hgbook
annotate en/mq.tex @ 25:9d5b6d303ef5
Make it 2/3 through documenting MQ commands.
Add a note on a few quirks of how patches represent data.
Add a note on a few quirks of how patches represent data.
author | Bryan O'Sullivan <bos@serpentine.com> |
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date | Sun Jul 09 23:18:39 2006 -0700 (2006-07-09) |
parents | 187702df428b |
children | 1bc6c1f0192a |
rev | line source |
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bos@1 | 1 \chapter{Managing change with Mercurial Queues} |
bos@1 | 2 \label{chap:mq} |
bos@1 | 3 |
bos@1 | 4 \section{The patch management problem} |
bos@1 | 5 \label{sec:mq:patch-mgmt} |
bos@1 | 6 |
bos@1 | 7 Here is a common scenario: you need to install a software package from |
bos@1 | 8 source, but you find a bug that you must fix in the source before you |
bos@1 | 9 can start using the package. You make your changes, forget about the |
bos@1 | 10 package for a while, and a few months later you need to upgrade to a |
bos@1 | 11 newer version of the package. If the newer version of the package |
bos@1 | 12 still has the bug, you must extract your fix from the older source |
bos@1 | 13 tree and apply it against the newer version. This is a tedious task, |
bos@1 | 14 and it's easy to make mistakes. |
bos@1 | 15 |
bos@1 | 16 This is a simple case of the ``patch management'' problem. You have |
bos@1 | 17 an ``upstream'' source tree that you can't change; you need to make |
bos@1 | 18 some local changes on top of the upstream tree; and you'd like to be |
bos@1 | 19 able to keep those changes separate, so that you can apply them to |
bos@1 | 20 newer versions of the upstream source. |
bos@1 | 21 |
bos@1 | 22 The patch management problem arises in many situations. Probably the |
bos@1 | 23 most visible is that a user of an open source software project will |
bos@3 | 24 contribute a bug fix or new feature to the project's maintainers in the |
bos@1 | 25 form of a patch. |
bos@1 | 26 |
bos@1 | 27 Distributors of operating systems that include open source software |
bos@1 | 28 often need to make changes to the packages they distribute so that |
bos@1 | 29 they will build properly in their environments. |
bos@1 | 30 |
bos@1 | 31 When you have few changes to maintain, it is easy to manage a single |
bos@15 | 32 patch using the standard \texttt{diff} and \texttt{patch} programs |
bos@15 | 33 (see section~\ref{sec:mq:patch} for a discussion of these tools). |
bos@1 | 34 Once the number of changes grows, it starts to makes sense to maintain |
bos@1 | 35 patches as discrete ``chunks of work,'' so that for example a single |
bos@1 | 36 patch will contain only one bug fix (the patch might modify several |
bos@1 | 37 files, but it's doing ``only one thing''), and you may have a number |
bos@1 | 38 of such patches for different bugs you need fixed and local changes |
bos@3 | 39 you require. In this situation, if you submit a bug fix patch to the |
bos@1 | 40 upstream maintainers of a package and they include your fix in a |
bos@1 | 41 subsequent release, you can simply drop that single patch when you're |
bos@1 | 42 updating to the newer release. |
bos@1 | 43 |
bos@1 | 44 Maintaining a single patch against an upstream tree is a little |
bos@1 | 45 tedious and error-prone, but not difficult. However, the complexity |
bos@1 | 46 of the problem grows rapidly as the number of patches you have to |
bos@1 | 47 maintain increases. With more than a tiny number of patches in hand, |
bos@1 | 48 understanding which ones you have applied and maintaining them moves |
bos@1 | 49 from messy to overwhelming. |
bos@1 | 50 |
bos@1 | 51 Fortunately, Mercurial includes a powerful extension, Mercurial Queues |
bos@1 | 52 (or simply ``MQ''), that massively simplifies the patch management |
bos@1 | 53 problem. |
bos@1 | 54 |
bos@1 | 55 \section{The prehistory of Mercurial Queues} |
bos@1 | 56 \label{sec:mq:history} |
bos@1 | 57 |
bos@1 | 58 During the late 1990s, several Linux kernel developers started to |
bos@1 | 59 maintain ``patch series'' that modified the behaviour of the Linux |
bos@1 | 60 kernel. Some of these series were focused on stability, some on |
bos@1 | 61 feature coverage, and others were more speculative. |
bos@1 | 62 |
bos@1 | 63 The sizes of these patch series grew rapidly. In 2002, Andrew Morton |
bos@1 | 64 published some shell scripts he had been using to automate the task of |
bos@1 | 65 managing his patch queues. Andrew was successfully using these |
bos@1 | 66 scripts to manage hundreds (sometimes thousands) of patches on top of |
bos@1 | 67 the Linux kernel. |
bos@1 | 68 |
bos@1 | 69 \subsection{A patchwork quilt} |
bos@1 | 70 \label{sec:mq:quilt} |
bos@1 | 71 |
bos@1 | 72 |
bos@1 | 73 In early 2003, Andreas Gruenbacher and Martin Quinson borrowed the |
bos@2 | 74 approach of Andrew's scripts and published a tool called ``patchwork |
bos@2 | 75 quilt''~\cite{web:quilt}, or simply ``quilt'' |
bos@2 | 76 (see~\cite{gruenbacher:2005} for a paper describing it). Because |
bos@2 | 77 quilt substantially automated patch management, it rapidly gained a |
bos@2 | 78 large following among open source software developers. |
bos@1 | 79 |
bos@1 | 80 Quilt manages a \emph{stack of patches} on top of a directory tree. |
bos@1 | 81 To begin, you tell quilt to manage a directory tree; it stores away |
bos@1 | 82 the names and contents of all files in the tree. To fix a bug, you |
bos@1 | 83 create a new patch (using a single command), edit the files you need |
bos@1 | 84 to fix, then ``refresh'' the patch. |
bos@1 | 85 |
bos@1 | 86 The refresh step causes quilt to scan the directory tree; it updates |
bos@1 | 87 the patch with all of the changes you have made. You can create |
bos@1 | 88 another patch on top of the first, which will track the changes |
bos@1 | 89 required to modify the tree from ``tree with one patch applied'' to |
bos@1 | 90 ``tree with two patches applied''. |
bos@1 | 91 |
bos@1 | 92 You can \emph{change} which patches are applied to the tree. If you |
bos@1 | 93 ``pop'' a patch, the changes made by that patch will vanish from the |
bos@1 | 94 directory tree. Quilt remembers which patches you have popped, |
bos@1 | 95 though, so you can ``push'' a popped patch again, and the directory |
bos@1 | 96 tree will be restored to contain the modifications in the patch. Most |
bos@1 | 97 importantly, you can run the ``refresh'' command at any time, and the |
bos@1 | 98 topmost applied patch will be updated. This means that you can, at |
bos@1 | 99 any time, change both which patches are applied and what |
bos@1 | 100 modifications those patches make. |
bos@1 | 101 |
bos@1 | 102 Quilt knows nothing about revision control tools, so it works equally |
bos@3 | 103 well on top of an unpacked tarball or a Subversion repository. |
bos@1 | 104 |
bos@1 | 105 \subsection{From patchwork quilt to Mercurial Queues} |
bos@1 | 106 \label{sec:mq:quilt-mq} |
bos@1 | 107 |
bos@1 | 108 In mid-2005, Chris Mason took the features of quilt and wrote an |
bos@1 | 109 extension that he called Mercurial Queues, which added quilt-like |
bos@1 | 110 behaviour to Mercurial. |
bos@1 | 111 |
bos@1 | 112 The key difference between quilt and MQ is that quilt knows nothing |
bos@1 | 113 about revision control systems, while MQ is \emph{integrated} into |
bos@1 | 114 Mercurial. Each patch that you push is represented as a Mercurial |
bos@1 | 115 changeset. Pop a patch, and the changeset goes away. |
bos@1 | 116 |
bos@1 | 117 This integration makes understanding patches and debugging their |
bos@1 | 118 effects \emph{enormously} easier. Since every applied patch has an |
