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Mon Sep 2 01:23:40 2013 UTC (8 years, 10 months ago) by dholland
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oops fix typo; thanks agc

    1: ## Using Mercurial and mq to work on NetBSD
    3: This page contains directions for using Mercurial as a commit buffer
    4: for NetBSD.
    6: (It will not do you much good if you're trying to convert the master
    7: NetBSD tree to Mercurial or to work with such a converted tree.)
    9: ### What it is
   11: Mercurial is a distributed version control system ("DVCS").
   12: mq is an extension to Mercurial for handling patch queues.
   13: The concept of patch queues was introduced by Quilt some years back.
   15: This document assumes you already know more or less how to use
   16: Mercurial but may not have used mq before.
   18: ### The model we're using here
   20: What we're going to do is commit a NetBSD CVS working tree into a
   21: Mercurial repository.
   22: You can then use Mercurial to merge; it is better at this than CVS.
   23: You can also commit changes locally and ship them back to the CVS
   24: master later; this is useful in a variety of ways.
   25: You can potentially also clone the Mercurial tree and work jointly
   26: with other people, but there are limits to this as we'll discuss in a
   27: moment.
   29: Because the NetBSD tree is rather large, you will find that if you
   30: commit the whole thing into Mercurial that a number of operations
   31: (anything that scans the working tree for changes) become annoyingly
   32: slow.
   33: It isn't slow enough to be unusable, and it's quite a bit faster than a
   34: comparable CVS option (like running cvs update from the top level),
   35: but it's slow enough to be annoying.
   37: For this reason, in most cases, I recommend committing only part of
   38: the tree into Mercurial and telling it to ignore the rest. This means
   39: you can't in general usefully clone the resulting Mercurial repo
   40: (although that depends on exactly what you leave out) but this is not
   41: a major problem unless you're specifically trying to work with someone
   42: else.
   44: So the basic model here is that you check out a CVS working tree and
   45: use Mercurial to manage local changes to part of it, then later on
   46: commit those changes back to the master CVS repository.
   48: ### Branches vs. patches
   50: There are two ways you can manage your changes: as a branch, or as a
   51: patch queue.
   52: The advantage of a patch queue is that you can easily commit each
   53: patch individually back to CVS, and you can go back and forth between
   54: them and debug and polish each one separately.
   55: The disadvantage is that the merge facilities are (as far as I know
   56: anyway) relatively limited.
   58: Conversely, if you commit your changes to a branch, you get all the
   59: native merging support in Mercurial.
   60: However, it is painful to try to commit anything other than one big
   61: diff for the whole branch back to CVS.
   62: (You might be able to do it via bookmarks and rebasing, but I've never
   63: tried and have no desire to figure out how.)
   65: If you don't want to keep the incremental history of your local
   66: commits, use a branch.
   67: If you do, use a patch queue.
   69: It is possible to use multiple branches to allow you to commit back in
   70: several stages.
   71: However, managing this is a major pain and I don't recommend it -- you
   72: might get away with two branches but more than that is probably a bad
   73: idea.
   75: There's a Mercurial extension called the "patch branch extension" that
   76: lets you manage a whole graph of patches using branches.
   77: I haven't tried using it in some years; at the time it had scaling
   78: problems such that it became horrifyingly slow once you had more than
   79: a handful of such branches.
   80: That might have been improved in the meantime; if you find yourself
   81: wanting to use both branches and patches, it might be worth looking
   82: into.
   84: It is also fairly probable that there is now a solution for merging
   85: with patch queues; it's been a while since I had time to look closely.
   87: ### Setting up
   89: First, check out a CVS working tree.
   90: You probably want to use a different one for each project, because
   91: different projects require changing different parts of the tree and so
   92: you will probably want to have Mercurial ignore different subtrees for
   93: different projects.
   94: (At least, I find it so; it depends on what you're working on.)
   96: 	% cvs -d checkout -P src
   98: Now create a Mercurial repository at the top level.
   99: (If you are working only in a subtree and you are *sure* that you will
  100: never need to change anything in other parts of the tree, you can
  101: create the Mercurial repository in a subtree.
  102: But unless you're absolutely certain, don't take the risk.)
  104: 	% cd src
  105: 	% hg init
  107: If you're going to be using a patch queue, now enable mq.
  109: 	% vi .hg/hgrc
  110: and add
  111: 	[extensions]
  112: =
  113: (Since the extension is built into Mercurial, that's all you need.)
