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| author | jerojasro@localhost |
|---|---|
| date | Thu Oct 16 23:09:25 2008 -0500 (2008-10-16) |
| parents | |
| children | 8bedea2b8d60 |
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1 \chapter{Administración de Versiones y desarrollo ramificado}
2 \label{chap:branch}
4 Mercurial ofrece varios mecanismos que le permitirán administrar un
5 proyecto que avanza en múltiples frentes simultáneamente. Para
6 entender estos mecanismos, demos un vistazo a la estructura usual de
7 un proyecto de software.
9 Muchos proyectos de software liberan una versión``mayor'' que contiene
10 nuevas características substanciales. En paralelo, pueden liberar
11 versiones ``menores''. Estas usualmente son idénticas a las
12 versiones mayores en las cuales están basadas, pero con arreglo de
13 algunos fallos.
15 En este capítulo, comenzaremos hablando de cómo mantener registro de
16 las etapas del proyecto como las liberaciones de una
17 versión. Continuaremos hablando del flujo de trabajo entre las
18 diferentes fases de un proyecto, y como puede ayudar Mercurial a
19 independizar y administrar tal trabajo.
21 \section{Dar un nombre persistente a una revisión}
23 Cuando se decide a otorgar a una revisión el nombre particular de una
24 ``versión'', es buena idea grabar la identidad para tal revisión.
25 Lo cual permitirá reproducir tal versión en una fecha posterior, o el
26 propósito que se considere en ese momento (reproducir un fallo, portar
27 a una nueva plataforma, etc).
28 \interaction{tag.init}
30 Mercurial le permite dar un nombre permanente a cualquier revisión
31 usando la orden \hgcmd{tag}. Sin causa de sorpresa, esos nombres se llaman
32 ``tags''(etiquetas).
33 \interaction{tag.tag}
35 Un tag no es más que un ``nombre simbólico'' para una revisión. Los
36 tags existen únicamente para su conveniencia, dotándolo de una forma
37 permanente y sencilla para referirse a una revisión; Mercurial no
38 interpreta de ninguna manera los nombres de los tags que usted use.
39 Mercurial tampoco impone restricción alguna al nombre de un tag, más
40 allá de lo necesario para asegurar que un tag puede parsearse sin
41 ambigüedades. El nombre de un tag no puede tener ninguno de los
42 caracteres siguientes:
43 \begin{itemize}
44 \item Dos puntos (ASCII 58, ``\texttt{:}'')
45 \item Retroceso (return) (ASCII 13, ``\Verb+\r+'')
46 \item Nueva línea (ASCII 10, ``\Verb+\n+'')
47 \end{itemize}
49 Puede usar la orden \hgcmd{tags} para observar los tags presentes en
50 su repositorio. Al desplegarse, cada revisión marcada se identifica
51 primero con su nombre, después el número de revisión y finalmente con
52 un hash único de la revisión.
53 \interaction{tag.tags}
54 Note que \texttt{tip} aparece en la lista de \hgcmd{tags}. El tag
55 \texttt{tip} es un tag ``flotante'' especial, que identifica siempre
56 la revisión más nueva en el repositorio.
58 Al desplegar la orden \hgcmd{tags}, los tags se listan en orden
59 inverso, por número de revisión. Lo que significa usualmente que los
60 tags más recientes se listan antes que los más antiguos. También
61 significa que el tag \texttt{tip} siempre aparecerá como primer tag
62 listado al desplegar la orden \hgcmd{tags}.
64 Cuando ejecuta \hgcmd{log}, se desplegará la revisión que tenga los
65 tags asociados a ella, se imprimirán tales tags.
66 \interaction{tag.log}
68 Siempre que requiera indicar un ~ID de revisión a una Orden de
69 Mercurial, aceptará un nombre de tag en su lugar. Internamente,
70 Mercurial traducirá su nombre de tag en el ~ID de revisión
71 correspondiente, y lo usará.
72 \interaction{tag.log.v1.0}
74 There's no limit on the number of tags you can have in a repository,
75 or on the number of tags that a single revision can have. As a
76 practical matter, it's not a great idea to have ``too many'' (a number
77 which will vary from project to project), simply because tags are
78 supposed to help you to find revisions. If you have lots of tags, the
79 ease of using them to identify revisions diminishes rapidly.
81 For example, if your project has milestones as frequent as every few
82 days, it's perfectly reasonable to tag each one of those. But if you
83 have a continuous build system that makes sure every revision can be
84 built cleanly, you'd be introducing a lot of noise if you were to tag
85 every clean build. Instead, you could tag failed builds (on the
86 assumption that they're rare!), or simply not use tags to track
87 buildability.