bos@1 | 119 associated changeset, you can use \hgcmdargs{log}{\emph{filename}} to |
bos@1 | 120 see which changesets and patches affected a file. You can use the |
bos@1 | 121 \hgext{bisect} extension to binary-search through all changesets and |
bos@1 | 122 applied patches to see where a bug got introduced or fixed. You can |
bos@1 | 123 use the \hgcmd{annotate} command to see which changeset or patch |
bos@1 | 124 modified a particular line of a source file. And so on. |
bos@1 | 125 |
bos@1 | 126 Because quilt does not care about revision control tools, it is still |
bos@1 | 127 a tremendously useful piece of software to know about for situations |
bos@1 | 128 where you cannot use Mercurial and MQ. |
bos@19 | 129 |
bos@19 | 130 \section{Understanding patches} |
bos@19 | 131 |
bos@19 | 132 Because MQ doesn't hide its patch-oriented nature, it is helpful to |
bos@19 | 133 understand what patches are, and a little about the tools that work |
bos@19 | 134 with them. |
bos@19 | 135 |
bos@19 | 136 The traditional Unix \command{diff} command compares two files, and |
bos@19 | 137 prints a list of differences between them. The \command{patch} command |
bos@19 | 138 understands these differences as \emph{modifications} to make to a |
bos@19 | 139 file. Take a look at figure~\ref{ex:mq:diff} for a simple example of |
bos@19 | 140 these commands in action. |
bos@19 | 141 |
bos@19 | 142 \begin{figure}[ht] |
bos@19 | 143 \interaction{mq.diff.diff} |
bos@19 | 144 \caption{Simple uses of the \command{diff} and \command{patch} commands} |
bos@19 | 145 \label{ex:mq:diff} |
bos@19 | 146 \end{figure} |
bos@19 | 147 |
bos@19 | 148 The type of file that \command{diff} generates (and \command{patch} |
bos@19 | 149 takes as input) is called a ``patch'' or a ``diff''; there is no |
bos@19 | 150 difference between a patch and a diff. (We'll use the term ``patch'', |
bos@19 | 151 since it's more commonly used.) |
bos@19 | 152 |
bos@19 | 153 A patch file can start with arbitrary text; the \command{patch} |
bos@19 | 154 command ignores this text, but MQ uses it as the commit message when |
bos@19 | 155 creating changesets. To find the beginning of the patch content, |
bos@19 | 156 \command{patch} searches for the first line that starts with the |
bos@19 | 157 string ``\texttt{diff~-}''. |
bos@19 | 158 |
bos@19 | 159 MQ works with \emph{unified} diffs (\command{patch} can accept several |
bos@19 | 160 other diff formats, but MQ doesn't). A unified diff contains two |
bos@19 | 161 kinds of header. The \emph{file header} describes the file being |
bos@19 | 162 modified; it contains the name of the file to modify. When |
bos@19 | 163 \command{patch} sees a new file header, it looks for a file with that |
bos@19 | 164 name to start modifying. |
bos@19 | 165 |
bos@19 | 166 After the file header comes a series of \emph{hunks}. Each hunk |
bos@19 | 167 starts with a header; this identifies the range of line numbers within |
bos@19 | 168 the file that the hunk should modify. Following the header, a hunk |
bos@19 | 169 starts and ends with a few (usually three) lines of text from the |
bos@19 | 170 unmodified file; these are called the \emph{context} for the hunk. If |
bos@19 | 171 there's only a small amount of context between successive hunks, |
bos@19 | 172 \command{diff} doesn't print a new hunk header; it just runs the hunks |
bos@19 | 173 together, with a few lines of context between modifications. |
bos@19 | 174 |
bos@19 | 175 Each line of context begins with a space character. Within the hunk, |
bos@19 | 176 a line that begins with ``\texttt{-}'' means ``remove this line,'' |
bos@19 | 177 while a line that begins with ``\texttt{+}'' means ``insert this |
bos@19 | 178 line.'' For example, a line that is modified is represented by one |
bos@19 | 179 deletion and one insertion. |
bos@19 | 180 |
bos@19 | 181 We will return to ome of the more subtle aspects of patches later (in |
bos@19 | 182 section~\ref{ex:mq:adv-patch}), but you should have enough information |
bos@19 | 183 now to use MQ. |
bos@19 | 184 |
bos@2 | 185 \section{Getting started with Mercurial Queues} |
bos@2 | 186 \label{sec:mq:start} |
bos@1 | 187 |
bos@3 | 188 Because MQ is implemented as an extension, you must explicitly enable |
bos@3 | 189 before you can use it. (You don't need to download anything; MQ ships |
bos@3 | 190 with the standard Mercurial distribution.) To enable MQ, edit your |
bos@4 | 191 \tildefile{.hgrc} file, and add the lines in figure~\ref{ex:mq:config}. |
bos@2 | 192 |
bos@12 | 193 \begin{figure}[ht] |
bos@4 | 194 \begin{codesample4} |
bos@4 | 195 [extensions] |
bos@4 | 196 hgext.mq = |
bos@4 | 197 \end{codesample4} |
bos@4 | 198 \label{ex:mq:config} |
bos@4 | 199 \caption{Contents to add to \tildefile{.hgrc} to enable the MQ extension} |
bos@4 | 200 \end{figure} |
bos@3 | 201 |
bos@3 | 202 Once the extension is enabled, it will make a number of new commands |
bos@7 | 203 available. To verify that the extension is working, you can use |
bos@7 | 204 \hgcmd{help} to see if the \hgcmd{qinit} command is now available; see |
bos@7 | 205 the example in figure~\ref{ex:mq:enabled}. |
bos@3 | 206 |
bos@12 | 207 \begin{figure}[ht] |
bos@4 | 208 \interaction{mq.qinit-help.help} |
bos@4 | 209 \caption{How to verify that MQ is enabled} |
bos@4 | 210 \label{ex:mq:enabled} |
bos@4 | 211 \end{figure} |
bos@1 | 212 |
bos@8 | 213 You can use MQ with \emph{any} Mercurial repository, and its commands |
bos@8 | 214 only operate within that repository. To get started, simply prepare |
bos@8 | 215 the repository using the \hgcmd{qinit} command (see |
bos@7 | 216 figure~\ref{ex:mq:qinit}). This command creates an empty directory |
bos@16 | 217 called \sdirname{.hg/patches}, where MQ will keep its metadata. As |
bos@7 | 218 with many Mercurial commands, the \hgcmd{qinit} command prints nothing |
bos@7 | 219 if it succeeds. |
bos@7 | 220 |
bos@12 | 221 \begin{figure}[ht] |
bos@7 | 222 \interaction{mq.tutorial.qinit} |
bos@7 | 223 \caption{Preparing a repository for use with MQ} |
bos@7 | 224 \label{ex:mq:qinit} |
bos@7 | 225 \end{figure} |
bos@7 | 226 |
bos@12 | 227 \begin{figure}[ht] |
bos@7 | 228 \interaction{mq.tutorial.qnew} |
bos@7 | 229 \caption{Creating a new patch} |
bos@7 | 230 \label{ex:mq:qnew} |
bos@7 | 231 \end{figure} |
bos@7 | 232 |
bos@8 | 233 \subsection{Creating a new patch} |
bos@8 | 234 |
bos@8 | 235 To begin work on a new patch, use the \hgcmd{qnew} command. This |
bos@7 | 236 command takes one argument, the name of the patch to create. MQ will |
bos@16 | 237 use this as the name of an actual file in the \sdirname{.hg/patches} |
bos@7 | 238 directory, as you can see in figure~\ref{ex:mq:qnew}. |
bos@7 | 239 |
bos@16 | 240 Also newly present in the \sdirname{.hg/patches} directory are two |
bos@16 | 241 other files, \sfilename{series} and \sfilename{status}. The |
bos@16 | 242 \sfilename{series} file lists all of the patches that MQ knows about |
bos@8 | 243 for this repository, with one patch per line. Mercurial uses the |
bos@16 | 244 \sfilename{status} file for internal book-keeping; it tracks all of the |
bos@7 | 245 patches that MQ has \emph{applied} in this repository. |
bos@7 | 246 |
bos@7 | 247 \begin{note} |
bos@16 | 248 You may sometimes want to edit the \sfilename{series} file by hand; |
bos@7 | 249 for example, to change the sequence in which some patches are |
bos@16 | 250 applied. However, manually editing the \sfilename{status} file is |
bos@7 | 251 almost always a bad idea, as it's easy to corrupt MQ's idea of what |
bos@7 | 252 is happening. |
bos@7 | 253 \end{note} |
bos@7 | 254 |
bos@8 | 255 Once you have created your new patch, you can edit files in the |
