hgbook
view en/hook.tex @ 134:b727a63518d4
Minor updates to race description.
| author | Bryan O'Sullivan <bos@serpentine.com> |
|---|---|
| date | Fri Jul 21 22:42:19 2006 -0700 (2006-07-21) |
| parents | d1a3394f8bcf |
| children | 0707489b90fd |
line source
1 \chapter{Handling repository events with hooks}
2 \label{chap:hook}
4 Mercurial offers a powerful mechanism to let you perform automated
5 actions in response to events that occur in a repository. In some
6 cases, you can even control Mercurial's response to those events.
8 The name Mercurial uses for one of these actions is a \emph{hook}.
9 Hooks are called ``triggers'' in some revision control systems, but
10 the two names refer to the same idea.
12 \section{An overview of hooks in Mercurial}
14 Here is a brief list of the hooks that Mercurial supports. We will
15 revisit each of these hooks in more detail later, in
16 section~\ref{sec:hook:ref}.
18 \begin{itemize}
19 \item[\small\hook{changegroup}] This is run after a group of
20 changesets has been brought into the repository from elsewhere.
21 \item[\small\hook{commit}] This is run after a new changeset has been
22 created in the local repository.
23 \item[\small\hook{incoming}] This is run once for each new changeset
24 that is brought into the repository from elsewhere. Notice the
25 difference from \hook{changegroup}, which is run once per
26 \emph{group} of changesets brought in.
27 \item[\small\hook{outgoing}] This is run after a group of changesets
28 has been transmitted from this repository.
29 \item[\small\hook{prechangegroup}] This is run before starting to
30 bring a group of changesets into the repository.
31 \item[\small\hook{precommit}] Controlling. This is run before starting
32 a commit.
33 \item[\small\hook{preoutgoing}] Controlling. This is run before
34 starting to transmit a group of changesets from this repository.
35 \item[\small\hook{pretag}] Controlling. This is run before creating a tag.
36 \item[\small\hook{pretxnchangegroup}] Controlling. This is run after a
37 group of changesets has been brought into the local repository from
38 another, but before the transaction completes that will make the
39 changes permanent in the repository.
40 \item[\small\hook{pretxncommit}] Controlling. This is run after a new
41 changeset has been created in the local repository, but before the
42 transaction completes that will make it permanent.
43 \item[\small\hook{preupdate}] Controlling. This is run before starting
44 an update or merge of the working directory.
45 \item[\small\hook{tag}] This is run after a tag is created.
46 \item[\small\hook{update}] This is run after an update or merge of the
47 working directory has finished.
48 \end{itemize}
49 Each of the hooks whose description begins with the word
50 ``Controlling'' has the ability to determine whether an activity can
51 proceed. If the hook succeeds, the activity may proceed; if it fails,
52 the activity is either not permitted or undone, depending on the hook.
54 \section{Hooks and security}
56 \subsection{Hooks are run with your privileges}
58 When you run a Mercurial command in a repository, and the command
59 causes a hook to run, that hook runs on \emph{your} system, under
60 \emph{your} user account, with \emph{your} privilege level. Since
61 hooks are arbitrary pieces of executable code, you should treat them
62 with an appropriate level of suspicion. Do not install a hook unless
63 you are confident that you know who created it and what it does.
65 In some cases, you may be exposed to hooks that you did not install
66 yourself. If you work with Mercurial on an unfamiliar system,
67 Mercurial will run hooks defined in that system's global \hgrc\ file.
69 If you are working with a repository owned by another user, Mercurial
70 can run hooks defined in that user's repository, but it will still run
71 them as ``you''. For example, if you \hgcmd{pull} from that
72 repository, and its \sfilename{.hg/hgrc} defines a local
73 \hook{outgoing} hook, that hook will run under your user account, even
74 though you don't own that repository.
76 \begin{note}
77 This only applies if you are pulling from a repository on a local or
78 network filesystem. If you're pulling over http or ssh, any
79 \hook{outgoing} hook will run under whatever account is executing
80 the server process, on the server.
