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1 \chapter{Customising the output of Mercurial}
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2 \label{chap:template}
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3
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4 Mercurial provides a powerful mechanism to let you control how it
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5 displays information. The mechanism is based on templates. You can
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6 use templates to generate specific output for a single command, or to
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7 customise the entire appearance of the built-in web interface.
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8
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9 \section{Using precanned output styles}
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10 \label{sec:style}
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11
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12 Packaged with Mercurial are some output styles that you can use
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13 immediately. A style is simply a precanned template that someone
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14 wrote and installed somewhere that Mercurial can find.
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15
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16 Before we take a look at Mercurial's bundled styles, let's review its
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17 normal output.
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18
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19 \interaction{template.simple.normal}
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20
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21 This is somewhat informative, but it takes up a lot of space---five
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22 lines of output per changeset. The \texttt{compact} style reduces
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23 this to three lines, presented in a sparse manner.
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24
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25 \interaction{template.simple.compact}
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26
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27 The \texttt{changelog} style hints at the expressive power of
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28 Mercurial's templating engine. This style attempts to follow the GNU
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29 Project's changelog guidelines\cite{web:changelog}.
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30
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31 \interaction{template.simple.changelog}
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32
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33 You will not be shocked to learn that Mercurial's default output style
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34 is named \texttt{default}.
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35
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36 \subsection{Setting a default style}
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37
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38 You can modify the output style that Mercurial will use for every
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39 command by editing your \hgrc\ file, naming the style you would
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40 prefer to use.
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41
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42 \begin{codesample2}
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43 [ui]
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44 style = compact
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45 \end{codesample2}
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46
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47 If you write a style of your own, you can use it by either providing
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48 the path to your style file, or copying your style file into a
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49 location where Mercurial can find it (typically the \texttt{templates}
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50 subdirectory of your Mercurial install directory).
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51
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52 \section{Commands that support styles and templates}
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53
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54 All of Mercurial's ``\texttt{log}-like'' commands let you use styles
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55 and templates: \hgcmd{incoming}, \hgcmd{log}, \hgcmd{outgoing}, and
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56 \hgcmd{tip}.
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57
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58 As I write this manual, these are so far the only commands that
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59 support styles and templates. Since these are the most important
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60 commands that need customisable output, there has been little pressure
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61 from the Mercurial user community to add style and template support to
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62 other commands.
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63
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64 \section{The basics of templating}
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65
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66 At its simplest, a Mercurial template is a piece of text. Some of the
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67 text never changes, while other parts are \emph{expanded}, or replaced
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68 with new text, when necessary.
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69
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70 Before we continue, let's look again at a simple example of
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71 Mercurial's normal output.
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72
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73 \interaction{template.simple.normal}
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74
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75 Now, let's run the same command, but using a template to change its
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76 output.
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77
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78 \interaction{template.simple.simplest}
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79
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80 The example above illustrates the simplest possible template; it's
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81 just a piece of static text, printed once for each changeset. The
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82 \hgopt{log}{--template} option to the \hgcmd{log} command tells
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83 Mercurial to use the given text as the template when printing each
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84 changeset.
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85
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86 Notice that the template string above ends with the text
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87 ``\Verb+\n+''. This is an \emph{escape sequence}, telling Mercurial
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88 to print a newline at the end of each template item. If you omit this
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89 newline, Mercurial will run each piece of output together. See
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90 section~\ref{sec:template:escape} for more details of escape sequences.
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91
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92 A template that prints a fixed string of text all the time isn't very
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93 useful; let's try something a bit more complex.
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94
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95 \interaction{template.simple.simplesub}
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96
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97 As you can see, the string ``\Verb+{desc}+'' in the template has been
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98 replaced in the output with the description of each changeset. Every
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99 time Mercurial finds text enclosed in curly braces (``\texttt{\{}''
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100 and ``\texttt{\}}''), it will try to replace the braces and text with
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101 the expansion of whatever is inside. To print a literal curly brace,
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102 you must escape it, as described in section~\ref{sec:template:escape}.
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103
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104 \section{Common template keywords}
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105 \label{sec:template:keyword}
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106
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107 You can start writing simple templates immediately using the keywords
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108 below.
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109
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110 \begin{itemize}
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111 \item[\tplkword{author}] String. The unmodified author of the changeset.
