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Sun Dec 14 03:15:45 2014 UTC (6 years, 10 months ago) by dholland
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    1: ## Mercurial usage for NetBSD
    2: (hypothetically assuming the repositories have been converted)
    3: 
    4: Here are some directions for how one would use Mercurial after a
    5: NetBSD transition from CVS to Mercurial.
    6: Most of this is pretty trivial (especially for anyone who's used
    7: Mercurial before...)
    8: 
    9: There is a lot of FUD circulating about using a distributed version
   10: control system, what with talk of "workflows" and "topic branches" and
   11: other unfamiliar terms.
   12: Most of this arises from git user communities and git advocates;
   13: because git is screwy, using git is more complicated than using other
   14: better designed tools.
   15: Also, those suffering from Stockholm syndrome with respect to git tend
   16: to believe that the complexities of git are inherent to distributed
   17: version control, which is not the case; and many other people have been
   18: alarmed (or scared, or confused) by things such people have told them.
   19: 
   20: ### Basic usage
   21: 
   22: First, NetBSD will go on using a central master repository. There is
   23: nothing to be gained by changing this; we have the project
   24: infrastructure to support it, and ultimately there has to be some tree
   25: somewhere that constitutes the master copy regardless.
   26: 
   27: Therefore, the basic usage is almost entirely unchanged:
   28: 
   29:     CVS                                 Mercurial
   30: 
   31:     cvs checkout                        hg clone
   32:     cvs update -dP                      hg pull && hg update
   33:     cvs -n update                       hg status
   34:     cvs log file                        hg log file  [or just hg log]
   35: 
   36:     cvs update -p file                  hg cat file
   37:     cvs annotate                        hg annotate
   38:     cvs diff -u                         hg diff
   39:     cvs add                             hg add
   40:     cvs rm                              hg rm
   41:     [no can do]                         hg cp
   42:     [no can do]                         hg mv
   43:     cvs commit                          hg commit && hg push
   44:     cvs tag                             hg tag
   45: 
   46: You will notice that CVS's update and commit have been divided into
   47: two now-separable actions: in Mercurial, pull fetches changes from a
   48: remote repository but doesn't affect your working tree, and update
   49: updates your working tree to (by default) the latest new changes.
   50: Similarly, commit integrates changes from your working tree, but
   51: locally only; push publishes those changes to the remote repository.
   52: 
   53: This means that you can commit many times before pushing; this is
   54: often desirable if you're working on something nontrivial and you want
   55: to wait until it's ready before shipping it out.
   56: 
   57: There is one catch, which is that other people can commit (and push to
   58: the master repository) while you're working. You can mostly avoid
   59: this, if you haven't committed anything locally yet, by doing "hg pull
   60: && hg update" before committing, which will merge into your
   61: uncommitted changes and works exactly like updating before committing
   62: in CVS. However, if you've committed a number of changes, or someone
   63: got a new change in right between when you last pulled and when you
   64: committed, you need to do an explicit merge instead, and then you can
   65: push.
   66: 
   67: In the simple case, you do an explicit merge as follows:
   68:                                         hg pull
   69:                                         hg merge
   70:                                         hg commit
   71: 
   72: When you get a merge conflict, you first need to resolve it (in the
   73: usual way by editing) and then you must tag it resolved in hg before
   74: hg will let you commit, like this:
   75:                                         hg resolve -m file
   76: 
   77: You can list unresolved conflicts thus:
   78:                                         hg resolve -l
   79: 
   80: Note that even with the explicit merge this is almost exactly
   81: equivalent to the CVS behavior when someone commits ahead of you.
   82: The chief difference is that because Mercurial does whole-tree
   83: commits, *any* change ahead of you needs to be merged, not just one
   84: that touches the same files you've edited.
   85: 
   86: There is one gotcha, which is that you can't do explicit merges in a
   87: tree with uncommitted changes. The best way around this is to stash
   88: your changes:
   89:                                         hg stash
   90:                                         hg merge
   91:                                         ...whatever merge stuff...
