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1 \chapter{Managing change with Mercurial Queues}
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2 \label{chap:mq}
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3
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4 \section{The patch management problem}
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5 \label{sec:mq:patch-mgmt}
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6
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7 Here is a common scenario: you need to install a software package from
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8 source, but you find a bug that you must fix in the source before you
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9 can start using the package. You make your changes, forget about the
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10 package for a while, and a few months later you need to upgrade to a
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11 newer version of the package. If the newer version of the package
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12 still has the bug, you must extract your fix from the older source
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13 tree and apply it against the newer version. This is a tedious task,
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14 and it's easy to make mistakes.
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15
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16 This is a simple case of the ``patch management'' problem. You have
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17 an ``upstream'' source tree that you can't change; you need to make
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18 some local changes on top of the upstream tree; and you'd like to be
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19 able to keep those changes separate, so that you can apply them to
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20 newer versions of the upstream source.
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21
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22 The patch management problem arises in many situations. Probably the
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23 most visible is that a user of an open source software project will
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24 contribute a bug fix or new feature to the project's maintainers in the
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25 form of a patch.
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26
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27 Distributors of operating systems that include open source software
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28 often need to make changes to the packages they distribute so that
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29 they will build properly in their environments.
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30
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31 When you have few changes to maintain, it is easy to manage a single
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32 patch using the standard \command{diff} and \command{patch} programs
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33 (see section~\ref{sec:mq:patch} for a discussion of these tools).
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34 Once the number of changes grows, it starts to makes sense to maintain
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35 patches as discrete ``chunks of work,'' so that for example a single
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36 patch will contain only one bug fix (the patch might modify several
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37 files, but it's doing ``only one thing''), and you may have a number
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38 of such patches for different bugs you need fixed and local changes
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39 you require. In this situation, if you submit a bug fix patch to the
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40 upstream maintainers of a package and they include your fix in a
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41 subsequent release, you can simply drop that single patch when you're
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42 updating to the newer release.
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43
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44 Maintaining a single patch against an upstream tree is a little
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45 tedious and error-prone, but not difficult. However, the complexity
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46 of the problem grows rapidly as the number of patches you have to
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47 maintain increases. With more than a tiny number of patches in hand,
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48 understanding which ones you have applied and maintaining them moves
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49 from messy to overwhelming.
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50
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51 Fortunately, Mercurial includes a powerful extension, Mercurial Queues
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52 (or simply ``MQ''), that massively simplifies the patch management
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53 problem.
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54
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55 \section{The prehistory of Mercurial Queues}
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56 \label{sec:mq:history}
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57
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58 During the late 1990s, several Linux kernel developers started to
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59 maintain ``patch series'' that modified the behaviour of the Linux
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60 kernel. Some of these series were focused on stability, some on
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61 feature coverage, and others were more speculative.
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62
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63 The sizes of these patch series grew rapidly. In 2002, Andrew Morton
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64 published some shell scripts he had been using to automate the task of
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65 managing his patch queues. Andrew was successfully using these
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66 scripts to manage hundreds (sometimes thousands) of patches on top of
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67 the Linux kernel.
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68
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69 \subsection{A patchwork quilt}
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70 \label{sec:mq:quilt}
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71
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72 In early 2003, Andreas Gruenbacher and Martin Quinson borrowed the
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73 approach of Andrew's scripts and published a tool called ``patchwork
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74 quilt''~\cite{web:quilt}, or simply ``quilt''
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75 (see~\cite{gruenbacher:2005} for a paper describing it). Because
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76 quilt substantially automated patch management, it rapidly gained a
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77 large following among open source software developers.
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78
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79 Quilt manages a \emph{stack of patches} on top of a directory tree.
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80 To begin, you tell quilt to manage a directory tree, and tell it which
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81 files you want to manage; it stores away the names and contents of
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82 those files. To fix a bug, you create a new patch (using a single
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83 command), edit the files you need to fix, then ``refresh'' the patch.
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84
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85 The refresh step causes quilt to scan the directory tree; it updates
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86 the patch with all of the changes you have made. You can create
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87 another patch on top of the first, which will track the changes
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88 required to modify the tree from ``tree with one patch applied'' to
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89 ``tree with two patches applied''.
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90
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91 You can \emph{change} which patches are applied to the tree. If you
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92 ``pop'' a patch, the changes made by that patch will vanish from the
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93 directory tree. Quilt remembers which patches you have popped,
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94 though, so you can ``push'' a popped patch again, and the directory
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95 tree will be restored to contain the modifications in the patch. Most
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96 importantly, you can run the ``refresh'' command at any time, and the
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97 topmost applied patch will be updated. This means that you can, at
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98 any time, change both which patches are applied and what
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99 modifications those patches make.
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100
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101 Quilt knows nothing about revision control tools, so it works equally
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102 well on top of an unpacked tarball or a Subversion repository.
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103
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104 \subsection{From patchwork quilt to Mercurial Queues}
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105 \label{sec:mq:quilt-mq}
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106
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107 In mid-2005, Chris Mason took the features of quilt and wrote an
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108 extension that he called Mercurial Queues, which added quilt-like
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109 behaviour to Mercurial.
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110
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111 The key difference between quilt and MQ is that quilt knows nothing
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112 about revision control systems, while MQ is \emph{integrated} into
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113 Mercurial. Each patch that you push is represented as a Mercurial
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114 changeset. Pop a patch, and the changeset goes away.
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115
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116 Because quilt does not care about revision control tools, it is still
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117 a tremendously useful piece of software to know about for situations
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118 where you cannot use Mercurial and MQ.
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119
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120 \section{The huge advantage of MQ}
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121
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122 I cannot overstate the value that MQ offers through the unification of
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123 patches and revision control.
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124
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125 A major reason that patches have persisted in the free software and
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126 open source world---in spite of the availability of increasingly
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127 capable revision control tools over the years---is the \emph{agility}
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128 they offer.
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129
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130 Traditional revision control tools make a permanent, irreversible
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131 record of everything that you do. While this has great value, it's
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132 also somewhat stifling. If you want to perform a wild-eyed
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133 experiment, you have to be careful in how you go about it, or you risk
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134 leaving unneeded---or worse, misleading or destabilising---traces of
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135 your missteps and errors in the permanent revision record.
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136
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137 By contrast, MQ's marriage of distributed revision control with
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138 patches makes it much easier to isolate your work. Your patches live
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139 on top of normal revision history, and you can make them disappear or
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140 reappear at will. If you don't like a patch, you can drop it. If a
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141 patch isn't quite as you want it to be, simply fix it---as many times
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142 as you need to, until you have refined it into the form you desire.
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143
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144 As an example, the integration of patches with revision control makes
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145 understanding patches and debugging their effects---and their
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146 interplay with the code they're based on---\emph{enormously} easier.
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147 Since every applied patch has an associated changeset, you can use
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148 \hgcmdargs{log}{\emph{filename}} to see which changesets and patches
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149 affected a file. You can use the \hgext{bisect} extension to
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150 binary-search through all changesets and applied patches to see where
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151 a bug got introduced or fixed. You can use the \hgcmd{annotate}
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152 command to see which changeset or patch modified a particular line of
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153 a source file. And so on.
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154
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155 \section{Understanding patches}
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156 \label{sec:mq:patch}
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157
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158 Because MQ doesn't hide its patch-oriented nature, it is helpful to
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159 understand what patches are, and a little about the tools that work
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160 with them.
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161
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162 The traditional Unix \command{diff} command compares two files, and
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163 prints a list of differences between them. The \command{patch} command
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164 understands these differences as \emph{modifications} to make to a
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165 file. Take a look at figure~\ref{ex:mq:diff} for a simple example of
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166 these commands in action.
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167
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168 \begin{figure}[ht]
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169 \interaction{mq.dodiff.diff}
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170 \caption{Simple uses of the \command{diff} and \command{patch} commands}
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171 \label{ex:mq:diff}
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172 \end{figure}
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173
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174 The type of file that \command{diff} generates (and \command{patch}
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175 takes as input) is called a ``patch'' or a ``diff''; there is no
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176 difference between a patch and a diff. (We'll use the term ``patch'',
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177 since it's more commonly used.)
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178
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179 A patch file can start with arbitrary text; the \command{patch}
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180 command ignores this text, but MQ uses it as the commit message when
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181 creating changesets. To find the beginning of the patch content,
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182 \command{patch} searches for the first line that starts with the
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183 string ``\texttt{diff~-}''.
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184
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185 MQ works with \emph{unified} diffs (\command{patch} can accept several
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186 other diff formats, but MQ doesn't). A unified diff contains two
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187 kinds of header. The \emph{file header} describes the file being
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188 modified; it contains the name of the file to modify. When
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189 \command{patch} sees a new file header, it looks for a file with that
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190 name to start modifying.