  114: You can if you prefer also put this in your .hgrc so mq is always on.
  115: Then do
  116: 	hg qinit -c
  117: The -c option tells mq that you'll be checkpointing your patches,
  118: which is usually a good idea.
  120: Now prepare a .hgignore file.
  121: This file contains one regular expression per line; Mercurial ignores
  122: files (and subdirectories) whose paths from the repository root match
  123: one of the regexps.
  124: Add at least:
  125: 	^CVS$
  126: 	/CVS$
  127: to ignore all the CVS control directories in the CVS checkout.
  128: While you can commit these to Mercurial, there's no point and it gets
  129: awkward if owing to mistakes later you end up having to merge them.
  131: If you aren't arranging to put the tree's object directories somewhere
  132: else, then also add
  133: 	^obj\.[0-9a-z]$
  134: 	/obj\.[0-9a-z]$
  135: and you might want
  136: 	^sys/arch/[0-9a-z]*/compile/[A-Z]
  137: to ignore kernel build directories.
  139: Ignore subtrees that you aren't working in.
  140: You don't have to bother to be very selective; the goal is to rapidly
  141: rule out a few large subtrees that you definitely don't care about, in
  142: order to avoid wasting time scanning them for changes.
  143: Unless you plan to be working with 3rd-party software,
  145: 	^external$
  146: 	^gnu/dist$
  148: is a good starting point.
  149: Alternatively, if you aren't going to be working on MD kernel stuff or
  150: bootloaders,
  152: 	^sys/arch$
  154: is a good choice as it's also large.
  156: You can always unignore stuff later, so don't worry about remote
  157: possibilities.
  159: Now commit the .hgignore file:
  161: 	% hg add .hgignore
  162: 	% hg commit -m 'add .hgignore file' .hgignore
  164: Now add and commit the contents of the working tree:
  166: 	% hg add
  167: 	% hg commit -m 'HEAD of 20130101'
  168: (or whatever date)
  170: You are now in business.
  172: ### Working
  174: If you're using a branch, remember to change branches before you
  175: commit anything:
  176: 	% hg branch mystuff
  177: You want to keep the default branch an untouched CVS tree so you can
  178: use Mercurial to merge.
  179: (And also so you can use Mercurial to extract diffs against CVS HEAD
  180: and so forth.)
  182: Similarly, if you're using a patch queue, put everything in patches
  183: and don't commit.
  184: (There's a section below about working with mq if you aren't familiar
  185: with it.)
  187: You can edit and build and test as normal.
  188: Use hg commit or hg qrefresh to sync stuff into Mercurial.
  190: If you're using mq, it's a good idea to checkpoint your patch queue
  191: periodically.
  192: This is done as follows:
  193: 	% hg qcommit
  194: The patches directory (.hg/patches) is stored in its own Mercurial
  195: repository, and this commits the patches to that repository.
  196: If necessary you can then fetch older versions of the patches back and
  197: so forth.
  199: ### Updating from CVS
  201: First, make sure all your changes are committed.
  202: (If you have unfinished changes that aren't ready to commit, there's a
  203: Mercurial extension for stashing them temporarily.
  204: If you have stuff that you don't want to commit at all, like debugging
  205: printouts or quick hacks, it's often convenient to keep those in their
  206: own mq patch, even if you aren't using mq for development.)
  208: Now go back to a clean CVS tree.
  209: If using branches, go back to the default branch:
  210: 	% hg update -r default
  211: If using mq, pop all the patches:
  212: 	% hg qpop -a
  214: DO NOT run cvs update until/unless you have done this; it will make a
  215: mess.
  216: When you eventually do this by accident, see the section below on
  217: recovering from mistakes.
  219: Now run cvs update from the top of the source tree:
  220: 	% cvs -q update -dP
  222: You should get no conflicts from CVS and nothing should show as
  223: modified.
  224: (It is usually a good habit to save the cvs update output to a file to
  225: be able to check this.)
  227: Tell hg to sync up:
  228: 	% hg addremove
  230: Use hg to check what it thinks has changed:
  231: 	% hg status
  233: Commit the changes to Mercurial:
  234: 	% hg commit -m 'Updated to 20130202"
  236: Now you get to merge.
  238: If you're using a branch, you want to merge the changes into your
  239: branch rather than merge your branch into the changes:
  240: 	% hg update -r mystuff
  241: 	% hg merge default
  242: 	(edit and resolve as needed)
  243: 	% hg commit -m 'sync with HEAD'
  245: If it tells you "update crosses branches" when trying to update back
  246: to your branch, update to the parent changeset (the previous version
  247: from CVS) first, as that's an ancestor of your branch.