   92:                                         hg unstash
   93: 
   94: You can also do the merge in another tree; because Mercurial is a
   95: distributed tool, you can create a temporary copy of your tree, or
   96: push the changes you need to another tree you already have, do the
   97: work there, and push the results back. Let's suppose you have two
   98: trees, "src" and "scratch", where you never keep uncommitted changes
   99: in "scratch" so it can be used for this kind of thing. Then you can do
  100: the following (starting at the top of src):
  101: 
  102:                                         hg push ../scratch
  103:                                         cd ../scratch
  104:                                         hg update
  105:                                         hg merge
  106:                                         ...whatever merge stuff, including commit...
  107:                                         cd ../src
  108:                                         hg pull ../scratch
  109:                                         hg update
  110: 
  111: ### Disconnected operation
  112: 
  113: Mercurial is a distributed system, and works by cloning the entire
  114: history into each tree you create.
  115: This has its downsides; but it means that you get disconnected
  116: operation for free.
  117: The only operations that need to contact the master repository are
  118: push, pull, incoming, and outgoing.
  119: 
  120: ### Some other bits
  121: 
  122: A commit with no descendents (that is, the most recent commit on any
  123: line of development) is called a "head".
  124: You can list these as follows:
  125:                                         hg heads
  126: 
  127: This will include commits that have descendents only on other
  128: branches, e.g. the last commit on a development branch that's been
  129: merged but not closed. Use "-t" ("topological heads") to hide these.
  130: 
  131: You can see what "hg pull" and "hg push" are going to do via "hg
  132: incoming" and "hg outgoing" respectively.
  133: (FWIW, git can't do this.)
  134: 
  135: If you interrupt Mercurial (or Mercurial gets interrupted, e.g. by a
  136: system crash) you want to do this afterwards:
  137:                                         hg recover
  138: 
  139: and if you have reason to think the repository might be corrupt you
  140: can check it like this:
  141:                                         hg verify
  142: 
  143: ### Development branches
  144: 
  145: A development branch is one where you're working on some new feature
  146: and you expect to merge the branch into the trunk later.
  147: Unlike in CVS, this is very cheap in Mercurial.
  148: The following are the operations you need, using "libc13" as an
  149: example branch name.
  150: 
  151: Note that even if you're working on something nontrivial that will
  152: take a number of commits, if you aren't intending to push the changes
  153: out before they're done you don't need to make a branch and there's
  154: nothing gained by doing so.
  155: However, if you expect to be working over a long period of time on a
  156: major effort (such as the mythical libc version bump), and/or you
  157: want or expect other developers to contribute or at least test your
  158: changes before they're done, go ahead and create a branch.
  159: 
  160: Create a new branch:
  161: 
  162:     cvs update -dP                      hg pull && hg update            (if needed)
  163:     update doc/BRANCHES                 update doc/BRANCHES             (if appropriate)
  164:     cvs commit doc/BRANCHES             hg commit doc/BRANCHES          (if needed)
  165:     cvs tag libc13-base                 hg tag libc13-base
  166:     cvs ph'tagn                         hg branch libc13
  167:     [make first change]                 [make first change]
  168:     cvs commit                          hg commit
  169:                                         hg push
  170: 
  171: Mercurial warns you that branches are permanent and expensive; this
  172: warning is aimed at git users who ought to be creating bookmarks
  173: instead and not something you need to be concerned about.
  174: 
  175: Check out a new tree on a branch:
  176:     cvs co -P -rlibc13                  hg clone [url]
  177:                                         cd src
  178:                                         hg update -r libc13
  179: 
  180: Switch to a new tree on a branch:
  181:     cvs up -dP -A -rlibc13              hg pull                         (if needed)
  182:                                         hg update -r libc13
  183: 
  184: Note that if you have uncommitted changes, Mercurial will balk at
  185: crossing from one branch to another because it doesn't know how to
  186: merge them.
  187: In that case do this:
  188:                                         hg update -r libc13-base
  189:                                         [resolve conflicts if needed]
  190:                                         hg update -r libc13
  191:                                         [resolve conflicts if needed]
  192: 
  193: Check which branch you're currently on:
  194: 
  195:     cat CVS/Tag                         hg branch
  196: 
  197: See list of branches:
  198:     [no can do reliably]                hg branches     
  199: 
  200: Note that unlike with CVS there's no version-control-related reason to
  201: get a new tree just to work on a branch.
  202: (Although of course it's still possible to commit to the wrong branch
  203: by accident.)