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191
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192 After the file header comes a series of \emph{hunks}. Each hunk
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193 starts with a header; this identifies the range of line numbers within
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194 the file that the hunk should modify. Following the header, a hunk
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195 starts and ends with a few (usually three) lines of text from the
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196 unmodified file; these are called the \emph{context} for the hunk. If
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197 there's only a small amount of context between successive hunks,
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198 \command{diff} doesn't print a new hunk header; it just runs the hunks
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199 together, with a few lines of context between modifications.
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200
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201 Each line of context begins with a space character. Within the hunk,
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202 a line that begins with ``\texttt{-}'' means ``remove this line,''
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203 while a line that begins with ``\texttt{+}'' means ``insert this
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204 line.'' For example, a line that is modified is represented by one
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205 deletion and one insertion.
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206
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207 We will return to some of the more subtle aspects of patches later (in
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208 section~\ref{sec:mq:adv-patch}), but you should have enough information
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209 now to use MQ.
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210
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211 \section{Getting started with Mercurial Queues}
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212 \label{sec:mq:start}
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213
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214 Because MQ is implemented as an extension, you must explicitly enable
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215 before you can use it. (You don't need to download anything; MQ ships
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216 with the standard Mercurial distribution.) To enable MQ, edit your
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217 \tildefile{.hgrc} file, and add the lines in figure~\ref{ex:mq:config}.
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218
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219 \begin{figure}[ht]
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220 \begin{codesample4}
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221 [extensions]
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222 hgext.mq =
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223 \end{codesample4}
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224 \label{ex:mq:config}
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225 \caption{Contents to add to \tildefile{.hgrc} to enable the MQ extension}
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226 \end{figure}
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227
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228 Once the extension is enabled, it will make a number of new commands
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229 available. To verify that the extension is working, you can use
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230 \hgcmd{help} to see if the \hgxcmd{mq}{qinit} command is now available; see
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231 the example in figure~\ref{ex:mq:enabled}.
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232
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233 \begin{figure}[ht]
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234 \interaction{mq.qinit-help.help}
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235 \caption{How to verify that MQ is enabled}
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236 \label{ex:mq:enabled}
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237 \end{figure}
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238
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239 You can use MQ with \emph{any} Mercurial repository, and its commands
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240 only operate within that repository. To get started, simply prepare
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241 the repository using the \hgxcmd{mq}{qinit} command (see
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242 figure~\ref{ex:mq:qinit}). This command creates an empty directory
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243 called \sdirname{.hg/patches}, where MQ will keep its metadata. As
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244 with many Mercurial commands, the \hgxcmd{mq}{qinit} command prints nothing
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245 if it succeeds.
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246
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247 \begin{figure}[ht]
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248 \interaction{mq.tutorial.qinit}
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249 \caption{Preparing a repository for use with MQ}
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250 \label{ex:mq:qinit}
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251 \end{figure}
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252
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253 \begin{figure}[ht]
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254 \interaction{mq.tutorial.qnew}
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255 \caption{Creating a new patch}
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256 \label{ex:mq:qnew}
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257 \end{figure}
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258
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259 \subsection{Creating a new patch}
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260
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261 To begin work on a new patch, use the \hgxcmd{mq}{qnew} command. This
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262 command takes one argument, the name of the patch to create. MQ will
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263 use this as the name of an actual file in the \sdirname{.hg/patches}
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264 directory, as you can see in figure~\ref{ex:mq:qnew}.
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265
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266 Also newly present in the \sdirname{.hg/patches} directory are two
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267 other files, \sfilename{series} and \sfilename{status}. The
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268 \sfilename{series} file lists all of the patches that MQ knows about
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269 for this repository, with one patch per line. Mercurial uses the
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270 \sfilename{status} file for internal book-keeping; it tracks all of the
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271 patches that MQ has \emph{applied} in this repository.
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272
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273 \begin{note}
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274 You may sometimes want to edit the \sfilename{series} file by hand;
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275 for example, to change the sequence in which some patches are
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276 applied. However, manually editing the \sfilename{status} file is
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277 almost always a bad idea, as it's easy to corrupt MQ's idea of what
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278 is happening.
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279 \end{note}
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280
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281 Once you have created your new patch, you can edit files in the
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282 working directory as you usually would. All of the normal Mercurial
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283 commands, such as \hgcmd{diff} and \hgcmd{annotate}, work exactly as
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284 they did before.
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285
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286 \subsection{Refreshing a patch}
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287
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288 When you reach a point where you want to save your work, use the
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289 \hgxcmd{mq}{qrefresh} command (figure~\ref{ex:mq:qnew}) to update the patch
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290 you are working on. This command folds the changes you have made in
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291 the working directory into your patch, and updates its corresponding
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292 changeset to contain those changes.
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293
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294 \begin{figure}[ht]
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295 \interaction{mq.tutorial.qrefresh}
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296 \caption{Refreshing a patch}
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297 \label{ex:mq:qrefresh}
|
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bos@8
|
298 \end{figure}
|
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bos@8
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299
|
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bos@233
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300 You can run \hgxcmd{mq}{qrefresh} as often as you like, so it's a good way
|
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bos@13
|
301 to ``checkpoint'' your work. Refresh your patch at an opportune
|
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bos@8
|
302 time; try an experiment; and if the experiment doesn't work out,
|
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bos@8
|
303 \hgcmd{revert} your modifications back to the last time you refreshed.
|
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bos@8
|
304
|
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bos@12
|
305 \begin{figure}[ht]
|
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bos@8
|
306 \interaction{mq.tutorial.qrefresh2}
|
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bos@8
|
307 \caption{Refresh a patch many times to accumulate changes}
|
|
bos@8
|
308 \label{ex:mq:qrefresh2}
|
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bos@8
|
309 \end{figure}
|
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bos@8
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310
|
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bos@8
|
311 \subsection{Stacking and tracking patches}
|
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bos@8
|
312
|
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bos@8
|
313 Once you have finished working on a patch, or need to work on another,
|
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bos@233
|
314 you can use the \hgxcmd{mq}{qnew} command again to create a new patch.
|
|
bos@8
|
315 Mercurial will apply this patch on top of your existing patch. See
|
|
bos@8
|
316 figure~\ref{ex:mq:qnew2} for an example. Notice that the patch
|
|
bos@8
|
317 contains the changes in our prior patch as part of its context (you
|
|
bos@8
|
318 can see this more clearly in the output of \hgcmd{annotate}).
|
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bos@8
|
319
|
|
bos@12
|
320 \begin{figure}[ht]
|
|
bos@8
|
321 \interaction{mq.tutorial.qnew2}
|
|
bos@8
|
322 \caption{Stacking a second patch on top of the first}
|
|
bos@8
|
323 \label{ex:mq:qnew2}
|
|
bos@8
|
324 \end{figure}
|
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bos@8
|
325
|
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bos@233
|
326 So far, with the exception of \hgxcmd{mq}{qnew} and \hgxcmd{mq}{qrefresh}, we've
|
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bos@27
|
327 been careful to only use regular Mercurial commands. However, MQ
|
|
bos@27
|
328 provides many commands that are easier to use when you are thinking
|
|
bos@27
|
329 about patches, as illustrated in figure~\ref{ex:mq:qseries}:
|
|
bos@8
|
330
|
|
bos@8
|
331 \begin{itemize}
|
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bos@233
|
332 \item The \hgxcmd{mq}{qseries} command lists every patch that MQ knows
|
|
bos@8
|
333 about in this repository, from oldest to newest (most recently
|
|
bos@8
|
334 \emph{created}).
|
|
bos@233
|
335 \item The \hgxcmd{mq}{qapplied} command lists every patch that MQ has
|
|
bos@8
|
336 \emph{applied} in this repository, again from oldest to newest (most
|
|
bos@8
|
337 recently applied).
|
|
bos@8
|
338 \end{itemize}
|
|
bos@8
|
339
|
|
bos@12
|
340 \begin{figure}[ht]
|
|
bos@8
|
341 \interaction{mq.tutorial.qseries}
|
|
bos@233
|
342 \caption{Understanding the patch stack with \hgxcmd{mq}{qseries} and
|
|
bos@233
|
343 \hgxcmd{mq}{qapplied}}
|
|
bos@8
|
344 \label{ex:mq:qseries}
|
|
bos@8
|
345 \end{figure}
|
|
bos@8
|
346
|
|
bos@8
|
347 \subsection{Manipulating the patch stack}
|
|
bos@8
|
348
|
|
bos@8
|
349 The previous discussion implied that there must be a difference
|
|
bos@11
|
350 between ``known'' and ``applied'' patches, and there is. MQ can
|
|
bos@11
|
351 manage a patch without it being applied in the repository.