bos@8 | 256 working directory as you usually would. All of the normal Mercurial |
bos@8 | 257 commands, such as \hgcmd{diff} and \hgcmd{annotate}, work exactly as |
bos@8 | 258 they did before. |
bos@19 | 259 |
bos@8 | 260 \subsection{Refreshing a patch} |
bos@8 | 261 |
bos@8 | 262 When you reach a point where you want to save your work, use the |
bos@8 | 263 \hgcmd{qrefresh} command (figure~\ref{ex:mq:qnew}) to update the patch |
bos@8 | 264 you are working on. This command folds the changes you have made in |
bos@8 | 265 the working directory into your patch, and updates its corresponding |
bos@8 | 266 changeset to contain those changes. |
bos@8 | 267 |
bos@12 | 268 \begin{figure}[ht] |
bos@8 | 269 \interaction{mq.tutorial.qrefresh} |
bos@8 | 270 \caption{Refreshing a patch} |
bos@8 | 271 \label{ex:mq:qrefresh} |
bos@8 | 272 \end{figure} |
bos@8 | 273 |
bos@8 | 274 You can run \hgcmd{qrefresh} as often as you like, so it's a good way |
bos@13 | 275 to ``checkpoint'' your work. Refresh your patch at an opportune |
bos@8 | 276 time; try an experiment; and if the experiment doesn't work out, |
bos@8 | 277 \hgcmd{revert} your modifications back to the last time you refreshed. |
bos@8 | 278 |
bos@12 | 279 \begin{figure}[ht] |
bos@8 | 280 \interaction{mq.tutorial.qrefresh2} |
bos@8 | 281 \caption{Refresh a patch many times to accumulate changes} |
bos@8 | 282 \label{ex:mq:qrefresh2} |
bos@8 | 283 \end{figure} |
bos@8 | 284 |
bos@8 | 285 \subsection{Stacking and tracking patches} |
bos@8 | 286 |
bos@8 | 287 Once you have finished working on a patch, or need to work on another, |
bos@8 | 288 you can use the \hgcmd{qnew} command again to create a new patch. |
bos@8 | 289 Mercurial will apply this patch on top of your existing patch. See |
bos@8 | 290 figure~\ref{ex:mq:qnew2} for an example. Notice that the patch |
bos@8 | 291 contains the changes in our prior patch as part of its context (you |
bos@8 | 292 can see this more clearly in the output of \hgcmd{annotate}). |
bos@8 | 293 |
bos@12 | 294 \begin{figure}[ht] |
bos@8 | 295 \interaction{mq.tutorial.qnew2} |
bos@8 | 296 \caption{Stacking a second patch on top of the first} |
bos@8 | 297 \label{ex:mq:qnew2} |
bos@8 | 298 \end{figure} |
bos@8 | 299 |
bos@8 | 300 So far, with the exception of \hgcmd{qnew} and \hgcmd{qrefresh}, we've |
bos@8 | 301 been careful to only use regular Mercurial commands. However, there |
bos@8 | 302 are more ``natural'' commands you can use when thinking about patches |
bos@8 | 303 with MQ, as illustrated in figure~\ref{ex:mq:qseries}: |
bos@8 | 304 |
bos@8 | 305 \begin{itemize} |
bos@8 | 306 \item The \hgcmd{qseries} command lists every patch that MQ knows |
bos@8 | 307 about in this repository, from oldest to newest (most recently |
bos@8 | 308 \emph{created}). |
bos@8 | 309 \item The \hgcmd{qapplied} command lists every patch that MQ has |
bos@8 | 310 \emph{applied} in this repository, again from oldest to newest (most |
bos@8 | 311 recently applied). |
bos@8 | 312 \end{itemize} |
bos@8 | 313 |
bos@12 | 314 \begin{figure}[ht] |
bos@8 | 315 \interaction{mq.tutorial.qseries} |
bos@8 | 316 \caption{Understanding the patch stack with \hgcmd{qseries} and |
bos@8 | 317 \hgcmd{qapplied}} |
bos@8 | 318 \label{ex:mq:qseries} |
bos@8 | 319 \end{figure} |
bos@8 | 320 |
bos@8 | 321 \subsection{Manipulating the patch stack} |
bos@8 | 322 |
bos@8 | 323 The previous discussion implied that there must be a difference |
bos@11 | 324 between ``known'' and ``applied'' patches, and there is. MQ can |
bos@11 | 325 manage a patch without it being applied in the repository. |
bos@8 | 326 |
bos@8 | 327 An \emph{applied} patch has a corresponding changeset in the |
bos@8 | 328 repository, and the effects of the patch and changeset are visible in |
bos@8 | 329 the working directory. You can undo the application of a patch using |
bos@12 | 330 the \hgcmd{qpop} command. MQ still \emph{knows about}, or manages, a |
bos@12 | 331 popped patch, but the patch no longer has a corresponding changeset in |
bos@12 | 332 the repository, and the working directory does not contain the changes |
bos@12 | 333 made by the patch. Figure~\ref{fig:mq:stack} illustrates the |
bos@12 | 334 difference between applied and tracked patches. |
bos@12 | 335 |
bos@12 | 336 \begin{figure}[ht] |
bos@12 | 337 \centering |
bos@12 | 338 \grafix{mq-stack} |
bos@12 | 339 \caption{Applied and unapplied patches in the MQ patch stack} |
bos@12 | 340 \label{fig:mq:stack} |
bos@8 | 341 \end{figure} |
bos@8 | 342 |
bos@8 | 343 You can reapply an unapplied, or popped, patch using the \hgcmd{qpush} |
bos@8 | 344 command. This creates a new changeset to correspond to the patch, and |
bos@8 | 345 the patch's changes once again become present in the working |
bos@8 | 346 directory. See figure~\ref{ex:mq:qpop} for examples of \hgcmd{qpop} |
bos@8 | 347 and \hgcmd{qpush} in action. Notice that once we have popped a patch |
bos@8 | 348 or two patches, the output of \hgcmd{qseries} remains the same, while |
bos@8 | 349 that of \hgcmd{qapplied} has changed. |
bos@8 | 350 |
bos@12 | 351 \begin{figure}[ht] |
bos@12 | 352 \interaction{mq.tutorial.qpop} |
bos@12 | 353 \caption{Modifying the stack of applied patches} |
bos@12 | 354 \label{ex:mq:qpop} |
bos@11 | 355 \end{figure} |
bos@11 | 356 |
bos@8 | 357 MQ does not limit you to pushing or popping one patch. You can have |
bos@8 | 358 no patches, all of them, or any number in between applied at some |
bos@8 | 359 point in time. |
bos@8 | 360 |
bos@13 | 361 \subsection{Working on several patches at once} |
bos@13 | 362 |
bos@13 | 363 The \hgcmd{qrefresh} command always refreshes the \emph{topmost} |
bos@13 | 364 applied patch. This means that you can suspend work on one patch (by |
bos@13 | 365 refreshing it), pop or push to make a different patch the top, and |
bos@13 | 366 work on \emph{that} patch for a while. |
bos@13 | 367 |
bos@13 | 368 Here's an example that illustrates how you can use this ability. |
bos@13 | 369 Let's say you're developing a new feature as two patches. The first |
bos@18 | 370 is a change to the core of your software, and the second---layered on |
bos@18 | 371 top of the first---changes the user interface to use the code you just |
bos@13 | 372 added to the core. If you notice a bug in the core while you're |
bos@13 | 373 working on the UI patch, it's easy to fix the core. Simply |
bos@13 | 374 \hgcmd{qrefresh} the UI patch to save your in-progress changes, and |
bos@13 | 375 \hgcmd{qpop} down to the core patch. Fix the core bug, |
bos@13 | 376 \hgcmd{qrefresh} the core patch, and \hgcmd{qpush} back to the UI |
bos@13 | 377 patch to continue where you left off. |
bos@13 | 378 |
bos@19 | 379 \section{More about patches} |
bos@19 | 380 \label{sec:mq:adv-patch} |
bos@19 | 381 |
bos@19 | 382 MQ uses the GNU \command{patch} command to apply patches, so it's |
bos@19 | 383 helpful to know about a few more detailed aspects of how |
bos@19 | 384 \command{patch} works. |
bos@14 | 385 |
bos@14 | 386 When \command{patch} applies a hunk, it tries a handful of |
bos@14 | 387 successively less accurate strategies to try to make the hunk apply. |
bos@14 | 388 This falling-back technique often makes it possible to take a patch |
bos@14 | 389 that was generated against an old version of a file, and apply it |
bos@14 | 390 against a newer version of that file. |
bos@14 | 391 |
bos@14 | 392 First, \command{patch} tries an exact match, where the line numbers, |
bos@14 | 393 the context, and the text to be modified must apply exactly. If it |
bos@14 | 394 cannot make an exact match, it tries to find an exact match for the |