81 \end{note}
83 XXX To see what hooks are defined in a repository, use the
84 \hgcmdargs{config}{hooks} command. If you are working in one
85 repository, but talking to another that you do not own (e.g.~using
86 \hgcmd{pull} or \hgcmd{incoming}), remember that it is the other
87 repository's hooks you should be checking, not your own.
89 \subsection{Hooks do not propagate}
91 In Mercurial, hooks are not revision controlled, and do not propagate
92 when you clone, or pull from, a repository. The reason for this is
93 simple: a hook is a completely arbitrary piece of executable code. It
94 runs under your user identity, with your privilege level, on your
95 machine.
97 It would be extremely reckless for any distributed revision control
98 system to implement revision-controlled hooks, as this would offer an
99 easily exploitable way to subvert the accounts of users of the
100 revision control system.
102 Since Mercurial does not propagate hooks, if you are collaborating
103 with other people on a common project, you should not assume that they
104 are using the same Mercurial hooks as you are, or that theirs are
105 correctly configured. You should document the hooks you expect people
106 to use.
108 In a corporate intranet, this is somewhat easier to control, as you
109 can for example provide a ``standard'' installation of Mercurial on an
110 NFS filesystem, and use a site-wide \hgrc\ file to define hooks that
111 all users will see. However, this too has its limits; see below.
113 \subsection{Hooks can be overridden}
115 Mercurial allows you to override a hook definition by redefining the
116 hook. You can disable it by setting its value to the empty string, or
117 change its behaviour as you wish.
119 If you deploy a system-~or site-wide \hgrc\ file that defines some
120 hooks, you should thus understand that your users can disable or
121 override those hooks.
123 \subsection{Ensuring that critical hooks are run}
125 Sometimes you may want to enforce a policy that you do not want others
126 to be able to work around. For example, you may have a requirement
127 that every changeset must pass a rigorous set of tests. Defining this
128 requirement via a hook in a site-wide \hgrc\ won't work for remote
129 users on laptops, and of course local users can subvert it at will by
130 overriding the hook.
132 Instead, you can set up your policies for use of Mercurial so that
133 people are expected to propagate changes through a well-known
134 ``canonical'' server that you have locked down and configured
135 appropriately.
137 One way to do this is via a combination of social engineering and
138 technology. Set up a restricted-access account; users can push
139 changes over the network to repositories managed by this account, but
140 they cannot log into the account and run normal shell commands. In
141 this scenario, a user can commit a changeset that contains any old
142 garbage they want.
144 When someone pushes a changeset to the server that everyone pulls
145 from, the server will test the changeset before it accepts it as
146 permanent, and reject it if it fails to pass the test suite. If
147 people only pull changes from this filtering server, it will serve to
148 ensure that all changes that people pull have been automatically
149 vetted.
151 \section{Care with \texttt{pretxn} hooks in a shared-access repository}
153 If you want to use hooks to so some automated work in a repository
154 that a number of people have shared access to, you need to be careful
155 in how you do this.
157 Mercurial only locks a repository when it is writing to the
158 repository, and only the parts of Mercurial that write to the
159 repository pay attention to locks. Write locks are necessary to
160 prevent multiple simultaneous writers from scribbling on each other's
161 work, corrupting the repository.
163 Because Mercurial is careful with the order in which it reads and
164 writes data, it does not need to acquire a lock when it wants to read
165 data from the repository. The parts of Mercurial that read from the
166 repository never pay attention to locks. This lockless reading scheme
167 greatly increases performance and concurrency.
169 With great performance comes a trade-off, though, one which has the
170 potential to cause you trouble unless you're aware of it. To describe
171 this requires a little detail about how Mercurial adds changesets to a
172 repository and reads those changes.
174 When Mercurial \emph{writes} metadata, it writes it straight into the
175 destination file. It writes file data first, then manifest data
176 (which contains pointers to the new file data), then changelog data
177 (which contains pointers to the new manifest data). Before the first
178 write to each file, it stores a record of where the end of the file
179 was in its transaction log. If the transaction must be rolled back,
180 Mercurial simply truncates each file back to te size it was before the
181 transaction began.
183 When Mercurial \emph{reads} metadata, it reads the changelog first,
184 then everything else. Since a reader will only access parts of the
185 manifest or file metadata that it can see in the changelog, it can
186 never see partially written data.