|
|
bos@8
|
352
|
|
bos@8
|
353 An \emph{applied} patch has a corresponding changeset in the
|
|
bos@8
|
354 repository, and the effects of the patch and changeset are visible in
|
|
bos@8
|
355 the working directory. You can undo the application of a patch using
|
|
bos@233
|
356 the \hgxcmd{mq}{qpop} command. MQ still \emph{knows about}, or manages, a
|
|
bos@12
|
357 popped patch, but the patch no longer has a corresponding changeset in
|
|
bos@12
|
358 the repository, and the working directory does not contain the changes
|
|
bos@12
|
359 made by the patch. Figure~\ref{fig:mq:stack} illustrates the
|
|
bos@12
|
360 difference between applied and tracked patches.
|
|
bos@12
|
361
|
|
bos@12
|
362 \begin{figure}[ht]
|
|
bos@12
|
363 \centering
|
|
jeffpc@35
|
364 \grafix{mq-stack}
|
|
bos@12
|
365 \caption{Applied and unapplied patches in the MQ patch stack}
|
|
bos@12
|
366 \label{fig:mq:stack}
|
|
bos@8
|
367 \end{figure}
|
|
bos@8
|
368
|
|
bos@233
|
369 You can reapply an unapplied, or popped, patch using the \hgxcmd{mq}{qpush}
|
|
bos@8
|
370 command. This creates a new changeset to correspond to the patch, and
|
|
bos@8
|
371 the patch's changes once again become present in the working
|
|
bos@233
|
372 directory. See figure~\ref{ex:mq:qpop} for examples of \hgxcmd{mq}{qpop}
|
|
bos@233
|
373 and \hgxcmd{mq}{qpush} in action. Notice that once we have popped a patch
|
|
bos@233
|
374 or two patches, the output of \hgxcmd{mq}{qseries} remains the same, while
|
|
bos@233
|
375 that of \hgxcmd{mq}{qapplied} has changed.
|
|
bos@8
|
376
|
|
bos@12
|
377 \begin{figure}[ht]
|
|
bos@12
|
378 \interaction{mq.tutorial.qpop}
|
|
bos@12
|
379 \caption{Modifying the stack of applied patches}
|
|
bos@12
|
380 \label{ex:mq:qpop}
|
|
bos@11
|
381 \end{figure}
|
|
bos@11
|
382
|
|
bos@27
|
383 \subsection{Pushing and popping many patches}
|
|
bos@27
|
384
|
|
bos@233
|
385 While \hgxcmd{mq}{qpush} and \hgxcmd{mq}{qpop} each operate on a single patch at
|
|
bos@27
|
386 a time by default, you can push and pop many patches in one go. The
|
|
bos@234
|
387 \hgxopt{mq}{qpush}{-a} option to \hgxcmd{mq}{qpush} causes it to push all
|
|
bos@234
|
388 unapplied patches, while the \hgxopt{mq}{qpop}{-a} option to \hgxcmd{mq}{qpop}
|
|
bos@27
|
389 causes it to pop all applied patches. (For some more ways to push and
|
|
bos@27
|
390 pop many patches, see section~\ref{sec:mq:perf} below.)
|
|
bos@27
|
391
|
|
bos@27
|
392 \begin{figure}[ht]
|
|
bos@27
|
393 \interaction{mq.tutorial.qpush-a}
|
|
bos@27
|
394 \caption{Pushing all unapplied patches}
|
|
bos@27
|
395 \label{ex:mq:qpush-a}
|
|
bos@27
|
396 \end{figure}
|
|
bos@27
|
397
|
|
bos@27
|
398 \subsection{Safety checks, and overriding them}
|
|
bos@27
|
399
|
|
bos@27
|
400 Several MQ commands check the working directory before they do
|
|
bos@27
|
401 anything, and fail if they find any modifications. They do this to
|
|
bos@27
|
402 ensure that you won't lose any changes that you have made, but not yet
|
|
bos@27
|
403 incorporated into a patch. Figure~\ref{ex:mq:add} illustrates this;
|
|
bos@233
|
404 the \hgxcmd{mq}{qnew} command will not create a new patch if there are
|
|
bos@27
|
405 outstanding changes, caused in this case by the \hgcmd{add} of
|
|
bos@27
|
406 \filename{file3}.
|
|
bos@27
|
407
|
|
bos@27
|
408 \begin{figure}[ht]
|
|
bos@27
|
409 \interaction{mq.tutorial.add}
|
|
bos@27
|
410 \caption{Forcibly creating a patch}
|
|
bos@27
|
411 \label{ex:mq:add}
|
|
bos@27
|
412 \end{figure}
|
|
bos@27
|
413
|
|
bos@27
|
414 Commands that check the working directory all take an ``I know what
|
|
bos@27
|
415 I'm doing'' option, which is always named \option{-f}. The exact
|
|
bos@27
|
416 meaning of \option{-f} depends on the command. For example,
|
|
bos@234
|
417 \hgcmdargs{qnew}{\hgxopt{mq}{qnew}{-f}} will incorporate any outstanding
|
|
bos@27
|
418 changes into the new patch it creates, but
|
|
bos@234
|
419 \hgcmdargs{qpop}{\hgxopt{mq}{qpop}{-f}} will revert modifications to any
|
|
bos@27
|
420 files affected by the patch that it is popping. Be sure to read the
|
|
bos@27
|
421 documentation for a command's \option{-f} option before you use it!
|
|
bos@8
|
422
|
|
bos@13
|
423 \subsection{Working on several patches at once}
|
|
bos@13
|
424
|
|
bos@233
|
425 The \hgxcmd{mq}{qrefresh} command always refreshes the \emph{topmost}
|
|
bos@13
|
426 applied patch. This means that you can suspend work on one patch (by
|
|
bos@13
|
427 refreshing it), pop or push to make a different patch the top, and
|
|
bos@13
|
428 work on \emph{that} patch for a while.
|
|
bos@13
|
429
|
|
bos@13
|
430 Here's an example that illustrates how you can use this ability.
|
|
bos@13
|
431 Let's say you're developing a new feature as two patches. The first
|
|
bos@18
|
432 is a change to the core of your software, and the second---layered on
|
|
bos@18
|
433 top of the first---changes the user interface to use the code you just
|
|
bos@13
|
434 added to the core. If you notice a bug in the core while you're
|
|
bos@13
|
435 working on the UI patch, it's easy to fix the core. Simply
|
|
bos@233
|
436 \hgxcmd{mq}{qrefresh} the UI patch to save your in-progress changes, and
|
|
bos@233
|
437 \hgxcmd{mq}{qpop} down to the core patch. Fix the core bug,
|
|
bos@233
|
438 \hgxcmd{mq}{qrefresh} the core patch, and \hgxcmd{mq}{qpush} back to the UI
|
|
bos@13
|
439 patch to continue where you left off.
|
|
bos@13
|
440
|
|
bos@19
|
441 \section{More about patches}
|
|
bos@19
|
442 \label{sec:mq:adv-patch}
|
|
bos@19
|
443
|
|
bos@19
|
444 MQ uses the GNU \command{patch} command to apply patches, so it's
|
|
bos@26
|
445 helpful to know a few more detailed aspects of how \command{patch}
|
|
bos@26
|
446 works, and about patches themselves.
|
|
bos@26
|
447
|
|
bos@26
|
448 \subsection{The strip count}
|
|
bos@26
|
449
|
|
bos@26
|
450 If you look at the file headers in a patch, you will notice that the
|
|
bos@26
|
451 pathnames usually have an extra component on the front that isn't
|
|
bos@26
|
452 present in the actual path name. This is a holdover from the way that
|
|
bos@26
|
453 people used to generate patches (people still do this, but it's
|
|
bos@26
|
454 somewhat rare with modern revision control tools).
|
|
bos@26
|
455
|
|
bos@26
|
456 Alice would unpack a tarball, edit her files, then decide that she
|
|
bos@26
|
457 wanted to create a patch. So she'd rename her working directory,
|
|
bos@26
|
458 unpack the tarball again (hence the need for the rename), and use the
|
|
bos@26
|
459 \cmdopt{diff}{-r} and \cmdopt{diff}{-N} options to \command{diff} to
|
|
bos@26
|
460 recursively generate a patch between the unmodified directory and the
|
|
bos@26
|
461 modified one. The result would be that the name of the unmodified
|
|
bos@26
|
462 directory would be at the front of the left-hand path in every file
|
|
bos@26
|
463 header, and the name of the modified directory would be at the front
|
|
bos@26
|
464 of the right-hand path.
