bos@34: \chapter{Handling repository events with hooks}
bos@34: \label{chap:hook}
bos@34: 
bos@34: Mercurial offers a powerful mechanism to let you perform automated
bos@34: actions in response to events that occur in a repository.  In some
bos@34: cases, you can even control Mercurial's response to those events.
bos@34: 
bos@34: The name Mercurial uses for one of these actions is a \emph{hook}.
bos@34: Hooks are called ``triggers'' in some revision control systems, but
bos@34: the two names refer to the same idea.
bos@34: 
bos@38: \section{An overview of hooks in Mercurial}
bos@38: 
bos@41: Here is a brief list of the hooks that Mercurial supports.  We will
bos@41: revisit each of these hooks in more detail later, in
bos@41: section~\ref{sec:hook:ref}.
bos@41: 
bos@38: \begin{itemize}
bos@38: \item[\small\hook{changegroup}] This is run after a group of
bos@41:   changesets has been brought into the repository from elsewhere.
bos@38: \item[\small\hook{commit}] This is run after a new changeset has been
bos@41:   created in the local repository.
bos@38: \item[\small\hook{incoming}] This is run once for each new changeset
bos@38:   that is brought into the repository from elsewhere.  Notice the
bos@38:   difference from \hook{changegroup}, which is run once per
bos@41:   \emph{group} of changesets brought in.
bos@38: \item[\small\hook{outgoing}] This is run after a group of changesets
bos@41:   has been transmitted from this repository.
bos@38: \item[\small\hook{prechangegroup}] This is run before starting to
bos@41:   bring a group of changesets into the repository.
bos@41: \item[\small\hook{precommit}] Controlling. This is run before starting
bos@41:   a commit.
bos@41: \item[\small\hook{preoutgoing}] Controlling. This is run before
bos@41:   starting to transmit a group of changesets from this repository.
bos@41: \item[\small\hook{pretag}] Controlling. This is run before creating a tag.
bos@41: \item[\small\hook{pretxnchangegroup}] Controlling. This is run after a
bos@41:   group of changesets has been brought into the local repository from
bos@41:   another, but before the transaction completes that will make the
bos@41:   changes permanent in the repository.
bos@41: \item[\small\hook{pretxncommit}] Controlling. This is run after a new
bos@41:   changeset has been created in the local repository, but before the
bos@41:   transaction completes that will make it permanent.
bos@41: \item[\small\hook{preupdate}] Controlling. This is run before starting
bos@41:   an update or merge of the working directory.
bos@38: \item[\small\hook{tag}] This is run after a tag is created.
bos@38: \item[\small\hook{update}] This is run after an update or merge of the
bos@38:   working directory has finished.
bos@38: \end{itemize}
bos@41: Each of the hooks whose description begins with the word
bos@41: ``Controlling'' has the ability to determine whether an activity can
bos@41: proceed.  If the hook succeeds, the activity may proceed; if it fails,
bos@41: the activity is either not permitted or undone, depending on the hook.
bos@38: 
bos@38: \section{Hooks and security}
bos@38: 
bos@38: \subsection{Hooks are run with your privileges}
bos@38: 
bos@38: When you run a Mercurial command in a repository, and the command
bos@41: causes a hook to run, that hook runs on \emph{your} system, under
bos@41: \emph{your} user account, with \emph{your} privilege level.  Since
bos@41: hooks are arbitrary pieces of executable code, you should treat them
bos@41: with an appropriate level of suspicion.  Do not install a hook unless
bos@41: you are confident that you know who created it and what it does.
bos@38: 
bos@38: In some cases, you may be exposed to hooks that you did not install
bos@38: yourself.  If you work with Mercurial on an unfamiliar system,
bos@38: Mercurial will run hooks defined in that system's global \hgrc\ file.
bos@38: 
bos@38: If you are working with a repository owned by another user, Mercurial
bos@41: can run hooks defined in that user's repository, but it will still run
bos@41: them as ``you''.  For example, if you \hgcmd{pull} from that
bos@41: repository, and its \sfilename{.hg/hgrc} defines a local
bos@41: \hook{outgoing} hook, that hook will run under your user account, even
bos@41: though you don't own that repository.
bos@38: 
bos@38: \begin{note}
bos@38:   This only applies if you are pulling from a repository on a local or
bos@38:   network filesystem.  If you're pulling over http or ssh, any
bos@41:   \hook{outgoing} hook will run under whatever account is executing
bos@41:   the server process, on the server.
bos@38: \end{note}
bos@38: 
bos@38: XXX To see what hooks are defined in a repository, use the
bos@38: \hgcmdargs{config}{hooks} command.  If you are working in one
bos@38: repository, but talking to another that you do not own (e.g.~using
bos@38: \hgcmd{pull} or \hgcmd{incoming}), remember that it is the other
bos@38: repository's hooks you should be checking, not your own.
bos@38: 
bos@38: \subsection{Hooks do not propagate}
bos@38: 
bos@38: In Mercurial, hooks are not revision controlled, and do not propagate
bos@38: when you clone, or pull from, a repository.  The reason for this is
bos@38: simple: a hook is a completely arbitrary piece of executable code.  It
bos@38: runs under your user identity, with your privilege level, on your
bos@38: machine.
bos@38: 
bos@38: It would be extremely reckless for any distributed revision control
bos@38: system to implement revision-controlled hooks, as this would offer an
bos@38: easily exploitable way to subvert the accounts of users of the
bos@38: revision control system.
bos@38: 
bos@38: Since Mercurial does not propagate hooks, if you are collaborating
bos@38: with other people on a common project, you should not assume that they
bos@38: are using the same Mercurial hooks as you are, or that theirs are
bos@38: correctly configured.  You should document the hooks you expect people
bos@38: to use.
bos@38: 
bos@38: In a corporate intranet, this is somewhat easier to control, as you
bos@38: can for example provide a ``standard'' installation of Mercurial on an
bos@38: NFS filesystem, and use a site-wide \hgrc\ file to define hooks that
bos@38: all users will see.  However, this too has its limits; see below.
bos@38: 
bos@38: \subsection{Hooks can be overridden}
bos@38: 
bos@38: Mercurial allows you to override a hook definition by redefining the
bos@38: hook.  You can disable it by setting its value to the empty string, or
bos@38: change its behaviour as you wish.
bos@38: 
bos@38: If you deploy a system-~or site-wide \hgrc\ file that defines some
bos@38: hooks, you should thus understand that your users can disable or
bos@38: override those hooks.
bos@38: 
bos@38: \subsection{Ensuring that critical hooks are run}
bos@38: 
bos@38: Sometimes you may want to enforce a policy that you do not want others
bos@38: to be able to work around.  For example, you may have a requirement
bos@38: that every changeset must pass a rigorous set of tests.  Defining this
bos@38: requirement via a hook in a site-wide \hgrc\ won't work for remote
bos@38: users on laptops, and of course local users can subvert it at will by
bos@38: overriding the hook.
bos@38: 
bos@38: Instead, you can set up your policies for use of Mercurial so that
bos@38: people are expected to propagate changes through a well-known
bos@38: ``canonical'' server that you have locked down and configured
bos@38: appropriately.
bos@38: 
bos@38: One way to do this is via a combination of social engineering and
bos@38: technology.  Set up a restricted-access account; users can push
bos@38: changes over the network to repositories managed by this account, but
bos@38: they cannot log into the account and run normal shell commands.  In
bos@38: this scenario, a user can commit a changeset that contains any old
bos@38: garbage they want.
bos@38: 
bos@38: When someone pushes a changeset to the server that everyone pulls
bos@38: from, the server will test the changeset before it accepts it as
bos@38: permanent, and reject it if it fails to pass the test suite.  If
bos@38: people only pull changes from this filtering server, it will serve to
bos@38: ensure that all changes that people pull have been automatically
bos@38: vetted.
bos@38: 
bos@41: \section{Using hooks with shared access to a repository}
bos@41: 
bos@41: If you want to use hooks to so some automated work in a repository
bos@54: that a number of people have shared access to, you need to be careful
bos@41: in how you do this.
bos@41: 
bos@41: Mercurial only locks a repository when it is writing to the
bos@41: repository, and only the parts of Mercurial that write to the
bos@41: repository pay attention to locks.  Write locks are necessary to
bos@41: prevent multiple simultaneous writers from scribbling on each other's
bos@41: work, corrupting the repository.
bos@41: 
bos@41: Because Mercurial is careful with the order in which it reads and
bos@41: writes data, it does not need to acquire a lock when it wants to read
bos@41: data from the repository.  The parts of Mercurial that read from the
bos@41: repository never pay attention to locks.  This lockless reading scheme
bos@41: greatly increases performance and concurrency.
bos@41: 
bos@41: With great performance comes a trade-off, though, one which has the
bos@41: potential to cause you trouble unless you're aware of it.  To describe
bos@41: this requires a little detail about how Mercurial adds changesets to a
bos@41: repository and reads those changes.