188 Some controlling hooks (\hook{pretxncommit} and
189 \hook{pretxnchangegroup}) run when a transaction is almost complete.
190 All of the metadata has been written, but Mercurial can still roll the
191 transaction back and cause the newly-written data to disappear.
193 If one of these hooks runs for long, it opens a window of time during
194 which a reader can see the metadata for changesets that are not yet
195 permanent, and should not be thought of as ``really there''. The
196 longer the hook runs, the longer that window is open.
198 \subsection{The problem illustrated}
200 In principle, a good use for the \hook{pretxnchangegroup} hook would
201 be to automatically build and test incoming changes before they are
202 accepted into a central repository. This could let you guarantee that
203 nobody can push changes to this repository that ``break the build''.
204 But if a client can pull changes while they're being tested, the
205 usefulness of the test is zero; an unsuspecting someone can pull
206 untested changes, potentially breaking their build.
208 The safest technological answer to this challenge is to set up such a
209 ``gatekeeper'' repository as \emph{unidirectional}. Let it take
210 changes pushed in from the outside, but do not allow anyone to pull
211 changes from it (use the \hook{preoutgoing} hook to lock it down).
212 Configure a \hook{changegroup} hook so that if a build or test
213 succeeds, the hook will push the new changes out to another repository
214 that people \emph{can} pull from.
216 In practice, putting a centralised bottleneck like this in place is
217 not often a good idea, and transaction visibility has nothing to do
218 with the problem. As the size of a project---and the time it takes to
219 build and test---grows, you rapidly run into a wall with this ``try
220 before you buy'' approach, where you have more changesets to test than
221 time in which to deal with them. The inevitable result is frustration
222 on the part of all involved.
224 An approach that scales better is to get people to build and test
225 before they push, then run automated builds and tests centrally
226 \emph{after} a push, to be sure all is well. The advantage of this
227 approach is that it does not impose a limit on the rate at which the
228 repository can accept changes.
230 \section{A short tutorial on using hooks}
231 \label{sec:hook:simple}
233 It is easy to write a Mercurial hook. Let's start with a hook that
234 runs when you finish a \hgcmd{commit}, and simply prints the hash of
235 the changeset you just created. The hook is called \hook{commit}.
237 \begin{figure}[ht]
238 \interaction{hook.simple.init}
239 \caption{A simple hook that runs when a changeset is committed}
240 \label{ex:hook:init}
241 \end{figure}
243 All hooks follow the pattern in example~\ref{ex:hook:init}. You add
244 an entry to the \rcsection{hooks} section of your \hgrc\. On the left
245 is the name of the event to trigger on; on the right is the action to
246 take. As you can see, you can run an arbitrary shell command in a
247 hook. Mercurial passes extra information to the hook using
248 environment variables (look for \envar{HG\_NODE} in the example).
250 \subsection{Performing multiple actions per event}
252 Quite often, you will want to define more than one hook for a
253 particular kind of event, as shown in example~\ref{ex:hook:ext}.
254 Mercurial lets you do this by adding an \emph{extension} to the end of
255 a hook's name. You extend a hook's name by giving the name of the
256 hook, followed by a full stop (the ``\texttt{.}'' character), followed
257 by some more text of your choosing. For example, Mercurial will run
258 both \texttt{commit.foo} and \texttt{commit.bar} when the
259 \texttt{commit} event occurs.
261 \begin{figure}[ht]
262 \interaction{hook.simple.ext}
263 \caption{Defining a second \hook{commit} hook}
264 \label{ex:hook:ext}
265 \end{figure}
267 To give a well-defined order of execution when there are multiple
268 hooks defined for an event, Mercurial sorts hooks by extension, and
269 executes the hook commands in this sorted order. In the above
270 example, it will execute \texttt{commit.bar} before
271 \texttt{commit.foo}, and \texttt{commit} before both.
273 It is a good idea to use a somewhat descriptive extension when you
274 define a new hook. This will help you to remember what the hook was
275 for. If the hook fails, you'll get an error message that contains the
276 hook name and extension, so using a descriptive extension could give
277 you an immediate hint as to why the hook failed (see
278 section~\ref{sec:hook:perm} for an example).