|
|
bos@26
|
465
|
|
bos@26
|
466 Since someone receiving a patch from the Alices of the net would be
|
|
bos@26
|
467 unlikely to have unmodified and modified directories with exactly the
|
|
bos@26
|
468 same names, the \command{patch} command has a \cmdopt{patch}{-p}
|
|
bos@26
|
469 option that indicates the number of leading path name components to
|
|
bos@26
|
470 strip when trying to apply a patch. This number is called the
|
|
bos@26
|
471 \emph{strip count}.
|
|
bos@26
|
472
|
|
bos@26
|
473 An option of ``\texttt{-p1}'' means ``use a strip count of one''. If
|
|
bos@26
|
474 \command{patch} sees a file name \filename{foo/bar/baz} in a file
|
|
bos@26
|
475 header, it will strip \filename{foo} and try to patch a file named
|
|
bos@26
|
476 \filename{bar/baz}. (Strictly speaking, the strip count refers to the
|
|
bos@26
|
477 number of \emph{path separators} (and the components that go with them
|
|
bos@26
|
478 ) to strip. A strip count of one will turn \filename{foo/bar} into
|
|
bos@26
|
479 \filename{bar}, but \filename{/foo/bar} (notice the extra leading
|
|
bos@26
|
480 slash) into \filename{foo/bar}.)
|
|
bos@26
|
481
|
|
bos@26
|
482 The ``standard'' strip count for patches is one; almost all patches
|
|
bos@26
|
483 contain one leading path name component that needs to be stripped.
|
|
bos@26
|
484 Mercurial's \hgcmd{diff} command generates path names in this form,
|
|
bos@26
|
485 and the \hgcmd{import} command and MQ expect patches to have a strip
|
|
bos@26
|
486 count of one.
|
|
bos@26
|
487
|
|
bos@26
|
488 If you receive a patch from someone that you want to add to your patch
|
|
bos@26
|
489 queue, and the patch needs a strip count other than one, you cannot
|
|
bos@233
|
490 just \hgxcmd{mq}{qimport} the patch, because \hgxcmd{mq}{qimport} does not yet
|
|
bos@26
|
491 have a \texttt{-p} option (see~\bug{311}). Your best bet is to
|
|
bos@233
|
492 \hgxcmd{mq}{qnew} a patch of your own, then use \cmdargs{patch}{-p\emph{N}}
|
|
bos@26
|
493 to apply their patch, followed by \hgcmd{addremove} to pick up any
|
|
bos@233
|
494 files added or removed by the patch, followed by \hgxcmd{mq}{qrefresh}.
|
|
bos@26
|
495 This complexity may become unnecessary; see~\bug{311} for details.
|
|
bos@26
|
496 \subsection{Strategies for applying a patch}
|
|
bos@14
|
497
|
|
bos@14
|
498 When \command{patch} applies a hunk, it tries a handful of
|
|
bos@14
|
499 successively less accurate strategies to try to make the hunk apply.
|
|
bos@14
|
500 This falling-back technique often makes it possible to take a patch
|
|
bos@14
|
501 that was generated against an old version of a file, and apply it
|
|
bos@14
|
502 against a newer version of that file.
|
|
bos@14
|
503
|
|
bos@14
|
504 First, \command{patch} tries an exact match, where the line numbers,
|
|
bos@14
|
505 the context, and the text to be modified must apply exactly. If it
|
|
bos@14
|
506 cannot make an exact match, it tries to find an exact match for the
|
|
bos@14
|
507 context, without honouring the line numbering information. If this
|
|
bos@14
|
508 succeeds, it prints a line of output saying that the hunk was applied,
|
|
bos@14
|
509 but at some \emph{offset} from the original line number.
|
|
bos@14
|
510
|
|
bos@14
|
511 If a context-only match fails, \command{patch} removes the first and
|
|
bos@14
|
512 last lines of the context, and tries a \emph{reduced} context-only
|
|
bos@14
|
513 match. If the hunk with reduced context succeeds, it prints a message
|
|
bos@14
|
514 saying that it applied the hunk with a \emph{fuzz factor} (the number
|
|
bos@14
|
515 after the fuzz factor indicates how many lines of context
|
|
bos@14
|
516 \command{patch} had to trim before the patch applied).
|
|
bos@14
|
517
|
|
bos@14
|
518 When neither of these techniques works, \command{patch} prints a
|
|
bos@14
|
519 message saying that the hunk in question was rejected. It saves
|
|
bos@17
|
520 rejected hunks (also simply called ``rejects'') to a file with the
|
|
bos@17
|
521 same name, and an added \sfilename{.rej} extension. It also saves an
|
|
bos@17
|
522 unmodified copy of the file with a \sfilename{.orig} extension; the
|
|
bos@17
|
523 copy of the file without any extensions will contain any changes made
|
|
bos@17
|
524 by hunks that \emph{did} apply cleanly. If you have a patch that
|
|
bos@17
|
525 modifies \filename{foo} with six hunks, and one of them fails to
|
|
bos@17
|
526 apply, you will have: an unmodified \filename{foo.orig}, a
|
|
bos@17
|
527 \filename{foo.rej} containing one hunk, and \filename{foo}, containing
|
|
bos@17
|
528 the changes made by the five successful five hunks.
|
|
bos@14
|
529
|
|
bos@25
|
530 \subsection{Some quirks of patch representation}
|
|
bos@25
|
531
|
|
bos@25
|
532 There are a few useful things to know about how \command{patch} works
|
|
bos@25
|
533 with files.
|
|
bos@25
|
534 \begin{itemize}
|
|
bos@25
|
535 \item This should already be obvious, but \command{patch} cannot
|
|
bos@25
|
536 handle binary files.
|
|
bos@25
|
537 \item Neither does it care about the executable bit; it creates new
|
|
bos@25
|
538 files as readable, but not executable.
|
|
bos@25
|
539 \item \command{patch} treats the removal of a file as a diff between
|
|
bos@25
|
540 the file to be removed and the empty file. So your idea of ``I
|
|
bos@25
|
541 deleted this file'' looks like ``every line of this file was
|
|
bos@25
|
542 deleted'' in a patch.
|
|
bos@25
|
543 \item It treats the addition of a file as a diff between the empty
|
|
bos@25
|
544 file and the file to be added. So in a patch, your idea of ``I
|
|
bos@25
|
545 added this file'' looks like ``every line of this file was added''.
|
|
bos@25
|
546 \item It treats a renamed file as the removal of the old name, and the
|
|
bos@25
|
547 addition of the new name. This means that renamed files have a big
|
|
bos@25
|
548 footprint in patches. (Note also that Mercurial does not currently
|
|
bos@25
|
549 try to infer when files have been renamed or copied in a patch.)
|
|
bos@25
|
550 \item \command{patch} cannot represent empty files, so you cannot use
|
|
bos@25
|
551 a patch to represent the notion ``I added this empty file to the
|
|
bos@25
|
552 tree''.
|
|
bos@25
|
553 \end{itemize}
|
|
bos@14
|
554 \subsection{Beware the fuzz}
|
|
bos@14
|
555
|
|
bos@14
|
556 While applying a hunk at an offset, or with a fuzz factor, will often
|
|
bos@14
|
557 be completely successful, these inexact techniques naturally leave
|
|
bos@14
|
558 open the possibility of corrupting the patched file. The most common
|
|
bos@14
|
559 cases typically involve applying a patch twice, or at an incorrect
|
|
bos@233
|
560 location in the file. If \command{patch} or \hgxcmd{mq}{qpush} ever
|
|
bos@14
|
561 mentions an offset or fuzz factor, you should make sure that the
|
|
bos@14
|
562 modified files are correct afterwards.
|
|
bos@14
|
563
|
|
bos@14
|
564 It's often a good idea to refresh a patch that has applied with an
|
|
bos@14
|
565 offset or fuzz factor; refreshing the patch generates new context
|
|
bos@14
|
566 information that will make it apply cleanly. I say ``often,'' not
|
|
bos@14
|
567 ``always,'' because sometimes refreshing a patch will make it fail to
|
|
bos@14
|
568 apply against a different revision of the underlying files. In some
|
|
bos@14
|
569 cases, such as when you're maintaining a patch that must sit on top of
|
|
bos@14
|
570 multiple versions of a source tree, it's acceptable to have a patch
|
|
bos@14
|
571 apply with some fuzz, provided you've verified the results of the
|
|
bos@14
|
572 patching process in such cases.