bos@14 | 395 context, without honouring the line numbering information. If this |
bos@14 | 396 succeeds, it prints a line of output saying that the hunk was applied, |
bos@14 | 397 but at some \emph{offset} from the original line number. |
bos@14 | 398 |
bos@14 | 399 If a context-only match fails, \command{patch} removes the first and |
bos@14 | 400 last lines of the context, and tries a \emph{reduced} context-only |
bos@14 | 401 match. If the hunk with reduced context succeeds, it prints a message |
bos@14 | 402 saying that it applied the hunk with a \emph{fuzz factor} (the number |
bos@14 | 403 after the fuzz factor indicates how many lines of context |
bos@14 | 404 \command{patch} had to trim before the patch applied). |
bos@14 | 405 |
bos@14 | 406 When neither of these techniques works, \command{patch} prints a |
bos@14 | 407 message saying that the hunk in question was rejected. It saves |
bos@17 | 408 rejected hunks (also simply called ``rejects'') to a file with the |
bos@17 | 409 same name, and an added \sfilename{.rej} extension. It also saves an |
bos@17 | 410 unmodified copy of the file with a \sfilename{.orig} extension; the |
bos@17 | 411 copy of the file without any extensions will contain any changes made |
bos@17 | 412 by hunks that \emph{did} apply cleanly. If you have a patch that |
bos@17 | 413 modifies \filename{foo} with six hunks, and one of them fails to |
bos@17 | 414 apply, you will have: an unmodified \filename{foo.orig}, a |
bos@17 | 415 \filename{foo.rej} containing one hunk, and \filename{foo}, containing |
bos@17 | 416 the changes made by the five successful five hunks. |
bos@14 | 417 |
bos@25 | 418 \subsection{Some quirks of patch representation} |
bos@25 | 419 |
bos@25 | 420 There are a few useful things to know about how \command{patch} works |
bos@25 | 421 with files. |
bos@25 | 422 \begin{itemize} |
bos@25 | 423 \item This should already be obvious, but \command{patch} cannot |
bos@25 | 424 handle binary files. |
bos@25 | 425 \item Neither does it care about the executable bit; it creates new |
bos@25 | 426 files as readable, but not executable. |
bos@25 | 427 \item \command{patch} treats the removal of a file as a diff between |
bos@25 | 428 the file to be removed and the empty file. So your idea of ``I |
bos@25 | 429 deleted this file'' looks like ``every line of this file was |
bos@25 | 430 deleted'' in a patch. |
bos@25 | 431 \item It treats the addition of a file as a diff between the empty |
bos@25 | 432 file and the file to be added. So in a patch, your idea of ``I |
bos@25 | 433 added this file'' looks like ``every line of this file was added''. |
bos@25 | 434 \item It treats a renamed file as the removal of the old name, and the |
bos@25 | 435 addition of the new name. This means that renamed files have a big |
bos@25 | 436 footprint in patches. (Note also that Mercurial does not currently |
bos@25 | 437 try to infer when files have been renamed or copied in a patch.) |
bos@25 | 438 \item \command{patch} cannot represent empty files, so you cannot use |
bos@25 | 439 a patch to represent the notion ``I added this empty file to the |
bos@25 | 440 tree''. |
bos@25 | 441 \end{itemize} |
bos@14 | 442 \subsection{Beware the fuzz} |
bos@14 | 443 |
bos@14 | 444 While applying a hunk at an offset, or with a fuzz factor, will often |
bos@14 | 445 be completely successful, these inexact techniques naturally leave |
bos@14 | 446 open the possibility of corrupting the patched file. The most common |
bos@14 | 447 cases typically involve applying a patch twice, or at an incorrect |
bos@14 | 448 location in the file. If \command{patch} or \hgcmd{qpush} ever |
bos@14 | 449 mentions an offset or fuzz factor, you should make sure that the |
bos@14 | 450 modified files are correct afterwards. |
bos@14 | 451 |
bos@14 | 452 It's often a good idea to refresh a patch that has applied with an |
bos@14 | 453 offset or fuzz factor; refreshing the patch generates new context |
bos@14 | 454 information that will make it apply cleanly. I say ``often,'' not |
bos@14 | 455 ``always,'' because sometimes refreshing a patch will make it fail to |
bos@14 | 456 apply against a different revision of the underlying files. In some |
bos@14 | 457 cases, such as when you're maintaining a patch that must sit on top of |
bos@14 | 458 multiple versions of a source tree, it's acceptable to have a patch |
bos@14 | 459 apply with some fuzz, provided you've verified the results of the |
bos@14 | 460 patching process in such cases. |
bos@14 | 461 |
bos@15 | 462 \subsection{Handling rejection} |
bos@15 | 463 |
bos@15 | 464 If \hgcmd{qpush} fails to apply a patch, it will print an error |
bos@16 | 465 message and exit. If it has left \sfilename{.rej} files behind, it is |
bos@15 | 466 usually best to fix up the rejected hunks before you push more patches |
bos@15 | 467 or do any further work. |
bos@15 | 468 |
bos@15 | 469 If your patch \emph{used to} apply cleanly, and no longer does because |
bos@15 | 470 you've changed the underlying code that your patches are based on, |
bos@17 | 471 Mercurial Queues can help; see section~\ref{sec:mq:merge} for details. |
bos@15 | 472 |
bos@15 | 473 Unfortunately, there aren't any great techniques for dealing with |
bos@16 | 474 rejected hunks. Most often, you'll need to view the \sfilename{.rej} |
bos@15 | 475 file and edit the target file, applying the rejected hunks by hand. |
bos@15 | 476 |
bos@16 | 477 If you're feeling adventurous, Neil Brown, a Linux kernel hacker, |
bos@16 | 478 wrote a tool called \command{wiggle}~\cite{web:wiggle}, which is more |
bos@16 | 479 vigorous than \command{patch} in its attempts to make a patch apply. |
bos@15 | 480 |
bos@15 | 481 Another Linux kernel hacker, Chris Mason (the author of Mercurial |
bos@15 | 482 Queues), wrote a similar tool called \command{rej}~\cite{web:rej}, |
bos@15 | 483 which takes a simple approach to automating the application of hunks |
bos@15 | 484 rejected by \command{patch}. \command{rej} can help with four common |
bos@15 | 485 reasons that a hunk may be rejected: |
bos@15 | 486 |
bos@15 | 487 \begin{itemize} |
bos@15 | 488 \item The context in the middle of a hunk has changed. |
bos@15 | 489 \item A hunk is missing some context at the beginning or end. |
bos@18 | 490 \item A large hunk might apply better---either entirely or in |
bos@18 | 491 part---if it was broken up into smaller hunks. |
bos@15 | 492 \item A hunk removes lines with slightly different content than those |
bos@15 | 493 currently present in the file. |
bos@15 | 494 \end{itemize} |
bos@15 | 495 |
bos@15 | 496 If you use \command{wiggle} or \command{rej}, you should be doubly |
bos@15 | 497 careful to check your results when you're done. |
bos@15 | 498 |
bos@17 | 499 \section{Getting the best performance out of MQ} |
bos@17 | 500 |
bos@17 | 501 MQ is very efficient at handling a large number of patches. I ran |
bos@17 | 502 some performance experiments in mid-2006 for a talk that I gave at the |
bos@17 | 503 2006 EuroPython conference~\cite{web:europython}. I used as my data |
bos@17 | 504 set the Linux 2.6.17-mm1 patch series, which consists of 1,738 |
bos@17 | 505 patches. I applied thes on top of a Linux kernel repository |
bos@17 | 506 containing all 27,472 revisions between Linux 2.6.12-rc2 and Linux |
bos@17 | 507 2.6.17. |
bos@17 | 508 |
bos@17 | 509 On my old, slow laptop, I was able to |
bos@17 | 510 \hgcmdargs{qpush}{\hgopt{qpush}{-a}} all 1,738 patches in 3.5 minutes, |
bos@17 | 511 and \hgcmdargs{qpop}{\hgopt{qpop}{-a}} them all in 30 seconds. I |
bos@17 | 512 could \hgcmd{qrefresh} one of the biggest patches (which made 22,779 |
bos@17 | 513 lines of changes to 287 files) in 6.6 seconds. |
