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author Javier Rojas <jerojasro@devnull.li>
date Thu Oct 30 00:28:59 2008 -0500 (2008-10-30)
parents 7ca1186c422f
children 7f1572c365d2
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jerojasro@381 1 \chapter{Una gira de Mercurial: fusionar trabajo}
jerojasro@336 2 \label{chap:tour-merge}
jerojasro@336 3
jerojasro@383 4 Hasta ahora hemos cubierto cómo clonar un repositorio, hacer cambios,
jerojasro@383 5 y jalar o empujar dichos cambios de un repositorio a otro. Nuestro
jerojasro@383 6 siguiente paso es \emph{fusionar} cambios de repositorios separados.
jerojasro@383 7
jerojasro@383 8 % TODO cambié streams por líneas. check please
jerojasro@383 9 \section{Fusionar líneas de trabajo}
jerojasro@383 10
jerojasro@383 11 Fusionar es una parte fundamental de trabajar con una herramienta
jerojasro@383 12 de control distribuido de versiones.
jerojasro@336 13 \begin{itemize}
jerojasro@383 14 \item Alicia y Roberto tienen cada uno una copia personal del
jerojasro@383 15 repositorio de un proyecto en el que están trabajando. Alicia
jerojasro@383 16 arregla un fallo en su repositorio; Roberto añade una nueva
jerojasro@383 17 característica en el suyo. Ambos desean que el repositorio
jerojasro@383 18 compartido contenga el arreglo del fallo y la nueva
jerojasro@383 19 característica.
jerojasro@383 20 \item Frecuentemente trabajo en varias tareas diferentes en un mismo
jerojasro@383 21 proyecto al mismo tiempo, cada una aislada convenientemente de las
jerojasro@383 22 otras en su propio repositorio. Trabajar de esta manera significa
jerojasro@383 23 que a menudo debo fusionar una parte de mi propio trabajo con
jerojasro@383 24 otra.
jerojasro@336 25 \end{itemize}
jerojasro@336 26
jerojasro@383 27 Como fusionar es una operación tan necesaria y común, Mercurial la
jerojasro@383 28 facilita. Revisemos el proceso. Empezaremos clonando (otro)
jerojasro@383 29 % TODO poner interrogante de apertura
jerojasro@383 30 repositorio (ve lo seguido que aparecen?) y haciendo un cambio en él.
jerojasro@336 31 \interaction{tour.merge.clone}
jerojasro@383 32 Ahora deberíamos tener dos copias de \filename{hello.c} con contenidos
jerojasro@383 33 diferentes. El historial de los dos repositorios diverge ahora, como
jerojasro@383 34 se ilustra en la figura~\ref{fig:tour-merge:sep-repos}.
jerojasro@336 35 \interaction{tour.merge.cat}
jerojasro@336 36
jerojasro@336 37 \begin{figure}[ht]
jerojasro@336 38 \centering
jerojasro@336 39 \grafix{tour-merge-sep-repos}
jerojasro@383 40 \caption{Historial reciente divergente de los repositorios
jerojasro@383 41 \dirname{my-hello} y \dirname{my-new-hello}}
jerojasro@336 42 \label{fig:tour-merge:sep-repos}
jerojasro@336 43 \end{figure}
jerojasro@336 44
jerojasro@383 45 Ya sabemos que jalar los cambios desde nuestro repositorio
jerojasro@383 46 \dirname{my-hello} no tendrá efecto en el directorio de trabajo.
jerojasro@336 47 \interaction{tour.merge.pull}
jerojasro@336 48 However, the \hgcmd{pull} command says something about ``heads''.
jerojasro@336 49
jerojasro@336 50 \subsection{Head changesets}
jerojasro@336 51
jerojasro@336 52 A head is a change that has no descendants, or children, as they're
jerojasro@336 53 also known. The tip revision is thus a head, because the newest
jerojasro@336 54 revision in a repository doesn't have any children, but a repository
jerojasro@336 55 can contain more than one head.
jerojasro@336 56
jerojasro@336 57 \begin{figure}[ht]
jerojasro@336 58 \centering
jerojasro@336 59 \grafix{tour-merge-pull}
jerojasro@336 60 \caption{Repository contents after pulling from \dirname{my-hello} into
jerojasro@336 61 \dirname{my-new-hello}}
jerojasro@336 62 \label{fig:tour-merge:pull}
jerojasro@336 63 \end{figure}
jerojasro@336 64
jerojasro@336 65 In figure~\ref{fig:tour-merge:pull}, you can see the effect of the
jerojasro@336 66 pull from \dirname{my-hello} into \dirname{my-new-hello}. The history
jerojasro@336 67 that was already present in \dirname{my-new-hello} is untouched, but a
jerojasro@336 68 new revision has been added. By referring to
jerojasro@336 69 figure~\ref{fig:tour-merge:sep-repos}, we can see that the
jerojasro@336 70 \emph{changeset ID} remains the same in the new repository, but the
jerojasro@336 71 \emph{revision number} has changed. (This, incidentally, is a fine
jerojasro@336 72 example of why it's not safe to use revision numbers when discussing
jerojasro@336 73 changesets.) We can view the heads in a repository using the
jerojasro@336 74 \hgcmd{heads} command.