|
|
bos@14
|
573
|
|
bos@15
|
574 \subsection{Handling rejection}
|
|
bos@15
|
575
|
|
bos@233
|
576 If \hgxcmd{mq}{qpush} fails to apply a patch, it will print an error
|
|
bos@16
|
577 message and exit. If it has left \sfilename{.rej} files behind, it is
|
|
bos@15
|
578 usually best to fix up the rejected hunks before you push more patches
|
|
bos@15
|
579 or do any further work.
|
|
bos@15
|
580
|
|
bos@15
|
581 If your patch \emph{used to} apply cleanly, and no longer does because
|
|
bos@15
|
582 you've changed the underlying code that your patches are based on,
|
|
bos@17
|
583 Mercurial Queues can help; see section~\ref{sec:mq:merge} for details.
|
|
bos@15
|
584
|
|
bos@15
|
585 Unfortunately, there aren't any great techniques for dealing with
|
|
bos@16
|
586 rejected hunks. Most often, you'll need to view the \sfilename{.rej}
|
|
bos@15
|
587 file and edit the target file, applying the rejected hunks by hand.
|
|
bos@15
|
588
|
|
bos@16
|
589 If you're feeling adventurous, Neil Brown, a Linux kernel hacker,
|
|
bos@16
|
590 wrote a tool called \command{wiggle}~\cite{web:wiggle}, which is more
|
|
bos@16
|
591 vigorous than \command{patch} in its attempts to make a patch apply.
|
|
bos@15
|
592
|
|
bos@15
|
593 Another Linux kernel hacker, Chris Mason (the author of Mercurial
|
|
bos@254
|
594 Queues), wrote a similar tool called
|
|
bos@254
|
595 \command{mpatch}~\cite{web:mpatch}, which takes a simple approach to
|
|
bos@254
|
596 automating the application of hunks rejected by \command{patch}. The
|
|
bos@254
|
597 \command{mpatch} command can help with four common reasons that a hunk
|
|
bos@254
|
598 may be rejected:
|
|
bos@15
|
599
|
|
bos@15
|
600 \begin{itemize}
|
|
bos@15
|
601 \item The context in the middle of a hunk has changed.
|
|
bos@15
|
602 \item A hunk is missing some context at the beginning or end.
|
|
bos@18
|
603 \item A large hunk might apply better---either entirely or in
|
|
bos@18
|
604 part---if it was broken up into smaller hunks.
|
|
bos@15
|
605 \item A hunk removes lines with slightly different content than those
|
|
bos@15
|
606 currently present in the file.
|
|
bos@15
|
607 \end{itemize}
|
|
bos@15
|
608
|
|
bos@254
|
609 If you use \command{wiggle} or \command{mpatch}, you should be doubly
|
|
bos@55
|
610 careful to check your results when you're done. In fact,
|
|
bos@254
|
611 \command{mpatch} enforces this method of double-checking the tool's
|
|
bos@55
|
612 output, by automatically dropping you into a merge program when it has
|
|
bos@55
|
613 done its job, so that you can verify its work and finish off any
|
|
bos@55
|
614 remaining merges.
|
|
bos@15
|
615
|
|
bos@17
|
616 \section{Getting the best performance out of MQ}
|
|
bos@27
|
617 \label{sec:mq:perf}
|
|
bos@17
|
618
|
|
bos@17
|
619 MQ is very efficient at handling a large number of patches. I ran
|
|
bos@17
|
620 some performance experiments in mid-2006 for a talk that I gave at the
|
|
bos@17
|
621 2006 EuroPython conference~\cite{web:europython}. I used as my data
|
|
bos@17
|
622 set the Linux 2.6.17-mm1 patch series, which consists of 1,738
|
|
gb@66
|
623 patches. I applied these on top of a Linux kernel repository
|
|
bos@17
|
624 containing all 27,472 revisions between Linux 2.6.12-rc2 and Linux
|
|
bos@17
|
625 2.6.17.
|
|
bos@17
|
626
|
|
bos@17
|
627 On my old, slow laptop, I was able to
|
|
bos@234
|
628 \hgcmdargs{qpush}{\hgxopt{mq}{qpush}{-a}} all 1,738 patches in 3.5 minutes,
|
|
bos@234
|
629 and \hgcmdargs{qpop}{\hgxopt{mq}{qpop}{-a}} them all in 30 seconds. (On a
|
|
bos@50
|
630 newer laptop, the time to push all patches dropped to two minutes.) I
|
|
bos@233
|
631 could \hgxcmd{mq}{qrefresh} one of the biggest patches (which made 22,779
|
|
bos@17
|
632 lines of changes to 287 files) in 6.6 seconds.
|
|
bos@17
|
633
|
|
bos@17
|
634 Clearly, MQ is well suited to working in large trees, but there are a
|
|
bos@17
|
635 few tricks you can use to get the best performance of it.
|
|
bos@17
|
636
|
|
bos@17
|
637 First of all, try to ``batch'' operations together. Every time you
|
|
bos@233
|
638 run \hgxcmd{mq}{qpush} or \hgxcmd{mq}{qpop}, these commands scan the working
|
|
bos@17
|
639 directory once to make sure you haven't made some changes and then
|
|
bos@233
|
640 forgotten to run \hgxcmd{mq}{qrefresh}. On a small tree, the time that
|
|
bos@17
|
641 this scan takes is unnoticeable. However, on a medium-sized tree
|
|
bos@17
|
642 (containing tens of thousands of files), it can take a second or more.
|
|
bos@17
|
643
|
|
bos@233
|
644 The \hgxcmd{mq}{qpush} and \hgxcmd{mq}{qpop} commands allow you to push and pop
|
|
bos@17
|
645 multiple patches at a time. You can identify the ``destination
|
|
bos@233
|
646 patch'' that you want to end up at. When you \hgxcmd{mq}{qpush} with a
|
|
bos@17
|
647 destination specified, it will push patches until that patch is at the
|
|
bos@233
|
648 top of the applied stack. When you \hgxcmd{mq}{qpop} to a destination, MQ
|
|
bos@50
|
649 will pop patches until the destination patch is at the top.
|
|
bos@17
|
650
|
|
bos@17
|
651 You can identify a destination patch using either the name of the
|
|
bos@17
|
652 patch, or by number. If you use numeric addressing, patches are
|
|
bos@17
|
653 counted from zero; this means that the first patch is zero, the second
|
|
bos@17
|
654 is one, and so on.
|
|
bos@17
|
655
|
|
bos@15
|
656 \section{Updating your patches when the underlying code changes}
|
|
bos@15
|
657 \label{sec:mq:merge}
|
|
bos@15
|
658
|
|
bos@17
|
659 It's common to have a stack of patches on top of an underlying
|
|
bos@17
|
660 repository that you don't modify directly. If you're working on
|
|
bos@17
|
661 changes to third-party code, or on a feature that is taking longer to
|
|
bos@17
|
662 develop than the rate of change of the code beneath, you will often
|
|
bos@17
|
663 need to sync up with the underlying code, and fix up any hunks in your
|
|
bos@17
|
664 patches that no longer apply. This is called \emph{rebasing} your
|
|
bos@17
|
665 patch series.
|
|
bos@17
|
666
|
|
bos@234
|
667 The simplest way to do this is to \hgcmdargs{qpop}{\hgxopt{mq}{qpop}{-a}}
|
|
bos@17
|
668 your patches, then \hgcmd{pull} changes into the underlying
|
|
bos@234
|
669 repository, and finally \hgcmdargs{qpush}{\hgxopt{mq}{qpop}{-a}} your
|
|
bos@17
|
670 patches again. MQ will stop pushing any time it runs across a patch
|
|
bos@17
|
671 that fails to apply during conflicts, allowing you to fix your
|
|
bos@233
|
672 conflicts, \hgxcmd{mq}{qrefresh} the affected patch, and continue pushing
|
|
bos@17
|
673 until you have fixed your entire stack.
|
|
bos@17
|
674
|
|
bos@17
|
675 This approach is easy to use and works well if you don't expect
|
|
bos@17
|
676 changes to the underlying code to affect how well your patches apply.
|
|
bos@17
|
677 If your patch stack touches code that is modified frequently or
|
|
bos@17
|
678 invasively in the underlying repository, however, fixing up rejected
|
|
bos@17
|
679 hunks by hand quickly becomes tiresome.
|
|
bos@17
|
680
|
|
bos@17
|
681 It's possible to partially automate the rebasing process. If your
|
|
bos@17
|
682 patches apply cleanly against some revision of the underlying repo, MQ
|
|
bos@17
|
683 can use this information to help you to resolve conflicts between your
|
|
bos@17
|
684 patches and a different revision.