bos@41: 
bos@41: When Mercurial \emph{writes} metadata, it writes it straight into the
bos@41: destination file.  It writes file data first, then manifest data
bos@41: (which contains pointers to the new file data), then changelog data
bos@41: (which contains pointers to the new manifest data).  Before the first
bos@41: write to each file, it stores a record of where the end of the file
bos@41: was in its transaction log.  If the transaction must be rolled back,
bos@54: Mercurial simply truncates each file back to the size it was before the
bos@41: transaction began.
bos@41: 
bos@41: When Mercurial \emph{reads} metadata, it reads the changelog first,
bos@41: then everything else.  Since a reader will only access parts of the
bos@41: manifest or file metadata that it can see in the changelog, it can
bos@41: never see partially written data.
bos@41: 
bos@41: Some controlling hooks (\hook{pretxncommit} and
bos@41: \hook{pretxnchangegroup}) run when a transaction is almost complete.
bos@41: All of the metadata has been written, but Mercurial can still roll the
bos@41: transaction back and cause the newly-written data to disappear.
bos@41: 
bos@41: If one of these hooks runs for long, it opens a window in which a
bos@41: reader can see the metadata for changesets that are, strictly
bos@41: speaking, not yet permanent.  The longer the hook runs, the bigger the
bos@41: window.
bos@41: 
bos@41: A good use for the \hook{pretxnchangegroup} hook would be to
bos@41: automatically build and test incoming changes before they are accepted
bos@41: into the repository, so that you can guarantee that nobody can push
bos@41: changes to this repository that ``break the build''.  But if a client
bos@41: can pull changes while they're being tested, the usefulness of the
bos@41: test is zero; someone can pull untested changes.
bos@41: 
bos@41: The safest answer to this challenge is to set up such a ``gatekeeper''
bos@41: repository as \emph{unidirectional}.  It can take changes pushed in
bos@41: from the outside, but nobody can pull changes from it.  Use the
bos@41: \hook{preoutgoing} hook to lock it down.  Configure a
bos@41: \hook{changegroup} hook so that if a build or test succeeds, the hook
bos@41: will push the new changes out to another repository that people
bos@41: \emph{can} pull from.
bos@41: 
bos@34: \section{A short tutorial on using hooks}
bos@34: \label{sec:hook:simple}
bos@34: 
bos@34: It is easy to write a Mercurial hook.  Let's start with a hook that
bos@34: runs when you finish a \hgcmd{commit}, and simply prints the hash of
bos@34: the changeset you just created.  The hook is called \hook{commit}.
bos@34: 
bos@34: \begin{figure}[ht]
bos@34:   \interaction{hook.simple.init}
bos@34:   \caption{A simple hook that runs when a changeset is committed}
bos@34:   \label{ex:hook:init}
bos@34: \end{figure}
bos@34: 
bos@34: All hooks follow the pattern in example~\ref{ex:hook:init}.  You add
bos@34: an entry to the \rcsection{hooks} section of your \hgrc\.  On the left
bos@34: is the name of the event to trigger on; on the right is the action to
bos@34: take.  As you can see, you can run an arbitrary shell command in a
bos@34: hook.  Mercurial passes extra information to the hook using
bos@34: environment variables (look for \envar{HG\_NODE} in the example).
bos@34: 
bos@34: \subsection{Performing multiple actions per event}
bos@34: 
bos@34: Quite often, you will want to define more than one hook for a
bos@34: particular kind of event, as shown in example~\ref{ex:hook:ext}.
bos@34: Mercurial lets you do this by adding an \emph{extension} to the end of
bos@34: a hook's name.  You extend a hook's name by giving the name of the
bos@34: hook, followed by a full stop (the ``\texttt{.}'' character), followed
bos@34: by some more text of your choosing.  For example, Mercurial will run
bos@34: both \texttt{commit.foo} and \texttt{commit.bar} when the
bos@34: \texttt{commit} event occurs.
bos@34: 
bos@34: \begin{figure}[ht]
bos@34:   \interaction{hook.simple.ext}
bos@34:   \caption{Defining a second \hook{commit} hook}
bos@34:   \label{ex:hook:ext}
bos@34: \end{figure}
bos@34: 
bos@34: To give a well-defined order of execution when there are multiple
bos@34: hooks defined for an event, Mercurial sorts hooks by extension, and
bos@34: executes the hook commands in this sorted order.  In the above
bos@34: example, it will execute \texttt{commit.bar} before
bos@34: \texttt{commit.foo}, and \texttt{commit} before both.
bos@34: 
bos@34: It is a good idea to use a somewhat descriptive extension when you
bos@34: define a new hook.  This will help you to remember what the hook was
bos@34: for.  If the hook fails, you'll get an error message that contains the
bos@34: hook name and extension, so using a descriptive extension could give
bos@34: you an immediate hint as to why the hook failed (see
bos@34: section~\ref{sec:hook:perm} for an example).
bos@34: 
bos@34: \subsection{Controlling whether an activity can proceed}
bos@34: \label{sec:hook:perm}
bos@34: 
bos@34: In our earlier examples, we used the \hook{commit} hook, which is
bos@34: run after a commit has completed.  This is one of several Mercurial
bos@34: hooks that run after an activity finishes.  Such hooks have no way of
bos@34: influencing the activity itself.
bos@34: 
bos@34: Mercurial defines a number of events that occur before an activity
bos@34: starts; or after it starts, but before it finishes.  Hooks that
bos@34: trigger on these events have the added ability to choose whether the
bos@34: activity can continue, or will abort.  
bos@34: 
bos@34: The \hook{pretxncommit} hook runs after a commit has all but
bos@34: completed.  In other words, the metadata representing the changeset
bos@34: has been written out to disk, but the transaction has not yet been
bos@34: allowed to complete.  The \hook{pretxncommit} hook has the ability to
bos@34: decide whether the transaction can complete, or must be rolled back.
bos@34: 
bos@34: If the \hook{pretxncommit} hook exits with a status code of zero, the
bos@34: transaction is allowed to complete; the commit finishes; and the
bos@34: \hook{commit} hook is run.  If the \hook{pretxncommit} hook exits with
bos@34: a non-zero status code, the transaction is rolled back; the metadata
bos@34: representing the changeset is erased; and the \hook{commit} hook is
bos@34: not run.
bos@34: 
bos@34: \begin{figure}[ht]
bos@34:   \interaction{hook.simple.pretxncommit}
bos@34:   \caption{Using the \hook{pretxncommit} hook to control commits}
bos@34:   \label{ex:hook:pretxncommit}
bos@34: \end{figure}
bos@34: 
bos@34: The hook in example~\ref{ex:hook:pretxncommit} checks that a commit
bos@34: comment contains a bug ID.  If it does, the commit can complete.  If
bos@34: not, the commit is rolled back.
bos@34: 
bos@37: \section{Writing your own hooks}
bos@37: 
bos@37: When you are writing a hook, you might find it useful to run Mercurial
bos@37: either with the \hggopt{-v} option, or the \rcitem{ui}{verbose} config
bos@37: item set to ``true''.  When you do so, Mercurial will print a message
bos@37: before it calls each hook.
bos@37: 
bos@37: \subsection{Choosing how your hook should run}
bos@37: \label{sec:hook:lang}
bos@34: 
bos@34: You can write a hook either as a normal program---typically a shell
bos@37: script---or as a Python function that is executed within the Mercurial
bos@34: process.
bos@34: 
bos@34: Writing a hook as an external program has the advantage that it
bos@34: requires no knowledge of Mercurial's internals.  You can call normal
bos@34: Mercurial commands to get any added information you need.  The
bos@34: trade-off is that external hooks are slower than in-process hooks.
bos@34: 
bos@34: An in-process Python hook has complete access to the Mercurial API,
bos@34: and does not ``shell out'' to another process, so it is inherently
bos@34: faster than an external hook.  It is also easier to obtain much of the
bos@34: information that a hook requires by using the Mercurial API than by
bos@34: running Mercurial commands.
bos@34: 
bos@34: If you are comfortable with Python, or require high performance,
bos@34: writing your hooks in Python may be a good choice.  However, when you
bos@34: have a straightforward hook to write and you don't need to care about
bos@34: performance (probably the majority of hooks), a shell script is
bos@34: perfectly fine.
bos@34: 
bos@37: \subsection{Hook parameters}
bos@34: \label{sec:hook:param}
bos@34: 
bos@34: Mercurial calls each hook with a set of well-defined parameters.  In
bos@34: Python, a parameter is passed as a keyword argument to your hook
bos@34: function.  For an external program, a parameter is passed as an
bos@34: environment variable.
bos@34: 
bos@34: Whether your hook is written in Python or as a shell script, the
bos@37: hook-specific parameter names and values will be the same.  A boolean
bos@37: parameter will be represented as a boolean value in Python, but as the
bos@37: number 1 (for ``true'') or 0 (for ``false'') as an environment
bos@37: variable for an external hook.  If a hook parameter is named
bos@37: \texttt{foo}, the keyword argument for a Python hook will also be
bos@51: named \texttt{foo}, while the environment variable for an external
bos@51: hook will be named \texttt{HG\_FOO}.