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112 \item[\tplkword{branches}] String. The name of the branch on which
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113 the changeset was committed. Will be empty if the branch name was
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114 \texttt{default}.
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115 \item[\tplkword{date}] Date information. The date when the changeset
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116 was committed. This is \emph{not} human-readable; you must pass it
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117 through a filter that will render it appropriately. See
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118 section~\ref{sec:template:filter} for more information on filters.
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119 The date is expressed as a pair of numbers. The first number is a
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120 Unix UTC timestamp (seconds since January 1, 1970); the second is
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121 the offset of the committer's timezone from UTC, in seconds.
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122 \item[\tplkword{desc}] String. The text of the changeset description.
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123 \item[\tplkword{files}] List of strings. All files modified, added, or
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124 removed by this changeset.
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125 \item[\tplkword{file\_adds}] List of strings. Files added by this
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126 changeset.
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127 \item[\tplkword{file\_dels}] List of strings. Files removed by this
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128 changeset.
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129 \item[\tplkword{node}] String. The changeset identification hash, as a
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130 40-character hexadecimal string.
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131 \item[\tplkword{parents}] List of strings. The parents of the
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132 changeset.
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133 \item[\tplkword{rev}] Integer. The repository-local changeset revision
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134 number.
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135 \item[\tplkword{tags}] List of strings. Any tags associated with the
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136 changeset.
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137 \end{itemize}
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138
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139 A few simple experiments will show us what to expect when we use these
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140 keywords; you can see the results in
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141 figure~\ref{fig:template:keywords}.
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142
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143 \begin{figure}
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144 \interaction{template.simple.keywords}
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145 \caption{Template keywords in use}
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146 \label{fig:template:keywords}
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147 \end{figure}
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148
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149 As we noted above, the date keyword does not produce human-readable
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150 output, so we must treat it specially. This involves using a
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151 \emph{filter}, about which more in section~\ref{sec:template:filter}.
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152
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153 \interaction{template.simple.datekeyword}
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154
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155 \section{Escape sequences}
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156 \label{sec:template:escape}
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157
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158 Mercurial's templating engine recognises the most commonly used escape
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159 sequences in strings. When it sees a backslash (``\Verb+\+'')
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160 character, it looks at the following character and substitutes the two
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161 characters with a single replacement, as described below.
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162
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163 \begin{itemize}
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164 \item[\Verb+\textbackslash\textbackslash+] Backslash, ``\Verb+\+'',
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165 ASCII~134.
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166 \item[\Verb+\textbackslash n+] Newline, ASCII~12.
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167 \item[\Verb+\textbackslash r+] Carriage return, ASCII~15.
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168 \item[\Verb+\textbackslash t+] Tab, ASCII~11.
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169 \item[\Verb+\textbackslash v+] Vertical tab, ASCII~13.
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170 \item[\Verb+\textbackslash \{+] Open curly brace, ``\Verb+{+'', ASCII~173.
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171 \item[\Verb+\textbackslash \}+] Close curly brace, ``\Verb+}+'', ASCII~175.
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172 \end{itemize}
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173
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174 As indicated above, if you want the expansion of a template to contain
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175 a literal ``\Verb+\+'', ``\Verb+{+'', or ``\Verb+{+'' character, you
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176 must escape it.
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177
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178 \section{Filtering keywords to change their results}
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179 \label{sec:template:filter}
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180
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181 Some of the results of template expansion are not immediately easy to
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182 use. Mercurial lets you specify an optional chain of \emph{filters}
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183 to modify the result of expanding a keyword. You have already seen a
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184 common filter, \tplkwfilt{date}{isodate}, in action above, to make a
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185 date readable.
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186
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187 Below is a list of the most commonly used filters that Mercurial
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188 supports. While some filters can be applied to any text, others can
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189 only be used in specific circumstances. The name of each filter is
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190 followed first by an indication of where it can be used, then a
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191 description of its effect.
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192
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193 \begin{itemize}
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194 \item[\tplfilter{addbreaks}] Any text. Add an XHTML ``\Verb+<br/>+''
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195 tag before the end of every line except the last. For example,
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196 ``\Verb+foo\nbar+'' becomes ``\Verb+foo<br/>\nbar+''.
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197 \item[\tplkwfilt{date}{age}] \tplkword{date} keyword. Render the
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198 age of the date, relative to the current time. Yields a string like
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199 ``\Verb+10 minutes+''.