|
|
bos@17
|
685
|
|
bos@17
|
686 The process is a little involved.
|
|
bos@17
|
687 \begin{enumerate}
|
|
bos@17
|
688 \item To begin, \hgcmdargs{qpush}{-a} all of your patches on top of
|
|
bos@17
|
689 the revision where you know that they apply cleanly.
|
|
bos@17
|
690 \item Save a backup copy of your patch directory using
|
|
bos@234
|
691 \hgcmdargs{qsave}{\hgxopt{mq}{qsave}{-e} \hgxopt{mq}{qsave}{-c}}. This prints
|
|
bos@17
|
692 the name of the directory that it has saved the patches in. It will
|
|
bos@17
|
693 save the patches to a directory called
|
|
bos@17
|
694 \sdirname{.hg/patches.\emph{N}}, where \texttt{\emph{N}} is a small
|
|
bos@17
|
695 integer. It also commits a ``save changeset'' on top of your
|
|
bos@17
|
696 applied patches; this is for internal book-keeping, and records the
|
|
bos@17
|
697 states of the \sfilename{series} and \sfilename{status} files.
|
|
bos@17
|
698 \item Use \hgcmd{pull} to bring new changes into the underlying
|
|
bos@17
|
699 repository. (Don't run \hgcmdargs{pull}{-u}; see below for why.)
|
|
bos@17
|
700 \item Update to the new tip revision, using
|
|
bos@17
|
701 \hgcmdargs{update}{\hgopt{update}{-C}} to override the patches you
|
|
bos@17
|
702 have pushed.
|
|
bos@234
|
703 \item Merge all patches using \hgcmdargs{qpush}{\hgxopt{mq}{qpush}{-m}
|
|
bos@234
|
704 \hgxopt{mq}{qpush}{-a}}. The \hgxopt{mq}{qpush}{-m} option to \hgxcmd{mq}{qpush}
|
|
bos@17
|
705 tells MQ to perform a three-way merge if the patch fails to apply.
|
|
bos@17
|
706 \end{enumerate}
|
|
bos@17
|
707
|
|
bos@234
|
708 During the \hgcmdargs{qpush}{\hgxopt{mq}{qpush}{-m}}, each patch in the
|
|
bos@17
|
709 \sfilename{series} file is applied normally. If a patch applies with
|
|
bos@233
|
710 fuzz or rejects, MQ looks at the queue you \hgxcmd{mq}{qsave}d, and
|
|
bos@17
|
711 performs a three-way merge with the corresponding changeset. This
|
|
bos@17
|
712 merge uses Mercurial's normal merge machinery, so it may pop up a GUI
|
|
bos@17
|
713 merge tool to help you to resolve problems.
|
|
bos@17
|
714
|
|
bos@17
|
715 When you finish resolving the effects of a patch, MQ refreshes your
|
|
bos@17
|
716 patch based on the result of the merge.
|
|
bos@17
|
717
|
|
bos@17
|
718 At the end of this process, your repository will have one extra head
|
|
bos@17
|
719 from the old patch queue, and a copy of the old patch queue will be in
|
|
bos@17
|
720 \sdirname{.hg/patches.\emph{N}}. You can remove the extra head using
|
|
bos@234
|
721 \hgcmdargs{qpop}{\hgxopt{mq}{qpop}{-a} \hgxopt{mq}{qpop}{-n} patches.\emph{N}}
|
|
bos@17
|
722 or \hgcmd{strip}. You can delete \sdirname{.hg/patches.\emph{N}} once
|
|
bos@17
|
723 you are sure that you no longer need it as a backup.
|
|
bos@13
|
724
|
|
bos@50
|
725 \section{Identifying patches}
|
|
bos@50
|
726
|
|
bos@50
|
727 MQ commands that work with patches let you refer to a patch either by
|
|
bos@50
|
728 using its name or by a number. By name is obvious enough; pass the
|
|
bos@233
|
729 name \filename{foo.patch} to \hgxcmd{mq}{qpush}, for example, and it will
|
|
bos@55
|
730 push patches until \filename{foo.patch} is applied.
|
|
bos@55
|
731
|
|
bos@55
|
732 As a shortcut, you can refer to a patch using both a name and a
|
|
bos@55
|
733 numeric offset; \texttt{foo.patch-2} means ``two patches before
|
|
bos@55
|
734 \texttt{foo.patch}'', while \texttt{bar.patch+4} means ``four patches
|
|
bos@55
|
735 after \texttt{bar.patch}''.
|
|
bos@50
|
736
|
|
bos@50
|
737 Referring to a patch by index isn't much different. The first patch
|
|
bos@233
|
738 printed in the output of \hgxcmd{mq}{qseries} is patch zero (yes, it's one
|
|
bos@50
|
739 of those start-at-zero counting systems); the second is patch one; and
|
|
bos@50
|
740 so on
|
|
bos@50
|
741
|
|
bos@50
|
742 MQ also makes it easy to work with patches when you are using normal
|
|
bos@50
|
743 Mercurial commands. Every command that accepts a changeset ID will
|
|
bos@50
|
744 also accept the name of an applied patch. MQ augments the tags
|
|
bos@50
|
745 normally in the repository with an eponymous one for each applied
|
|
bos@50
|
746 patch. In addition, the special tags \index{tags!special tag
|
|
bos@50
|
747 names!\texttt{qbase}}\texttt{qbase} and \index{tags!special tag
|
|
bos@50
|
748 names!\texttt{qtip}}\texttt{qtip} identify the ``bottom-most'' and
|
|
bos@50
|
749 topmost applied patches, respectively.
|
|
bos@50
|
750
|
|
bos@50
|
751 These additions to Mercurial's normal tagging capabilities make
|
|
bos@50
|
752 dealing with patches even more of a breeze.
|
|
bos@50
|
753 \begin{itemize}
|
|
bos@50
|
754 \item Want to patchbomb a mailing list with your latest series of
|
|
bos@50
|
755 changes?
|
|
bos@50
|
756 \begin{codesample4}
|
|
bos@50
|
757 hg email qbase:qtip
|
|
bos@50
|
758 \end{codesample4}
|
|
bos@231
|
759 (Don't know what ``patchbombing'' is? See
|
|
bos@231
|
760 section~\ref{sec:hgext:patchbomb}.)
|
|
bos@50
|
761 \item Need to see all of the patches since \texttt{foo.patch} that
|
|
bos@50
|
762 have touched files in a subdirectory of your tree?
|
|
bos@50
|
763 \begin{codesample4}
|
|
bos@50
|
764 hg log -r foo.patch:qtip \emph{subdir}
|
|
bos@50
|
765 \end{codesample4}
|
|
bos@50
|
766 \end{itemize}
|
|
bos@50
|
767
|
|
bos@50
|
768 Because MQ makes the names of patches available to the rest of
|
|
bos@50
|
769 Mercurial through its normal internal tag machinery, you don't need to
|
|
bos@50
|
770 type in the entire name of a patch when you want to identify it by
|
|
bos@50
|
771 name.
|
|
bos@50
|
772
|
|
bos@50
|
773 \begin{figure}[ht]
|
|
bos@155
|
774 \interaction{mq.id.output}
|
|
bos@50
|
775 \caption{Using MQ's tag features to work with patches}
|
|
bos@50
|
776 \label{ex:mq:id}
|
|
bos@50
|
777 \end{figure}
|
|
bos@50
|
778
|
|
bos@50
|
779 Another nice consequence of representing patch names as tags is that
|
|
bos@50
|
780 when you run the \hgcmd{log} command, it will display a patch's name
|
|
bos@50
|
781 as a tag, simply as part of its normal output. This makes it easy to
|
|
bos@50
|
782 visually distinguish applied patches from underlying ``normal''
|
|
bos@50
|
783 revisions. Figure~\ref{ex:mq:id} shows a few normal Mercurial
|
|
bos@50
|
784 commands in use with applied patches.
|
|
bos@50
|
785
|
|
bos@26
|
786 \section{Useful things to know about}
|
|
bos@26
|
787
|
|
bos@26
|
788 There are a number of aspects of MQ usage that don't fit tidily into
|
|
bos@26
|
789 sections of their own, but that are good to know. Here they are, in
|
|
bos@26
|
790 one place.
|
|
bos@26
|
791
|
|
bos@26
|
792 \begin{itemize}
|
|
bos@233
|
793 \item Normally, when you \hgxcmd{mq}{qpop} a patch and \hgxcmd{mq}{qpush} it
|
|
bos@26
|
794 again, the changeset that represents the patch after the pop/push
|
|
bos@26
|
795 will have a \emph{different identity} than the changeset that
|
|
bos@224
|
796 represented the hash beforehand. See
|
|
bos@224
|
797 section~\ref{sec:mqref:cmd:qpush} for information as to why this is.