89 If you want to remove a tag that you no longer want, use
90 \hgcmdargs{tag}{--remove}.
91 \interaction{tag.remove}
92 You can also modify a tag at any time, so that it identifies a
93 different revision, by simply issuing a new \hgcmd{tag} command.
94 You'll have to use the \hgopt{tag}{-f} option to tell Mercurial that
95 you \emph{really} want to update the tag.
96 \interaction{tag.replace}
97 There will still be a permanent record of the previous identity of the
98 tag, but Mercurial will no longer use it. There's thus no penalty to
99 tagging the wrong revision; all you have to do is turn around and tag
100 the correct revision once you discover your error.
102 Mercurial stores tags in a normal revision-controlled file in your
103 repository. If you've created any tags, you'll find them in a file
104 named \sfilename{.hgtags}. When you run the \hgcmd{tag} command,
105 Mercurial modifies this file, then automatically commits the change to
106 it. This means that every time you run \hgcmd{tag}, you'll see a
107 corresponding changeset in the output of \hgcmd{log}.
108 \interaction{tag.tip}
110 \subsection{Handling tag conflicts during a merge}
112 You won't often need to care about the \sfilename{.hgtags} file, but
113 it sometimes makes its presence known during a merge. The format of
114 the file is simple: it consists of a series of lines. Each line
115 starts with a changeset hash, followed by a space, followed by the
116 name of a tag.
118 If you're resolving a conflict in the \sfilename{.hgtags} file during
119 a merge, there's one twist to modifying the \sfilename{.hgtags} file:
120 when Mercurial is parsing the tags in a repository, it \emph{never}
121 reads the working copy of the \sfilename{.hgtags} file. Instead, it
122 reads the \emph{most recently committed} revision of the file.
124 An unfortunate consequence of this design is that you can't actually
125 verify that your merged \sfilename{.hgtags} file is correct until
126 \emph{after} you've committed a change. So if you find yourself
127 resolving a conflict on \sfilename{.hgtags} during a merge, be sure to
128 run \hgcmd{tags} after you commit. If it finds an error in the
129 \sfilename{.hgtags} file, it will report the location of the error,
130 which you can then fix and commit. You should then run \hgcmd{tags}
131 again, just to be sure that your fix is correct.
133 \subsection{Tags and cloning}
135 You may have noticed that the \hgcmd{clone} command has a
136 \hgopt{clone}{-r} option that lets you clone an exact copy of the
137 repository as of a particular changeset. The new clone will not
138 contain any project history that comes after the revision you
139 specified. This has an interaction with tags that can surprise the
140 unwary.
142 Recall that a tag is stored as a revision to the \sfilename{.hgtags}
143 file, so that when you create a tag, the changeset in which it's
144 recorded necessarily refers to an older changeset. When you run
145 \hgcmdargs{clone}{-r foo} to clone a repository as of tag
146 \texttt{foo}, the new clone \emph{will not contain the history that
147 created the tag} that you used to clone the repository. The result
148 is that you'll get exactly the right subset of the project's history
149 in the new repository, but \emph{not} the tag you might have expected.
151 \subsection{When permanent tags are too much}
153 Since Mercurial's tags are revision controlled and carried around with
154 a project's history, everyone you work with will see the tags you
155 create. But giving names to revisions has uses beyond simply noting
156 that revision \texttt{4237e45506ee} is really \texttt{v2.0.2}. If
157 you're trying to track down a subtle bug, you might want a tag to
158 remind you of something like ``Anne saw the symptoms with this
159 revision''.
161 For cases like this, what you might want to use are \emph{local} tags.
162 You can create a local tag with the \hgopt{tag}{-l} option to the
163 \hgcmd{tag} command. This will store the tag in a file called
164 \sfilename{.hg/localtags}. Unlike \sfilename{.hgtags},
165 \sfilename{.hg/localtags} is not revision controlled. Any tags you
166 create using \hgopt{tag}{-l} remain strictly local to the repository
167 you're currently working in.
169 \section{The flow of changes---big picture vs. little}
171 To return to the outline I sketched at the beginning of a chapter,
172 let's think about a project that has multiple concurrent pieces of
173 work under development at once.
175 There might be a push for a new ``main'' release; a new minor bugfix
176 release to the last main release; and an unexpected ``hot fix'' to an
177 old release that is now in maintenance mode.
179 The usual way people refer to these different concurrent directions of
180 development is as ``branches''. However, we've already seen numerous
181 times that Mercurial treats \emph{all of history} as a series of
182 branches and merges. Really, what we have here is two ideas that are
183 peripherally related, but which happen to share a name.