280 \subsection{Controlling whether an activity can proceed}
281 \label{sec:hook:perm}
283 In our earlier examples, we used the \hook{commit} hook, which is
284 run after a commit has completed. This is one of several Mercurial
285 hooks that run after an activity finishes. Such hooks have no way of
286 influencing the activity itself.
288 Mercurial defines a number of events that occur before an activity
289 starts; or after it starts, but before it finishes. Hooks that
290 trigger on these events have the added ability to choose whether the
291 activity can continue, or will abort.
293 The \hook{pretxncommit} hook runs after a commit has all but
294 completed. In other words, the metadata representing the changeset
295 has been written out to disk, but the transaction has not yet been
296 allowed to complete. The \hook{pretxncommit} hook has the ability to
297 decide whether the transaction can complete, or must be rolled back.
299 If the \hook{pretxncommit} hook exits with a status code of zero, the
300 transaction is allowed to complete; the commit finishes; and the
301 \hook{commit} hook is run. If the \hook{pretxncommit} hook exits with
302 a non-zero status code, the transaction is rolled back; the metadata
303 representing the changeset is erased; and the \hook{commit} hook is
304 not run.
306 \begin{figure}[ht]
307 \interaction{hook.simple.pretxncommit}
308 \caption{Using the \hook{pretxncommit} hook to control commits}
309 \label{ex:hook:pretxncommit}
310 \end{figure}
312 The hook in example~\ref{ex:hook:pretxncommit} checks that a commit
313 comment contains a bug ID. If it does, the commit can complete. If
314 not, the commit is rolled back.
316 \section{Writing your own hooks}
318 When you are writing a hook, you might find it useful to run Mercurial
319 either with the \hggopt{-v} option, or the \rcitem{ui}{verbose} config
320 item set to ``true''. When you do so, Mercurial will print a message
321 before it calls each hook.
323 \subsection{Choosing how your hook should run}
324 \label{sec:hook:lang}
326 You can write a hook either as a normal program---typically a shell
327 script---or as a Python function that is executed within the Mercurial
328 process.
330 Writing a hook as an external program has the advantage that it
331 requires no knowledge of Mercurial's internals. You can call normal
332 Mercurial commands to get any added information you need. The
333 trade-off is that external hooks are slower than in-process hooks.
335 An in-process Python hook has complete access to the Mercurial API,
336 and does not ``shell out'' to another process, so it is inherently
337 faster than an external hook. It is also easier to obtain much of the
338 information that a hook requires by using the Mercurial API than by
339 running Mercurial commands.
341 If you are comfortable with Python, or require high performance,
342 writing your hooks in Python may be a good choice. However, when you
343 have a straightforward hook to write and you don't need to care about
344 performance (probably the majority of hooks), a shell script is
345 perfectly fine.
347 \subsection{Hook parameters}
348 \label{sec:hook:param}
350 Mercurial calls each hook with a set of well-defined parameters. In
351 Python, a parameter is passed as a keyword argument to your hook
352 function. For an external program, a parameter is passed as an
353 environment variable.
355 Whether your hook is written in Python or as a shell script, the
356 hook-specific parameter names and values will be the same. A boolean
357 parameter will be represented as a boolean value in Python, but as the
358 number 1 (for ``true'') or 0 (for ``false'') as an environment
359 variable for an external hook. If a hook parameter is named
360 \texttt{foo}, the keyword argument for a Python hook will also be
361 named \texttt{foo} Python, while the environment variable for an
362 external hook will be named \texttt{HG\_FOO}.
364 \subsection{Hook return values and activity control}
366 A hook that executes successfully must exit with a status of zero if
367 external, or return boolean ``false'' if in-process. Failure is
368 indicated with a non-zero exit status from an external hook, or an
369 in-process hook returning boolean ``true''. If an in-process hook
370 raises an exception, the hook is considered to have failed.
372 For a hook that controls whether an activity can proceed, zero/false
373 means ``allow'', while non-zero/true/exception means ``deny''.