|
|
bos@26
|
798 \item It's not a good idea to \hgcmd{merge} changes from another
|
|
bos@26
|
799 branch with a patch changeset, at least if you want to maintain the
|
|
bos@26
|
800 ``patchiness'' of that changeset and changesets below it on the
|
|
bos@26
|
801 patch stack. If you try to do this, it will appear to succeed, but
|
|
bos@26
|
802 MQ will become confused.
|
|
bos@26
|
803 \end{itemize}
|
|
bos@50
|
804
|
|
bos@16
|
805 \section{Managing patches in a repository}
|
|
bos@106
|
806 \label{sec:mq:repo}
|
|
bos@16
|
807
|
|
bos@16
|
808 Because MQ's \sdirname{.hg/patches} directory resides outside a
|
|
bos@16
|
809 Mercurial repository's working directory, the ``underlying'' Mercurial
|
|
bos@16
|
810 repository knows nothing about the management or presence of patches.
|
|
bos@16
|
811
|
|
bos@16
|
812 This presents the interesting possibility of managing the contents of
|
|
bos@16
|
813 the patch directory as a Mercurial repository in its own right. This
|
|
bos@16
|
814 can be a useful way to work. For example, you can work on a patch for
|
|
bos@233
|
815 a while, \hgxcmd{mq}{qrefresh} it, then \hgcmd{commit} the current state of
|
|
bos@16
|
816 the patch. This lets you ``roll back'' to that version of the patch
|
|
bos@16
|
817 later on.
|
|
bos@16
|
818
|
|
bos@26
|
819 You can then share different versions of the same patch stack among
|
|
bos@26
|
820 multiple underlying repositories. I use this when I am developing a
|
|
bos@26
|
821 Linux kernel feature. I have a pristine copy of my kernel sources for
|
|
bos@26
|
822 each of several CPU architectures, and a cloned repository under each
|
|
bos@26
|
823 that contains the patches I am working on. When I want to test a
|
|
bos@26
|
824 change on a different architecture, I push my current patches to the
|
|
bos@26
|
825 patch repository associated with that kernel tree, pop and push all of
|
|
bos@26
|
826 my patches, and build and test that kernel.
|
|
bos@16
|
827
|
|
bos@16
|
828 Managing patches in a repository makes it possible for multiple
|
|
bos@16
|
829 developers to work on the same patch series without colliding with
|
|
bos@16
|
830 each other, all on top of an underlying source base that they may or
|
|
bos@16
|
831 may not control.
|
|
bos@16
|
832
|
|
bos@17
|
833 \subsection{MQ support for patch repositories}
|
|
bos@16
|
834
|
|
bos@16
|
835 MQ helps you to work with the \sdirname{.hg/patches} directory as a
|
|
bos@16
|
836 repository; when you prepare a repository for working with patches
|
|
bos@234
|
837 using \hgxcmd{mq}{qinit}, you can pass the \hgxopt{mq}{qinit}{-c} option to
|
|
bos@16
|
838 create the \sdirname{.hg/patches} directory as a Mercurial repository.
|
|
bos@16
|
839
|
|
bos@16
|
840 \begin{note}
|
|
bos@234
|
841 If you forget to use the \hgxopt{mq}{qinit}{-c} option, you can simply go
|
|
bos@16
|
842 into the \sdirname{.hg/patches} directory at any time and run
|
|
bos@16
|
843 \hgcmd{init}. Don't forget to add an entry for the
|
|
bos@17
|
844 \sfilename{status} file to the \sfilename{.hgignore} file, though
|
|
bos@104
|
845
|
|
bos@234
|
846 (\hgcmdargs{qinit}{\hgxopt{mq}{qinit}{-c}} does this for you
|
|
bos@17
|
847 automatically); you \emph{really} don't want to manage the
|
|
bos@17
|
848 \sfilename{status} file.
|
|
bos@16
|
849 \end{note}
|
|
bos@16
|
850
|
|
bos@16
|
851 As a convenience, if MQ notices that the \dirname{.hg/patches}
|
|
bos@16
|
852 directory is a repository, it will automatically \hgcmd{add} every
|
|
bos@16
|
853 patch that you create and import.
|
|
bos@16
|
854
|
|
bos@233
|
855 Finally, MQ provides a shortcut command, \hgxcmd{mq}{qcommit}, that runs
|
|
bos@16
|
856 \hgcmd{commit} in the \sdirname{.hg/patches} directory. This saves
|
|
bos@16
|
857 some cumbersome typing.
|
|
bos@16
|
858
|
|
bos@16
|
859 \subsection{A few things to watch out for}
|
|
bos@16
|
860
|
|
bos@16
|
861 MQ's support for working with a repository full of patches is limited
|
|
bos@16
|
862 in a few small respects.
|
|
bos@16
|
863
|
|
bos@16
|
864 MQ cannot automatically detect changes that you make to the patch
|
|
bos@16
|
865 directory. If you \hgcmd{pull}, manually edit, or \hgcmd{update}
|
|
bos@16
|
866 changes to patches or the \sfilename{series} file, you will have to
|
|
bos@234
|
867 \hgcmdargs{qpop}{\hgxopt{mq}{qpop}{-a}} and then
|
|
bos@234
|
868 \hgcmdargs{qpush}{\hgxopt{mq}{qpush}{-a}} in the underlying repository to
|
|
bos@17
|
869 see those changes show up there. If you forget to do this, you can
|
|
bos@17
|
870 confuse MQ's idea of which patches are applied.
|
|
bos@16
|
871
|
|
bos@26
|
872 \section{Third party tools for working with patches}
|
|
bos@19
|
873 \label{sec:mq:tools}
|
|
bos@16
|
874
|
|
bos@16
|
875 Once you've been working with patches for a while, you'll find
|
|
bos@16
|
876 yourself hungry for tools that will help you to understand and
|
|
bos@16
|
877 manipulate the patches you're dealing with.
|
|
bos@16
|
878
|
|
bos@16
|
879 The \command{diffstat} command~\cite{web:diffstat} generates a
|
|
bos@16
|
880 histogram of the modifications made to each file in a patch. It
|
|
bos@18
|
881 provides a good way to ``get a sense of'' a patch---which files it
|
|
bos@16
|
882 affects, and how much change it introduces to each file and as a
|
|
bos@16
|
883 whole. (I find that it's a good idea to use \command{diffstat}'s
|
|
bos@241
|
884 \cmdopt{diffstat}{-p} option as a matter of course, as otherwise it
|
|
bos@241
|
885 will try to do clever things with prefixes of file names that
|
|
bos@241
|
886 inevitably confuse at least me.)
|
|
bos@16
|
887
|
|
bos@19
|
888 \begin{figure}[ht]
|
|
bos@19
|
889 \interaction{mq.tools.tools}
|
|
bos@19
|
890 \caption{The \command{diffstat}, \command{filterdiff}, and \command{lsdiff} commands}
|
|
bos@19
|
891 \label{ex:mq:tools}
|
|
bos@19
|
892 \end{figure}
|
|
bos@19
|
893
|
|
bos@16
|
894 The \package{patchutils} package~\cite{web:patchutils} is invaluable.
|
|
bos@16
|
895 It provides a set of small utilities that follow the ``Unix
|
|
bos@16
|
896 philosophy;'' each does one useful thing with a patch. The
|
|
bos@16
|
897 \package{patchutils} command I use most is \command{filterdiff}, which
|
|
bos@16
|
898 extracts subsets from a patch file. For example, given a patch that
|
|
bos@16
|
899 modifies hundreds of files across dozens of directories, a single
|
|
bos@16
|
900 invocation of \command{filterdiff} can generate a smaller patch that
|
|
bos@106
|
901 only touches files whose names match a particular glob pattern. See
|
|
bos@106
|
902 section~\ref{mq-collab:tips:interdiff} for another example.
|
|
bos@16
|
903
|
|
bos@19
|
904 \section{Good ways to work with patches}
|
|
bos@19
|
905
|
|
bos@19
|
906 Whether you are working on a patch series to submit to a free software
|
|
bos@19
|
907 or open source project, or a series that you intend to treat as a
|
|
bos@19
|
908 sequence of regular changesets when you're done, you can use some
|
|
bos@19
|
909 simple techniques to keep your work well organised.
|
|
bos@19
|
910
|
|
bos@19
|
911 Give your patches descriptive names. A good name for a patch might be
|
|
bos@19
|
912 \filename{rework-device-alloc.patch}, because it will immediately give
|
|
bos@19
|
913 you a hint what the purpose of the patch is. Long names shouldn't be
|
|
bos@19
|
914 a problem; you won't be typing the names often, but you \emph{will} be
|
|
bos@233
|
915 running commands like \hgxcmd{mq}{qapplied} and \hgxcmd{mq}{qtop} over and over.