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200 \item[\tplfilter{basename}] Any text, but most useful for the
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201 \tplkword{files} keyword and its relatives. Treat the text as a
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202 path, and return the basename. For example, ``\Verb+foo/bar/baz+''
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203 becomes ``\Verb+baz+''.
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204 \item[\tplkwfilt{date}{date}] \tplkword{date} keyword. Render a date
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205 in a similar format to the Unix \tplkword{date} command, but with
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206 timezone included. Yields a string like
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207 ``\Verb+Mon Sep 04 15:13:13 2006 -0700+''.
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208 \item[\tplkwfilt{author}{domain}] Any text, but most useful for the
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209 \tplkword{author} keyword. Finds the first string that looks like
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210 an email address, and extract just the domain component. For
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211 example, ``\Verb+Bryan O'Sullivan <bos@serpentine.com>+'' becomes
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212 ``\Verb+serpentine.com+''.
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213 \item[\tplkwfilt{author}{email}] Any text, but most useful for the
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214 \tplkword{author} keyword. Extract the first string that looks like
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215 an email address. For example,
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216 ``\Verb+Bryan O'Sullivan <bos@serpentine.com>+'' becomes
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217 ``\Verb+bos@serpentine.com+''.
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218 \item[\tplfilter{escape}] Any text. Replace the special XML/XHTML
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219 characters ``\Verb+&+'', ``\Verb+<+'' and ``\Verb+>+'' with
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220 XML entities.
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221 \item[\tplfilter{fill68}] Any text. Wrap the text to fit in 68
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222 columns. This is useful before you pass text through the
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223 \tplfilter{tabindent} filter, and still want it to fit in an
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224 80-column fixed-font window.
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225 \item[\tplfilter{fill76}] Any text. Wrap the text to fit in 76
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226 columns.
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227 \item[\tplfilter{firstline}] Any text. Yield the first line of text,
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228 without any trailing newlines.
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229 \item[\tplkwfilt{date}{hgdate}] \tplkword{date} keyword. Render the
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230 date as a pair of readable numbers. Yields a string like
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231 ``\Verb+1157407993 25200+''.
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232 \item[\tplkwfilt{date}{isodate}] \tplkword{date} keyword. Render the
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233 date as a text string in ISO~8601 format. Yields a string like
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234 ``\Verb+2006-09-04 15:13:13 -0700+''.
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235 \item[\tplfilter{obfuscate}] Any text, but most useful for the
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236 \tplkword{author} keyword. Yield the input text rendered as a
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237 sequence of XML entities. This helps to defeat some particularly
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238 stupid screen-scraping email harvesting spambots.
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239 \item[\tplkwfilt{author}{person}] Any text, but most useful for the
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240 \tplkword{author} keyword. Yield the text before an email address.
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241 For example, ``\Verb+Bryan O'Sullivan <bos@serpentine.com>+''
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242 becomes ``\Verb+Bryan O'Sullivan+''.
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243 \item[\tplkwfilt{date}{rfc822date}] \tplkword{date} keyword. Render a
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244 date using the same format used in email headers. Yields a string
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245 like ``\Verb+Mon, 04 Sep 2006 15:13:13 -0700+''.
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246 \item[\tplkwfilt{node}{short}] Changeset hash. Yield the short form
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247 of a changeset hash, i.e.~a 12-byte hexadecimal string.
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248 \item[\tplkwfilt{date}{shortdate}] \tplkword{date} keyword. Render
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249 the year, month, and day of the date. Yields a string like
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250 ``\Verb+2006-09-04+''.
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251 \item[\tplfilter{strip}] Any text. Strip all leading and trailing
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252 whitespace from the string.
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253 \item[\tplfilter{tabindent}] Any text. Yield the text, with every line
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254 except the first starting with a tab character.
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255 \item[\tplfilter{urlescape}] Any text. Escape all characters that are
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256 considered ``special'' by URL parsers. For example, \Verb+foo bar+
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257 becomes \Verb+foo%20bar+.
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258 \item[\tplkwfilt{author}{user}] Any text, but most useful for the
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259 \tplkword{author} keyword. Return the ``user'' portion of an email
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260 address. For example,
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261 ``\Verb+Bryan O'Sullivan <bos@serpentine.com>+'' becomes
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262 ``\Verb+bos+''.