bos@37: 
bos@37: \subsection{Hook return values and activity control}
bos@37: 
bos@37: A hook that executes successfully must exit with a status of zero if
bos@37: external, or return boolean ``false'' if in-process.  Failure is
bos@37: indicated with a non-zero exit status from an external hook, or an
bos@37: in-process hook returning boolean ``true''.  If an in-process hook
bos@37: raises an exception, the hook is considered to have failed.
bos@37: 
bos@37: For a hook that controls whether an activity can proceed, zero/false
bos@37: means ``allow'', while non-zero/true/exception means ``deny''.
bos@37: 
bos@37: \subsection{Writing an external hook}
bos@37: 
bos@37: When you define an external hook in your \hgrc\ and the hook is run,
bos@37: its value is passed to your shell, which interprets it.  This means
bos@37: that you can use normal shell constructs in the body of the hook.
bos@37: 
bos@37: An executable hook is always run with its current directory set to a
bos@37: repository's root directory.
bos@37: 
bos@37: Each hook parameter is passed in as an environment variable; the name
bos@37: is upper-cased, and prefixed with the string ``\texttt{HG\_}''.
bos@37: 
bos@37: With the exception of hook parameters, Mercurial does not set or
bos@37: modify any environment variables when running a hook.  This is useful
bos@37: to remember if you are writing a site-wide hook that may be run by a
bos@37: number of different users with differing environment variables set.
bos@37: In multi-user situations, you should not rely on environment variables
bos@37: being set to the values you have in your environment when testing the
bos@37: hook.
bos@37: 
bos@37: \subsection{Telling Mercurial to use an in-process hook}
bos@37: 
bos@37: The \hgrc\ syntax for defining an in-process hook is slightly
bos@37: different than for an executable hook.  The value of the hook must
bos@37: start with the text ``\texttt{python:}'', and continue with the
bos@37: fully-qualified name of a callable object to use as the hook's value.
bos@37: 
bos@37: The module in which a hook lives is automatically imported when a hook
bos@37: is run.  So long as you have the module name and \envar{PYTHONPATH}
bos@37: right, it should ``just work''.
bos@37: 
bos@37: The following \hgrc\ example snippet illustrates the syntax and
bos@37: meaning of the notions we just described.
bos@37: \begin{codesample2}
bos@37:   [hooks]
bos@37:   commit.example = python:mymodule.submodule.myhook
bos@37: \end{codesample2}
bos@37: When Mercurial runs the \texttt{commit.example} hook, it imports
bos@37: \texttt{mymodule.submodule}, looks for the callable object named
bos@37: \texttt{myhook}, and calls it.
bos@37: 
bos@37: \subsection{Writing an in-process hook}
bos@37: 
bos@37: The simplest in-process hook does nothing, but illustrates the basic
bos@37: shape of the hook API:
bos@37: \begin{codesample2}
bos@37:   def myhook(ui, repo, **kwargs):
bos@37:       pass
bos@37: \end{codesample2}
bos@37: The first argument to a Python hook is always a
bos@37: \pymodclass{mercurial.ui}{ui} object.  The second is a repository object;
bos@37: at the moment, it is always an instance of
bos@37: \pymodclass{mercurial.localrepo}{localrepository}.  Following these two
bos@37: arguments are other keyword arguments.  Which ones are passed in
bos@37: depends on the hook being called, but a hook can ignore arguments it
bos@37: doesn't care about by dropping them into a keyword argument dict, as
bos@37: with \texttt{**kwargs} above.
bos@34: 
bos@44: \section{Some hook examples}
bos@44: 
bos@49: \subsection{Writing meaningful commit messages}
bos@49: 
bos@49: It's hard to imagine a useful commit message being very short.  The
bos@49: simple \hook{pretxncommit} hook of figure~\ref{ex:hook:msglen.run}
bos@49: will prevent you from committing a changeset with a message that is
bos@49: less than ten bytes long.
bos@49: 
bos@49: \begin{figure}[ht]
bos@49:   \interaction{hook.msglen.run}
bos@49:   \caption{A hook that forbids overly short commit messages}
bos@49:   \label{ex:hook:msglen.run}
bos@49: \end{figure}
bos@49: 
bos@49: \subsection{Checking for trailing whitespace}
bos@44: 
bos@44: An interesting use of a commit-related hook is to help you to write
bos@44: cleaner code.  A simple example of ``cleaner code'' is the dictum that
bos@44: a change should not add any new lines of text that contain ``trailing
bos@44: whitespace''.  Trailing whitespace is a series of space and tab
bos@44: characters at the end of a line of text.  In most cases, trailing
bos@44: whitespace is unnecessary, invisible noise, but it is occasionally
bos@49: problematic, and people often prefer to get rid of it.
bos@44: 
bos@44: You can use either the \hook{precommit} or \hook{pretxncommit} hook to
bos@44: tell whether you have a trailing whitespace problem.  If you use the
bos@44: \hook{precommit} hook, the hook will not know which files you are
bos@44: committing, so it will have to check every modified file in the
bos@44: repository for trailing white space.  If you want to commit a change
bos@44: to just the file \filename{foo}, but the file \filename{bar} contains
bos@44: trailing whitespace, doing a check in the \hook{precommit} hook will
bos@44: prevent you from committing \filename{foo} due to the problem with
bos@44: \filename{bar}.  This doesn't seem right.
bos@44: 
bos@44: Should you choose the \hook{pretxncommit} hook, the check won't occur
bos@44: until just before the transaction for the commit completes.  This will
bos@44: allow you to check for problems only the exact files that are being
bos@44: committed.  However, if you entered the commit message interactively
bos@44: and the hook fails, the transaction will roll back; you'll have to
bos@44: re-enter the commit message after you fix the trailing whitespace and
bos@44: run \hgcmd{commit} again.
bos@44: 
bos@44: \begin{figure}[ht]
bos@44:   \interaction{hook.ws.simple}
bos@44:   \caption{A simple hook that checks for trailing whitespace}
bos@44:   \label{ex:hook:ws.simple}
bos@44: \end{figure}
bos@44: 
bos@44: Figure~\ref{ex:hook:ws.simple} introduces a simple \hook{pretxncommit}
bos@44: hook that checks for trailing whitespace.  This hook is short, but not
bos@44: very helpful.  It exits with an error status if a change adds a line
bos@44: with trailing whitespace to any file, but does not print any
bos@49: information that might help us to identify the offending file or
bos@49: line.  It also has the nice property of not paying attention to
bos@49: unmodified lines; only lines that introduce new trailing whitespace
bos@49: cause problems.
bos@49: 
bos@49: \begin{figure}[ht]
bos@49:   \interaction{hook.ws.better}
bos@49:   \caption{A better trailing whitespace hook}
bos@49:   \label{ex:hook:ws.better}
bos@49: \end{figure}
bos@49: 
bos@49: The example of figure~\ref{ex:hook:ws.better} is much more complex,
bos@49: but also more useful.  It parses a unified diff to see if any lines
bos@49: add trailing whitespace, and prints the name of the file and the line
bos@49: number of each such occurrence.  Even better, if the change adds
bos@49: trailing whitespace, this hook saves the commit comment and prints the
bos@49: name of the save file before exiting and telling Mercurial to roll the
bos@49: transaction back, so you can use
bos@49: \hgcmdargs{commit}{\hgopt{commit}{-l}~\emph{filename}} to reuse the
bos@49: saved commit message once you've corrected the problem.
bos@49: 
bos@49: As a final aside, note in figure~\ref{ex:hook:ws.better} the use of
bos@49: \command{perl}'s in-place editing feature to get rid of trailing
bos@49: whitespace from a file.  This is concise and useful enough that I will
bos@49: reproduce it here.
bos@49: \begin{codesample2}
bos@54:   perl -pi -e 's,\\s+\$,,' filename
bos@49: \end{codesample2}
bos@49: 
bos@49: \section{Bundled hooks}
bos@49: 
bos@49: Mercurial ships with several bundled hooks.  You can find them in the
bos@49: \dirname{hgext} directory of a Mercurial source tree.  If you are
bos@49: using a Mercurial binary package, the hooks will be located in the
bos@49: \dirname{hgext} directory of wherever your package installer put
bos@49: Mercurial.
bos@49: 
bos@49: \subsection{\hgext{acl}---access control for parts of a repository}
bos@49: 
bos@49: The \hgext{acl} extension lets you control which remote users are
bos@49: allowed to push changesets to a networked server.  You can protect any
bos@49: portion of a repository (including the entire repo), so that a
bos@49: specific remote user can push changes that do not affect the protected
bos@49: portion.
bos@49: 
bos@49: This extension implements access control based on the identity of the
bos@49: user performing a push, \emph{not} on who committed the changesets
bos@62: they're pushing.  It makes sense to use this hook only if you have a
bos@62: locked-down server environment that authenticates remote users, and
bos@62: you want to be sure that only specific users are allowed to push
bos@62: changes to that server.
bos@62: 
bos@62: \subsubsection{Configuring the \hook{acl} hook}
bos@62: 
bos@62: In order to manage incoming changesets, the \hgext{acl} hook must be
bos@62: used as a \hook{pretxnchangegroup} hook.  This lets it see which files
bos@62: are modified by each incoming changeset, and roll back a group of
bos@62: changesets if they modify ``forbidden'' files.  Example:
bos@62: \begin{codesample2}
bos@62:   [hooks]
bos@62:   pretxnchangegroup.acl = python:hgext.acl.hook
bos@62: \end{codesample2}
bos@62: 
bos@62: The \hgext{acl} extension is configured using three sections.  
