a mechanism to
return a list of improvements that can be made to a repository.
Each improvement is effectively an action that an upgrade will
perform. Associated with each of these improvements is metadata
that will be used to inform users what's wrong and what an
upgrade will do.

Each "improvement" is categorized as a "deficiency" or an
"optimization." TBH, I'm not thrilled about the terminology and
am receptive to constructive bikeshedding. The main difference
between a "deficiency" and an "optimization" is a deficiency
is always corrected (if it deviates from the current config) and
an "optimization" is an optional action that goes above and beyond
to improve the state of the repository (usually by requiring more
CPU during upgrade).

Our initial set of improvements identifies missing repository
requirements, a single, easily correctable problem with
changelog storage, and a set of "optimizations" related to delta
recalculation.

The main "upgraderepo" function has been expanded to handle
improvements. It queries for the list of improvements and determines
which of them will run based on the current repository state and user

I went through numerous iterations of the output format before
settling on a ReST-inspired definition list format. (I used
bulleted lists in the first submission of this commit and could
not get it to format just right.) Even with the various iterations,
I'm still not super thrilled with the format. But, this is a debug*
command, so that should mean we can refine the output without BC
concerns.

mercurial/repair.py

@@ -1,495 +1,773 b''
 # repair.py - functions for repository repair for mercurial
 #
 # Copyright 2005, 2006 Chris Mason <[e-mail]>
 # Copyright 2007 Matt Mackall
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import errno
 import hashlib
 
 from .i18n import _
 from .node import short
 from . import (
     bundle2,
     changegroup,
     error,
     exchange,
     obsolete,
     util,
 )
 
 def _bundle(repo, bases, heads, node, suffix, compress=True):
     """create a bundle with the specified revisions as a backup"""
     cgversion = changegroup.safeversion(repo)
 
     cg = changegroup.changegroupsubset(repo, bases, heads, 'strip',
                                        version=cgversion)
     backupdir = "strip-backup"
     vfs = repo.vfs
     if not vfs.isdir(backupdir):
         vfs.mkdir(backupdir)
 
     # Include a hash of all the nodes in the filename for uniqueness
     allcommits = repo.set('%ln::%ln', bases, heads)
     allhashes = sorted(c.hex() for c in allcommits)
     totalhash = hashlib.sha1(''.join(allhashes)).hexdigest()
     name = "%s/%s-%s-%s.hg" % (backupdir, short(node), totalhash[:8], suffix)
 
     comp = None
     if cgversion != '01':
         bundletype = "HG20"
         if compress:
             comp = 'BZ'
     elif compress:
         bundletype = "HG10BZ"
     else:
         bundletype = "HG10UN"
     return bundle2.writebundle(repo.ui, cg, name, bundletype, vfs,
                                    compression=comp)
 
 def _collectfiles(repo, striprev):
     """find out the filelogs affected by the strip"""
     files = set()
 
     for x in xrange(striprev, len(repo)):
         files.update(repo[x].files())
 
     return sorted(files)
 
 def _collectbrokencsets(repo, files, striprev):
     """return the changesets which will be broken by the truncation"""
     s = set()
     def collectone(revlog):
         _, brokenset = revlog.getstrippoint(striprev)
         s.update([revlog.linkrev(r) for r in brokenset])
 
     collectone(repo.manifestlog._revlog)
     for fname in files:
         collectone(repo.file(fname))
 
     return s
 
 def strip(ui, repo, nodelist, backup=True, topic='backup'):
     # This function operates within a transaction of its own, but does
     # not take any lock on the repo.
     # Simple way to maintain backwards compatibility for this
     # argument.
     if backup in ['none', 'strip']:
         backup = False
 
     repo = repo.unfiltered()
     repo.destroying()
 
     cl = repo.changelog
     # TODO handle undo of merge sets
     if isinstance(nodelist, str):
         nodelist = [nodelist]
     striplist = [cl.rev(node) for node in nodelist]
     striprev = min(striplist)
 
     files = _collectfiles(repo, striprev)
     saverevs = _collectbrokencsets(repo, files, striprev)
 