  204: Get a new tree if and only if you want to have a different tree for
  205: administrative reasons.
  206: 
  207: Sync your branch with the trunk ("HEAD" in CVS):
  208: 
  209:     cvs ph'tagn                         hg merge default
  210:     [resolve conflicts]                 [resolve conflicts]
  211:     cvs commit                          hg commit
  212:                                         hg push
  213: 
  214: When you're done with your branch, in Mercurial you can "close" it so
  215: it's no longer active.
  216: This causes it to disappear from some reports, reduces some internal
  217: management overheads, and prevents accidental commits on it.
  218: 
  219:     [no can do]                         hg commit --close-branch
  220: 
  221: Don't forget to update doc/BRANCHES too.
  222: 
  223: ### Vendor branches
  224: 
  225: A vendor branch is one where code from a third party is committed in
  226: unmodified state, so it can be updated easily from upstream later.
  227: 
  228: Note that in CVS vendor branches are magic (in a bad way); in
  229: Mercurial we'll just use an ordinary branch. We'll start it from the
  230: empty revision so it doesn't contain any unwanted rubbish.
  231: 
  232: To start a new vendor branch for the upstream package "frobozz",
  233: assuming you've already written frobozz2netbsd if one's needed:
  234: 
  235:     mkdir tmp
  236:     cd tmp
  237:                                         hg update -r0000
  238:                                         mkdir external && cd external
  239:                                         mkdir bsd && cd bsd
  240:                                         mkdir frobozz && cd frobozz
  241:     tar -xvzf frobozz-1.0.tgz           tar -xvzf frobozz-1.0.tgz
  242:     mv frobozz-1.0 dist                 mv frobozz-1.0 dist
  243:     cp .../frobozz2netbsd .             cp .../frobozz2netbsd .
  244:     ./frobozz2netbsd                    ./frobozz2netbsd                (if needed)
  245:     cvs import src/distrib/bsd/frobozz \
  246:       FROBOZZ frobozz-1-0
  247:                                         hg add
  248:                                         hg branch FROBOZZ
  249:                                         hg commit
  250:                                         hg tag frobozz-1-0
  251:     cd ../src
  252:     cvs update -dP
  253:                                         hg update -r default
  254:                                         hg merge FROBOZZ
  255:                                         hg commit
  256:     [hack as needed]                    [hack as needed]
  257:     cvs commit                          hg commit
  258:                                         hg push
  259:     cd ..
  260:     rm -r tmp
  261: 
  262: Note that in both cases this imports frobozz2netbsd on the branch;
  263: this seems the most convenient but I'm not sure if it's been our
  264: standard procedure.
  265: 
  266: To update "frobozz" to 1.1:
  267: 
  268:     mkdir tmp
  269:     cd tmp
  270:                                         hg update -rFROBOZZ
  271:                                         cd external/bsd/frobozz
  272:     tar -xvzf frobozz-1.1.tgz           tar -xvzf frobozz-1.1.tgz
  273:                                         rm -r dist
  274:     mv frobozz-1.1 dist                 mv frobozz-1.1 dist
  275:     ./frobozz2netbsd                    ./frobozz2netbsd
  276:     cvs import src/distrib/bsd/frobozz \
  277:       FROBOZZ frobozz-1-0
  278:                                         hg addremove
  279:                                         hg commit
  280:                                         hg tag frobozz-1-1
  281:     cd ..
  282:     mkdir tmp2 && cd tmp2
  283:     cvs ph'tagn
  284:                                         hg update -r default
  285:                                         hg merge FROBOZZ
  286:     [resolve conflicts]                 [resolve conflicts]
  287:     cvs commit                          hg commit
  288:     cd ../src
  289:     cvs update -dP
  290:     [hack as needed]                    [hack as needed]
  291:     cvs commit                          hg commit
  292:                                         hg push
  293:     cd ..
  294:     rm -r tmp tmp2
  295: 
  296: ### Release branches
  297: 
  298: A release branch is one that diverges from the main branch and is not
  299: expected to be merged back into it.
  300: However, changes from the main branch are (individually) merged into
  301: it after review.
  302: 
  303: Creating a release branch in Mercurial is the same as creating a
  304: feature branch; see above.
  305: So is checking it out.
  306: Committing a change to a release branch is no different from
  307: committing to the default branch or any other branch.