bos@62: 
bos@62: The \rcsection{acl} section has only one entry, \rcitem{acl}{sources},
bos@62: which lists the sources of incoming changesets that the hook should
bos@62: pay attention to.  You don't normally need to configure this section.
bos@62: \begin{itemize}
bos@64: \item[\rcitem{acl}{serve}] Control incoming changesets that are arriving
bos@62:   from a remote repository over http or ssh.  This is the default
bos@62:   value of \rcitem{acl}{sources}, and usually the only setting you'll
bos@62:   need for this configuration item.
bos@64: \item[\rcitem{acl}{pull}] Control incoming changesets that are
bos@64:   arriving via a pull from a local repository.
bos@64: \item[\rcitem{acl}{push}] Control incoming changesets that are
bos@64:   arriving via a push from a local repository.
bos@64: \item[\rcitem{acl}{bundle}] Control incoming changesets that are
bos@64:   arriving from another repository via a bundle.
bos@62: \end{itemize}
bos@62: 
bos@62: The \rcsection{acl.allow} section controls the users that are allowed to
bos@62: add changesets to the repository.  If this section is not present, all
bos@62: users that are not explicitly denied are allowed.  If this section is
bos@62: present, all users that are not explicitly allowed are denied (so an
bos@62: empty section means that all users are denied).
bos@62: 
bos@62: The \rcsection{acl.deny} section determines which users are denied
bos@62: from adding changesets to the repository.  If this section is not
bos@62: present or is empty, no users are denied.
bos@62: 
bos@62: The syntaxes for the \rcsection{acl.allow} and \rcsection{acl.deny}
bos@62: sections are identical.  On the left of each entry is a glob pattern
bos@62: that matches files or directories, relative to the root of the
bos@62: repository; on the right, a user name.
bos@62: 
bos@62: In the following example, the user \texttt{docwriter} can only push
bos@62: changes to the \dirname{docs} subtree of the repository, while
bos@62: \texttt{intern} can push changes to any file or directory except
bos@62: \dirname{source/sensitive}.
bos@62: \begin{codesample2}
bos@62:   [acl.allow]
bos@62:   docs/** = docwriter
bos@62: 
bos@62:   [acl.deny]
bos@62:   source/sensitive/** = intern
bos@62: \end{codesample2}
bos@62: 
bos@62: \subsubsection{Testing and troubleshooting}
bos@62: 
bos@62: If you want to test the \hgext{acl} hook, run it with Mercurial's
bos@62: debugging output enabled.  Since you'll probably be running it on a
bos@62: server where it's not convenient (or sometimes possible) to pass in
bos@62: the \hggopt{--debug} option, don't forget that you can enable
bos@62: debugging output in your \hgrc:
bos@62: \begin{codesample2}
bos@62:   [ui]
bos@62:   debug = true
bos@62: \end{codesample2}
bos@62: With this enabled, the \hgext{acl} hook will print enough information
bos@62: to let you figure out why it is allowing or forbidding pushes from
bos@62: specific users.
bos@62: 
bos@62: \subsection{\hgext{bugzilla}---integration with Bugzilla}
bos@62: 
bos@62: The \hgext{bugzilla} extension adds a comment to a Bugzilla bug
bos@62: whenever it finds a reference to that bug ID in a commit comment.  You
bos@62: can install this hook on a shared server, so that any time a remote
bos@62: user pushes changes to this server, the hook gets run.  
bos@62: 
bos@62: It adds a comment to the bug that looks like this (you can configure
bos@62: the contents of the comment---see below):
bos@62: \begin{codesample2}
bos@62:   Changeset aad8b264143a, made by Joe User <joe.user@domain.com> in
bos@62:   the frobnitz repository, refers to this bug.
bos@62: 
bos@62:   For complete details, see
bos@62:   http://hg.domain.com/frobnitz?cmd=changeset;node=aad8b264143a
bos@62: 
bos@62:   Changeset description:
bos@62:         Fix bug 10483 by guarding against some NULL pointers
bos@62: \end{codesample2}
bos@62: The value of this hook is that it automates the process of updating a
bos@62: bug any time a changeset refers to it.  If you configure the hook
bos@62: properly, it makes it easy for people to browse straight from a
bos@62: Bugzilla bug to a changeset that refers to that bug.
bos@62: 
bos@62: You can use the code in this hook as a starting point for some more
bos@62: exotic Bugzilla integration recipes.  Here are a few possibilities:
bos@62: \begin{itemize}
bos@62: \item Require that every changeset pushed to the server have a valid
bos@62:   bug~ID in its commit comment.  In this case, you'd want to configure
bos@62:   the hook as a \hook{pretxncommit} hook.  This would allow the hook
bos@62:   to reject changes that didn't contain bug IDs.
bos@62: \item Allow incoming changesets to automatically modify the
bos@62:   \emph{state} of a bug, as well as simply adding a comment.  For
bos@62:   example, the hook could recognise the string ``fixed bug 31337'' as
bos@62:   indicating that it should update the state of bug 31337 to
bos@62:   ``requires testing''.
bos@62: \end{itemize}
bos@62: 
bos@62: \subsubsection{Configuring the \hook{bugzilla} hook}
bos@62: \label{sec:hook:bugzilla:config}
bos@62: 
bos@62: You should configure this hook in your server's \hgrc\ as an
bos@62: \hook{incoming} hook, for example as follows:
bos@62: \begin{codesample2}
bos@62:   [hooks]
bos@62:   incoming.bugzilla = python:hgext.bugzilla.hook
bos@62: \end{codesample2}
bos@62: 
bos@62: Because of the specialised nature of this hook, and because Bugzilla
bos@62: was not written with this kind of integration in mind, configuring
bos@62: this hook is a somewhat involved process.
bos@62: 
bos@62: Before you begin, you must install the MySQL bindings for Python on
bos@62: the host(s) where you'll be running the hook.  If this is not
bos@62: available as a binary package for your system, you can download it
bos@62: from~\cite{web:mysql-python}.
bos@62: 
bos@62: Configuration information for this hook lives in the
bos@62: \rcsection{bugzilla} section of your \hgrc.
bos@62: \begin{itemize}
bos@64: \item[\rcitem{bugzilla}{version}] The version of Bugzilla installed on
bos@64:   the server.  The database schema that Bugzilla uses changes
bos@62:   occasionally, so this hook has to know exactly which schema to use.
bos@62:   At the moment, the only version supported is \texttt{2.16}.
bos@64: \item[\rcitem{bugzilla}{host}] The hostname of the MySQL server that
bos@64:   stores your Bugzilla data.  The database must be configured to allow
bos@64:   connections from whatever host you are running the \hook{bugzilla}
bos@64:   hook on.
bos@64: \item[\rcitem{bugzilla}{user}] The username with which to connect to
bos@64:   the MySQL server.  The database must be configured to allow this
bos@64:   user to connect from whatever host you are running the
bos@64:   \hook{bugzilla} hook on.  This user must be able to access and
bos@64:   modify Bugzilla tables.  The default value of this item is
bos@64:   \texttt{bugs}, which is the standard name of the Bugzilla user in a
bos@64:   MySQL database.
bos@64: \item[\rcitem{bugzilla}{password}] The MySQL password for the user you
bos@62:   configured above.  This is stored as plain text, so you should make
bos@62:   sure that unauthorised users cannot read the \hgrc\ file where you
bos@62:   store this information.
bos@64: \item[\rcitem{bugzilla}{db}] The name of the Bugzilla database on the
bos@64:   MySQL server.  The default value of this item is \texttt{bugs},
bos@64:   which is the standard name of the MySQL database where Bugzilla
bos@64:   stores its data.
bos@64: \item[\rcitem{bugzilla}{notify}] If you want Bugzilla to send out a
bos@64:   notification email to subscribers after this hook has added a
bos@64:   comment to a bug, you will need this hook to run a command whenever
bos@64:   it updates the database.  The command to run depends on where you
bos@64:   have installed Bugzilla, but it will typically look something like
bos@64:   this, if you have Bugzilla installed in
bos@64:   \dirname{/var/www/html/bugzilla}:
bos@62:   \begin{codesample4}
bos@62:     cd /var/www/html/bugzilla && ./processmail %s nobody@nowhere.com
bos@62:   \end{codesample4}
bos@62:   The Bugzilla \texttt{processmail} program expects to be given a
bos@62:   bug~ID (the hook replaces ``\texttt{\%s}'' with the bug~ID) and an
bos@62:   email address.  It also expects to be able to write to some files in
bos@62:   the directory that it runs in.  If Bugzilla and this hook are not
bos@62:   installed on the same machine, you will need to find a way to run
bos@62:   \texttt{processmail} on the server where Bugzilla is installed.