  249: If you're using mq, the thing to do now is to push all your patches,
  250: and if any reject, clean up the mess and refresh them.
  252: If patch tells you "hunk N succeeded at offset MMM with fuzz Q", it's
  253: a good idea to manually inspect the results -- patch being what it is,
  254: sometimes this means it's done the wrong thing.
  255: Edit if needed.
  256: Then (even if you didn't edit) refresh the patch so it won't happen
  257: again.
  259: As I said above, it's quite likely that by now there's a better scheme
  260: for merging with mq that I don't know about yet.
  262: ### Pushing back to CVS
  264: When you're ready to push your changes back to CVS (so they're really
  265: committed), first (unless you're absolutely sure it's not necessary)
  266: update from CVS as above and merge.
  267: Then:
  269: If you're using a branch, go back to the default branch and merge your
  270: changes into it:
  271: 	% hg update -r default
  272: 	% hg merge mystuff
  273: 	% hg commit -m "prepare to commit back to cvs"
  274: Now cvs add any new directories and files; be sure not to forget this.
  275: It is a good idea to crosscheck with cvs diff and/or cvs update:
  276: 	% cvs diff -up | less
  277: 	% cvs -nq update -dP
  278: Then you can cvs commit:
  279: 	% cvs commit
  280: Because of RCSIDs, committing into cvs changes the source files.
  281: So now you need to do:
  282: 	% hg commit -m 'cvs committed'
  283: and if you intend to keep working in this tree, you want to merge that
  284: changeset back into your branch to avoid having it cause merge
  285: conflicts later.
  286: Do that as above.
  289: If you're using a patch queue, usually it's because you want to commit
  290: each patch back to CVS individually.
  291: First pop all the patches:
  292: 	% hg qpop -a
  293: Now, for each patch:
  294: 	% hg qpush
  295: 	% hg qfinish -a
  296: 	% cvs commit
  297: 	% hg commit -m "cvs committed previous"
  298: With a long patch queue, you'll want to use the patch comments as the
  299: CVS commit messages.
  300: Also, running cvs commit from the top for every patch is horribly slow.
  301: Both these problems can be fixed by putting the following in a script:
  302: 	hg log -v -r. | sed '1,/^description:$/d' > patch-message
  303: 	cat patch-message
  304: 	echo -n 'cvs commit -F patch-message '
  305: 	hg log -v -r. | grep '^files:' | sed 's/^files://'
  306: (I call this "") and then the procedure is:
  307: 	% hg qpop -a
  308: then for each patch:
  309: 	% hg qpush && hg qfinish -a &&
  310: 	% cvs commit [as directed]
  311: 	% hg commit -m "cvs committed previous"
  312: (This could be automated further but doing so seems unwise.)
  314: ### Using CVS within Mercurial
  316: You can successfully do any read-only CVS operation in the hybrid
  317: tree: diff, annotate, log, update -p, etc.
  318: Read-write operations should be avoided; if you mix upstream changes
  319: with your changes you will find it much harder to commit upstream
  320: later, and you may get weird merge conflicts or even accidentally
  321: revert other people's changes and cause problems.
  323: If you clone the Mercurial tree and you didn't include the CVS control
  324: files in it, you won't be able to do CVS operations from clones.
  325: Including the CVS control files in the Mercurial tree is one way
  326: around that.
  328: You will find that any large CVS operation on a clone is horribly
  329: slow.
  330: This is because making a clone causes CVS to think all the files in
  331: the clone have been modified since you last ran it; it then re-fetches
  332: every file you ask it about so it can update its own information.
  333: For this reason cloning the Mercurial tree usually isn't worthwhile
  334: and even when it is, including the CVS files in the Mercurial tree
  335: isn't.
  337: Another consequence of this: do not try to cvs update in a cloned
  338: Mercurial repository; use only the original.
  339: Updating a clone basically downloads the entire tree over again from
  340: the CVS server.
  343: It is known that some operations that muck with the timestamps in a
  344: CVS working tree can cause CVS to lose data.
  345: It is not clear if hg clone is such an operation; don't be the person
  346: who finds out the hard way.
  348: ### Recovering from mistakes
  350: The most common mistake is CVS updating when the Mercurial tree is not
  351: in the proper state from that; e.g. onto your branch or while you have
  352: patches applied.