  308: 
  309: TODO: we should probably use the Mercurial cherrypick extension for at
  310: least some release branch pullups; I don't know how to do that offhand
  311: without looking it up.
  312: 
  313: Tagging a release:
  314: 
  315:     cvs rtag -r netbsd-7 \              hg tag -r netbsd-7 \
  316:       netbsd-7-0-RELEASE                  netbsd-7-0-RELEASE
  317: 
  318: Viewing the changes on a branch:
  319: 
  320:     cvs log > file                      hg log -b netbsd-7
  321:     [page through and curse]
  322: 
  323: Extracting tarballs:
  324: 
  325:     mkdir tmp
  326:     cd tmp
  327:     cvs export -r netbsd-7-0-RELEASE \  hg archive -r netbsd-7-0-RELEASE \
  328:       src                                 ../netbsd-7.0.tar.gz
  329:     mv src netbsd-7.0
  330:     tar -cvzf ../netbsd-7.0.tar.gz \
  331:       netbsd-7.0
  332:     cd ..
  333:     rm -r tmp
  334: 
  335: 
  336: ### Reverting a bad commit
  337: 
  338: Sometimes somebody commits something that needs to be unwound later.
  339: In CVS you have to track down each per-file change and undo each one
  340: separately, then commit them all.
  341: In Mercurial, because Mercurial has whole-tree commits, you can do it
  342: with a single command.
  343: 
  344:     cvs update -j1.6 -j1.5 foo.c
  345:     cvs update -j1.9 -j1.8 bar.c
  346:     cvs update -j1.15 -j1.14 baz.c
  347:                                         hg backout -r 101abcde
  348:     [resolve conflicts]                 [resolve conflicts]
  349:     cvs commit                          hg commit
  350:                                         hg push
  351: 
  352: Note that apparently if you use hg backout to back out the most recent
  353: commit, it auto-commits.
  354: (This seems to me like a UI bug.)
  355: 
  356: ### Carrying local changes
  357: 
  358: In CVS you can keep uncommitted changes in your tree indefinitely with
  359: no ill effects.
  360: (Or at least, no ill effects until you want to commit other changes to
  361: the same files, run into merge conflicts, or hit PR 42961.)
  362: 
  363: In Mercurial having uncommitted changes keeps you from doing explicit
  364: merges, which you need to do much more often than in CVS.
  365: There are several ways around this:
  366: 
  367: * You can stash your uncommitted changes any time you need to merge.
  368: This works fine but it quickly becomes a nuisance.
  369: * You can use different trees for hacking and for building the system
  370: for install, since presumably you only need the local changes in
  371: the latter case.
  372: This works fine until you need to shift partially-completed hacking to
  373: the installable tree, and then becomes painful.
  374: * You can commit your local changes as "secret" using the evolve
  375: extension (I recommend reading the docs for the evolve extension);
  376: then they're committed and can be merged and so on, but won't get
  377: pushed back to the master repository.
  378: The downside of this is that you can't readily distribute your local
  379: changes among your own repositories.
  380: * You can use the mq patch queue extension and store your local
  381: changes as patches against the tree; then they can be popped off
  382: easily for other work.
  383: The downside of this is that merging stuff into your local changes
  384: becomes awkward.
  385: * You can finish your local changes so they can be committed upstream :-)
  386: 
  387: None of these solutions is perfect, but one or the other of these
  388: approaches is probably good enough in most cases.
  389: 
  390: ### Reverting stuff locally
  391: 
  392: In CVS you can use "cvs update" to pin a subtree down to a specific
  393: point in history, where it will stay while you update the rest of the
  394: tree around it.
  395: (Accidental engagement of this feature is probably as common as
  396: intentional use...)
  397: 
  398: There is no direct equivalent in Mercurial.
  399: However, you can easily alter a file or subtree to roll it back to a
  400: specific point in history, and then carry the resulting diff as a
  401: local modification until whatever issue prompted you to do this gets
  402: sorted out.
  403: 
  404: To revert to a specific version:
  405:                                         hg revert -r rev subtree
  406: To revert to a specific date:
  407:                                         hg revert -d date subtree
  408: 
  409: 
  410: ### Other stuff
  411: 
  412: Have I forgotten anything?
  413: Email me questions...

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