bos@62: \end{itemize}
bos@62: 
bos@62: \subsubsection{Mapping committer names to Bugzilla user names}
bos@62: 
bos@62: By default, the \hgext{bugzilla} hook tries to use the email address
bos@62: of a changeset's committer as the Bugzilla user name with which to
bos@62: update a bug.  If this does not suit your needs, you can map committer
bos@62: email addresses to Bugzilla user names using a \rcsection{usermap}
bos@62: section.
bos@62: 
bos@62: Each item in the \rcsection{usermap} section contains an email address
bos@62: on the left, and a Bugzilla user name on the right.
bos@62: \begin{codesample2}
bos@62:   [usermap]
bos@62:   jane.user@example.com = jane
bos@62: \end{codesample2}
bos@62: You can either keep the \rcsection{usermap} data in a normal \hgrc, or
bos@62: tell the \hgext{bugzilla} hook to read the information from an
bos@62: external \filename{usermap} file.  In the latter case, you can store
bos@62: \filename{usermap} data by itself in (for example) a user-modifiable
bos@62: repository.  This makes it possible to let your users maintain their
bos@64: own \rcitem{bugzilla}{usermap} entries.  The main \hgrc\ file might
bos@64: look like this:
bos@62: \begin{codesample2}
bos@62:   # regular hgrc file refers to external usermap file
bos@62:   [bugzilla]
bos@62:   usermap = /home/hg/repos/userdata/bugzilla-usermap.conf
bos@62: \end{codesample2}
bos@62: While the \filename{usermap} file that it refers to might look like
bos@62: this:
bos@62: \begin{codesample2}
bos@62:   # bugzilla-usermap.conf - inside a hg repository
bos@62:   [usermap]
bos@62:   stephanie@example.com = steph
bos@62: \end{codesample2}
bos@62: 
bos@62: \subsubsection{Configuring the text that gets added to a bug}
bos@62: 
bos@62: You can configure the text that this hook adds as a comment; you
bos@62: specify it in the form of a Mercurial template.  Several \hgrc\
bos@62: entries (still in the \rcsection{bugzilla} section) control this
bos@62: behaviour.
bos@62: \begin{itemize}
bos@62: \item[\texttt{strip}] The number of leading path elements to strip
bos@62:   from a repository's path name to construct a partial path for a URL.
bos@62:   For example, if the repositories on your server live under
bos@62:   \dirname{/home/hg/repos}, and you have a repository whose path is
bos@62:   \dirname{/home/hg/repos/app/tests}, then setting \texttt{strip} to
bos@62:   \texttt{4} will give a partial path of \dirname{app/tests}.  The
bos@62:   hook will make this partial path available when expanding a
bos@62:   template, as \texttt{webroot}.
bos@62: \item[\texttt{template}] The text of the template to use.  In addition
bos@62:   to the usual changeset-related variables, this template can use
bos@62:   \texttt{hgweb} (the value of the \texttt{hgweb} configuration item
bos@62:   above) and \texttt{webroot} (the path constructed using
bos@62:   \texttt{strip} above).
bos@62: \end{itemize}
bos@62: 
bos@64: In addition, you can add a \rcitem{web}{baseurl} item to the
bos@64: \rcsection{web} section of your \hgrc.  The \hgext{bugzilla} hook will
bos@64: make this available when expanding a template, as the base string to
bos@64: use when constructing a URL that will let users browse from a Bugzilla
bos@64: comment to view a changeset.  Example:
bos@64: \begin{codesample2}
bos@64:   [web]
bos@64:   baseurl = http://hg.domain.com/
bos@64: \end{codesample2}
bos@64: 
bos@62: Here is an example set of \hgext{bugzilla} hook config information.
bos@62: \begin{codesample2}
bos@62:   [bugzilla]
bos@62:   host = bugzilla.example.com
bos@62:   password = mypassword
bos@62:   version = 2.16
bos@62:   # server-side repos live in /home/hg/repos, so strip 4 leading
bos@62:   # separators
bos@62:   strip = 4
bos@62:   hgweb = http://hg.example.com/
bos@62:   usermap = /home/hg/repos/notify/bugzilla.conf
bos@62:   template = Changeset \{node|short\}, made by \{author\} in the \{webroot\}
bos@62:     repo, refers to this bug.\\nFor complete details, see 
bos@62:     \{hgweb\}\{webroot\}?cmd=changeset;node=\{node|short\}\\nChangeset
bos@62:     description:\\n\\t\{desc|tabindent\}
bos@62: \end{codesample2}
bos@62: 
bos@62: \subsubsection{Testing and troubleshooting}
bos@62: 
bos@62: The most common problems with configuring the \hgext{bugzilla} hook
bos@62: relate to running Bugzilla's \filename{processmail} script and mapping
bos@62: committer names to user names.
bos@62: 
bos@62: Recall from section~\ref{sec:hook:bugzilla:config} above that the user
bos@62: that runs the Mercurial process on the server is also the one that
bos@62: will run the \filename{processmail} script.  The
bos@62: \filename{processmail} script sometimes causes Bugzilla to write to
bos@62: files in its configuration directory, and Bugzilla's configuration
bos@62: files are usually owned by the user that your web server runs under.
bos@62: 
bos@62: You can cause \filename{processmail} to be run with the suitable
bos@62: user's identity using the \command{sudo} command.  Here is an example
bos@62: entry for a \filename{sudoers} file.
bos@62: \begin{codesample2}
bos@62:   hg_user = (httpd_user) NOPASSWD: /var/www/html/bugzilla/processmail-wrapper %s
bos@62: \end{codesample2}
bos@62: This allows the \texttt{hg\_user} user to run a
bos@62: \filename{processmail-wrapper} program under the identity of
bos@62: \texttt{httpd\_user}.
bos@62: 
bos@62: This indirection through a wrapper script is necessary, because
bos@62: \filename{processmail} expects to be run with its current directory
bos@62: set to wherever you installed Bugzilla; you can't specify that kind of
bos@62: constraint in a \filename{sudoers} file.  The contents of the wrapper
bos@62: script are simple:
bos@62: \begin{codesample2}
bos@62:   #!/bin/sh
bos@62:   cd `dirname $0` && ./processmail "$1" nobody@example.com
bos@62: \end{codesample2}
bos@62: It doesn't seem to matter what email address you pass to
bos@62: \filename{processmail}.
bos@62: 
bos@62: If your \rcsection{usermap} is not set up correctly, users will see an
bos@62: error message from the \hgext{bugzilla} hook when they push changes
bos@62: to the server.  The error message will look like this:
bos@62: \begin{codesample2}
bos@62:   cannot find bugzilla user id for john.q.public@example.com
bos@62: \end{codesample2}
bos@62: What this means is that the committer's address,
bos@62: \texttt{john.q.public@example.com}, is not a valid Bugzilla user name,
bos@62: nor does it have an entry in your \rcsection{usermap} that maps it to
bos@62: a valid Bugzilla user name.
bos@62: 
bos@62: \subsection{\hgext{notify}---send email notifications}
bos@62: 
bos@62: Although Mercurial's built-in web server provides RSS feeds of changes
bos@62: in every repository, many people prefer to receive change
bos@62: notifications via email.  The \hgext{notify} hook lets you send out
bos@62: notifications to a set of email addresses whenever changesets arrive
bos@62: that those subscribers are interested in.
bos@62: 
bos@62: As with the \hgext{bugzilla} hook, the \hgext{notify} hook is
bos@62: template-driven, so you can customise the contents of the notification
bos@62: messages that it sends.
bos@62: 
bos@62: By default, the \hgext{notify} hook includes a diff of every changeset
bos@63: that it sends out; you can limit the size of the diff, or turn this
bos@62: feature off entirely.  It is useful for letting subscribers review
bos@62: changes immediately, rather than clicking to follow a URL.
bos@62: 
bos@62: \subsubsection{Configuring the \hgext{notify} hook}
bos@62: 
bos@62: You can set up the \hgext{notify} hook to send one email message per
bos@62: incoming changeset, or one per incoming group of changesets (all those
bos@62: that arrived in a single pull or push).
bos@62: \begin{codesample2}
bos@62:   [hooks]
bos@62:   # send one email per group of changes
bos@62:   changegroup.notify = python:hgext.notify.hook
bos@62:   # send one email per change
bos@62:   incoming.notify = python:hgext.notify.hook
bos@62: \end{codesample2}
bos@62: 
bos@62: Configuration information for this hook lives in the
bos@62: \rcsection{notify} section of a \hgrc\ file.
bos@62: \begin{itemize}
bos@62: \item[\rcitem{notify}{test}] By default, this hook does not send out
bos@62:   email at all; instead, it prints the message that it \emph{would}
bos@62:   send.  Set this item to \texttt{false} to allow email to be sent.
bos@62:   The reason that sending of email is turned off by default is that it
bos@62:   takes several tries to configure this extension exactly as you would
bos@62:   like, and it would be bad form to spam subscribers with a number of
bos@62:   ``broken'' notifications while you debug your configuration.
bos@62: \item[\rcitem{notify}{config}] The path to a configuration file that
bos@63:   contains subscription information.  This is kept separate from the
bos@62:   main \hgrc\ so that you can maintain it in a repository of its own.