375 \subsection{Writing an external hook}
377 When you define an external hook in your \hgrc\ and the hook is run,
378 its value is passed to your shell, which interprets it. This means
379 that you can use normal shell constructs in the body of the hook.
381 An executable hook is always run with its current directory set to a
382 repository's root directory.
384 Each hook parameter is passed in as an environment variable; the name
385 is upper-cased, and prefixed with the string ``\texttt{HG\_}''.
387 With the exception of hook parameters, Mercurial does not set or
388 modify any environment variables when running a hook. This is useful
389 to remember if you are writing a site-wide hook that may be run by a
390 number of different users with differing environment variables set.
391 In multi-user situations, you should not rely on environment variables
392 being set to the values you have in your environment when testing the
393 hook.
395 \subsection{Telling Mercurial to use an in-process hook}
397 The \hgrc\ syntax for defining an in-process hook is slightly
398 different than for an executable hook. The value of the hook must
399 start with the text ``\texttt{python:}'', and continue with the
400 fully-qualified name of a callable object to use as the hook's value.
402 The module in which a hook lives is automatically imported when a hook
403 is run. So long as you have the module name and \envar{PYTHONPATH}
404 right, it should ``just work''.
406 The following \hgrc\ example snippet illustrates the syntax and
407 meaning of the notions we just described.
408 \begin{codesample2}
409 [hooks]
410 commit.example = python:mymodule.submodule.myhook
411 \end{codesample2}
412 When Mercurial runs the \texttt{commit.example} hook, it imports
413 \texttt{mymodule.submodule}, looks for the callable object named
414 \texttt{myhook}, and calls it.
416 \subsection{Writing an in-process hook}
418 The simplest in-process hook does nothing, but illustrates the basic
419 shape of the hook API:
420 \begin{codesample2}
421 def myhook(ui, repo, **kwargs):
422 pass
423 \end{codesample2}
424 The first argument to a Python hook is always a
425 \pymodclass{mercurial.ui}{ui} object. The second is a repository object;
426 at the moment, it is always an instance of
427 \pymodclass{mercurial.localrepo}{localrepository}. Following these two
428 arguments are other keyword arguments. Which ones are passed in
429 depends on the hook being called, but a hook can ignore arguments it
430 doesn't care about by dropping them into a keyword argument dict, as
431 with \texttt{**kwargs} above.
433 \section{Hook reference}
434 \label{sec:hook:ref}
436 \subsection{In-process hook execution}
438 An in-process hook is called with arguments of the following form:
439 \begin{codesample2}
440 def myhook(ui, repo, **kwargs):
441 pass
442 \end{codesample2}
443 The \texttt{ui} parameter is a \pymodclass{mercurial.ui}{ui} object.
444 The \texttt{repo} parameter is a
445 \pymodclass{mercurial.localrepo}{localrepository} object. The
446 names and values of the \texttt{**kwargs} parameters depend on the
447 hook being invoked, with the following common features:
448 \begin{itemize}
449 \item If a parameter is named \texttt{node} or
450 \texttt{parent\emph{N}}, it will contain a hexadecimal changeset ID.
451 The empty string is used to represent ``null changeset ID'' instead
452 of a string of zeroes.
453 \item Boolean-valued parameters are represented as Python
454 \texttt{bool} objects.
455 \end{itemize}
457 An in-process hook is called without a change to the process's working
458 directory (unlike external hooks, which are run in the root of the
459 repository). It must not change the process's working directory. If
460 it were to do so, it would probably cause calls to the Mercurial API,
461 or operations after the hook finishes, to fail.
463 If a hook returns a boolean ``false'' value, it is considered to
464 have succeeded. If it returns a boolean ``true'' value or raises an
465 exception, it is considered to have failed.
467 \subsection{External hook execution}
469 An external hook is passed to the user's shell for execution, so
470 features of that shell, such as variable substitution and command
471 redirection, are available. The hook is run in the root directory of
472 the repository.
474 Hook parameters are passed to the hook as environment variables. Each
475 environment variable's name is converted in upper case and prefixed
476 with the string ``\texttt{HG\_}''. For example, if the name of a
477 parameter is ``\texttt{node}'', the name of the environment variable
478 representing that parameter will be ``\texttt{HG\_NODE}''.
