~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2005-2011 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

"""Repository formats built around versioned files."""

from __future__ import absolute_import

from bzrlib.lazy_import import lazy_import

lazy_import(globals(), """

import itertools

from bzrlib import (

    check,

    config as _mod_config,

    debug,

    fetch as _mod_fetch,

    fifo_cache,

    gpg,

    graph,

    inventory_delta,

    lru_cache,

    osutils,

    revision as _mod_revision,

    serializer as _mod_serializer,

    static_tuple,

    symbol_versioning,

    tsort,

    ui,

    versionedfile,

    vf_search,

    )

from bzrlib.recordcounter import RecordCounter

from bzrlib.revisiontree import InventoryRevisionTree

from bzrlib.testament import Testament

from bzrlib.i18n import gettext

""")

from bzrlib import (

    errors,

    )

from bzrlib.decorators import (

    needs_read_lock,

    needs_write_lock,

    only_raises,

    )

from bzrlib.inventory import (

    Inventory,

    InventoryDirectory,

    ROOT_ID,

    entry_factory,

    )

from bzrlib.repository import (

    CommitBuilder,

    InterRepository,

    MetaDirRepository,

    RepositoryFormatMetaDir,

    Repository,

    RepositoryFormat,

    )

from bzrlib.trace import (

    mutter

    )

class VersionedFileRepositoryFormat(RepositoryFormat):

    """Base class for all repository formats that are VersionedFiles-based."""

    supports_full_versioned_files = True

    supports_versioned_directories = True

    supports_unreferenced_revisions = True

    # Should commit add an inventory, or an inventory delta to the repository.

    _commit_inv_deltas = True

    # What order should fetch operations request streams in?

    # The default is unordered as that is the cheapest for an origin to

    # provide.

    _fetch_order = 'unordered'

    # Does this repository format use deltas that can be fetched as-deltas ?

    # (E.g. knits, where the knit deltas can be transplanted intact.

    # We default to False, which will ensure that enough data to get

    # a full text out of any fetch stream will be grabbed.

    _fetch_uses_deltas = False

class VersionedFileCommitBuilder(CommitBuilder):

    """Commit builder implementation for versioned files based repositories.

    """

    # this commit builder supports the record_entry_contents interface

    supports_record_entry_contents = True

    # the default CommitBuilder does not manage trees whose root is versioned.

    _versioned_root = False

    def __init__(self, repository, parents, config_stack, timestamp=None,

                 timezone=None, committer=None, revprops=None,

                 revision_id=None, lossy=False):

        super(VersionedFileCommitBuilder, self).__init__(repository,

            parents, config_stack, timestamp, timezone, committer, revprops,

            revision_id, lossy)

        try:

            basis_id = self.parents[0]

        except IndexError:

            basis_id = _mod_revision.NULL_REVISION

        self.basis_delta_revision = basis_id

        self.new_inventory = Inventory(None)

        self._basis_delta = []

        self.__heads = graph.HeadsCache(repository.get_graph()).heads

        # memo'd check for no-op commits.

        self._any_changes = False

        # API compatibility, older code that used CommitBuilder did not call

        # .record_delete(), which means the delta that is computed would not be

        # valid. Callers that will call record_delete() should call

        # .will_record_deletes() to indicate that.

        self._recording_deletes = False

    def will_record_deletes(self):

        """Tell the commit builder that deletes are being notified.

        This enables the accumulation of an inventory delta; for the resulting

        commit to be valid, deletes against the basis MUST be recorded via

        builder.record_delete().

        """

        self._recording_deletes = True

    def any_changes(self):

        """Return True if any entries were changed.

        This includes merge-only changes. It is the core for the --unchanged

        detection in commit.

        :return: True if any changes have occured.

        """

        return self._any_changes

    def _ensure_fallback_inventories(self):

        """Ensure that appropriate inventories are available.