     # Some revisions with rev > striprev may not be descendants of striprev.
     # We have to find these revisions and put them in a bundle, so that
     # we can restore them after the truncations.
     # To create the bundle we use repo.changegroupsubset which requires
     # the list of heads and bases of the set of interesting revisions.
     # (head = revision in the set that has no descendant in the set;
     #  base = revision in the set that has no ancestor in the set)
     tostrip = set(striplist)
     saveheads = set(saverevs)
     for r in cl.revs(start=striprev + 1):
         if any(p in tostrip for p in cl.parentrevs(r)):
             tostrip.add(r)
 
         if r not in tostrip:
             saverevs.add(r)
             saveheads.difference_update(cl.parentrevs(r))
             saveheads.add(r)
     saveheads = [cl.node(r) for r in saveheads]
 
     # compute base nodes
     if saverevs:
         descendants = set(cl.descendants(saverevs))
         saverevs.difference_update(descendants)
     savebases = [cl.node(r) for r in saverevs]
     stripbases = [cl.node(r) for r in tostrip]
 
     # For a set s, max(parents(s) - s) is the same as max(heads(::s - s)), but
     # is much faster
     newbmtarget = repo.revs('max(parents(%ld) - (%ld))', tostrip, tostrip)
     if newbmtarget:
         newbmtarget = repo[newbmtarget.first()].node()
     else:
         newbmtarget = '.'
 
     bm = repo._bookmarks
     updatebm = []
     for m in bm:
         rev = repo[bm[m]].rev()
         if rev in tostrip:
             updatebm.append(m)
 
     # create a changegroup for all the branches we need to keep
     backupfile = None
     vfs = repo.vfs
     node = nodelist[-1]
     if backup:
         backupfile = _bundle(repo, stripbases, cl.heads(), node, topic)
         repo.ui.status(_("saved backup bundle to %s\n") %
                        vfs.join(backupfile))
         repo.ui.log("backupbundle", "saved backup bundle to %s\n",
                     vfs.join(backupfile))
     tmpbundlefile = None
     if saveheads:
         # do not compress temporary bundle if we remove it from disk later
         tmpbundlefile = _bundle(repo, savebases, saveheads, node, 'temp',
                             compress=False)
 
     mfst = repo.manifestlog._revlog
 
     curtr = repo.currenttransaction()
     if curtr is not None:
         del curtr  # avoid carrying reference to transaction for nothing
         msg = _('programming error: cannot strip from inside a transaction')
         raise error.Abort(msg, hint=_('contact your extension maintainer'))
 
     try:
         with repo.transaction("strip") as tr:
             offset = len(tr.entries)
 
             tr.startgroup()
             cl.strip(striprev, tr)
             mfst.strip(striprev, tr)
             if 'treemanifest' in repo.requirements: # safe but unnecessary
                                                     # otherwise
                 for unencoded, encoded, size in repo.store.datafiles():
                     if (unencoded.startswith('meta/') and
                         unencoded.endswith('00manifest.i')):
                         dir = unencoded[5:-12]
                         repo.manifestlog._revlog.dirlog(dir).strip(striprev, tr)
             for fn in files:
                 repo.file(fn).strip(striprev, tr)
             tr.endgroup()
 
             for i in xrange(offset, len(tr.entries)):
                 file, troffset, ignore = tr.entries[i]
                 with repo.svfs(file, 'a', checkambig=True) as fp:
                     fp.truncate(troffset)
                 if troffset == 0:
                     repo.store.markremoved(file)
 
         if tmpbundlefile:
             ui.note(_("adding branch\n"))
             f = vfs.open(tmpbundlefile, "rb")
             gen = exchange.readbundle(ui, f, tmpbundlefile, vfs)
             if not repo.ui.verbose:
                 # silence internal shuffling chatter
                 repo.ui.pushbuffer()
             if isinstance(gen, bundle2.unbundle20):
                 with repo.transaction('strip') as tr:
                     tr.hookargs = {'source': 'strip',
                                    'url': 'bundle:' + vfs.join(tmpbundlefile)}
                     bundle2.applybundle(repo, gen, tr, source='strip',
                                         url='bundle:' + vfs.join(tmpbundlefile))
             else:
                 gen.apply(repo, 'strip', 'bundle:' + vfs.join(tmpbundlefile),
                           True)
             if not repo.ui.verbose:
                 repo.ui.popbuffer()
             f.close()
         repo._phasecache.invalidate()
 
         for m in updatebm:
             bm[m] = repo[newbmtarget].node()
         lock = tr = None
         try:
             lock = repo.lock()
             tr = repo.transaction('repair')
             bm.recordchange(tr)
             tr.close()
         finally:
             tr.release()
             lock.release()
 