bos@62:   People can then clone that repository, update their subscriptions,
bos@62:   and push the changes back to your server.
bos@62: \item[\rcitem{notify}{strip}] The number of leading path separator
bos@62:   characters to strip from a repository's path, when deciding whether
bos@62:   a repository has subscribers.  For example, if the repositories on
bos@62:   your server live in \dirname{/home/hg/repos}, and \hgext{notify} is
bos@62:   considering a repository named \dirname{/home/hg/repos/shared/test},
bos@62:   setting \rcitem{notify}{strip} to \texttt{4} will cause
bos@62:   \hgext{notify} to trim the path it considers down to
bos@62:   \dirname{shared/test}, and it will match subscribers against that.
bos@62: \item[\rcitem{notify}{template}] The template text to use when sending
bos@62:   messages.  This specifies both the contents of the message header
bos@62:   and its body.
bos@62: \item[\rcitem{notify}{maxdiff}] The maximum number of lines of diff
bos@62:   data to append to the end of a message.  If a diff is longer than
bos@62:   this, it is truncated.  By default, this is set to 300.  Set this to
bos@62:   \texttt{0} to omit diffs from notification emails.
bos@62: \item[\rcitem{notify}{sources}] A list of sources of changesets to
bos@62:   consider.  This lets you limit \hgext{notify} to only sending out
bos@62:   email about changes that remote users pushed into this repository
bos@62:   via a server, for example.  See section~\ref{sec:hook:sources} for
bos@62:   the sources you can specify here.
bos@62: \end{itemize}
bos@62: 
bos@62: If you set the \rcitem{web}{baseurl} item in the \rcsection{web}
bos@62: section, you can use it in a template; it will be available as
bos@62: \texttt{webroot}.
bos@62: 
bos@62: Here is an example set of \hgext{notify} configuration information.
bos@62: \begin{codesample2}
bos@62:   [notify]
bos@62:   # really send email
bos@62:   test = false
bos@62:   # subscriber data lives in the notify repo
bos@62:   config = /home/hg/repos/notify/notify.conf
bos@62:   # repos live in /home/hg/repos on server, so strip 4 "/" chars
bos@62:   strip = 4
bos@62:   template = X-Hg-Repo: \{webroot\}\\n\\\\
bos@62:     Subject: \{webroot\}: \{desc|firstline|strip\}\\n\\\\
bos@62:     From: \{author\}\\n\\\\
bos@62:     \\n\\\\
bos@62:     changeset \{node|short\} in \{root\}\\n\\\\
bos@62:     details: \{baseurl\}\{webroot\}?cmd=changeset;node=\{node|short\}\\n\\\\
bos@62:     description:\\n\\\\
bos@62:     \\t\{desc|tabindent|strip\}
bos@62: 
bos@62:   [web]
bos@62:   baseurl = http://hg.example.com/
bos@62: \end{codesample2}
bos@62: 
bos@62: This will produce a message that looks like the following:
bos@62: \begin{codesample2}
bos@62:   X-Hg-Repo: tests/slave
bos@62:   Subject: tests/slave: Handle error case when slave has no buffers
bos@62:   Date: Wed,  2 Aug 2006 15:25:46 -0700 (PDT)
bos@62: 
bos@62:   changeset 3cba9bfe74b5 in /home/hg/repos/tests/slave
bos@62:   details: http://hg.example.com/tests/slave?cmd=changeset;node=3cba9bfe74b5
bos@62:   description:
bos@62:           Handle error case when slave has no buffers
bos@62:   diffs (54 lines):
bos@62: 
bos@62:   diff -r 9d95df7cf2ad -r 3cba9bfe74b5 include/tests.h
bos@62:   --- a/include/tests.h      Wed Aug 02 15:19:52 2006 -0700
bos@62:   +++ b/include/tests.h      Wed Aug 02 15:25:26 2006 -0700
bos@62:   @@ -212,6 +212,15 @@ static __inline__ void test_headers(void *h)
bos@62:   [...snip...]
bos@62: \end{codesample2}
bos@62: 
bos@62: \subsubsection{Testing and troubleshooting}
bos@62: 
bos@62: Do not forget that by default, the \hgext{notify} extension \emph{will
bos@62:   not send any mail} until you explicitly configure it to do so, by
bos@62: setting \rcitem{notify}{test} to \texttt{false}.  Until you do that,
bos@62: it simply prints the message it \emph{would} send.
bos@44: 
bos@64: \section{Information for writers of hooks}
bos@41: \label{sec:hook:ref}
bos@39: 
bos@39: \subsection{In-process hook execution}
bos@39: 
bos@39: An in-process hook is called with arguments of the following form:
bos@39: \begin{codesample2}
bos@39:   def myhook(ui, repo, **kwargs):
bos@39:       pass
bos@39: \end{codesample2}
bos@39: The \texttt{ui} parameter is a \pymodclass{mercurial.ui}{ui} object.
bos@39: The \texttt{repo} parameter is a
bos@39: \pymodclass{mercurial.localrepo}{localrepository} object.  The
bos@39: names and values of the \texttt{**kwargs} parameters depend on the
bos@39: hook being invoked, with the following common features:
bos@39: \begin{itemize}
bos@39: \item If a parameter is named \texttt{node} or
bos@39:   \texttt{parent\emph{N}}, it will contain a hexadecimal changeset ID.
bos@39:   The empty string is used to represent ``null changeset ID'' instead
bos@39:   of a string of zeroes.
bos@62: \item If a parameter is named \texttt{url}, it will contain the URL of
bos@62:   a remote repository, if that can be determined.
bos@39: \item Boolean-valued parameters are represented as Python
bos@39:   \texttt{bool} objects.
bos@39: \end{itemize}
bos@39: 
bos@39: An in-process hook is called without a change to the process's working
bos@39: directory (unlike external hooks, which are run in the root of the
bos@62: repository).  It must not change the process's working directory, or
bos@62: it will cause any calls it makes into the Mercurial API to fail.
bos@62: 
bos@62: If a hook returns a boolean ``false'' value, it is considered to have
bos@62: succeeded.  If it returns a boolean ``true'' value or raises an
bos@62: exception, it is considered to have failed.  A useful way to think of
bos@62: the calling convention is ``tell me if you fail''.
bos@62: 
bos@62: Note that changeset IDs are passed into Python hooks as hexadecimal
bos@62: strings, not the binary hashes that Mercurial's APIs normally use.  To
bos@62: convert a hash from hex to binary, use the
bos@62: \pymodfunc{mercurial.node}{bin} function.
bos@39: 
bos@39: \subsection{External hook execution}
bos@39: 
bos@62: An external hook is passed to the shell of the user running Mercurial.
bos@62: Features of that shell, such as variable substitution and command
bos@39: redirection, are available.  The hook is run in the root directory of
bos@62: the repository (unlike in-process hooks, which are run in the same
bos@62: directory that Mercurial was run in).
bos@39: 
bos@39: Hook parameters are passed to the hook as environment variables.  Each
bos@39: environment variable's name is converted in upper case and prefixed
bos@39: with the string ``\texttt{HG\_}''.  For example, if the name of a
bos@39: parameter is ``\texttt{node}'', the name of the environment variable
bos@39: representing that parameter will be ``\texttt{HG\_NODE}''.
bos@39: 
bos@39: A boolean parameter is represented as the string ``\texttt{1}'' for
bos@39: ``true'', ``\texttt{0}'' for ``false''.  If an environment variable is
bos@39: named \envar{HG\_NODE}, \envar{HG\_PARENT1} or \envar{HG\_PARENT2}, it
bos@39: contains a changeset ID represented as a hexadecimal string.  The
bos@39: empty string is used to represent ``null changeset ID'' instead of a
bos@62: string of zeroes.  If an environment variable is named
bos@62: \envar{HG\_URL}, it will contain the URL of a remote repository, if
bos@62: that can be determined.
bos@39: 
bos@39: If a hook exits with a status of zero, it is considered to have
bos@39: succeeded.  If it exits with a non-zero status, it is considered to
bos@39: have failed.
bos@39: 
bos@62: \subsection{Finding out where changesets come from}
bos@62: 
bos@62: A hook that involves the transfer of changesets between a local
bos@62: repository and another may be able to find out information about the
bos@62: ``far side''.  Mercurial knows \emph{how} changes are being
bos@62: transferred, and in many cases \emph{where} they are being transferred
bos@62: to or from.
bos@62: 
bos@62: \subsubsection{Sources of changesets}
bos@62: \label{sec:hook:sources}
bos@62: 
bos@62: Mercurial will tell a hook what means are, or were, used to transfer
bos@62: changesets between repositories.  This is provided by Mercurial in a
bos@62: Python parameter named \texttt{source}, or an environment variable named
bos@62: \envar{HG\_SOURCE}.
bos@62: 
bos@62: \begin{itemize}
bos@62: \item[\texttt{serve}] Changesets are transferred to or from a remote
bos@62:   repository over http or ssh.
bos@62: \item[\texttt{pull}] Changesets are being transferred via a pull from
bos@62:   one repository into another.
bos@62: \item[\texttt{push}] Changesets are being transferred via a push from
bos@62:   one repository into another.