        This only applies to repositories that are stacked, and is about

        enusring the stacking invariants. Namely, that for any revision that is

        present, we either have all of the file content, or we have the parent

        inventory and the delta file content.

        """

        if not self.repository._fallback_repositories:

            return

        if not self.repository._format.supports_chks:

            raise errors.BzrError("Cannot commit directly to a stacked branch"

                " in pre-2a formats. See "

                "https://bugs.launchpad.net/bzr/+bug/375013 for details.")

        # This is a stacked repo, we need to make sure we have the parent

        # inventories for the parents.

        parent_keys = [(p,) for p in self.parents]

        parent_map = self.repository.inventories._index.get_parent_map(parent_keys)

        missing_parent_keys = set([pk for pk in parent_keys

                                       if pk not in parent_map])

        fallback_repos = list(reversed(self.repository._fallback_repositories))

        missing_keys = [('inventories', pk[0])

                        for pk in missing_parent_keys]

        resume_tokens = []

        while missing_keys and fallback_repos:

            fallback_repo = fallback_repos.pop()

            source = fallback_repo._get_source(self.repository._format)

            sink = self.repository._get_sink()

            stream = source.get_stream_for_missing_keys(missing_keys)

            missing_keys = sink.insert_stream_without_locking(stream,

                self.repository._format)

        if missing_keys:

            raise errors.BzrError('Unable to fill in parent inventories for a'

                                  ' stacked branch')

    def commit(self, message):

        """Make the actual commit.

        :return: The revision id of the recorded revision.

        """

        self._validate_unicode_text(message, 'commit message')

        rev = _mod_revision.Revision(

                       timestamp=self._timestamp,

                       timezone=self._timezone,

                       committer=self._committer,

                       message=message,

                       inventory_sha1=self.inv_sha1,

                       revision_id=self._new_revision_id,

                       properties=self._revprops)

        rev.parent_ids = self.parents

        if self._config_stack.get('create_signatures') == _mod_config.SIGN_ALWAYS:

            testament = Testament(rev, self.revision_tree())

            plaintext = testament.as_short_text()

            self.repository.store_revision_signature(

                gpg.GPGStrategy(self._config_stack), plaintext,

                self._new_revision_id)

        self.repository._add_revision(rev)

        self._ensure_fallback_inventories()

        self.repository.commit_write_group()

        return self._new_revision_id

    def abort(self):

        """Abort the commit that is being built.

        """

        self.repository.abort_write_group()

    def revision_tree(self):

        """Return the tree that was just committed.

        After calling commit() this can be called to get a

        RevisionTree representing the newly committed tree. This is

        preferred to calling Repository.revision_tree() because that may

        require deserializing the inventory, while we already have a copy in

        memory.

        """

        if self.new_inventory is None:

            self.new_inventory = self.repository.get_inventory(

                self._new_revision_id)

        return InventoryRevisionTree(self.repository, self.new_inventory,

            self._new_revision_id)

    def finish_inventory(self):

        """Tell the builder that the inventory is finished.

        :return: The inventory id in the repository, which can be used with

            repository.get_inventory.

        """

        if self.new_inventory is None:

            # an inventory delta was accumulated without creating a new

            # inventory.

            basis_id = self.basis_delta_revision

            # We ignore the 'inventory' returned by add_inventory_by_delta

            # because self.new_inventory is used to hint to the rest of the

            # system what code path was taken

            self.inv_sha1, _ = self.repository.add_inventory_by_delta(

                basis_id, self._basis_delta, self._new_revision_id,

                self.parents)

        else:

            if self.new_inventory.root is None:

                raise AssertionError('Root entry should be supplied to'

                    ' record_entry_contents, as of bzr 0.10.')

                self.new_inventory.add(InventoryDirectory(ROOT_ID, '', None))

            self.new_inventory.revision_id = self._new_revision_id

            self.inv_sha1 = self.repository.add_inventory(

                self._new_revision_id,

                self.new_inventory,

                self.parents

                )

        return self._new_revision_id

    def _check_root(self, ie, parent_invs, tree):

        """Helper for record_entry_contents.