jerojasro@336 75 \interaction{tour.merge.heads}
jerojasro@336 76
jerojasro@336 77 \subsection{Performing the merge}
jerojasro@336 78
jerojasro@336 79 What happens if we try to use the normal \hgcmd{update} command to
jerojasro@336 80 update to the new tip?
jerojasro@336 81 \interaction{tour.merge.update}
jerojasro@336 82 Mercurial is telling us that the \hgcmd{update} command won't do a
jerojasro@336 83 merge; it won't update the working directory when it thinks we might
jerojasro@336 84 be wanting to do a merge, unless we force it to do so. Instead, we
jerojasro@336 85 use the \hgcmd{merge} command to merge the two heads.
jerojasro@336 86 \interaction{tour.merge.merge}
jerojasro@336 87
jerojasro@336 88 \begin{figure}[ht]
jerojasro@336 89 \centering
jerojasro@336 90 \grafix{tour-merge-merge}
jerojasro@336 91 \caption{Working directory and repository during merge, and
jerojasro@336 92 following commit}
jerojasro@336 93 \label{fig:tour-merge:merge}
jerojasro@336 94 \end{figure}
jerojasro@336 95
jerojasro@336 96 This updates the working directory so that it contains changes from
jerojasro@336 97 \emph{both} heads, which is reflected in both the output of
jerojasro@336 98 \hgcmd{parents} and the contents of \filename{hello.c}.
jerojasro@336 99 \interaction{tour.merge.parents}
jerojasro@336 100
jerojasro@336 101 \subsection{Committing the results of the merge}
jerojasro@336 102
jerojasro@336 103 Whenever we've done a merge, \hgcmd{parents} will display two parents
jerojasro@336 104 until we \hgcmd{commit} the results of the merge.
jerojasro@336 105 \interaction{tour.merge.commit}
jerojasro@336 106 We now have a new tip revision; notice that it has \emph{both} of
jerojasro@336 107 our former heads as its parents. These are the same revisions that
jerojasro@336 108 were previously displayed by \hgcmd{parents}.
jerojasro@336 109 \interaction{tour.merge.tip}
jerojasro@336 110 In figure~\ref{fig:tour-merge:merge}, you can see a representation of
jerojasro@336 111 what happens to the working directory during the merge, and how this
jerojasro@336 112 affects the repository when the commit happens. During the merge, the
jerojasro@336 113 working directory has two parent changesets, and these become the
jerojasro@336 114 parents of the new changeset.
jerojasro@336 115
jerojasro@336 116 \section{Merging conflicting changes}
jerojasro@336 117
jerojasro@336 118 Most merges are simple affairs, but sometimes you'll find yourself
jerojasro@336 119 merging changes where each modifies the same portions of the same
jerojasro@336 120 files. Unless both modifications are identical, this results in a
jerojasro@336 121 \emph{conflict}, where you have to decide how to reconcile the
jerojasro@336 122 different changes into something coherent.
jerojasro@336 123
jerojasro@336 124 \begin{figure}[ht]
jerojasro@336 125 \centering
jerojasro@336 126 \grafix{tour-merge-conflict}
jerojasro@336 127 \caption{Conflicting changes to a document}
jerojasro@336 128 \label{fig:tour-merge:conflict}
jerojasro@336 129 \end{figure}
jerojasro@336 130
jerojasro@336 131 Figure~\ref{fig:tour-merge:conflict} illustrates an instance of two
jerojasro@336 132 conflicting changes to a document. We started with a single version
jerojasro@336 133 of the file; then we made some changes; while someone else made
jerojasro@336 134 different changes to the same text. Our task in resolving the
jerojasro@336 135 conflicting changes is to decide what the file should look like.
jerojasro@336 136
jerojasro@336 137 Mercurial doesn't have a built-in facility for handling conflicts.