bos@17 | 514 |
bos@17 | 515 Clearly, MQ is well suited to working in large trees, but there are a |
bos@17 | 516 few tricks you can use to get the best performance of it. |
bos@17 | 517 |
bos@17 | 518 First of all, try to ``batch'' operations together. Every time you |
bos@17 | 519 run \hgcmd{qpush} or \hgcmd{qpop}, these commands scan the working |
bos@17 | 520 directory once to make sure you haven't made some changes and then |
bos@17 | 521 forgotten to run \hgcmd{qrefresh}. On a small tree, the time that |
bos@17 | 522 this scan takes is unnoticeable. However, on a medium-sized tree |
bos@17 | 523 (containing tens of thousands of files), it can take a second or more. |
bos@17 | 524 |
bos@17 | 525 The \hgcmd{qpush} and \hgcmd{qpop} commands allow you to push and pop |
bos@17 | 526 multiple patches at a time. You can identify the ``destination |
bos@17 | 527 patch'' that you want to end up at. When you \hgcmd{qpush} with a |
bos@17 | 528 destination specified, it will push patches until that patch is at the |
bos@17 | 529 top of the applied stack. When you \hgcmd{qpop} to a destination, MQ |
bos@17 | 530 will pop patches until the destination patch \emph{is no longer} |
bos@17 | 531 applied. |
bos@17 | 532 |
bos@17 | 533 You can identify a destination patch using either the name of the |
bos@17 | 534 patch, or by number. If you use numeric addressing, patches are |
bos@17 | 535 counted from zero; this means that the first patch is zero, the second |
bos@17 | 536 is one, and so on. |
bos@17 | 537 |
bos@15 | 538 \section{Updating your patches when the underlying code changes} |
bos@15 | 539 \label{sec:mq:merge} |
bos@15 | 540 |
bos@17 | 541 It's common to have a stack of patches on top of an underlying |
bos@17 | 542 repository that you don't modify directly. If you're working on |
bos@17 | 543 changes to third-party code, or on a feature that is taking longer to |
bos@17 | 544 develop than the rate of change of the code beneath, you will often |
bos@17 | 545 need to sync up with the underlying code, and fix up any hunks in your |
bos@17 | 546 patches that no longer apply. This is called \emph{rebasing} your |
bos@17 | 547 patch series. |
bos@17 | 548 |
bos@17 | 549 The simplest way to do this is to \hgcmdargs{qpop}{\hgopt{qpop}{-a}} |
bos@17 | 550 your patches, then \hgcmd{pull} changes into the underlying |
bos@17 | 551 repository, and finally \hgcmdargs{qpush}{\hgopt{qpop}{-a}} your |
bos@17 | 552 patches again. MQ will stop pushing any time it runs across a patch |
bos@17 | 553 that fails to apply during conflicts, allowing you to fix your |
bos@17 | 554 conflicts, \hgcmd{qrefresh} the affected patch, and continue pushing |
bos@17 | 555 until you have fixed your entire stack. |
bos@17 | 556 |
bos@17 | 557 This approach is easy to use and works well if you don't expect |
bos@17 | 558 changes to the underlying code to affect how well your patches apply. |
bos@17 | 559 If your patch stack touches code that is modified frequently or |
bos@17 | 560 invasively in the underlying repository, however, fixing up rejected |
bos@17 | 561 hunks by hand quickly becomes tiresome. |
bos@17 | 562 |
bos@17 | 563 It's possible to partially automate the rebasing process. If your |
bos@17 | 564 patches apply cleanly against some revision of the underlying repo, MQ |
bos@17 | 565 can use this information to help you to resolve conflicts between your |
bos@17 | 566 patches and a different revision. |
bos@17 | 567 |
bos@17 | 568 The process is a little involved. |
bos@17 | 569 \begin{enumerate} |
bos@17 | 570 \item To begin, \hgcmdargs{qpush}{-a} all of your patches on top of |
bos@17 | 571 the revision where you know that they apply cleanly. |
bos@17 | 572 \item Save a backup copy of your patch directory using |
bos@17 | 573 \hgcmdargs{qsave}{\hgopt{qsave}{-e} \hgopt{qsave}{-c}}. This prints |
bos@17 | 574 the name of the directory that it has saved the patches in. It will |
bos@17 | 575 save the patches to a directory called |
bos@17 | 576 \sdirname{.hg/patches.\emph{N}}, where \texttt{\emph{N}} is a small |
bos@17 | 577 integer. It also commits a ``save changeset'' on top of your |
bos@17 | 578 applied patches; this is for internal book-keeping, and records the |
bos@17 | 579 states of the \sfilename{series} and \sfilename{status} files. |
bos@17 | 580 \item Use \hgcmd{pull} to bring new changes into the underlying |
bos@17 | 581 repository. (Don't run \hgcmdargs{pull}{-u}; see below for why.) |
bos@17 | 582 \item Update to the new tip revision, using |
bos@17 | 583 \hgcmdargs{update}{\hgopt{update}{-C}} to override the patches you |
bos@17 | 584 have pushed. |
bos@17 | 585 \item Merge all patches using \hgcmdargs{qpush}{\hgopt{qpush}{-m} |
bos@17 | 586 \hgopt{qpush}{-a}}. The \hgopt{qpush}{-m} option to \hgcmd{qpush} |
bos@17 | 587 tells MQ to perform a three-way merge if the patch fails to apply. |
bos@17 | 588 \end{enumerate} |
bos@17 | 589 |
bos@17 | 590 During the \hgcmdargs{qpush}{\hgopt{qpush}{-m}}, each patch in the |
bos@17 | 591 \sfilename{series} file is applied normally. If a patch applies with |
bos@17 | 592 fuzz or rejects, MQ looks at the queue you \hgcmd{qsave}d, and |
bos@17 | 593 performs a three-way merge with the corresponding changeset. This |
bos@17 | 594 merge uses Mercurial's normal merge machinery, so it may pop up a GUI |
bos@17 | 595 merge tool to help you to resolve problems. |
bos@17 | 596 |
bos@17 | 597 When you finish resolving the effects of a patch, MQ refreshes your |
bos@17 | 598 patch based on the result of the merge. |
bos@17 | 599 |
bos@17 | 600 At the end of this process, your repository will have one extra head |
bos@17 | 601 from the old patch queue, and a copy of the old patch queue will be in |
bos@17 | 602 \sdirname{.hg/patches.\emph{N}}. You can remove the extra head using |
bos@17 | 603 \hgcmdargs{qpop}{\hgopt{qpop}{-a} \hgopt{qpop}{-n} patches.\emph{N}} |
bos@17 | 604 or \hgcmd{strip}. You can delete \sdirname{.hg/patches.\emph{N}} once |
bos@17 | 605 you are sure that you no longer need it as a backup. |
bos@13 | 606 |
bos@16 | 607 \section{Managing patches in a repository} |
bos@16 | 608 |
bos@16 | 609 Because MQ's \sdirname{.hg/patches} directory resides outside a |
bos@16 | 610 Mercurial repository's working directory, the ``underlying'' Mercurial |
bos@16 | 611 repository knows nothing about the management or presence of patches. |
bos@16 | 612 |
bos@16 | 613 This presents the interesting possibility of managing the contents of |
bos@16 | 614 the patch directory as a Mercurial repository in its own right. This |
bos@16 | 615 can be a useful way to work. For example, you can work on a patch for |
bos@16 | 616 a while, \hgcmd{qrefresh} it, then \hgcmd{commit} the current state of |
bos@16 | 617 the patch. This lets you ``roll back'' to that version of the patch |
bos@16 | 618 later on. |
bos@16 | 619 |
bos@16 | 620 In addition, you can then share different versions of the same patch |
bos@16 | 621 stack among multiple underlying repositories. I use this when I am |
bos@16 | 622 developing a Linux kernel feature. I have a pristine copy of my |
bos@16 | 623 kernel sources for each of several CPU architectures, and a cloned |
bos@16 | 624 repository under each that contains the patches I am working on. When |
bos@16 | 625 I want to test a change on a different architecture, I push my current |
bos@16 | 626 patches to the patch repository associated with that kernel tree, pop |
bos@16 | 627 and push all of my patches, and build and test that kernel. |
bos@16 | 628 |
bos@16 | 629 Managing patches in a repository makes it possible for multiple |