        :param ie: An entry being added.

        :param parent_invs: The inventories of the parent revisions of the

            commit.

        :param tree: The tree that is being committed.

        """

        # In this revision format, root entries have no knit or weave When

        # serializing out to disk and back in root.revision is always

        # _new_revision_id

        ie.revision = self._new_revision_id

    def _require_root_change(self, tree):

        """Enforce an appropriate root object change.

        This is called once when record_iter_changes is called, if and only if

        the root was not in the delta calculated by record_iter_changes.

        :param tree: The tree which is being committed.

        """

        if len(self.parents) == 0:

            raise errors.RootMissing()

        entry = entry_factory['directory'](tree.path2id(''), '',

            None)

        entry.revision = self._new_revision_id

        self._basis_delta.append(('', '', entry.file_id, entry))

    def _get_delta(self, ie, basis_inv, path):

        """Get a delta against the basis inventory for ie."""

        if not basis_inv.has_id(ie.file_id):

            # add

            result = (None, path, ie.file_id, ie)

            self._basis_delta.append(result)

            return result

        elif ie != basis_inv[ie.file_id]:

            # common but altered

            # TODO: avoid tis id2path call.

            result = (basis_inv.id2path(ie.file_id), path, ie.file_id, ie)

            self._basis_delta.append(result)

            return result

        else:

            # common, unaltered

            return None

    def _heads(self, file_id, revision_ids):

        """Calculate the graph heads for revision_ids in the graph of file_id.

        This can use either a per-file graph or a global revision graph as we

        have an identity relationship between the two graphs.

        """

        return self.__heads(revision_ids)

    def get_basis_delta(self):

        """Return the complete inventory delta versus the basis inventory.

        This has been built up with the calls to record_delete and

        record_entry_contents. The client must have already called

        will_record_deletes() to indicate that they will be generating a

        complete delta.

        :return: An inventory delta, suitable for use with apply_delta, or

            Repository.add_inventory_by_delta, etc.

        """

        if not self._recording_deletes:

            raise AssertionError("recording deletes not activated.")

        return self._basis_delta

    def record_delete(self, path, file_id):

        """Record that a delete occured against a basis tree.

        This is an optional API - when used it adds items to the basis_delta

        being accumulated by the commit builder. It cannot be called unless the

        method will_record_deletes() has been called to inform the builder that

        a delta is being supplied.

        :param path: The path of the thing deleted.

        :param file_id: The file id that was deleted.

        """

        if not self._recording_deletes:

            raise AssertionError("recording deletes not activated.")

        delta = (path, None, file_id, None)

        self._basis_delta.append(delta)

        self._any_changes = True

        return delta

    def record_entry_contents(self, ie, parent_invs, path, tree,

        content_summary):

        """Record the content of ie from tree into the commit if needed.

        Side effect: sets ie.revision when unchanged

        :param ie: An inventory entry present in the commit.

        :param parent_invs: The inventories of the parent revisions of the

            commit.

        :param path: The path the entry is at in the tree.

        :param tree: The tree which contains this entry and should be used to

            obtain content.

        :param content_summary: Summary data from the tree about the paths

            content - stat, length, exec, sha/link target. This is only

            accessed when the entry has a revision of None - that is when it is

            a candidate to commit.

        :return: A tuple (change_delta, version_recorded, fs_hash).

            change_delta is an inventory_delta change for this entry against

            the basis tree of the commit, or None if no change occured against

            the basis tree.

            version_recorded is True if a new version of the entry has been

            recorded. For instance, committing a merge where a file was only

            changed on the other side will return (delta, False).

            fs_hash is either None, or the hash details for the path (currently

            a tuple of the contents sha1 and the statvalue returned by

            tree.get_file_with_stat()).

