1.1 --- a/en/branch.tex	Mon Apr 16 14:19:31 2007 -0700
     1.2 +++ b/en/branch.tex	Mon Apr 16 16:11:24 2007 -0700
     1.3 @@ -1,7 +1,122 @@
     1.4 -\chapter{Managing branchy development}
     1.5 +\chapter{Managing releases and branchy development}
     1.6  \label{chap:branch}
     1.7  
     1.8 +Mercurial provides two ways for you to manage a project that is making
     1.9 +progress on multiple fronts at once.  To understand these mechanisms,
    1.10 +let's first take a look at a fairly normal software project structure.
    1.11  
    1.12 +Many software projects issue periodic ``major'' releases that contain
    1.13 +substantial new features.  In parallel, they may issue ``minor''
    1.14 +releases.  These are usually identical to the major releases off which
    1.15 +they're based, but with a few bugs fixed.
    1.16 +
    1.17 +\section{Giving a persistent name to a revision}
    1.18 +
    1.19 +Once you decide that you'd like to call a particular revision a
    1.20 +``release'', it's a good idea to record the identity of that revision.
    1.21 +This will let you reproduce that release at a later date, for whatever
    1.22 +purpose you might need at the time (reproducing a bug, porting to a
    1.23 +new platform, etc).
    1.24 +\interaction{tag.init}
    1.25 +
    1.26 +Mercurial lets you give a permanent name to any revision using the
    1.27 +\hgcmd{tag} command.  Not surprisingly, these names are called
    1.28 +``tags''.
    1.29 +\interaction{tag.tag}
    1.30 +
    1.31 +A tag is nothing more than a ``symbolic name'' for a revision.  Tags
    1.32 +exist purely for your convenience, so that you have a handy permanent
    1.33 +way to refer to a revision; Mercurial doesn't interpret the tag names
    1.34 +you use in any way.  Neither does Mercurial place any restrictions on
    1.35 +the name of a tag, beyond a few that are necessary to ensure that a
    1.36 +tag can be parsed unambiguously.  A tag name cannot contain any of the
    1.37 +following characters:
    1.38 +\begin{itemize}
    1.39 +\item Colon (ASCII 58, ``\texttt{:}'')
    1.40 +\item Carriage return (ASCII 13, ``\texttt{$\backslash$r}'')
    1.41 +\item Newline (ASCII 10, ``\texttt{$\backslash$n}'')
    1.42 +\end{itemize}
    1.43 +
    1.44 +You can use the \hgcmd{tags} command to display the tags present in
    1.45 +your repository.  In the output, each tagged revision is identified
    1.46 +first by its name, then by revision number, and finally by the unique
    1.47 +hash of the revision.  
    1.48 +\interaction{tag.tags}
    1.49 +Notice that \texttt{tip} is listed in the output of \hgcmd{tags}.  The
    1.50 +\texttt{tip} tag is a special ``floating'' tag, which always
    1.51 +identifies the newest revision in the repository.
    1.52 +
    1.53 +In the output of the \hgcmd{tags} command, tags are listed in reverse
    1.54 +order, by revision number.  This usually means that recent tags are
    1.55 +listed before older tags.  It also means that \texttt{tip} is always
    1.56 +going to be the first tag listed in the output of \hgcmd{tags}.
    1.57 +
    1.58 +When you run \hgcmd{log}, if it displays a revision that has tags
    1.59 +associated with it, it will print those tags.
    1.60 +\interaction{tag.log}
    1.61 +
    1.62 +Any time you need to provide a revision~ID to a Mercurial command, the
    1.63 +command will accept a tag name in its place.  Internally, Mercurial
    1.64 +will translate your tag name into the corresponding revision~ID, then
    1.65 +use that.
    1.66 +\interaction{tag.log.v1.0}
    1.67 +
    1.68 +There's no limit on the number of tags you can have in a repository,
    1.69 +or on the number of tags that a single revision can have.  As a
    1.70 +practical matter, it's not a great idea to have ``too many'' (a number
    1.71 +which will vary from project to project), simply because tags are
    1.72 +supposed to help you to find revisions.  If you have lots of tags, the
    1.73 +ease of using them to identify revisions diminishes rapidly.
    1.74 +
    1.75 +For example, if your project has milestones as frequent as every few
    1.76 +days, it's perfectly reasonable to tag each one of those.  But if you
    1.77 +have a continuous build system that makes sure every revision can be
    1.78 +built cleanly, you'd be introducing a lot of noise if you were to tag
    1.79 +every clean build.  Instead, you could tag failed builds (on the
    1.80 +assumption that they're rare!), or simply not use tags to track
    1.81 +buildability.
    1.82 +
    1.83 +If you want to remove a tag that you no longer want, use
    1.84 +\hgcmdargs{tag}{--remove}.  
    1.85 +\interaction{tag.remove}
    1.86 +You can also modify a tag at any time, so that it identifies a
    1.87 +different revision, by simply issuing a new \hgcmd{tag} command.
    1.88 +You'll have to use the \hgopt{tag}{-f} option to tell Mercurial that
    1.89 +you \emph{really} want to update the tag.
    1.90 +\interaction{tag.replace}
    1.91 +There will still be a permanent record of the previous identity of the
    1.92 +tag, but Mercurial will no longer use it.
    1.93 +
    1.94 +Mercurial stores tags in a normal revision-controlled file in your
    1.95 +repository.  If you've created any tags, you'll find them in a file
    1.96 +named \sfilename{.hgtags}.  When you run the \hgcmd{tag} command,
    1.97 +Mercurial modifies this file, then automatically commits the change to
    1.98 +it.  This means that every time you run \hgcmd{tag}, you'll see a
    1.99 +corresponding changeset in the output of \hgcmd{log}.
   1.100 +\interaction{tag.tip}
   1.101 +
   1.102 +\subsection{Handling tag conflicts during a merge}
   1.103 +
   1.104 +You won't often need to care about the \sfilename{.hgtags} file, but
   1.105 +it sometimes makes its presence known during a merge.  The format of
   1.106 +the file is simple: it consists of a series of lines.  Each line
   1.107 +starts with a changeset hash, followed by a space, followed by the
   1.108 +name of a tag.
   1.109 +
   1.110 +If you're resolving a conflict in the \sfilename{.hgtags} file during
   1.111 +a merge, there's one twist to modifying the \sfilename{.hgtags} file:
   1.112 +when Mercurial is parsing the tags in a repository, it \emph{never}
   1.113 +reads the working copy of the \sfilename{.hgtags} file.  Instead, it
   1.114 +reads the \emph{most recently committed} revision of the file.
   1.115 +
   1.116 +An unfortunate consequence of this design is that you can't actually
   1.117 +verify that your merged \sfilename{.hgtags} file is correct until
   1.118 +\emph{after} you've committed a change.  So if you find yourself
   1.119 +resolving a conflict on \sfilename{.hgtags} during a merge, be sure to
   1.120 +run \hgcmd{tags} after you commit.  If it finds an error in the
   1.121 +\sfilename{.hgtags} file, it will report the location of the error,
   1.122 +which you can then fix and commit.  You should then run \hgcmd{tags}
   1.123 +again, just to be sure that your fix is correct.
   1.124  
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