  354: The basic strategy for this is to use hg revert to restore the part of
  355: the tree it knows about, then go back to CVS, clean up the mess there,
  356: and update properly.
  358: If you're using a branch:
  359: 	% hg revert -C
  360: 	% hg update -r default
  361: If you're using a patch queue:
  362: 	% hg revert -C
  363: 	% hg qpop -a
  365: The problem is, CVS will now think you've changed every file that
  366: Mercurial is managing, and the modifications are to revert all the
  367: changes that have happened since your previous update.
  368: You do *not* want that to turn into reality.
  369: Hunt down (with cvs -n update) any files that CVS thinks are modified,
  370: then rm them and run cvs update on them.
  371: CVS will print "Warning: foo was lost" and restore an unmodified copy.
  373: When you have no files left that CVS thinks are modified, do a CVS
  374: update on the whole tree and merge it as described above.
  375: (You must do this, as the parts of the tree that Mercurial is ignoring
  376: will otherwise be out of sync with the parts it's managing.)
  378: If you stored the CVS control files in Mercurial, then the revert will
  379: restore them, but your tree will still be inconsistent so you still
  380: need to do a proper update and merge immediately.
  382: ### mq
  384: The basic idea of mq (like quilt) is it maintains a series of patches
  385: against the source tree, that are to be applied in order.
  386: By applying them or removing them one at a time, you can move the tree
  387: to any intermediate state; and then you can update the topmost patch,
  388: insert a new patch, or whatever.
  390: To see the list of patches:
  391: 	% hg qseries
  393: To apply the next patch:
  394: 	% hg qpush
  396: To remove the current patch:
  397: 	% hg qpop
  399: To merge current working tree changes into the current patch:
  400: 	% hg qrefresh
  402: To also update the current patch's change comment:
  403: 	% hg qrefresh -e
  405: To collect current working tree changes (if any) into a new patch:
  406: 	% hg qnew PATCHNAME 
  408: When there's an mq patch applied, you can't commit.
  409: (Doing qrefresh is basically equivalent to committing the current
  410: patch.)
  411: Diff will show the changes against the last refreshed version of the
  412: current patch; to see the complete changes for the current patch
  413: (including current changes), use "hg qdiff".
  415: You can delete patches with "hg qrm" and rename them with "hg qmv".
  417: Patches are applied with patch, unfortunately, which means that if
  418: they don't apply (which can happen if you or someone else changes
  419: something under one) you get .rej files you have to clean up by hand
  420: rather than a Mercurial merge.
  422: When a patch is ready to be committed for real, you do "hg qfinish" on
  423: it.
  424: This removes it from the patch queue and converts it to a normal
  425: Mercurial changeset.
  427: To change the ordering of patches, you edit the file
  428: .hg/patches/series.
  429: If the patches aren't orthogonal you'll have to fix the rejections
  430: when you next apply them.
  431: (Don't do this with patches that are currently applied.)
  433: Use "hg help mq" to see the full list of mq-related commands.
  435: I'm sure there are better mq tutorials out there.
  437: ### Using mq
  439: The basic process when using mq is that you start a new patch, edit
  440: and hack for a while, use hg qrefresh to commit it (once or many
  441: times), and when you're done go on to the next one.
  443: If you find a bug in an earlier patch, you can go back to the patch
  444: that introduced it and fix the bug there, creating a new version of
  445: the offending patch that no longer contains the bug.
  446: (Or you can create a new patch that fixes the bug, but insert it
  447: immediately after the patch that created the bug.)
  449: When a patch is ready to be seen by other people, you "finish" it and
  450: then it becomes a normal immutable changeset.
  452: One catch is that you can't push or pop the patch queue while you have
  453: unsynced (uncommitted) changes.
  454: There are two ways around this; there's a separate "stash" extension
  455: that lets you put unfinished changes aside while you do something else.
  456: Or, alternatively, you can create a new temporary patch holding your
  457: unfinished changes, and then later use hg qfold to combine that with
  458: the patch you originally meant this for.
  460: A variant of this problem is when you discover a bug, open an editor,
  461: fix it, and then realize that you wanted to make the edit in an
  462: earlier patch.
  463: Then you go to pop the queue and it complains that you have a modified
  464: file.
  465: If the modification in question is the only uncommitted change, the
  466: best way to deal with this is to create a new patch for it, then pop
  467: to where you wanted it to go and use hg qfold to apply it there.

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