        """

        if self.new_inventory.root is None:

            if ie.parent_id is not None:

                raise errors.RootMissing()

            self._check_root(ie, parent_invs, tree)

        if ie.revision is None:

            kind = content_summary[0]

        else:

            # ie is carried over from a prior commit

            kind = ie.kind

        # XXX: repository specific check for nested tree support goes here - if

        # the repo doesn't want nested trees we skip it ?

        if (kind == 'tree-reference' and

            not self.repository._format.supports_tree_reference):

            # mismatch between commit builder logic and repository:

            # this needs the entry creation pushed down into the builder.

            raise NotImplementedError('Missing repository subtree support.')

        self.new_inventory.add(ie)

        # TODO: slow, take it out of the inner loop.

        try:

            basis_inv = parent_invs[0]

        except IndexError:

            basis_inv = Inventory(root_id=None)

        # ie.revision is always None if the InventoryEntry is considered

        # for committing. We may record the previous parents revision if the

        # content is actually unchanged against a sole head.

        if ie.revision is not None:

            if not self._versioned_root and path == '':

                # repositories that do not version the root set the root's

                # revision to the new commit even when no change occurs (more

                # specifically, they do not record a revision on the root; and

                # the rev id is assigned to the root during deserialisation -

                # this masks when a change may have occurred against the basis.

                # To match this we always issue a delta, because the revision

                # of the root will always be changing.

                if basis_inv.has_id(ie.file_id):

                    delta = (basis_inv.id2path(ie.file_id), path,

                        ie.file_id, ie)

                else:

                    # add

                    delta = (None, path, ie.file_id, ie)

                self._basis_delta.append(delta)

                return delta, False, None

            else:

                # we don't need to commit this, because the caller already

                # determined that an existing revision of this file is

                # appropriate. If it's not being considered for committing then

                # it and all its parents to the root must be unaltered so

                # no-change against the basis.

                if ie.revision == self._new_revision_id:

                    raise AssertionError("Impossible situation, a skipped "

                        "inventory entry (%r) claims to be modified in this "

                        "commit (%r).", (ie, self._new_revision_id))

                return None, False, None

        # XXX: Friction: parent_candidates should return a list not a dict

        #      so that we don't have to walk the inventories again.

        parent_candidate_entries = ie.parent_candidates(parent_invs)

        head_set = self._heads(ie.file_id, parent_candidate_entries.keys())

        heads = []

        for inv in parent_invs:

            if inv.has_id(ie.file_id):

                old_rev = inv[ie.file_id].revision

                if old_rev in head_set:

                    heads.append(inv[ie.file_id].revision)

                    head_set.remove(inv[ie.file_id].revision)

        store = False

        # now we check to see if we need to write a new record to the

        # file-graph.

        # We write a new entry unless there is one head to the ancestors, and

        # the kind-derived content is unchanged.

        # Cheapest check first: no ancestors, or more the one head in the

        # ancestors, we write a new node.

        if len(heads) != 1:

            store = True

        if not store:

            # There is a single head, look it up for comparison

            parent_entry = parent_candidate_entries[heads[0]]

            # if the non-content specific data has changed, we'll be writing a

            # node:

            if (parent_entry.parent_id != ie.parent_id or

                parent_entry.name != ie.name):

                store = True

        # now we need to do content specific checks:

        if not store:

            # if the kind changed the content obviously has

            if kind != parent_entry.kind:

                store = True

        # Stat cache fingerprint feedback for the caller - None as we usually

        # don't generate one.

        fingerprint = None

        if kind == 'file':

            if content_summary[2] is None:

                raise ValueError("Files must not have executable = None")

            if not store:

                # We can't trust a check of the file length because of content

                # filtering...

                if (# if the exec bit has changed we have to store:

                    parent_entry.executable != content_summary[2]):

                    store = True

                elif parent_entry.text_sha1 == content_summary[3]:

                    # all meta and content is unchanged (using a hash cache

                    # hit to check the sha)

                    ie.revision = parent_entry.revision

                    ie.text_size = parent_entry.text_size

                    ie.text_sha1 = parent_entry.text_sha1

                    ie.executable = parent_entry.executable

                    return self._get_delta(ie, basis_inv, path), False, None

                else:

                    # Either there is only a hash change(no hash cache entry,

                    # or same size content change), or there is no change on

                    # this file at all.

                    # Provide the parent's hash to the store layer, so that the

                    # content is unchanged we will not store a new node.

                    nostore_sha = parent_entry.text_sha1

            if store:

                # We want to record a new node regardless of the presence or

                # absence of a content change in the file.

                nostore_sha = None

            ie.executable = content_summary[2]

            file_obj, stat_value = tree.get_file_with_stat(ie.file_id, path)

            try:

                text = file_obj.read()

            finally:

                file_obj.close()

            try:

                ie.text_sha1, ie.text_size = self._add_text_to_weave(

                    ie.file_id, text, heads, nostore_sha)

                # Let the caller know we generated a stat fingerprint.

                fingerprint = (ie.text_sha1, stat_value)

            except errors.ExistingContent:

                # Turns out that the file content was unchanged, and we were

                # only going to store a new node if it was changed. Carry over

                # the entry.

                ie.revision = parent_entry.revision

                ie.text_size = parent_entry.text_size

                ie.text_sha1 = parent_entry.text_sha1

                ie.executable = parent_entry.executable

                return self._get_delta(ie, basis_inv, path), False, None

        elif kind == 'directory':

            if not store:

                # all data is meta here, nothing specific to directory, so

                # carry over:

                ie.revision = parent_entry.revision

                return self._get_delta(ie, basis_inv, path), False, None

            self._add_text_to_weave(ie.file_id, '', heads, None)

        elif kind == 'symlink':

            current_link_target = content_summary[3]

            if not store:

                # symlink target is not generic metadata, check if it has

                # changed.

                if current_link_target != parent_entry.symlink_target:

                    store = True

            if not store:

                # unchanged, carry over.

                ie.revision = parent_entry.revision

                ie.symlink_target = parent_entry.symlink_target

                return self._get_delta(ie, basis_inv, path), False, None

            ie.symlink_target = current_link_target

            self._add_text_to_weave(ie.file_id, '', heads, None)

        elif kind == 'tree-reference':

            if not store:

                if content_summary[3] != parent_entry.reference_revision:

                    store = True

            if not store:

                # unchanged, carry over.

                ie.reference_revision = parent_entry.reference_revision

                ie.revision = parent_entry.revision

                return self._get_delta(ie, basis_inv, path), False, None

            ie.reference_revision = content_summary[3]

            if ie.reference_revision is None:

                raise AssertionError("invalid content_summary for nested tree: %r"

                    % (content_summary,))

            self._add_text_to_weave(ie.file_id, '', heads, None)

        else:

            raise NotImplementedError('unknown kind')

        ie.revision = self._new_revision_id

        # The initial commit adds a root directory, but this in itself is not

        # a worthwhile commit.

        if (self.basis_delta_revision != _mod_revision.NULL_REVISION or

            path != ""):

            self._any_changes = True

        return self._get_delta(ie, basis_inv, path), True, fingerprint

    def record_iter_changes(self, tree, basis_revision_id, iter_changes,

        _entry_factory=entry_factory):

        """Record a new tree via iter_changes.

        :param tree: The tree to obtain text contents from for changed objects.

        :param basis_revision_id: The revision id of the tree the iter_changes

            has been generated against. Currently assumed to be the same

            as self.parents[0] - if it is not, errors may occur.

        :param iter_changes: An iter_changes iterator with the changes to apply

            to basis_revision_id. The iterator must not include any items with

            a current kind of None - missing items must be either filtered out

            or errored-on before record_iter_changes sees the item.

        :param _entry_factory: Private method to bind entry_factory locally for

            performance.

