D533: effectflag: store an empty effect flag for the moment
lothiraldan (Boris Feld)
phabricator at mercurial-scm.org
Mon Aug 28 11:02:43 UTC 2017
lothiraldan created this revision.
Herald added a subscriber: mercurial-devel.
Herald added a reviewer: hg-reviewers.
REVISION SUMMARY
The idea behind effect flag is to store additional information in obs-markers
about what changed between a changeset and its successor(s). It's a low-level
information that comes without guarantees.
This information can be computed a posteriori, but only if we have all
changesets locally. This is not the case with distributed workflows where you
work with several people or on several computers (eg: laptop + build server).
Storing the effect-flag as a bitfield has several advantages:
- It's compact, we are using one byte per obs-marker at most for the effect- flag.
- It's compoundable, the obsfate log approach needs to display evolve history that could spans several obs-markers. Computing the effect-flag between a changeset and its grand-grand-grand-successor is simple thanks to the bitfield.
The effect-flag design has also some limitations:
- Evolving a changeset and reverting these changes just after would lead to two obs-markers with the same effect-flag without information that the first and third changesets are the same.
The effect-flag current design is a trade-off between compactness and
usefulness.
Storing this information helps commands to display a more complete and
understandable evolve history. For example, obslog (an Evolve command) use it
to improve its output:
x f9b900605b26 (34302) obscache: skip updating outdated obscache...
| rewritten(parent) by Matthieu Laneuville <matthieu.laneuville at octobus... |
| rewritten(content) by Boris Feld <boris.feld at octobus.net> |
|
The effect flag is stored in obs-markers metadata while we iterate on the
information we want to store. We plan to extend the existing obsmarkers
bit-field when the effect flag design will be stabilized.
It's different from the CommitCustody concept, effect-flag are not signed and
can be forged. It's also different from the operation metadata as the command
name (for example: amend) could alter a changeset in different ways (changing
the content with hg amend, changing the description with hg amend -e, changing
the user with hg amend -U). Also it's compatible with every custom command
that writes obs-markers without needing to be updated.
The effect-flag is placed behind an experimental flag set to off by default.
Hook the saving of effect flag in create markers, but store only an empty one
for the moment, I will refine the values in effect flag in following patches.
For more information, see:
https://www.mercurial-scm.org/wiki/ChangesetEvolutionDevel#Record_types_of_operation
REPOSITORY
rHG Mercurial
REVISION DETAIL
https://phab.mercurial-scm.org/D533
AFFECTED FILES
mercurial/obsolete.py
mercurial/obsutil.py
CHANGE DETAILS
diff --git a/mercurial/obsutil.py b/mercurial/obsutil.py
--- a/mercurial/obsutil.py
+++ b/mercurial/obsutil.py
@@ -305,6 +305,19 @@
foreground = set(repo.set('%ln::', known))
return set(c.node() for c in foreground)
+# logic around storing and using effect flags
+EFFECTFLAGFIELD = "ef1"
+
+def geteffectflag(relation):
+ """ From an obs-marker relation, compute what changed between the
+ predecessor and the successor.
+ """
+ effects = 0
+
+ source = relation[0]
+
+ return effects
+
def getobsoleted(repo, tr):
"""return the set of pre-existing revisions obsoleted by a transaction"""
torev = repo.unfiltered().changelog.nodemap.get
diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -1036,6 +1036,11 @@
if useoperation and operation:
metadata['operation'] = operation
+ # Effect flag metadata handling
+ saveeffectflag = repo.ui.configbool('experimental',
+ 'evolution.effect-flags',
+ False)
+
tr = repo.transaction('add-obsolescence-marker')
try:
markerargs = []
@@ -1059,6 +1064,13 @@
raise error.Abort(_("changeset %s cannot obsolete itself")
% prec)
+ # Effect flag can be different by relation
+ if saveeffectflag:
+ # The effect flag is saved in a versioned field name for future
+ # evolution
+ effectflag = obsutil.geteffectflag(rel)
+ localmetadata[obsutil.EFFECTFLAGFIELD] = "%d" % effectflag
+
# Creating the marker causes the hidden cache to become invalid,
# which causes recomputation when we ask for prec.parents() above.
# Resulting in n^2 behavior. So let's prepare all of the args
To: lothiraldan, #hg-reviewers
Cc: mercurial-devel
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