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Opportunities for improvement on GNU Arch
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Bazaar-NG is based on the GNU Arch system, and inherits a lot of its
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design from Arch. However, there are several things we will change in
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Baz to (we hope) improve the user experience.
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The core design of Arch is good, brilliant even. It can scale from
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small projects too large ones, and is a good foundation for building
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tools on top. However, the design is far too complex, both in
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concepts and execution. So the plan is to cut out as many things as
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we can, add a few other good concepts from other systems, and try to
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make it into a whole that is consistent and understandable.
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No other system is able to express this valuable idea: "I merged all
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these changes from other people; here is the result."
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However, it should *also* be possible to bring in perfect-fit
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patches without creating a new commit.
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Find a common ancestor on diverged and cross-merged branches.
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* Apply isolated changesets.
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We should extend this by having a good way to send changesets by
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email, preferably readable even by people who are not using Arch.
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* GPG signing of commits.
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Open source hackers almost all have GPG keys already, and GPG deals
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with a lot of PKI functions to do with propagating, signing and
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Signed commits are interesting in many ways, not least of which in
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detecting intrusion to code servers.
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* Anonymous downloads can be done without an active server.
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Good for security; also very good for people who do not have a
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permnanently-connected machine on which they can install their own
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software, or which is very tightly secured.
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It's neat that you can upload over only sftp/ftp, but I'm not sure
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it's really worth the hassle; getting properly atomic operations
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over remote-file protocols is hard.
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* Clean and transparent storage format.
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This is a neat hack, and gives people assurance that they can get
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their data back out again even if the tool disappears. Very nice.
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(Bazaar-NG won't keep the exact same format, but the ideas will be
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* Relatively easily parseable/scriptable shell interface. Good for
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people writing web/emacs/editor/IDE interfaces, or scripts based it.
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* Automatically build (and hardlink) revision libraries, with
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I don't know how many people want *every* revision in a library, but
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it can be handy to have a few key ones.
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In general making use of hardlinks when they are available and safe
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* Rely on ssh for remote access, authentication, and confidentiality.
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* Patch headers separate from patch bodies. (Sometimes you only want
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* Autogeneration of Changelogs -- but should be in GNU format, at
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least optionally. I'm not convinced auto-updating them in the tree
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is worthwhile; it makes merges wierd.
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It seems useful to prevent accidental commits to things that are
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meant to be stable. However, the set-once nature of sealing is
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undesirable, because people can make mistakes or want to seal more
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One possibility is to have a voluntary write-protect flag set on
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branches that should not normally be updated. One can remove the
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flag if it turns out it was set wrongly.
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* ``resolved`` command in Bazaar-1.1
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Good for preventing accidental breakage.
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* Multi-level undo -- though could perhaps be more understandable,
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perhaps through ``undo-history``.
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One lesson from usability design is that it does not always work to
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have a complex model and then try to hide complexity in the user
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interface. If you want something to be a joy to use, that must be
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designed in from the bottom up.
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(Some developers may react to tla by thinking "eww, how gross" on
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particular points. As much as possible we might like to fix these.)
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* General impression that the tool is telling you how to run your life.
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* Non-standard terminology
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Arch uses terms like "version" and "category" in ways that are
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confusing to people accustomed to other version control systems.
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Therefore: development proceeds on a *branch*, which is a series of
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*revisions*. Simple and obvious.
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* Command-line options are wierdly inconsistent with both other
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systems, with each others, and with what people would like to do.
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For example, I would think the obvious usage is ``bzr diff [FILE]``,
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but ``tla diff`` does not let you specify a file at all.
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Most commands should take filenames as their argument: log, diff,
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* Despite having too many commands, there are massive and glaring
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gaps, such reverting a single file or a tree.
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* Commands are too different from what people are used to in CVS, and
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often not for a good reason.
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* Identifiers are too long. In part this is because Arch tries to
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have identifiers which are both human-assigned and universally unique.
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* Archive names are probably unnecessary.
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* Part of the reason for complexity in archives is that the Arch
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design wants to be able to go and find patches on other branches at
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a later time. (This is not really implemented or used at the
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I think the complexity is unjustified: changesets and revisions have
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universally unique names so they can simply be archived, either on
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the machine of the person who wants them or on a central site like
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* The tool is *unforgiving*; if people create a branch with the wrong
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name it will be around forever.
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* Branches are heaviweight; a record always persists in the archive.
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Sometimes it is good to create micro-branches, try something out,
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and then discard them. If nobody wants the changes, there is no
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reason for the tool to keep them.
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* Working offline requires creating a new branch and merging back and
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forth. This is both more work than it should be, and also polutes
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the "story" told by branching.
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As much as possible, the *accidental* difference of the location of
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the repository should not effect the *semantics* of branches.
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(However, some merging may obviously be necessary when there is
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* Archive registration. This causes confusion and is unnecessary.
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Proposed solutions such as archive aliases or an additional command
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to register-and-get make it worse.
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* Wierd file names (``++`` and ``,,``, which persist in user
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directories and cause breakage of many tools. Gives a bad
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impression, and it's even worse when people have to interact with
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* Overly-long identifiers. (One advantage of pointing to branches
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using filenames or URLs is that the length of the path depends on
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how close it is to the users location, and they can more easily use
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* Too slow by default.
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Arch can be made fast, but in the hands of a nonexpert user it is
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often slow. For most users, disk is cheaper than CPU time, which is
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cheaper than network roundtrips. The performance model should be
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transparent -- users should not be surprised that something is slow.