        :return: A generator of (file_id, relpath, fs_hash) tuples for use with

            tree._observed_sha1.

        """

        # Create an inventory delta based on deltas between all the parents and

        # deltas between all the parent inventories. We use inventory delta's 

        # between the inventory objects because iter_changes masks

        # last-changed-field only changes.

        # Working data:

        # file_id -> change map, change is fileid, paths, changed, versioneds,

        # parents, names, kinds, executables

        merged_ids = {}

        # {file_id -> revision_id -> inventory entry, for entries in parent

        # trees that are not parents[0]

        parent_entries = {}

        ghost_basis = False

        try:

            revtrees = list(self.repository.revision_trees(self.parents))

        except errors.NoSuchRevision:

            # one or more ghosts, slow path.

            revtrees = []

            for revision_id in self.parents:

                try:

                    revtrees.append(self.repository.revision_tree(revision_id))

                except errors.NoSuchRevision:

                    if not revtrees:

                        basis_revision_id = _mod_revision.NULL_REVISION

                        ghost_basis = True

                    revtrees.append(self.repository.revision_tree(

                        _mod_revision.NULL_REVISION))

        # The basis inventory from a repository 

        if revtrees:

            basis_tree = revtrees[0]

        else:

            basis_tree = self.repository.revision_tree(

                _mod_revision.NULL_REVISION)

        basis_inv = basis_tree.root_inventory

        if len(self.parents) > 0:

            if basis_revision_id != self.parents[0] and not ghost_basis:

                raise Exception(

                    "arbitrary basis parents not yet supported with merges")

            for revtree in revtrees[1:]:

                for change in revtree.root_inventory._make_delta(basis_inv):

                    if change[1] is None:

                        # Not present in this parent.

                        continue

                    if change[2] not in merged_ids:

                        if change[0] is not None:

                            basis_entry = basis_inv[change[2]]

                            merged_ids[change[2]] = [

                                # basis revid

                                basis_entry.revision,

                                # new tree revid

                                change[3].revision]

                            parent_entries[change[2]] = {

                                # basis parent

                                basis_entry.revision:basis_entry,

                                # this parent 

                                change[3].revision:change[3],

                                }

                        else:

                            merged_ids[change[2]] = [change[3].revision]

                            parent_entries[change[2]] = {change[3].revision:change[3]}

                    else:

                        merged_ids[change[2]].append(change[3].revision)

                        parent_entries[change[2]][change[3].revision] = change[3]

        else:

            merged_ids = {}

        # Setup the changes from the tree:

        # changes maps file_id -> (change, [parent revision_ids])

        changes= {}

        for change in iter_changes:

            # This probably looks up in basis_inv way to much.

            if change[1][0] is not None:

                head_candidate = [basis_inv[change[0]].revision]

            else:

                head_candidate = []

            changes[change[0]] = change, merged_ids.get(change[0],

                head_candidate)

        unchanged_merged = set(merged_ids) - set(changes)

        # Extend the changes dict with synthetic changes to record merges of

        # texts.

        for file_id in unchanged_merged:

            # Record a merged version of these items that did not change vs the

            # basis. This can be either identical parallel changes, or a revert

            # of a specific file after a merge. The recorded content will be

            # that of the current tree (which is the same as the basis), but

            # the per-file graph will reflect a merge.

            # NB:XXX: We are reconstructing path information we had, this

            # should be preserved instead.

            # inv delta  change: (file_id, (path_in_source, path_in_target),

            #   changed_content, versioned, parent, name, kind,

            #   executable)

            try:

                basis_entry = basis_inv[file_id]

            except errors.NoSuchId:

                # a change from basis->some_parents but file_id isn't in basis

                # so was new in the merge, which means it must have changed

                # from basis -> current, and as it hasn't the add was reverted

                # by the user. So we discard this change.

                pass

            else:

                change = (file_id,

                    (basis_inv.id2path(file_id), tree.id2path(file_id)),

                    False, (True, True),

                    (basis_entry.parent_id, basis_entry.parent_id),

                    (basis_entry.name, basis_entry.name),

                    (basis_entry.kind, basis_entry.kind),

                    (basis_entry.executable, basis_entry.executable))

                changes[file_id] = (change, merged_ids[file_id])