bos@16 | 630 developers to work on the same patch series without colliding with |
bos@16 | 631 each other, all on top of an underlying source base that they may or |
bos@16 | 632 may not control. |
bos@16 | 633 |
bos@17 | 634 \subsection{MQ support for patch repositories} |
bos@16 | 635 |
bos@16 | 636 MQ helps you to work with the \sdirname{.hg/patches} directory as a |
bos@16 | 637 repository; when you prepare a repository for working with patches |
bos@17 | 638 using \hgcmd{qinit}, you can pass the \hgopt{qinit}{-c} option to |
bos@16 | 639 create the \sdirname{.hg/patches} directory as a Mercurial repository. |
bos@16 | 640 |
bos@16 | 641 \begin{note} |
bos@16 | 642 If you forget to use the \hgopt{qinit}{-c} option, you can simply go |
bos@16 | 643 into the \sdirname{.hg/patches} directory at any time and run |
bos@16 | 644 \hgcmd{init}. Don't forget to add an entry for the |
bos@17 | 645 \sfilename{status} file to the \sfilename{.hgignore} file, though |
bos@17 | 646 (\hgcmdargs{qinit}{\hgopt{qinit}{-c}} does this for you |
bos@17 | 647 automatically); you \emph{really} don't want to manage the |
bos@17 | 648 \sfilename{status} file. |
bos@16 | 649 \end{note} |
bos@16 | 650 |
bos@16 | 651 As a convenience, if MQ notices that the \dirname{.hg/patches} |
bos@16 | 652 directory is a repository, it will automatically \hgcmd{add} every |
bos@16 | 653 patch that you create and import. |
bos@16 | 654 |
bos@16 | 655 Finally, MQ provides a shortcut command, \hgcmd{qcommit}, that runs |
bos@16 | 656 \hgcmd{commit} in the \sdirname{.hg/patches} directory. This saves |
bos@16 | 657 some cumbersome typing. |
bos@16 | 658 |
bos@16 | 659 \subsection{A few things to watch out for} |
bos@16 | 660 |
bos@16 | 661 MQ's support for working with a repository full of patches is limited |
bos@16 | 662 in a few small respects. |
bos@16 | 663 |
bos@16 | 664 MQ cannot automatically detect changes that you make to the patch |
bos@16 | 665 directory. If you \hgcmd{pull}, manually edit, or \hgcmd{update} |
bos@16 | 666 changes to patches or the \sfilename{series} file, you will have to |
bos@17 | 667 \hgcmdargs{qpop}{\hgopt{qpop}{-a}} and then |
bos@17 | 668 \hgcmdargs{qpush}{\hgopt{qpush}{-a}} in the underlying repository to |
bos@17 | 669 see those changes show up there. If you forget to do this, you can |
bos@17 | 670 confuse MQ's idea of which patches are applied. |
bos@16 | 671 |
bos@16 | 672 \section{Commands for working with patches} |
bos@19 | 673 \label{sec:mq:tools} |
bos@16 | 674 |
bos@16 | 675 Once you've been working with patches for a while, you'll find |
bos@16 | 676 yourself hungry for tools that will help you to understand and |
bos@16 | 677 manipulate the patches you're dealing with. |
bos@16 | 678 |
bos@16 | 679 The \command{diffstat} command~\cite{web:diffstat} generates a |
bos@16 | 680 histogram of the modifications made to each file in a patch. It |
bos@18 | 681 provides a good way to ``get a sense of'' a patch---which files it |
bos@16 | 682 affects, and how much change it introduces to each file and as a |
bos@16 | 683 whole. (I find that it's a good idea to use \command{diffstat}'s |
bos@16 | 684 \texttt{-p} option as a matter of course, as otherwise it will try to |
bos@16 | 685 do clever things with prefixes of file names that inevitably confuse |
bos@16 | 686 at least me.) |
bos@16 | 687 |
bos@19 | 688 \begin{figure}[ht] |
bos@19 | 689 \interaction{mq.tools.tools} |
bos@19 | 690 \caption{The \command{diffstat}, \command{filterdiff}, and \command{lsdiff} commands} |
bos@19 | 691 \label{ex:mq:tools} |
bos@19 | 692 \end{figure} |
bos@19 | 693 |
bos@16 | 694 The \package{patchutils} package~\cite{web:patchutils} is invaluable. |
bos@16 | 695 It provides a set of small utilities that follow the ``Unix |
bos@16 | 696 philosophy;'' each does one useful thing with a patch. The |
bos@16 | 697 \package{patchutils} command I use most is \command{filterdiff}, which |
bos@16 | 698 extracts subsets from a patch file. For example, given a patch that |
bos@16 | 699 modifies hundreds of files across dozens of directories, a single |
bos@16 | 700 invocation of \command{filterdiff} can generate a smaller patch that |
bos@16 | 701 only touches files whose names match a particular glob pattern. |
bos@16 | 702 |
bos@19 | 703 \section{Good ways to work with patches} |
bos@19 | 704 |
bos@19 | 705 Whether you are working on a patch series to submit to a free software |
bos@19 | 706 or open source project, or a series that you intend to treat as a |
bos@19 | 707 sequence of regular changesets when you're done, you can use some |
bos@19 | 708 simple techniques to keep your work well organised. |
bos@19 | 709 |
bos@19 | 710 Give your patches descriptive names. A good name for a patch might be |
bos@19 | 711 \filename{rework-device-alloc.patch}, because it will immediately give |
bos@19 | 712 you a hint what the purpose of the patch is. Long names shouldn't be |
bos@19 | 713 a problem; you won't be typing the names often, but you \emph{will} be |
bos@19 | 714 running commands like \hgcmd{qapplied} and \hgcmd{qtop} over and over. |
bos@19 | 715 Good naming becomes especially important when you have a number of |
bos@19 | 716 patches to work with, or if you are juggling a number of different |
bos@19 | 717 tasks and your patches only get a fraction of your attention. |
bos@19 | 718 |
bos@19 | 719 Be aware of what patch you're working on. Use the \hgcmd{qtop} |
bos@19 | 720 command and skim over the text of your patches frequently---for |
bos@19 | 721 example, using \hgcmdargs{tip}{\hgopt{tip}{-p}})---to be sure of where |
bos@19 | 722 you stand. I have several times worked on and \hgcmd{qrefresh}ed a |
bos@19 | 723 patch other than the one I intended, and it's often tricky to migrate |
bos@19 | 724 changes into the right patch after making them in the wrong one. |
bos@19 | 725 |
bos@19 | 726 For this reason, it is very much worth investing a little time to |
bos@19 | 727 learn how to use some of the third-party tools I described in |
bos@19 | 728 section~\ref{sec:mq:tools}, particularly \command{diffstat} and |
bos@19 | 729 \command{filterdiff}. The former will give you a quick idea of what |
bos@19 | 730 changes your patch is making, while the latter makes it easy to splice |
bos@19 | 731 hunks selectively out of one patch and into another. |
bos@19 | 732 |
bos@19 | 733 \section{MQ cookbook} |
bos@19 | 734 |
bos@19 | 735 \subsection{Manage ``trivial'' patches} |
bos@19 | 736 |
bos@19 | 737 Because the overhead of dropping files into a new Mercurial repository |
bos@19 | 738 is so low, it makes a lot of sense to manage patches this way even if |
bos@19 | 739 you simply want to make a few changes to a source tarball that you |
bos@19 | 740 downloaded. |
bos@19 | 741 |
bos@19 | 742 Begin by downloading and unpacking the source tarball, |
bos@19 | 743 and turning it into a Mercurial repository. |
bos@19 | 744 \interaction{mq.tarball.download} |
bos@19 | 745 |
bos@19 | 746 Continue by creating a patch stack and making your changes. |
bos@19 | 747 \interaction{mq.tarball.qinit} |
bos@19 | 748 |
bos@19 | 749 Let's say a few weeks or months pass, and your package author releases |
bos@19 | 750 a new version. First, bring their changes into the repository. |
bos@19 | 751 \interaction{mq.tarball.newsource} |
bos@19 | 752 The pipeline starting with \hgcmd{locate} above deletes all files in |
bos@19 | 753 the working directory, so that \hgcmd{commit}'s |
bos@19 | 754 \hgopt{commit}{--addremove} option can actually tell which files have |
bos@19 | 755 really been removed in the newer version of the source. |
bos@19 | 756 |
bos@19 | 757 Finally, you can apply your patches on top of the new tree. |