480 A boolean parameter is represented as the string ``\texttt{1}'' for
481 ``true'', ``\texttt{0}'' for ``false''. If an environment variable is
482 named \envar{HG\_NODE}, \envar{HG\_PARENT1} or \envar{HG\_PARENT2}, it
483 contains a changeset ID represented as a hexadecimal string. The
484 empty string is used to represent ``null changeset ID'' instead of a
485 string of zeroes.
487 If a hook exits with a status of zero, it is considered to have
488 succeeded. If it exits with a non-zero status, it is considered to
489 have failed.
491 \subsection{The \hook{changegroup} hook}
492 \label{sec:hook:changegroup}
494 This hook is run after a group of pre-existing changesets has been
495 added to the repository, for example via a \hgcmd{pull} or
496 \hgcmd{unbundle}. This hook is run once per operation that added one
497 or more changesets. This is in contrast to the \hook{incoming} hook,
498 which is run once per changeset, regardless of whether the changesets
499 arrive in a group.
501 Some possible uses for this hook include kicking off an automated
502 build or test of the added changesets, updating a bug database, or
503 notifying subscribers that a repository contains new changes.
505 Parameters to this hook:
506 \begin{itemize}
507 \item[\texttt{node}] A changeset ID. The changeset ID of the first
508 changeset in the group that was added. All changesets between this
509 and \index{tags!\texttt{tip}}\texttt{tip}, inclusive, were added by
510 a single \hgcmd{pull}, \hgcmd{push} or \hgcmd{unbundle}.
511 \end{itemize}
513 See also: \hook{incoming} (section~\ref{sec:hook:incoming}),
514 \hook{prechangegroup} (section~\ref{sec:hook:prechangegroup}),
515 \hook{pretxnchangegroup} (section~\ref{sec:hook:pretxnchangegroup})
517 \subsection{The \hook{commit} hook}
518 \label{sec:hook:commit}
520 This hook is run after a new changeset has been created.
522 Parameters to this hook:
523 \begin{itemize}
524 \item[\texttt{node}] A changeset ID. The changeset ID of the newly
525 committed changeset.
526 \item[\texttt{parent1}] A changeset ID. The changeset ID of the first
527 parent of the newly committed changeset.
528 \item[\texttt{parent2}] A changeset ID. The changeset ID of the second
529 parent of the newly committed changeset.
530 \end{itemize}
532 See also: \hook{precommit} (section~\ref{sec:hook:precommit}),
533 \hook{pretxncommit} (section~\ref{sec:hook:pretxncommit})
535 \subsection{The \hook{incoming} hook}
536 \label{sec:hook:incoming}
538 This hook is run after a pre-existing changeset has been added to the
539 repository, for example via a \hgcmd{push}. If a group of changesets
540 was added in a single operation, this hook is called once for each
541 added changeset.
543 You can use this hook for the same purposes as the \hook{changegroup}
544 hook (section~\ref{sec:hook:changegroup}); it's simply more convenient
545 sometimes to run a hook once per group of changesets, while othher
546 times it's handier once per changeset.
548 Parameters to this hook:
549 \begin{itemize}
550 \item[\texttt{node}] A changeset ID. The ID of the newly added
551 changeset.
552 \end{itemize}
554 See also: \hook{changegroup} (section~\ref{sec:hook:changegroup}) \hook{prechangegroup} (section~\ref{sec:hook:prechangegroup}), \hook{pretxnchangegroup} (section~\ref{sec:hook:pretxnchangegroup})
556 \subsection{The \hook{outgoing} hook}
557 \label{sec:hook:outgoing}
559 This hook is run after a group of changesets has been propagated out
560 of this repository, for example by a \hgcmd{push} or \hgcmd{bundle}
561 command.
563 One possible use for this hook is to notify administrators that
564 changes have been pulled.
566 Parameters to this hook:
567 \begin{itemize}
568 \item[\texttt{node}] A changeset ID. The changeset ID of the first
569 changeset of the group that was sent.
570 \item[\texttt{source}] A string. The source of the of the operation.