        # changes contains tuples with the change and a set of inventory

        # candidates for the file.

        # inv delta is:

        # old_path, new_path, file_id, new_inventory_entry

        seen_root = False # Is the root in the basis delta?

        inv_delta = self._basis_delta

        modified_rev = self._new_revision_id

        for change, head_candidates in changes.values():

            if change[3][1]: # versioned in target.

                # Several things may be happening here:

                # We may have a fork in the per-file graph

                #  - record a change with the content from tree

                # We may have a change against < all trees  

                #  - carry over the tree that hasn't changed

                # We may have a change against all trees

                #  - record the change with the content from tree

                kind = change[6][1]

                file_id = change[0]

                entry = _entry_factory[kind](file_id, change[5][1],

                    change[4][1])

                head_set = self._heads(change[0], set(head_candidates))

                heads = []

                # Preserve ordering.

                for head_candidate in head_candidates:

                    if head_candidate in head_set:

                        heads.append(head_candidate)

                        head_set.remove(head_candidate)

                carried_over = False

                if len(heads) == 1:

                    # Could be a carry-over situation:

                    parent_entry_revs = parent_entries.get(file_id, None)

                    if parent_entry_revs:

                        parent_entry = parent_entry_revs.get(heads[0], None)

                    else:

                        parent_entry = None

                    if parent_entry is None:

                        # The parent iter_changes was called against is the one

                        # that is the per-file head, so any change is relevant

                        # iter_changes is valid.

                        carry_over_possible = False

                    else:

                        # could be a carry over situation

                        # A change against the basis may just indicate a merge,

                        # we need to check the content against the source of the

                        # merge to determine if it was changed after the merge

                        # or carried over.

                        if (parent_entry.kind != entry.kind or

                            parent_entry.parent_id != entry.parent_id or

                            parent_entry.name != entry.name):

                            # Metadata common to all entries has changed

                            # against per-file parent

                            carry_over_possible = False

                        else:

                            carry_over_possible = True

                        # per-type checks for changes against the parent_entry

                        # are done below.

                else:

                    # Cannot be a carry-over situation

                    carry_over_possible = False

                # Populate the entry in the delta

                if kind == 'file':

                    # XXX: There is still a small race here: If someone reverts the content of a file

                    # after iter_changes examines and decides it has changed,

                    # we will unconditionally record a new version even if some

                    # other process reverts it while commit is running (with

                    # the revert happening after iter_changes did its

                    # examination).

                    if change[7][1]:

                        entry.executable = True

                    else:

                        entry.executable = False

                    if (carry_over_possible and

                        parent_entry.executable == entry.executable):

                            # Check the file length, content hash after reading

                            # the file.

                            nostore_sha = parent_entry.text_sha1

                    else:

                        nostore_sha = None

                    file_obj, stat_value = tree.get_file_with_stat(file_id, change[1][1])

                    try:

                        text = file_obj.read()

                    finally:

                        file_obj.close()

                    try:

                        entry.text_sha1, entry.text_size = self._add_text_to_weave(

                            file_id, text, heads, nostore_sha)

                        yield file_id, change[1][1], (entry.text_sha1, stat_value)

                    except errors.ExistingContent:

                        # No content change against a carry_over parent

                        # Perhaps this should also yield a fs hash update?

                        carried_over = True

                        entry.text_size = parent_entry.text_size

                        entry.text_sha1 = parent_entry.text_sha1

                elif kind == 'symlink':

                    # Wants a path hint?

                    entry.symlink_target = tree.get_symlink_target(file_id)

                    if (carry_over_possible and

                        parent_entry.symlink_target == entry.symlink_target):

                        carried_over = True