         # remove undo files
         for undovfs, undofile in repo.undofiles():
             try:
                 undovfs.unlink(undofile)
             except OSError as e:
                 if e.errno != errno.ENOENT:
                     ui.warn(_('error removing %s: %s\n') %
                             (undovfs.join(undofile), str(e)))
 
     except: # re-raises
         if backupfile:
             ui.warn(_("strip failed, backup bundle stored in '%s'\n")
                     % vfs.join(backupfile))
         if tmpbundlefile:
             ui.warn(_("strip failed, unrecovered changes stored in '%s'\n")
                     % vfs.join(tmpbundlefile))
             ui.warn(_("(fix the problem, then recover the changesets with "
                       "\"hg unbundle '%s'\")\n") % vfs.join(tmpbundlefile))
         raise
     else:
         if tmpbundlefile:
             # Remove temporary bundle only if there were no exceptions
             vfs.unlink(tmpbundlefile)
 
     repo.destroyed()
     # return the backup file path (or None if 'backup' was False) so
     # extensions can use it
     return backupfile
 
 def rebuildfncache(ui, repo):
     """Rebuilds the fncache file from repo history.
 
     Missing entries will be added. Extra entries will be removed.
     """
     repo = repo.unfiltered()
 
     if 'fncache' not in repo.requirements:
         ui.warn(_('(not rebuilding fncache because repository does not '
                   'support fncache)\n'))
         return
 
     with repo.lock():
         fnc = repo.store.fncache
         # Trigger load of fncache.
         if 'irrelevant' in fnc:
             pass
 
         oldentries = set(fnc.entries)
         newentries = set()
         seenfiles = set()
 
         repolen = len(repo)
         for rev in repo:
             ui.progress(_('rebuilding'), rev, total=repolen,
                         unit=_('changesets'))
 
             ctx = repo[rev]
             for f in ctx.files():
                 # This is to minimize I/O.
                 if f in seenfiles:
                     continue
                 seenfiles.add(f)
 
                 i = 'data/%s.i' % f
                 d = 'data/%s.d' % f
 
                 if repo.store._exists(i):
                     newentries.add(i)
                 if repo.store._exists(d):
                     newentries.add(d)
 
         ui.progress(_('rebuilding'), None)
 
         if 'treemanifest' in repo.requirements: # safe but unnecessary otherwise
             for dir in util.dirs(seenfiles):
                 i = 'meta/%s/00manifest.i' % dir
                 d = 'meta/%s/00manifest.d' % dir
 
                 if repo.store._exists(i):
                     newentries.add(i)
                 if repo.store._exists(d):
                     newentries.add(d)
 
         addcount = len(newentries - oldentries)
         removecount = len(oldentries - newentries)
         for p in sorted(oldentries - newentries):
             ui.write(_('removing %s\n') % p)
         for p in sorted(newentries - oldentries):
             ui.write(_('adding %s\n') % p)
 
         if addcount or removecount:
             ui.write(_('%d items added, %d removed from fncache\n') %
                      (addcount, removecount))
             fnc.entries = newentries
             fnc._dirty = True
 
             with repo.transaction('fncache') as tr:
                 fnc.write(tr)
         else:
             ui.write(_('fncache already up to date\n'))
 
 def stripbmrevset(repo, mark):
     """
     The revset to strip when strip is called with -B mark
 
     Needs to live here so extensions can use it and wrap it even when strip is
     not enabled or not present on a box.
     """
     return repo.revs("ancestors(bookmark(%s)) - "
                      "ancestors(head() and not bookmark(%s)) - "
                      "ancestors(bookmark() and not bookmark(%s))",
                      mark, mark, mark)
 
 def deleteobsmarkers(obsstore, indices):
     """Delete some obsmarkers from obsstore and return how many were deleted
 
     'indices' is a list of ints which are the indices
     of the markers to be deleted.
 
