Annotation of wikisrc/users/dholland/hgnb.mdwn, revision 1.10

1.1       dholland    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: 
1.10    ! dholland   29:     CVS                                 Mercurial
1.3       dholland   30: 
1.10    ! dholland   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
1.1       dholland   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:
1.10    ! dholland   68:                                         hg pull
        !            69:                                         hg merge
        !            70:                                         hg commit
1.1       dholland   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:
1.10    ! dholland   75:                                         hg resolve -m file
1.1       dholland   76: 
                     77: You can list unresolved conflicts thus:
1.10    ! dholland   78:                                         hg resolve -l
1.1       dholland   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:
1.10    ! dholland   89:                                         hg stash
        !            90:                                         hg merge
        !            91:                                         ...whatever merge stuff...
        !            92:                                         hg unstash
1.1       dholland   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: 
1.10    ! dholland  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
1.1       dholland  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:
1.10    ! dholland  125:                                         hg heads
1.1       dholland  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:
1.10    ! dholland  137:                                         hg recover
1.1       dholland  138: 
                    139: and if you have reason to think the repository might be corrupt you
                    140: can check it like this:
1.10    ! dholland  141:                                         hg verify
1.1       dholland  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: 
1.10    ! dholland  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
1.1       dholland  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:
1.10    ! dholland  176:     cvs co -P -rlibc13                  hg clone [url]
        !           177:                                         cd src
        !           178:                                         hg update -r libc13
1.1       dholland  179: 
                    180: Switch to a new tree on a branch:
1.10    ! dholland  181:     cvs up -dP -A -rlibc13              hg pull                         (if needed)
        !           182:                                         hg update -r libc13
1.1       dholland  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:
1.10    ! dholland  188:                                         hg update -r libc13-base
        !           189:                                         [resolve conflicts if needed]
        !           190:                                         hg update -r libc13
        !           191:                                         [resolve conflicts if needed]
1.1       dholland  192: 
                    193: Check which branch you're currently on:
                    194: 
1.10    ! dholland  195:     cat CVS/Tag                         hg branch
1.1       dholland  196: 
                    197: See list of branches:
1.10    ! dholland  198:     [no can do reliably]                hg branches     
1.1       dholland  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: 
1.10    ! dholland  209:     cvs ph'tagn                         hg merge default
        !           210:     [resolve conflicts]                 [resolve conflicts]
        !           211:     cvs commit                          hg commit
        !           212:                                         hg push
1.1       dholland  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: 
1.10    ! dholland  219:     [no can do]                         hg commit --close-branch
1.1       dholland  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: 
1.10    ! dholland  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
1.1       dholland  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: 
1.10    ! dholland  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
1.1       dholland  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: 
1.10    ! dholland  315:     cvs rtag -r netbsd-7 \              hg tag -r netbsd-7 \
        !           316:       netbsd-7-0-RELEASE                  netbsd-7-0-RELEASE
1.1       dholland  317: 
                    318: Viewing the changes on a branch:
                    319: 
1.10    ! dholland  320:     cvs log > file                      hg log -b netbsd-7
        !           321:     [page through and curse]
1.1       dholland  322: 
                    323: Extracting tarballs:
                    324: 
1.10    ! dholland  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: 
1.1       dholland  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: 
1.10    ! dholland  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
1.1       dholland  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:
1.10    ! dholland  405:                                         hg revert -r rev subtree
1.1       dholland  406: To revert to a specific date:
1.10    ! dholland  407:                                         hg revert -d date subtree
1.1       dholland  408: 
                    409: 
                    410: ### Other stuff
                    411: 
                    412: Have I forgotten anything?
                    413: Email me questions...

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