|
|
bos@19
|
916 Good naming becomes especially important when you have a number of
|
|
bos@19
|
917 patches to work with, or if you are juggling a number of different
|
|
bos@19
|
918 tasks and your patches only get a fraction of your attention.
|
|
bos@19
|
919
|
|
bos@233
|
920 Be aware of what patch you're working on. Use the \hgxcmd{mq}{qtop}
|
|
bos@19
|
921 command and skim over the text of your patches frequently---for
|
|
bos@19
|
922 example, using \hgcmdargs{tip}{\hgopt{tip}{-p}})---to be sure of where
|
|
bos@233
|
923 you stand. I have several times worked on and \hgxcmd{mq}{qrefresh}ed a
|
|
bos@19
|
924 patch other than the one I intended, and it's often tricky to migrate
|
|
bos@19
|
925 changes into the right patch after making them in the wrong one.
|
|
bos@19
|
926
|
|
bos@19
|
927 For this reason, it is very much worth investing a little time to
|
|
bos@19
|
928 learn how to use some of the third-party tools I described in
|
|
bos@19
|
929 section~\ref{sec:mq:tools}, particularly \command{diffstat} and
|
|
bos@19
|
930 \command{filterdiff}. The former will give you a quick idea of what
|
|
bos@19
|
931 changes your patch is making, while the latter makes it easy to splice
|
|
bos@19
|
932 hunks selectively out of one patch and into another.
|
|
bos@19
|
933
|
|
bos@19
|
934 \section{MQ cookbook}
|
|
bos@19
|
935
|
|
bos@19
|
936 \subsection{Manage ``trivial'' patches}
|
|
bos@19
|
937
|
|
bos@19
|
938 Because the overhead of dropping files into a new Mercurial repository
|
|
bos@19
|
939 is so low, it makes a lot of sense to manage patches this way even if
|
|
bos@19
|
940 you simply want to make a few changes to a source tarball that you
|
|
bos@19
|
941 downloaded.
|
|
bos@19
|
942
|
|
bos@19
|
943 Begin by downloading and unpacking the source tarball,
|
|
bos@19
|
944 and turning it into a Mercurial repository.
|
|
bos@19
|
945 \interaction{mq.tarball.download}
|
|
bos@19
|
946
|
|
bos@19
|
947 Continue by creating a patch stack and making your changes.
|
|
bos@19
|
948 \interaction{mq.tarball.qinit}
|
|
bos@19
|
949
|
|
bos@19
|
950 Let's say a few weeks or months pass, and your package author releases
|
|
bos@19
|
951 a new version. First, bring their changes into the repository.
|
|
bos@19
|
952 \interaction{mq.tarball.newsource}
|
|
bos@19
|
953 The pipeline starting with \hgcmd{locate} above deletes all files in
|
|
bos@19
|
954 the working directory, so that \hgcmd{commit}'s
|
|
bos@19
|
955 \hgopt{commit}{--addremove} option can actually tell which files have
|
|
bos@19
|
956 really been removed in the newer version of the source.
|
|
bos@19
|
957
|
|
bos@19
|
958 Finally, you can apply your patches on top of the new tree.
|
|
bos@19
|
959 \interaction{mq.tarball.repush}
|
|
bos@19
|
960
|
|
bos@19
|
961 \subsection{Combining entire patches}
|
|
bos@19
|
962 \label{sec:mq:combine}
|
|
bos@19
|
963
|
|
bos@233
|
964 MQ provides a command, \hgxcmd{mq}{qfold} that lets you combine entire
|
|
bos@55
|
965 patches. This ``folds'' the patches you name, in the order you name
|
|
bos@55
|
966 them, into the topmost applied patch, and concatenates their
|
|
bos@55
|
967 descriptions onto the end of its description. The patches that you
|
|
bos@55
|
968 fold must be unapplied before you fold them.
|
|
bos@55
|
969
|
|
bos@55
|
970 The order in which you fold patches matters. If your topmost applied
|
|
bos@233
|
971 patch is \texttt{foo}, and you \hgxcmd{mq}{qfold} \texttt{bar} and
|
|
bos@55
|
972 \texttt{quux} into it, you will end up with a patch that has the same
|
|
bos@55
|
973 effect as if you applied first \texttt{foo}, then \texttt{bar},
|
|
bos@55
|
974 followed by \texttt{quux}.
|
|
bos@19
|
975
|
|
bos@19
|
976 \subsection{Merging part of one patch into another}
|
|
bos@19
|
977
|
|
bos@19
|
978 Merging \emph{part} of one patch into another is more difficult than
|
|
bos@19
|
979 combining entire patches.
|
|
bos@19
|
980
|
|
bos@19
|
981 If you want to move changes to entire files, you can use
|
|
bos@19
|
982 \command{filterdiff}'s \cmdopt{filterdiff}{-i} and
|
|
bos@19
|
983 \cmdopt{filterdiff}{-x} options to choose the modifications to snip
|
|
bos@19
|
984 out of one patch, concatenating its output onto the end of the patch
|
|
bos@19
|
985 you want to merge into. You usually won't need to modify the patch
|
|
bos@19
|
986 you've merged the changes from. Instead, MQ will report some rejected
|
|
bos@233
|
987 hunks when you \hgxcmd{mq}{qpush} it (from the hunks you moved into the
|
|
bos@233
|
988 other patch), and you can simply \hgxcmd{mq}{qrefresh} the patch to drop
|
|
bos@19
|
989 the duplicate hunks.
|
|
bos@19
|
990
|
|
bos@19
|
991 If you have a patch that has multiple hunks modifying a file, and you
|
|
bos@19
|
992 only want to move a few of those hunks, the job becomes more messy,
|
|
bos@19
|
993 but you can still partly automate it. Use \cmdargs{lsdiff}{-nvv} to
|
|
bos@19
|
994 print some metadata about the patch.
|
|
bos@19
|
995 \interaction{mq.tools.lsdiff}
|
|
bos@19
|
996
|
|
bos@19
|
997 This command prints three different kinds of number:
|
|
bos@19
|
998 \begin{itemize}
|
|
bos@26
|
999 \item (in the first column) a \emph{file number} to identify each file
|
|
bos@26
|
1000 modified in the patch;
|
|
bos@26
|
1001 \item (on the next line, indented) the line number within a modified
|
|
bos@26
|
1002 file where a hunk starts; and
|
|
bos@26
|
1003 \item (on the same line) a \emph{hunk number} to identify that hunk.
|
|
bos@19
|
1004 \end{itemize}
|
|
bos@19
|
1005
|
|
bos@19
|
1006 You'll have to use some visual inspection, and reading of the patch,
|
|
bos@19
|
1007 to identify the file and hunk numbers you'll want, but you can then
|
|
bos@19
|
1008 pass them to to \command{filterdiff}'s \cmdopt{filterdiff}{--files}
|
|
bos@19
|
1009 and \cmdopt{filterdiff}{--hunks} options, to select exactly the file
|
|
bos@19
|
1010 and hunk you want to extract.
|
|
bos@19
|
1011
|
|
bos@19
|
1012 Once you have this hunk, you can concatenate it onto the end of your
|
|
bos@19
|
1013 destination patch and continue with the remainder of
|
|
bos@19
|
1014 section~\ref{sec:mq:combine}.
|
|
bos@26
|
1015
|
|
bos@26
|
1016 \section{Differences between quilt and MQ}
|
|
bos@26
|
1017
|
|
bos@26
|
1018 If you are already familiar with quilt, MQ provides a similar command
|
|
bos@26
|
1019 set. There are a few differences in the way that it works.
|
|
bos@26
|
1020
|
|
bos@26
|
1021 You will already have noticed that most quilt commands have MQ
|
|
bos@26
|
1022 counterparts that simply begin with a ``\texttt{q}''. The exceptions
|
|
bos@26
|
1023 are quilt's \texttt{add} and \texttt{remove} commands, the
|
|
bos@26
|
1024 counterparts for which are the normal Mercurial \hgcmd{add} and
|
|
bos@26
|
1025 \hgcmd{remove} commands. There is no MQ equivalent of the quilt
|
|
bos@26
|
1026 \texttt{edit} command.
|
|
bos@50
|
1027
|
|
bos@1
|
1028 %%% Local Variables:
|
|
bos@1
|
1029 %%% mode: latex
|
|
bos@1
|
1030 %%% TeX-master: "00book"
|
|
bos@1
|
1031 %%% End:
|