     Every invocation of this function completely rewrites the obsstore file,
     skipping the markers we want to be removed. The new temporary file is
     created, remaining markers are written there and on .close() this file
     gets atomically renamed to obsstore, thus guaranteeing consistency."""
     if not indices:
         # we don't want to rewrite the obsstore with the same content
         return
 
     left = []
     current = obsstore._all
     n = 0
     for i, m in enumerate(current):
         if i in indices:
             n += 1
             continue
         left.append(m)
 
     newobsstorefile = obsstore.svfs('obsstore', 'w', atomictemp=True)
     for bytes in obsolete.encodemarkers(left, True, obsstore._version):
         newobsstorefile.write(bytes)
     newobsstorefile.close()
     return n
 
 def upgraderequiredsourcerequirements(repo):
     """Obtain requirements required to be present to upgrade a repo.
 
     An upgrade will not be allowed if the repository doesn't have the
     requirements returned by this function.
     """
     return set([
         # Introduced in Mercurial 0.9.2.
         'revlogv1',
         # Introduced in Mercurial 0.9.2.
         'store',
     ])
 
 def upgradeblocksourcerequirements(repo):
     """Obtain requirements that will prevent an upgrade from occurring.
 
     An upgrade cannot be performed if the source repository contains a
     requirements in the returned set.
     """
     return set([
         # The upgrade code does not yet support these experimental features.
         # This is an artificial limitation.
         'manifestv2',
         'treemanifest',
         # This was a precursor to generaldelta and was never enabled by default.
         # It should (hopefully) not exist in the wild.
         'parentdelta',
         # Upgrade should operate on the actual store, not the shared link.
         'shared',
     ])
 
 def upgradesupportremovedrequirements(repo):
     """Obtain requirements that can be removed during an upgrade.
 
     If an upgrade were to create a repository that dropped a requirement,
     the dropped requirement must appear in the returned set for the upgrade
     to be allowed.
     """
     return set()
 
 def upgradesupporteddestrequirements(repo):
     """Obtain requirements that upgrade supports in the destination.
 
     If the result of the upgrade would create requirements not in this set,
     the upgrade is disallowed.
 
     Extensions should monkeypatch this to add their custom requirements.
     """
     return set([
         'dotencode',
         'fncache',
         'generaldelta',
         'revlogv1',
         'store',
     ])
 
 def upgradeallowednewrequirements(repo):
     """Obtain requirements that can be added to a repository during upgrade.
 
     This is used to disallow proposed requirements from being added when
     they weren't present before.
 
     We use a list of allowed requirement additions instead of a list of known
     bad additions because the whitelist approach is safer and will prevent
     future, unknown requirements from accidentally being added.
     """
     return set([
         'dotencode',
         'fncache',
         'generaldelta',
     ])
 