bos@19 | 758 \interaction{mq.tarball.repush} |
bos@19 | 759 |
bos@19 | 760 \subsection{Combining entire patches} |
bos@19 | 761 \label{sec:mq:combine} |
bos@19 | 762 |
bos@19 | 763 It's easy to combine entire patches. |
bos@19 | 764 |
bos@19 | 765 \begin{enumerate} |
bos@19 | 766 \item \hgcmd{qpop} your applied patches until neither patch is |
bos@19 | 767 applied. |
bos@19 | 768 \item Concatenate the patches that you want to combine together: |
bos@19 | 769 \begin{codesample4} |
bos@19 | 770 cat patch-to-drop.patch >> patch-to-augment.patch |
bos@19 | 771 \end{codesample4} |
bos@19 | 772 The description from the first patch (if you have one) will be used |
bos@19 | 773 as the commit comment when you \hgcmd{qpush} the combined patch. |
bos@19 | 774 Edit the patch description if you need to. |
bos@19 | 775 \item Use the \hgcmd{qdel} command to delete the patch you're dropping |
bos@19 | 776 from the \sfilename{series} file. |
bos@19 | 777 \item \hgcmd{qpush} the combined patch. Fix up any rejects. |
bos@19 | 778 \item \hgcmd{qrefresh} the combined patch to tidy it up. |
bos@19 | 779 \end{enumerate} |
bos@19 | 780 |
bos@19 | 781 \subsection{Merging part of one patch into another} |
bos@19 | 782 |
bos@19 | 783 Merging \emph{part} of one patch into another is more difficult than |
bos@19 | 784 combining entire patches. |
bos@19 | 785 |
bos@19 | 786 If you want to move changes to entire files, you can use |
bos@19 | 787 \command{filterdiff}'s \cmdopt{filterdiff}{-i} and |
bos@19 | 788 \cmdopt{filterdiff}{-x} options to choose the modifications to snip |
bos@19 | 789 out of one patch, concatenating its output onto the end of the patch |
bos@19 | 790 you want to merge into. You usually won't need to modify the patch |
bos@19 | 791 you've merged the changes from. Instead, MQ will report some rejected |
bos@19 | 792 hunks when you \hgcmd{qpush} it (from the hunks you moved into the |
bos@19 | 793 other patch), and you can simply \hgcmd{qrefresh} the patch to drop |
bos@19 | 794 the duplicate hunks. |
bos@19 | 795 |
bos@19 | 796 If you have a patch that has multiple hunks modifying a file, and you |
bos@19 | 797 only want to move a few of those hunks, the job becomes more messy, |
bos@19 | 798 but you can still partly automate it. Use \cmdargs{lsdiff}{-nvv} to |
bos@19 | 799 print some metadata about the patch. |
bos@19 | 800 \interaction{mq.tools.lsdiff} |
bos@19 | 801 |
bos@19 | 802 This command prints three different kinds of number: |
bos@19 | 803 \begin{itemize} |
bos@19 | 804 \item a \emph{file number} to identify each file modified in the patch; |
bos@19 | 805 \item the line number within a modified file that a hunk starts at; and |
bos@19 | 806 \item a \emph{hunk number} to identify that hunk. |
bos@19 | 807 \end{itemize} |
bos@19 | 808 |
bos@19 | 809 You'll have to use some visual inspection, and reading of the patch, |
bos@19 | 810 to identify the file and hunk numbers you'll want, but you can then |
bos@19 | 811 pass them to to \command{filterdiff}'s \cmdopt{filterdiff}{--files} |
bos@19 | 812 and \cmdopt{filterdiff}{--hunks} options, to select exactly the file |
bos@19 | 813 and hunk you want to extract. |
bos@19 | 814 |
bos@19 | 815 Once you have this hunk, you can concatenate it onto the end of your |
bos@19 | 816 destination patch and continue with the remainder of |
bos@19 | 817 section~\ref{sec:mq:combine}. |
bos@25 | 818 \section{MQ command reference} |
bos@25 | 819 \label{sec:mq:cmdref} |
bos@25 | 820 |
bos@25 | 821 For an overview of the commands provided by MQ, use the command |
bos@25 | 822 \hgcmdargs{help}{mq}. |
bos@25 | 823 |
bos@25 | 824 \subsection{\hgcmd{qapplied}---print applied patches} |
bos@25 | 825 |
bos@25 | 826 The \hgcmd{qapplied} command prints the current stack of applied |
bos@25 | 827 patches. Patches are printed in oldest-to-newest order, so the last |
bos@25 | 828 patch in the list is the ``top'' patch. |
bos@25 | 829 |
bos@25 | 830 \subsection{\hgcmd{qcommit}---commit changes in the queue repository} |
bos@25 | 831 |
bos@25 | 832 The \hgcmd{qcommit} command commits any outstanding changes in the |
bos@25 | 833 \sdirname{.hg/patches} repository. This command only works if the |
bos@25 | 834 \sdirname{.hg/patches} directory is a repository, i.e.~you created the |
bos@25 | 835 directory using \hgcmdargs{qinit}{\hgopt{qinit}{-c}} or ran |
bos@25 | 836 \hgcmd{init} in the directory after running \hgcmd{qinit}. |
bos@25 | 837 |
bos@25 | 838 This command is shorthand for \hgcmdargs{commit}{--cwd .hg/patches}. |
bos@25 | 839 |
bos@25 | 840 \subsection{\hgcmd{qdelete}---delete a patch from the |
bos@25 | 841 \sfilename{series} file} |
bos@25 | 842 |
bos@25 | 843 The \hgcmd{qdelete} command removes the entry for a patch from the |
bos@25 | 844 \sfilename{series} file in the \sdirname{.hg/patches} directory. It |
bos@25 | 845 does not delete the patch file, nor does it pop the patch if the patch |
bos@25 | 846 is already applied. |
bos@25 | 847 |
bos@25 | 848 \subsection{\hgcmd{qdiff}---print a diff of the topmost applied patch} |
bos@25 | 849 |
bos@25 | 850 The \hgcmd{qdiff} command prints a diff of the topmost applied patch. |
bos@25 | 851 It is equivalent to \hgcmdargs{diff}{-r-2:-1}. |
bos@25 | 852 |
bos@25 | 853 \subsection{\hgcmd{qimport}---import a third-party patch into the queue} |
bos@25 | 854 |
bos@25 | 855 The \hgcmd{qimport} command adds an entry for an external patch to the |
bos@25 | 856 \sfilename{series} file, and copies the patch into the |
bos@25 | 857 \sdirname{.hg/patches} directory. It adds the entry immediately after |
bos@25 | 858 the topmost applied patch, but does not push the patch. |
bos@25 | 859 |
bos@25 | 860 If the \sdirname{.hg/patches} directory is a repository, |
bos@25 | 861 \hgcmd{qimport} automatically does an \hgcmd{add} of the imported |
bos@25 | 862 patch. |
bos@25 | 863 |
bos@25 | 864 \subsection{\hgcmd{qinit}---prepare a repository to work with MQ} |
bos@25 | 865 |
bos@25 | 866 The \hgcmd{qinit} command prepares a repository to work with MQ. It |
bos@25 | 867 creates a directory called \sdirname{.hg/patches}. |
bos@25 | 868 |
bos@25 | 869 Options: |
bos@25 | 870 \begin{itemize} |
bos@25 | 871 \item[\hgopt{qinit}{-c}] Create \sdirname{.hg/patches} as a repository |
bos@25 | 872 in its own right. Also creates a \sfilename{.hgignore} file that |
bos@25 | 873 will ignore the \sfilename{status} file. |
bos@25 | 874 \end{itemize} |
bos@25 | 875 |
bos@25 | 876 When the \sdirname{.hg/patches} directory is a repository, the |
bos@25 | 877 \hgcmd{qimport} and \hgcmd{qnew} commands automatically \hgcmd{add} |
bos@25 | 878 new patches. |
bos@25 | 879 |
bos@25 | 880 \subsection{\hgcmd{qnew}---create a new patch} |
bos@25 | 881 |
bos@25 | 882 The \hgcmd{qnew} command creates a new patch. It takes one mandatory |
bos@25 | 883 argument, the name to use for the patch file. The newly created patch |
bos@25 | 884 is created empty by default. It is added to the \sfilename{series} |
bos@25 | 885 file after the current topmost applied patch, and is immediately |
bos@25 | 886 pushed on top of that patch. |
bos@25 | 887 |
bos@25 | 888 If \hgcmd{qnew} finds modified files in the working directory, it will |
bos@25 | 889 refuse to create a new patch unless the \hgopt{qnew}{-f} option is |
bos@25 | 890 used (see below). This behaviour allows you to \hgcmd{qrefresh} your |
bos@25 | 891 topmost applied patch before you apply a new patch on top of it. |
bos@25 | 892 |
bos@25 | 893 Options: |
bos@25 | 894 \begin{itemize} |
bos@25 | 895 \item[\hgopt{qnew}{-f}] Create a new patch if the contents of the |
bos@25 | 896 working directory are modified. Any outstanding modifications are |