571 If a remote client pulled changes from this repository,
572 \texttt{source} will be \texttt{serve}. If the client that obtained
573 changes from this repository was local, \texttt{source} will be
574 \texttt{bundle}, \texttt{pull}, or \texttt{push}, depending on the
575 operation the client performed.
576 \end{itemize}
578 See also: \hook{preoutgoing} (section~\ref{sec:hook:preoutgoing})
580 \subsection{The \hook{prechangegroup} hook}
581 \label{sec:hook:prechangegroup}
583 This controlling hook is run before Mercurial begins to add a group of
584 changesets from another repository.
586 This hook does not have any information about the changesets to be
587 added, because it is run before transmission of those changesets is
588 allowed to begin. If this hook fails, the changesets will not be
589 transmitted.
591 One use for this hook is to prevent external changes from being added
592 to a repository, for example to ``freeze'' a server-hosted branch
593 temporarily or permanently.
595 This hook is not passed any parameters.
597 See also: \hook{changegroup} (section~\ref{sec:hook:changegroup}),
598 \hook{incoming} (section~\ref{sec:hook:incoming}), ,
599 \hook{pretxnchangegroup} (section~\ref{sec:hook:pretxnchangegroup})
601 \subsection{The \hook{precommit} hook}
602 \label{sec:hook:precommit}
604 This hook is run before Mercurial begins to commit a new changeset.
605 It is run before Mercurial has any of the metadata for the commit,
606 such as the files to be committed, the commit message, or the commit
607 date.
609 One use for this hook is to disable the ability to commit new
610 changesets, while still allowing incoming changesets. Another is to
611 run a build or test, and only allow the commit to begin if the build
612 or test succeeds.
614 Parameters to this hook:
615 \begin{itemize}
616 \item[\texttt{parent1}] A changeset ID. The changeset ID of the first
617 parent of the working directory.
618 \item[\texttt{parent2}] A changeset ID. The changeset ID of the second
619 parent of the working directory.
620 \end{itemize}
621 If the commit proceeds, the parents of the working directory will
622 become the parents of the new changeset.
624 See also: \hook{commit} (section~\ref{sec:hook:commit}),
625 \hook{pretxncommit} (section~\ref{sec:hook:pretxncommit})
627 \subsection{The \hook{preoutgoing} hook}
628 \label{sec:hook:preoutgoing}
630 This hook is invoked before Mercurial knows the identities of the
631 changesets to be transmitted.
633 One use for this hook is to prevent changes from being transmitted to
634 another repository.
636 Parameters to this hook:
637 \begin{itemize}
638 \item[\texttt{source}] A string. The source of the operation that is
639 attempting to obtain changes from this repository. See the
640 documentation for the \texttt{source} parameter to the
641 \hook{outgoing} hook, in section~\ref{sec:hook:outgoing}, for
642 possible values of this parameter..
643 \end{itemize}
645 See also: \hook{outgoing} (section~\ref{sec:hook:outgoing})
647 \subsection{The \hook{pretag} hook}
648 \label{sec:hook:pretag}
650 This controlling hook is run before a tag is created. If the hook
651 succeeds, creation of the tag proceeds. If the hook fails, the tag is
652 not created.
654 Parameters to this hook:
655 \begin{itemize}
656 \item[\texttt{local}] A boolean. Whether the tag is local to this
657 repository instance (i.e.~stored in \sfilename{.hg/tags}) or managed
658 by Mercurial (stored in \sfilename{.hgtags}).
659 \item[\texttt{node}] A changeset ID. The ID of the changeset to be tagged.
660 \item[\texttt{tag}] A string. The name of the tag to be created.
661 \end{itemize}
663 If the tag to be created is revision-controlled, the \hook{precommit}
664 and \hook{pretxncommit} hooks (sections~\ref{sec:hook:commit}
665 and~\ref{sec:hook:pretxncommit}) will also be run.