+deficiency = 'deficiency'
+optimisation = 'optimization'
+
+class upgradeimprovement(object):
+    """Represents an improvement that can be made as part of an upgrade.
+
+    The following attributes are defined on each instance:
+
+    name
+       Machine-readable string uniquely identifying this improvement. It
+       will be mapped to an action later in the upgrade process.
+
+    type
+       Either ``deficiency`` or ``optimisation``. A deficiency is an obvious
+       problem. An optimization is an action (sometimes optional) that
+       can be taken to further improve the state of the repository.
+
+    description
+       Message intended for humans explaining the improvement in more detail,
+       including the implications of it. For ``deficiency`` types, should be
+       worded in the present tense. For ``optimisation`` types, should be
+       worded in the future tense.
+
+    upgrademessage
+       Message intended for humans explaining what an upgrade addressing this
+       issue will do. Should be worded in the future tense.
+
+    fromdefault (``deficiency`` types only)
+       Boolean indicating whether the current (deficient) state deviates
+       from Mercurial's default configuration.
+
+    fromconfig (``deficiency`` types only)
+       Boolean indicating whether the current (deficient) state deviates
+       from the current Mercurial configuration.
+    """
+    def __init__(self, name, type, description, upgrademessage, **kwargs):
+        self.name = name
+        self.type = type
+        self.description = description
+        self.upgrademessage = upgrademessage
+
+        for k, v in kwargs.items():
+            setattr(self, k, v)
+
+def upgradefindimprovements(repo):
+    """Determine improvements that can be made to the repo during upgrade.
+
+    Returns a list of ``upgradeimprovement`` describing repository deficiencies
+    and optimizations.
+    """
+    # Avoid cycle: cmdutil -> repair -> localrepo -> cmdutil
+    from . import localrepo
+
+    newreporeqs = localrepo.newreporequirements(repo)
+
+    improvements = []
+
+    # We could detect lack of revlogv1 and store here, but they were added
+    # in 0.9.2 and we don't support upgrading repos without these
+    # requirements, so let's not bother.
+
+    if 'fncache' not in repo.requirements:
+        improvements.append(upgradeimprovement(
+            name='fncache',
+            type=deficiency,
+            description=_('long and reserved filenames may not work correctly; '
+                          'repository performance is sub-optimal'),
+            upgrademessage=_('repository will be more resilient to storing '
+                             'certain paths and performance of certain '
+                             'operations should be improved'),
+            fromdefault=True,
+            fromconfig='fncache' in newreporeqs))
+
+    if 'dotencode' not in repo.requirements:
+        improvements.append(upgradeimprovement(
+            name='dotencode',
+            type=deficiency,
+            description=_('storage of filenames beginning with a period or '
+                          'space may not work correctly'),
+            upgrademessage=_('repository will be better able to store files '
+                             'beginning with a space or period'),
+            fromdefault=True,
+            fromconfig='dotencode' in newreporeqs))
+
+    if 'generaldelta' not in repo.requirements:
+        improvements.append(upgradeimprovement(
+            name='generaldelta',
+            type=deficiency,
+            description=_('deltas within internal storage are unable to '
+                          'choose optimal revisions; repository is larger and '
+                          'slower than it could be; interaction with other '
+                          'repositories may require extra network and CPU '
+                          'resources, making "hg push" and "hg pull" slower'),
+            upgrademessage=_('repository storage will be able to create '
+                             'optimal deltas; new repository data will be '
+                             'smaller and read times should decrease; '
+                             'interacting with other repositories using this '
+                             'storage model should require less network and '
+                             'CPU resources, making "hg push" and "hg pull" '
+                             'faster'),
+            fromdefault=True,
+            fromconfig='generaldelta' in newreporeqs))
+
+    # Mercurial 4.0 changed changelogs to not use delta chains. Search for
+    # changelogs with deltas.
+    cl = repo.changelog
+    for rev in cl:
+        chainbase = cl.chainbase(rev)
+        if chainbase != rev:
+            improvements.append(upgradeimprovement(
+                name='removecldeltachain',
+                type=deficiency,
+                description=_('changelog storage is using deltas instead of '
+                              'raw entries; changelog reading and any '
+                              'operation relying on changelog data are slower '
+                              'than they could be'),
+                upgrademessage=_('changelog storage will be reformated to '
+                                 'store raw entries; changelog reading will be '
+                                 'faster; changelog size may be reduced'),
+                fromdefault=True,
+                fromconfig=True))
+            break
+
+    # Now for the optimizations.
+
+    # These are unconditionally added. There is logic later that figures out
+    # which ones to apply.
+
+    improvements.append(upgradeimprovement(
+        name='redeltaparent',
+        type=optimisation,
+        description=_('deltas within internal storage will be recalculated to '
+                      'choose an optimal base revision where this was not '
+                      'already done; the size of the repository may shrink and '
+                      'various operations may become faster; the first time '
+                      'this optimization is performed could slow down upgrade '
+                      'execution considerably; subsequent invocations should '
+                      'not run noticeably slower'),
+        upgrademessage=_('deltas within internal storage will choose a new '
+                         'base revision if needed')))
+
+    improvements.append(upgradeimprovement(
+        name='redeltamultibase',
+        type=optimisation,
+        description=_('deltas within internal storage will be recalculated '
+                      'against multiple base revision and the smallest '
+                      'difference will be used; the size of the repository may '
+                      'shrink significantly when there are many merges; this '
+                      'optimization will slow down execution in proportion to '
+                      'the number of merges in the repository and the amount '
+                      'of files in the repository; this slow down should not '
+                      'be significant unless there are tens of thousands of '
+                      'files and thousands of merges'),
+        upgrademessage=_('deltas within internal storage will choose an '
+                         'optimal delta by computing deltas against multiple '
+                         'parents; may slow down execution time '
+                         'significantly')))
+
+    improvements.append(upgradeimprovement(
+        name='redeltaall',
+        type=optimisation,
+        description=_('deltas within internal storage will always be '
+                      'recalculated without reusing prior deltas; this will '
+                      'likely make execution run several times slower; this '
+                      'optimization is typically not needed'),
+        upgrademessage=_('deltas within internal storage will be fully '
+                         'recomputed; this will likely drastically slow down '
+                         'execution time')))
+
+    return improvements
+
+def upgradedetermineactions(repo, improvements, sourcereqs, destreqs,
+                            optimize):
+    """Determine upgrade actions that will be performed.
+
+    Given a list of improvements as returned by ``upgradefindimprovements``,
+    determine the list of upgrade actions that will be performed.
+
+    The role of this function is to filter improvements if needed, apply
+    recommended optimizations from the improvements list that make sense,
+    etc.
+
+    Returns a list of action names.
+    """
+    newactions = []
+
+    knownreqs = upgradesupporteddestrequirements(repo)
+
+    for i in improvements:
+        name = i.name
+
+        # If the action is a requirement that doesn't show up in the
+        # destination requirements, prune the action.
+        if name in knownreqs and name not in destreqs:
+            continue
+
+        if i.type == deficiency:
+            newactions.append(name)
+
+    newactions.extend(o for o in sorted(optimize) if o not in newactions)
+
+    # FUTURE consider adding some optimizations here for certain transitions.
+    # e.g. adding generaldelta could schedule parent redeltas.
+
+    return newactions
+
 def upgraderepo(ui, repo, run=False, optimize=None):
     """Upgrade a repository in place."""
     # Avoid cycle: cmdutil -> repair -> localrepo -> cmdutil
     from . import localrepo
 