jerojasro@336 138 Instead, it runs an external program called \command{hgmerge}. This
jerojasro@336 139 is a shell script that is bundled with Mercurial; you can change it to
jerojasro@336 140 behave however you please. What it does by default is try to find one
jerojasro@336 141 of several different merging tools that are likely to be installed on
jerojasro@336 142 your system. It first tries a few fully automatic merging tools; if
jerojasro@336 143 these don't succeed (because the resolution process requires human
jerojasro@336 144 guidance) or aren't present, the script tries a few different
jerojasro@336 145 graphical merging tools.
jerojasro@336 146
jerojasro@336 147 It's also possible to get Mercurial to run another program or script
jerojasro@336 148 instead of \command{hgmerge}, by setting the \envar{HGMERGE}
jerojasro@336 149 environment variable to the name of your preferred program.
jerojasro@336 150
jerojasro@336 151 \subsection{Using a graphical merge tool}
jerojasro@336 152
jerojasro@336 153 My preferred graphical merge tool is \command{kdiff3}, which I'll use
jerojasro@336 154 to describe the features that are common to graphical file merging
jerojasro@336 155 tools. You can see a screenshot of \command{kdiff3} in action in
jerojasro@336 156 figure~\ref{fig:tour-merge:kdiff3}. The kind of merge it is
jerojasro@336 157 performing is called a \emph{three-way merge}, because there are three
jerojasro@336 158 different versions of the file of interest to us. The tool thus
jerojasro@336 159 splits the upper portion of the window into three panes:
jerojasro@336 160 \begin{itemize}
jerojasro@336 161 \item At the left is the \emph{base} version of the file, i.e.~the
jerojasro@336 162 most recent version from which the two versions we're trying to
jerojasro@336 163 merge are descended.
jerojasro@336 164 \item In the middle is ``our'' version of the file, with the contents
jerojasro@336 165 that we modified.
jerojasro@336 166 \item On the right is ``their'' version of the file, the one that
jerojasro@336 167 from the changeset that we're trying to merge with.
jerojasro@336 168 \end{itemize}
jerojasro@336 169 In the pane below these is the current \emph{result} of the merge.
jerojasro@336 170 Our task is to replace all of the red text, which indicates unresolved
jerojasro@336 171 conflicts, with some sensible merger of the ``ours'' and ``theirs''
jerojasro@336 172 versions of the file.
jerojasro@336 173
jerojasro@336 174 All four of these panes are \emph{locked together}; if we scroll
jerojasro@336 175 vertically or horizontally in any of them, the others are updated to
jerojasro@336 176 display the corresponding sections of their respective files.
jerojasro@336 177
jerojasro@336 178 \begin{figure}[ht]
jerojasro@336 179 \centering
jerojasro@336 180 \grafix{kdiff3}
jerojasro@336 181 \caption{Using \command{kdiff3} to merge versions of a file}
jerojasro@336 182 \label{fig:tour-merge:kdiff3}
jerojasro@336 183 \end{figure}
jerojasro@336 184
jerojasro@336 185 For each conflicting portion of the file, we can choose to resolve
jerojasro@336 186 the conflict using some combination of text from the base version,
jerojasro@336 187 ours, or theirs. We can also manually edit the merged file at any
jerojasro@336 188 time, in case we need to make further modifications.
jerojasro@336 189
jerojasro@336 190 There are \emph{many} file merging tools available, too many to cover
jerojasro@336 191 here. They vary in which platforms they are available for, and in
jerojasro@336 192 their particular strengths and weaknesses. Most are tuned for merging
jerojasro@336 193 files containing plain text, while a few are aimed at specialised file
jerojasro@336 194 formats (generally XML).
jerojasro@336 195
jerojasro@336 196 \subsection{A worked example}
jerojasro@336 197
jerojasro@336 198 In this example, we will reproduce the file modification history of
jerojasro@336 199 figure~\ref{fig:tour-merge:conflict} above. Let's begin by creating a
jerojasro@336 200 repository with a base version of our document.
jerojasro@336 201 \interaction{tour-merge-conflict.wife}
jerojasro@336 202 We'll clone the repository and make a change to the file.
jerojasro@336 203 \interaction{tour-merge-conflict.cousin}
jerojasro@336 204 And another clone, to simulate someone else making a change to the
jerojasro@336 205 file. (This hints at the idea that it's not all that unusual to merge
jerojasro@336 206 with yourself when you isolate tasks in separate repositories, and
jerojasro@336 207 indeed to find and resolve conflicts while doing so.)
jerojasro@336 208 \interaction{tour-merge-conflict.son}
jerojasro@336 209 Having created two different versions of the file, we'll set up an
jerojasro@336 210 environment suitable for running our merge.