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* Tagging onto branches.
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Unifying tags and commits is interesting, but the result is hard to
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mentally model; even Arch maintainers can't say exactly how it is
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supposed to work in some cases.
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* Reinventing the world from scratch in libhackerlab/frob/pika/xl.
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Those are all fine projects and may be useful in the future, but
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they are totally unnecessary to write a great version control
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system. It is not an enormous project; it is not CPU-cycle
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critical; something like Python will be fine.
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* Lack (for the moment) of an active server.
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Given that network traffic is the most expensive thing, we can
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possibly get a better solution by having intelligence on both sides
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of the link. Suppose we want to get just one file from a previous
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* Poor Windows/Mac support.
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Even though many developers only work on Linux, this still holds a
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tool back. The reason is this: at least some projects have some
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developers on Windows some of the time. Those projects can't switch
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to Arch. Most people want to only learn one tool deeply, so it
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Don't make any overly Unixy assumptions. Avoid too-cute filesystem
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Being in Python should help with portability: people do need to
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install it, but many developers will already have it and the total
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burden is possibly less than that of installing C requisite
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* Quirky filename support.
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Files with non-ascii names, or names containing whitespace tend to
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be handled poorly, perhaps partly because of arch's shell heritage.
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By swallowing XML we do at least get automatic quoting of wierd
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strings, and we will always use UTF-8 for internal storage.
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* Complex file-id-tagging
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Nobody should be expected to understand this. There are two basic
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cases: people want to auto-add everything, and want to add by hand.
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Both can be reasonably accomodated in a simpler system.
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* Complex naming-convention regexps in ``.arch-inventory`` and
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``{arch}/id-tagging-method``. (The fact that there are two
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overlapping mechanisms with very different names is also bad.)
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All this complexity basically just comes down to versioned, ignored,
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unknown, the same as in every other system. So we might as well
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There are relatively few cases where regexps help more than globs,
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and people do find them more complex. Even experienced users can
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forget to escape ``\.``. We can have a bit of flexibility with
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(say) zsh-style extended globs like ``*.(pyo|pyc)``.
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* Some files inside ``{arch}`` are meant to be edited by the user, and
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some are not. This is a flaw common to other systems, including
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Bitkeeper. The user should be clear on whether they should touch
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things in a directory or not.
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* Source-librarian function works poorly.
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It is not the place of a tool to force people to stay organized; it
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should just facilitate it. In any case, a library without
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descriptive text is of little use. So bazaar-ng does not force
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three-level naming but rather lets people arrange their own trees,
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and put on their own descriptions (either within the tree, or by
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e.g. having a wiki page listing branches, descriptions and URLs.)
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* Whining about inode mismatches on pristines/revlibs.
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It's fine that there is validation, but the tool should not show off
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its limitations. Just do the right thing.
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* More generally, not quite enough consistency/safety checking.
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* Unclear what commands work on subdirs and what works on the whole
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* Hard to share work on a single branch -- though still not really too
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* Lack of partial commits of added/deleted files.
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* Separate id tags for each file; simple implementation but probably
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costs too much disk space.
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* Way too many deeply-nested directories; should be just one.
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* ``.listing`` files are ugly and a point of failure. They can cause
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trouble on some servers which limit access to dot files.
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Isn't it possible to have the top-level file be predictable and find
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everything else needed from there?
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* Summary separate from log message.
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Simpler to just have one message, and let people extract the first
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line/sentence if they wish.
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Rather than 'keywords', let arbitrary properties be attached to the
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revision at the time of commit.
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Simpler disconnected operation
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------------------------------
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A basic distributed VCS operation is to make it easy to work on an
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offline laptop. Arch can do this in a few ways, but none of them are
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http://wiki.gnuarch.org/moin.cgi/mini_5fTravellingOftenWithArch
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Yaron Minsky writes (2005-01-18):
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I was wondering what people considered to be a good setup for using
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Arch on a laptop. Here's the basic situation. I have a few projects
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that reside in arch repositories on my desktop computer. Basically,
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I'd like to be able to do commits from my laptop, and have those
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commits eventually migrate up to the main repository. I understand
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that the right way of doing this is to set up archives on the laptop.
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But what's the cleanest way of doing this? And is there some way of
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making the commits I do on the laptop show up cleanly and individually
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on the desktop once they are merged in?
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baz default is much less strict.
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Much of tla depends on being able to categorize files. Some hangovers
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from larch -- eg precious and backup are essentially the same. junk
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is never deleted today.
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Automatic version control with 'untagged-source source'. But this is
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- having the feature at all
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- complex way to define it
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Default of 166 lines.
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Remove id-tagging-method command or at most make it read-only. If
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people really want to use deprecated methods they can just edit the
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So we can ship a default id-tagging which works the same as CVS/Svn:
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give warnings for files that are not known to be junk. This is the
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default in baz right now.
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Also we have .arch-inventory, which is per-directory.
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Why not have 'baz ignore FILENAME'? To remove ignores, perhaps you
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have to edit the .arch-inventory. Print "FILTER added to
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PATH/.arch-inventory"; create and baz-add this file if it doesn't.
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Docs should perhaps emphasize .arch-inventory as the basic method and
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only mention =tagging-method as an advanced topic.
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Should this really be regexps, or just file globs?
b'\\ No newline at end of file'
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doc/todo-from-arch.txt