+    optimize = set(optimize or [])
     repo = repo.unfiltered()
 
     # Ensure the repository can be upgraded.
     missingreqs = upgraderequiredsourcerequirements(repo) - repo.requirements
     if missingreqs:
         raise error.Abort(_('cannot upgrade repository; requirement '
                             'missing: %s') % _(', ').join(sorted(missingreqs)))
 
     blockedreqs = upgradeblocksourcerequirements(repo) & repo.requirements
     if blockedreqs:
         raise error.Abort(_('cannot upgrade repository; unsupported source '
                             'requirement: %s') %
                           _(', ').join(sorted(blockedreqs)))
 
     # FUTURE there is potentially a need to control the wanted requirements via
     # command arguments or via an extension hook point.
     newreqs = localrepo.newreporequirements(repo)
 
     noremovereqs = (repo.requirements - newreqs -
                    upgradesupportremovedrequirements(repo))
     if noremovereqs:
         raise error.Abort(_('cannot upgrade repository; requirement would be '
                             'removed: %s') % _(', ').join(sorted(noremovereqs)))
 
     noaddreqs = (newreqs - repo.requirements -
                  upgradeallowednewrequirements(repo))
     if noaddreqs:
         raise error.Abort(_('cannot upgrade repository; do not support adding '
                             'requirement: %s') %
                           _(', ').join(sorted(noaddreqs)))
 
     unsupportedreqs = newreqs - upgradesupporteddestrequirements(repo)
     if unsupportedreqs:
         raise error.Abort(_('cannot upgrade repository; do not support '
                             'destination requirement: %s') %
                           _(', ').join(sorted(unsupportedreqs)))
 