bos@62: \item[\texttt{bundle}] Changesets are being transferred to or from a
bos@62:   bundle.
bos@62: \end{itemize}
bos@62: 
bos@62: \subsubsection{Where changes are going---remote repository URLs}
bos@62: \label{sec:hook:url}
bos@62: 
bos@62: When possible, Mercurial will tell a hook the location of the ``far
bos@62: side'' of an activity that transfers changeset data between
bos@62: repositories.  This is provided by Mercurial in a Python parameter
bos@62: named \texttt{url}, or an environment variable named \envar{HG\_URL}.
bos@62: 
bos@62: This information is not always known.  If a hook is invoked in a
bos@62: repository that is being served via http or ssh, Mercurial cannot tell
bos@62: where the remote repository is, but it may know where the client is
bos@62: connecting from.  In such cases, the URL will take one of the
bos@62: following forms:
bos@62: \begin{itemize}
bos@62: \item \texttt{remote:ssh:\emph{ip-address}}---remote ssh client, at
bos@62:   the given IP address.
bos@62: \item \texttt{remote:http:\emph{ip-address}}---remote http client, at
bos@62:   the given IP address.  If the client is using SSL, this will be of
bos@62:   the form \texttt{remote:https:\emph{ip-address}}.
bos@62: \item Empty---no information could be discovered about the remote
bos@62:   client.
bos@62: \end{itemize}
bos@62: 
bos@64: \section{Hook reference}
bos@64: 
bos@64: \subsection{\hook{changegroup}---after remote changesets added}
bos@39: \label{sec:hook:changegroup}
bos@39: 
bos@40: This hook is run after a group of pre-existing changesets has been
bos@40: added to the repository, for example via a \hgcmd{pull} or
bos@40: \hgcmd{unbundle}.  This hook is run once per operation that added one
bos@41: or more changesets.  This is in contrast to the \hook{incoming} hook,
bos@41: which is run once per changeset, regardless of whether the changesets
bos@41: arrive in a group.
bos@41: 
bos@41: Some possible uses for this hook include kicking off an automated
bos@41: build or test of the added changesets, updating a bug database, or
bos@41: notifying subscribers that a repository contains new changes.
bos@40: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{node}] A changeset ID.  The changeset ID of the first
bos@40:   changeset in the group that was added.  All changesets between this
bos@40:   and \index{tags!\texttt{tip}}\texttt{tip}, inclusive, were added by
bos@40:   a single \hgcmd{pull}, \hgcmd{push} or \hgcmd{unbundle}.
bos@62: \item[\texttt{source}] A string.  The source of these changes.  See
bos@62:   section~\ref{sec:hook:sources} for details.
bos@62: \item[\texttt{url}] A URL.  The location of the remote repository, if
bos@62:   known.  See section~\ref{sec:hook:url} for more information.
bos@40: \end{itemize}
bos@40: 
bos@40: See also: \hook{incoming} (section~\ref{sec:hook:incoming}),
bos@40: \hook{prechangegroup} (section~\ref{sec:hook:prechangegroup}),
bos@40: \hook{pretxnchangegroup} (section~\ref{sec:hook:pretxnchangegroup})
bos@39: 
bos@64: \subsection{\hook{commit}---after a new changeset is created}
bos@39: \label{sec:hook:commit}
bos@39: 
bos@40: This hook is run after a new changeset has been created.
bos@40: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{node}] A changeset ID.  The changeset ID of the newly
bos@40:   committed changeset.
bos@40: \item[\texttt{parent1}] A changeset ID.  The changeset ID of the first
bos@40:   parent of the newly committed changeset.
bos@40: \item[\texttt{parent2}] A changeset ID.  The changeset ID of the second
bos@40:   parent of the newly committed changeset.
bos@40: \end{itemize}
bos@40: 
bos@40: See also: \hook{precommit} (section~\ref{sec:hook:precommit}),
bos@40: \hook{pretxncommit} (section~\ref{sec:hook:pretxncommit})
bos@40: 
bos@64: \subsection{\hook{incoming}---after one remote changeset is added}
bos@40: \label{sec:hook:incoming}
bos@40: 
bos@40: This hook is run after a pre-existing changeset has been added to the
bos@40: repository, for example via a \hgcmd{push}.  If a group of changesets
bos@40: was added in a single operation, this hook is called once for each
bos@40: added changeset.
bos@40: 
bos@41: You can use this hook for the same purposes as the \hook{changegroup}
bos@41: hook (section~\ref{sec:hook:changegroup}); it's simply more convenient
bos@54: sometimes to run a hook once per group of changesets, while other
bos@41: times it's handier once per changeset.
bos@41: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{node}] A changeset ID.  The ID of the newly added
bos@39:   changeset.
bos@62: \item[\texttt{source}] A string.  The source of these changes.  See
bos@62:   section~\ref{sec:hook:sources} for details.
bos@62: \item[\texttt{url}] A URL.  The location of the remote repository, if
bos@62:   known.  See section~\ref{sec:hook:url} for more information.
bos@40: \end{itemize}
bos@40: 
bos@40: See also: \hook{changegroup} (section~\ref{sec:hook:changegroup}) \hook{prechangegroup} (section~\ref{sec:hook:prechangegroup}), \hook{pretxnchangegroup} (section~\ref{sec:hook:pretxnchangegroup})
bos@40: 
bos@64: \subsection{\hook{outgoing}---after changesets are propagated}
bos@40: \label{sec:hook:outgoing}
bos@40: 
bos@40: This hook is run after a group of changesets has been propagated out
bos@40: of this repository, for example by a \hgcmd{push} or \hgcmd{bundle}
bos@40: command.
bos@40: 
bos@41: One possible use for this hook is to notify administrators that
bos@41: changes have been pulled.
bos@41: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{node}] A changeset ID.  The changeset ID of the first
bos@40:   changeset of the group that was sent.
bos@62: \item[\texttt{source}] A string.  The source of the of the operation
bos@62:   (see section~\ref{sec:hook:sources}).  If a remote client pulled
bos@62:   changes from this repository, \texttt{source} will be
bos@62:   \texttt{serve}.  If the client that obtained changes from this
bos@62:   repository was local, \texttt{source} will be \texttt{bundle},
bos@62:   \texttt{pull}, or \texttt{push}, depending on the operation the
bos@62:   client performed.
bos@62: \item[\texttt{url}] A URL.  The location of the remote repository, if
bos@62:   known.  See section~\ref{sec:hook:url} for more information.
bos@40: \end{itemize}
bos@40: 
bos@40: See also: \hook{preoutgoing} (section~\ref{sec:hook:preoutgoing})
bos@40: 
bos@64: \subsection{\hook{prechangegroup}---before starting to add remote changesets}
bos@40: \label{sec:hook:prechangegroup}
bos@40: 
bos@41: This controlling hook is run before Mercurial begins to add a group of
bos@41: changesets from another repository.
bos@41: 
bos@41: This hook does not have any information about the changesets to be
bos@41: added, because it is run before transmission of those changesets is
bos@41: allowed to begin.  If this hook fails, the changesets will not be
bos@41: transmitted.
bos@41: 
bos@41: One use for this hook is to prevent external changes from being added
bos@62: to a repository.  For example, you could use this to ``freeze'' a
bos@62: server-hosted branch temporarily or permanently so that users cannot
bos@62: push to it, while still allowing a local administrator to modify the
bos@62: repository.
bos@62: 
bos@62: Parameters to this hook:
bos@62: \begin{itemize}
bos@62: \item[\texttt{source}] A string.  The source of these changes.  See
bos@62:   section~\ref{sec:hook:sources} for details.
bos@62: \item[\texttt{url}] A URL.  The location of the remote repository, if
bos@62:   known.  See section~\ref{sec:hook:url} for more information.
bos@62: \end{itemize}
bos@40: 
bos@40: See also: \hook{changegroup} (section~\ref{sec:hook:changegroup}),
bos@40: \hook{incoming} (section~\ref{sec:hook:incoming}), ,
bos@40: \hook{pretxnchangegroup} (section~\ref{sec:hook:pretxnchangegroup})
bos@40: 
bos@64: \subsection{\hook{precommit}---before starting to commit a changeset}
bos@40: \label{sec:hook:precommit}
bos@40: 
bos@41: This hook is run before Mercurial begins to commit a new changeset.
bos@41: It is run before Mercurial has any of the metadata for the commit,
bos@41: such as the files to be committed, the commit message, or the commit
bos@41: date.
bos@41: 
bos@41: One use for this hook is to disable the ability to commit new
bos@41: changesets, while still allowing incoming changesets.  Another is to
bos@41: run a build or test, and only allow the commit to begin if the build
bos@41: or test succeeds.
bos@40: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{parent1}] A changeset ID.  The changeset ID of the first
bos@40:   parent of the working directory.
bos@40: \item[\texttt{parent2}] A changeset ID.  The changeset ID of the second
bos@40:   parent of the working directory.
bos@40: \end{itemize}
bos@40: If the commit proceeds, the parents of the working directory will
bos@40: become the parents of the new changeset.