bos@25 | 897 added to the newly created patch, so after this command completes, |
bos@25 | 898 the working directory will no longer be modified. |
bos@25 | 899 \item[\hgopt{qnew}{-m}] Use the given text as the commit message. |
bos@25 | 900 This text will be stored at the beginning of the patch file, before |
bos@25 | 901 the patch data. |
bos@25 | 902 \end{itemize} |
bos@25 | 903 |
bos@25 | 904 \subsection{\hgcmd{qnext}---print the name of the next patch} |
bos@25 | 905 |
bos@25 | 906 The \hgcmd{qnext} command prints the name name of the next patch in |
bos@25 | 907 the \sfilename{series} file after the topmost applied patch. This |
bos@25 | 908 patch will become the topmost applied patch if you run \hgcmd{qpush}. |
bos@25 | 909 |
bos@25 | 910 \subsection{\hgcmd{qpop}---pop patches off the stack} |
bos@25 | 911 |
bos@25 | 912 The \hgcmd{qpop} command removes applied patches from the top of the |
bos@25 | 913 stack of applied patches. By default, it removes only one patch. |
bos@25 | 914 |
bos@25 | 915 This command removes the changesets that represent the popped patches |
bos@25 | 916 from the repository, and updates the working directory to undo the |
bos@25 | 917 effects of the patches. |
bos@25 | 918 |
bos@25 | 919 This command takes an optional argument, which it uses as the name or |
bos@25 | 920 index of the patch to pop to. If given a name, it will pop patches |
bos@25 | 921 until the named patch is no longer applied. If given a number, |
bos@25 | 922 \hgcmd{qpop} treats the number as an index into the entries in the |
bos@25 | 923 series file, counting from zero (empty lines and lines containing only |
bos@25 | 924 comments do not count). It pops patches until the patch identified by |
bos@25 | 925 the given index is no longer applied. |
bos@25 | 926 |
bos@25 | 927 The \hgcmd{qpop} command does not read or write patches or the |
bos@25 | 928 \sfilename{series} file. It is thus safe to \hgcmd{qpop} a patch that |
bos@25 | 929 you have removed from the \sfilename{series} file, or a patch that you |
bos@25 | 930 have renamed or deleted entirely. In the latter two cases, use the |
bos@25 | 931 name of the patch as it was when you applied it. |
bos@25 | 932 |
bos@25 | 933 By default, the \hgcmd{qpop} command will not pop any patches if the |
bos@25 | 934 working directory has been modified. You can override this behaviour |
bos@25 | 935 using the \hgopt{qpop}{-f} option, which reverts all modifications in |
bos@25 | 936 the working directory. |
bos@25 | 937 |
bos@25 | 938 Options: |
bos@25 | 939 \begin{itemize} |
bos@25 | 940 \item[\hgopt{qpop}{-a}] Pop all applied patches. This returns the |
bos@25 | 941 repository to its state before you applied any patches. |
bos@25 | 942 \item[\hgopt{qpop}{-f}] Forcibly revert any modifications to the |
bos@25 | 943 working directory when popping. |
bos@25 | 944 \item[\hgopt{qpop}{-n}] Pop a patch from the named queue. |
bos@25 | 945 \end{itemize} |
bos@25 | 946 |
bos@25 | 947 The \hgcmd{qpop} command removes one line from the end of the |
bos@25 | 948 \sfilename{status} file for each patch that it pops. |
bos@25 | 949 \subsection{\hgcmd{qprev}---print the name of the previous patch} |
bos@25 | 950 |
bos@25 | 951 The \hgcmd{qprev} command prints the name of the patch in the |
bos@25 | 952 \sfilename{series} file that comes before the topmost applied patch. |
bos@25 | 953 This will become the topmost applied patch if you run \hgcmd{qpop}. |
bos@25 | 954 |
bos@25 | 955 \subsection{\hgcmd{qpush}---push patches onto the stack} |
bos@25 | 956 |
bos@25 | 957 The \hgcmd{qpush} command adds patches onto the applied stack. By |
bos@25 | 958 default, it adds only one patch. |
bos@25 | 959 |
bos@25 | 960 This command creates a new changeset to represent each applied patch, |
bos@25 | 961 and updates the working directory to apply the effects of the patches. |
bos@25 | 962 |
bos@25 | 963 The data used when creating a changeset are as follows: |
bos@25 | 964 \begin{itemize} |
bos@25 | 965 \item The commit date and time zone are the current date and time |
bos@25 | 966 zone. Because these data are used to compute the identity of a |
bos@25 | 967 changeset, this means that if you \hgcmd{qpop} a patch and |
bos@25 | 968 \hgcmd{qpush} it again, the changeset that you push will have a |
bos@25 | 969 different identity than the changeset you popped. |
bos@25 | 970 \item The author is the same as the default used by the \hgcmd{commit} |
bos@25 | 971 command. |
bos@25 | 972 \item The commit message is any text from the patch file that comes |
bos@25 | 973 before the first diff header. If there is no such text, a default |
bos@25 | 974 commit message is used that identifies the name of the patch. |
bos@25 | 975 \end{itemize} |
bos@25 | 976 |
bos@25 | 977 Options: |
bos@25 | 978 \begin{itemize} |
bos@25 | 979 \item[\hgopt{qpush}{-a}] Push all unapplied patches from the |
bos@25 | 980 \sfilename{series} file until there are none left to push. |
bos@25 | 981 \item[\hgopt{qpush}{-l}] Add the name of the patch to the end |
bos@25 | 982 of the commit message. |
bos@25 | 983 \item[\hgopt{qpush}{-m}] If a patch fails to apply cleanly, use the |
bos@25 | 984 entry for the patch in another saved queue to compute the parameters |
bos@25 | 985 for a three-way merge, and perform a three-way merge using the |
bos@25 | 986 normal Mercurial merge machinery. Use the resolution of the merge |
bos@25 | 987 as the new patch content. |
bos@25 | 988 \item[\hgopt{qpush}{-n}] Use the named queue if merging while pushing. |
bos@25 | 989 \end{itemize} |
bos@25 | 990 |
bos@25 | 991 The \hgcmd{qpush} command reads, but does not modify, the |
bos@25 | 992 \sfilename{series} file. It appends one line to the \hgcmd{status} |
bos@25 | 993 file for each patch that it pushes. |
bos@25 | 994 |
bos@25 | 995 \subsection{\hgcmd{qrefresh}---update the topmost applied patch} |
bos@25 | 996 |
bos@25 | 997 The \hgcmd{qrefresh} command updates the topmost applied patch. It |
bos@25 | 998 modifies the patch, removes the old changeset that represented the |
bos@25 | 999 patch, and creates a new changeset to represent the modified patch. |
bos@25 | 1000 |
bos@25 | 1001 The \hgcmd{qrefresh} command looks for the following modifications: |
bos@25 | 1002 \begin{itemize} |
bos@25 | 1003 \item Changes to the commit message, i.e.~the text before the first |
bos@25 | 1004 diff header in the patch file, are reflected in the new changeset |
bos@25 | 1005 that represents the patch. |
bos@25 | 1006 \item Modifications to tracked files in the working directory are |
bos@25 | 1007 added to the patch. |
bos@25 | 1008 \item Changes to the files tracked using \hgcmd{add}, \hgcmd{copy}, |
bos@25 | 1009 \hgcmd{remove}, or \hgcmd{rename}. Added files and copy and rename |
bos@25 | 1010 destinations are added to the patch, while removed files and rename |
bos@25 | 1011 sources are removed. |
bos@25 | 1012 \end{itemize} |
bos@25 | 1013 |
bos@25 | 1014 Even if \hgcmd{qrefresh} detects no changes, it still recreates the |
bos@25 | 1015 changeset that represents the patch. This causes the identity of the |
bos@25 | 1016 changeset to differ from the previous changeset that identified the |
bos@25 | 1017 patch. |
bos@25 | 1018 |
bos@25 | 1019 \section{MQ file reference} |
bos@25 | 1020 |
bos@25 | 1021 |
bos@25 | 1022 \subsection{The \sfilename{series} file} |
bos@25 | 1023 |
bos@25 | 1024 |
bos@25 | 1025 \subsection{The \sfilename{status} file} |
bos@25 | 1026 |
bos@25 | 1027 |
bos@19 | 1028 |
bos@1 | 1029 %%% Local Variables: |
bos@1 | 1030 %%% mode: latex |
bos@1 | 1031 %%% TeX-master: "00book" |
bos@1 | 1032 %%% End: |