+    # Find and validate all improvements that can be made.
+    improvements = upgradefindimprovements(repo)
+    for i in improvements:
+        if i.type not in (deficiency, optimisation):
+            raise error.Abort(_('unexpected improvement type %s for %s') % (
+                i.type, i.name))
+
+    # Validate arguments.
+    unknownoptimize = optimize - set(i.name for i in improvements
+                                     if i.type == optimisation)
+    if unknownoptimize:
+        raise error.Abort(_('unknown optimization action requested: %s') %
+                          ', '.join(sorted(unknownoptimize)),
+                          hint=_('run without arguments to see valid '
+                                 'optimizations'))
+
+    actions = upgradedetermineactions(repo, improvements, repo.requirements,
+                                      newreqs, optimize)
+
     def printrequirements():
         ui.write(_('requirements\n'))
         ui.write(_('   preserved: %s\n') %
                  _(', ').join(sorted(newreqs & repo.requirements)))
 
         if repo.requirements - newreqs:
             ui.write(_('   removed: %s\n') %
                      _(', ').join(sorted(repo.requirements - newreqs)))
 
         if newreqs - repo.requirements:
             ui.write(_('   added: %s\n') %
                      _(', ').join(sorted(newreqs - repo.requirements)))
 
         ui.write('\n')
 
+    def printupgradeactions():
+        for action in actions:
+            for i in improvements:
+                if i.name == action:
+                    ui.write('%s\n   %s\n\n' %
+                             (i.name, i.upgrademessage))
+
     if not run:
+        fromdefault = []
+        fromconfig = []
+        optimizations = []
+
+        for i in improvements:
+            assert i.type in (deficiency, optimisation)
+            if i.type == deficiency:
+                if i.fromdefault:
+                    fromdefault.append(i)
+                if i.fromconfig:
+                    fromconfig.append(i)
+            else:
+                optimizations.append(i)
+
+        if fromdefault or fromconfig:
+            fromconfignames = set(x.name for x in fromconfig)
+            onlydefault = [i for i in fromdefault
+                           if i.name not in fromconfignames]
+
+            if fromconfig:
+                ui.write(_('repository lacks features recommended by '
+                           'current config options:\n\n'))
+                for i in fromconfig:
+                    ui.write('%s\n   %s\n\n' % (i.name, i.description))
+
+            if onlydefault:
+                ui.write(_('repository lacks features used by the default '
+                           'config options:\n\n'))
+                for i in onlydefault:
+                    ui.write('%s\n   %s\n\n' % (i.name, i.description))
+
+            ui.write('\n')
+        else:
+            ui.write(_('(no feature deficiencies found in existing '
+                       'repository)\n'))
+
         ui.write(_('performing an upgrade with "--run" will make the following '
                    'changes:\n\n'))
 
         printrequirements()
+        printupgradeactions()
+
+        unusedoptimize = [i for i in improvements
+                          if i.name not in actions and i.type == optimisation]
+        if unusedoptimize:
+            ui.write(_('additional optimizations are available by specifying '
+                     '"--optimize <name>":\n\n'))
+            for i in unusedoptimize:
+                ui.write(_('%s\n   %s\n\n') % (i.name, i.description))

tests/test-upgrade-repo.t

@@ -1,51 +1,182 b''
   $ cat >> $HGRCPATH << EOF
   > [extensions]
   > share =
   > EOF
 
 store and revlogv1 are required in source
 
   $ hg --config format.usestore=false init no-store
   $ hg -R no-store debugupgraderepo
   abort: cannot upgrade repository; requirement missing: store
   [255]
 
   $ hg init no-revlogv1
   $ cat > no-revlogv1/.hg/requires << EOF
   > dotencode
   > fncache
   > generaldelta
   > store
   > EOF
 
   $ hg -R no-revlogv1 debugupgraderepo
   abort: cannot upgrade repository; requirement missing: revlogv1
   [255]
 
 Cannot upgrade shared repositories
 
   $ hg init share-parent
   $ hg -q share share-parent share-child
 
   $ hg -R share-child debugupgraderepo
   abort: cannot upgrade repository; unsupported source requirement: shared
   [255]
 
 Do not yet support upgrading manifestv2 and treemanifest repos
 
   $ hg --config experimental.manifestv2=true init manifestv2
   $ hg -R manifestv2 debugupgraderepo
   abort: cannot upgrade repository; unsupported source requirement: manifestv2
   [255]
 