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263 \end{itemize}
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264
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265 \begin{figure}
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266 \interaction{template.simple.manyfilters}
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267 \caption{Template filters in action}
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268 \label{fig:template:filters}
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269 \end{figure}
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270
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271 \begin{note}
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272 If you try to apply a filter to a piece of data that it cannot
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273 process, Mercurial will fail and print a Python exception. For
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274 example, trying to run the output of the \tplkword{desc} keyword
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275 into the \tplkwfilt{date}{isodate} filter is not a good idea.
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276 \end{note}
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277
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278 \subsection{Combining filters}
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279
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280 It is easy to combine filters to yield output in the form you would
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281 like. The following chain of filters tidies up a description, then
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282 makes sure that it fits cleanly into 68 columns, then indents it by a
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283 further 8~characters (at least on Unix-like systems, where a tab is
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284 conventionally 8~characters wide).
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285
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286 \interaction{template.simple.combine}
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287
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288 Note the use of ``\Verb+\t+'' (a tab character) in the template to
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289 force the first line to be indented; this is necessary since
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290 \tplkword{tabindent} indents all lines \emph{except} the first.
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291
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292 Keep in mind that the order of filters in a chain is significant. The
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293 first filter is applied to the result of the keyword; the second to
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294 the result of the first filter; and so on. For example, using
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295 \Verb+fill68|tabindent+ gives very different results from
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296 \Verb+tabindent|fill68+.
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297
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298
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299 \section{From templates to styles}
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300
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301 A command line template provides a quick and simple way to format some
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302 output. Templates can become verbose, though, and it's useful to be
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303 able to give a template a name. A style file is a template with a
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304 name, stored in a file.
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305
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306 More than that, using a style file unlocks the power of Mercurial's
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307 templating engine in ways that are not possible using the command line
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308 \hgopt{log}{--template} option.
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309
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310 \subsection{The simplest of style files}
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311
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312 Our simple style file contains just one line:
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313
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314 \interaction{template.simple.rev}
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315
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316 This tells Mercurial, ``if you're printing a changeset, use the text
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317 on the right as the template''.
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318
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319 \subsection{Style file syntax}
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320
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321 The syntax rules for a style file are simple.
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322
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323 \begin{itemize}
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324 \item The file is processed one line at a time.
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325
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326 \item Leading and trailing white space are ignored.
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327
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328 \item Empty lines are skipped.
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329
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330 \item If a line starts with either of the characters ``\texttt{\#}'' or
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331 ``\texttt{;}'', the entire line is treated as a comment, and skipped
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332 as if empty.
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333
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334 \item A line starts with a keyword. This must start with an
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335 alphabetic character or underscore, and can subsequently contain any
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336 alphanumeric character or underscore. (In regexp notation, a
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337 keyword must match \Verb+[A-Za-z_][A-Za-z0-9_]*+.)
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338
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339 \item The next element must be an ``\texttt{=}'' character, which can
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340 be preceded or followed by an arbitrary amount of white space.
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341
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342 \item If the rest of the line starts and ends with matching quote
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343 characters (either single or double quote), it is treated as a
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344 template body.
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345
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346 \item If the rest of the line \emph{does not} start with a quote
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347 character, it is treated as the name of a file; the contents of this
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348 file will be read and used as a template body.
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349 \end{itemize}
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350
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351 \section{Style files by example}
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352
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353 To illustrate how to write a style file, we will construct a few by
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354 example. Rather than provide a complete style file and walk through
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355 it, we'll mirror the usual process of developing a style file by
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356 starting with something very simple, and walking through a series of
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357 successively more complete examples.
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358
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359 \subsection{Identifying mistakes in style files}
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360
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361 If Mercurial encounters a problem in a style file you are working on,
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362 it prints a terse error message that, once you figure out what it
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363 means, is actually quite useful.
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364
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365 \interaction{template.svnstyle.syntax.input}
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366
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367 Notice that \filename{broken.style} attempts to define a
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368 \texttt{changeset} keyword, but forgets to give any content for it.
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369 When instructed to use this style file, Mercurial promptly complains.
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370
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371 \interaction{template.svnstyle.syntax.error}
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372
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373 This error message looks intimidating, but it is not too hard to
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374 follow.