667 See also: \hook{tag} (section~\ref{sec:hook:tag})
669 \subsection{The \hook{pretxnchangegroup} hook}
670 \label{sec:hook:pretxnchangegroup}
672 This controlling hook is run before a transaction---that manages the
673 addition of a group of new changesets from outside the
674 repository---completes. If the hook succeeds, the transaction
675 completes, and all of the changesets become permanent within this
676 repository. If the hook fails, the transaction is rolled back, and
677 the data for the changesets is erased.
679 This hook can access the metadata associated with the almost-added
680 changesets, but it should not do anything permanent with this data.
681 It must also not modify the working directory.
683 While this hook is running, if other Mercurial processes access this
684 repository, they will be able to see the almost-added changesets as if
685 they are permanent. This may lead to race conditions if you do not
686 take steps to avoid them.
688 This hook can be used to automatically vet a group of changesets. If
689 the hook fails, all of the changesets are ``rejected'' when the
690 transaction rolls back.
692 Parameters to this hook are the same as for the \hook{changegroup}
693 hook; see section~\ref{sec:hook:changegroup} for details.
695 See also: \hook{changegroup} (section~\ref{sec:hook:changegroup}),
696 \hook{incoming} (section~\ref{sec:hook:incoming}),
697 \hook{prechangegroup} (section~\ref{sec:hook:prechangegroup})
699 \subsection{The \hook{pretxncommit} hook}
700 \label{sec:hook:pretxncommit}
702 This controlling hook is run before a transaction---that manages a new
703 commit---completes. If the hook succeeds, the transaction completes
704 and the changeset becomes permanent within this repository. If the
705 hook fails, the transaction is rolled back, and the commit data is
706 erased.
708 This hook can access the metadata associated with the almost-new
709 changeset, but it should not do anything permanent with this data. It
710 must also not modify the working directory.
712 While this hook is running, if other Mercurial processes access this
713 repository, they will be able to see the almost-new changeset as if it
714 is permanent. This may lead to race conditions if you do not take
715 steps to avoid them.
717 Parameters to this hook are the same as for the \hook{commit} hook;
718 see section~\ref{sec:hook:commit} for details.
720 See also: \hook{precommit} (section~\ref{sec:hook:precommit})
722 \subsection{The \hook{preupdate} hook}
723 \label{sec:hook:preupdate}
725 This controlling hook is run before an update or merge of the working
726 directory begins. It is run only if Mercurial's normal pre-update
727 checks determine that the update or merge can proceed. If the hook
728 succeeds, the update or merge may proceed; if it fails, the update or
729 merge does not start.
731 Parameters to this hook:
732 \begin{itemize}
733 \item[\texttt{parent1}] A changeset ID. The ID of the parent that the
734 working directory is to be updated to. If the working directory is
735 being merged, it will not change this parent.
736 \item[\texttt{parent2}] A changeset ID. Only set if the working
737 directory is being merged. The ID of the revision that the working
738 directory is being merged with.
739 \end{itemize}
741 See also: \hook{update} (section~\ref{sec:hook:update})
743 \subsection{The \hook{tag} hook}
744 \label{sec:hook:tag}
746 This hook is run after a tag has been created.
748 Parameters to this hook are the same as for the \hook{pretag} hook;
749 see section~\ref{sec:hook:pretag} for details.
751 If the created tag is revision-controlled, the \hook{commit} hook
752 (section~\ref{sec:hook:commit}) is run before this hook.
754 See also: \hook{pretag} (section~\ref{sec:hook:pretag})
756 \subsection{The \hook{update} hook}
757 \label{sec:hook:update}
759 This hook is run after an update or merge of the working directory
760 completes. Since a merge can fail (if the external \command{hgmerge}
761 command fails to resolve conflicts in a file), this hook communicates
762 whether the update or merge completed cleanly.
764 \begin{itemize}
765 \item[\texttt{error}] A boolean. Indicates whether the update or
766 merge completed successfully.
767 \item[\texttt{parent1}] A changeset ID. The ID of the parent that the
768 working directory was updated to. If the working directory was
769 merged, it will not have changed this parent.
770 \item[\texttt{parent2}] A changeset ID. Only set if the working
771 directory was merged. The ID of the revision that the working
772 directory was merged with.
773 \end{itemize}
775 See also: \hook{preupdate} (section~\ref{sec:hook:preupdate})
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