   $ hg --config experimental.treemanifest=true init treemanifest
   $ hg -R treemanifest debugupgraderepo
   abort: cannot upgrade repository; unsupported source requirement: treemanifest
   [255]
 
 Cannot add manifestv2 or treemanifest requirement during upgrade
 
   $ hg init disallowaddedreq
   $ hg -R disallowaddedreq --config experimental.manifestv2=true --config experimental.treemanifest=true debugupgraderepo
   abort: cannot upgrade repository; do not support adding requirement: manifestv2, treemanifest
   [255]
+
+An upgrade of a repository created with recommended settings only suggests optimizations
+
+  $ hg init empty
+  $ cd empty
+  $ hg debugupgraderepo
+  (no feature deficiencies found in existing repository)
+  performing an upgrade with "--run" will make the following changes:
+  
+  requirements
+     preserved: dotencode, fncache, generaldelta, revlogv1, store
+  
+  additional optimizations are available by specifying "--optimize <name>":
+  
+  redeltaparent
+     deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower
+  
+  redeltamultibase
+     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
+  
+  redeltaall
+     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
+  
+
+--optimize can be used to add optimizations
+
+  $ hg debugupgrade --optimize redeltaparent
+  (no feature deficiencies found in existing repository)
+  performing an upgrade with "--run" will make the following changes:
+  
+  requirements
+     preserved: dotencode, fncache, generaldelta, revlogv1, store
+  
+  redeltaparent
+     deltas within internal storage will choose a new base revision if needed
+  
+  additional optimizations are available by specifying "--optimize <name>":
+  
+  redeltamultibase
+     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
+  
+  redeltaall
+     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
+  
+
+Various sub-optimal detections work
+
+  $ cat > .hg/requires << EOF
+  > revlogv1
+  > store
+  > EOF
+
+  $ hg debugupgraderepo
+  repository lacks features recommended by current config options:
+  
+  fncache
+     long and reserved filenames may not work correctly; repository performance is sub-optimal
+  
+  dotencode
+     storage of filenames beginning with a period or space may not work correctly
+  
+  generaldelta
+     deltas within internal storage are unable to choose optimal revisions; repository is larger and slower than it could be; interaction with other repositories may require extra network and CPU resources, making "hg push" and "hg pull" slower
+  
+  
+  performing an upgrade with "--run" will make the following changes:
+  
+  requirements
+     preserved: revlogv1, store
+     added: dotencode, fncache, generaldelta
+  
+  fncache
+     repository will be more resilient to storing certain paths and performance of certain operations should be improved
+  
+  dotencode
+     repository will be better able to store files beginning with a space or period
+  
+  generaldelta
+     repository storage will be able to create optimal deltas; new repository data will be smaller and read times should decrease; interacting with other repositories using this storage model should require less network and CPU resources, making "hg push" and "hg pull" faster
+  
+  additional optimizations are available by specifying "--optimize <name>":
+  
+  redeltaparent
+     deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower
+  
+  redeltamultibase
+     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
+  
+  redeltaall
+     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
+  
+
+  $ hg --config format.dotencode=false debugupgraderepo
+  repository lacks features recommended by current config options:
+  
+  fncache
+     long and reserved filenames may not work correctly; repository performance is sub-optimal
+  
+  generaldelta
+     deltas within internal storage are unable to choose optimal revisions; repository is larger and slower than it could be; interaction with other repositories may require extra network and CPU resources, making "hg push" and "hg pull" slower
+  
+  repository lacks features used by the default config options:
+  
+  dotencode
+     storage of filenames beginning with a period or space may not work correctly
+  
+  
+  performing an upgrade with "--run" will make the following changes:
+  
+  requirements
+     preserved: revlogv1, store
+     added: fncache, generaldelta
+  
+  fncache
+     repository will be more resilient to storing certain paths and performance of certain operations should be improved
+  
+  generaldelta
+     repository storage will be able to create optimal deltas; new repository data will be smaller and read times should decrease; interacting with other repositories using this storage model should require less network and CPU resources, making "hg push" and "hg pull" faster
+  
+  additional optimizations are available by specifying "--optimize <name>":
+  
+  redeltaparent
+     deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower
+  
+  redeltamultibase
+     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
+  
+  redeltaall
+     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
+  
+