184 \begin{itemize}
185 \item ``Big picture'' branches represent the sweep of a project's
186 evolution; people give them names, and talk about them in
187 conversation.
188 \item ``Little picture'' branches are artefacts of the day-to-day
189 activity of developing and merging changes. They expose the
190 narrative of how the code was developed.
191 \end{itemize}
193 \section{Managing big-picture branches in repositories}
195 The easiest way to isolate a ``big picture'' branch in Mercurial is in
196 a dedicated repository. If you have an existing shared
197 repository---let's call it \texttt{myproject}---that reaches a ``1.0''
198 milestone, you can start to prepare for future maintenance releases on
199 top of version~1.0 by tagging the revision from which you prepared
200 the~1.0 release.
201 \interaction{branch-repo.tag}
202 You can then clone a new shared \texttt{myproject-1.0.1} repository as
203 of that tag.
204 \interaction{branch-repo.clone}
206 Afterwards, if someone needs to work on a bug fix that ought to go
207 into an upcoming~1.0.1 minor release, they clone the
208 \texttt{myproject-1.0.1} repository, make their changes, and push them
209 back.
210 \interaction{branch-repo.bugfix}
211 Meanwhile, development for the next major release can continue,
212 isolated and unabated, in the \texttt{myproject} repository.
213 \interaction{branch-repo.new}
215 \section{Don't repeat yourself: merging across branches}
217 In many cases, if you have a bug to fix on a maintenance branch, the
218 chances are good that the bug exists on your project's main branch
219 (and possibly other maintenance branches, too). It's a rare developer
220 who wants to fix the same bug multiple times, so let's look at a few
221 ways that Mercurial can help you to manage these bugfixes without
222 duplicating your work.
224 In the simplest instance, all you need to do is pull changes from your
225 maintenance branch into your local clone of the target branch.
226 \interaction{branch-repo.pull}
227 You'll then need to merge the heads of the two branches, and push back
228 to the main branch.
229 \interaction{branch-repo.merge}
231 \section{Naming branches within one repository}
233 In most instances, isolating branches in repositories is the right
234 approach. Its simplicity makes it easy to understand; and so it's
235 hard to make mistakes. There's a one-to-one relationship between
236 branches you're working in and directories on your system. This lets
237 you use normal (non-Mercurial-aware) tools to work on files within a
238 branch/repository.
240 If you're more in the ``power user'' category (\emph{and} your
241 collaborators are too), there is an alternative way of handling
242 branches that you can consider. I've already mentioned the
243 human-level distinction between ``small picture'' and ``big picture''
244 branches. While Mercurial works with multiple ``small picture''
245 branches in a repository all the time (for example after you pull
246 changes in, but before you merge them), it can \emph{also} work with
247 multiple ``big picture'' branches.
249 The key to working this way is that Mercurial lets you assign a
250 persistent \emph{name} to a branch. There always exists a branch
251 named \texttt{default}. Even before you start naming branches
252 yourself, you can find traces of the \texttt{default} branch if you
253 look for them.
255 As an example, when you run the \hgcmd{commit} command, and it pops up
256 your editor so that you can enter a commit message, look for a line
257 that contains the text ``\texttt{HG: branch default}'' at the bottom.
258 This is telling you that your commit will occur on the branch named
259 \texttt{default}.
261 To start working with named branches, use the \hgcmd{branches}
262 command. This command lists the named branches already present in
263 your repository, telling you which changeset is the tip of each.
264 \interaction{branch-named.branches}
265 Since you haven't created any named branches yet, the only one that
266 exists is \texttt{default}.
268 To find out what the ``current'' branch is, run the \hgcmd{branch}
269 command, giving it no arguments. This tells you what branch the
270 parent of the current changeset is on.
271 \interaction{branch-named.branch}
273 To create a new branch, run the \hgcmd{branch} command again. This
274 time, give it one argument: the name of the branch you want to create.
275 \interaction{branch-named.create}
277 After you've created a branch, you might wonder what effect the
278 \hgcmd{branch} command has had. What do the \hgcmd{status} and
279 \hgcmd{tip} commands report?
280 \interaction{branch-named.status}
281 Nothing has changed in the working directory, and there's been no new
282 history created. As this suggests, running the \hgcmd{branch} command
283 has no permanent effect; it only tells Mercurial what branch name to
284 use the \emph{next} time you commit a changeset.
286 When you commit a change, Mercurial records the name of the branch on
287 which you committed. Once you've switched from the \texttt{default}
288 branch to another and committed, you'll see the name of the new branch
289 show up in the output of \hgcmd{log}, \hgcmd{tip}, and other commands
290 that display the same kind of output.