bos@40: 
bos@40: See also: \hook{commit} (section~\ref{sec:hook:commit}),
bos@40: \hook{pretxncommit} (section~\ref{sec:hook:pretxncommit})
bos@40: 
bos@64: \subsection{\hook{preoutgoing}---before starting to propagate changesets}
bos@40: \label{sec:hook:preoutgoing}
bos@40: 
bos@40: This hook is invoked before Mercurial knows the identities of the
bos@40: changesets to be transmitted.
bos@40: 
bos@41: One use for this hook is to prevent changes from being transmitted to
bos@41: another repository.
bos@41: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{source}] A string.  The source of the operation that is
bos@62:   attempting to obtain changes from this repository (see
bos@62:   section~\ref{sec:hook:sources}).  See the documentation for the
bos@62:   \texttt{source} parameter to the \hook{outgoing} hook, in
bos@62:   section~\ref{sec:hook:outgoing}, for possible values of this
bos@62:   parameter.
bos@62: \item[\texttt{url}] A URL.  The location of the remote repository, if
bos@62:   known.  See section~\ref{sec:hook:url} for more information.
bos@40: \end{itemize}
bos@40: 
bos@40: See also: \hook{outgoing} (section~\ref{sec:hook:outgoing})
bos@40: 
bos@64: \subsection{\hook{pretag}---before tagging a changeset}
bos@40: \label{sec:hook:pretag}
bos@40: 
bos@41: This controlling hook is run before a tag is created.  If the hook
bos@41: succeeds, creation of the tag proceeds.  If the hook fails, the tag is
bos@41: not created.
bos@41: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{local}] A boolean.  Whether the tag is local to this
bos@40:   repository instance (i.e.~stored in \sfilename{.hg/tags}) or managed
bos@40:   by Mercurial (stored in \sfilename{.hgtags}).
bos@40: \item[\texttt{node}] A changeset ID.  The ID of the changeset to be tagged.
bos@40: \item[\texttt{tag}] A string.  The name of the tag to be created.
bos@40: \end{itemize}
bos@40: 
bos@40: If the tag to be created is revision-controlled, the \hook{precommit}
bos@40: and \hook{pretxncommit} hooks (sections~\ref{sec:hook:commit}
bos@40: and~\ref{sec:hook:pretxncommit}) will also be run.
bos@40: 
bos@40: See also: \hook{tag} (section~\ref{sec:hook:tag})
bos@40: 
bos@64: \subsection{\hook{pretxnchangegroup}---before completing addition of
bos@64:   remote changesets}
bos@40: \label{sec:hook:pretxnchangegroup}
bos@40: 
bos@41: This controlling hook is run before a transaction---that manages the
bos@41: addition of a group of new changesets from outside the
bos@41: repository---completes.  If the hook succeeds, the transaction
bos@41: completes, and all of the changesets become permanent within this
bos@41: repository.  If the hook fails, the transaction is rolled back, and
bos@41: the data for the changesets is erased.
bos@41: 
bos@41: This hook can access the metadata associated with the almost-added
bos@41: changesets, but it should not do anything permanent with this data.
bos@41: It must also not modify the working directory.
bos@41: 
bos@41: While this hook is running, if other Mercurial processes access this
bos@41: repository, they will be able to see the almost-added changesets as if
bos@41: they are permanent.  This may lead to race conditions if you do not
bos@41: take steps to avoid them.
bos@41: 
bos@41: This hook can be used to automatically vet a group of changesets.  If
bos@41: the hook fails, all of the changesets are ``rejected'' when the
bos@41: transaction rolls back.
bos@41: 
bos@62: Parameters to this hook:
bos@62: \begin{itemize}
bos@62: \item[\texttt{node}] A changeset ID.  The changeset ID of the first
bos@62:   changeset in the group that was added.  All changesets between this
bos@62:   and \index{tags!\texttt{tip}}\texttt{tip}, inclusive, were added by
bos@62:   a single \hgcmd{pull}, \hgcmd{push} or \hgcmd{unbundle}.
bos@62: \item[\texttt{source}] A string.  The source of these changes.  See
bos@62:   section~\ref{sec:hook:sources} for details.
bos@62: \item[\texttt{url}] A URL.  The location of the remote repository, if
bos@62:   known.  See section~\ref{sec:hook:url} for more information.
bos@62: \end{itemize}
bos@40: 
bos@40: See also: \hook{changegroup} (section~\ref{sec:hook:changegroup}),
bos@40: \hook{incoming} (section~\ref{sec:hook:incoming}),
bos@40: \hook{prechangegroup} (section~\ref{sec:hook:prechangegroup})
bos@40: 
bos@64: \subsection{\hook{pretxncommit}---before completing commit of new changeset}
bos@40: \label{sec:hook:pretxncommit}
bos@40: 
bos@41: This controlling hook is run before a transaction---that manages a new
bos@41: commit---completes.  If the hook succeeds, the transaction completes
bos@41: and the changeset becomes permanent within this repository.  If the
bos@41: hook fails, the transaction is rolled back, and the commit data is
bos@41: erased.
bos@41: 
bos@41: This hook can access the metadata associated with the almost-new
bos@41: changeset, but it should not do anything permanent with this data.  It
bos@41: must also not modify the working directory.
bos@41: 
bos@41: While this hook is running, if other Mercurial processes access this
bos@41: repository, they will be able to see the almost-new changeset as if it
bos@41: is permanent.  This may lead to race conditions if you do not take
bos@41: steps to avoid them.
bos@41: 
bos@62: Parameters to this hook:
bos@62: \begin{itemize}
bos@62: \item[\texttt{node}] A changeset ID.  The changeset ID of the newly
bos@62:   committed changeset.
bos@62: \item[\texttt{parent1}] A changeset ID.  The changeset ID of the first
bos@62:   parent of the newly committed changeset.
bos@62: \item[\texttt{parent2}] A changeset ID.  The changeset ID of the second
bos@62:   parent of the newly committed changeset.
bos@62: \end{itemize}
bos@40: 
bos@40: See also: \hook{precommit} (section~\ref{sec:hook:precommit})
bos@40: 
bos@64: \subsection{\hook{preupdate}---before updating or merging working directory}
bos@40: \label{sec:hook:preupdate}
bos@40: 
bos@41: This controlling hook is run before an update or merge of the working
bos@41: directory begins.  It is run only if Mercurial's normal pre-update
bos@41: checks determine that the update or merge can proceed.  If the hook
bos@41: succeeds, the update or merge may proceed; if it fails, the update or
bos@41: merge does not start.
bos@41: 
bos@40: Parameters to this hook:
bos@40: \begin{itemize}
bos@40: \item[\texttt{parent1}] A changeset ID.  The ID of the parent that the
bos@40:   working directory is to be updated to.  If the working directory is
bos@40:   being merged, it will not change this parent.
bos@40: \item[\texttt{parent2}] A changeset ID.  Only set if the working
bos@40:   directory is being merged.  The ID of the revision that the working
bos@40:   directory is being merged with.
bos@40: \end{itemize}
bos@40: 
bos@40: See also: \hook{update} (section~\ref{sec:hook:update})
bos@40: 
bos@64: \subsection{\hook{tag}---after tagging a changeset}
bos@40: \label{sec:hook:tag}
bos@40: 
bos@41: This hook is run after a tag has been created.
bos@41: 
bos@62: Parameters to this hook:
bos@62: \begin{itemize}
bos@62: \item[\texttt{local}] A boolean.  Whether the new tag is local to this
bos@62:   repository instance (i.e.~stored in \sfilename{.hg/tags}) or managed
bos@62:   by Mercurial (stored in \sfilename{.hgtags}).
bos@62: \item[\texttt{node}] A changeset ID.  The ID of the changeset that was
bos@62:   tagged.
bos@62: \item[\texttt{tag}] A string.  The name of the tag that was created.
bos@62: \end{itemize}
bos@40: 
bos@40: If the created tag is revision-controlled, the \hook{commit} hook
bos@41: (section~\ref{sec:hook:commit}) is run before this hook.
bos@40: 
bos@40: See also: \hook{pretag} (section~\ref{sec:hook:pretag})
bos@40: 
bos@64: \subsection{\hook{update}---after updating or merging working directory}
bos@40: \label{sec:hook:update}
bos@40: 
bos@41: This hook is run after an update or merge of the working directory
bos@41: completes.  Since a merge can fail (if the external \command{hgmerge}
bos@41: command fails to resolve conflicts in a file), this hook communicates
bos@41: whether the update or merge completed cleanly.
bos@41: 
bos@40: \begin{itemize}
bos@40: \item[\texttt{error}] A boolean.  Indicates whether the update or
bos@40:   merge completed successfully.
bos@40: \item[\texttt{parent1}] A changeset ID.  The ID of the parent that the
bos@40:   working directory was updated to.  If the working directory was
bos@40:   merged, it will not have changed this parent.
bos@40: \item[\texttt{parent2}] A changeset ID.  Only set if the working
bos@40:   directory was merged.  The ID of the revision that the working
bos@40:   directory was merged with.
bos@40: \end{itemize}
bos@40: 
bos@40: See also: \hook{preupdate} (section~\ref{sec:hook:preupdate})
bos@34: 
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