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375
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376 \begin{itemize}
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377 \item The first component is simply Mercurial's way of saying ``I am
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378 giving up''.
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379 \begin{codesample4}
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380 \textbf{abort:} broken.style:1: parse error
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381 \end{codesample4}
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382
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383 \item Next comes the name of the style file that contains the error.
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384 \begin{codesample4}
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385 abort: \textbf{broken.style}:1: parse error
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386 \end{codesample4}
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387
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388 \item Following the file name is the line number where the error was
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389 encountered.
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390 \begin{codesample4}
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391 abort: broken.style:\textbf{1}: parse error
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392 \end{codesample4}
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393
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394 \item Finally, a description of what went wrong.
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395 \begin{codesample4}
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396 abort: broken.style:1: \textbf{parse error}
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397 \end{codesample4}
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398 The description of the problem is not always clear (as in this
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399 case), but even when it is cryptic, it is almost always trivial to
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400 visually inspect the offending line in the style file and see what
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401 is wrong.
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402 \end{itemize}
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403
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404 \subsection{Uniquely identifying a repository}
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405
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406 If you would like to be able to identify a Mercurial repository
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407 ``fairly uniquely'' using a short string as an identifier, you can
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408 use the first revision in the repository.
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409 \interaction{template.svnstyle.id}
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410 This is not guaranteed to be unique, but it is nevertheless useful in
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411 many cases.
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412 \begin{itemize}
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413 \item It will not work in a completely empty repository, because such
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414 a repository does not have a revision~zero.
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415 \item Neither will it work in the (extremely rare) case where a
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416 repository is a merge of two or more formerly independent
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417 repositories, and you still have those repositories around.
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418 \end{itemize}
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419 Here are some uses to which you could put this identifier:
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420 \begin{itemize}
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421 \item As a key into a table for a database that manages repositories
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422 on a server.
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423 \item As half of a \{\emph{repository~ID}, \emph{revision~ID}\} tuple.
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424 Save this information away when you run an automated build or other
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425 activity, so that you can ``replay'' the build later if necessary.
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426 \end{itemize}
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427
|
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428 \subsection{Mimicking Subversion's output}
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429
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430 Let's try to emulate the default output format used by another
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431 revision control tool, Subversion.
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432 \interaction{template.svnstyle.short}
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433
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434 Since Subversion's output style is fairly simple, it is easy to
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435 copy-and-paste a hunk of its output into a file, and replace the text
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436 produced above by Subversion with the template values we'd like to see
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437 expanded.
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438 \interaction{template.svnstyle.template}
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439
|
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440 There are a few small ways in which this template deviates from the
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441 output produced by Subversion.
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442 \begin{itemize}
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443 \item Subversion prints a ``readable'' date (the ``\texttt{Wed, 27 Sep
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444 2006}'' in the example output above) in parentheses. Mercurial's
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445 templating engine does not provide a way to display a date in this
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446 format without also printing the time and time zone.
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447 \item We emulate Subversion's printing of ``separator'' lines full of
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448 ``\texttt{-}'' characters by ending the template with such a line.
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449 We use the templating engine's \tplkword{header} keyword to print a
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450 separator line as the first line of output (see below), thus
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451 achieving similar output to Subversion.
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452 \item Subversion's output includes a count in the header of the number
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453 of lines in the commit message. We cannot replicate this in
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454 Mercurial; the templating engine does not currently provide a filter
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455 that counts the number of items it is passed.
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456 \end{itemize}
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457 It took me no more than a minute or two of work to replace literal
|
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458 text from an example of Subversion's output with some keywords and
|
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459 filters to give the template above. The style file simply refers to
|
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460 the template.
|
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461 \interaction{template.svnstyle.style}
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462
|
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463 We could have included the text of the template file directly in the
|
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464 style file by enclosing it in quotes and replacing the newlines with
|
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simon@313
|
465 ``\verb!\n!'' sequences, but it would have made the style file too
|
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466 difficult to read. Readability is a good guide when you're trying to
|
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467 decide whether some text belongs in a style file, or in a template
|
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|
468 file that the style file points to. If the style file will look too
|
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469 big or cluttered if you insert a literal piece of text, drop it into a
|
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|
470 template instead.
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471
|
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472 %%% Local Variables:
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473 %%% mode: latex
|
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474 %%% TeX-master: "00book"
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475 %%% End:
|