291 \interaction{branch-named.commit}
292 The \hgcmd{log}-like commands will print the branch name of every
293 changeset that's not on the \texttt{default} branch. As a result, if
294 you never use named branches, you'll never see this information.
296 Once you've named a branch and committed a change with that name,
297 every subsequent commit that descends from that change will inherit
298 the same branch name. You can change the name of a branch at any
299 time, using the \hgcmd{branch} command.
300 \interaction{branch-named.rebranch}
301 In practice, this is something you won't do very often, as branch
302 names tend to have fairly long lifetimes. (This isn't a rule, just an
303 observation.)
305 \section{Dealing with multiple named branches in a repository}
307 If you have more than one named branch in a repository, Mercurial will
308 remember the branch that your working directory on when you start a
309 command like \hgcmd{update} or \hgcmdargs{pull}{-u}. It will update
310 the working directory to the tip of this branch, no matter what the
311 ``repo-wide'' tip is. To update to a revision that's on a different
312 named branch, you may need to use the \hgopt{update}{-C} option to
313 \hgcmd{update}.
315 This behaviour is a little subtle, so let's see it in action. First,
316 let's remind ourselves what branch we're currently on, and what
317 branches are in our repository.
318 \interaction{branch-named.parents}
319 We're on the \texttt{bar} branch, but there also exists an older
320 \hgcmd{foo} branch.
322 We can \hgcmd{update} back and forth between the tips of the
323 \texttt{foo} and \texttt{bar} branches without needing to use the
324 \hgopt{update}{-C} option, because this only involves going backwards
325 and forwards linearly through our change history.
326 \interaction{branch-named.update-switchy}
328 If we go back to the \texttt{foo} branch and then run \hgcmd{update},
329 it will keep us on \texttt{foo}, not move us to the tip of
330 \texttt{bar}.
331 \interaction{branch-named.update-nothing}
333 Committing a new change on the \texttt{foo} branch introduces a new
334 head.
335 \interaction{branch-named.foo-commit}
337 \section{Branch names and merging}
339 As you've probably noticed, merges in Mercurial are not symmetrical.
340 Let's say our repository has two heads, 17 and 23. If I
341 \hgcmd{update} to 17 and then \hgcmd{merge} with 23, Mercurial records
342 17 as the first parent of the merge, and 23 as the second. Whereas if
343 I \hgcmd{update} to 23 and then \hgcmd{merge} with 17, it records 23
344 as the first parent, and 17 as the second.
346 This affects Mercurial's choice of branch name when you merge. After
347 a merge, Mercurial will retain the branch name of the first parent
348 when you commit the result of the merge. If your first parent's
349 branch name is \texttt{foo}, and you merge with \texttt{bar}, the
350 branch name will still be \texttt{foo} after you merge.
352 It's not unusual for a repository to contain multiple heads, each with
353 the same branch name. Let's say I'm working on the \texttt{foo}
354 branch, and so are you. We commit different changes; I pull your
355 changes; I now have two heads, each claiming to be on the \texttt{foo}
356 branch. The result of a merge will be a single head on the
357 \texttt{foo} branch, as you might hope.
359 But if I'm working on the \texttt{bar} branch, and I merge work from
360 the \texttt{foo} branch, the result will remain on the \texttt{bar}
361 branch.
362 \interaction{branch-named.merge}
364 To give a more concrete example, if I'm working on the
365 \texttt{bleeding-edge} branch, and I want to bring in the latest fixes
366 from the \texttt{stable} branch, Mercurial will choose the ``right''
367 (\texttt{bleeding-edge}) branch name when I pull and merge from
368 \texttt{stable}.
370 \section{Branch naming is generally useful}
372 You shouldn't think of named branches as applicable only to situations
373 where you have multiple long-lived branches cohabiting in a single
374 repository. They're very useful even in the one-branch-per-repository
375 case.
377 In the simplest case, giving a name to each branch gives you a
378 permanent record of which branch a changeset originated on. This
379 gives you more context when you're trying to follow the history of a
380 long-lived branchy project.
382 If you're working with shared repositories, you can set up a
383 \hook{pretxnchangegroup} hook on each that will block incoming changes
384 that have the ``wrong'' branch name. This provides a simple, but
385 effective, defence against people accidentally pushing changes from a
386 ``bleeding edge'' branch to a ``stable'' branch. Such a hook might
387 look like this inside the shared repo's \hgrc.
388 \begin{codesample2}
389 [hooks]
390 pretxnchangegroup.branch = hg heads --template '{branches} ' | grep mybranch
391 \end{codesample2}
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