jerojasro@336 211 \interaction{tour-merge-conflict.pull}
jerojasro@336 212
jerojasro@336 213 In this example, I won't use Mercurial's normal \command{hgmerge}
jerojasro@336 214 program to do the merge, because it would drop my nice automated
jerojasro@336 215 example-running tool into a graphical user interface. Instead, I'll
jerojasro@336 216 set \envar{HGMERGE} to tell Mercurial to use the non-interactive
jerojasro@336 217 \command{merge} command. This is bundled with many Unix-like systems.
jerojasro@336 218 If you're following this example on your computer, don't bother
jerojasro@336 219 setting \envar{HGMERGE}.
jerojasro@336 220 \interaction{tour-merge-conflict.merge}
jerojasro@336 221 Because \command{merge} can't resolve the conflicting changes, it
jerojasro@336 222 leaves \emph{merge markers} inside the file that has conflicts,
jerojasro@336 223 indicating which lines have conflicts, and whether they came from our
jerojasro@336 224 version of the file or theirs.
jerojasro@336 225
jerojasro@336 226 Mercurial can tell from the way \command{merge} exits that it wasn't
jerojasro@336 227 able to merge successfully, so it tells us what commands we'll need to
jerojasro@336 228 run if we want to redo the merging operation. This could be useful
jerojasro@336 229 if, for example, we were running a graphical merge tool and quit
jerojasro@336 230 because we were confused or realised we had made a mistake.
jerojasro@336 231
jerojasro@336 232 If automatic or manual merges fail, there's nothing to prevent us from
jerojasro@336 233 ``fixing up'' the affected files ourselves, and committing the results
jerojasro@336 234 of our merge:
jerojasro@336 235 \interaction{tour-merge-conflict.commit}
jerojasro@336 236
jerojasro@336 237 \section{Simplifying the pull-merge-commit sequence}
jerojasro@336 238 \label{sec:tour-merge:fetch}
jerojasro@336 239
jerojasro@336 240 The process of merging changes as outlined above is straightforward,
jerojasro@336 241 but requires running three commands in sequence.
jerojasro@336 242 \begin{codesample2}
jerojasro@336 243 hg pull
jerojasro@336 244 hg merge
jerojasro@336 245 hg commit -m 'Merged remote changes'
jerojasro@336 246 \end{codesample2}
jerojasro@336 247 In the case of the final commit, you also need to enter a commit
jerojasro@336 248 message, which is almost always going to be a piece of uninteresting
jerojasro@336 249 ``boilerplate'' text.
jerojasro@336 250
jerojasro@336 251 It would be nice to reduce the number of steps needed, if this were
jerojasro@336 252 possible. Indeed, Mercurial is distributed with an extension called
jerojasro@336 253 \hgext{fetch} that does just this.
jerojasro@336 254
jerojasro@336 255 Mercurial provides a flexible extension mechanism that lets people
jerojasro@336 256 extend its functionality, while keeping the core of Mercurial small
jerojasro@336 257 and easy to deal with. Some extensions add new commands that you can
jerojasro@336 258 use from the command line, while others work ``behind the scenes,''
jerojasro@336 259 for example adding capabilities to the server.
jerojasro@336 260
jerojasro@336 261 The \hgext{fetch} extension adds a new command called, not
jerojasro@336 262 surprisingly, \hgcmd{fetch}. This extension acts as a combination of
jerojasro@336 263 \hgcmd{pull}, \hgcmd{update} and \hgcmd{merge}. It begins by pulling
jerojasro@336 264 changes from another repository into the current repository. If it
jerojasro@336 265 finds that the changes added a new head to the repository, it begins a
jerojasro@336 266 merge, then commits the result of the merge with an
jerojasro@336 267 automatically-generated commit message. If no new heads were added,
jerojasro@336 268 it updates the working directory to the new tip changeset.
jerojasro@336 269
jerojasro@336 270 Enabling the \hgext{fetch} extension is easy. Edit your
jerojasro@336 271 \sfilename{.hgrc}, and either go to the \rcsection{extensions} section
jerojasro@336 272 or create an \rcsection{extensions} section. Then add a line that
jerojasro@336 273 simply reads ``\Verb+fetch +''.
jerojasro@336 274 \begin{codesample2}
jerojasro@336 275 [extensions]
jerojasro@336 276 fetch =
jerojasro@336 277 \end{codesample2}
jerojasro@336 278 (Normally, on the right-hand side of the ``\texttt{=}'' would appear
jerojasro@336 279 the location of the extension, but since the \hgext{fetch} extension
jerojasro@336 280 is in the standard distribution, Mercurial knows where to search for
jerojasro@336 281 it.)
jerojasro@336 282
jerojasro@336 283 %%% Local Variables:
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